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





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