Virtual.lab声固耦合的隔声量仿真分析教程.docx

FEM Direct Vibro-Acoustic Analysis Case TutorialObjective:The goal of this tutorial is to calculate the acoustic response of a glass/PVB plate (a laminated safety glass with a Polyvinyl butyral layer in between). The tutorial includes using the following analysis cases: Structural Modal case Direct Structural Forced Response Direct Structural Vibro-Acoustic Response Transmission LossThemodel contains a Visco-elastic frequency-dependent material.Pre-Requisites:Software Configurations that are needed to run the tutorial: Licenses to set up the case in LMS Virtual.Lab: Desktop (VL-HEV.21.1 or equivalent) and Finite Element Acoustics (VL-VAM.36.2) When solving the acoustic response case, the license for product LMS Virtual.Lab FEM Vibro-Acoustics Structural Solver VL-VAM.45.2 is needed. Solving the Random Post-processing case to get the Transmission Loss curve will require the license for Random Vibro Acoustic Analysis (VL-NVP.20.3)Tutorial Data Files:StructuralGroups.xmlSAFyoung.xlsLaminatedStructure.bdfFPmesh.bdfAMLsender.bdfAMLreceiver.bdfAcousticGroups.xmlAll data files can be found on the APPS n DOCS DVD, in an archive calledVAM_DirectVA-TL. For ease of use, it is best to copy all files to a local folder.STEP BY STEP Tutorial:STEP 1 After starting LMS Virtual.Lab, create a new document in the Acoustic Harmonic FEM Workbench (Start Acoustics Acoustic Harmonic FEM).STEP 2Select File Import from the main menu. The Import command can also be selected from the contextual menu of the Links Manager, by right clicking A file selector window appears allowing you to specify the file type and the file name. For more details, see Importing DataSelect the file type NASTRAN Bulk File (*.bdf, *.NS, *.nas, *.dat) and browse for the file LaminatedStructure.bdf and click the Open button. A new dialog box appears requesting the selection of data that needs to be imported from the file. The data entries that are not available in the file are grayed out.Select in Split into Multiple Mesh Parts under Mesh Creation and set the unit system to Meter, Kilogram, Second, click the OK button. STEP 3Next, the different structural materials will be defined. The two outer layers of the panel are made of Glass. To incorporate the 2% structural damping of this material, it will be modeled as a viscoelastic material with a constant complex Young modulus. The inner layer is made of PVB.Insert Materials New Materials New Viscoelastic Material.Right-click on the Materials feature in the Specification Tree New Materials New Viscoelastic MaterialDefine the materials as follows:GLASSPVBYoung ModulusConstantPoisson RatioMass DensityYoung ModulusPoisson RatioMass DensityRealImaginary0.232500 kg_m3Frequency Dependent0.491066 kg_m37.15e+011 N_m21.401e+009 N_m2The PVB material at the center of the windshield has strong frequency dependent stiffness properties and is nearly incompressible. The frequency dependency can be incorporated in a viscoelastic material using an edited load function. The values can be imported from the Excel document SAFyoung.xls as follows:Check Frequency Dependent, and right-click the input field.Select New Function.In the Attributes tab, enter as Name Youngs modulus PVB.In the Values tab, click the Import a file button, and browse to the excel file to select it.Switch the Data Format to Linear Amplitude/Phase (deg) because the file contains the values like that. Click the Import button.Click the OK button of the Function Editor GUI. Click the OK button on the Material GUI.On the Edited Load Function Set, create (using the context menu) a 2D display of type Complex (Edited Load Function) on the Youngs modulus and check the curve:STEP 4Defining two Structural 3D properties for Glass and PVB, applied to the structural groups Glass (with the defined material Glass) and PVB (with the defined material PVB). Insert Properties New Structural Properties Create 3D-PropertyRight-click on the Properties feature in the Specification Tree New Structural Properties Create 3D-Property Before the following steps please make sure the Mesh Parts are defined as types:PROPERTY0 StructuralGlass StructuralPVB StructuralThis can be done by going to Tools Set Mesh Parts TypeRight-click on the mesh in the Specification Tree, Set Mesh Part Type Set as Structural Mesh PartSTEP 5In the next step, the model mesh will