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MECHANICA

QUICK REFERENCE GUIDE

Sandy_McKinney_2015 creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Creo Elements/Pro 5.0 Mechanica

Quick Reference Guide

By Thiagu Palaniappan

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CREO ELEMENTS/PRO 5.0 MECHANICA QUICK REFERENCE GUIDE i

INTRODUCTION creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Mechanica Technology MANUAL CONVERGENCE IN H-METHOD Deformed Model Graph of Max Stress vs

P-loop pass

Mechanica technology is fundamentally different than con- Convergence is achieved manually in the h-method. In or-

ventional FEA tools. Traditional analysis tools use the “h” der to get accurate results, the user has to refine the mesh

method. Mechanica uses the unique “p” method. H ele- until the solution stops changing, which is considered a con-

ments break the model into small linear elements, while verged solution.

Mechanica’s p elements map the underlying geometry of

the model without any linear simplification. In the h Sandy_McKinney_2015

method, the smaller the elements, the more accurate the

answer is. In the p method, instead of adding more and

more elements, Mechanica adds more math to the existing

elements to get a more accurate answer. Solution quality is

gained not by mesh refinement, but by the automatic raising

of the polynomial order of the elements. Thus, the burden of

getting an accurate answer shifts from the user to the soft-

ware.

Mechanica P-mesh H-method FEA approach on a cantilever beam. P-method approach in Mechanica 1

Traditional P-mesh AUTOMATIC CONVERGENCE IN P-METHOD INTRODUCTION

Mechanica Technology In Mechanica, convergence is achieved automatically by an

adaptive process wherein the polynomial order of the equa-

tions to solve the analysis is increased with each analysis

pass irrespective of the mesh characteristics. This is shown

at right. Mechanica can use up to the ninth order polyno-

mial to achieve a converged solution. This adaptive process

is done during post processing, thereby avoiding any time-

consuming manual pre-processing to get an accurate solu-

tion.

Back to Table of Contents

INTRODUCTION ADVANCED MECHANICA creo elements/pro 5.0 mechanica

Mechanica Modules Advanced Mechanica has all the basic Mechanica functional- QUICK REFERENCE GUIDE

ity plus some additional capabilities.

MECHANICA LITE CAPABILITIES FATIGUE ADVISOR

Structural: Large deformation, pre-stress static, pre-

Mechanica Lite is included with every seat of Creo Elements/ Fatigue Advisor is required to run a fatigue analysis in

Pro and does not require a Mechanica license. It is a limited- stress modal analyses, contact with friction Mechanica. A fatigue analysis establishes whether the prod-

functionality, trial version of Mechanica that allows static Vibration: Dynamic time, dynamic frequency, dynamic uct is susceptible to fatigue damage when subjected to cy-

structural analysis on both parts and assemblies that have clic loading.

total surface counts of up to 200. To access Mechanica Lite random, dynamic shock analyses

from within Creo Elements/Pro, click APPLICATIONS > Thermal: Transient thermal analysis CAPABILITIES

MECHANICA. A guiding interface will walk the user through Supports 2D model types: Plane strain, plane stress, Predicts damage and cycles of failure

the model setup since the standard Mechanica toolbars are Confidence of life prediction

not available in Lite mode. 2D–axisymmetric Parametric life optimization study

Materials: Orthotropic and transversely isotropic, non-

MECHANICA (BASIC MECHANICA) Mechanica Operating Modes

linear materials (hyperelastic, elastoplastic)

Mechanica, or basic Mechanica, is a module for Creo Ele- Idealizations: Advanced masses, advanced shells for INTEGRATED MODE

ments/Pro that allows users to perform structural and ther-

mal simulations on product designs. It is fully integrated laminate layups (composites), advanced springs, ad- In integrated mode, Mechanica is accessed from within Creo

with Creo Elements/Pro with an easy-to-use interface. vanced bolted connections including preload Elements/Pro and is fully integrated into the application.

CAPABILITIES The easiest way to check if the user has an Advanced This mode is typically used by Creo Elements/Pro users.

Structural: Static, contact, modal, buckling analyses Mechanica license is to try selecting references of one of the

Thermal: Steady state thermal analysis only 2D model types in the advanced options of Mechanica INDEPENDENT MODE

Materials: Isotropic analysis only model setup.

Idealization: Beams, simple shells, simple masses, sim- Independent mode can be used without Creo Elements/Pro.

NOTE: It relies on the independent Mechanica user interface for all

ple and to ground springs There is complete upward model compatibility from simulation modeling, analysis, and design study execution

Design Study: Standard, sensitivity, optimization Mechanica Lite to full Mechanica (basic or advanced). and results viewing. This is typically used when the CAD

system being used is not Creo Elements/Pro.

Mechanica Modules Back to Table of Contents

FEM MODE

FEM Mode allows the creation of the traditional FEA h-mesh.

Post processing is done using third-party solvers like ANSYS/

NASTRAN.

NATIVE MODE

Native Mode is the default mode of Mechanica and allows

the creation of p-mesh and solving using the p-method.

FEM mode mesh (h) Native mode mesh (p)

INTRODUCTION 2

PROCESS WORKFLOW creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

MODEL GEOMETRY CHECK GEOMETRY Creo Elements/Pro to

CREATION AND DEFEATURE Mechanica

Mechanica can analyze designs done in Creo Elements/Pro Sandy_McKinney_2015Before bringing the model into Mechanica, remove all ge- MATERIAL PROPERTIES

or imported with a neutral file from other CAD systems. It is ometry checks in Creo Elements/Pro by clicking on INFO > IDEALIZATIONS

important to create analysis-friendly parts and assemblies. GEOMETRY CHECKS. Typically, geometry checks will prevent

For example, always create finishing features towards the Mechanica from creating a successful mesh. This could be CONNECTIONS IN ASSEMBLY

end in order to allow for easy defeaturing of the model be- due to a tiny edge, sliver surface, etc. Changing the accuracy CONSTRAINTS

fore taking it into Mechanica. Otherwise, when trying to of the model to remove geometry checks is not recom- LOADS

suppress features not necessary for analysis, required fea- mended because while this might remove the geometry MESH

tures may end up suppressed as well. check, it could cause a regeneration geometry failure which

again contributes to the Mechanica mesh failure. DEFINE ANALYSIS

It is a good practice to follow feature-based modeling in- Always check for interferences and clearances in assembly

stead of including rounds, chamfers, drafts, or holes in the models before activating Mechanica. By default, Mechanica

sketch. Otherwise, it can become a huge task to remove assumes that mated parts are bonded or welded. It is impor-

them during analysis. tant to make sure the interface between parts in Mechanica

are clearly defined based on expected behavior.

If the model geometry has constant thickness, use the Ex-

trude Thicken command or the shell feature in order to auto- Suppress features like chamfers, outer rounds, and drafts as

mate Mechanica shell mesh idealization creation. these will increase the mesh elements but will not change

the analysis results.

The dimensioning scheme should have analysis intent so

that the design can be optimized based on the analysis re-

sults. This will help in selecting appropriate dimensions for

conducting “what if?” scenario design studies such as sensi-

tivity and optimization.

Creo Elements/Pro features such as datum curves and

sketches can be reused in Mechanica to create surface re-

gions (foot prints) and to refine the mesh by adding more

nodes along the curves and sketches. Datum points created

in Creo Elements/Pro can be reused to increase mesh density

as well as assign point loads or constraints.

Relations and parameters can be used while running design

studies within Mechanica. Relations help capture the design

intent while changing the design variable to achieve a cer-

tain analysis objective. Parameters can be used to vary

Mechanica properties such as material properties and loads

while running sensitivity or optimization studies.

Process Workflow Back to Table of Contents 3

PROCESS WORKFLOW creo elements/pro 5.0 mechanica

CONVERGENCE SETUP QUICK REFERENCE GUIDE

RUN ANALYSIS AND

Mechanica Process Overview 2. RUNNING THE ANALYSIS

REVIEW RESULTS

DESIGN VARIABLES AND The following basic four-step process can be used to analyze This step starts with the analysis type definition. Every analy-

most models in Mechanica: sis type has its own requirements. For example, if you want

SHAPE ANIMATE to run a vibration analysis, you will need to define a modal

SENSITIVITY STUDY 1. Building the analysis model (pre-processing) analysis first.

OPTIMIZATION STUDY 2. Running the analysis (post-processing)

REVIEW OPTIMIZATION RESULTS 3. Reviewing the analysis The next step is to set up the memory allocation and post

4. Improving the design process storage location information. The convergence cri-

Process Workflow teria can also be defined at this stage. You can then run the

1. BUILDING THE ANALYSIS MODEL analysis and review the status.

This step starts with Creo Elements/Pro geometry creation, 3. REVIEWING THE ANALYSIS

which is more than just the creation of shapes. Analysis in-

tent can be captured with coordinate systems and unit set- Once the analysis is successfully completed, the results can

ups, dimensions, relations, parent-child relationships and be reviewed in several formats including fringe plots, graphs,

model defeaturing. and vector plots.

The next step is to assign material. New materials can be 4. IMPROVING THE DESIGN

created or reused from the standard Mechanica library or

from a custom library. Based on the material type, additional Based on the analysis results, the design can be improved by

properties like material orientation need to be defined. running design studies like standard design, sensitivity, opti-

mization, or feasibility. But before running any design study,

Mechanica features like loads and constraints must be de- design variables and parameters should be defined, and a

fined in order to run any type of analysis. Mesh creation is regeneration check should be done using shape animate.

optional, since Mechanica creates the mesh automatically

during the analysis run. Optional analysis features like ideali-

zations, regions, and interfaces can also be defined.

Back to Table of Contents PROCESS WORKFLOW 4

GEOMETRY PREPARATION creo elements/pro 5.0 mechanica

Several steps should be taken to ensure that the Creo Ele- Sandy_McKinney_2015CHECK GEOMETRY QUICK REFERENCE GUIDE

ments/Pro geometry is acceptable for meshing in

Mechanica. Most analyses are carried out on existing de- Info > Geometry Checks: Highlights any geometry with Small surfaces created by unaligned surfaces

signs or imported geometry. The design model often con- unclear design intent. A geometry check also refers to a

tains features like rounds, chamfers, small holes, 3D text, or potential regeneration or geometry problem within the A narrow surface created by exterior ribs on a round.

thin geometry that are not important to the analysis model. model. All GeomChecks must be cleaned up for successful The rib on the right with the exterior rounds removed

These features do not alter the stress or deformation results, meshing. If GeomCheck is grayed out, the design intent of will mesh with many fewer elements.

but due to their small sizes, they could generate a large all features is clear.

number of finite elements. Mechanica will compute the

results for each of these elements, and for a large assembly, Analysis > Geometry > Slope: Colors the part according to

this might be computationally expensive. Mechanica could surface slope. This allows easy determination of whether or

run into memory limitation issues during the post process of not edges are sharp and also ensures that geometry changes

the analysis. When using Mechanica, always focus on the are smooth in blends and sweeps.

essentials of the design and not the cosmetics. The follow-

ing methods can better prepare geometry for Mechanica Analysis > Model > Short Edge: Highlights small edges.

analysis.

Analysis > Model > Global Interference: Highlights any

SUPPRESS FEATURES areas of interference for assemblies. Interference should be

avoided in assembly analysis.

Suppress all features that do not have a significant contribu-

tion to the analysis results. It is also important to suppress EXAMPLES OF GEOMETRY THAT ARE DIFFICULT

features which can create small or difficult to mesh surfaces TO MESH

such as rounds, unaligned features, and variable section

blends and sweeps. When Mechanica encounters the following situations during

meshing, it will try to automatically change the mesh set-

REMOVE SURF tings so as to create a successful mesh. However, there is the

potential for a non-converged solution at these locations.

If suppressing features causes regeneration failure, an alter- The geometry preparation phase is critical for mesh genera-

nate method is to remove surf. The Remove feature enables tions as well as final solution accuracy.

you to remove geometry without the need to alter feature

history, reroute, or redefine a number of other features. Small surface created by rounds

When you remove geometry, the neighboring surfaces are

extended or trimmed to converge and close the empty area.

Select a surface, surface set, or single closed-loop chain and

click EDIT > REMOVE.

SIMPLIFIED REPS

In assembly mode, components that will not contribute to

the analysis results can be excluded and a representation

saved for use in Mechanica. This method is better than sup-

pressing the components, as suppressing could cause a re-

generation failure in Creo Elements/Pro.

Geometry Preparation Back to Table of Contents Edges with zero angle 5

GEOMETRY PREPARATION

UNITS creo elements/pro 5.0 mechanica

Mechanica uses the model’s principle system of units to per- QUICK REFERENCE GUIDE

form analyses and store simulation data. This system deter-

mines the default units in which the analysis results are cal- UNIT OPTIONS WITHIN MECHANICA

culated and reported. However, you can override the de-

fault unit system while applying loads and constraints and Heterogeneous units are supported within Mechanica. Units

defining result windows. of all modeling entities can be set on the fly.

The Units Manager in Creo Elements/Pro allows you to Units in results can be changed during the result window

change the principle unit system and to check the units of definition.

the derived quantities. For example, if the principle unit

system is IPS, then the units of stress is psi, but if the princi-

ple unit system is mmNs, the stress is reported in MPA. Click

the Info button in the units manager to access the full list of

derived quantities for each unit system.

The default principle system in Creo Elements/Pro is inch Units of derived quantities 6

lbm second. It is recommended to use IPS instead so that

the force can be applied in pound force (lbf) and the stress Back to Table of Contents

reported in psi. The material property units need not match

the principle units system. For example, Young's modulus

may be assigned in MPA, but the stress can be reported in

psi. The units of all parts in an assembly should match the

principle unit system of the assembly file before taking the

assembly into Mechanica. If the units are inconsistent in the

assembly, Mechanica will prompt you to convert. This auto-

matic conversion of units may not work on family table in-

stances until the generic model is converted manually.

