Random Vibration in Optistruct

Hi Guys,

I am simulating random vibration in optistruct. I have input psd in (m/s^2)/Hz, model content in mm, output required is stress in MPa. I submitted 1 run and  i am getting high stress which are not realistic. Unit excitation is 9810 (SPCD) and I have submitted another run with unit excitation 1 (SPCD), here i am getting very low stress which is not realistic. Can anyone suggest me the right procedure. I guess i have mistake in unit conversion. If anyone having dummy procedure file please share me.

Thanks all in advance

looking forward to get some input from experienced analyst.