be imported from two Nastran input files. They each contain a mesh on which we will apply an AML property (Automatically Matched Layer), one on the receiver side, and one on the sender side.:File Import Acoustic Mesh Model Mesh., and select the file AMLreceiver.bdfUse Meter, Kilogram and Seconds units, and include the materials and properties.Similarly, import AMLsender.bdf. At this point the mesh parts type definition window should look like this: STEP 6 Inserting the New Material and properties for the new imported meshesInsert a new Acoustic material as follows (use the default values for air):Insert also a New Fluid Property. Call it also air, use the just definedmaterial Air, and apply it to the two Acoustic mesh parts (Sender and Receiver side).STEP 7To facilitate the creation of the structural and acoustic model, some element groups have been predefined in xml files. To import these groups, first create mesh group sets. Insert a New Group Set, either from the contextual menu or withInsert Mesh Grouping Group Set.By right clicking the Group Set feature in the Specification Tree, insert a mesh group named Structural Groups, and in it import the 5 groups from the file StructuralGroups.xml.Right-click the Group Set, and use Mesh Grouping Group Selection Dialog:Similarly insert a mesh group named Acoustic Groups, and in it import the 4 groups from the file AcousticGroups.xmlRight-click the group set, and use againMesh Grouping Group Selection Dialog:Step 8Save the analysis, but without closing. SETTING UP THE ACOUSTIC CASESStep 1Insert a new acoustic automatically matched layer property to take into account the semi-infinite extent of the sender and receiver rooms. Insert a new AML property by right-clicking Properties, use New Acoustic Properties Automatically Matched Layer Property.Apply it to the two Acoustic groups AML Receiver and AML Sender. Switch the Radiation surface to User Defined, and select the AML Receiver group.Step 2Insert a Direct Vibro-Acoustic Response Analysis Case to compute the structural response and acoustic pressure fields in both the sender and receiver acoustic domains for each of the distributed plane wave excitations: To perform this calculation use No Load function Set and No Load Vector Set.Create new sets for all the rest.STEP 3Expand the Direct Vibro-Acoustic Response Analysis Case from the Specification Tree, right-click the Boundary Condition Set and use Acoustic Sources Distributed Plane Waves. with a Refinement Level of 2, a Radius of 4m, and an Acoustic Pressure on 1Pa. The plane waves will be used to excite the system and to calculate the transmission loss characteristics of the panel. Since the panel is not aligned with the xy plane, this coordinate plane cannot be used to define the location of the plane wave sources. So, for the Half Space Plane select Plane defined by Group and select the acoustic group Coupling Sender. Select the Negative Half Space side.Click the OK button to generate a set of 12 spatially distributed plane waves. By now the model should look similar to this:Step 4We will now restrain the border of the glass panel.Right-click the Restraint Set, add an Advanced Restraint on the 3 Translational DOFs, and use as support the Structural Group BCs.Step 5Coupling surface definition will be used to couple the upper and lower surfaces of the panel to the envelope surface of the acoustic cavity. When setting the Coupling Surface, the coupling between the structure and the fluid is on both sides.To correctly define the two-sided coupling in a transmission loss calculation, two coupling surfaces need to be created. From the Coupling Surface Set.1 feature, double-click the Coupling Surface Set.1, and add the twosurfaces: Structural Group CouplingSender and Acoustic Group Coupling Sender. Use a tolerance of 10mm and select as Coupling Type One side. Click the Apply button. Do the same for the Receiver Side in the end you should have two Coupling surfaces: Step 6Double-click on the Direct Vibro-Acoustic Response solution to update the analysis parameters. In the current tutorial, the response at the center frequencies of the third octave bands between 160Hz and 2000Hz will be analyzed. In the Result Specifications tab, select User Defined values for the Argument Axis Definition and remove the standard analysis frequency range. Add a new frequency