This example problem demonstrates the use of FLUID221 to predict the sound pressure in an impedance tube loaded with the perforated material using a Johnson-Champoux-Allard equivalent fluid model.

The frequency-dependent perforated material properties are defined.

The sound-hard boundary is applied to the walls of the pipe except for the inlet.

/batch,list
/title, JCA model with frequency-dependent parameters
/nopr
/prep7
FREQ1 = 2000                 ! beginnng frequency
FREQ2 = 4000                 ! ending frequency
SPEED  = 343                 ! sound speed
DENSITY= 1.2                 ! mass density
NUM_EPW    = 8               ! no. of element per wavelength
NUM_STEPS  = 3               ! number of frequencies

RESIS1 = 10000               ! resistivity at FREQ1 
RESIS2 = 10800               ! resistivity at FREQ2 
PORO1 = 0.88                 ! porosity at FREQ1 
PORO2 = 0.98                 ! porosity at FREQ2
TORTU1 = 1.00                ! tortuosity at FREQ1 
TORTU2 = 1.04                ! tortuosity at FREQ2
VISCL = 129e-6               ! viscous characteristic length
THERL  = 198e-6              ! thermal characteristic length
                             ! define geometry
DIM_WIDTH  = 30e-3
DIM_PERF   = 51.44e-3
DIM_WAVELNG= SPEED/FREQ2
DIM_ESIZE  = DIM_WAVELNG/NUM_EPW
DIM_LENGTH = 5*DIM_PERF

LOADING    = 1e3/SPEED*2
                             ! define element
et,1,221		
keyopt,1,2,1		
et,2,221		
keyopt,2,2,1
                             ! define real constant		
r,1
r,2
                             ! define material
mp,sonc,1,SPEED
mp,dens,1,DENSITY
mpcopy,,1,2                  ! copy material model data
                             ! define frequency-dependent JCA model
tb,perf,2,,,JCA
tbfield,freq,FREQ1
tbdata,1,RESIS1,PORO1,TORTU1,VISCL,THERL
tbfield,freq,FREQ2
tbdata,1,RESIS2,PORO2,TORTU2,VISCL,THERL		
                             ! create geometry
block,,DIM_WIDTH,,DIM_LENGTH,,DIM_WIDTH
block,,DIM_WIDTH,,-DIM_PERF,,DIM_WIDTH
nummrg,kp,1e-8,1e-8
                             ! create mesh
vsel,s,loc,y,-DIM_PERF,0
vatt,2,2,2
vsel,all
esize,DIM_ESIZE
vmesh,all
                             ! define loads
asel,s,loc,y,DIM_LENGTH
nsla,s,1
bf,all,mass,LOADING            ! mass source
sf,all,inf                   ! Robin radiation boundary flag
allsel,all
finish
                             ! perform a solution
/solu
antype,harmic
harfrq,1000,4000
hropt,auto	
nsubst,3
solve
finish
                             ! post-processing
/post1
*dim,pre,array,NUM_STEPS
*dim,frq,array,NUM_STEPS
*do,i,1,NUM_STEPS
set,1,i
*get,frq(i),active,,set,freq ! get resonant frequency
*get,pre(i),NODE,79,pres     ! get pressure at node 79
*enddo
/com,
/com,              ***** Mechanical APDL Results *****
/com,
/com,          Frequency (Hz)             Pressure (Pa)
*vwrite,frq(1),pre(1)
(7X,F15.4,10x,F15.4)
finish