Ansys2Excite_UsersGuide.pdf

Edition 01/2013

© AVL List Gmbh 2013. All right reserved

Interfacing with ANSYS Users Guide

AVL EXCITE POWER UNIT VERSION 2013

EXCITE Power Unit v2013 Interfacing with ANSYS – Users Guide

25-Jan-2013 i

AVL LIST GmbH Hans-List-Platz 1, A-8020 Graz, Austria http://www.avl.com AST Local Support Contact: www.avl.com/ast-worldwide

Revision Date Description Document No.

A 28-Jan-2005 ANSYS v8.1 – EXCITE v6.1.2 – Users Guide 06.0310.4772 B 07-Oct-2005 ANSYS – EXCITE v6.1.2 – Users Guide 06.0310.4779 C 09-Feb-2007 ANSYS – EXCITE v7.0.1 – Users Guide 06.0310.0701 D 31-May-2007 ANSYS – EXCITE v7.0.2 – Users Guide 06.0310.0702 E 20-Jul-2009 ANSYS – EXCITE v2009.1 – Users Guide 06.0310.2009 F 30-Mar-2010 ANSYS – EXCITE v2010.0 – Users Guide 06.0310.2010.0 G 19-Nov-2010 ANSYS – EXCITE v2010 – Users Guide 06.0310.2010 H 29-Jul-2011 ANSYS – EXCITE v2011 – Users Guide 06.0310.2011 I 25-Jan-2013 ANSYS – EXCITE v2013 – Users Guide 06.0310.2013

Copyright © 2013, AVL List GmbH

All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language, or computer language, in any form or by any means, electronic, mechanical, magnetic, optical, chemical, manual, or otherwise, without prior written consent of AVL.

This document describes the ANSYS / AVL EXCITE Power Unit interface tool. It does not attempt to discuss all of required theories to obtain successful solutions. It is your responsibility to determine if you have sufficient knowledge and understanding to apply this software appropriately.

This software and document are distributed solely on an as is basis. The entire risk as to their quality and performance is with you. Should either the software or this document prove defective, you (and not AVL or its distributors) assume the entire cost of all necessary servicing, repair, or correction. AVL and its distributors will not be liable for direct, indirect, incidental, or consequential damages resulting from any defect in the software or this document, even if they have been advised of the possibility of such damage.

The names of the software and hardware products used in this manual are mostly the respective trademarks or registered trademarks of their companies.

ANSYS is a registered trademark of ANSYS Inc.

http://www.avl.com/

http://www.avl.com/ast-worldwide


25-Jan-2013 i

Table of Contents 1. Introduction ____________________________________________________________________ 1-1

1.1. Prerequisites _________________________________________________________________ 1-1 1.2. More Information _____________________________________________________________ 1-1

2. Overview _______________________________________________________________________ 2-1

3. Interface Procedure ____________________________________________________________ 3-1 3.1. Create EXCITE Power Unit Input Body Property File (*.exb) ______________________ 3-1

3.1.1. ANSYS Steps ______________________________________________________________ 3-2 3.1.2. EXCITE Power Unit Steps _________________________________________________ 3-19

3.2. Postprocessing with ANSYS ___________________________________________________ 3-22 3.2.1. Map EXCITE EHD/ENHD Pressure Results _________________________________ 3-22 3.2.2. Map EXCITE EPIL Pressure Results _______________________________________ 3-27 3.2.3. Create Transient Load Step Files ___________________________________________ 3-30

4. Tips & Tricks ___________________________________________________________________ 4-1

5. Troubleshooting ________________________________________________________________ 5-1

6. Appendix _______________________________________________________________________ 6-1 6.1. Static Reduction _______________________________________________________________ 6-1 6.2. Dynamic Reduction ____________________________________________________________ 6-1

6.2.1. Random Vibration Method __________________________________________________ 6-2

Interfacing with ANSYS – Users Guide EXCITE Power Unit v2013

ii 25-Jan-2013

List of Figures Figure 3-1: Connecting a Structure to an Interface Point ................................................................ 3-4 Figure 3-2: Create Regular Mesh Window ........................................................................................ 3-5 Figure 3-3: Create Regular EHD Mesh Window ............................................................................... 3-6 Figure 3-4: Input parameter description ........................................................................................... 3-7 Figure 3-5: Irregular and Regular Mesh for Condensation .............................................................. 3-8 Figure 3-6: Listing of Correctly Created Contact .............................................................................. 3-9 Figure 3-7: Ansys Contact Manager .................................................................................................. 3-9 Figure 3-8: Create Regular EPIL Mesh Window............................................................................. 3-10 Figure 3-9: Create Regular EPIL Mesh – Input Data ..................................................................... 3-11 Figure 3-10: Create Regular EPIL Mesh – Input Data ................................................................... 3-11 Figure 3-11: Node Component “PISTON_PRESS” not created ..................................................... 3-12 Figure 3-12: Regular Piston Mesh ................................................................................................... 3-13 Figure 3-13: Top Piston and Epil Contacts ..................................................................................... 3-13 Figure 3-14: “Create Input Files for AVL EXCITE” Menu ............................................................ 3-16 Figure 3-15: FEM Preferences Window .......................................................................................... 3-19 Figure 3-16: Convert FE Data Window ........................................................................................... 3-20 Figure 3-17: EXCITE Power Unit – Results Control – Control Parameters Window ................... 3-21 Figure 3-18: EXCITE Power Unit – Results Control – Common Results Window........................ 3-22 Figure 3-19: Select FE Analysis Type Window ............................................................................... 3-23 Figure 3-20: Linear Static/Transient Stress Analysis Window ...................................................... 3-23 Figure 3-21: Linear Static/Transient Stress Analysis – Boundaries Window ................................ 3-24 Figure 3-22: Map EXCITE EHD Pressure for Linear Static/Trans. Stress Analysis Window ...... 3-26 Figure 3-23: Linear Static/Transient Stress Analysis - Boundaries Window ................................ 3-28 Figure 3-24: Map EXCITE EPIL Pressure for Linear Static Stress Analysis Window ................. 3-29 Figure 3-25: Create Input for Stress Recovery from AVL Excite Results ...................................... 3-31 Figure 3-26: Solve Load Step Files Window .................................................................................... 3-31


25-Jan-2013 1-1

1. INTRODUCTION This document describes how to interact between ANSYS and EXCITE Power Unit. It is recommended to use Ansys v12 and higher as there have been great improvements, especially in Component Mode Synthesis substructuring.

The current version of Interface Ansys to Excite v2013 must be used with Ansys v12, when using the CMS method for substructuring.

