Q) I would like to apply a load for pressure stiffening effects in a PSD analysis with a pressure PSD. However, that pressure loading will be considered in the PSD analysis, so how do I separate the prestress and PSD pressure loads?
A) A prestressed modal analysis can be performed to accomplish this. First, run the static analysis with the prestress pressure and the PSTRES,ON command. Then, remove the preload pressure and apply the PSD pressure in the modal analysis (with PSTRES,ON). This will create the load vector of only the PSD pressure loading. Lastly, the PSD analysis can be run as usual.
Please note that this method includes the stress stiffening effects from the first pressure loading, so the stiffness changes, but the PSD results only include the loading effects from the PSD pressure loading.
An example model is below, where the preload is a membrane pressure loading and the PSD load is an internal pressure loading.
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finish
/clear
MYRADIUS=3
/view,1,1,2,3
/triad,off
/auto
/prep7
et,1,181
keyopt,1,3,2
r,1,0.1
mp,ex ,1,10e6
mp,nuxy,1,.3
mp,dens,1,0.1/386.1
cylind,MYRADIUS,,0,5,0,90
vdele,all
csys,1
asel,s,loc,x,MYRADIUS
asel,inve
adele,all,,,1
csys,0
allsel,all
mshape,0
mshkey,1
esize,MYRADIUS*2*acos(-1)/80
amesh,all
lsel,s,loc,z,0
nsll,s,1
d,all,rotx
d,all,roty
d,all,uz
lsel,s,loc,x,0
nsll,s,1
d,all,ux
d,all,roty
d,all,rotz
lsel,s,loc,y,0
nsll,s,1
d,all,rotx
d,all,uy
d,all,rotz
lsel,s,loc,z,5
nsll,s,1
sf,all,pres,-1e3
allsel,all
eplot
finish
/solu
antype,static
pstres,on
ematwr,yes
solve
finish
/solu
antype,modal
modopt,lanb,10
mxpand,10
pstres,on
sfedele,all,all,pres
sfe,all,1,pres,,1e3
allsel,all
solve
finish
/solu
antype,spectr
spopt,psd
psdunit,1,pres
psdfrq,1,,1,5e3
psdval,1,1e6,1e6
lvscale,1
dmprat,0.05
pfact,1,node
psdres,disp,rel
psdcom
solve
finish
/post26
numvar,20
store,psd,5
nsol,2,node(MYRADIUS,0,5),u,x
nsol,4,node(MYRADIUS,0,5),u,z
rpsd,12,2,,,,UX_NOPRESTRESS
rpsd,14,4
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Q) I would like to apply a load for pressure stiffening effects in a PSD analysis with a pressure PSD. However, that pressure loading will be considered in the PSD analysis, so how do I separate the prestress and PSD pressure loads? A) A prestressed modal analysis can be performed to accomplish this. First, run the static analysis with the prestress pressure and the PSTRES,ON command. Then, remove the preload pressure and apply the PSD pressure in the modal analysis (with PSTRES,ON). This will create the load vector of only the PSD pressure loading. Lastly, the PSD analysis can be run as usual. Please note that this method includes the stress stiffening effects from the first pressure loading, so the stiffness changes, but the PSD results only include the loading effects from the PSD pressure loading. An example model is below, where the preload is a membrane pressure loading and the PSD load is an internal pressure loading. ------------------------------- finish /clear MYRADIUS=3 /view,1,1,2,3 /triad,off /auto /prep7 et,1,181 keyopt,1,3,2 r,1,0.1 mp,ex ,1,10e6 mp,nuxy,1,.3 mp,dens,1,0.1/386.1 cylind,MYRADIUS,,0,5,0,90 vdele,all csys,1 asel,s,loc,x,MYRADIUS asel,inve adele,all,,,1 csys,0 allsel,all mshape,0 mshkey,1 esize,MYRADIUS*2*acos(-1)/80 amesh,all lsel,s,loc,z,0 nsll,s,1 d,all,rotx d,all,roty d,all,uz lsel,s,loc,x,0 nsll,s,1 d,all,ux d,all,roty d,all,rotz lsel,s,loc,y,0 nsll,s,1 d,all,rotx d,all,uy d,all,rotz lsel,s,loc,z,5 nsll,s,1 sf,all,pres,-1e3 allsel,all eplot finish /solu antype,static pstres,on ematwr,yes solve finish /solu antype,modal modopt,lanb,10 mxpand,10 pstres,on sfedele,all,all,pres sfe,all,1,pres,,1e3 allsel,all solve finish /solu antype,spectr spopt,psd psdunit,1,pres psdfrq,1,,1,5e3 psdval,1,1e6,1e6 lvscale,1 dmprat,0.05 pfact,1,node psdres,disp,rel psdcom solve finish /post26 numvar,20 store,psd,5 nsol,2,node(MYRADIUS,0,5),u,x nsol,4,node(MYRADIUS,0,5),u,z rpsd,12,2,,,,UX_NOPRESTRESS rpsd,14,4,,,,UZ_NOPRESTRESS /gropt,logx,on plvar,12,14 ------------------------------- |
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