MD Nastran R2.1 Installation and Operations Guide

MSC.Software

EFEA 2010 Tutorial

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Disclaimer MSC.Software Corporation reserves the right to make changes in specifications and other information contained in this document without prior notice. The concepts, methods, and examples presented in this text are for illustrative and educational purposes only, and are not intended to be exhaustive or to apply to any particular engineering problem or design. MSC.Software Corporation assumes no liability or responsibility to any person or company for direct or indirect damages resulting from the use of any information contained herein. User Documentation: Copyright © 2010 MSC.Software Corporation and its licensors. Portions of this document are licensed from Michigan Engineering Services LLC. Printed in U.S.A. All Rights Reserved. This notice shall be marked on any reproduction of this documentation, in whole or in part. Any reproduction or distribution of this document, in whole or in part, without the prior written consent of MSC.Software Corporation is prohibited. This software may contain certain third-party software that is protected by copyright and licensed from MSC.Software suppliers. MSC, MD, Dytran, Marc, MSC Nastran, MD Nastran, MSC Patran, MD Patran, OpenFSI, the MSC.Software corporate logo, and Simulating Reality are trademarks or registered trademarks of the MSC.Software Corporation in the United States and/or other countries. NASTRAN is a registered trademark of NASA. PAMCRASH is a trademark or registered trademark of ESI Group. SAMCEF is a trademark or registered trademark of Samtech SA. LS-DYNA is a trademark or registered trademark of Livermore Software Technology Corporation. ANSYS is a registered trademark of SAS IP, Inc., a wholly owned subsidiary of ANSYS Inc. ABAQUS is a registered trademark of ABAQUS Inc. All other brand names, product names or trademarks belong to their respective owners. PCGLSS 6.0, Copyright © 1992-2005, Computational Applications and System Integration Inc. All rights reserved. PCGLSS 6.0 is licensed from Computational Applications and System Integration Inc. METIS is copyrighted by the regents of the University of Minnesota. A copy of the METIS product documentation is included with this installation. Please see "A Fast and High Quality Multilevel Scheme for Partitioning Irregular Graphs". George Karypis and Vipin Kumar. SIAM Journal on Scientific Computing, Vol. 20, No. 1, pp. 359-392, 1999.

Revision 0. July 9, 2010

MDNA:V2010:Z:TUTR:Z:DC-EFEA

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In the current version of the EFEA software, structures can be simulated by two-

dimensional (2-D) elements, for plate- or shell-type structures, or one-dimensional (1-D)

elements, for beam-type structures. This version allows the modeling of 3-D acoustic

elements. This includes the use of 3-D elements to simulate acoustic media. Some

special elements to simulate the spring/isolator, acoustic treatment, etc., are also available

in Version 2.0 of EFEA (Refer to the EFEA 2010 User’s Guide).

This document serves as an introduction to using the EFEA software. There are also six

example problems at the end of the tutorial which provides an in-depth idea of specific

steps needed to accomplish the tasks outlined here. The basic steps in creating an EFEA

model are:

Step 1: Create the conventional FEA model using pre-processing software

Step 2: Run the Pre-EFEA code on the conventional FEA model

Step 3: Modify the EFEA model file generated by the Pre-EFEA code

Step 4: Run the EFEA code on the modified EFEA model file

Step 5: Post-process the EFEA results file in PATRAN

In the remainder of this tutorial, a simple cylindrical structural model with an interior

acoustic medium is used as an example to outline and further explain the above steps.

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Step 1: Create the conventional FEA model using pre-processing software

Users can generate the FEA model in any available pre-process software, i.e. Patran or

MSC.SimXpert . Refer to the corresponding user’s manual for an explanation of

generating the finite element model in the selected software. The size of each element

can be large, as long as the model captures the main geometric characteristics of the

physical system it models.