1.1. Prerequisites It is advantageous if the user is already:

• familiar with the concept of reduced structured model of engine parts

• experienced in using ANSYS software

• experienced in using EXCITE Power Unit software

1.2. More Information The user may also refer to:

• ANSYS Documentation, especially

♦ Advanced Analysis Technique Guide - Chapter 9 - Substructuring

♦ Advanced Analysis Techniques Guide - Chapter 11 – Component Mode Synthesis

♦ Advanced Analysis Technique Guide - Chapter 12 - Rigid Body Dynamics and the ANSYS-ADAMS Interface

♦ Advanced Analysis Technique Guide - Chapter 14 - User-Programmable Features and Nonstandard Uses

♦ Structural Analysis Guide - Chapter 3 - Modal Analysis

♦ Structural Analysis Guide - Chapter 5 - Transient Dynamic Analysis

♦ Structural Analysis Guide - Chapter 6 - Spectrum Analysis

♦ Multibody Analysis Guide

♦ Contact Technology Guide

• EXCITE Power Unit Documentation


25-Jan-2013 2-1

2. OVERVIEW The ANSYS to EXCITE Power Unit interface can be used to:

1. Create the EXCITE Power Unit input files from the whole or partial FE models of engine parts.

2. Create the regular condensation mesh over the irregular FE model mesh – especially for bearing analysis (EHD2 joint) and piston liner analysis (EPIL joint).

3. Map the EHD/ENHD/EPIL pressure results from the EXCITE Power Unit simulation to FE model mesh.

4. Create the load step file(s) needed for calculation of stresses/stress history from the EXCITE Power Unit simulation results

The current version of the interface supports all EXCITE Power Unit body types:

• FLEXIBLE

• RIGID

The current version of the interface creates the following EXCITE Power Unit input data blocks depending on the body and solution type.

Table 1: Overview of FE Input Data Blocks for EXCITE Power Unit

Block Name Description

DOFT table of degrees of freedom – full FE model

EINF element information (type, group, nodes) – full FE model

GEOM node list and coordinates – full FE model

DOFP table of degrees of freedom – partial FE model

EINP element information (type, group, nodes) – partial FE model

GEOP node list and coordinates – partial FE model

EIGV body eigenfrequencies

LCV load step load vector

BMASS body mass and inertia properties

KXX (reduced) stiffness matrix

MXX (reduced) mass matrix

DXX (reduced) damping matrix

KDIC element dictionary table

KELM bar element stiffness matrices

MFF lumped mass matrix of full (unreduced) model

X2OA transformation matrix linking omitted degrees of freedom to analysis set of degrees of freedom (transposed) – full FE model


2-2 25-Jan-2013

X4OA transformation matrix linking omitted degrees of freedom to analysis set of degrees of freedom (transposed) – partial FE model

PHA eigenvectors for each calculated eigenfrequencies

MGPS expanded nodal stress results for each calculated eigenfrequencies


25-Jan-2013 3-1

3. INTERFACE PROCEDURE This chapter describes the ANSYS to EXCITE Power Unit interface procedure.

3.1. Create EXCITE Power Unit Input Body Property File (*.exb) To generate the body property file (*.exb) for an EXCITE Power Unit calculation, the following steps (described in detail in sections 3.1.1 and 3.1.2.) have to be performed in ANSYS:

1 Create the FE model of the EXCITE Power Unit body.

2 Define the MDOF's (Master Degrees Of Freedom) on nodes where the body should be connected to other bodies via joints or where the external forces should be applied. Especially for applying EHD/ENHD/EPIL joints if the model mesh is irregular at the joint surfaces, then create the regular mesh for condensation.

3 Define the boundary conditions and load steps (optional).

4 Execute the “EXCITE” command with appropriate parameters for the current body or open the AVL EXCITE Input interface window. Enter the necessary parameters and select OK.

The “EXCITE” command will generate the following files, depending on the FE model preparation and defined parameters :

<bodyname>.DOFT

<bodyname>.GEOM

<bodyname>.EINF

<bodyname>.DOFP

<bodyname>.GEOP

<bodyname>.EINP

<bodyname>.BMASS

<bodyname>.EIGV

<bodyname>.KDIC

<bodyname>.KELM

<bodyname>.OUT4

<bodyname>_MFF.OUT4

<bodyname>_DAMP.OUT4

<bodyname>_X2OA.OUT4

<bodyname>_X4OA.OUT4

<bodyname>_MEIG.OUT4

<bodyname>_MGPS.OUT

where <bodyname> is the defined EXCITE Power Unit body name (Condensed Model name).

The next steps will be done in EXCITE Power Unit.

5 Create an appropriate folder in the fem/ subfolder of the EXCITE Power Unit project path (FE Model Directory) and copy all generated files to this new folder.

6 Start EXCITE Power Unit and select Options | FEM Preferences. Under FE-Interface select ANSYS and define the used unit system in FE model.


3-2 25-Jan-2013

7 Open Utilities – Convert FE Data, select FE Solver ANSYS and appropriate version. Select the FE Model Directory, define the name of the Condensed Model, select 3D File (*.EINF file), if existing, and the Root Name of condensed Files. Check other buttons that matches your model and simulation. The utility will convert the input files to the new EXCITE body property file (*.exb). Optionally, the former geometry file *_GEOM.meg can be created, which can be used either as 3D File representation or for the internal data recovery.

8 Select the body from the Elements list and define the properties. At FE Model select at 3D Model either ‘From Condensed Model’ or FE mesh and select file <Condensed_Model>_GEOM.meg from the FE Model Directory folder. For Condensed Model select the appropriate <Condensed_Model>.exb file.

9 Finish creating the EXCITE Power Unit model, set the simulation and results parameters, and start the simulation.

10 To calculate the stress history, the steps described in section 3.2 should be performed.

3.1.1. ANSYS Steps Start the new ANSYS session.

3.1.1.1. Create FE Model The first step is to create the model following the usual ANSYS procedure:

!----- start of model input file

/FILENAM, ! Jobname /TITLE,.... /PREP7 ! Enter preprocessor ET,1, ! define element type MP,1 ! define material properties R, ! define real constants N,1,x,y,z ! define nodes EN,1,… ! define elements D,1,UX ....... ! define boundary conditions (optionally) …….. ....... M,1,all . . . ! define master DOF’s ....... SAVE ! Save the model- (this database will be used later) FINISH ! --------- end of model input file

This ANSYS database will be used later to create the EXCITE Power Unit input files and to apply the EXCITE Simulation results on model for the Stress and/or Full Transient Dynamic analysis.


25-Jan-2013 3-3

Note: It is important in element and node creation to keep the node and element numbering as low as possible (use ANSYS command “NUMCMP , node” and “NUMCMP , elem” )

3.1.1.2. Modelling Interface (Master) Points When building a model that will be used in an EXCITE Power Unit simulation, an important consideration is how to represent interface points within the structure. An interface point is a node that will have an applied joint or force in the EXCITE Power Unit model. Note that in EXCITE Power Unit the forces can only be applied to interface points.

