abaqus经典声学分析例题acoustics-lecture6

1、Structural-Acoustic Analysis with ABAQUSLecture 6Additional ExamplesCopyright 2005 ABAQUS, Inc.Overview Sloshing Effect of Surface Treatments on Room Acoustics Nonlinear Structural Behavior Coupled Piezoelectric and Acoustic Analysis Acoustics of a Truck Cab: Fully Coupled Analysis Acoustics of a Tr

2、uck Cab: Sequential Analysis SummarySloshingSloshing Spherical acoustic radiation in Mode 1 Reference: Junger, M.C. and Feit, D., Sound, Structures, and Their Interaction, MIT Press, pp. 200-203, 1972. Physical Description: A steel (r = 7800 kg/m3, E = 210 GPa, n = 0.3) spherical shell of radius 1 m

3、 and thickness 0.05 m is immersed in an infinite volume of air (r = 1.25 kg/m3, K = 128000 Pa, c = 320 m/s). The sphere is driven as a rigid body to excite mode 1 using the*BOUNDARY, TYPE=DISPLACEMENT option. A frequency range of 10 Hz to 204 Hz, corresponding to ka 0.2 to4.0 is analyzed using *STEA

4、DY STATE DYNAMICS, DIRECT. Nonconforming shell (S8R) and acoustic infinite element (ACIN3D4) meshes are used. Fluid-solid coupling through use of the *TIE option.Structural-Acoustic Analysis with ABAQUSL6 .5Sloshing Meshes (shells in orange)Copyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis wit

5、h ABAQUSL6 .11Sloshing Pressure magnitudes at 158.7 HzCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .7Sloshing Pressure magnitude resultsCopyright 2005 ABAQUS, Inc.Analytical solution: P = rc2 u(ka)2(ka)2 + 2 2 + (ka)6)freq (Hz)kaNode 1776Node 35Analytical10.00000000.19634954

6、12.515560002.516710002.5140472912.85690000.2524446414.206560004.208540004.2044314816.53000000.3245657917.080980007.084410007.0783558221.25240000.41728989812.032500012.038600012.030235127.32390000.53650352220.691600020.702600020.692059635.13010000.68977790035.980600036.001400035.987947745.16640000.88

7、684019062.603100062.641500062.610501558.06990001856000105.924000105.79847974.65980001.46594174166.575000166.689000166.27310195.98930001.88474550238.751000238.874000237.975417123.4120002.42318895319.106000319.087000317.622889158.6700003.11547816412.658000412.448000410.202606204.0000004.0

8、0553063528.079000527.194000524.38585311(ka)2 - 2)2 + (2ka)2Structural-Acoustic Analysis with ABAQUSEffect of Surface Treatments on Room AcousticsCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .11Effect of Surface Treatments on Room Acoustics Example: Small room coupled to inle

9、t and exhaust ducts. Uniform forcing at inlet end. Exhaust to exterior modeled using a small hemisphere of air and the spherical radiation condition. At the frequency shown, the inlet excitation has excited a standing wave in the room.Copyright 2005 ABAQUS, Inc.Effect of Surface Treatments on Room A

10、coustics Acoustic-only mesh of room, ducts, and exterior; no treatment:Effect of Surface Treatments on Room Acoustics Add acoustic treatments to ceiling, wall, and floor of room:Effect of Surface Treatments on Room Acoustics With acoustic treatment:Structural-Acoustic Analysis with ABAQUSNonlinear S

11、tructural BehaviorCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .17Nonlinear Structural Behavior Structural analysis can include effects from several sources of nonlinearity: Material nonlinearities Examples: Metal plasticity, crushable foam Geometric nonlinearities Examples:

12、 Pre-tensioning of a cable, snap-through behavior of an arch Contact nonlinearities Contact is inherently nonlinear because the contact constraintsare either on or off; they do not vary smoothly.Copyright 2005 ABAQUS, Inc.Nonlinear Structural Behavior Multistep analysis General analysis steps can ha

13、ve linear or nonlinear behavior. The end condition of one general step provides the base state for the next general step. If an earlier general step includes nonlinear behavior, the nonlinear solution is included in subsequent steps. Acoustic analysis includes the effects of previous nonlinear gener

