How can I do a harmonic analysis of a small AC voltage on top of a DC bias? Can you provide an example?
The transducer element, TRANS126 accepts a DC bias input, but if you can't use that feature the following procedure may work. It moves the model to the deformed position after the static analysis, which will make the model capacitance reflect the DC voltage. 1. Perform a static analysis with DC voltage 2. Issue UPCOORD,1.0 to move the mesh to the deformed position to make electrostatic forces correct in the harmonic. 3. Remove DC voltage and run harmonic with forces due to AC voltage. Here's a sample input file using this procedure. fini /clear /prep7 et,1,223,1001 ! Structural and Volt DOF et,2,183 ! structural only mp,perx,1,1000 mp,ex,1,1e6 mp,nuxy,1,0 mp,ex,2,1e11 mp,dens,2,1000 mp,nuxy,2,0 rect,,1,,.01 rect,,1,.01,.02 numm,kp esize,.005 amesh,1 mat,2 amesh,2 nsel,s,loc,x,0 nsel,a,loc,y,0 d,all,ux,0 d,all,uy,0 nsel,s,loc,x,1 d,all,ux,0 nsel,s,loc,y,0 d,all,volt,0 nsel,s,loc,y,.01,.02 d,all,volt,10000 ! DC voltage nsel,all fini /solu solve upcoord,1 ! Move mesh to deformed position fini /solu nsel,s,loc,y,.01,.02 d,all,volt,25 ! Replace DC voltage with AC voltage and compute electrostatic forces nsel,all solve fini /prep7 ! change element type to plane183 (structural) type,2 emodif,all,type fini /solu antype,harm ldread,forc ! Read electrostatic forces due to AC voltage and apply harf,100 dmprat,.001 solve fini /post1 set,1,1 plns,uy 

