In a randomvibration analysis, how can I plot the output PSD against input PSD?
If you calculate the response PSD at the base in absolute terms (DATUM=1), then you essentially have obtained a POST26 variable of the input PSD. Then, you can calculate the response PSD of whatever other node you want, and you can plot both POST26 variables at the same time. Here is an example: FINISH /CLEAR /PREP7 ET,1,4 MP,EX,1,2E11 MP,NUXY,1,0.3 MP,DENS,1,8000 R,1,4,1.333,1.333,2,2,0 RMORE,0,2.2496,1.177,1.177 N,1,0 N,11,10 FILL E,1,2 EGEN,10,1,1 FINISH /SOLU ANTYPE,MODAL MODOPT,LANB,12 MXPAND,,,,YES OUTRES,ALL,ALL D,1,ALL D,11,ALL SOLVE FINISH /SOLU ANTYPE,SPECTR SPOPT,PSD,,YES DMPRAT,0.02 PSDUNIT,1,ACCG,9814.56 PSDFRQ,1,,10,100,1000,10000 PSDVAL,1,10,50,50,10 D,1,UY,1 D,11,UY,1 PSDCOM PSDRES,DISP,REL PSDRES,VELO,ABS PSDRES,ACEL,ABS PFACT,1,BASE SOLVE FINISH /POST26 /AXLAB,X,Frequency [Hz] /AXLAB,Y,Acceleration [accel^2/Hz] /GROPT,LOGX,ON /GROPT,LOGY,ON STORE,PSD,10 NSOL,2,1,U,Y RPSD,3,2,,3,1,Input PSD NSOL,4,6,U,Y RPSD,5,4,,3,1,Output PSD PLVAR,3,5 FINISH 