Units

MATERIALS AND MATERIAL PROPERTIES creo elements/pro 5.0 mechanica

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Material assignment is a prerequisite for creating the mesh Sandy_McKinney_2015HYPERELASTIC Material Properties

and running any analysis in Mechanica. Materials can be

assigned to the analysis model in either Creo Elements/Pro A hyperelastic material is a nonlinear material like rubber The following material properties are required to run struc-

or Mechanica. The default material library can be custom- that exhibits instantaneous elastic response to large strains. tural analysis:

ized to include user defined materials. Materials properties Mechanica supports several mathematical models of hypere-

are also available at matweb.com. New materials can be lastic material. The solution accuracy depends on the selec- Density

saved to either the model or to the library. tion method of the material model. Young’s modulus

Poisson’s ratio

In part mode, materials can be assigned to the entire model Define by tests: Using this option, the experimental CTE (coefficient of thermal expansion, required if calcu-

or to a volume region. In assembly mode, materials can be data for stress and strain can be specified and the best

assigned to various components, beam and shell idealiza- fitting model for the data can be found. lating stress and deformation due to thermal expan-

tions, and spot weld connections. sion)

Material model coefficients: Using this option, the

Material Types value of coefficients for a material model can be de- The following material properties are required to run a ther-

fined. The following material models are available: mal analysis:

Based on the stress-strain response of the material, Arruda-Boyce, Mooney-Rivlin, Neo-Hookean, Polyno-

Mechanica can analyze linear, hyperelastic and elastoplastic mial order 2, Reduced Poly. Order 2, and Yeoh. Specific heat capacity

material types. Thermal conductivity

ELASTOPLASTIC

LINEAR Material Orientation

When the load is increased beyond the yield strength, mate-

Mechanica can simulate different types of linear materials : rials can undergo plastic deformation. Mechanica defines Material orientations are used to define the principal mate-

Isotropic, Orthotropic, and Transversely Isotropic. elastoplastic materials using isotropic hardening laws, which rial directions for orthotropic or transversely isotropic mate-

are rules that describe the relationship between the flow rials.

Isotropic: Material with an infinite number of planes of stress and effective plastic strain for a material. The elasto-

material symmetry. Material properties are the same in plastic material definition is done using one of the following The material library file is mmatl.lib, which is located in the

all directions. methods: Creo Elements/Pro load point.

Orthotropic: Material with symmetry relative to three Using test data: Stress and strain values from the test

perpendicular planes. Material properties are required data can be specified to find the best-fit curve for a ma-

as three different values. terial model.

Transversely Isotropic: Material with rotational sym- Using material constants: Material constants are

metry about an axis. Two values for each material prop- specified based on Perfect Plasticity, Linear Hardening,

erty are required—one for the plane of isotropy and Power Law, or Exponential Law.

one for the remaining principal material direction.

Materials and Material Properties Back to Table of Contents MATERIALS AND MATERIAL PROPERTIES 7

SIMULATION FEATURES creo elements/pro 5.0 mechanica

Simulation features are those created in Mechanica such as Only one boundary at a time can be used to split a surface. QUICK REFERENCE GUIDE

surface and volume regions, datum features and user de- In order to create surface regions using multiple boundaries

fined measures. Since these features are created in as shown, two surface region features have to be created. Mesh density increased due to the volume region.

Mechanica mode, they are not available in the standard

mode of Creo Elements/Pro. In the images below, loads and constrains are applied to

surface regions. More nodes and elements are automatically

Surface Region added to a surface region during mesh generation.

Surface regions are footprints on the analysis model that can

be used for applying loads or constraints and for increasing

the mesh density. They are created by splitting a surface by

either sketching a boundary or by selecting existing curves

chains.

When splitting curved surfaces, there is no need to project Volume Region Results display only for the volume region.

the sketched curve on to the surface. During the creation of

the surface region, the curve is projected automatically as Volume regions can split solids into three-dimensional re- Datum Features

shown below for the surface region on the shaft. gions. Analysis results can be viewed based on volumes

making it easier to check internal stresses and strains. Vol- Any datum feature created within Mechanica mode is

ume regions also help in increasing the mesh density. In grouped under the simulation features and are not available

thermal analysis, heat loads can be added to internal sur- for reuse in the standard mode of Creo Elements/Pro. Typi-

faces of a parent volume. Volume regions are created using cally, datum features created in Mechanica are user-defined

one extrude, re- coordinate systems for applying loads and constraints, da-

volve, sweep, tum points for increasing mesh density, point load and con-

blend, or variable straints, and sketches for creating regions.

section sweep.

Always create surface regions before defining midsurfaces Back to Table of Contents 8

for shell idealizations, as creating surface regions will invali-

date existing shell pairs.

Simulation Features

MEASURES—PREDEFINED, USER-DEFINED, AUTOMATICALLY-DEFINED creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Measures in Mechanica are evaluated at the end of every User-defined Measures Automatically-defined Measures

successful analysis completion. User-defined measures are

location specific and can be created as probes in the analysis Similar to predefined measures, user-defined measures are Automatically-defined measures are a specific set of meas-

model to track certain outputs like stress, force, velocity, or measures that can evaluate a quantity, but can be custom- ures are automatically defined by Mechanica based on the

acceleration. For example, in a vibration analysis, a user- ized with additional flexibility and functionality. These can type of modeling entities like contacts regions, fastener con-

defined measure to track acceleration at a certain critical be location-specific, time-specific, or frequency-specific nections, or thermal resistance.

location can simulate an accelerometer. Mechanica uses quantities. They can be used to monitor specific aspects of

three types of measures—predefined, user-defined, and the model’s performance like stress or strain at a point in a INTERFACE MEASURES

automatically defined. particular direction. In dynamic analyses, user defined meas-

ures can be used to monitor the model performance like When a contact interface with friction or a thermal resistance

Predefined Measures position, acceleration or velocity at a point. interface is created, the measures shown below are auto-

Sandy_McKinney_2015 matically defined by Mechanica.

Mechanica evaluates a set of predefined quantities based on

the analysis type. These are not location-specific and are

evaluated over the entire analysis model. Among the vari-

ous measures evaluated during a structural analysis typical

measures of interest are von Mises stress, maximum princi-

pal stress, and maximum displacement. For a thermal analy-

sis, the maximum heat flux, and maximum and minimum

temperatures are important predefined measures.

Quantities available to create user defined measures FASTENER CONNECTION MEASURES

For fastener connections, the measures show below are

automatically created.

Predefined structural measures Predefined thermal measures Tracking the deflection of a point location along a direction MEASURES 9

Predefined, User-defined, Automatically-defined Back to Table of Contents

IDEALIZATIONS—SHELLS creo elements/pro 5.0 mechanica

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Idealizations are Mechanica elements that represent the STANDARD SHELLS MIDSURFACE SHELLS

design geometry with elements like beams, shells, springs

and masses. They simplify the fully detailed 3D geometry There are two types of standard shells, simple and advanced. A midsurface shell is created by selecting the pairs of sur-

and are computationally less expensive than a simulation faces, as shown below. Mechanica can automatically detect

without simplification, thereby allowing faster simulation. SIMPLE STANDARD SHELLS opposing surfaces with the selection of one surface.

Simple standard shells are typically applied on surface mod-

Shell Idealization els by associating a thickness and a material, as shown be- In complex models that have large number of surface pairs,

low. it is recommended to use the Auto Detect Shell Pairs option

Thin areas of a model can be represented as shells which is a by specifying the characteristic thickness in the model.

surface with associated thickness. Shells or surface elements Mechanica will search for all shell pairs with a thickness less

are made of quads and triangles which is computationally than the characteristic thickness.

more efficient than the default solid elements like tetra,

wedge and brick. Shell idealizations can be used in struc-

tures with constant thickness that is relatively small com-

pared to the length and width.

There are two types of shells—standard and midsurface.

Standard shells are created by selecting a surface reference

from a model and specifying a material and thickness. Mid-

surface shells are created by selecting surface pairs in the

model. Mechanica will compress the surface pairs into a

single midsurface as shown by the green shell midsurface in

the below example.

ADVANCED STANDARD SHELLS

Advanced standard shells allows homogeneous shells or

shells with laminate properties, as shown below. The layup

below consists of some plies of carbon fabric on either side

of some foam core.

Analysis Model Shell Midsurface

Default Solid Mesh (Tetra) Shell Mesh ( Quad, Tri)

Shells Back to Table of Contents IDEALIZATIONS 10

IDEALIZATIONS—SHELLS creo elements/pro 5.0 mechanica

The midsurface creation on the entire analysis model can be QUICK REFERENCE GUIDE

reviewed by selecting AUTOGEM > REVIEW GEOMETRY…

Shell surfaces are displayed in green by default. If you are using surface regions and shell idealizations, the

surface regions should be created before the shell idealiza-

Sandy_McKinney_2015 tion definition.

Typically, analysis models in Mechanica are composed of

both solid and shell elements. In assemblies and parts, the

thin areas can be defined as shells while the rest of the

analysis model can be solids. The ribs in the model below

are defined as midsurface shells while the rest of the model

is solid.

SHELL PROPERTIES Laminate Stiffness By default, shell idealizations or elements are displayed in

green and solid elements are displayed in blue. The shell to

Thickness: For standard shells, the thickness needs to A laminate layup is a number of shells, with each shell hav- solid elements connection is automatically taken care of by

be specified after selecting the surface. For midsurface ing its own midsurface. The stress in each ply is calculated link elements, which are displayed in purple.

shells, the thickness is automatically assigned to the during the analysis. The laminate layup consists of a number

shell based on the distance between the surface pairs of plies stacked on each other. The layer repetition pattern

selected. can be specified using one of three symmetry options. For

example, a three layer laminate (a, b, c) would change as

Material: Material needs to be assigned manually. follows:

Material orientations: For orthotropic and trans-

Symmetrical: a b c c b a

versely isotropic materials, the material orientation and Antisymmetrical: a b c –c –b –a

properties in those directions are required. No symmetry: a b c

Shell property (laminate properties): Advanced

shells can be used to simulate composites or laminates For analysis models that contain shell idealizations, do not

by specifying the laminate layup or the laminate stiff- use the surface that will be compressed during midsurface

ness. creation for applying loads and constraints.

Laminate Layup Loads and constraints can be applied on the top or bottom

surfaces and the side edges but not on the side surfaces.

Shells IDEALIZATIONS 11

Back to Table of Contents

IDEALIZATIONS—BEAMS Standard beam sections are defined by selecting the cross creo elements/pro 5.0 mechanica

section shape and specifying required dimensions. The fol-

Beam Idealization lowing standard shapes are available: QUICK REFERENCE GUIDE

Beam idealizations represent structures whose length is The BSCS is used as the reference coordinate system for de-

much greater than the other dimensions. They are one- fining the beam cross section shape. The x-axis is along the

dimensional idealizations and are created by applying a 2D length of the beam. Y and z directions are determined by

cross section to a curve. Rather than analyzing an extruded Mechanica.

section using the solid elements, beam idealization allows

faster simulation by defining the cross section properties. The BCPCS is located at the centroid of the section. The

Typical references used to create beams are curves and BSCS is coincident with the BCPCS for general sections and

points. all standard sections except channel and L sections.

Mechanica automatically determines the BCPCS for channel,

L, and sketched sections. Beam section properties are re-

ported based on BCPCS.

Analysis model Beam idealization

BEAM SECTIONS Beam sections can also be sketched. The area parameters

are calculated based on this sketched geometry.

There are three types of beam sections:

Beam sections can be created on the fly as needed, or stored

General and retrieved from a library of cross-sections. Beam sections BEAM RELEASE

Standard can also be saved in a library file called mbmsct.lib, and the

Sketched beam section directory can be specified as a config.pro op- Mechanica will fix all degrees of freedom at beam ends by

tion (sim_beamsection_path). default. With beam release, certain degrees of freedom can

General beam sections are defined by providing the cross be released at the ends of the beam. The BACS is used for

section properties and do have a specific shape. BEAM ORIENTATION specifying beam releases. The following degrees of freedom

can be released at beam ends:

The following properties are required to define a general Beam orientation affects how the beam relates to the axis

beam section: where Mechanica applies loads and calculates analysis re- Translational: Dx, Dy, Dz

sults. The following three types of coordinate systems are Rotational: Rx, Ry, Rz

Area associated to beams:

2D moments of Beam releases are

Beam action coordinate system (BACS) indicated by this

inertia Beam shape coordinate system (BSCS) graphic icon at the

Torsional stiff- Beam centroidal principal coordinate system (BCPCS) end of the beam. An arrow-

head indicates a translational

ness The BACS is used as a reference while applying forces and DOF, and a ring indicates

Shear parame- moments on beams. It is located on the curve that is used to rotational DOF.

create the beam. The x-axis is always parallel to the axis of

ters the beam or normal to beam section. The y-axis direction is

Stress grids user-defined.

Beams Back to Table of Contents IDEALIZATIONS 12

IDEALIZATIONS—SPRING, MASS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Spring Idealization Sandy_McKinney_2015 MASS TYPES

Spring idealizations must be attached to at least one point in

A spring idealization represents a linear elastic spring con- the analysis model—either a datum point or a vertex. Simple: This is the default mass type wherein the distri-

nection that can be defined from one point to another or Springs can act as constraints as well. bution can be specified as total mass or the mass per

from point to ground. It adds translational or torsional resis- point to be distributed over all of the points selected.

tance between two points in an analysis model. Mass Idealization The mass must be specified.

