ABAQUS声学分析-acoustics-lecture6.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,Copyright 2005 ABAQUS,Inc.,Structural-Acoustic Analysis with ABAQUS,L6.,*,Structural-Acoustic Analysis with ABAQUS,Additional Examples,Lecture 6,深圳,ABAQUS,培训,深圳,ANSYS,培训,深圳,ANSYS,深圳,ABAQUS,深圳有限元培训,ABAQUS,培训,ANSYS,培训,Structural-Acoustic Analysis with ABAQUS,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 Truck Cab:Sequential Analysis,Summary,Structural-Acoustic Analysis with ABAQUS,Sloshing,Structural-Acoustic Analysis with ABAQUS,Sloshing,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/m,3,E,=,210,GPa,n,=,0.3,)spherical shell of radius,1,m and thickness,0.05,m is immersed in an infinite volume of air(,r,=,1.25,kg/m,3,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,to,4.0,is analyzed using,*STEADY 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 ABAQUS,Sloshing,Meshes(shells in orange),Structural-Acoustic Analysis with ABAQUS,Sloshing,Pressure magnitudes at 158.7 Hz,Structural-Acoustic Analysis with ABAQUS,Sloshing,Pressure magnitude results,freq(Hz)ka Node 1776 Node 35 Analytical,10.0000000 0.196349541 2.51556000 2.51671000 2.51404729 12.8569000 0.252444641 4.20656000 4.20854000 4.20443148 16.5300000 0.324565791 7.08098000 7.08441000 7.07835582 21.2524000 0.417289898 12.0325000 12.0386000 12.0302351 27.3239000 0.536503522 20.6916000 20.7026000 20.6920596 35.1301000 0.689777900 35.9806000 36.0014000 35.9879477 45.1664000 0.886840190 62.6031000 62.6415000 62.6105015 58.0699000 1.14019982 105.856000 105.924000 105.798479 74.6598000 1.46594174 166.575000 166.689000 166.273101 95.9893000 1.88474550 238.751000 238.874000 237.975417 123.412000 2.42318895 319.106000 319.087000 317.622889 158.670000 3.11547816 412.658000 412.448000 410.202606 204.000000 4.00553063 528.079000 527.194000 524.385853,Analytical solution:,Structural-Acoustic Analysis with ABAQUS,Effect of Surface Treatments on Room Acoustics,Structural-Acoustic Analysis with ABAQUS,Effect of Surface Treatments on Room Acoustics,Example:Small room coupled to inlet 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.,Structural-Acoustic Analysis with ABAQUS,Effect of Surface Treatments on Room Acoustics,Acoustic-only mesh of room,ducts,and exterior;no treatment:,Structural-Acoustic Analysis with ABAQUS,Effect of Surface Treatments on Room Acoustics,Add acoustic treatments to ceiling,wall,and floor of room:,Structural-Acoustic Analysis with ABAQUS,Effect of Surface Treatments on Room Acoustics,With acoustic treatment:,Structural-Acoustic Analysis with ABAQUS,Nonlinear Structural Behavior,Structural-Acoustic Analysis with ABAQUS,Nonlinear Structural Behavior,Structural analysis can include effects from several sources of nonlinearity:,Material nonlinearities,Examples:Metal plasticity,crushable foam,Geometric nonlinearities,Examples:Pre-tensioning of a cable,snap-through behavior of an arch,Contact nonlinearities,Contact is inherently nonlinear because the contact constraints are either on or off;they do not vary smoothly.,Structural-Acoustic Analysis with ABAQUS,Nonlinear Structural Behavior,Multistep analysis,General,analysis steps can have 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 general 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.,Structural-Acoustic Analysis with ABAQUS,Nonlinear Structural Behavior,Example:Sound transmission through a rubber door seal.,Step 1,:Static structural analysis to deform the rubber seal into its final position.,Rigid surface moves upward,causing the rubber to deform.,Acoustic mesh is automatically updated based with the use of adaptive meshing.,Air,Rigid surface,Rubber seal,d,Structural-Acoustic Analysis with ABAQUS,Nonlinear Structural Behavior,Step 2,:Steady-state dynamic analysis 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 medium,Contours of acoustic pressure,Structural-Acoustic Analysis with ABAQUS,Coupled Piezoelectric and Acoustic Analysis,Structural-Acoustic Analysis with ABAQUS,Coupled 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 coupled 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,.,Structural-Acoustic Analysis with ABAQUS,Coupled Piezoelectric and Acoustic Analysis,Example:fluid-coupled motion of a transducer,Half-axisymmetric model of piezoelectric solid,brass head mass,and fluid:,fluid,piezoelectric material,head mass,Structural-Acoustic Analysis with ABAQUS,Coupled Piezoelectric and Acoustic Analysis,Apply electrical forcing across piezoelectric material using the,*,DSECHARGE 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 through frequencies using the,*,STEADY STATE DYNAMICS,DIRECT procedure to find onset of degraded transduction due to head mass vibration.,Structural-Acoustic Analysis with ABAQUS,Coupled Piezoelectric and Acoustic Analysis,Acoustic pressure at 36866 Hz:,Structural-Acoustic Analysis with ABAQUS,Coupled Piezoelectric and Acoustic Analysis,Acoustic pressure at 37342 Hz:Head mass mode distorts acoustic field.