This example problem demonstrates the use of FLUID221 to predict the acoustic transmission loss of a muffler.
The radius and length of the chamber are 0.0766445 m and 0.2032 m, respectively.
The radius and length of the inlet and outlet pipe are 0.0174625 m and 0.104775 m, respectively.
/batch,list
/title, Transmission Loss of Muffle
/show,png
/nopr
/PREP7
rho=1.2041 ! air mass density
c0=343.24 ! air sound speed
z0=rho*c0
freqE=3000 ! highest working frequency
wave=c0/freqE ! wavelength at the highest frequency
p=1
vn=-p/(rho*c0) ! normal velocity excitation
! define element and materials
et,1,221,,1 ! tet uncoupled element
mp,dens,1,rho ! material
mp,sonc,1,c0
! create the model
rapipe=0.0174625
lpipe=0.104775
rchamb=0.0766445
lchamb=0.2032
cylind,0,rapipe,0,lpipe,0,180
cylind,0,rchamb,lpipe,lpipe+lchamb,0,180
cylind,0,rapipe,lpipe+lchamb,2*lpipe+lchamb,0,180
vsel,all
vglue,all
! mesh the geometry
h=wave/10 ! 10 elements/per wavelength
esize,h
type,1
mat,1
vmesh,all
nummrg,all
! define excitation and boundary conditions on inlet and outlet port
nsel,s,loc,z,0 ! nodes on inlet
sf,all,port,1 ! inlet port
sf,all,shld,vn ! normal velocity
sf,all,impd,z0 ! impedance boundary on inlet
nsel,s,loc,z,2*lpipe+lchamb ! nodes on outlet
sf,all,port,2 ! outlet port
sf,all,inf ! radiation boundary on outlet
alls
fini
! perform solutions
/solu
antype,harmic
hropt,auto
kbc,1
harf,0,freqE
nsub,60 ! 50 Hz interval with 60 steps
solve
finish
! post-processing
/post1
pras,pall,1,all,,,,,1,2 ! print sound power data
plas,tl,1,all,,,,,1,2 ! plot transmission loss
/show,png
set,l,60
/view,,1,1,1
plnsol,pres ! plot pressure
plvect,sndi,,,,vect,node,on ! plot sound intensity vector
/show,close
fini