*parameter
factor=1.e0
acousticbulk=20000.0*factor
acousticdens=1.e-4*factor
*NODE
**
**
*Element, type=AC2D4,elset=air
*Element, type=CPE4,elset=solid
**27,  59,  53,  54,  58
*Solid Section, elset=air, material=air
1.,
*Solid Section, elset=solid, material=solid
1.,
*Material, name=air
*Acoustic Medium
<acousticbulk>,
*Density
<acousticdens>,
*Material, name=solid
*Density
1.e-1
*Elastic
1000.,0.
***************
*surface,name=air
air,s2
*surface,name=solid
27,s4
*tie,name=airsol,adjust=yes
air,solid
*****************
*nset,nset=retained,unsorted
*nset,nset=n58
*nset,nset=n154
*nset,nset=nout
*boundary
53,1,2
54,1,2
********************************************
*step
*frequency,norm=mass
12,,,-1
*output,field
*node output
u,por
*end step
******************
*step
*substructure generate,type=z1,overwrite,libr=small_ac2d4,
recovery matrix=yes, mass matrix=yes
*boundary,op=new
*substructure load case,name=load58
*cload
58,2,1.058
*substructure load case,name=load154
*cload
154,1,10.54
*retained nodal dofs,sorted=no
retained,
**
**
*retained eigenmodes,generate
**
**
*substructure matrix output, stiffness=yes,file=small_ac2d4,
mass=yes, recovery=yes,sload=yes
*end step
******************************************