Once a finite element model is created, it must be exported in a MSC.NASTRAN short

format data file. This single data file should include all model elements (1-, or 2-D

elements for structure and 3-D elements for acoustic media, if any) and their properties

(material and geometric properties, if available). For a 3-D acoustic model, EFEA

Version 2.0 supports CHEXA (8-node), CPENTA (6-node) and CTETRA (4-node)

elements. As in the current version, EFEA Version 2.0 supports CQUAD4 (4-node) and

CTRIA3 (3-node) elements for the 2-D structural model, and CBAR and CBEAM (2-

node) elements for a 1-D beam model. Each structural node and element, and each

acoustic node and element must have a unique ID number. Before exporting the FEA

model into a Nastran data file, the user must ensure the equivalence is done on the model,

that is, all duplicated or temporary nodes have been removed. There is one case where

duplicated nodes are needed when creating the conventional FE model. This case is

explained in the following paragraph.

When generating the FE model, if both structure (simulated by CQUAD4 or CTRIA3

elements) and acoustic elements (simulated by CHEXA, CPENTA or CTETRA elements)

exist in the model, the elements on the interface between the structure and acoustic

medium need to be matched. Duplicated nodes with different IDs should be used for

matched structural elements and acoustic elements on the interface. Figures 1-1 and 1-2

are included as an example to illustrate this concept. Figure 1-1 shows a FE model for a

cylindrical structure. This FE model includes 1,314 CQUAD4 elements and 1,316 nodes.

Figure 1-2 shows the 3-D FE model simulating the interior acoustic medium surrounded

by the cylinder. This 3-D FE model includes 3,540 CHEXA elements and 4,242 nodes.

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In creating the model that includes both the cylinder and the medium, the elements on the

interface between the structure and the outer surface of the acoustic medium need to be

matched. Nodes with identical locations but different IDs are used for structural elements

and acoustic elements on the interface. Because of this necessary duplication of nodes,

there are 5,558 nodes, as opposed to 4,242 if equivalence is done, in the final model.

Figure 1-1: Conventional FEA model for the structure

Figure 1-2: Conventional FEA model for the interior acoustic medium

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If there are beams attached to plates when generating the FE model, the beam element

and the corresponding connecting edge of the plate element should be matched. Contrary

to the case for acoustic and structural elements outlined above, the same nodes should be

used for the beam element (CBAR) and plate element (CQUAD4 CTRIA3) at the

attachment point, not duplicate nodes. Hence, the whole model should not have duplicate

nodes except the nodes on the interface of structure and acoustic medium.

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Step 2: Run the Pre-EFEA code on the conventional FEA model

There are two input files to the Pre-EFEA code. The FE model constructed in Step 1 is

the first input. A “data.inp” file is the second input. The content of the “data.inp” file

for the cylindrical structural model example is shown below in Figure 2-1.

Figure 2-1: “data.inp” file

The “data.inp” file allows users to specify the name of the FE model data file. In this

example, “example1.dat” is the NASTRAN data file of the cylinder model, as denoted by

the keyword ‘FILE’. This is the only required entry in the “data.inp” file. The

“data.inp” file also allows the user to control some parameters, i.e. the criterion angle for

identifying the plate-plate joints (ANGLE) and the criterion distance for identifying the

plate-acoustic joints (DIST). Refer to the EFEA 2010 User’s Guide for detailed

definitions for these available functions. Once the “data.inp” file has been created, the

Pre-EFEA code is ready to run.

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The Pre-EFEA code reads in the FE model specified by the “data.inp” file and detects all

geometric features, changes in material properties, intersections between components,

and interfaces between structural and acoustic elements. Once these actions have been

completed, the Pre-EFEA code automatically:

• Disconnects the model at each structural joint location (plate-to-plate, plate-to-

beam) by adding appropriate nodes and by updating the connectivity of the

associated structural elements.

• Creates all the necessary joints (PJOINT with/without stiffener, BPJOINT)

among structural elements or between structural and acoustic elements

(PAJOINT, APAJOINT).

• Outputs the EFEA input data file which contains all the nodes and elements for

the structural and acoustic parts of the model, including modified node numbers

and accordingly updated element connectivity at the joints, and all the necessary

cards which define the joint connections. The available material and geometric

properties defined in the FE model will also be output into the EFEA input data

file using the proper format required by EFEA.

