Firstly I really feel so lucky to find this forum. Since I don't have a strong physics background but now dealing with many problems directly related to physics.(adsbygoogle = window.adsbygoogle || []).push({});

I'm now doing some simulation in comsol and need to solve some PDEs. I'm using this PDE coefficient form in comsol. The equations need to be solved are:

-[tex]\rho[/tex][tex]\omega[/tex]^{2}[tex]\vec{u}[/tex]- [tex]\nabla[/tex]T=0

[tex]\nabla \vec{D}[/tex] = 0

[tex]\vec{E}[/tex] = -[tex]\nabla V[/tex]

T=c^{E}S-eE_{i}

D_{i}=[tex]\epsilon[/tex]S

The equations specify the behavior of a piezoelectric substrate when subjected to an electric field. In these equations the variable need to be solved is [tex]\vec{u}[/tex]=[tex]\vec{u}[/tex](u,v,w,V).

Then PDE coefficient form in comsol is: -[tex]\nabla[/tex][tex]\cdot[/tex](C[tex]\nabla[/tex][tex]\vec{u}[/tex]+[tex]\alpha[/tex][tex]\vec{u}[/tex]-[tex]\gamma[/tex])+a[tex]\vec{u}[/tex]+[tex]\beta[/tex][tex]\cdot[/tex][tex]\nabla[/tex][tex]\vec{u}[/tex]=[tex]\vec{f}[/tex]

in this step I need to transfer my equations to this PDE coefficient form.

Then I need to specify the boundary condition:

The neumann boundary condition in comsol coefficient form specifies:

n[tex]\cdot[/tex](C[tex]\nabla[/tex][tex]\vec{u}[/tex]+[tex]\alpha[/tex][tex]\vec{u}[/tex]-[tex]\gamma[/tex])+q[tex]\vec{u}[/tex]=[tex]\vec{g}[/tex]

The mixed boundary condition in comsol coefficient form specifies:

n[tex]\cdot[/tex](C[tex]\nabla[/tex][tex]\vec{u}[/tex]+[tex]\alpha[/tex][tex]\vec{u}[/tex]-[tex]\gamma[/tex])+q[tex]\vec{u}[/tex]=[tex]\vec{g}[/tex]-h^{T}[tex]\mu[/tex]

h[tex]\vec{u}[/tex]=[tex]\vec{r}[/tex]

q, g,h,r are coefficients I need to fill in according to my specicial case.

one of the boundary conditions writes V=V_{p}, n[tex]\cdot[/tex]=0. And I really not sure how to define this in the mixed boundary condition and decide the value of q,g,h,r. Could anyone with comsol experience give me some hint?

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# Question related to fill in boundary conditions in comsol

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