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duplicate nodes problem for a vibro-acoustic problem
 
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umut.tabak
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Joined: 08 Apr 2012
Posts: 30

PostPosted: Sun Jan 10, 2016 2:48 pm  Reply with quote

Dear all,

I would like to use SOLSH190 elements for a coupled internal vibro-acoustic problem.

I am creating a thin volume that I mesh with solsh190 elements and a coupled fluid volume with fluid30 elements. However, since there are two volumes, I could not manage to couple them on the interface. What I mean is that on the interfacing surface between the fluid and the thin surface there are duplicate nodes due to the above mentioned modelling approach, one set in the fluid side and one set on the structure side.

As expected, Ansys gives a lot of warnings and aborts the solution due this modelling problem, I believe.

I am using mesh200 elements in order to create the thin surface mesh in APDL.Later, I am deleting these elements in the mesh extrusion operation.

My apdl code is below, I would appreciate if someone could help me on this point.

Code:

fini
/clear, start
! define some parameters
! box dimensions
lx = 0.15
ly = 0.1
lz = 0.1
tol = 1e-8
filename = 'vibro_solsh190'
/filname, filename, 1
! thickness of the structural plate
th = 0.001
! extrusion parameter
vz = lz
! number of divisions for the solsh
! structural face
ndiv_s = 1
esize_v = 0.01
/prep7
! create the top face from
! which the extrusion will take
! place
k,1,0,0,lz
k,2,lx,0,lz
k,3,lx,ly,lz
k,4,0,ly,lz
! area 1
a,1,2,3,4
! create the fluid volume
blc4,0,0,lx,ly,lz
! define
! element types
et,1,190
et,2,30,,1 ! pure acoustic
et,3,30,,0 ! interface element with
           ! the structure

et,4,200 ! background mesh element
! define them as 3D-quad elements
! you can think them as fictitous domain
! elements
keyopt,4,1,6
! mesh200 has no dof or properties
! and does not contribute to solution either
! material properties
! structure
MP, EX, 1, 69e9
MP, PRXY, 1, 0.33
MP, DENS, 1, 2800
! material properties
! fluid: water
mp,dens,2,1000
mp,sonc,2,1500

! set the element type to be assigned to
! subsequently defined elements
! use mesh200 elements for background mesh
! specify element
! size and mesh the area
type, 4    ! does not have material property
esize, 0.01
amesh, 1
! set the properties for
! the extrusion of the mesh
type, 1
mat, 1
ESIZE,0,ndiv_s             ! THICKNESS DENSITY FOR SOLSH190
! the below line is to
! clear the area when volume
! mesh is done
! EXTOPT,ACLEAR,1          ! CLEAR AREA WHEN VOLUME GENERATION IS DONE
EXTOPT,ACLEAR,1
VOFFSET,1,th               ! GENERATES A VOLUME, OFFSET FROM A GIVEN AREA

! fluid volume side
mat,  2
type, 2
esize, 0.01
vmesh, 1
!
! select and fix the
! structural dofs of the
! plate around the
! circumference
allsel
! settings related to the
! vibro-acoustic coupling
! select the top surface
nsel, s, loc, z, lz-tol, lz+tol
! select the nodes
! attached to the area
! modify the properties of the interface element
esln
! unselect the solsh190
! elements from the selected set
esel, u, type, , 1
emodif, all, type, 3
allsel
! set the fsi interface
nsel, s, loc, z, lz-tol,lz+tol
! select the nodes attached to the area
esln
! unselect the solsh190
! elements from the selected set
esel, u, type, , 1
sf, all, fsi, 1
allsel

! select the nodes on the
! areas where the boundary
! conditions are to be applied
asel,s,area,,9
asel,a,area,,10
asel,a,area,,11
asel,a,area,,12
! select all the nodes
! associated to the areas
nsla,s,1
! apply the boundary constraints
! solsh190 has only UX, UY, UZ
d,all,UX,0
d,all,UY,0
d,all,UZ,0
! advance to solution phase
! ---------------------------------
/SOLU
ANTYPE, MODAL
MODOPT, UNSYM, 21
MXPAND, 21
EMATWRITE,YES
solve
! finalize
allsel
fini


_________________
Umut Tabak
Delft University of Technology
Precision and Microsystems Engineering
Engineering Dynamics
Mekelweg 2, Delft, The Netherlands
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Martin Liddle
User


Joined: 15 Aug 2008
Posts: 1274
Location: Chesterfield, UK

PostPosted: Tue Jan 12, 2016 11:56 am  Reply with quote

You would be much more likely to get a reply if you post the question in an email to the mailing list at

xansys-temp@xansystest.info
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Martin Liddle, Tynemouth Computer Services,
Chesterfield, UK.
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