The user should consider the following when modelling the interface points:

• Force (applied directly or via a joint) should be applied to the structure by distributing it over an area rather than applying it at a single node.

• If there is no node in the structure where you can apply the force or joint in EXCITE Power Unit (for example, a pin centre), create a geometric location for that point.

Use the following guidelines to determine the best way to model the interface points for your structure:

• Define all nodes where external forces and connections will be applied as interface points. For introducing rotational degrees-of-freedom in models which consist of solid elements, use constraint equations or a spider web of beam elements (as shown in Figure 3-1). A good practice for modelling interface points is to reinforce the area using beam elements or constraint equations. Using one of these techniques will distribute the force over an area rather than applying it to a single node, which would be unrealistic. If using a spider web of beam elements, use a high stiffness and a small negligible mass for the beams. Otherwise, the stiffness and mass of your model will be altered, which could result in eigenmodes and frequencies that do not represent the original model.

• You may use constraint equation commands such as CE and CERIG to attach the interface node (for example, CERIG,MASTE,SLAVE,UXYZ, where MASTE is the interface node). Avoid the RBE3 command since problems can occur with the master degrees of freedom. If you use constraint equations, mesh the interface point with a MASS21 element (use KEYOPT(3) = 0) that has small (negligible) masses and inertias (1.E-12).

• Do not define interface points that lie next to each other and are connected by constraint equations or short beams. This type of connection would require too many eigenmodes and result in a model that is not well conditioned.

Figure 3-1 shows three different ways of attaching an interface point to a structure. The first two examples (a and b) demonstrate valid methods of attachment. The third example (c) demonstrates a poor method of attachment that should not be used.


3-4 25-Jan-2013

Figure 3-1: Connecting a Structure to an Interface Point

Each method depicted in Figure 3-1 is described as follows:

a) Constraint equations connect the interface point to the structure. This method is recommended because:

• Force is distributed over an area.

• A MASS21 element is used to define the six degrees of freedom of the interface point.

• Moment loads are transmitted.

b) A spider web of beams connects the interface point to the structure. This method is recommended (and preferred) because:

• Force is distributed over an area.

• A MASS21 element is not necessary (because the beams supply the six degrees of freedom).

• Moment loads are transmitted.

c) One beam is used to connect the interface point to the structure. This is not recommended because:

• The force is applied to the structure at a single node.

• Solid elements do not have rotational degrees of freedom. Therefore, moments will not be properly transmitted from the interface point to the structure (a spider web scheme should be used).

3.1.1.3. Create Regular over Irregular FE model Mesh

Today, most of the FE meshes are created by “free mesher” generating an irregular tetrahedral mesh. For bearing shell structures using (T)EHD2/EPIL/ENHD joints it is necessary to have regular mesh for Master DOF definition.

Note: If you create your model which include bearings ( Crankshaft, Conrod or Main Bearing Wall) from geometry (volumes, areas), please use the Ansys feature for meshing the transition elements (pyramid) to create connection between regular mesh on bearing shell and the irregular for the rest of the structure. Such model is a clean Ansys model which runs fast and creates results directly.

For example see the verification example VM210.


25-Jan-2013 3-5

The regular mesh is possible to create by two interface utilities, "create regular mesh" which uses Ansys transition elements (recomended), and "create EHD mesh" which uses Ansys 3-D contact elements.

a) Create regular mesh

If it is possible, create the regular bearing shell mesh by using interface procedure "create regular mesh". Open the AVL-Menu "create regular mesh", fill up necesery data and press the OK buton.

Enter data for the following (see Fig.3-4. for parameter explanation):

cpoint1 the coordinates of the center point of the edge of the EXCITE Power Unit bearing/joint; this point must lie on the intersection of the rotational axis and the plane through one side of the joint

radius joint/bearing radius

depth bearing depth/width

rotax direction of axis of rotation x|y|z (default value is z)

divr number of regular mesh division in radial direction (default value is 40)

diva number of regular mesh division in axial direction (default value is 5)

bsheld Bearing shell thickness

The new transition (pyramid) elements will be created with regular mesh on one side and conected to the iregular mesh from the other side.

Figure 3-2: Create Regular Mesh Window


3-6 25-Jan-2013

b) Create EHD mesh

The connection between two meshes will be made by 3-D Contact elements.

Note: Due to the very sensitive definition of contact elements, here are some hints on how the contact pair should be defined:

• the target elements should be defined over surface in contact of solid elements

• the contact elements should be defined over regular mesh of shell/membrane elements

• the normal of target and contact elements should point to each other • the surface of contact elements must lie, and must be equal or smaller of target

surface (not a one node of contact elements must not be outside the target surface)

All those hints are considered in the appropriate macro to create sufficient contact pairs.

The first step is to create a node component TARGET from all nodes on external bearing/joint surface which are in contact.

From the AVL EXCITE menu select Create EHD Mesh to open the following dialog:

Figure 3-3: Create Regular EHD Mesh Window


25-Jan-2013 3-7

Figure 3-4: Input parameter description

Enter data for the following:

cpoint1 the coordinates of the center point of the edge of the EXCITE Power Unit bearing/joint; this point must lie on the intersection of the rotational axis and the plane through one side of the joint

radius joint/bearing radius

depth bearing depth/width

rotax direction of axis of rotation x|y|z (default value is z)

divr number of regular mesh division in radial direction (default value is 40)


From defined values the ANSYS macro EHD_MESH.MAC will:

• create the cylindrical working plane with origin in “cpoint1”, and working axis “wz” oriented to “rotax” direction

• check if the node component “TARGET” exists. If not, it will be created from the selected nodes which lie on external surface at “radius”. Check carefully if such created surface nodes are correct

• create the TARGE170 elements over the faces of solid elements defined by selected nodes (node component TARGET)


3-8 25-Jan-2013

• create the new (divr x diva) mesh of nodes (component “CONTACT”) in a plane of bearing radius

• create the thin membrane SHELL181 elements over the contact nodes

• create the contact CONTA173 elements over the membrane elements

• define the MDOF’s in contact nodes

The result of this procedure is shown in the following figure.

Figure 3-5: Irregular and Regular Mesh for Condensation

Note: It is always recommended to check whether the contact pair is set up correctly. From the command prompt enter Ansys command “CNCHECK” and Ansys will perform checking of the contact pair. If the contact pair is set up correctly, you’ll get the similar list to the following Ansys list window below:


25-Jan-2013 3-9

Figure 3-6: Listing of Correctly Created Contact

Also, you can open the Ansys Contact Manager and check the created contact.

Figure 3-7: Ansys Contact Manager

Note: Although the created contact pair looks good and it is initially closed, it should stay closed during the analysis. The best way to check this is to perform simple free-free Block Lanczos modal analysis up to 100 modes without expanding modes and use lumped mass approximation. The correct model is given, when there is no single mode of the contact element.