Figure 2-2 shows the plate-plate joints (red lines) generated by Pre-EFEA for the

cylindrical structural model example.

Figure 2-2: Plate-plate joint (red lines) generated by Pre-EFEA code

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Pre-EFEA will output the generated EFEA model into a data file with the name “model-

all.dat”. The summary information on the EFEA model is written into the “pre_efea.log”

file. An example of the “pre_efea.log” for the cylinder model is shown below in Figure

2-3:

Figure 2-3: “pre_efea.log” file

Based on the availability of material and geometric properties (i.e. PSHELL and MAT1

entries for plate or shell properties, PBAR entry for beam properties) in the original FE

model file, Pre-EFEA will also output the corresponding material (i.e. MPLATE,

MBAR, or MRIB cards) and geometric properties (i.e. PLATE, PBAR, or RIB cards) in

EFEA format (some entries may not complete and need to be manually modified by users

as explained in the next section). A sampling of the properties output by Pre-EFEA for

the cylinder model is included below in Figure 2-4:

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Figure 2-4: Property definition part of “model-all.dat” output file

Following the property definition part, the “model-all.dat” file lists the grid nodes,

elements and PJOINT entries for the structure model. The grid nodes, elements and

JPLAC/JACPLAC entries for the acoustic model are listed at the end of the file.

Refer to the EFEA 2010 User’s Guide for detailed definitions of each entry.

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Step 3: Modify the EFEA model file generated by the Pre-EFEA code

Users need to manually modify the EFEA input data file created from the Pre-EFEA code

in order to provide information about:

• The excitation (input powers or forces, locations, and frequencies). The

cards used to define the excitation in the current version of EFEA include:

PLATEF, PLATEB, PLATEIP, PLATESH, ACOUS, ASOURCE,

EDPLTB, EDPLTIP, EDPLTSH, EDACS, PWAVE, and TBL. Refer to

the EFEA 2010 User’s Guide for detailed definitions of each entry.

• Material properties (for the structural components and for each acoustic

domain). The cards used to define the material properties in the current

version of EFEA include: MPLATE, PACOUS, MBAR, MRIB, and

MISO. Refer to the EFEA 2010 User’s Guide for detailed definitions of

each entry.

• Geometry properties (for the radiation efficiency computations). The cards

used to define the geometry properties in the current version of EFEA

include: PLATE, PBAR, RIB, ISO, EFEA_PS, and LGOPENING. Refer

to the EFEA 2010 User’s Guide for detailed definitions of each entry.

• Acoustic absorption properties for representing acoustic treatment. The

cards used to define the acoustic absorption in the current version of EFEA

include: TMMAT and TMDFACE. Refer to the EFEA 2010 User’s Guide

for detailed definitions of each entry.

• The solver option (by METHOD card. Refer to the EFEA 2010 User’s

Guide for detailed definitions of this entry).

• The format of the requested output. The cards used to specify the output

information in the current version of EFEA include: OUTFILE, OUTSTR,

OUTACS, OUTBM, OUTDB, REFSPL and REFE. Refer to the EFEA

2010 User’s Guide for detailed definitions of each entry.

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Excitation and output type selection must also be manually added. The following Figures

3-1 and 3-2 illustrate the modified entries for the cylinder model:

Figure 3-1: Modified“model-all.dat” output; FREQ and SUBCASE 1

Figure 3-2: Modified“model-all.dat” output; output format, etc.

Refer to the EFEA 2010 User’s Guide for detailed definitions of each entry.

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Step 4: Run the EFEA code on the modified EFEA model file

After Step 3 is completed, the EFEA model file is ready for analysis. Refer to the EFEA

2010 User’s Guide for the syntax of running EFEA.

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Step 5: Post-process the EFEA results file in PATRAN

When PATRAN is specified using the OUTFILE keyword in Step 3, the output from

EFEA will be ready for post-processing using PATRAN. EFEA will output multiple

result files in PATRAN *.nod format. Unlike the PUNCH format files in Step 5a, each

of these files corresponds to a combination of one analyzed frequency and one subcase.

