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How to apply a space and time dependent boundary condition?

Posted 19 oct. 2017, 05:01 UTC−4 Version 5.3 4 Replies

Ngoc Nguyen
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Hi everyone,

I am trying to apply a sinusoidal prescribed displacement to the edge of a plate for 5 periods of the signal.

The applied signal has the form of F1(y,t)=u1(y)cos(2.pi.f0.t)+u2(y)sin(2.pi.f0.t) for prescribed component in x direction and F2(y,t)=v1(y)cos(2.pi.f0.t)+v2(y)sin(2.pi.f0.t) for prescribed component in y direction.

The variable y is associated with the mesh grid, i.e. the values of y are the values of the node positions along the extremity of the plate.

The four functions u1, u2, v1, v2 are interpolation functions which the discrete data sets I already have.

Is there any possible way to set up this kind of boundary conditions in COMSOL? I really appreciate if anyone can help me with this troublesome issue.

Bests,

Ngoc

4 Replies Last Post 24 oct. 2017, 05:24 UTC−4
Henrik Sönnerlind COMSOL Employee

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Posted: 7 years ago 19 oct. 2017, 10:01 UTC−4

Hi Ngoc,

Basically, you just type in the expressions in the text fields for the prescribed displacements.

u1(y)*cos(2*pi*f0*t)+u2(y)*sin(2*pi*f0*t)

f0 can be defined as a parameter.

For a more general discussion of how boundary conditions can be modified, see also

https://www.comsol.se/blogs/how-to-make-boundary-conditions-conditional-in-your-simulation/

Regards,

Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi Ngoc, Basically, you just type in the expressions in the text fields for the prescribed displacements. u1(y)\*cos(2\*pi\*f0\*t)+u2(y)\*sin(2\*pi\*f0\*t) f0 can be defined as a parameter. For a more general discussion of how boundary conditions can be modified, see also https://www.comsol.se/blogs/how-to-make-boundary-conditions-conditional-in-your-simulation/ Regards, Henrik
Ngoc Nguyen
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Posted: 7 years ago 23 oct. 2017, 08:17 UTC−4

Hi Henrik,

Thank you for answering my question. I have applied the prescribed BCs for my model and it worked when I used only Solids Mechanics physic. However, when I added Electrostatic and Piezoelectric effect for time analysis, COMSOL could not find converged solutions. Can you help me figure out where I did it wrong? I attached both models (before and after the electrostatic physic is added) here.

Bests,

Ngoc Nguyen

Hi Henrik, Thank you for answering my question. I have applied the prescribed BCs for my model and it worked when I used only Solids Mechanics physic. However, when I added Electrostatic and Piezoelectric effect for time analysis, COMSOL could not find converged solutions. Can you help me figure out where I did it wrong? I attached both models (before and after the electrostatic physic is added) here. Bests, Ngoc Nguyen
Henrik Sönnerlind COMSOL Employee

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Posted: 7 years ago 23 oct. 2017, 11:09 UTC−4

Hi Ngoc,

The first sanity check would be that the electric problem is grounded somewhere.

Regards, Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi Ngoc, The first sanity check would be that the electric problem is grounded somewhere. Regards, Henrik
Ngoc Nguyen
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Posted: 7 years ago 24 oct. 2017, 05:24 UTC−4

Hi Henrik,

Yes, it is indeed due to the lack of electrical boundary conditions. The simple plate model works now. I am moving on to a more complicated structure. Thank you and have a good day.

Bests,

Ngoc

Hi Henrik, Yes, it is indeed due to the lack of electrical boundary conditions. The simple plate model works now. I am moving on to a more complicated structure. Thank you and have a good day. Bests, Ngoc

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