Now the model is ready for condensation.


3-10 25-Jan-2013

c) Create EPIL regular mesh

For the piston EPIL joint, the steps for creating regular mesh for condensation over the irregular FE model mesh is similar to EHD joints.

The first step, if the piston pressure should be applied, is to create the node component “PISTON_PRESS” from all nodes on piston top.

From the AVL EXCITE menu select Create EPIL Mesh to open the following dialog:

Figure 3-8: Create Regular EPIL Mesh Window

Enter data for the following:

cpoint1 coordinates of the reference point of the EPIL joint; this point must lie on the intersection of the vertical piston axis and the plane through the lower end of the piston

radius piston radius

p_hight total piston height; this value should be input when you want to define master nodes for applying piston pressure; in that case the node component TARGET_P should be created with all nodes on the piston top surfaces

s_hight piston skirt height up to first ring

vertix direction of vertical axis (default value is z)

thrust direction of anti-thrust side (default value is x)

divr number of regular mesh division in angular direction (default value is 16)


angle angle from anti-thrust side (default value is 45)


25-Jan-2013 3-11

The following figures describe the input values:

Figure 3-9: Create Regular EPIL Mesh – Input Data

Figure 3-10: Create Regular EPIL Mesh – Input Data

From defined values the ANSYS macro EPIL_MESH.MAC will:

• create the cylindrical working plane with origin in “cpoint1”, and working axis “wz” oriented to “rotax” direction


3-12 25-Jan-2013

• check if the piston height is defined. If p_hight > 0 than search for the node component “PISTON_PRESS”. If not defined, the note will be issued (Figure 3-9) and the action will be stopped. Define the node component “PISTON_PRESS” and start “Create EPIL Mesh” once again.

• if the PISTON_PRESS is defined and p_hight > 0, than macro will create the TARGE170 elements over the solid element faces defined by selected nodes, create the new regular (16x4) mesh of nodes in cylindrical coordinate system (component “CONTACT”) in a plane of piston top, create the membrane SHELL181 elements over the contact nodes, create the contact CONTA173 elements and define the MDOF’s in contact nodes ( Figure 3.10)

• select the nodes in a plane of piston radius from +angle to –angle, from wz=0 to S_hight, and create node component TARGETE

• create the TARGE170 elements over the solid elements faces attached to node component TARGETE

• create the new (divr x diva) mesh of nodes (component “CONTACT”) in a plane of piston radius

• create the membrane SHELL181 elements over the contact nodes

• create the contact CONTA173 elements in membrane nodes

• define the MDOF’s in contact nodes

The result of this procedure is shown in the following figures.

Figure 3-11: Node Component “PISTON_PRESS” not created


25-Jan-2013 3-13

Figure 3-12: Regular Piston Mesh

Figure 3-13: Top Piston and Epil Contacts

Note: It is always recommended to check whether the contact pair is set up correctly. From the command prompt enter Ansys command “CNCHECK, Option, RID1, RID2, RINC” and Ansys will perform checking of the pair in contact.

Also, perform all other checks mentioned under 3.1.1.3. a).


3-14 25-Jan-2013

3.1.1.4. Preparing FE Model for Partial Calculation Not only for the full FE model, it is possible to perform the condensation on a part of the Excite Body FE mesh, partial FE mesh.

The model should be prepared on the following way:

• from the full FE model select the elements that make up the part you want to analyze

• create the Element Component from selected elements and name it “u_set”

• save the Ansys database

The model is prepared for condensation, i.e. for the next step “Start the Interface Calculation”.

Note: partial condensation will only be implemented if element component “u_set” is defined in your Ansys FE model

3.1.1.5. Start the Interface Calculation After the FE model has been created and Master DOF’s applied to those degrees of freedom which should be available in the EXCITE Power Unit model, the command EXCITE should be executed from the command prompt or from EXCITE Power Unit Menu to obtain all the input files for EXCITE Power Unit.

Command Mode

EXCITE, OUTNAME, NMODES, BODYTYP, DICT, DMAT, LOADV, ELCALC, ’USRNAME’, MTXOUT, USECMS, NOLMM

Where:

OUTNAME EXCITE Power Unit default body name key that will be associated to the output files

Generic 1 GearShaft1 10

Piston 2 GearWheel1 11

Conrod 3 Wheel1 12

Crankshaft 4 Chassis1 13

BalancerSh1 5 Exhaust1 14

BalancerSh2 6 MB-Wall 15

Engine 7 B-Pin 16

Powerunit1 8 P-Pin 17

Disc1 9 Shaft1 18

NMODES number of modes for dynamic reduction

BODYTYP the EXCITE Power Unit body type selection


25-Jan-2013 3-15

o RIGID

o FLEXIBLE

DICT create bar element dictionary table and matrices, no/ yes

DMAT create reduced structural damping matrix, no/yes

LOADV create load cases vector, no/yes

ELCALC calculate element stresses (used for modal data recovery), no/yes

‘usrname’ user defined name that will be associated with the output files (optional). It will overwrite predefined OUTNAME.

It should be put in single quotes. MTXOUT create full mass matrix and/or recovery matrix

1 - create MFF only,

2 - create X2OA only,

3 - create both,

4 – do not write out _X2OA.OUT4 file. For the later Excite Recovery

the Ansys binary file <bodyname_genCMS.tcms> will be used.

USECMS use Component Mode Synthesis (CMS), yes/no (for more information see ANSYS online documentation – Advanced Guide). The calculation method for CMS is set to fixed.

Note: CMS does not yet support damping matrix reduction

NOLMM use lumped mass matrix approach, yes/no


3-16 25-Jan-2013

GUI Mode

The EXCITE command can also be executed from the AVL EXCITE menu in GUI. Select Start Excite button to open the following Create Input files for AVL EXCITE window.

Figure 3-14: “Create Input Files for AVL EXCITE” Menu


25-Jan-2013 3-17

Select the EXCITE Body default name or type the user name in USRNAME field.

Select the body type and define the number of modes for dynamic reduction if needed (see APPENDIX for more details about reduction).

If there are any beam elements in the model and body type (NOD6) requires element dictionary table, activate DICT parameter.

This option will create element dictionary table (file named [OUTNAME].KDIC) and the beam element stiffness matrices (file named [OUTNAME].KELM).

The DMAT key will activate the extraction of the reduced structure damping matrix, if the damping parameters are included in the FE model, and will be written to the file <bodyname>_DAMP.OUT4 in block DXX.

The LOADV option will activate the creation of the load case vector file (<bodyname>.LCV) from previously created ANSYS load step files (<jobname>.s01 etc).

