This example problem demonstrates the use of the Rayleigh integral to predict the sound far field of a piston with infinite baffle. A quarter of the piston is modeled without any acoustic elements under the assumption that the fluid does not influence the structural motion. The radiated sound far field is efficiently computed by the Rayleigh integral during postprocessing.
The material properties of the piston with the radius 0.1 m and thickness 0.01 m are:
Elastic moduli = 210 GPa Minor Poisson's ratios = 0.28 Mass density = 7800 kg/m3
The acoustic domain is the air with mass density = 1.21 kg/m3 and sound speed = 345 m/s.
For more information, see Acoustic Output Quantities in the Mechanical APDL Theory Reference.
/batch, list /nopr /prep7 pi=acos(-1.) a=0.1 ! radius of the piston d=0.01 ! thickness of the piston h=a/5 ! mesh size rho=1.21 ! air mass density c0=345 ! sound speed in the air k=10 ! wave number frq=k*c0/(2.*pi) ! working frequency omega=2.*pi*frq ! working angular frequency vn=-1 ! normal velocity in z direction un=-vn/omega ! displacement in z direction et,1,186 ! structural element mp,dens,1,7800 ! mass density of the piston mp,ex,1,2.1e11 ! elastic moduli of the piston mp,nuxy,1,.28 ! poison's ratio of the piston cyl4,0.,0.,0.,0.,a,90,-d ! 1/4 piston model esize,h type,1 mat,1 mshape,1,3d vmesh,all ! meshing alls nsel,s,loc,z,-d d,all,uz,0,un ! imaginary displacement constrain nsel,s,loc,z,0 sf,all,mxwf ! flag radiation surface alls fini /solu antype,harmic ! define harmonic analysis harfrq,frq,frq ! solving frequency nsubst,1 ! sub-step solve ! solve fini /post1 set,1,1 hfsym,,shb,shb ! indicate boundary condition on symm planes R = 0.05 ! observation point prfar,plat,sumc,0,0,1,0,0,1,R,,,rho,c0 ! amplitude of pressure prfar,plat,phsc,0,0,1,0,0,1,R,,,rho,c0 ! phase angle of pressure prfar,plat,splc,0,0,1,0,0,1,R,,,rho,c0 ! sound pressure level prfar,plat,pwl,0,0,1,0,0,1,,,,rho,c0 ! radiated sound power level fini