Analysis model with spring elements A mass idealization is a one-point element that can be used Advanced: This mass type allows only the mass per

to represent a concentrated mass at a point without a speci- point distribution. Properties like mass and moments of

SPRING TYPES fied shape or geometry. In an assembly analysis, compo- intertia can be specified relative to a coordinate system.

nents that contribute only mass and not stiffness to the as-

Simple: The spring is defined by specifying extensional sembly can be simplified as mass idealizations. For inertial Component at Point: This mass type is available only

and torsional stiffness values. loads, moments of inertia can be specified without including in assembly mode. The mass properties of a selected

the actual geometry. component (part or subassembly) are applied to this

Advanced: The spring is defined by specifying magni- type of mass idealization.

tude and direction of components for extensional and Back to Table of Contents

torsional stiffness. The component at point mass type is typically useful

when using simplified representations of analysis mod-

To Ground: The spring is defined by specifying the els. The excluded component's mass properties are

orientation of the components for the extensional and assigned to the point.

torsional stiffness relative to a selected coordinate sys-

tem. It is important to note that the mass idealization will predict

the way a model will behave due to an object at a point in

SPRING PROPERTIES the model and will not predict what happens to the object

itself. If the behavior of the object itself is also one of the

Extensional (Kxx,Kyy,Kzz) and torsional stiffness (Txx,Tyy,Tzz) goals of the analysis, the full geometry of the object has to

can be specified in directions other than those directly in line be included without any kind of idealization.

with the spring’s starting and ending points. These proper-

ties are required for Advanced or To Ground springs. If a component will be simplified in Mechanica using a mass

Spring, Mass element, it is a good practice to analyze the mass properties

in Creo Elements/Pro. The center of gravity can be calcu-

lated which can then be used in Mechanica for the location

of the mass element.

MASS PROPERTIES

The two main mass

properties are mass

and moments of iner-

tia. Moments of inertia

are specified about

each mass element’s

center of gravity rela-

tive to the axes and

principal planes of the

WCS.

IDEALIZATIONS 13

CONNECTIONS—WELDS creo elements/pro 5.0 mechanica

Weld Connections QUICK REFERENCE GUIDE

Weld connections are used to connect midsurface shells in Spot Weld

assembly mode. End and perimeter welds are used for ex-

tending or creating shell elements between midsurface WELD REFERENCES:

components. Spot welds are used to connect components End Welds: Select two surfaces in any order.

using beams. Perimeter Welds: Select the doubler surface first, then

the base surface, and then the edges.

WELD TYPES Spot Weld: Select surfaces in any order and then select a

datum point.

End weld

Perimeter weld The query selection can be used to select the appropriate

Spot weld surfaces when creating weld connections.

Weld feature

WELD PROPERTIES:

END WELD Perimeter weld: Specify shell thickness

In assembly models that use shell idealizations, when there Spot weld: Specify material and diameter

is a T or L, angled or oblique configuration, end welds can be

used to connect the midsurfaces as shown below. WELD FEATURE

Welds created using the Creo Elements/Pro welding applica-

PERIMETER WELD Perimeter weld tion can be referenced in Mechanica mode using the weld

In assembly models that have a parallel configuration, pe- feature option. The groove and fillet weld features can be

rimeter welds can be used to connect the shell midsurfaces SPOT WELD reused in Mechanica for solids and shell midsurface connec-

along the perimeter of one of the parts. Spot welds are used for modeling structural assembly con- tivity. The weld features created in Creo Elements/Pro

nections like glue tabs, spot welds, rivets, and bolted con- should be surface welds and not lightweight welds.

End and perimeter welds do not simulate actual welds of nections. They accurately transfer load from one part to the

real world. They are just used to connect midsurfaces for other but should not be used to predict localized stresses When using welded connections, the stress in the weld may

shell idealizations. End welds and perimeter welds are not near connection points. They can be created on parts that appear higher than it actually is due to areas of theoretically

required for solid idealizations, for which two parts touching are solids or shells or both. Surfaces connected with spot infinite stress near the weld. The intent for using weld con-

each other are automatically assumed to be welded by de- welds should be within 15 degrees of being parallel to each nections is to predict the failure of components in the analy-

fault. This default interface can be changed. other. sis model and not failure in the weld itself. If the goal of the

analysis is to predict failure in the weld itself, then model the

A spot weld connection is represented by a beam with a welds using solids and rather than using weld connections.

circular cross section. It connects two surfaces in a circular

spot at a point. The datum point used to specify the spot

weld location does not have to be on either of the two sur-

faces being connected. The point is just projected onto the

surface. The beam is connected to the two surfaces by a

special link element, and the surface at the diameter of the

spot weld will be rigid. When using shells, the beam ends

are projected to the midsurface during analysis run.

Welds Back to Table of Contents CONNECTIONS 14

CONNECTIONS—INTERFACE creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Interface Sandy_McKinney_2015CONTACT INTERFACE Infinite friction: Con-

tact analysis in

When analyzing assemblies in Mechanica, components with Contact interface enable a contact analysis to determine the Mechanica can analyze

coincident surfaces can be handled using an interface, which non-linear forces generated by two separate components only the normal forces

controls how Mechanica will treat a particular pair of mated coming into contact. It prevents surfaces from being and not the friction

or overlapping surfaces during meshing and analysis. The merged, prevents interpenetration, and calculates contact forces, so instead of

structure mode and thermal mode of Mechanica have differ- pressures and contact area when running a contact analysis. constraining the models

ent types of interfaces. The default interface can be set in Contacts can be defined between a pair of surfaces or be- in contact in the tan-

the Mechanica Model Setup dialog box. tween components. These references can be selected in the gential direction to

Interface Definition dialog box. Contacts can also be created prevent rigid body mo-

Structure Interface types: automatically with auto detect option by setting selection tion, the infinite friction

Free filtering tolerance like maximum separation distance and option can be checked.

Contact angle between the surfaces.

Bonded Create slippage indi-

CONTACT INTERFACE DEFINITION PROPERTIES cators: The coefficient

Thermal Interface types References: Specific surface pairs can be selected, or in of static friction can be

Adiabatic used to determine

Bonded a complex geometry situation, the component pairs can whether the component would have slipped or not.

Thermal Resistance be selected. Stresses due to friction are not calculated.

Split surfaces: Surfaces are split along the boundaries

FREE INTERFACE that help in generating a compatible mesh. PREREQUISITES FOR CONTACT INTERFACE:

Generate compatible mesh: The position of the nodes The distance between the surfaces can be no larger

Free interfaces prevent surfaces from being merged and on each of the coincident surfaces will overlap or be

should be defined along surfaces that should not be compatible. than one half the average diagonal lengths of both

merged. Otherwise, the analysis model would have a much surfaces.

larger stiffness than it should. The surfaces cannot be at an angle greater than 36

degrees with respect to each other.

With a free interface, applied forces do not transfer between Contact interface is not valid for shell or beam ele-

connected components or surfaces. Mechanica will not pre- ments.

vent interpenetration between components except along

surfaces that have specifically been assigned a contact or BONDED INTERFACE

bonded interface.

If the default interface is Bonded, all components that are

Free interfaces can be created by either selecting surface- mated together or that have coincident surfaces will be

surface or component-component. It can also be set as the merged or assumed to be welded. If a bonded interface is

default interface. If the default interface is set to free, all created between two surfaces, Mechanica automatically

components are free as individual bodies. creates a force measure to calculate the magnitude of resul-

tant force over the bonded surface.

The default interface selection will depend largely on how

much time is spent assigning interfaces. If most compo-

nents are bonded or welded together and only one pair of

components or surfaces have contact between them, then it

is recommended to set the default interface to bonded and

assign contact interface where needed.

Interface Back to Table of Contents CONNECTIONS 15

CONNECTIONS—LINKS, FASTENERS creo elements/pro 5.0 mechanica

Links WEIGHTED LINKS QUICK REFERENCE GUIDE

RIGID LINKS Weighted links are used to distribute masses or loads acting Fastener Connection

at a single source point over a collection of geometric enti-

A rigid link connects geometric entities such as surfaces, ties through which the load is transferred. Fasteners simulate an assembly’s bolts and screws with a

curves, and points so that they remain rigidly connected series of springs. They fasten two components at a specific

during an analysis and will not have any displacement rela- Weighted links transfer load in a balanced manner. This is a location or hole and simulate the load path within the as-

tive to each other. great method to simplify complex assemblies in that it rep- sembly and the amount of load carried by each bolt or

resent them as a point mass and distributes load transfer. screw.

Rigid links are typically used in situations where the entities A weighted link is defined using two types of entities: The stiffness of the fastener can be input manually, or

being selected are not in direct contact with each other and Dependent Side (point): This is the source point Mechanica can calculate stiffness based on references and

hence would not be bonded by the assembly. Simple rigid materials specified.

links acts in all directions whereas advanced rigid links allow where the mass or force is assigned.

control of the degrees of freedom of the link. Independent Side (points, edges, surfaces): The ef- FASTENER TYPES

In the example below, the midsurface gaps between the two fect of the dependent side is distributed over the enti- Bolts: Created on solid or shell element components.

components will prevent analysis using shells. The rigid ties on the independent side. Screws: Created only for solid element components.

connection between the side surfaces fixes the issue by al- The translational DOF (degrees of freedom) for the in- Simple fasteners: Created using the material and shaft

lowing no relative displacement between the edges of the dependent side can be specified.

midsurface. Entities on the independent side determine the motion diameter specified.

of a single point on the dependent side. Thus, the Advanced fasteners: Created based on material and

source point follows the average motion of the target

node group. shaft diameter or spring properties. They have addi-

It is recommended to use weighted links for connecting a tional options like preload, restrict rotations for the fas-

mass element to the model without stiffening the structure. tened parts, and fastener carrying shear.

Although this could be used to distribute forces as well, it is

similar to the TLAP (total load at point) option used in loads.

Links, Fasteners Back to Table of Contents CONNECTIONS 16

CONNECTIONS Sandy_McKinney_2015 PREREQUISITES FOR FASTENERS: creo elements/pro 5.0 mechanica

Fastener connections can only pass through two

ADVANCED FASTENER DEFINITION QUICK REFERENCE GUIDE

components, and the analysis model must be an

Advanced fasteners have the following properties: assembly. To correct this, the value of the preload needs to be ad-

The holes used for creating fasteners must be a right justed. Because the static deformation is linear, the preload

Stiffness: Stiffness is computed using either using di- cylindrical hole, or the hole must be perpendicular should be scaled by the ratio between the applied preload

ameter and material or spring stiffness properties to the component surface and have straight sides. force value and the reported tensile force value.

The two holes should have approximately the same

Diameter diameter. The axes of the holes must be approxi- Here is the procedure to apply this correction:

Material mately parallel to each other.

Fix Rotations: This option allows Mechanica to auto- For bolt type fasteners the holes must completely 1. Set up the fastener connections with the desired pre-

penetrate both parts. If one of the hole is a blind or load force value.

matically prevent rotation of fastened components variable depth hole, then a bolt connection cannot

about the bolt or screw. An alternate method of pre- be created. 2. Do not apply any external loads. But for the analysis to

venting rotation is to use constraints on the fastened For screw type fasteners, one of the holes selected run we would need a dummy load value of zero. So set

components or to add more fasteners. for references must be a blind hole and the other a the value of the external load on the analysis model to

Carries Shear: If this option is checked, the fastener through hole. be zero.

carries the shear force that passes through the fastener Fasteners may not work if the two parts are interfer-

connection. If this option is cleared, Mechanica as- ing with each other or if there are intervening com- 3. After applying constraints, run the analysis.

sumes that the shear force passes through the compo- ponents. 4. Check the fastener tensile force reported in the analysis

nents by friction where the components meet.

Fix Separation: This will ensure that the fastened com- FASTENER PRELOAD report file (Fastener1_tensile_force). This will not be

ponents do not interpenetrate. equal to the preload force applied.

Preload force: This will simulate the degree to which Preload compresses fastened components together and 5. Change the preload force in the fastener connection to

the bolt or screw will be tightened and the fastener will creates a state where any external force has to relieve this the following calculated correct preload force and apply

compress the components. compression before the fasteners begin to deform. There- external load values as necessary and run the analysis.

Fastener Head and Nut Diameter fore, when a fastener has preload applied, it will shoulder Correction ratio (CR) = preload force/fastener tensile

Separation Test Diameter only a small portion of any external load until separation force

occurs. In Mechanica, fasteners are implemented as springs. Correct preload force = original preload force x CR

The stiffness of which is calculated by default from the di-

mensions of the holes selected. Preload is implemented by FASTENER MEASURES

setting the natural length of the spring to be shorter than

the distance between the ends of each hole. Preload is not The following measures are automatically defined measures

non-linear, and it does not take the stiffness of the fastened for fastener connections:

components into consideration.

Fastener_tensile_force

PRELOAD FORCE VALUE ADJUSTMENT Fastener_tensile_stress

Fasteners_shear_force

With zero load on the analysis model, the expectation is that Fasteners_shear_stress

the fastener tensile force will be equal to the preload force Fasteners_separation_stress

value. Because the fastener is implemented as a spring, the

preload causes the fastened components to deform under NOTE:

preload. As of the Creo Elements/Pro 5.0 (Pro/ENGINEER Wildfire

5.0) release, an Advanced Mechanica license is required

to apply preload force.

Fasteners Back to Table of Contents CONNECTIONS 17

MESH (AUTOGEM) MESH REFINEMENT creo elements/pro 5.0 mechanica

Mesh Since Mechanica uses the p-method solver, for most analysis QUICK REFERENCE GUIDE

there is no need for mesh refinement. But if a converged

Typically, Mechanica generates mesh during the analysis solution could not be achieved within the ninth order poly- The following options can be used to refine the mesh:

run, but it is a good practice to create and check the mesh nomial, then mesh refinement can be used to get a con-

before running the analysis. Mechanica uses AutoGEM verged solution. AutoGEM control

(automatic geometric element mesher) to generate and Change AutoGEM settings

control the mesh. Based on the Mechanica operating mode, Mesh refinement should be done only if the analysis reports Surface region

the resulting mesh can be either p-mesh or h-mesh. By de- a non-converged solution in a multi-pass analysis. The area Volume region

fault, p-mesh is generated when using the native mode, but that requires refinement can be identified in the p-level Datum points

if the FEM mode option is used then the traditional h-mesh fringe plot. The element edges that reached ninth order are

is generated. It is always recommended to use the default the non-converged solution areas that need refinement as AUTOGEM CONTROL

native mode p-mesh to create geometric element mesh. shown below with the red color edges. The AutoGEM Control dialog box has several methods to

The FEM mode should be used only when using a third party control the mesh distribution on the analysis model. These

solver like Ansys or Nastran that requires the traditional h- mesh control options exert additional influence beyond the

mesh. software defaults.

