04-Nvh Modal Response Part II

ETA NVH Analysis Modal Response Part II

BETA CAE Systems S.A. Tutorial 4 MR.II - 1 ETA Tutorials

Tutorial 4

ETA

NVH : Modal Response Part II Table of Contents

1. Introduction ............................................................................................................... 2

1.1. Prerequisites ............................................................................................................. 2

1.2. Problem Description ................................................................................................ 2 1.3. Data Files ................................................................................................................. 2

2. Post Processing Procedure ...................................................................................... 3 2.1. Read Model Geometry ............................................................................................. 3 2.2. Define Results and Create Loadcase........................................................................ 4 2.3. Read Acoustic Coupling from NASTRAN *.pch file ............................................. 5

2.4. Define Panels ........................................................................................................... 6

2.5. Calculate PPF (acoustic coupling from Nastran) ..................................................... 7

2.6. Plot Panel Participation Factors from NASTRAN *.pch file .................................. 8 2.7. Curves Handling ..................................................................................................... 9 2.8. Calculate PPF (acoustic coupling from META) .................................................... 10



1. Introduction

This tutorial highlights some of the ETA features oriented in NVH Analysis. Using the Modal Response tool, it is also possible to calculate Acoustic Responses for a coupled fluid-structure analysis. The steps are the same as the ones for the calculation of structural responses with the addition of the definition of Acoustic coupling data. Not all capabilities are demonstrated in this tutorial. The user may also refer to ETA Users Guide for the

functionality of ETA and detailed description of functions and procedures.

1.1. Prerequisites

It is recommended for users who have never used ETA before to read the Introduction Tutorial. For old

ETA users it would be helpful referring to ETA Release Notes.

1.2. Problem Description

The purpose of this tutorial is to calculate Panel Participation Factors (PPF) in two ways:

- Calculated by ETA using Acoustic coupling from Nastran.

- Calculated by ETA using acoustic coupling

created by ETA.

and compare these results with those included in the Nastran *.pch file.

1.3. Data Files

The files required for this tutorial are:

/tutorials/mETA_tutorials/04-NVH/NVH_CAR_FE.nas

/tutorials/mETA_tutorials/04-NVH/NVH_CAR_FE.op2

/tutorials/mETA_tutorials/04-NVH/NVH_CAR_FE.pch



2. Post Processing Procedure

2.1. Read Model Geometry

1. Switch to the Read Results tab and press the button to open the File Manager. For this tutorial select the file: ../04-NVH/NVH_CAR_FE.nas

and press Open.

2. Model is read and should appear as it is shown in the image on the left.

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2.2. Define Results and Create Loadcase

1. Open the Modal Response tool from Calculate > Modal Response. Load the model eigenmodes from the *.op2 results file, by invoking the File Manager, pressing the button. Open the ../04-NVH/NVH_CAR_FE.op2

file as the Modal Results File. Modes are now listed inside the Mode-Frequency table. On top the Structural modes are listed, while at bottom, Fluid (cavity) modes are listed.

At the beginning of each type of modes, Rigid Body modes for structure or fluid appear (frequency < 1E-02). TIP: B Ratio is by default equal to 0.02. However, when reading the loadcases from the *.nas input file, then the B Ratio values are updated automatically.

2. Switch to Frequency Response tab and press Read.

Select file: ../04-NVH/NVH_CAR_FE.nas

and press Open to read in

loadcases, as these are defined in the NASTRAN input file. TIP: Press New to define

loadcases manually.

3. Loadcases are listed in tree view, and Start, End, Step values are updated. Also the B Ratio values in the Modes tab are updated.

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TIP



1. Select loadcase 1002 and press Exclude, to exclude it from the calculation.

2. Select loadcase 1001 and type node id 2000001 in Enter Node Ids field. Node is added in the Response Dofs list.

Node 2000001 corresponds to one of the four microphone positions. TIP: There are several ways to

add nodes in this list. For example choosing Adv. Filter and

specifying the name of the node: e.g. add > Nodes > name > ? (for filtering names) > mic*

and then deleting all except from Node 2000001.

2.3. Read Acoustic Coupling from NASTRAN *.pch file

3. Switch to Acoustic Coupling tab and press Read to load the acoustic coupling calculated by NASTRAN output in the *.pch file. Select: ../04-NVH/ NVH_CAR_FE.pch

file and press Open.

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2.4. Define Panels

1. Press New to define Panels.

2. Set advance filter syntax as

shown in the image below. add > Groups >name > PANEL_* Set Output > Group Panels and press Ok to define panels.

TIP: Use ? in the name field in

order to open a window with all the available names.

3. Exclude PANEL_BOARD and PANEL_FIREWALL from the Panels Participation Factor by pressing Exclude button.

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TIP



2.5. Calculate PPF (acoustic coupling from Nastran)

1. Select Panel Participation Factors in 2D Plot tab and press Calculate.

2. A 2d plot curve of the Panel Participation Factors is created. Change Y plot axis to db(A) filter by clicking with the Right mouse button on the Y axis and changing Scale Type to db(A) filter. Type 2e-11 and press

Enter.

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2.6. Plot Panel Participation Factors from NASTRAN *.pch file

1. Switch to Read Results > Curves tab and press to read history results file. Select file: ../04-NVH/NVH_CAR_FE.pch

and press Open.

2. Set the options as shown in the image on the left.

3. Select ROOF and TUNNEL panels only, Modal Response result and press Read.

4. Panel Participation Factors read from the *.pch file are appended in the same plot.

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2.7. Curves Handling

TIP: Select 1st and 3

rd curve and

select Or from the Right mouse button menu. Click once with the Left Mouse button inside the 2d Plot window to set the focus on it and use Ctrl+Up/Down arrows to visually compare different pairs of curves. Panel Participation Factors calculated by Nastran are

identical with those calculated by

ETA using acoustic coupling from Nastran.

TIP: It is possible to apply a lot of

different functions on curves from Calculate > Curve Functions.

TIP



2.8. Calculate PPF (acoustic coupling from META)

1. The first step is to create acoustic coupling

in ETA. Switch to window MetaPost and open Part Manager . Select FLUID_PIDS part and select Or from the Right mouse button menu.

2. Only the fluid part of the model is visible.

3. Press the Inv focus button to invert visibility

of parts.

4. Only the structural part of the model is visible.

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1. Open Sets and press New to create a new set . Type the name of the set e.g. STRUCT and press Enter. The new set is added in the list.

2. Switch back to Modal Response tool > Acoustic Coupling tab and press New to

create acoustic coupling in ETA.

3. In Fluid-Structure Interface define the group names as shown in the image on the left. Press Calculate.

4. Exclude acoustic coupling from NASTRAN (*.pch) by selecting it, in the Fluid-Structure Interface list and pressing Exclude > Selected. Then press again Calculate.

Panel Participation Factors are calculated using acoustic

coupling created by ETA.

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1. Repeat the same steps are described on chapter 2.7 in order to compare the curves. Panel Participation Factors calculated by Nastran are identical with those calculated by

ETA using acoustic coupling

from ETA.

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04-Nvh Modal Response Part II

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