eigenfrequency edit

Dear Sir

I need some help, i am working on calculation of eigenfrequency for a disk. in comsol i can calculate 2D eigenfrequency without thickness consideration , if i use 3D simulation ,comsol calculate eigenfrequency with out of plane displacement but i need to calculate 3D eigenfrequency of a disk only with inplane displacement. please guide me how i can do that.
Thank you before
mehdi.