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1、Copyright 2005 ABAQUS,Inc.Modeling Acoustic Problems Using ABAQUSLecture 3Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.2OverviewAcoustic Element TypesMaximum Element SizeExternal Meshed DomainBoundary ConditionsLoadsExterior Problems using Infinite ElementsAnalysis Procedures
2、OutputStructural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.Acoustic Element TypesStructural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.4Acoustic Element TypesAcoustic elements are available in linear and quadratic interpolation.ABAQUS/Standard has first-and second-order f
3、ull integration elements:Quadrilateral and triangular for planar and axisymmetric domains(AC2D3,AC2D4,AC2D6,AC2D8,ACAX3,ACAX4,ACAX6,ACAX8)Hexahedral,tetrahedral,and wedge for three-dimensional domains(AC3D4,AC3D6,AC3D8,AC3D10,AC3D15,AC3D20)One-dimensional acoustic links to model acoustic channels(AC
4、1D2,AC1D3)Examples:Piping,ducts,small openings between large regionsStructural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.5Acoustic Element TypesABAQUS/Explicit has first-order reduced integration elements:Quadrilateral and triangular for planar and axisymmetric domains(AC2D3,AC2D4R,A
5、CAX3,ACAX4R)Hexahedral and tetrahedral for three-dimensional domains(AC3D4,AC3D8R)Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.6Acoustic Element TypesAcoustic-structural interface(ASI)coupling elements(ABAQUS/Standard only):Provide the coupling effects between an acoustic mes
6、h and a structural mesh.Can be defined two different ways:User can explicitly create ASI elements.User can allow ASI elements to be generated internally and automatically,using TIE constraints between the fluid and solid surfaces.TIE constraints are available for both ABAQUS/Standard and ABAQUS/Expl
7、icit and will be discussed further in the next lecture.Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.7Acoustic Element TypesAcoustic infinite elements:Available in both ABAQUS/Standard and ABAQUS/Explicit*.Provided for exterior problems.Have surface topology and are similar to
8、 structural infinite elements.Generally defined on a terminating surface of a region of acoustic finite elements.Formulation is considerably more accurate than impedance-type boundary conditions for complex wave fieldsninth order implementation.Can be coupled directly to a structural surface using T
9、IE constraints.In general,acoustic infinite elements will provide higher accuracy when used instead of impedance-type boundaries at the same distance from the structure.*For ABAQUS/Explicit,this represents a significant advance over the published literature on infinite elements.Structural-Acoustic A
10、nalysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.8Acoustic Element Types Element selection Interpolation orderSecond-order elements are generally much more accurate than first-order acoustic elements for a given number of degrees of freedom.First-order elements are slightly faster and are included fo
11、r convenience.Both first-and second-order acoustic meshes work well together with structural meshes.Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.9Acoustic Element Types Element shapeQuad/hex elements are slightly more accurate than tri/tet elements.Often tri/tet elements requ
12、ire less effort in creating the mesh.General commentsThere are no problems associated with using different integration orders or different element shapes on the fluid and solid meshes.ABAQUS/Explicit offers reduced integration elements with automatic hourglass control,making hourglassing extremely u
13、nlikely.Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.10Acoustic Element TypesAcoustic importAcoustic elements may be imported between ABAQUS/Standard and ABAQUS/Explicit.This enables coupled fluid-solid analyses such as:Eigenanalysis(ABAQUS/Standard)of post-shock(ABAQUS/Expli
14、cit)structures.Transient dynamic(ABAQUS/Explicit)analysis of systems under static preload(ABAQUS/Standard).The interface for acoustic import is identical to that for general import in ABAQUS.Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.Maximum Element SizeStructural-Acoustic Ana
15、lysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.12Maximum Element SizeElement sizeRelated to maximum frequency(or minimum wavelength)Higher frequency response requires smaller elements.Wavelength decreases with increasing frequency,so there is an upper frequency limit for a given mesh.Maximum element
16、sizeFor reasonable accuracy at least six representative internodal intervals(nmin)should fit into the shortest acoustic wavelength of interest.An“internodal interval”is defined as the distance from a node to its nearest neighbor in an element.Structural-Acoustic Analysis with ABAQUSCopyright 2005 ABAQUS,Inc.L3.13 Maximum Element SizeFor example,the maximum element size for a linear element is half the maximum element size for a quadratic element.Use the following relationships to determine the m