The ELCALC option will activate calculation of element stresses in expansion pass of substructuring procedure. If MTXOUT is on, the following files will be created:

<bodyname>_MEIG.OUT4 containing the eigenvectors of the reduced structure and <bodyname>_MGPS.OUT containing the stress tensors of the defined element set for each eigenvector in MEIG

The MTXOUT option will activate creation of transformation matrix file <bodyname>_X2OA.OUT4 (code > 2) and full mass matrix file <bodyname>_MFF.OUT4 (code = 1) for body type CON6. Code 4 will prevent ASCII output of file _X2OA.OUT4. In that case for Excite Recovery the Ansys binary file <bodyname_genCMS.tcms> will be used. This will save lot of interface run time, especially for large models (more than 1 mil elements).

The USECMS option, if active, will perform Component Mode Synthesis (CMS) reduction, otherwise, the Power Spectral Density (PSD) method will be used for reduction. For CMS method the number of modes (NMODES) must be greater than zero. For more about PSD and CMS methods see ANSYS documentation.

The NOLMM option specifies whether the “lumped mass matrix formulation LUMPM” will be used (Yes/On – default) or not (No/Off). The default value is appropriate for most models. Only in special cases and with the full control of the user, the value “No/Off” can be used.

Select OK to start the process.

ANSYS will perform all calculations and prepare the input files for the EXCITE Power Unit simulation. The file format for the mass and stiffness matrices is the Nastran OUTPUT4 file format. All files generated by ANSYS to EXCITE Power Unit Interface are ASCII files and thus platform independent.

Note: The condensation for CON6 bodies with CMS method can be performed only as a batch job due to the TCMS option. Please read the Ansys manual how to perform the batch jobs for different platforms: Operation Guide – Ch. 3. Running the Ansys Program – 3.4. Batch Mode.

The instruction for different platform follows.


3-18 25-Jan-2013

3.1.1.6. Starting Batch Mode from the UNIX/Linux Command Line

To start batch mode from the UNIX/Linux command line:

Foreground execution (ksh or sh shells): ansys120 -b -p productvar < inputname > outputname 2>&1

Background execution (ksh or sh shells): nohup ansys120 -b -p productvar < inputname > outputname 2>&1 &

The nohup command tells the system to ignore hang-up signals, enabling the ANSYS program to continue executing if you log off from the system.

Foreground execution (csh shell): ansys120 -b -p productvar < inputname > &outputname

Background execution (csh shell): nohup ansys120 -b -p productvar < inputname > &outputname &

3.1.1.7. Starting Batch Mode from the Windows Command Line

You can also start a batch job in Windows by issuing the ANSYS execution command directly from the MS-DOS command prompt window or create the “bat” file with the command string inside (all in one line). The format for the command depends on whether you want ANSYS to run in the foreground or the background:

Foreground execution: "<drive>:\Program Files\Ansys Inc\V120\ANSYS\bin\<platform>\ansys120" -b -i inputname -o outputname

Background execution: start /min "<drive>:\Program Files\Ansys Inc\V120\ANSYS\bin\<platform>\ansys120" -b -i inputname -o outputname

In upper commands the “inputname” is the name of input file with the following instructions:

! ----------------------------- example of input file ---------------------

RESUME, Conrod,db ! read in Ansys database

! /INPUT, Fname, Ext ! or input model data from external file

! CDREAD, Option, Fname, ext ! or input model from archive file

!EXCITE,OUTNAME,NMODES,BODYTYP,DICT,DMAT,LOADV,ELCALC,USRNAME,MTXOUT,USECMS,NOLMM

EXCITE, 3, 20, 2, , , , , , 1, 1,

! --------------------------- end of file ---------------------------------


25-Jan-2013 3-19

3.1.1.8. EXCITE Command Background - Excite Macro The base of the EXCITE command is the macro called EXCITE.MAC, which can be found in AVL-ANSYS installation folder ($AVLAST_HOME/EXCITE/<version>/fem/ansys).

You can copy the contest of that folder to any other folder for your convenient. But, the “EXCITE” command will be recognized by the Ansys only if you define the ansys environment variable ANSYS_MACROLIB to point to the folder where interface macros are placed.

So, if you already have this environment variable defined, copy the interface macros to the folder defined by your ANSYS_MACROLIB variable.

3.1.2. EXCITE Power Unit Steps When the input files are created, the next step is to start the EXCITE Power Unit session.

3.1.2.1. Set FE-Interface Preferences After opening EXCITE Power Unit, the first step is to define the FE-Interface Preferences. Select Options | FEM Preferences to open the following window:

Figure 3-15: FEM Preferences Window

Under FE-Interface select ANSYS. Additionally select the global Axes of the FE-Model and the correct unit system, which has been used for creating the FE model.

3.1.2.2. Convert FE Data Before setting up the EXCITE model, the generated ANSYS interface files for each flexible body have to be converted to the new EXCITE body property file (*.exb).

Therefore open Utilities – Convert FE Data dialog and enter/select the following data:


3-20 25-Jan-2013

Figure 3-16: Convert FE Data Window

• select FE Solver ANSYS and appropriate version

• select the FE Model Directory

• select 3D Mesh File i.e. Ansys Element Info File (*.EINF file)

• type the name of the EXB file (if it is blank, the EXB file will have the name of the condensed body)

• select the Root Name of DOFT/OUT4 Files from the ANSYS interface files

• check in other buttons which are appropriate to the model

The utility will scan all available interface files and convert them to the new EXCITE body property file (*.exb). Optionally, if a 3D File (*.EINF) has been defined, the former geometry file *_GEOM.meg can be created, which can be used either as 3D File representation or for the internal data recovery.

3.1.2.3. Create EXCITE Power Unit Model Select the body from the Elements list and define the properties. At FE Model select at 3D Model either ‘From Condensed Model’ or ‘FE mesh’ and select <Condensed_Model>_GEOM.meg from the FE Model Directory folder.

For Condensed Model select the appropriate <Condensed_Model>.exb file.

3.1.2.4. Run Create Model and Simulation Define the appropriate Control Parameters, Case and Model Parameters and run the analysis.


25-Jan-2013 3-21

3.1.2.5. Perform Result Evaluation To calculate stress history later with ANSYS, some additional results parameters need to be defined in Results Control.

First, all results need to be calculated on time base. Activate Time in Control Parameters Output Results versus. This will create the results file (extension .GID) with the channel “Time” in the first column, which is needed for the ANSYS Transient Dynamic Analysis.

Figure 3-17: EXCITE Power Unit – Results Control – Control Parameters Window

Select Common Results Nodal Results and activate Relative for of All Connected Nodes and of All Loaded Nodes. This will create the correct load for the ANSYS Transient Dynamic Analysis later.


3-22 25-Jan-2013

Figure 3-18: EXCITE Power Unit – Results Control – Common Results Window

Perform the task Create Results to get the appropriate GIDAS result files.

