This example problem demonstrates the use of the FLUID220 element to predict the transmission loss of a structural panel under excitation from a diffuse sound field.
The material properties of the 0.7m x 0.5m x 0.005m structural panel with fixed edges are:
Elastic moduli = 210 GPa Minor Poisson's ratios = 0.28 Mass density = 7800 kg/m3 Constant structural damping coefficient = 0.005
The receiving domain is the air with mass density = 1.225 kg/m3 and sound speed = 340 m/s.
The FSI between the acoustic incident wave and the structural shell is taken into account.
The diffuse sound field is defined in the global Cartesian coordinate system, as follows:
Reference sphere radius = 15 m Power spectral density = 1.0 (Watt/Hz) Mass density = 1.225 kg/m3 Sound speed = 340 m/s Maximum incident angle = 90o Number of parallel rings = 20 Sampling option = ALL (initializes the random generator of incident planar wave phases and samples the phases at each solving frequency)
Perfectly matched layers (PML) are used for truncation of the open space. For more information, see Perfectly Matched Layers (PML) in the Mechanical APDL Theory Reference.
/batch,list /title, A Structural Panel under the Excitation of the Diffuse Sound Field /prep7 /nopr et,11,200,7 ! 2d quad element for meshing et,1,220,,0 ! coupled acoustic element et,2,220,,1,,1 ! acoustic PML element et,3,281 ! structure shell element et,4,154 ! surface element mp,dens,1,1.225 ! the air mass density mp,sonc,1,340 ! sound speed in the air mp,dens,2,7800 ! steel mass density mp,ex ,2,2.1e11 ! steel elastic moduli mp,nuxy,2,.28 ! steel minor Poisson's ratios mp,DMPS,2,0.005 ! steel constant structural damping coefficient a0=0.7 ! length of the panel b0=0.5 ! width of the panel dz=2*a0 dpml=0.2 abuf=a0/8 bbuf=b0/8 h=a0/10 ! mesh size *dim,a,array,6 *dim,b,array,6 a(3)=-a0/2 a(4)=a0/2 a(2)=a(3)-abuf a(1)=a(2)-dpml a(5)=a(4)+abuf a(6)=a(5)+dpml b(3)=-b0/2 b(4)=b0/2 b(2)=b(3)-bbuf b(1)=b(2)-dpml b(5)=b(4)+bbuf b(6)=b(5)+dpml esize,h *do,i,1,5 *do,j,1,5 rect,a(i),a(i+1),b(j),b(j+1) *enddo *enddo aglue,all type,11 amesh,all ! mesh 2d surface asel,s,loc,x,a(2),a(5) asel,r,loc,y,b(2),b(5) cm,a1,area alls nsiz=nint(dz/0.3) npml=3 cmsel,s,a1 type,1 ! generate 3d coupled acoustic element mat,1 esize,,nsiz vext,all,,,,,-dz alls asel,s,loc,z,0 asel,u,,,a1 type,2 ! generate 3d acoustic PML element mat,1 esize,,nsiz vext,all,,,,,-dz alls nsel,s,loc,z,0 nsel,r,loc,x,a(3),a(4) nsel,r,loc,y,b(3),b(4) cm,nod1,node ! group vibro-acoustics FSI interface nodes sf,all,fsi ! flag FSI interface alls type,2 ! generate the rest of 3d acoustic PML element mat,1 asel,s,loc,z,-dz esize,,npml vext,all,,,,,-dpml alls asel,s,loc,z,0 aclear,all etdel,11 alls nummrg,all alls nsel,s,loc,x,a(1) nsel,a,loc,x,a(6) nsel,a,loc,y,b(1) nsel,a,loc,y,b(6) nsel,a,loc,z,-dz-dpml d,all,pres,0 ! pressure constrains on PML exterior surface alls sectype,2,shell secdata,0.005,2 cmsel,s,nod1 ! select FSI interface nodes type,3 mat,2 secn,2 esurf ! generate shell element alls nummrg,all alls esel,s,type,,3 ! select shell element type,4 mat,2 esurf ! generate surface element alls nummrg,all alls ! fix panel edges nsel,s,loc,z,0 nsel,r,loc,x,a(3) nsel,r,loc,y,b(3),b(4) d,all,ux,0 d,all,uy,0 d,all,uz,0 nsel,s,loc,z,0 nsel,r,loc,x,a(4) nsel,r,loc,y,b(3),b(4) d,all,ux,0 d,all,uy,0 d,all,uz,0 nsel,s,loc,z,0 nsel,r,loc,x,a(3),a(4) nsel,r,loc,y,b(3) d,all,ux,0 d,all,uy,0 d,all,uz,0 nsel,s,loc,z,0 nsel,r,loc,x,a(3),a(4) nsel,r,loc,y,b(4) d,all,ux,0 d,all,uy,0 d,all,uz,0 alls ! define diffuse sound field dfswave,0,15,1,1.225,340,90,20,all finish /solu antype,harmic harfrq,65,75 nsubst,10 msolve,5,0.1,2 ! five samples finish /post1 /show,png pras,dfst,avg,all ! print average transmission loss plas,dfst,avg,all ! plot average transmission loss finish