CREATE P-MESH 1. Edge Distribution: This specifies the number of nodes

and their placement intervals along curves or edges.

In order to create the mesh, the material property has to be

assigned first. The element type of the resulting mesh— This method is typically used as shown below to in-

solid, shell, etc.—depends on the type of idealization de- crease the number of nodes on the hole and side edges

fined. that reached the ninth order polynomial and could not

converge with the default number of nodes and ele-

ments.

The mesh can be saved for reuse during analysis run. The Back to Table of Contents MESH 18

mesh file for part is a .mmp file and the mesh file for an as-

sembly is a .mma file. Before starting the analysis post proc-

ess, the settings can be configured to use mesh from exist-

ing file in the Run Settings dialog box.

Mesh (AutoGEM)

MESH (AUTOGEM) 4. Maximum element size: Use this method to control creo elements/pro 5.0 mechanica

the maximum size of the elements created by the mesh

2. Minimum edge length: This method is used to ignore generator. This can be applied to the entire analysis QUICK REFERENCE GUIDE

edges and datum curves with a length smaller than or model as shown below or to specific volumes, surfaces,

equal to a specified length with options to keep or re- edges, or curves. 7. Hard curve: This method is similar to the hard points

tain certain edges except that datum curves can be selected to guide the

for meshing. By mesh creation process as shown below with the circular

default, AutoGEM curve concentric to the hole.

will mesh all

edges of the

analysis model.

Sandy_McKinney_2015

3. Isolate for exclusion: This method is used to isolate 5. Edge length by curvature: This method is used to AUTOGEM SETTINGS

selected points, edges, curves, surfaces, volume, and create smaller elements adjacent to curved surfaces The default AutoGEM settings are optimized to give a supe-

components from the model during analysis. The se- such as areas near curves, fillets, and holes that are rior mesh on typical analysis models. But AutoGEM many

lected geometry is isolated with options to exclude it likely to have high stress concentrations. A dense mesh not be able to mesh all models using these default limit set-

during convergence is achieved by specifying the ratio of the element edge tings. When the mesh creation fails, the default settings can

and measure calcu- length to the radius of curvature as shown below near be changed as follows.

lations. Preselected the hole surface. Insert points: Add points to create a valid mesh.

singularities like Move or delete existing points: Relocate or remove

reentrant corners, 6. Hard points: This method is used to select points on

point loads and the analysis model to guide the mesh creation process. existing points for optimal element configuration.

constraints, and AutoGEM will use these hard points as automatic ele- Modify or delete existing points: Modify or delete

edge loads and con- ment nodes. Points can be created or existing points

straints can also be can be selected. existing elements to optimize or complete element

excluded using this creation.

method. Singulari- Automatic interrupt: Stop AutoGEM after it creates a

ties are areas of specific percentage of elements.

theoretically infinite Ignore unpaired surfaces: Unpaired surfaces will be

stress which are excluded from mesh.

undesirable as they Remove unopposed surfaces: Unopposed surfaces

can skew analysis are excluded from the mesh.

results.

Back to Table of Contents 19

Mesh (AutoGEM)

MESH (AUTOGEM) creo elements/pro 5.0 mechanica

Create links where needed: Links created to connect MESH DIAGNOSTICS QUICK REFERENCE GUIDE

shell-solid elements or solid quads-solid triangular

faces. The mesh diagnostics will highlight areas on the analysis Minimum Surface Dimension: This setting ensures

model that Mechanica is having problems meshing due to that all surfaces whose dimensions exceed the mini-

Create bonding elements: These bonding elements the existing limits as shown below. mum will be retained. AutoGEM merges each of the

are created to link parts in assemblies. surfaces whose dimensions are less than the minimum

In such situations AutoGEM will try to automatically change into an edge whose length represents the original sur-

Detailed fillet modeling: This will create additional the default settings and create a successful mesh. If it fails face. If the resulting edge is shorter than the value that

elements near fillets for a smooth fringe plot. again, then the settings can be changed manually or the appears in the minimum edge length field, AutoGEM

geometry tolerance setting can be edited. will merge the surface into a vertex.

Display AutoGEM prompts: During meshing, prompts GEOMETRY TOLERANCE

or message boxes will be displayed that require action If the analysis model fails to mesh, the geometry tolerance Minimum Cusp Angle: This refers to the minimum

or confirmation to continue meshing. settings can be changed to work around the problem. angle of the cusp formed when two arcs meet or an arc

meets an edge or surface. AutoGEM eliminates any

Element types: Set element types for solids and shells. angle less than this value by moving the node at the

Tetrahedral elements are the default for solids, and this end of the surfaces or edges to the nearest location that

can be changed to allow other type elements like forms an acceptable angle and hence shortens the sur-

wedge and brick elements. The default setting for faces or edges.

shells is to create quads, but this can be changed to

create triangles only. Merge Tolerance: This is the distance below which

AutoGEM will merge mated or overlapping surfaces in

AUTOGEM LIMITS assemblies that have shell midsurfaces.

AutoGEM creates and edits the mesh using the following

limits and they can be edited when mesh fails. They can also GEOMETRY TOLERANCE BEST PRACTICES

be used to increase or decrease the number of elements. If a mesh fails because some of the edges in the

Allowable angles: Minimum and maximum edge and Minimum Edge Length: This setting ensures that all model are too small, resolve by increasing the mini-

face angles can be specified. edges whose length exceeds the minimum will be re- mum edge length tolerance value.

tained. AutoGEM and merges the end points of any If AutoGEM merges away a sliver surface for which

Max aspect ratio: Ratio between the longest and edge whose length is less than the minimum into a results are important, reduce the minimum surface

shortest length of a facet. single node. This minimum can be an absolute or rela- dimension to force AutoGEM to use that surface.

tive value. The tolerance values should not vary significantly

Max edge turn: Maximum angle that the normal to a from the defaults, as a good practice keep these

given edge of a facet can turn from start to end. Back to Table of Contents changes to within 10 percent of the default values.

Entering extremely large values might prevent

The default limits should be used as much as possible and meshing.

should be changed only when AutoGEM mesh creation fails

due to intricate geometry. Changing these limits might MESH TREATMENT OPTIONS

cause a non-converged solution. It is a good practice to

always check the p-level fringe plot. If the analysis model contain both solid and shell idealiza-

tion, AutoGEM can be directed to use solid only, midsurface

Mesh (AutoGEM) only, or solid and midsurface mesh treatment options.

AutoGEM selects this automatically but it can be changed if

an all-solid mesh should be used instead despite shells hav-

ing been defined in the analysis model.

MESH 20

CONSTRAINTS—DISPLACEMENT, BOLT TYPE creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Constraints simulate real world boundary conditions on the Sandy_McKinney_2015BOLT TYPE CONSTRAINT Most structural analyses require a constraint on the model to

analysis model. In structure mode, constraints are used to fix run a successful analysis. But for bodies in motion, the inertia

certain portions of the analysis model so that the model To simulate a bolt type constraint a cylindrical coordinate relief option allows the analysis to run without constraints.

cannot move or can move only in a predetermined way. system can be used with the Z axis along the axis of the hole. When inertia relief is used, Mechanica will create a new Car-

A surface region can be created for the bolt head contact tesian coordinate system internally, define a three point

Mechanica has the following types of structural constraints: area and constrained. constraint, and apply body loads to balance the applied

loads.

Displacement Constraints INSUFFICIENTLY CONSTRAINED MODELS

Planar, Pin and Ball Constraints Any geometry that is not constrained in the analysis model is

Symmetry Constraints When a model is insufficiently constrained, the Mechanica assumed to have all the translational and rotational degrees

solver engine will report it, and the analysis will have a fatal of freedom.

Displacement Constraint error. In order to resolve this, run a constrained modal analy-

sis with rigid mode search. The animation of this analysis Solid elements have three translational degrees of freedom

Displacement constraints are used to limit the degrees of result will help in finding the missing constraint in the analy- and no rotational degrees of freedom. Any face of a tetrahe-

freedom of an analysis model and also to prevent rigid body sis model. dral element cannot rotate without translation in one of the

motion. They are applied to portions of the model using a three directions. Mechanica will ignore rotational con-

geometric reference like surface (or surface region), edge or straints on solid.

curve, points. The selected geometry can be constrained in

translations and rotation in each of the coordinate system Constraints can simplify the analysis model. In assemblies,

axes using Free, Fixed, and Prescribed settings. certain components can be excluded from the analysis and

constraints can be used instead.

Every constraint is part of a constraint set. A constraint set is

a collection of constraints that act together at the same time Rotational constraints are valid for shell and beam idealiza-

on the analysis model. tions. When using shell elements, it is a good practice to not

apply constraints on side surfaces that get compressed away

By default, the displacement constraints are based on the during midsurface creation.

WCS (world coordinate system) of the analysis model. A user

-defined coordinate system can also be used as a reference

for special type of constraints, such as bolt type constraints,

using a cylindrical coordinate system.

Prescribed displacement is given when the exact displace-

ment is known but the load or force is not known. The pre-

scribed displacement will act as a load when the analysis is

run. Force required to create the prescribed displacement

can be calculated using a reaction measure at the constraint.

Displacement; Bolt Type; Insufficiently Constrained Models Back to Table of Contents CONSTRAINTS 21

CONSTRAINTS—PLANAR, PIN & BALL; SYMMETRY creo elements/pro 5.0 mechanica

Planar, Pin and Ball Constraints MIRROR SYMMETRY QUICK REFERENCE GUIDE

These constraints allow you to easily create engineering With mirror symmetry, one segment of a model is the mirror CYCLIC SYMMETRY

constraints. image of other segments. The model is cut in half through

the plane, and the constraint is applied through the surface Cyclic symmetry is applied to analysis models that are sym-

Planar constraints allow full planar movement but for solid idealization, through the edge for shell idealization, metrical about an axis, such as a fan blade or turbine. A seg-

constrains off-plane displacement. This constraint is or through a point for beam idealization that lies on the ment of the geometry is repeated in a cyclic manner but it is

valid only for planar surfaces. plane of symmetry. not a mirror image. This segment is a pie shaped wedge that

can reproduce the entire analysis model by copying it an

Pin constraints control the translation and rotation To cut the model in half for mirror symmetry, instead of cre- integer number of times about the axis of symmetry.

about the axes of a cylindrical surface in 3D analysis ating an extruded cut, it is a good practice to select a datum

models. This is very useful when a surface needs to plane and use the solidify feature (EDIT > SOLIDIFY) to re- During the creation of cyclic symmetry, Mechanica will calcu-

move in one or more directions while being held in move the other half of the model. late the angle of the pie based on the surfaces selected to

place in the remaining directions. Pin constraints can check if it can be copied an integer number of times to pro-

also specify angular and axial degrees of freedom as duce the entire analysis model. It will generate a warning, as

free or fixed. This constraint is valid only for cylindrical shown below, if it cannot.

surfaces.

Ball constraints represent a ball joint in which transla-

tion is fixed while rotation is free. This is valid for only

spherical surfaces.

Planar, pin and ball constraints are not valid for large defor-

mation analysis.

Symmetry Constraints When using mirror symmetry, it is important to reduce the Cyclic symmetry constraints should be applied before using

total load value by half. Do not reduce force per unit area AutoGEM to create the mesh. The surfaces selected for sym-

When the loads, constraints, and geometry of an analysis loads (i.e. pressure loads), as will be taken care of automati- metry must map to one another. Do not use cyclic symmetry

model are symmetrical, it is a good practice to subdivide the cally with the total load reduction. for modal and buckling analysis.

model and analyze a symmetric portion instead of the entire

model. This will greatly reduce the number of elements Do not use mirror symmetry when running modal and buck-

thereby saving analysis time and system resources. But ling analyses, as Mechanica will report only the modes that

when working on a symmetric section, an additional con- are symmetrical.

straint is required to prevent the model from deforming

through the plane of symmetry. There are two types of sym-

metry, mirror cyclic.

Planar, Pin and Ball; Symmetry Back to Table of Contents CONSTRAINTS 22

LOADS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Loads are applied to the analysis model to simulate what the DISTRIBUTION OPTIONS Interpolated over entity: Interpolation points with an

model must endure to perform its function. For structural associated scaling factor can be specified to vary the

analysis, a load can be a force, moment, pressure, accelera- Distribution options define how the load magnitude is inter- load over the selected entity.

tion, velocity, or temperature. For thermal analysis, a load is preted mathematically.

a heat condition. Most Mechanica load types are entity Sandy_McKinney_2015 Bearing Load

loads that are applied to specific geometry of the analysis Total load: This will distribute a load along the length

model like surfaces, edges or points. Some are body loads or area of the selected entity. The integral of the load Bearing loads are applied on holes or pins that are being

like gravity load and centrifugal load. over the selected entity is the total load value specified. pulled or pushed to one side. Axles, bolts, pins, rivets, and

shafts create stresses in the members they connect, along

Force/Moment Load Force per unit type: This applies a distributed load the bearing surface, or on surface of contact. This special

over the selected entities. The type of unit can be type of load is not uniformly distributed, and is based on

This is the most frequently used load type in Mechanica. It is length, area, or volume. The difference between this Mechanica’s built-in load function.

applied on geometric entities with a specific magnitude and type of load and a pressure load is that the direction of

direction. a pressure load will always be normal to the surface. Bearing loads act in the direction normal to the hole’s axis.