3.2. Postprocessing with ANSYS After the simulation has finished and the results have been created and stored in the Results folder, the ANSYS interface can be used to post-process the EXCITE Power Unit results to:

• map the pressure results from EXCITE Power Unit EHD/ENHD joint

• map the pressure results from EXCITE Power Unit EPIL joint and pressure on piston top

• create the transient ANSYS load step files from EXCITE Power Unit displacement results

3.2.1. Map EXCITE EHD/ENHD Pressure Results a) EXCITE Power Unit Steps

The first step is to select the results from EXCITE Power Unit and create the input files for ANSYS.

In the EXCITE Power Unit Main menu, select FE Analysis | Tasks | Add New Task and select ANSYS for FE Solver. The following window will be opened.


25-Jan-2013 3-23

Figure 3-19: Select FE Analysis Type Window

Select OK and the following window opens. Enter the necessary data.

Figure 3-20: Linear Static/Transient Stress Analysis Window

Define the results interval and increment.

Then select the Boundaries tab to access the fields shown in the following window.


3-24 25-Jan-2013

Figure 3-21: Linear Static/Transient Stress Analysis – Boundaries Window

For the Excite Joint, select Add and then select the appropriate joint.

Select OK to start the FE Task calculation and create the following files:

<joint_name>.acc file with selected time steps and acceleration for each time step

<joint_name>.grid file with coordinates of EXCITE Power Unit EHD/ENHD joint mesh

<joint_name>.press file with pressure data for each coordinate in grid file and for each time step defined in acc file

Those files are located in folder <Case_Set.Case>/fea/.

For more information about FE Analysis Tasks refer to the EXCITE Power Unit Users Guide.


25-Jan-2013 3-25

Note: Theoretically, external forces and inertia forces are in equilibrium. Due to numerical errors or due to mass discrepancies between EXCITE and ANSYS, this is insufficient to prevent a rigid-body motion of the FE-model. Hence, you must constrain the component against rigid-body motion in order to do a static structural analysis. The ANSYS offers the following options to achieve this:

• for the first option, you must manually add constraints to the ANSYS model that are compatible with the constraints used in the EXCITE model (if possible), or use common engineering sense to prevent rigid-body motion. This constrains must be defined in an external file with name “constrain.inp”. Or, as a second option

• add weak springs: The Ansys program adds weak springs (COMBIN14 elements) to the corners of the bounding box of the model. (For more information, see the WSPRINGS command documentation). The weak springs prevent rigid-body motion without influencing the stress results. (See Adding Weak Springs for more information on how the program adds weak springs to the model.)

b) ANSYS Steps

Open the new ANSYS session and read in the appropriate FE model (which was used for condensation). Create the node component PSURF1 (and PSURF2 if there are two joints) from nodes on bearing/joint surface. If the model need to be constrained, create the external file named "constrain.inp" containing the Ansys "D" commands for each constrained node and DOF, or use the Ansys command WSPRINGS to create constrains by week springs.

Typical applications:

• Single main bearing wall with one EHD2 joint

• Connecting rod with one or two EHD2 joints

From the AVL EXCITE menu select Map EHD Results to open the following dialog.


3-26 25-Jan-2013

Figure 3-22: Map EXCITE EHD Pressure for Linear Static/Trans. Stress Analysis Window

Change, if necessary, and fill the empty fields with the appropriate files. An animation can be performed if there is more than one time step in the acc or grid file. It is only for the visualization and check of input data.

Select OK to start ANSYS macro EHD_MAP.MAC. For each time step defined in the acc file, the macro will create ANSYS load step file <job_name>.s0x where x is the number of load step, starting from the last created load step file.

To run load steps, use the ANSYS command LSSOLVE or press “Solve Lin.StaticEHD/EPIL Stress” button from EXCITE Power Unit Menu.

The calculated results might be reviewed in the ANSYS Post-processor:

• for one load step in POST1

• for the time period in POST26


25-Jan-2013 3-27

3.2.2. Map EXCITE EPIL Pressure Results a) EXCITE Power Unit Steps

The first step is to select the results from EXCITE Power Unit and create the input files for ANSYS.

In the EXCITE Power Unit menu, select FE Analysis | Tasks | Add New Task and select ANSYS for FE Solver. Select OK and the Linear Static/Transient Stress Analysis window opens (7).

It is essential to apply all acting loads on the piston model:

• Gas force at piston top and top land

• EHD pressure force at piston skirt

• Joint reaction force at piston boss bearings

• Acceleration Load

Therefore select the Boundaries tab and

1. Select Forces/Displacements at Nodes and add the Excite body nodes of the piston boss bearings to apply the joint reaction forces.

2. Add EHD Pressure Load is selected. Add the EPIL joint to apply the EHD contact forces at piston skirt.

3. Select Add Acceleration Load and Get from Excite Global Results to apply the acceleration load.

4. Select Add Cylinder Pressure Load, define the Node Set/Nodes where the gas force was acting and the Bore Diameter to recalculate and generate the corresponding gas pressure.


3-28 25-Jan-2013

Figure 3-23: Linear Static/Transient Stress Analysis - Boundaries Window

Select OK to start the FE Task calculation and create the following files:

<body_name>.acc file with selected time steps and acceleration for each time step

<joint_name>.grid file with coordinates of EXCITE Power Unit EPIL joint mesh

<joint_name>.press file with pressure data for each coordinate in grid file and for each time step defined in acc file

<joint_name>_GAS.press file with top cylinder pressure data for each time step defined in acc file

Those files are located in folder <Case_Set.Case>/fea/.

For more information about EXCITE Power Unit FE Tasks refer to the EXCITE Power Unit Users Guide.


25-Jan-2013 3-29

Note: Theoretically, external forces and inertia forces are in equilibrium. Due to numerical errors or due to mass discrepancies between EXCITE and ANSYS, this is insufficient to prevent a rigid-body motion of the FE-model. Hence, you must constrain the component against rigid-body motion in order to do a static structural analysis. The ANSYS offers the following options to achieve this:

• for the first option, you must manually add constraints to the ANSYS model that are compatible with the constraints used in the EXCITE model (if possible), or use common engineering sense to prevent rigid-body motion. This constrains must be defined in an external file with name “constrain.inp”. Or, as a second option

• add weak springs: The Ansys program adds weak springs (COMBIN14 elements) to the corners of the bounding box of the model. (For more information, see the WSPRINGS command documentation). The weak springs prevent rigid-body motion without influencing the stress results. (See Adding Weak Springs for more information on how the program adds weak springs to the model.)

b) ANSYS Steps

Open the new ANSYS session and read in the appropriate FE model (which was used for condensation) and add weak springs or create the file with constrains.

Create the node component PSURF1 for nodes on piston skirt, and PSURF2 for piston nodes on top if the cylinder pressure is defined.

