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## what physics should i choose?

In order to note the deformity with voltage as input,which physics should i choose?

2 Replies Last Post Oct 5, 2012, 12:02 AM EDT
Posted: 5 years ago
Hi

to select the right physics, you should sketch down what you have, which variables are driving, which are dependent and need to be solved for. Then take the smallest list (to start with) and find the physics that answers this list.

1) You have a cantilever of a given geometry and solid material (rho, E, nu) it is fixed on one side and you apply an external load (force) on the other side (=boundary), your unknown are the deformation (u,v,w) so you should chose "solid" physics

2) You have an electric field in air (or vacuum) (epsilon_r) between two electrodes, top at voltage V and bottom at voltage = 0V = GND, you would use "ES" electrostatic as no current flow solving for V, still you can get out an electrostatic force

3) You want to couple the electrostatic force of 2) to the deformation of your beam of 1), in air (or vacuum), then you have a coupled model. Then you have 2 choices: you build it up from 3 "physics" (ALE+solid+EX in that order, where ALE is from the mathematics "physics" to link the deformation of the air/vacuum electrode gasp to the two ES physics, as the solid physics calculates a deformation of the beam = top electrode) or you use the combined "EMI" electromechanics physics that is "pre-cooked" (this one is certainly linked to MEMS or some other additional module)

So basically, hope my examples are clear, you decompose your model into fundamental, blocks depending on the "dependent variables" you need to solve for, and based on the known geometry, material, and BC (initial & boundary conditions) values you know.

In the beginning it feels difficult, but rapidly you will notice it becomes an automatism

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Good luck
Ivar

Posted: 5 years ago
Thank you very much Mr. Kjelberg.