Any load vector parallel to the hole axis will be ignored by

VECTOR DEFINITION OPTIONS Total load at point (TLAP): Computes and applies the Mechanica. Check the preview to make sure the bearing

equivalent shear, moment, and torsion of a point force load is acting in the correct direction and that the correct

Components: Three acting at a specified distance from a surface. Moments half of the hole is being loaded.

force components and applied to solid elements must use the TLAP option.

three moment compo- This is because solid elements cannot accept moments Pressure Load

nents can be specified as load input as they cannot be constrained in the rota-

with reference to the tional directions. Pressure is a distributed load created in fluids by the motion

WCS or a user defined of individual molecules. Pressure loads in Mechanica apply a

coordinate system. To apply moments and torque do not select the surface and distributed force per unit area. The main difference between

specify the moment value. Instead, use the TLAP option and the pressure load and the force/moment load is that the

Direction vector and specify the point at which the total load is applied mathe- direction of the pressure load will always be normal to the

magnitude: A direction matically but distributed on the surface as shown. The point surface while the force/moment load has a director vector.

vector is specified and a is created at the center, and the surface is selected for load

magnitude for the application. It is a good practice to use the surface sets option while se-

force/moment is also lecting multiple surfaces to apply pressure load. This allows

specified. Spatial variation options specify how the load is applied over quick selection of loop surfaces, seed and boundary surfaces,

the selected entity. and solid surfaces.

Direction points and

magnitude: Direction is defined by Uniform: Distribution will be uniform over the entity. LOADS 23

selecting two datum points and the Function of coordinates: An equation or table can be

magnitude is specified.

used to govern how the load varies with respect to the

Loads coordinate system.

Back to Table of Contents

LOADS creo elements/pro 5.0 mechanica

Centrifugal Load Temperature Load QUICK REFERENCE GUIDE

Centrifugal load is created by rotating objects that experi- Temperature load simulates a temperature change over the Before importing, the part for

ence two types of centrifugal loads—force and moment. analysis model. There are three temperature load types. which the loads will be exported

Centrifugal force pushes matter away from the center of should be defined. MDO’s Load

rotation and hence is a function of the angular velocity and Global Temperature: Specify Export command is located at FILE

the distance from the center. The inertial torque due to ac- a model temperature for the > USE IN STRUCTURE.

celeration is a function of the moments of inertia about the entire analysis model and a

axis of rotation and the angular acceleration. In Mechanica, reference temperature. Loads can be set to be exported

this is a body load and is not specific to geometry or compo- from mechanism dynamic analysis

nents. Density, axis of rotation, and angular velocity/ MEC/T temperature load: The based on the time index or maxi-

acceleration are required for applying centrifugal load. temperature field from a mum loads during the analysis.

Mechanica thermal analysis can

The units for angular velocity is always rad/s. If the model is be brought into the structure Importing the mechanism load

rotating at a speed of 2000 rpm then the value to be input in mode to check the stresses and into Mechanica will not automati-

angular velocity is 2000 x 2π/ 60 rad/s deformation due to thermal cally apply the loads to appropri-

expansion. ate references. This only imports

Gravity Load the load values and the direc-

External temperature load: tion. The load distribution has

With a gravity load, Mechanica simulates Can import an FNF (finite ele- to be done manually by select-

the effect of gravity by applying accelera- ment neutral file) file that con- ing references like surfaces,

tion due to gravity to the entire model. tains temperature field informa- edges, and points.

Thus, the gravity load is also a body load. tion.

Singularity

In an assembly, applying a gravity load All temperature load types require a

will apply the gravity load automatically reference temperature that is the When applying loads or con-

to all parts in the assembly. zero stress temperature of the analy- straints, singularity or theoreti-

sis model. cally infinite stress might occur

Depending on the unit system the accel- based on the idealization and

eration due to gravity is 9.81m/s², 32.2 ft/ The CTE is a required material property to check stress and the load reference used.

s² or 386.4 in/s² deformation due to thermal expansion. By default, a global

temperature load is applied to all components in an assem- BEST PRACTICES TO AVOID SINGULARITY

bly. If a component should not be affected by temperature,

then assign a CTE value of zero for the material property of For solid idealization, do not apply loads or constraints

that component. on points and edges as they do not have an area which

will cause the stress to become infinite. Only apply

Mechanism Load loads or constraints to surfaces or surface regions.

MDO in Creo Elements/Pro can calculate acceleration, mo- For shell idealization, do not apply loads or constraints

mentum and forces acting on each body in an assembly on points. Only apply loads or constraints to edges and

using rigid bodies but does not calculate deformation or surfaces.

stress. These can be imported into Mechanica using the

mechanism load type to calculate deformation and stress. For beam idealizations, there is no surface to select so

use points or edges to apply loads and constraints.

Another way to handle singularity is to use the Auto-

GEM control to exclude preselected singularities.

Loads Back to Table of Contents LOADS 24

ANALYSIS—STRUCTURAL creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Structural Analysis The output tab allows you to select or deselect output quan- MODAL ANALYSIS

tities based on the intent of running the analysis. If the main

A structural analysis is the calculation of a model’s response intent to run a static analysis is to do a deformation analysis A modal analysis is calculates the natural frequencies and

to a loading condition and its boundary conditions. Static, or to check how much the shape of the model changes, then mode shapes of an analysis model to determines the vibra-

modal, and buckling analyses can be done using a basic it is a good practice to deselect the stresses option in the tion characteristics of parts or assemblies. Modal analysis is a

Mechanica license. output tab. This will still calculate the maximum stress in the prerequisite for all dynamic analysis types such as dynamic

model but the fringe or graph output for stress will not be time, dynamic frequency, dynamic shock, and dynamic ran-

STATIC ANALYSIS available. Only the fringe output for displacement and p- dom.

level is available. This will save analysis time as well as disk

A static analysis is used to calculate deformations, stresses space. INPUT

and strains in response to specified loads and constraints. No loads are required for a

This type of analysis is typically performed on parts or assem- PLOTTING GRID RECOMMENDATIONS modal analysis. All loads and

blies in order to find the stress and displacement distribution The density of the plotting grid where Mechanica calculates prescribed displacement con-

over the entire product. The stress and displacement can be results can be set from 2 to 10 with the default setting at 4. straints, if any, are ignored

evaluated in different forms like fringe plots or graphs. However, this default setting may not be enough if stresses during the analysis run. The

vary rapidly over a single element, so it is recommended to model can be analyzed with or

INPUT increase the plotting grid to more accurately capture the without constraints. The mo-

The input for a static analysis is one or more load sets and peak results. The recommended plotting grid for most dal parameters can be evalu-

constraint sets. At least one loadset is required to run any analyses is 7. If the analysis model contains mostly beams it ated based on the number of

static analysis except when the analysis model has a pre- is recommended to set the plotting grid to 10. When this modes or by a specified fre-

scribed displacement constraint. At least one constraint set number is higher, the grid will be finer and Mechanica re- quency range.

is required to run a static analysis, but the Inertia Relief op- ports values of output quantities from more locations on

tion can be used to analyze models without applying any each element. If this value is lower, Mechanica takes less OUTPUT

constraints. time to calculate results and uses less disk space. Increasing The modal frequency values are

or decreasing the plotting grid may not impact the overall reported in the results report

solution, as it is primarily applied to the solution display. file, and mode shapes can be

Sandy_McKinney_2015 displayed using fringe plots.

In a modal analysis, the values of other quantities like dis-

placement are normalized, so the maximum value is always

1. This is because Mechanica will divide all displacements by

the maximum displacement. The modal frequency values

reported are always in cycles per unit of time.

OUTPUT

Typical outputs from a static analysis are stresses, strains and

deformations. Force reactions and user-defined measures at

certain locations on the analysis model can also be evaluated.

A plotting grid applied on a rectangular element

Structural Back to Table of Contents ANALYSIS—BASIC MECHANICA 25

ANALYSIS—STRUCTURAL CONTACT ANALYSIS creo elements/pro 5.0 mechanica

BUCKLING ANALYSIS Contact analysis is a type of static QUICK REFERENCE GUIDE

analysis that is typically used in

Buckling analysis is used to calculate the critical buckling assemblies that have a contact Contact analysis can be configured to display results based

load factor (BLF) for the analysis model with loads applied. interface defined. A contact in- on load intervals. This allows you to check how measures

When an analysis model is subjected to compressive loads terface is applied to a component of interest will vary based on the load variation.

and if the model has a high aspect ratio then it could buckle. or component surface that might

Buckling occurs when a model is subjected to a load less come into contact on application If the main intent of running a contact analysis is to get

than what is required for failure, but that causes the model of load. Otherwise, they could accurate contact pressures using the SPA convergence

to bend under compressive stresses. separate from each other during method, then it is a good practice to use the localized

load application. The load ap- mesh refinement option during the contact analysis defini-

INPUT plied and the resulting deformations and stresses are non- tion. This will improve the accuracy of contact pressure

A static analysis should be defined with loads and con- linear because the contact area varies based on the deforma- calculations.

straints. It is not required to run the static analysis. During tion of the model.

the buckling analysis definition, the static analysis is se- If the value of the slippage indicator becomes positive dur-

lected, which Mechanica uses to calculate stress stiffening in INPUT ing the contact analysis, there is a warning in the analysis

the model due to applied forces. The model’s elastic stiff- Contact analysis re- report that indicates that the models have slid each other.

ness due to geometry and material is calculated during the quires contact interface Contact analysis does not support the following:

buckling analysis. to be defined between Shells

surfaces or compo- Large deformation non-linearity

OUTPUT nents. Prescribed displacements using spherical and cylindri-

The main two outputs from a buckling analysis are BLF and

the mode shape for each buckling mode requested. A static analysis is de- cal coordinate systems

fined, and the nonlinear If there is a fatal error warning about insufficiently con-

If the load applied on the model is L, then the load at which option to include con- strained models, make sure the models in contact are pre-

the model will buckle is L x BLF. It is a good practice to ap- tacts must be selected. vented from tangential motion using either constraints or

ply a unit value for the load so that the BLF will be the critical infinite friction.

load. Buckling analysis should be used only for compressive OUTPUT

loads. The static analysis results should be used for getting Mechanica evaluates the total contact area and the maxi-

stress plots. mum contact pressure over all the contact interfaces in the

analysis model. Contact analysis can check if slippage has

occurred between the components in contact.

Contact analysis is defined within the static analysis defini-

tion, so all the typical measures evaluated for a static analysis

such as stresses, and deformations are also evaluated.

Since contact analysis is a non-linear analysis, Mechanica

uses several iterative steps to run the analysis. The default

maximum number of iterations is 200.

Structural Back to Table of Contents 26

ANALYSIS—THERMAL creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Steady State Thermal Analysis Sandy_McKinney_2015THERMAL CONVECTIVE BOUNDARY CONDI- PRESCRIBED TEMPERATURE BOUNDARY CONDI-

TIONS TIONS

This analyzes the steady-state thermal response of the analy-

sis model when subjected to heat loads and boundary con- These are typically applied to Similar to displacement constraints in structural analysis, a

ditions. In a thermal study, the energy is transferred due to a external surfaces that are ex- prescribed temperature or reference temperature is required

temperature gradient between surfaces and can occur by posed to air or fluid to simulate to be assigned to geometric references in thermal analysis.

one of three modes: the heat loss due to convection. This simulates a constant temperature to be maintained on

the selected references.

Conduction: Heat transfer through solids due to This heat transfer is:

change in temperature. For axisymmetric models, a thermal

Q = hAΔT cyclic symmetry boundary condition

Convection: Heat transfer between a model surface h: convection coefficient should be applied.

and the surrounding fluid. This can be free or forced. A: area

ΔT: temperature difference A mirror symmetry condition is not

Radiation: Heat transfer due to electromagnetic radia- applicable for thermal analysis mod-

tion. between the model sur- els. With mirror symmetry, the tem-

face and the surrounding perature on either side of the sym-

The native mode in Mechanica can simulate conduction and air temperature metry plane would be the same and

convection heat transfer. Radiation cannot be modeled thereby no heat transfer would oc-

directly but it can be simulated using convection if the radia- In order for Mechanica to simu- cur

tion is between a black body and another black enclosure late convection heat transfer, it

located at infinity. requires the following: IMPORT THERMAL RESULTS INTO STRUCTURE

HEAT LOADS Surfaces Typical output quantities from a thermal analysis are tem-

Convection heat transfer coefficient (h): This is typi- perature, temperature gradient, and heat flux. In order to

Heat loads are typically applied to calculate thermal stresses or mechanical stress due to ther-

geometric references or entire mod- cally derived by simulating the flow using a CFD tool. mal expansion, the results from a Mechanica thermal study

els to simulate a heat source or heat Bulk temperature: This is the temperature of surround- should be imported into structure mode to run a static

sink. Just like structural loads, the analysis.

heat load distribution and spatial ing air or fluid.

variation can be configured. Heat Analysis models can be switched between thermal and

loads can vary with time if the main The convection coefficient can be imported into Mechanica structure modes using the main menu, EDIT > MECHANICA

intent of the thermal analysis is to get using an external coefficients field file. MODEL SETUP.

a transient response instead of a

steady state response. If an external coefficients filed file is not imported, a positive

value for h can be entered as an empirical data or a standard

A positive heat load value represents value based on thermal databooks or hand calculations.

a heat source, and a negative value

represents a heat sink.