14、al steps. The most obvious effect is aligning the acoustic region with the deformed shape of the structure, including contact regions. Less obvious is the change in material properties, such as stiffness.Nonlinear Structural Behavior Example: Sound transmission through a rubber door seal. Step 1: St

15、atic structural analysis to deform the rubber seal into its final position. Rigid surface movesupward, causing thedrubber to deform.Air Acoustic mesh is automatically updated based with the use of adaptive meshing.Rigid surfaceRubber sealNonlinear Structural Behavior Step 2: Steady-state dynamic ana

16、lysis of the fully coupled system. The air and the rubber interact through their tied surfaces. Acoustic pressure is applied as a boundary condition to left side of the air mesh.Deformed seal in acoustic mediumContours of acoustic pressureStructural-Acoustic Analysis with ABAQUSCoupled Piezoelectric

17、 and Acoustic AnalysisCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .23Coupled Piezoelectric and Acoustic Analysis Piezoelectric analysis An electric potential gradient causes straining, and stress causes an electric potential gradient. Piezoelectric analysis by itself is a c

18、oupled electrical-stress analysis. Can be combined in a model with acoustic elements and the necessary structural-acoustic coupling. Often used in acoustics applications, such as speakers. Solved using*FREQUENCY,*MODAL DYNAMIC,*STEADY STATE DYNAMICS, or*STATIC.Copyright 2005 ABAQUS, Inc.Coupled Piez

19、oelectric and Acoustic Analysis Example: fluid-coupled motion of a transducer Half-axisymmetric model of piezoelectric solid, brass head mass, and fluid:fluidpiezoelectric materialhead massCoupled Piezoelectric and Acoustic Analysis Apply electrical forcing across piezoelectric material using the*DS

20、ECHARGE or *DECHARGE options. Couple acoustic fluid to the head mass solid elements using TIE constraints. Use water properties and fluid elements to approximate human tissue. Model radiation into the fluid exterior using the spherical boundary impedance (*IMPEDANCE PROPERTY, TYPE=SPHERICAL). Sweep

21、through frequencies using the*STEADY STATE DYNAMICS, DIRECTprocedure to find onset of degraded transduction due to head mass vibration.Coupled Piezoelectric and Acoustic Analysis Acoustic pressure at 36866 Hz:Coupled Piezoelectric and Acoustic Analysis Acoustic pressure at 37342 Hz: Head mass mode d

22、istorts acoustic field.Structural-Acoustic Analysis with ABAQUSAcoustics of a Truck Cab: Fully Coupled AnalysisCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .27Acoustics of a Truck Cab: Fully Coupled Analysis The objective is to show the acoustic field in and surrounding a mo

23、del truck cab due to the effect of loudspeakers. Cab structure is mounted on four elastic point-mounts, modeled as springs. Rest of truck is omitted from this analysis. Interior and exterior air are meshed automatically using tetrahedral elements. Exterior radiation is modeled using spherical radiat

24、ion impedance. Cab structure is modeled using shells and solids (for dashboard and seat). Acoustic excitation due to loudspeakers inside cab is modeled as concentrated loads on the acoustic fluid.Copyright 2005 ABAQUS, Inc.Acoustics of a Truck Cab: Fully Coupled Analysis Exterior and interior fluid

25、meshes are shown here. Neither mesh matches the cab shell mesh node- to-node. Each is modeled as a separate part and coupled using the TIE constraints.Acoustics of a Truck Cab: Fully Coupled Analysis In exterior problems it is good practice to inspect the phase of the acoustic pressure at the lowest

26、 frequency of interest to see if the radiation condition is performing properly. If the radiation condition is applied incorrectly, absent, or too close to the acoustic sources, the phase contours will show distortion near the boundary. Here, the contours look all right.Acoustics of a Truck Cab: Ful

27、ly Coupled Analysis The direct steady-state dynamics procedure is used to solve the coupled fluid-solid problem at 90 frequencies. Using ABAQUS/Viewer, we observe a peak in the structural motion amplitude at 110Hz. This involves large motions of the windshield and other panels.Structural-Acoustic An