From the AVL EXCITE menu select Map EPIL Results to open the following dialog:

Figure 3-24: Map EXCITE EPIL Pressure for Linear Static Stress Analysis Window


3-30 25-Jan-2013

Fill the empty fields with appropriate files. An animation can be performed if there is more than one time step in the acc or grid file. It is only for the visualization and check of input data.

Select OK.

This will start ANSYS macro EPIL_MAP.MAC. For each time step defined in acc file, the macro will create ANSYS load step file <job_name>.s0x where x is the number of the load step, starting from the last created load step file.

To run load step, use the ANSYS command LSSOLVE, or press “Solve Lin.StaticEHD/EPIL Stress” button from AVL EXCITE menu.




3.2.3. Create Transient Load Step Files Start the new ANSYS session, change the job name (working directory, title etc.) and Resume from ANSYS database for the appropriate Excite body.

Start the interface calculation by executing the command EXCITE_R (from the ANSYS Solution level) in Command Prompt or from AVL EXCITE menu/Excite Recovery:

Command Mode

EXCITE_R, BODYNAM1, EXTEND, EXRESDIR, STEPTIMS

where:

BODYNAM1 the name of the EXCITE body result file without extension (as there are many body result files in a form

“bodyname-masternode-DOF-rel.[EXTEND]”

user needs to define only one of them)

EXTEND EXCITE body results file extension (GID)

EXRESDIR the path to the EXCITE body results folder (it may be relative or absolute path)

STEPTIMS step increment for reading the EXCITE results

GUI Mode

The EXCITE_R command can be executed from the AVL EXCITE menu. Select Excite Recovery to open the following dialog:


25-Jan-2013 3-31

Figure 3-25: Create Input for Stress Recovery from AVL Excite Results

Select one of the EXCITE body result files by “Browsing” the folder containing the result GIDAS files. The file name is limited up to 32 characters, the file extension is limited up to 8 characters, and the folder path is limited up to 248 characters (ANSYS limits).

Enter the Time Step Increment for reading the EXCITE body results. Default value “1” means that every time step from the EXCITE result file will be read (value 2 means every second time step will be read). This value defines how many ANSYS Load Step files will be created. The EXCITE simulation might have several thousands of time steps, and for Time Step Increment=1 the same number of ANSYS Load Step files will be created. The user should define the desired number of time steps. Mostly it is sufficient to generate 240 – 360 time steps (each 2nd or 3rd deg CA).

Select OK to start creating ANSYS Load Step files.

ANSYS will create all Load Step files and place them in the current working folder.

The names of the files will be: <job_name>.s01, <job_name>.s02, <job_name>.s03, etc.

With the ANSYS command LSSOLVE (Solution Solve From LS Files), select which time steps will be used in the calculation.

Figure 3-26: Solve Load Step Files Window


3-32 25-Jan-2013

Note: Depending on the number of DOF’s in the model (the number of equations to be solved) and the number of load steps, the ANSYS output files might be very large (hundreds GB). It is recommended with ANSYS “Run-Time Stats” to investigate how much disk space is needed and how long the calculation will take.




The base of this command is the macro called EXCITE_R.MAC, which can be found in AVL-ANSYS Installation folder (see the Installation Guide for details).


25-Jan-2013 4-1

4. TIPS & TRICKS • It is always good, before starting the condensation, to check the FE model. Perform

the CMS substructure analysis on created model

________________

/solu

antyp,substructure seopt,subelem,2,0,,resolve cmsopt,fix, 20, ,, , , lumpm,on eqslv,sparse solve fini

___________________________________

• To connect the master nodes to the surrounding structure use the high stiffness BEAM4 elements with orientation defined by angles, not with the third node (read the Chapter 5.4. Master Degrees of Freedom in a Substructured Multibody Simulation in Multi Body Analysis Guide, search also for ‘spider’ technique). Here follows one of the possible 'spider' method:

MN = xx ! define master node ! ET,x,BEAM4 ! define baeam element R,x,..... ! use high stiffness MP,DENS,x,... ! ues low mass density ! NSEL,S ....... ! Select nodes to be connected to the Master node NSEL,A,,,MN ! add the master node to the selection ! Generate spider web of beams TYPE,x REAL,x MAT,x ! *GET,nmin,node,,num,min *GET,nnum,node,,count *SET,jj,0 *DO,jj,1,nnum-2 E,MN,nmin NSEL,u,,,nmin *GET,nmin,node,,num,min *ENDDO ! ALLS


4-2 25-Jan-2013

• Always put a MASS21 element with the very low masses and inertia masses to the master node (as a stand alone node, or as a part of elements with 3 DOF's per node). For real constant always use all values: MASSX, MASSY, MASSZ, IXX, IYY, IZZ, e.g. R,1,1.e-12,1.e-12,1.e-12,1.e-12,1.e-12,1.e-12

• If there are several parts connected into the one body (crankshaft with pully and fly wheel) use the same mesh on the both sides and merge the nodes, or use the Ansys contact and target elements (170, 173, 174 or 175) with keyopt(2)=2, keyopt(4)=1 (force distributed) or 2 (rigid surface) and keyopt(12)=5 or 6. If you are using rigid connection (CERIG or CE) it is always good to put dummy mass elements into the master and slave nodes. Here is one way how to do it:

_____________________________________________

/PREP7 NSEL,S,CE,,1,maxCEnumber ! select nodes with constrains ESLN,S ! select elements attached to selected nodes ESEL,U,TYPE,,solid_min,solid_max ! unselect solid elements NSLE,U ! unselect nodes attached to the mass elements ESEL,NONE ! unselect all elements ! cm,nomass,node ! create component with nodes ! ! create mass element properties et,max+1,mass21 mp,ex,max+1,210000 mp,nuxy,max+1,.3 mp,dens,max+1,1e-12 r,max+1,1e-12,1e-12,1e-12,1e-12,1e-12,1e-12 type,max+1 mat,max+1 real,max+1

NCOUNT = ndinqr(0,13) ! find the number of selected nodes NEXTNODE = 0 ! add mass elements

*do,i,1,NCOUNT *get,NEXTNODE,node,NEXTNODE,nxth e,NEXTNODE *enddo

____________________________________________________


25-Jan-2013 4-3

Current limitation (due to Ansys limitation)

• Command HBMAT must be used for output of the reduced mass and stiffness matrices because of accuracy (dumping the mass and stiffness matrices from the SUB file doesn't give the satisfied accuracy). For using this command in Ansys 11.0 modules Mechanical, it's necessary to install Ansys 11. Service Pack1.

• When dumping a .FULL file, the rows and columns corresponding to specified constraints (e.g., D commands) are eliminated from the system of equations and therefore are not written to the .MATRIX file. Also, rows and columns corresponding to eliminated (slave) degrees of freedom from coupling and/or constraint equations (e.g., CE, CP commands) are also eliminated from the system of equations and are not written to the .MATRIX file. The DOFs that are eliminated from any coupling and/or constraint equations are determined internally by the solution code and may not match what you specified via the CE/CP (or similar) commands.