Thermal Back to Table of Contents ANALYSIS—BASIC MECHANICA 27

CONVERGENCE—QUICK CHECK, SPA, MPA creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

The accuracy of Mechanica’s results is dependent on the Single-Pass Adaptive (SPA) Multi-Pass Adaptive (MPA)

convergence method used to solve the analysis. Conver-

gence is a situation wherein the results do not change with This method has a built-in convergence using stress error This convergence method gives the most accurate solution

respect to mesh parameters like polynomial order or the estimates. Mechanica will run the first pass using a polyno- since the convergence tolerance is controlled by the user

number of elements. Since Mechanica uses the p-method, mial order of 3 and calculates local stress errors. Based on and is not dependent on built-in error estimators.

the polynomial order is increased to achieve solution accu- these errors, Mechanica determines a new polynomial orders

racy. One of the following three convergence methods for each element edge and performs a final pass. A final Mechanica runs the first pass with an edge order of 1,

should be selected during the analysis definition stage: stress error is reported at the end of the analysis. This is a thereby using a linear equation to solve. In the second pass,

sampling of the local error estimates that were used to in- all element edge orders are increased to 2, thereby using a

Quick Check crease the polynomial order. quadratic equation to solve.

Single-Pass Adaptive (SPA)

Multi-Pass Adaptive (MPA) With the SPA method, the user does not control the conver- The results from the second pass and first pass are compared

gence tolerance, as it is built into the software. Always check for each element and element edge. If the difference is more

Quick Check the stress error and also the maximum edge order of the than the user-defined convergence tolerance percent, then

second or final pass. If the stress error is low, then there is no the edge order is increased to 3. If the difference is less than

Quick Check can be used to check the feasibility of an analy- need to run the analysis using the MPA method. If the stress the convergence tolerance percent then the same edge or-

sis to make sure that it can run without any major errors. error is high, it is better to run the analysis using the MPA der is retained. This process is repeated for several passes

Mechanica solves the analysis using a uniform polynomial method. until convergence is reached for all elements and element

order of three over the entire analysis model. This method edges.

does not do any kind of convergence. The biggest advantage of the SPA method is the relatively

short run time on complex analysis models as compared to The default minimum and maximum edge order should be

It is a good practice to run complex analysis using the quick the MPA method. used. If the analysis does not converge, then the minimum

check method first before running an MPA analysis. and maximum edge order can be changed. The default con-

The SPA method is available for static, modal, buckling, and vergence of10 percent is applied to all quantities selected for

Before running multiple analyses using batch files, a quick contact analyses. It is not available for pre-stress static analy- convergence. The recommended range for convergence is

check analysis should be run to make sure everything is fine sis. It is not recommended to use the SPA method for con- one to 25 percent.

with the analysis setup. tact analysis as it might result in very long run times.

It is a best practice is to begin with the default 10 percent

The results from a quick check should always be ignored, as and then check the report to see if the analysis converged or

it should only be used to look for any fatal errors during the not. If it is converged, then a lower convergence percent can

analysis run. If the quick check runs successfully without any be used to get more accurate results, although this will in-

errors, then the MPA or SPA method should also run success- crease the run time as Mechanica will need to go through

fully except for reasons such as disk space or memory issues. additional passes. The MPA method typically takes longer

than the SPA method but is more accurate.

Quick Check, SPA, MPA Back to Table of Contents 28

CONVERGENCE—MPA creo elements/pro 5.0 mechanica

MPA CONVERGE ON OPTIONS CONVERGE ON OPTIONS FOR THERMAL ANALYSIS QUICK REFERENCE GUIDE

CONVERGE ON OPTIONS FOR STRUCTURAL ANALYSIS CONVERGENCE GRAPHS

When using the MPA method for structural analyses like

static, pre-stress static, contact, and large deformation, the If the MPA report says that the analysis converged within the

convergence percent is applied to specific measures of inter- convergence percent, then plot the convergence graphs as

est or one of the options as shown below. shown. The x axis of this graph is the p-pass and the y axis is

the measure of interest like von Mises stress, max displace-

ment, temperature, or frequency.

Local Displacement, Local Strain Energy and Global Sandy_McKinney_2015 Local Temperatures and Local Energy Norms: If thisThe convergence graphs is the best way to check the quality

RMS Stress: This option will also converge on RMS option is selected, the convergence percent is applied of an MPA solution. The graph should have almost zero

stress in addition to displacement and strain energy. to the following: slope near the higher p-levels and a clear trend approaching

Temperatures along each element edge a value.

Local Displacement and Local Strain Energy: If this Energy norms of each element

option is selected, the convergence percent is applied If the MPA reports that the analysis did not converge within

to the following: Local Temperatures and Local and Global Energy the specified convergence percent, then the following op-

Displacements along each element edge Norms: This option will converge on global energy tions should be used to get a converged solution:

Total strain energy of each element norm which is the sum of the energy norms of all ele-

ments in the analysis model. Check the last pass maximum edge order, if this is nine

Measures: This is the recommended option wherein then Mechanica has reached the limit.

one or more measures of interest (i.e., maximum stress, Measures: This option will result in a faster analysis,

maximum displacement) can be selected for conver- with accuracy only for selected measures, such as maxi- Check the p-level fringe as shown below to identify the

gence. This option will give accurate results only for the mum temperature. location of the edges that reached ninth order polyno-

measure of interest and the analysis run time will be mial.

quicker compared to the other two options. EVALUATING MPA RESULTS

CONVERGE ON OPTIONS FOR MODAL ANALYSIS The first thing to look for after the completion of an analysis

In a modal analysis the frequency is the measure of interest using MPA method is for the message in the report about

and so this option should be selected. the convergence as shown here.

CONVERGE ON OPTIONS FOR BUCKLING ANALYSIS Back to Table of Contents Apply the mesh controls on these areas that have

Since the BLF is the measure of interest this options should reached the ninth order so that Mechanica can con-

be selected. verge within the specified percent.

MPA, 29

ANALYSIS RUN SETTINGS creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

Once the analysis is defined and ready to run, there are some In such situations it is a best practice to use the following Solver Type

settings to control the output folder locations, solver set- approaches to fix the issue:

tings, and element creation settings. Mechanica can be set to use either the direct or the iterative

Change the RAM allocation back to default setting of solver to run any analysis. Each solver uses a different

Output Folder Settings 128 MB. method to solve the simultaneous equations during analysis

run.

By default, all the analysis output files are created in the cur- Try SPA convergence method instead of MPA conver-

rent working directory. This can be changed in the run set- gence. The direct solver is the default solver as it requires less time,

tings or by setting the config option, SIM_RUN_OUT_DIR. disk space, and memory than the iterative solver. When

Reduce the plotting grid in the output settings. using the direct solver, if the ratio of elapsed time/CPU time

Mechanica creates a temporary folder containing temporary If you are running modal analysis, reduce the frequency is greater than four, then switch to the iterative solver. If

files during analysis run that is automatically removed as you are using the iterative solver and this ratio is greater

soon as the analysis is completed. The config option to set range or number of modes. than seven, then switch to direct solver. The elapsed time

directory for temporary files is SIM_RUN_TMP_DIR. Idealizations like shells, beams, mass, and spring should and CPU time is in the report file.

Mesh is typically generated by Mechanica during the analy- be used whenever possible. The default direct solver is recommend for the following:

sis run. If there is an existing mesh file—.mmp (part mesh De-feature the analysis model.

file) or .mma (assembly mesh file)—then check the run set- Check for symmetry. The analysis model contains thin features.

tings to use this mesh file instead of creating elements dur- Change the model type from 3D to one of the 2D model The analysis did not converge with the iterative solver.

ing run. If you are running more than one analysis on the The design study has analyses other than linear static,

model, then the mesh from an existing study can be used. types, if applicable.

Reduce the number of contact interfaces if running a such as contact analysis, modal or transient thermal.

Mechanica Solver Settings If the analysis model reports an insufficiently con-

static contact analysis.

The default memory allocation is set to 128 MB. The config strained error and wants to locate constraint problems.

option, SIM_SOLVER_MEMORY_ALLOCATION, can be used NOTE:

to set the memory allocation. The Mechanica solver had a memory limit of 8 GB on 64- The iterative solver can be used in the following situations:

bit operating systems until Pro/ENGINEER Wildfire 2.0.

The memory allocation for Mechanica solver should be set to Beginning with Wildfire 3.0, this 8 GB per process limit If you run out of disk space when using the direct solver.

half of the physical RAM of the computer. The default alloca- has been removed, and the model size to run Mechanica If the direct solver takes long time to complete.

tion will be able to run any analysis but changing it to half of analysis is almost unlimited. When running linear static analysis on solids.

physical RAM will improve the run time.

The iterative solver cannot be used in the following situa-

When the RAM allocation is set to more than half the RAM, tions.

the analysis might slow down or run into a fatal error as

shown at right. If the design study contains modal analyses.

If the local sensitivity or optimization design study con-

tains analyses that have temperature loads referencing

thermal analysis.

Analysis Run Settings Back to Table of Contents ANALYSIS RUN SETTINGS 30

RESULTS—FOLDER AND FILES; DISPLAY creo elements/pro 5.0 mechanica

QUICK REFERENCE GUIDE

After a successful analysis run, Mechanica will output solu- Sandy_McKinney_2015 The .rpt file is a text file containing the analysis sum- Results Display

tion files and the results can be displayed in several formats mary.

and options. Mechanica results are dis-

The .pas file contains a time log of various analysis and played in a separate result

Results Folder and Files file operations. window interface and is ac-

cessed using the rainbow

After an analysis is run, Mechanica will create a results folder The .err file has error messages that occur during the color icon as shown here.

to store all solution files and associated log files along with a analysis run.

copy of the analysis model. Below is an example results STUDY SELECTION

folder and the various files: There is a temporary

folder (.tmp) that is cre- The first step in results display is to select a results folder.

Analysis name: tristar_study ated during the analysis Results can be displayed without having the analysis model

Analysis model: tristar_design.prt run which contains the in session because the result folder always contains a back

stiffness matrix. This up copy of the analysis model. It is also not required to have

Contents of the results folder includes several files and a folder is automatically a Mechanica license in order to display results.

another subfolder containing solution files. deleted by Mechanica

upon successful completion of the analysis. DISPLAY TYPE

As soon as the analysis is completed, Mechanica will create a

backup of the analysis model and place it in the analysis ANALYSIS RESULT FILES IN WINDCHILL AND The results display is configured using the Result Window

results folder as shown above. In order to view results, the PRO/INTRALINK Definition dialog box. A successful analysis run is a prerequi-

results folder contents site to display any type of results. The following result dis-

and the subfolder con- The results folder can be compressed and saved to the active play types are available:

tents, shown here, are workspace when using Pro/INTRALINK or Windchill by using Fringe

required. the Vault Results option as shown here. Vectors

Graph

The VAULT RESULTS option is available Model

only after completion of the analysis

and after the analysis model is checked

in. This will create a compressed .mrs

file in the workspace. This compressed

file contains the entire results folder

and a snapshot of the analysis model.

The compressed results file can be

exported to a local directory.

Windchill creates a derived link from

the results file to the last checked in version of the analysis

model. However, this link does not result in automatic re-

trieval of results file when retrieving the analysis model. The

link only indicates that a particular version of the results

reference a particular version of the model and can be used

when doing a search within Windchill. With the release of

Creo 1.0, PTC plans to allow export of Mechanica results in .ol

(Creo Elements/View) format.

Folder and Files; Display Types Back to Table of Contents RESULTS 31

RESULTS—DISPLAY; GRAPH RESULT WINDOW DEFINITION creo elements/pro 5.0 mechanica

VECTOR GRAPH RESULT WINDOW DEFINITION QUICK REFERENCE GUIDE

During the definition of a graph type result window, the

Vectors display the directional behavior of a quantity as col- display location and display options are grayed out. The x– The graph’s appearance can be controlled using the FOR-

ored arrows that are superimposed over a transparent dis- and y-axis quantities needs to be specified. Based on the MAT > GRAPH option in the Result Window interface. This

play of the model. Each set of arrows represents a different type of the study or analysis, various options are available. will allow control of the x- and y-axis displays, data series

range of values for the quantity. Vector plots use arrow User-defined measures or system-defined measures can also display, and the main graph display properties like back-

length and color to indicate the magnitude of the quantity. be selected for graph results. ground color and label text.

Typical result window definition setups for a sensitivity

study, an optimization study, a static analysis, and an MPA

static analysis are shown below.

Sandy_McKinney_2015

By default, the vectors displayed are 3D. If the system mem- Sensitivity Study Optimization Study The preferred settings for the graph results window can ei-

ory is not sufficient to display 3D vector arrows, use the con- ther be set each time the results are brought into session or

fig option to display the vector plot using 2D arrows set permanently in a file. This is done using a graph prefer-

(SIM_PP_VECTOR_PLOT_ARROW_2D). ences file and a config option. The following procedure sets

up the graph preferences file:

GRAPHS

1. Create an empty text file.

Graph displays are typically used to view the results of sensi- 2. Set the config option, bmgr_pref_file, to point to the

tivity and optimization studies. They can also be used for

any analysis to view the graph of the quantity of interest, like text file.

displacement or stress with reference to geometric refer- 3. Customize the graph display using the FORMAT >

ence. In a vibration analysis, graph plots will output quantity

in reference to time or frequency steps. GRAPH options.

4. Select the SET DEFAULT button in the graph window

The graph results below are for a static analysis. The quan-

tity is in the y-axis of the graph, and the x-axis of the graph options dialog box. This will save all customizations

displays selected edge or curve length from the analysis done to the graph results to the text file created earlier.

model. For sensitivity studies, the y-axis the measure quan- 5. These settings will be used each time a graph is created.

tity and the x-axis is the variable design parameter.

Graph data can be exported as a text file with a .grt exten-

sion or as an Excel file.