The names of these files are in the form of “s_freq=XXX_subcase=YYY.nod” for plate

elements results, and “a_freq=XXX_subcase=YYY.nod” for acoustic elements results.

The ‘XXX’ and ‘YYY’ in these sample file names are the frequency value and subcase

ID respectively. A template file “snod.res_tmpl” for plate elements, and “anod.res_tmpl”

for acoustic elements will also be created for post-processing the results in PATRAN.

The structure model result files “s_freq=XXX_subcase=YYY.nod” contain the following

results: bending wave energy density, longitudinal wave energy density, shear wave

energy density and normal velocity. The acoustic model result files

“a_freq=XXX_subcase=YYY.nod” contain the following results: acoustic energy density,

acoustic pressure and acoustic sound pressure level. The following are the steps for post-

processing EFEA results in PATRAN.

(1) Load the model into PATRAN

i.) Copy the EFEA model data file into a new temp file.

ii.) Remove the lines with the keyword “FREQ”, “SUBCASE” and

“ENDSUBCASE” in the file.

iii.) Split the model data file into a structure model file and an acoustic model

file. As discussed in Step 2, in the model data file, the structure node and

element entries are followed by PJOINT entries, and then the acoustic

node and element entries. Hence, the model data file can be easily split

into a structure model file and an acoustic model file. The reason for

splitting the model data file is that the EFEA code output the results for

structure model and acoustic model into separate files.

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iv.) Import the desired (structure or acoustic) model into PATRAN using

MSC.Nastran Input template (Figures 5-2 & 5-3). In the following steps,

the acoustic model data file is used.

Figure 5-2: Import the EFEA model into PATRAN

Figure 5-3: Imported EFEA model

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(2) Load the PATRAN ‘.nod’ result template and import the result file

i.) Click and select [File] -> [Import] from main menu.

ii.) In the popup “Import” windows, select [Results] after [Object], and select

[PATRAN 2 .nod…] after [Format].

iii.) In the new popup “Template for PATRAN 2.5 Import Results” windows,

browse to the local directory where your EFEA model is located.

iv.) Select “anod.res_tmpl” file in that local directory, which is generated by

EFEA (Figure 5-4).

Figure 5-4: Load the PATRAN result template

v.) Click OK.

vi.) In the “Import” windows, browse to the local directory where your EFEA

model is located.

vii.) Select “a_freq=1000_subcase=1.nod” from the results file generated by

EFEA, as shown in Figure 5-5.

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viii.) Modified the “Zero Tolerance” value which is shown in the oval in Figure

5-5 to be 0. This step will avoid unnecessary filtering of results.

ix.) Click [Apply] (Figure 5-5).

Figure 5-5: Select the result file generated by EFEA

(3) Get contour plot

i.) Click [Results] from toolbar in PATRAN.

ii.) Select “SPL, Acoustic” at the windows located at the right side.

iii.) Click [Apply].

See Figure 5-6 for an example of a contour of the SPL distribution in the interior acoustic

medium of the cylinder example.

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Figure 5-6: Contour of SPL in acoustic cavity

In the “Select Fringe Result” box of Figure 5-6, there are only two available sets of

results: “Energy Density, Acoustic” and “SPL, Acoustic”. And the results for acoustic

pressure are not available. The reason is that the acoustic pressure values in the

“a_freq=1000_subcase=1.nod” file are all zeros, as shown in Figure 5-7. In order to

view the acoustic pressure values, the user needs to modify the EFEA data file so that the

entry “OUTACS SPL” shown in Figure 3-2 is changed to be “OUTACS SPL P”. Figure

5-8 shows the contour of the acoustic pressure distribution in the interior acoustic

medium of the cylinder example.

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Figure 5-7: PATRAN format file “a_freq=1000_subcase=1.nod”

Figure 5-8: Contour of acoustic pressure in acoustic cavity