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在ansys帮助文件中,7.5. Sample Piezoelectric-Circuit Analysis (Batch or Command Method)(11.0版)第一步是求静态电容值,求得电容值是CS= 1.275495662E-11法拉。而理论计算值应该是:C=εr*ε0*A/d,其中εr是Z方向介电常数(729),ε0是真空介电常数,A是极板面积(1毫米*1毫米),d是两极板距离(H=1毫米),故C=729*8.85*10^-12*1e-3*1e-3/1e-3=6.4516e-012法拉。
现在的疑问是,为什么仿真得到的值是计算值的2倍,我试过其他的例子,发现同样的问题,期待高手解决。
此处压电振子是边长1毫米的正方体。
命令流:
/batch,list
/prep7
/title,Transient and harmonic analyses of a piezoelectric circuit
/nopr
!
! Set up the model for the piezoelectric element
!
! Material properties for PZT-4
!
mp,DENS,1,7700 ! Density, kg/m**3
tb,DPER,1 ! Relative permittivity at constant strain
tbdata,1,729,635,729
! - Alternative input of permittivity if used with SOLID5
! mp,PERX,1,729
! mp,PERY,1,635
! mp,PERZ,1,729
!
tb,ANEL,1 ! Anisotropic elastic stiffness, N/m^2
tbdata,1,13.9E10,7.43E10,7.78E10 ! c11,c13,c12
tbdata,7,11.5E10,7.43E10 ! c33,c13
tbdata,12,13.9E10 ! c11
tbdata,16,2.56E10 ! c44
tbdata,19,2.56E10 ! c44
tbdata,21,3.06E10 ! c66
tb,PIEZ,1 ! Piezoelectric stress coefficients, C/m^2
tbdata,2,-5.2 ! e31
tbdata,5,15.1 ! e33
tbdata,8,-5.2 ! e31
tbdata,10,12.7 ! e15
tbdata,15,12.7 ! e15
!
! Define a piezoelectric cube (H = 1 mm)
!
H = 1e-3 ! Transducer size, m
block,0,H,0,H,0,H ! Define volume
et,1,SOLID226,1001 ! 3-D coupled-field brick, piezo option
esize,,2 ! Define the number of element divisions
! et,1,SOLID5,3 ! lower order 3-D coupled-field brick, piezo option
! esize,,3
mat,1 $ type,1 ! Set element attributes
numstr,node,14 ! Set starting node number for the solid model
vmesh,1 ! Generate nodes and elements
*get,Epz,elem,,count ! Get the number of solid elements
!
! Apply boundary conditions and loads to the piezoelectric transducer
!
nsel,s,loc,z,0 ! Define bottom electrode
cp,1,volt,all
*get,n_bot,node,0,num,min ! Get master node on bottom electrode
nsel,s,loc,z,H ! Define top electrode
cp,2,volt,all
*get,n_top,node,0,num,min ! Get master node on top electrode
nsel,s,loc,z,0 ! Impose displacement constraints
d,all,uz,0
nsel,r,loc,y,0
d,all,uy,0
nsel,r,loc,x,0
d,all,ux,0
nsel,all
d,n_bot,volt,0 ! Ground bottom electrode
d,n_top,volt,1 ! Apply unit voltage to top electrode
fini
!
! Determine static capacitance of the piezo-cube
!
/solu
antype,static ! Static analysis
solve
*get,Cs,node,n_top,rf,chrg ! Get electric charge on top electrode
! *get,Cs,node,n_top,rf,amps ! use AMPS label with SOLID5
Cs = abs(Cs) ! C = Q/V, where V = 1 Volt
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