Chandra Sekaran
Ansys Employee

You seem to be mixing up commands used for PSD analysis (SPOPT,PSD) and multipoint response spectrum analysis (SPOPT,MPRS). Commands like SED or SPFREQ, SPVAL are used for MPRS.  For PSD you specify the direction of excitation by giving a UNIT displacement to the nodes that are fixed in the modal analysis (e.g you select nodes fixed in X direction, then specify ux=1 to indicate that these nodes are to be excited in X direction). You also use PSDFRQ and PSDVAL commands to specify the input spectra.