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,The objective is to show the acoustic field in and surrounding a model 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 radiation 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.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,Exterior and interior fluid 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.,Structural-Acoustic Analysis with ABAQUS,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,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.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully 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 Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,The interior acoustic pressure field,POR(dB)at this frequency:,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,The exterior field shows radiation primarily to the front and top,with a peak underneath the cab.,Structural-Acoustic Analysis with ABAQUS,Acoustics 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 windshield panel motions are the most pronounced.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Fully Coupled Analysis,The exterior field at this frequency(298 Hz)shows radiation from the windshield and side panels.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,Structural-Acoustic Analysis with ABAQUS,Acoustics 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 global model.,Method,Global model,Submodel,1,Direct steady-state dynamics,Direct steady-state dynamics,2,Frequency extraction,Modal steady-state dynamics,Direct steady-state dynamics,3,Frequency extraction,Subspace projection steady-state dynamics,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Acoustics of a 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 frequency range.,Submodel:,Use direct steady-state dynamics over the same frequency range or a subset of this range.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,Computed pore pressure(POR dB)for exterior(below)and interior(next page)acoustic fields are nearly identical to the fully coupled results.,Global:,Direct steady-state dynamics,Submodel:,Direct steady-state dynamics,Fully coupled,Sequentially coupled,Structural-Acoustic Analysis with ABAQUS,Nearly identical behavior due to the low force amplitude exerted on the structure by the air.,Acoustics of a Truck Cab:Sequential Analysis,Fully coupled,Sequentially coupled,Global:,Direct steady-state dynamics,Submodel:,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Acoustics 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 frequencies,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 acoustics submodel.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,First eigenmode of the uncoupled,undamped structural system is at 108 Hz(using frequency extraction procedure):,Global:,Modal steady-state dynamics,Submodel:,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,The modal steady-state dynamics procedure yields the following solution(displacement magnitudes)at this frequency:,Fully coupled:110 Hz,Sequentially coupled:108 Hz,Global:,Modal steady-state dynamics,Submodel:,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,The direct steady-state dynamics procedure is used in the submodel at the same frequency(interior and exterior air shown):,Fully coupled,Sequentially coupled,Global:,Modal steady-state dynamics,Submodel:,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,Third method:Natural frequency extraction followed by subspace projection steady-state dynamics in 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.,Structural-Acoustic Analysis with ABAQUS,Acoustics of a Truck Cab:Sequential Analysis,The structural responses are reduced compared to those from the modal dynamics procedure(displacement magnitudes shown).,Global:,Subspace steady-state dynamics,Submodel:,Direct steady-state dynamics,Fully coupled,Sequentially coupled,Structural-Acoustic Analysis with ABAQUS,The submodel acoustic responses are also reduced.,Acoustics of a Truck Cab:Sequential Analysis,Fully coupled,Sequentially coupled,Global:,Subspace steady-state dynamics,Submodel:,Direct steady-state dynamics,Structural-Acoustic Analysis with ABAQUS,Summary,Structural-Acoustic Analysis with ABAQUS,Summary,Direct steady-state dynamics using a fully coupled model provides the greatest fidelity:structural damping and structural-acoustic coupling are included.,Sequential procedures neglect the transfer of momentum between solids and fluid during the initial(“global”)step.,This permits the structure and acoustic problems to be solved in sequence.,Of the sequential procedure alternatives,the use of direct steady-state dynamics in both the global and submodel analyses allows the greatest fidelity:only the fluid-solid coupling effect is neglected.,Using subspace projection steady-state dynamics for the global analysis permits individual modes of the structure to be emphasized in the analysis,and the corresponding acoustic field in the submodel to be computed.,The same is true of using modal steady-state dynamics in the global analysis,but structural damping effects are not included.,