• CMS does not yet support damping matrix reduction. ANSYS sets the matrix generation key to 2 automatically (SEOPT,SEMATR).

• For the versions prior to v14, Ansys doesn't allow to define array or table parameter greater than 2**28 because of unadjusted pointers. This gives an error even on 64-bit architecture

_____________________________

**** ERROR *** CP = 212.450 TIME= 18:13:56 Array or table parameter _EARRAY is too large for 32 bit address. The setting of parameter is not possible. .

_________________

According to that, in current interface the maximum element number might be 10,324,440. If you have higher elements numeration, renumber or compress the element numbers (NUMCMP,ELEM)

mk:@MSITStore:C:\PROGRA~1\ANSYSI~1\v110\COMMON~1\help\en-us\ANSYSH~1.CHM::/Hlp_C_D.html

mk:@MSITStore:C:\PROGRA~1\ANSYSI~1\v110\COMMON~1\help\en-us\ANSYSH~1.CHM::/Hlp_C_CE.html

mk:@MSITStore:C:\PROGRA~1\ANSYSI~1\v110\COMMON~1\help\en-us\ANSYSH~1.CHM::/Hlp_C_CP.html

mk:@MSITStore:C:\PROGRA~1\ANSYSI~1\v110\COMMON~1\help\en-us\ANSYSH~1.CHM::/Hlp_C_CE.html

mk:@MSITStore:C:\PROGRA~1\ANSYSI~1\v110\COMMON~1\help\en-us\ANSYSH~1.CHM::/Hlp_C_CP.html


25-Jan-2013 5-1

5. TROUBLESHOOTING If you have any problem using the ANSYS to EXCITE Power Unit Interface, contact the technical support to assist you at [email protected].

Please specify the following:

• ANSYS version

• ANSYS to Excite Interface version (can be find on top of EXCITE.MAC)

• EXCITE Power Unit version (can be found under Menu Help | About)

• hardware platform

• body type

• short description of the problem

• if possible, attach

♦ ANSYS model database (db, cdb) or model input file

♦ ANSYS ERR file

♦ ANSYS log file

♦ ANSYS out file (if exists)

♦ dbexc.parm (interface file – might be huge)

♦ the list or screenshot of the folder where interface was running

♦ any other information that might help in detecting the problem

mailto:[email protected]


25-Jan-2013 6-1

6. APPENDIX This chapter describes the theoretical background of ANSYS Reduction.

6.1. Static Reduction In order to obtain reduced mass and stiffness matrices as well as the corresponding tables of degrees of freedom and geometry the ANSYS substructure analysis features is used:

A substructure containing the whole FE model of the body is generated. Those degrees of freedom which should be available in the EXCITE Power Unit simulation are defined as the master degrees of freedom. Optionally, boundary conditions (constraints) can be set for the substructure.

The reduced mass and stiffness matrices with the dimension [nMDOF*nMDOF] are written to the filename.OUT4 file. The theoretical explanation is given below.

The substructure analysis uses the technique of matrix reduction to reduce the system matrices to a smaller set of DOF’s.

Consider the basic form of the static equations:

[ ] { } { }Fu =Κ (1)

{ }F includes nodal and pressure effects. The equations may be partitioned in two groups,

the master (retained) DOF’s, here denoted by the subscript "m", and the slave (removed) DOF’s, here denoted by the subscript "s".

=

s

m

s

m

sssm

msmm

FF

uu

KKKK

(2)

or expanding:

[ ] { } [ ] { } { }msmsmmm Fuu =Κ+Κ (3)

[ ] { } [ ] { } { }ssssmsm Fuu =Κ+Κ (4)

The master DOF’s should include all DOF’s of all nodes on surfaces that connect to other parts of the structure and all nodes where external forces will be applied.

6.2. Dynamic Reduction The dynamic behavior of the structure is obtained using the ANSYS Spectral Analysis features.

First, the constrained Modal Analysis (constrains are defined on nodes having the MDOF's) is performed and the modes are expanded, and then the participation factors of the Random Vibration (PSD) Analysis are calculated (for more information on Spectral Analysis refer to ANSYS Structural Analysis Guide, Chpt. 6). Those participation factors are then used for transformation of the stiffness and mass matrices obtained from the static reduction.

The theoretical explanation follows.


6-2 25-Jan-2013

6.2.1. Random Vibration Method For partially correlated nodal and base excitations, the complete equations of motions are segregated into the free and the restrained (support) DOF as:

=

+

+

0F

UU

KKKK

UU

CCCC

UU

MMMM

r

f

rrrf

frff

r

f

rrrf

frff

r

f

rrrf

frff

(5)

where { }fU are the free DOF and { }rU are the restrained DOF (excited by random

loading). { }F is the nodal force excitation activated by a value of force. The value of force

can be other than unity, allowing for scaling of the participation factors.

The free displacements can be decomposed into pseudo-static and dynamic parts as:

{ } { } { }dsf uuu += (6)

The pseudo-static displacements may be obtained from equation (5) by excluding the first two terms on the left-hand side of the equation and by replacing { }fu by { }su :

{ } [ ] [ ]{ } [ ]{ }rrfrffs uuu Α=ΚΚ−= −1 (7)

in which [ ] [ ] [ ]frff ΚΚ−=Α −1 . Physically, the elements along the thi column of [ ]Α are the

pseudo-static displacements due to a unit displacement of the support DOF’s excited by the thi base PSD. These displacements are written as load step 2 on the “.rst” file. Substituting

equations (7) and (6) into (5) and assuming light damping yields:

[ ]{ } [ ]{ } [ ]{ } { } [ ][ ] [ ]( ){ }rfrffaffaffdff üFuüCü Μ+ΑΜ−Κ++Μ −~ (8)

The second term on the right-hand side of the above equation represents the equivalent forces due to support excitations.

Using the mode superposition analysis

( ){ } [ ] ( ){ }tytud Φ= (9)

the above equations are decoupled yielding:

,22 jjjjjjj Gyyy =++ ωωξ ( )n...,,,j 21= (10)

where: n = number of mode shapes chosen for evaluation (input quantity NMODE)

jy = generalized displacements

jω and jξ = natural circular frequencies and modal damping ratios

The modal loads jG are defined by:

{ } { } jrT

jj üG γ+Γ= (11)


25-Jan-2013 6-3

The modal participation factors corresponding to support excitation are given by:

{ } [ ][ ] [ ]( ) { }jTfrffj ΦΜ+ΑΜ−=Γ (12)

and for nodal excitation:

{ } { }FTjj Φ=γ (13)

Ansys2Excite_UsersGuide.pdf

Documents

Transcript of Ansys2Excite_UsersGuide.pdf