28、alysis with ABAQUSL6 .29Acoustics of a Truck Cab: Fully Coupled Analysis The interior acoustic pressure field, POR (dB) at this frequency:Copyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .31Acoustics of a Truck Cab: Fully Coupled Analysis The exterior field shows radiation prima

29、rily to the front and top, with a peak underneath the cab.Copyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .31Acoustics of a Truck Cab: Fully Coupled Analysis Another structural peak amplitude occurs at 298 Hz, directly at the location of the acoustic source. Again, side and win

30、dshield panel motions are the most pronounced.Copyright 2005 ABAQUS, Inc.Acoustics of a Truck Cab: Fully Coupled Analysis The exterior field at this frequency (298 Hz) shows radiation from the windshield and side panels.Copyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSAcoustics of

31、a Truck Cab: Sequential AnalysisCopyright 2005 ABAQUS, Inc.Structural-Acoustic Analysis with ABAQUSL6 .43Acoustics of a Truck Cab: Sequential Analysis Example: Truck cab problem using sequential analysis Three variations are discussed here. They differ only in the analysis procedure used for the glo

32、bal model.MethodGlobal modelSubmodel1Direct steady-state dynamicsDirect steady-state dynamics2Frequency extractionModal steady-state dynamicsDirect steady-statedynamics3Frequency extractionSubspace projection steady-state dynamicsDirect steady-state dynamicsCopyright 2005 ABAQUS, Inc.Acoustics of a

33、Truck Cab: Sequential Analysis First method: Direct steady-state dynamics in both analyses Global model: Define node sets and element sets as described previously, and save the needed results to the output database (.odb) or results (.fil) file. Use direct steady-state dynamics over the desired freq

34、uency range. Submodel: Use direct steady-state dynamics over the same frequency range or a subset of this range.Acoustics of a Truck Cab: Sequential Analysis Computed pore pressure (PORdB) for exterior (below) and interior (next page) acoustic fields are nearly identical to the fully coupled results

35、.FullycoupledSequentially coupledGlobal:Direct steady-state dynamicsSubmodel: Direct steady-state dynamicsAcoustics of a Truck Cab: Sequential AnalysisFully coupledSequentially coupledNearly identical behavior due to the low force amplitude exerted on the structure by the air.Global:Direct steady-st

36、ate dynamicsSubmodel: Direct steady-state dynamicsAcoustics of a Truck Cab: Sequential Analysis Second method: Natural frequency extraction followed by modal steady- state dynamics in the global model Compute eigenmodes of the uncoupled structural system. Run the steady-state procedure at these freq

37、uencies, and use these results as the forcing functions for the submodel analysis. This procedure will IGNORE any damping due to structural material properties, but modal damping can be applied. Subsequently, use direct steady-state dynamics for the acousticssubmodel.Acoustics of a Truck Cab: Sequen

38、tial Analysis First eigenmode of the uncoupled, undamped structural system is at 108 Hz (using frequency extraction procedure):Global:Modal steady-state dynamicsSubmodel: Direct steady-state dynamicsAcoustics of a Truck Cab: Sequential Analysis The modal steady-state dynamics procedure yields the fo

39、llowing solution (displacement magnitudes) at this frequency:Fully coupled: 110 HzSequentially coupled: 108 HzGlobal:Modal steady-state dynamicsSubmodel: Direct steady-state dynamicsAcoustics of a Truck Cab: Sequential Analysis The direct steady-state dynamics procedure is used in the submodel at th

40、e same frequency (interior and exterior air shown):FullycoupledSequentiallycoupledGlobal:Modal steady-state dynamicsSubmodel: Direct steady-state dynamicsAcoustics of a Truck Cab: Sequential Analysis Third method: Natural frequency extraction followed by subspace projection steady-state dynamics in

41、the global model The natural frequencies and mode shapes are computed as in the previous procedure. The subspace projection steady-state dynamics procedure is used for the global model. This procedure differs from the modal steady-state dynamics procedure in that the original system of finite element equations, including structural damping terms, is projected onto the eigenmodes.Acoustics of a Truck Cab: Sequential Analysis The structural respo