range definition and select a Logarithmic Step definition with a starting frequency of 160Hz, an ending frequency of 2000Hz and a step of 1.122462048. Click the OK button to add the frequency range definition.Request Vector results at Field Points and for the Acoustic Potentials. No need to solve for Structural Displacements for now.Adjust the Solving Parameters. If your system is set up for parallel processing (see the Advanced Acoustic Installation manual), try one of the Parallelism types. Use the Direct solver.Adjust also the Job and Resources, e.g. to use multiple threads.Leave the Output Sets empty, meaning that results will be computed wherever possible.Step 7Update the Direct Vibro-Acoustic Response Solution to compute the acoustic pressure fields and structural deformations. This will take a while, as there are 23 frequencies and 12 load conditions. Save your model. Step 8Displaying the resultsOnce the computation is finished, right-click the Direct Vibro-Acoustic Response Solution Set.1 feature and select Generate Image from the contextual menu.or select the solution feature and click the Generate Image toolbar button.The Image Generation dialog box will appear, select the Pressure.Double-click the image feature in the Specification Tree, and inthe Occurrences tab select thefor example thefirst Load Condition (meaning the loading by the first distributed plane wave source) and set the frequency at 508Hz, click the OK button. For better visualization you can hide the Nodes and Elements feature, and the Boundary Conditions feature (with its plane wave sources).You can also display the 2D image curve for the Acoustic Power on the Kirchhoff surfaceRight-click the Direct Vibro-Acoustic Response Solution Set.1 feature and select New Function Display. from the contextual menu. The New Function Display dialog box will appear requesting you to select the different display images. Also you can use the button from the toolbar and select the Solution Set feature. A third possibility is to use the menu Insert 2D/3D Images New Function DisplaySelect the 2D Display from the list and click the Finish button.A new window, containing X- and Y-axes along with the Select Data dialog box will now appear. In the Select Data dialog box, select Kirchhoff Surface Radiation: S and click the Display button As each of the distributed plane wave sources are independent, the sound power can be obtained by simply adding the individual contributions. So, select all 12 Data Cases, and check the optionSum over data cases. Switch the x-axis format to Octaves, and the Y-axis to dB(RMS). You can use dot markers for the curve by right-clicking it, using the Options. command in its context menu, and then changing the settings in the Visualization tab. Save your modelStep 9To get the transmission loss curve, we need to divide the total acoustic power on the receiver side by the total power on the sender side. Before we can do that, we need to combine the individual cases (one for each distributed plane wave source) to get the total power curves.Insert a Random Post-processing Case with Insert Other Analysis Cases Random Post-Processing Case.Refer to the solution of the previous response case, and select to process for a Cross Power Set with Unitary Uncorrelated Load Cases:Update its solution using the context menu on its solution feature Random Response Solution Set.X. This will go fast.Right-click the sub-solution Global Indicator Set.X and create a New Function Display on it. Select the 2D Display as scenario, and click the Finish button.A 2D display window will appear with the Select Data dialog box open. In the General tab, switch the drop-down selector to Transmission Loss, and select the entry Coupled Surface:S and click the Display button.You can see a TL value of 30.461911 dB for the 319.996 Hz octave band:Theory for Panel Transmission LossCalculation of Transmission Loss using Vibro-Acoustic FEMThis topic describes how to set up a model and the computation to compute the Transmission Loss (e.g. for a panel) using the LMS Virtual.Lab tools.Step1. Import of an Acoustic and Structural meshImport an acoustic mesh and a structural mesh with the modal data in the Acoustic Harmonic FEM workbench. There is no need to have a field point mesh.Step2. Create a New Acoustic PropertyDefine the Acoustic Properties including fluid properties