LMS Virtual. Derivation method of lab acoustic simulation results

1、 brief introduction

Siemens LMS Virtual.Lab Provide an integrated software platform to simulate the quality attributes of mechanical systems , Such as structural integrity 、 Vibration and noise 、 Durability 、 System dynamics characteristics 、 Driving smoothness and handling stability .LMS Virtual.Lab Including all key process steps and required technologies , Each key attribute can be evaluated from beginning to end . Use LMS Virtual.Lab, Engineering teams can build accurate simulation models , Simulate its real performance , And can quickly and effectively evaluate and optimize the design scheme before the physical prototype construction .

among LMS Virtual.Lab Acoustics Acoustic simulation module , Its unique high-performance finite element model adaptive sequence （FEMAO） The acoustic solver is embedded in LMS Virtual.Lab, Make it adaptive to elements , So that the acoustic analysis in the whole frequency range has an accurate and efficient finite element mesh .LMS Virtual.Lab Acoustics It also enables you to perform scalable noise analysis for your product development process . For aeroacoustics ,LMS Virtual.Lab Acoustics Provides a high-performance algorithm to deal with TB Through computational fluid dynamics （CFD） The data generated . Integrated into the LMS Virtual.Lab Acoustics This algorithm can make the larger CFD Data sets are processed more efficiently , And achieve higher accuracy of the most complex prediction .

2、 Concept

2.1 Sound pressure

Sound pressure ： When sound waves travel through the air , The density of the air changes with sound waves , therefore , The regional pressure will also change , This is the sound pressure . The difference between the pressure in the presence of sound waves and the pressure without sound waves . When sound waves pass , The excess value of atmospheric pressure . Company ：Pa, Pascal . Scalar . The relationship between sound intensity and sound pressure ：I=P2/ρC. among ：ρC—— Air characteristic impedance ,ρC=415 N.s/m3. Sound pressure generally refers to the effective sound pressure , That is, the square root of sound pressure , For plane sound waves, the effective sound pressure is one-half of the root of the peak sound pressure . Sound intensity refers to the sound energy per unit area per unit time .

Sound pressure level （SPL Sound Pressure Level ） It refers to the measurement of the effective sound pressure relative to a reference value with a logarithmic ruler , In decibels （dB） To describe its relationship with the reference value . Human beings are for 1KHz The hearing threshold of the voice （ That is, the lowest sound pressure to produce hearing ） by 20µPa, It is usually used as the reference value of sound pressure level .

The most commonly used physical quantity for sound measurement is sound pressure , However, sound pressure level is usually used to describe the magnitude of sound pressure （Sound Pressure Level,SPL）. The audible sound pressure range of human ear is 2×10^-5Pa To 20Pa, The corresponding sound pressure level range is 0~120dB, therefore , The concept of sound pressure level is introduced, which is easy to describe the sound pressure with large linear variation .

Sound pressure level calculation formula Lp=20lg(p/p0)
In style ,
Lp: Sound pressure level （ Company ： Decibel ）;
p： Sound pressure （ Company ： Mr ）;
p0： Reference sound pressure , In the air p0=2×10 Of -5 Power （ Mr ）, namely 20 Micropa .

among ,pref Express 1000Hz Minimum audible sound pressure amplitude at human ear 20μPa. The sound pressure used for sound pressure level calculation in the above formula p It must be the root mean square value of sound pressure （RMS）, Or the mean square value of sound pressure （ If the 10 The logarithmic form of times ）.

2.2 A strong voice

A strong voice ： Sound energy per unit area perpendicular to the direction of sound propagation per unit time . Company ：W/m2. Sound intensity describes the spatial distribution of sound energy .

Although sound pressure is an important physical parameter of noise evaluation , However, the magnitude of sound pressure is directly related to the distance from the sound source and the environment in which it is measured , therefore , The sound radiation energy of a sound source cannot be measured simply by sound pressure . Sound power can be used to measure the sound radiation capacity of a sound source , It's a constant .

