problems with acoustic FSI
Dear users,
I've come to this forum since I'm new to Ansys and have some problems with an acoustic FSI calculation. In the scope of my master's thesis, I want to calculate the eigenfrequencies of an acoustic cavity. The cavity consists of a steel-walled box, which surrounds a volume of gas (air). The box was modeled with SOLID95-elements, the fluid was modeled with FLUID220-elements. The interface between fluid and solid was defined as an FSI-flag. Now, I want to investigate the influence of the box on the eigenfrequencies of the gas and vice versa. Unfortunately, the results of my calculation differ with every calculation up to a factor of 5. I have posted my APDL-code, does anybody know why this mistake happens? I'm very thankfull for every help.! My code: !!! preamble ================================================== ===== FINISH /CLEAR !/TITLE, Eigenmoden FSI-Volumen !!! preprocessor ================================================== = /PREP7 ! definition of parameters: Komp = 1420000 ! Kompressionsmodul bei Athmosphärendruck; Einheit: Pa rho0 = 12 C = SQRT(Komp/rho0) Ref = 0.00002 ! Referenzschalldruck E_x = 210000000000 E_y = 210000000000 E_z = 210000000000 nu_x = 0.3 nu_y = 0.3 nu_z = 0.3 rho = 7850 ! definition of element types: ET,1,FLUID220,,1 ! with FSI ET,2,FLUID220,,0 ! without FSI ET,3,SOLID95 ! definition of materials: !Material 1: MP,DENS,1,rho0 MP,SONC,1,C MP,MU,1,0 !Material 2: MP,DENS,2,rho0 MP,SONC,2,C MP,MU,2,0 !Material 3: MP,EX,3,E_x MP,EY,3,E_y MP,EZ,3,E_z MP,PRXY,3,nu_x MP,PRXZ,3,nu_z MP,PRYZ,3,nu_y MP,DENS,3,rho ! definition of geometry !lengths: L_x = 8 L_y = 3 L_z = 4 !lengths of fluid- and solid elements L_Ele_Fluid = 0.5 L_Ele_Solid = 0.5 ! definition of keypoints: S_X = L_x/2 S_Y = L_y/2 S_Z = L_z/2 ! keypoints of inner fluid body: K,1,S_X,-S_Y,S_Z K,2,-S_X,-S_Y,S_Z K,3,-S_X,-S_Y,-S_Z K,4,S_X,-S_Y,-S_Z K,5,S_X,S_Y,S_Z K,6,-S_X,S_Y,S_Z K,7,-S_X,S_Y,-S_Z K,8,S_X,S_Y,-S_Z ! keypoints of right outer fluid body: K,9,S_X+L_Ele_Solid,-S_Y,S_Z K,10,S_X,-S_Y,S_Z K,11,S_X,-S_Y,-S_Z K,12,S_X+L_Ele_Solid,-S_Y,-S_Z K,13,S_X+L_Ele_Solid,S_Y,S_Z K,14,S_X,S_Y,S_Z K,15,S_X,S_Y,-S_Z K,16,S_X+L_Ele_Solid,S_Y,-S_Z ! keypoints of left outer fluid body: K,17,-S_X,-S_Y,S_Z K,18,-(S_X+L_Ele_Solid),-S_Y,S_Z K,19,-(S_X+L_Ele_Solid),-S_Y,-S_Z K,20,-S_X,-S_Y,-S_Z K,21,-S_X,S_Y,S_Z K,22,-(S_X+L_Ele_Solid),S_Y,S_Z K,23,-(S_X+L_Ele_Solid),S_Y,-S_Z K,24,-S_X,S_Y,-S_Z ! keypoints of frontal outer fluid body: K,25,(S_X+L_Ele_Solid),-S_Y,(S_Z+L_Ele_Solid) K,26,-(S_X+L_Ele_Solid),-S_Y,(S_Z+L_Ele_Solid) K,27,-(S_X+L_Ele_Solid),-S_Y,S_Z K,28,(S_X+L_Ele_Solid),-S_Y,S_Z K,29,(S_X+L_Ele_Solid),S_Y,(S_Z+L_Ele_Solid) K,30,-(S_X+L_Ele_Solid),S_Y,(S_Z+L_Ele_Solid) K,31,-(S_X+L_Ele_Solid),S_Y,S_Z K,32,(S_X+L_Ele_Solid),S_Y,S_Z ! keypoints of back outer fluid body: K,33,(S_X+L_Ele_Solid),-S_Y,-(S_Z+L_Ele_Solid) K,34,-(S_X+L_Ele_Solid),-S_Y,-(S_Z+L_Ele_Solid) K,35,-(S_X+L_Ele_Solid),-S_Y,-S_Z K,36,(S_X+L_Ele_Solid),-S_Y,-S_Z K,37,(S_X+L_Ele_Solid),S_Y,-(S_Z+L_Ele_Solid) K,38,-(S_X+L_Ele_Solid),S_Y,-(S_Z+L_Ele_Solid) K,39,-(S_X+L_Ele_Solid),S_Y,-S_Z K,40,(S_X+L_Ele_Solid),S_Y,-S_Z ! keypoints of lower outer fluid body: K,41,(S_X+L_Ele_Solid),-(S_Y+L_Ele_Solid),(S_Z+L_Ele_Solid) K,42,-(S_X+L_Ele_Solid),-(S_Y+L_Ele_Solid),(S_Z+L_Ele_Solid) K,43,-(S_X+L_Ele_Solid),-(S_Y+L_Ele_Solid),-(S_Z+L_Ele_Solid) K,44,(S_X+L_Ele_Solid),-(S_Y+L_Ele_Solid),-(S_Z+L_Ele_Solid) K,45,(S_X+L_Ele_Solid),-(S_Y),(S_Z+L_Ele_Solid) K,46,-(S_X+L_Ele_Solid),-(S_Y),(S_Z+L_Ele_Solid) K,47,-(S_X+L_Ele_Solid),-(S_Y),-(S_Z+L_Ele_Solid) K,48,(S_X+L_Ele_Solid),-(S_Y),-(S_Z+L_Ele_Solid) ! keypoints of upper outer fluid body: K,49,(S_X+L_Ele_Solid),(S_Y),(S_Z+L_Ele_Solid) K,50,-(S_X+L_Ele_Solid),(S_Y),(S_Z+L_Ele_Solid) K,51,-(S_X+L_Ele_Solid),(S_Y),-(S_Z+L_Ele_Solid) K,52,(S_X+L_Ele_Solid),(S_Y),-(S_Z+L_Ele_Solid) K,53,(S_X+L_Ele_Solid),(S_Y+L_Ele_Solid),(S_Z+L_El e_Solid) K,54,-(S_X+L_Ele_Solid),(S_Y+L_Ele_Solid),(S_Z+L_Ele_Sol id) K,55,-(S_X+L_Ele_Solid),(S_Y+L_Ele_Solid),-(S_Z+L_Ele_Solid) K,56,(S_X+L_Ele_Solid),(S_Y+L_Ele_Solid),-(S_Z+L_Ele_Solid) !generation of volumes: V,1,2,3,4,5,6,7,8 ! Fluid mitte ! Volumen 1 V,9,10,11,12,13,14,15,16 ! Solid außen rechts ! Volumen 2 V,17,18,19,20,21,22,23,24 ! Solid außen links 3 V,25,26,27,28,29,30,31,32 ! Solid außen vorne 4 V,33,34,35,36,37,38,39,40 ! Solid außen hinten 5 V,41,42,43,44,45,46,47,48 ! Solid außen unten 7 V,49,50,51,52,53,54,55,56 ! Solid außen oben 6 ! meshing of volumes 2 to 7; SOLID95 TYPE,3 MAT,3 VSEL,S,VOLU,,2,7 ESIZE,L_Ele_Fluid VMESH,ALL VSEL,ALL ALLSEL ! coupling of degrees of freedom of solid bodies: ESEL,S,TYPE,,3,3 CPINTF,UX,0.0001 CPINTF,UY,0.0001 CPINTF,UZ,0.0001 ESEL,ALL ! meshing of volume1; FLUID220 TYPE,1 MAT,1 VSEL,S,VOLU,,1 ESIZE,L_Ele_Fluid VMESH,1,1 VSEL,ALL ESEL,S,TYPE,,1 NSEL,S,EXT ESLN,ALL EMODIF,ALL,TYPE,2 ALLSEL ! define FSI-flag at border fluid-solid ESEL,S,TYPE,,2 ! select fluid elements NSEL,S,EXT ! nodes on the exterior surface SF,ALL,FSI SFELIST,ALL,FSI ESEL,ALL NSEL,ALL !SFELIST,ALL,FSI ! contstrain displacements of solid volumes at all edges: NSEL,S,LOC,X,-(L_X/2 + L_Ele_Solid) !1 NSEL,R,LOC,Z,-(L_Z/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,-(L_X/2 + L_Ele_Solid) !2 NSEL,R,LOC,Z,(L_Z/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,(L_X/2 + L_Ele_Solid) !3 NSEL,R,LOC,Z,(-L_Z/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,(L_X/2 + L_Ele_Solid) !4 NSEL,R,LOC,Z,(L_Z/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,-(L_X/2 + L_Ele_Solid) !5 NSEL,R,LOC,Y,-(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,-(L_X/2 + L_Ele_Solid) !6 NSEL,R,LOC,Y,(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,(L_X/2 + L_Ele_Solid) !7 NSEL,R,LOC,Y,-(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,X,(L_X/2 + L_Ele_Solid) !8 NSEL,R,LOC,Y,(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,Z,-(L_Z/2 + L_Ele_Solid) !9 NSEL,R,LOC,Y,(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,Z,-(L_Z/2 + L_Ele_Solid) !10 NSEL,R,LOC,Y,-(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,Z,(L_Z/2 + L_Ele_Solid) !11 NSEL,R,LOC,Y,-(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL NSEL,S,LOC,Z,(L_Z/2 + L_Ele_Solid) !12 NSEL,R,LOC,Y,(L_Y/2 + L_Ele_Solid) D,ALL,ALL,0 NSEL,ALL FINISH ! /PREP7 !!! solution ================================================== ========================== /SOLU ANTYPE,2 MODOPT,UNSYM,40,1 MXPAND,40 SOLVE FINISH ! /SOLU Thanks in advance, Moritz Becker |
Don't know the problem, but if you search the "Knowledge Resources > Solutions" section on the ANSYS customer portal for "2026060" you'll find a similar example. Comparing the input files may help.
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