Static Analysis MPA Analysis

Display Types Back to Table of Contents RESULTS 33

RESULTS—DISPLAY TYPES; DISPLAY QUANTITY; DISPLAY LOCATION creo elements/pro 5.0 mechanica

MODEL Why do we need stress linearization reports? When looking QUICK REFERENCE GUIDE

at the distribution of stress through the thickness of a thin-

Models can display the analysis model geometry in a de- walled part, this report is useful to compare to the relevant Display Location

formed state or original state, a simple animation of how the ASME codes. The stress linearization utility can help evalu-

model deforms, or an optimized shape of the analysis model. ate a design’s compliance with industry standards, such as Based on the type of design study and idealizations in the

the ASME Boiler and Pressure Vessel code. analysis model, there are several options to specify the re-

The linearized stress of the analysis model can also be dis- sults display location.

played by selecting INFO > LINEARIZED STRESS QUERY. This Display Quantity All

report is generated by querying two locations on the analy- Beams

sis model. Mechanica calculates the total local coordinate During the result window definition, the display quantity, Curves

stress components at each point and then calculates mem- component, and units can be selected. Surfaces

brane, bending stress, peak stress, and total stress. These Volumes

values are calculated and reported with respect to a local Components/layers

coordinate system with the x-axis aligned with the line Contact surfaces

(stress classification line) connecting the two locations and During the results display of an assembly analysis model, the

with the origin at the midpoint of the line. An additional Components/Layers option is very useful. This can be used

point should be selected to define the xy plane. to show, hide or isolate specific components or layers of an

analysis model as shown below.

Along with typical quantities like

von Mises stress, displacement, If the analysis model is an assembly, the layer tree displays

and temperature, the P-level and the components and any layer containing beam or shell

failure index can also be displayed. definitions. If the analysis model is a part, the layer tree dis-

The failure index is the ratio of the plays only layers containing beam and shell definitions. ,It is

actual stress to the yield strength a good practice to use the isolate option to view the results

of the material and can be used to of selected components or layers and to use the blank op-

determine if the material failed tion to exclude a few components or layers from the display.

under the applied loading condi-

tions. If the failure index is less

than one, the material has not failed.

The failure index option

will be available in the

quantity tab only if the

material tensile yield

stress is specified in the

material property prior to

running the analysis. It is a good practice to include a factor

of safety while entering the yield strength of the material.

When the analysis model is an assembly that consists of sev-

eral materials, the failure index is very useful to determine

which material has failed, as it takes into account the yield

strength of the individual materials of the analysis model.

Display Types; Display Quantity; Display Location Back to Table of Contents RESULTS 34

RESULTS—DISPLAY LOCATION creo elements/pro 5.0 mechanica

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Dynamic query of a fringe plot allows you to check the quan- When viewing fringe plots, a cutting plane or capping sur- The visual characteristics of a displayed result window can

tity values anywhere on the analysis model. These queried face can be used to clip the analysis model to examine the be controlled by selecting FORMAT > RESULT WINDOW. The

values along with their location coordinates can also be dis- interior of the model. This can be created on non-animating appearance and range of values for fringe, contour, and vec-

played on the fringe plot and used in analysis reports. fringe or contour plots. Use INSERT > CUTTING/CAPPING tor plots can be controlled using FORMAT > LEGEND.

SURFS to create these plots.

A cutting surface will slice the analysis model and trim both

sides, whereas a capping surface will slice the model and

trim one of the two sides. More than one cutting surface can

be created, but only one capping surface can be created on

the analysis model, as shown below.

Sandy_McKinney_2015

Annotations of measures created When multiple result windows are displayed, the active win-

after the analysis can be displayed dow has a yellow border. Multiple windows can be selected

automatically. INFO > MEASURES using the SHIFT key to allow all selected windows to be for-

will give the list of measures calcu- matted together. Result windows can also be reordered or

lated, and there is a button to cre- swapped.

ate annotation on the fringe plot

automatically as shown at right. Cutting and capping surfaces are typically used on thick It is not required to have a Mechanica license or the analysis

Annotations can also be created models that may have significant variations of interior stress model in session to create, view, and edit result windows.

manually using INSERT > ANNOTA- or may have unseen deformations. The only requirement is access to the results folder. The

TION where there are options to result interface can be accessed in Creo Elements/Pro at

surround the text with a border, By default, Mechanica displays the outline of the model APPLICATIONS > MECHANICA RESULTS.

add a background color, or define when using cutting or capping surface. This outline can be

a shape with a mouse sketch. hidden using the config option, RESULTS 35

SIM_PP_SHOW_CAP_CUT_OUTLINE.

Display Location

Back to Table of Contents

RESULTS—RESULT WINDOW DEFINITION creo elements/pro 5.0 mechanica

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Result Window Definition These HTML reports capture the vital points of the analysis When comparing the legend values or graph ranges from

with options to include images and animations from the multiple result windows, use the UTILITIES > TIE option.

Result window definitions can be saved as .rwd files that can result window interface.

be retrieved later from the result interface. Common result The tie option can be applied only to the same types of

window definitions, such as von Mises plots and displace- Fringe plots can also be exported in VRML format. Use the result windows.

ment plots, can also be saved as a result window template config option SIM_PP_VRML_EXPORT_FORMAT to specify

(.rwt file) by selecting FILE > SAVE AS TEMPLATE. This will whether the export format is VRML 1.0 or VRML 2.0. The quantities displayed must be of the same general

save the definition and some attributes and can be used to category to tie the results. For example, a von Mises

quickly define new result windows based on the template The result windows can also be exported as an image and fringe plot cannot be tied to a displacement fringe plot.

file. saved to commonly used formats such as TIFF, and JPG.

It is a best practice to use the tie option when compar-

Analysis reports can be generated from within the results During the generation of analysis reports, the result window ing result windows from local sensitivity studies to

interface using FILE > EXPORT > HTML REPORT. interface can be used to capture specific orientations of the check the sensitivity of various design parameters.

analysis model that can reference existing saved views or

can create new views based on precise angles with reference While creating multiple result windows from the same de-

to the screen center or spin center as shown. Select VIEW > sign study or analysis, it is a good practice to use the copy

SPIN/PAN/ZOOM from the Result Window interface to access option to efficiently replicate existing result windows. This

this feature. The model displayed in the Mechanica result avoids the need to browse to the results folder to create a

window can be manipulated in the same way as in standard result window each time.

Creo Elements/Pro mode.

When the analysis has multiple loadsets, the result window

definition can be used to select or deselect specific loadsets

with options to apply a scaling factor to that loadset using

the table shown. Result plots can be viewed based on spe-

cific loadsets. This table can also include frequency, time

steps, modes, and load increments based on the design

study.

During the result window definition, if there is an error after

selecting the results folder, make sure the analysis has com-

pleted and check to see if the analysis was run with a newer

release of Creo Elements/Pro.

Result Window Definition Back to Table of Contents RESULTS 36

DESIGN STUDY—DESIGN VARIABLES, STANDARD DESIGN STUDY creo elements/pro 5.0 mechanica

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Design studies are used to evaluate “what if?” scenarios on Sandy_McKinney_2015Creo Elements/Pro parameters can be used to define design Standard Design Study

the analysis model. They can be used to determine the ef- variables like material properties or even load values by us-

fect of design variables and optimize the model based on ing the following steps: A standard design study can be used to run the analysis at

the analysis objectives. The following types of design stud- specific design variable values. The main advantage of run-

ies can be created in Mechanica: 1. Create Creo Elements/ ning this type of study is that the original analysis model

Pro parameters in stan- dimensions and parameters need not be changed but it

Standard Design Study dard mode. allows you to run consequential scenarios by changing these

Sensitivity Design Study dimensions and parameters within the design study.

Optimization Design Study 2. In Mechanica mode,

right-click on the value Standard design studies allow you to study the behavior of

Design Variables field and select Parame- the analysis model without actual modification. More than

ter. Choose a paramater one analysis can be selected for a design study, or a simple

Design variables are dimensions or parameters that can from the Creo Elements/ regeneration check with the specified new settings can be

change the shape and properties of the analysis model while Pro parameter list. done. Multiple standard design studies should be defined in

running design studies. Design variables can be created for order to run the analysis with different design variable set-

the following: 3. Use this parameter in tings.

design studies by select- The results folder for each design study will have the analysis

Dimensions ing the parameters icon model with the specified settings of the design study. So the

Creo Elements/Pro parameters in the design study defi- original model still has original settings but the analysis

Beam cross section properties nition dialog box. folder contains the model with new settings.

Material properties

Laminate layup shell properties When selecting Creo Elements/Pro dimensions as design

variables, it is a good practice to rename the dimension

Once the design variables are defined, Mechanica can be name (i.e, length, radius, thickness) instead of using the de-

instructed to perform the following- fault dimension name (i.e., d23, d10, d4).

Specify a different setting in a standard design study. Before running a sensitivity or optimization study, it is a

good practice to check for any regeneration failures using

Specify the range to vary in a sensitivity or optimization the shape animate option in the design study. Mechanica

study. will check if the range for the design variable is feasible from

a regeneration standpoint. The shape animate tool is ac-

cessed from the options button in the study definition dialog

box.

Design Variables, Standard Design Study Back to Table of Contents DESIGN STUDY 37

DESIGN STUDY—SENSITIVITY, OPTIMIZATION creo elements/pro 5.0 mechanica

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Sensitivity Study GLOBAL SENSITIVITY STUDY Optimization Study

There are two types of sensitivity studies in Mechanica: Global sensitivity studies are used to generate a much larger Optimization studies find

Local sensitivity study picture of how analysis objectives respond to changing one the value of the design

Global sensitivity study design variable over a specified range. variables needed to

Mechanica will run the analysis at regular intervals within the achieve the best design

LOCAL SENSITIVITY STUDY specified range. The number of intervals or steps are de- within specified limits

fined during the definition of the study. and goals. All design

Local sensitivity studies are used to check the effect of slight variables that passed the

changes in one or more design variables on the analysis The output from a global sensitivity study is a graph plot sensitivity studies are

objectives. with the x-axis being the design variable, and the y-axis be- used as a solution space

A base analysis is selected and all design variables are se- ing any measure or analysis objective like stress, displace- in optimization studies.

lected. The analysis is conducted changing the design vari- ment, temperature, frequency, etc. The global study result

able by +1% and –1% of the current or specified settings. graph can be used to decide on the best value of the design Design limits are typi-

Local sensitivity studies are output to graph plots. This graph variable to be used as a starting point in optimization stud- cally limits on the stress,

will have two points and a line connecting these two points ies. displacement, temperature, or frequency, for example. A

to compare slope. The slopes of each design variable can be goal such as to minimize the stress, mass, or any other meas-

compared to determine the most sensitive design variable. ure should be specified. An optimization study without a

Design variables having zero or a small slope relative to goal will find the nearest possible solution that satisfies the

other design variables can be eliminated from future global design limits, thereby doing a feasibility study.

sensitivity and optimization studies.

Optimization convergence is a toler-

While comparing the graph plots of a local sensitivity study, ance applied to the design limit

it is a good practice to tie (UTILITIES > TIE) the graph quantity values. Repeat p-loop convergence

(y-axis) as shown in the three graphs at right. For example, will instruct Mechanica to do the p-

the y-axis could be the von Mises stress, while the x-axis is level calculations for each shape

the design variable that has been perturbed by one percent. change iteration. Otherwise, it will

simply use the maximum edge or-

der of the initial iteration for all

other iterations.

When the range of the design variables is large, then it is a

good practice to use the remesh after each shape update

option.

Outputs from an optimization study include:

Graphs of measures against the iterations.

Standard results for the final optimized model.

Final design variable values. Use INFO > OPTIMIZE HIS-

TORY from the analysis dialog box to step through

every iteration value on the model.

Sensitivity, Optimization Back to Table of Contents DESIGN STUDY 38

ANALYSIS—PRESTRESS STATIC, PRESTRESS MODAL, LDA creo elements/pro 5.0 mechanica

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An Advanced Mechanica license is required for the following Sandy_McKinney_2015Prestress Modal Analysis INPUT

analysis types: In addition to the stan-

When static loads change the stiffness of the model, the dard static analysis input

Prestress Static modes and natural frequencies of the model will also change like loads and con-

Prestress Modal as they are dependent on the stiffness and mass distribution. straints, the load inter-

Large Deformation The prestress modal analysis should be used in such situa- vals can also be speci-

Dynamic (Vibration) Analysis tions. Rotating machinery with centrifugal load due to high fied. There some limita-

Transient Thermal RPM are subject to stress stiffening and spin softening, and tions for using LDA:

pre-stress modal analysis

Prestress Static Analysis can take these into ac- Beam and shell

count. elements are not

This type of analysis is used when the applied load changes supported.

the stiffness of the model. The effect of prestresses or pres- INPUT

tiffened structures on deformation, stress, and strain can be A previous static analysis No temperature

analyzed using a pre-stress static analysis, which takes into is required before defin- dependent material

account the loading for stiffness. ing the prestress modal properties.

analysis. As with any

INPUT modal analysis, the No bearing loads.

A previous static analysis and a new loadset are required as modes within a fre-

an input. As shown here in the Prestress Static Analysis Defi- quency range or the Remember to select the

nition dialog box, the static analysis will run first with just the number of modes can be Nonlinear and Calculate

initial_load, and the specified. Large Deformations

resulting model stiff- options in the Static

ness is calculated OUTPUT Analysis Definition dialog box.

before the application This is the same as any

of the new_load. modal analysis output. OUTPUT

This is the same as the standard static analysis output. If load

It is important to se- Large Deformation Analysis (LDA) intervals were given during the analysis definition, then

lect the loadsets as graph plots can be created between deflection and applied

shown so that the Large Deformation Analysis is used to simulate geometric load confirming the nonlinear response, as shown below. In

new loadset is ap- non-linearity and when rotations and strains are arbitrarily general, if the displacement is more than half of the thick-

plied after the stiff- large such as deformations in elastomers, plastically- ness of the part then the LDA option should be used.

ness calculation due deforming materials, fluids, and biological soft tissue. As of

to existing loadset. Creo Elements/Pro 5.0, Mechanica supports linear elastic and

The scale of the load hyperelastic materials for large deformation analysis.

applied in the previ-

ous static analysis can Why use LDA? The standard static analysis is based on linear

be increased. theory and assumes small deformations only. If the deflec-

tion in a plate is larger than one half of the plate thickness,

OUTPUT the middle surface of the plate is strained appreciably, so the

This is the same as any static analysis output. plate’s geometry is not the same as it was before deforma-

tion. When this condition of large deflection occurs, the

plate is actually stiffer than indicated by ordinary theory, and

the load-deflection relations are nonlinear.