Sound power level calculation formula Lw=10lg（W/W0）
In style ,
Lw： Sound power level （ Company ： Decibel ）;
W： Sound power （ Company ： watts ）;
W0： Reference sound power ,W0=10 Of -12 Power （ watts ）, namely 1 PIVA .

Sound energy power cannot be measured directly , Usually, the measured sound pressure is converted to .
The pressure of sound is the sound intensity I=p^2/(ρc), Or medium p Is the effective sound pressure ρ Is the air density c Is the speed of sound in the air .
Sound power W= A strong voice x area
Decibel , Also known as sound intensity level L, Expression is L=lg(I/I0)（ Where the reference sound pressure I0=10E-12(w/m^2, watts / Square meters ).

Sound power is defined as the sound energy radiated inward and outward by the sound source per unit time , Unit is W. Corresponding to sound pressure level , Sound power also has sound power level . Sound power level is the relative measurement of sound power and reference sound power , Defined as

among W Is the measured sound power ,W0=10^-12W Is the reference sound power . Sound power is an absolute quantity , Only related to the sound source , It has nothing to do with anything else , therefore , It is a physical property of the sound source .

2.3 Time domain

Time domain （ Time domain ,Time domain） It describes the relationship between mathematical function or physical signal and time . For example, the time-domain waveform of a signal can express the change of signal with time . It's the real world , Is the only domain that actually exists . Because our experience is developed and verified in the time domain , Have become accustomed to events occurring in chronological order . When evaluating the performance of digital products , It is usually analyzed in the time domain , Because the performance of the product is finally measured in the time domain .

The argument is time , That is, the horizontal axis is time , The vertical axis is the change of signal . Its dynamic signal x（t） Is a function describing the value of the signal at different times .

Two important parameters of clock waveform are clock cycle and rise time .

2.4 frequency domain

frequency domain （ Frequency domain ,frequency domain） It is a coordinate system used to describe the frequency characteristics of signals . In electronics , In control systems engineering and statistics , The frequency domain diagram shows the semaphores in each given frequency band in a frequency range . frequency domain , Especially in RF and communication systems , Frequency domain problems are also encountered in high-speed digital applications . The most important property of the frequency domain is ： It's not real , It's a mathematical construct . Time domain is the only objective domain , The frequency domain is a mathematical category that follows specific rules , The frequency domain is also called God's perspective by some scholars .

The independent variable is frequency , That is, the horizontal axis is the frequency , The vertical axis is the amplitude of the frequency signal , That is commonly known as spectrum diagram .

Sine wave is the only waveform in frequency domain , This is the most important rule in the frequency domain , That is, sine wave is a description of the frequency domain , Because any waveform in the frequency domain can be synthesized by sine wave . This is a very important property of sine wave .

Time domain analysis and frequency domain analysis are two observation surfaces of analog signals . Time domain analysis is to represent the relationship between dynamic signals with time axis as coordinates ; Frequency domain analysis is to change the signal into the coordinate of frequency axis . Generally speaking , The representation of time domain is more visual and intuitive , Frequency domain analysis is more concise , Analyzing problems is more profound and convenient . The trend of signal analysis is from time domain to frequency domain . However , They are interconnected , Be short of one cannot , Complement each other .

2.5 airspace

Space domain is called airspace for short （spatial domain）, Also known as image space (image space), Generally, this concept will appear in digital image processing , Refers to the space composed of image pixels . In image space, by length ( distance ) Processing pixel values directly as independent variables is called spatial domain processing .

2.6 Pressure acoustics

Pressure acoustics is “ Acoustic module ” Most commonly used features , It can be used to simulate pressure acoustic effects , For example, the scattering of sound 、 Diffraction 、 launch 、 Radiation and transmission . The simulation running in the frequency domain uses the Helmholtz equation , The time-domain simulation uses the classical scalar wave equation . In frequency domain , You can use finite element method and boundary element method , And hybrid finite element - The boundary element method . In the time domain , Time domain implicit can be used （ The finite element method ） And time domain explicit （dG-FEM） The formula .

