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.
et,1,223,1001 ! Structural and Volt DOF
et,2,183 ! structural only
d,all,volt,10000 ! DC voltage
upcoord,1 ! Move mesh to deformed position
d,all,volt,25 ! Replace DC voltage with AC voltage and compute electrostatic forces
/prep7 ! change element type to plane183 (structural)
ldread,forc ! Read electrostatic forces due to AC voltage and apply