and possible impedance on the panel. Create an Automatically Matched Layer (AML) property for the source room on all faces that are not coupled to the panel and not touching the joined wall. The wall must be a zero velocity boundary condition. Also create an Automatically Matched Layer (AML) on the anechoic room side, which is defined as a Kirchhoff surface.Step3. Insert the boundary conditionCreate an acoustic boundary condition by selecting Insert Acoustic Boundary Conditions and Sources Acoustic Boundary Condition and Source Set from the main menu. The Boundary Condition Set Creation dialog box appears as shown in the image below:Click the OK button to close the dialog box. A new Acoustic Boundary Conditions and Sources feature appears in the Specification Tree as shown in the image below:Now, similarly add to the Acoustic Boundary Condition and Sources an acoustic source of type Distributed Plane Waves in the source room.Step4. Insert a Vibro-Acoustic Response and Random Post-Processing Analysis Case Insert the Modal-based Vibro-Acoustic Response Analysis Case by selecting Insert FEM Analysis Cases Modal Based Vibro-Acoustic Response Analysis Case from the main menu, or click the Create a Modal Based Vibro-Acoustic Response Analysis Case button from the FEM Analysis Cases toolbar. Define the Mesh Mapping and select the structural shells and the two groups of acoustic faces (one in the source room and one in the receiver room). Compute the Modal-based Vibro-Acoustic Response Analysis case. It will compute the Incident Power and the Radiated Power for each source. Similarly, insert a Random Post-Processing Case, and Compute it. It will compute the Total Powers and store it in a sub-solution called Global Indicator Set as: Total Incident Power, having Physical Type as INPUT_POWER and Response ID as Coupled Surface:S. Total Power radiated by the Acoustic Mesh, having Physical Type as ACOUSTIC_POWER and Response ID as Kirchhoff Surface Radiation:S. If you have a field point mesh which is not needed to compute the Transmission Loss), it will also compute the Total Power on the Field Point Mesh having Physical Type as ACOUSTIC_POWER and Response ID as Field Point Mesh:S. The Random Response Solution Set computes also the Transmission Loss with the following formula:Where,is the Incident Poweris the Radiated PowerStep5: Post-ProcessingStandard results will be post-processed on the analysis cases.The Incident Power, Radiated Power and Transmission Loss are stored as Expressions, Load Functions by the Global Indicator Set, and can be displayed in a 2D Function Display.The Transmission Loss will be stored with Physical Type as ABSORPTIVITY and Response ID as Coupled Surface:S Manual calculation of Transmission Loss by using Edited Load FunctionStep1. Insert an Edited Load Function.To insert an Edited Load Function, select from the main menu Insert Functions Creator Edited Load Function or use the Create an Edited Load Function button available in the Functions Creator toolbar.Step2. Import Kirchhoff Surface Radiation:S function from Global Indicators of the Random Post-Processing Solution Set of the Acoustic document. Take only the Real Part.Step3. Again, import the function Acoustic Power on Field Point Mesh:S from Global Indicators of the Random Post-Processing Solution Set of the Structural document. Take only the Real Part and Amplitude of that Part.Step4. Multiply this function with 0.5. As the actual incident power is half the power through the field point mesh. This is because the incident pressure is imposed as total pressure on the wall.Step5. Now, divide these two functions and take the Log of that function and finally multiply it with 10. Step6. Create a 2D display To visualize the computed Transmission Loss, right-click the Edited load function in the Specification Tree and select the New Function Display option from the contextual menu. Select 2D Display from the list and click the Finish button. From the Select Data dialog box select Transmission Loss using the drop-down menu.BEM Symmetry Plane SetThe mathematical formulation of the Boundary Element method leads to dense matrices, with the consequence that a linear increase in model size N (number of nodes and elements, or more generally, number of DOFs) leads to A parabolic increase (order N*2) for the BEM matrix storage requirementsA c