No stress in PSD Analysis results
No stress in PSD Analysis results
(OP)
I am performing a PSD analysis in Ansys9.0 for an electronic housing by defining a based excited PSD loading G^2/Hz in acceleration. The housing was fixed through four brackets to vibration desk, however I can not find any stress in loadstep 3 to 5. I can only find displacement in resultant 1.7 and in x,y,z direction 0.9999. The displacement is also constant in total model except in the area of brakets the displament shows from zero to 1.7 (or 0.9999 for compoment displacement). Can some people to tell me, what could be the problem and how should I understand this. Actually in loadstep Modal analysis and PSD analyse the element stress output has been already selected.
This is my code:
!!! FE Model has been already constraint in bottom of four brakets.
/SOLU
ANTYPE,MODAL!
MODOPT,LANB,100,0,2000, ,OFF, ,0
LUMPM,1
PSTRES,0
SOLVE
FINISH
/SOLU
ANTYPE,MODAL!
EXPASS,ON
MXPAND,100,,,YES,!
SOLVE
FINISH
/SOLU
ANTYPE,SPECTR
SPOPT,PSD,,YES
PSDUNIT,1,accg,9800!mm,mpa,t, unit system
psdfrq,1,,1,10,20,80,400,2000
psdval,1,2.2e-2,2.2e-2,2.4e-3,2.4e-3,1.2e-4
NSEL,R,LOC,y,0
D,ALL,uy,1.0!Ux,Uy,Uz already constraint and now PSD loading applied also here.
ALLSEL,ALL
PFACT,1,BASE
PSDRES,DISP,ABS
PSDRES,VELO,ABS
PSDRES,ACEL,ABS
SOLVE
FINISH
/SOLU
ANTYPE,SPECTR
PSDCOM,0.005,100!or PSDCOM,0.0001,100
SOLVE
FINISH
/POST1
SET,LIST
SET,FIRST!
PRNSOL,DOF!
PRESOL,ELEM!
PRRSOL,F!
set,,,1,,,,103
FINISH
Hope somebody can help! many thanks!
This is my code:
!!! FE Model has been already constraint in bottom of four brakets.
/SOLU
ANTYPE,MODAL!
MODOPT,LANB,100,0,2000, ,OFF, ,0
LUMPM,1
PSTRES,0
SOLVE
FINISH
/SOLU
ANTYPE,MODAL!
EXPASS,ON
MXPAND,100,,,YES,!
SOLVE
FINISH
/SOLU
ANTYPE,SPECTR
SPOPT,PSD,,YES
PSDUNIT,1,accg,9800!mm,mpa,t, unit system
psdfrq,1,,1,10,20,80,400,2000
psdval,1,2.2e-2,2.2e-2,2.4e-3,2.4e-3,1.2e-4
NSEL,R,LOC,y,0
D,ALL,uy,1.0!Ux,Uy,Uz already constraint and now PSD loading applied also here.
ALLSEL,ALL
PFACT,1,BASE
PSDRES,DISP,ABS
PSDRES,VELO,ABS
PSDRES,ACEL,ABS
SOLVE
FINISH
/SOLU
ANTYPE,SPECTR
PSDCOM,0.005,100!or PSDCOM,0.0001,100
SOLVE
FINISH
/POST1
SET,LIST
SET,FIRST!
PRNSOL,DOF!
PRESOL,ELEM!
PRRSOL,F!
set,,,1,,,,103
FINISH
Hope somebody can help! many thanks!





RE: No stress in PSD Analysis results
RE: No stress in PSD Analysis results
I realised that my FE model probably was built too stiff, because the joints (screws and rivets)in my model mostly were simplified through VGLUE or CPs. I did a test calculation with reduced structure and then I can get stress and displacement in final loadstep. So I guess that my FE model probably too stiff and the total structure behaviours like a complete parts, so I can not find stress.
I will review my FE model and do further test calculations. Any way I will back again here.
Does any one know can we receive the stress and displacement directly in post1 in ansys9.0. How should we interpret the stress and displacement, which caution should we pay?!
RE: No stress in PSD Analysis results
First of all it sounds like you haven't made a simple test case to figure out everything before you moved on to a more difficult problem. I highly suggest taking that approach.
Secondly, you should have run a modal analysis and reviewed those results before running a PSD model. If the first mode of your structure occurs above 4000 Hz and the PSD curve goes from 20 to 2000 Hz, then it is not unreasonable to have very little stresses, possibily zero.
RE: No stress in PSD Analysis results
I changed LUMPM,1 into LUMPM,0 and looked the results in loadstep 3 and then I received reasonable displacement and stress. Anyone can tell me, why should we look the results in loadstep 3, how is about result from loadstep 4 and 5?
As I know, the stress and displacement from loadstep 3 is 1 sigma value, for the margin of safety should we convert 1 sigma stress into 3 sigma stress? Should we do the same thing for displacement?
Hope anyone can help me,thankls a lot!
RE: No stress in PSD Analysis results