3、 Site setting （Field Point）

LMS Virtual.Lab Acoustic The workbench can contain different types of grid parts , These components are listed under the node and element characteristics of the specification tree . The grid part belongs to one of the following three types :

• Structural grid part （Structural Mesh Part）:
  The structural mesh part is a structural finite element mesh , It represents the geometric and structural behavior of vibrating structures . This grid only exists in the structural part of acoustic vibration analysis , It will represent the dynamic characteristics of the structure ( In physical coordinate system or modal coordinate system ).

• Acoustic grid part （Acoustic Mesh Part）:
  The acoustic grid part is an acoustic grid , It only represents the geometry of the vibrating structure . This kind of grid has no structural characteristics . It only exists in the acoustic part of vibroacoustic analysis , Will affect the reflection of the sound field 、 Scattering and diffraction .

• Field grid part （Field Point Mesh Part）:
  Field grid part (FPM) Is a visual grid , It is used to calculate and represent the acoustic results of the space around the vibrating structure . This grid does not affect the acoustic solution : It is completely transparent to sound waves . The grid part of the field is displayed in translucent yellow by default .
  
  

• Insert a Plane Field Point Mesh

• Insert a Spherical Field Point Mesh

• Insert a Cylinder Field Point Mesh

• Insert a Box Field Point Mesh

• Insert a Point Set Field Point Mesh

• Insert an ISO Power Field Point Mesh

• Insert a Line Field Point Mesh

• Insert a Directivity Field Point Mesh

4、 Result export

4.1 Tools - Image Export

menu ： Tools -> 2D/3D Images… -> Image Export…

• Export ID:
  

• Export Coordinates:
  

LMS Virtual.Lab Structures With Dassault CATIA V5 And open SIMULIA Platform seamless integration , Expand and perfect CATIA V5 Of CAE function , For system level modeling and finite element preprocessing / Post processing provides a complete and independent integrated environment . These functions allow design and engineering teams to analyze the structural characteristics and performance of components and assemblies in the same environment , At the same time, it can also communicate with the initial CAD Models keep in close contact .

Of course, the files in the above two formats can also be accessed through LMS Virtual.Lab Secondary development VBA Interface batch automatic export .
its VBA The interface is actually based on catia Realized , You can refer to catia Development related documents .

https://catiadesign.org/_doc/V5Automation/online/CAAScdAniUseCases/CAAAniPostProSelection.htm

https://catiadesign.org/_doc/V5Automation/online/CAAScdAniUseCases/CAAAniPreproOnPublishSource.htm

https://catiadesign.org/_doc/V5Automation/generated/interfaces/CATAnalysisInterfaces/interface_AnalysisImage_33596.htm

• modular _ Export sound pressure level data .bas：

'***********************************************************************
' Purpose:  Export sound pressure level data at all frequency points （ Nodes on the field grid ）
' Author:  Xiaomu who loves reading 
' Date: 2022-02-21 
' Languages: VBA
' Platform: LMS Virtual.Lab 13.10
' ***********************************************************************

Attribute VB_Name = " modular _ Export sound pressure level data "
Sub CATMain()

Dim analysisDocument1 As AnalysisDocument
Set analysisDocument1 = CATIA.ActiveDocument

Dim analysisManager1 As AnalysisManager
Set analysisManager1 = analysisDocument1.Analysis

Dim analysisModels1 As AnalysisModels
Set analysisModels1 = analysisManager1.AnalysisModels

Dim analysisModel1 As AnalysisModel
Set analysisModel1 = analysisModels1.Item(1)

Dim analysisCases1 As AnalysisCases
Set analysisCases1 = analysisModel1.AnalysisCases