Prestress Static, PreStress Modal, LDA Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 39

ANALYSIS—DYNAMIC creo elements/pro 5.0 mechanica

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Dynamic Analysis Time function: The time history for the load or base excita- OUTPUT

tion is defined using a time function. By default, Mechanica Typical output from a dy-

There are four types of dynamic analysis, which are used to uses the built-in impulse function which uses the Dirac’s namic time analysis are

simulate the response of the analysis model to different Delta function to represent a sudden load. User-defined displacements, velocities,

types of vibration problems: time history can also be used by defining a symbolic func- accelerations, and stresses

tion of time or a table that has time versus magnitude of at different times. Output

Dynamic Time load, as shown here. intervals can be either auto-

Dynamic Frequency matically defined by

Dynamic Random Modes: By default, a dy- Mechanica or user-defined.

Dynamic Shock namic time analysis will

make use of all modes from Mass Participation Factors can be calcu-

The physical test equivalent of dynamic analysis is the shaker the modal analysis. The lated to get the cumulative mass partici-

table test. number of modes to be pation. If the cumulative mass participa-

used can be limited by using tion is less than 80 percent, then more

DYNAMIC TIME ANALYSIS the Below Specified Fre- modes should be requested in the modal

quency option. All dynamic analysis.

This type of analysis is used to calculate the response of analysis types in Mechanica

analysis models that are subjected to non-periodic or impul- require a modal analysis. Dynamic measures are not automatically

sive time dependent load. predefined in Mechanica, so before run-

Damping Coefficient: This is the percentage of relative ning the dynamic analysis, they have to

INPUT damping, or the ratio between the damping in the system created manually.

Load Definition: The loading can either be load functions and a critically damped system. A single damping coeffi-

or base excitation. Load functions define existing loads on cient can be assigned to all modes, or separate damping Below is a typical dynamic time analysis procedure:

the model with a time history. coefficients can be assigned to individual modes. It can also

be assigned as a function of frequency. 1. Define and run a modal analysis.

Base excitation defines acceleration vector based on time 2. Define the dynamic time analysis with the required

history. With base excitation, Mechanica can provide results The normal range of damping coefficient is zero to 50 per-

based on ground or supports. Stresses will be the same in cent. A damping coefficient of 100 percent means the analy- inputs.

both cases but displacements, velocities, and accelerations sis model is critically damped. In general, welded or bolted 3. Create dynamic measures like stress, acceleration, dis-

will be different based on the frame of reference. steel structures are given a damping coefficient of four per-

cent. placement, etc.

4. Run the dynamic time analysis with output intervals set

to automatic intervals.

5. Examine the analysis report for mass participation fac-

tors using base excitation loading. If cumulative mass

participation has reached 80 percent or more, there is

no need to request additional modes in modal analysis.

Otherwise, rerun the modal analysis by requesting more

modes in order to reach 80 percent cumulative mass

participation.

6. Create a graph plot between the measures, such as

stress versus time, and note the peak times at which the

stress is high.

7. Run the dynamic time analysis with the output intervals

set to user-defined, and specify the peak times from the

last step to calculate full results including fringe plots.

Dynamic Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 40

ANALYSIS—DYNAMIC creo elements/pro 5.0 mechanica

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DYNAMIC FREQUENCY ANALYSIS Sandy_McKinney_2015DYNAMIC RANDOM ANALYSIS In a dynamic random

analysis with base excita-

This type of analysis is used to calculate the response of This analysis is used to calculate the response of analysis tion loading, the value

analysis models that are subjected to a periodic, or cyclical, models that are subjected to non-cyclical vibrations and typed in the base excita-

frequency-dependent load. It is similar to the dynamic time have random vibration problems with the input in the form tion direction vector is

analysis except that the input is defined in the frequency of a power spectral density (PSD) function. squared and scaled by

domain instead of the time domain. Typically, the frequency the defined function. Even though the acceleration is re-

domain is used when the input to a vibration problem is too Generally, there are two approaches for evaluating structural ported in g²/Hz, the base excitation vector should have only

complex to be expressed in the time domain. response to dynamic loading—deterministic and statistical. the value of g in that unit system like 368.4 in/s² or 9.8 m/s².

In Mechanica, the deterministic approach is simulated using

INPUT the dynamic time or frequency analysis wherein the exact OUTPUT

This is the same as with the dy- time history or driving frequency and amplitude are known. The results from a dynamic random analysis are reported in

namic time analysis except that If the loading variation is not completely known but can be terms of response PSD. The values reported at specific out-

the default function used in a defined in a statistical sense like a PSD, then Mechanica can put interval values are spectral density values. For example,

dynamic frequency analysis is a simulate this using the dynamic random analysis. stress would be in psi²/Hz or MPA²/Hz and not in psi or MPA.

uniform function (instead of the Typical output from a dynamic random analysis are power

impulse function used in dy- Random vibration analysis represents the true environment spectral densities and RMS values of displacements, veloci-

namic time) that is a constant value equal to 1 (load is multi- in which airplanes, missiles, robots, and free standing struc- ties, accelerations, and stresses.

plied by 1 over the frequency range), with options to add tures must operate. In a random vibration, all frequencies

user-defined functions or a table to define the frequency might occur simultaneously so the overall response of the The area under the spectral density curve is the root mean

profile of the load. If the analysis model has multiple load- system is calculated statistically from the random vibration square. It can be assumed that naturally occurring vibration

sets, then the phase between the loads need to be defined. environment. follows a normal probability distribution function and so has

a mean of zero. If the mean is zero, then the root mean

OUTPUT INPUT square is equal to the standard deviation (σ or sigma). Re-

Typical output from a dynamic frequency analysis are ampli- In put for a dynamic random analysis is acceleration or force sults from a random vibration can be judged by using three

tude and phase of displacements, velocities, accelerations, over a range of frequencies called a spectrum. These are sigma results. There is a 0.3 percent probability that the

and stresses in the analysis model in response to a load oscil- typically obtained by sampling over a period of time, but are value could be higher than three standard deviations.

lating at different frequencies. The choice to use either a not time-dependent. A better statistical sampling in the

dynamic time or frequency analysis in any given case de- frequency domain will be obtained as the sampling time is The values of stress reported in a dynamic random analysis

pends upon whether the loading is periodic or non-periodic. increased. These measurements are referred to as Spectral are the RMS stresses and not the actual stress in the analysis

If the forcing load is periodic, then it is more convenient to or PSD or more specifically acceleration spectral density model at any point in time. If the maximum stress is found

perform a dynamic frequency analysis, but if the loading is (ASD) or force spectral density (FSD). to be 100 MPA, the three sigma value would be 300 MPA,

non-periodic or impulsive (shock loading), then the dynamic which means there is only 0.3% chance that the stress will be

time analysis should be used. higher than 300 MPA. Therefore, if the requirements specify

that the analysis model should be designed based on 3σ

stresses, create a measure for the root mean square of the

maximum stress and multiply the output by 3. Only vector

quantities of measures can be reported in a dynamic random

analysis. Measures calculating von Mises stress or maximum

displacement magnitude cannot be created or evaluated.

ASD input is typically obtained from empirical data. These

acceleration plots can also be obtained from documents

such as the MIL-STD-810.

Dynamic Back to Table of Contents 41

ANALYSIS—DYNAMIC, TRANSIENT THERMAL, FATIGUE, 2D MODEL TYPE creo elements/pro 5.0 mechanica

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DYNAMIC SHOCK ANALYSIS INPUT INPUT

A time-dependent heat load is applied on the model. The desired number of cycles

This type of analysis is used for seismic analysis and for solv- and the type of cyclic loading

ing vibration problems that are not stationary. It should not OUTPUT is required. A static analysis is

be used to analyze impact or impulsive loading. The thermal response as a function of time is reported. Out- also required to run the fatigue

put intervals with in the time range can be specified. analysis.

INPUT

The load input is a response In transient thermal analysis, the initial temperature has to OUTPUT

spectrum of either displace- be specified. This can either be a uniform temperature over A fatigue analysis can output

ment, velocity, or accelera- the model, or the steady state thermal analysis temperature the following:

tion. The response spectrum distribution can

is used as a weight factor to be applied using Log Life: The estimated

multiply each individual the MecT option. number of cycles until the

modal shape and then add The initial tem- model breaks.

them together by means of perature should

absolute sum or SRSS match with the Log Damage: The ratio of accumulated fatigue cycles

method. prescribed tem- and total number of cycles to failure. A value greater

perature values. than 1 indicates failure.

The absolute sum method assumes that the maximum dis-

placements for all the modes happen at the same time, but The accuracy value defined in transient thermal analysis is Factor of Safety: The permissible factor of safety on

in most cases when one mode achieves maximum response, the acceptable fractional temperature error used to deter- the input load.

other modal responses are less than their individual maxi- mine the time step.

mum. Thus, the absolute sum method over estimates the Confidence of Life: The ratio of calculated life to the

maximum response. A more realistic way to do this is to use Fatigue Analysis (Fatigue Advisor) target design life. A value below 1 indicates failure.

the SRSS method wherein the modal responses are summed

using the square root of the sum of the squares. SRSS is also When an analysis models is subjected to repeated cycles of Typically, fatigue failure consists of two phases, crack initia-

the recommended method for models where the frequen- loading and unloading, failure can occur due to fatigue even tion and crack growth. Fatigue analysis in Mechanica ana-

cies of major contributing modes are not very close to each if stresses developed are below safe values for static analysis. lyzes the crack initiation phase only, and therefore should

other. Fatigue analysis in Mechanica requires the Fatigue Advisor only be used to determine if a design is likely to suffer from

license. Fatigue-specific material properties such as surface fatigue problems and whether a more detailed analysis or

OUTPUT finish and material types should be specified. A generic set testing is required. Fatigue analysis follows the E-N ap-

Dynamic shock analysis will calculate maximum values of of fatigue properties are built into Mechanica for unalloyed proach or the strain life approach, which is also called low-

displacements, stresses, and mass participation factors in the steels, low alloy steels, titanium alloys, and aluminum alloys. cycle fatigue or local strain approach.

analysis model. Unmodeled features such as welds that cause stress concen-

trations can be accounted for using the fatigue strength 2D Model Type

Transient Thermal Analysis reduction factor. A value of 1 represents no unmodeled

features that cause stress concentrations. An Advanced Mechanica license allows you to simplify the

This type of analysis is used to calcu- analysis models to a 2D model type instead of the default 3D

late the temperature and heat flux in model. This should be set up be-

the analysis model over a specific fore entering Mechanica mode in

time period and to calculate the time the Mechanica model setup dialog

taken by the analysis model to heat box. The 2D surface selected

up or cool down. should contain the xy plane of the

coordinate system.

Dynamic, Transient Thermal, Fatigue, 2D Model Type Back to Table of Contents ANALYSIS—ADVANCED MECHANICA 42

ANALYSIS BEST PRACTICES creo elements/pro 5.0 mechanica

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Batch Files Sandy_McKinney_2015Problem: During fatal errors, Mechanica reports a list of ID Mechanica Process Guide

numbers.

Analyses on large models are computationally expensive Solution: Typically, the Analysis Diagnostics window will The Process Guide will walk you through each step in the

and take a significant amount of time to complete. In such help in such situations by automatic zoom in to the entity on simulation process in Mechanica.

situations, it is a good practice to use batch files for running the model. If the diagnostics window does not show up

the analysis. automatically, select INFO > DIAGNOSTICS. By default, Mechanica has predefined process guides for

If this option does not work, then use the independent static analysis, modal analysis, buckling analysis, and

1. Set up all analyses. mode Mechanica to look at these element IDs. Select FILE > Mechanica Lite. These templates for the process guide are in

2. Run a quick check analysis to make sure the analyses INDEPENDENT MECHANICA to launch the independent XML format. With XML knowledge, expert users can create

mode. Then click UTILITY > MACROS, select Entity_ID, and unique templates that capture a specific series of modeling

are feasible. click the Replay button. and analysis activities and instruct users on how to perform

3. Create batch files for each analysis, or append multiple those activities to a given standard.

Always double-check the material properties, because cer-

analyses in the model to one batch file. tain fatal errors could simply be due to a material property Verification Guide

4. At the end of the workday, just run the batch file value being 0 or no thermal property being assigned when

doing a thermal analysis. The Mechanica help section has a Verifi-

(double click the batch file) to execute analysis. When fatal errors occur in assemblies, it is a good practice to cation Guide that uses a series of prob-

always double check the connections between parts along lems to demonstrate the accuracy and

Creo Elements/Pro or Mechanica need not be launched with clearance and interference. efficiency of Mechanica by comparing

manually to execute the analysis run. Starting the batch Sometimes the engine error can be fixed just by restarting Mechanica’s results to those obtained by

file will automatically run the post process in the back- Creo Elements/Pro or by killing the msengine.exe process traditional analysis codes or theory.

ground, so it only needs access to the license. and restarting the analysis.

Fatal errors might also occur due to insufficient disk space or

How to Fix Fatal Errors During Analy- RAM requirements.

sis Run

There are several reasons for fatal errors that may occur dur-

ing analysis run. Here are some methods to fix such errors.

Problem: A very

common fatal error

is the insufficiently

constrained error

as shown.

Solution: The best

way to fix this is to

run a modal analy-

sis on the same

analysis model

with rigid mode

search. Once the analysis completes, review the animation

of the displacement for the modal analysis, as this will show

the rigid body mode.

Analysis Best Practices Back to Table of Contents ANALYSIS BEST PRACTICES 43

Sandy_McKinney_2015

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