Dim analysisCase1 As AnalysisCase
Set analysisCase1 = analysisCases1.Item(3)

Dim analysisSets1 As AnalysisSets
Set analysisSets1 = analysisCase1.AnalysisSets

Dim analysisSet1 As AnalysisSet
Set analysisSet1 = analysisSets1.Item("Acoustic Field Response Solution Set.1", catAnalysisSetSearchAll)

Dim analysisImages1 As AnalysisImages
Set analysisImages1 = analysisSet1.AnalysisImages

Dim analysisImage1 As AnalysisImage
Rem Set analysisImage1 = analysisImages1.Item("Pressure (nodal values).1")
Rem Set analysisImage1 = analysisImages1.Item("image1839.1")
Set analysisImage1 = analysisImages1.Item("Pressure Average Iso Amplitude on Deformed Mesh dB(RMS) with shift.1")

analysisImage1.Update

For i = 1 To 30
    analysisImage1.SetCurrentOccurrence (i)
    analysisImage1.Update
    
    OutputPath = CATIA.SystemService.Environ("CATTemp")
    Set fileSystem1 = CATIA.FileSystem
    Set folder1 = fileSystem1.GetFolder(OutputPath)
    
    Rem analysisImage1.ExportData folder1, "lms_" + Str(i), "txt"
    analysisImage1.ExportDataInGlobalAxis folder1, "lms_results_" & CStr(i), "txt", catSamCoordinateSystem_Cartesian, True

Next i

End Sub

Due to the above file content format, the output cannot be customized , Only in a fixed format .
Write first python Script , Once again, the above documents are processed in the format that meets our requirements .

• The sound pressure level data is processed again .py

#***********************************************************************
# Purpose:  Convert the sound pressure level data in a fixed format to a user-defined file format （ Nodes on the field grid ）
# Author:  Xiaomu who loves reading 
# Date: 2022-02-21 
# Languages: VBA
# Platform: Python 3.9.7 win64
' ***********************************************************************

for n in range(1, 31):

    lines = []
    with open("C:\\Users\\tomcat\\Desktop\\data\\lms_results_"+str(n)+".txt") as f:
        for line in f.readlines():
            # print(line)
            line_arr = line[:-1].split('\t')
            lines.append(line_arr[:-1])
        # print(line_arr)

    fo = open("C:\\Users\\tomcat\\Desktop\\data\\lms_"+str(n)+".vol", "wb")
    fo.write( "frames 1\n".encode('utf-8') )
    fo.write( "interval 1\n".encode('utf-8') )

    ######################################################
    fo.write( "points 12010\n".encode('utf-8') )
    for i in range(3, len(lines)):
        # print(lines[i])
        line = lines[i]
        s = str(i-2) +"\t"+ line[0] +"\t"+ line[1] +"\t"+ line[2]+"\n"
        fo.write( s.encode('utf-8') )

    ######################################################
    fo.write( "\n".encode('utf-8') )
    fo.write( "frame 1\n".encode('utf-8') )
    for i in range(3, len(lines)):
        # print(lines[i])
        line = lines[i]
        s = str(i-2) +"\t"+ line[3] +"\n"
        fo.write( s.encode('utf-8') )

    ######################################################
    fo.close()

4.2 Tools - Identify Nodes and Elements

menu ： Tools -> Inquire… -> Identify Nodes and Elements…


The small window on the right above “Select Group/Mesh Part” The value of the first text box in , You can select from the 3D model , It can also be found in the object tree on the left "Nodes and Elements" Branch face sub object selection .

Save as csv Software for documents Excel Open as follows ：

4.3 Insert - Report Results

Click the button in the picture above “Save As …”, Save data in list control as Excel The documents are as follows ：

4.4 Tools - Export Groups

4.5 file - Export Virtual.Lab Document

• Acoustic_Field_Response_Case.unv：
  
• Acoustic_Response_Case.unv：
  

Postscript

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