Discussion Forum

Behrooz,

Interesting problem. In what way does the solution to your stationary solid mechanics solution affect your time-dependent magnetic fields equations? I can imagine a time dependent solid mechanics solution affecting the mag. fields because of the geometry changes. But a stationary solid mechanics solution affecting time-dependent equations?

If there is a unidirectional coupling where the time-dependent mag. fields solution drives the solid mechanics solution with some sort of force. This you can do by a Step 1 and Step 2 set-up where you make sure to read the Step 1 results into Step 2 by using the "Values of Variables Not Solved For" section on your Step 2 settings window.

Best regards,
Josh Thomas
AltaSim Technologies

Hi Josh,

I have same problem. I am trying to solve Drift diffusion(time dependent ) and Joule heating(time independent ) equations simultaneously. One important thing in my simulation is that electrical conductivity and thermal conductivity are function of Temperature(T) and concentration (cA). I have solved the drift diffusion equation first with a constant temperature(T0) and then coupled with joule heating equation by changing T0 to T.

The coupling was done by copying the solution and then changing " initial values of variables Solved for for" in the dependent variables option of the solver 1. After solving thing I don't get any electric field or potential in solution.
Could you please advise me ? I have attached the file herewith.

Thanks,
Sanjoy

Sanjoy,

You say you have a time independent and a time dependent? But, both of your study steps are "Stationary"?

If both sets of equations are "stationary" and you do want to solve them simultaneously follow these steps:

If you want to solve equations "simultaneously" you will need to solve in one step rather than two steps. COMSOL will set up a default solver sequence for doing this. If you'd like to see the sequence then click Show Icon>Advanced Study Options and then right-click the Study node and select "Show Default Solver." Then expand the tree.

In your case, for the Joule Heating and Transport of Diluted Species the default sequence includes a "Fully Coupled" solver that solves one large linear system of equations that includes ALL equations (ie both Transport of Diluted Species and Joule Heating equations).

The way you have it set up now there is not a simultaneous solution.

See attached model (Study 2). FYI - You've got some other issues as well that probably relate to boundary conditions and fully defining the necessary conditions for all your physics. You've got a lot of physics going on in this model. Remember all equations need proper essential and natural boundary conditions for a properly defined problem and non-trivial solution.

Hope that helps some,

Best regards,
Josh Thomas
AltaSim Technologies

Sanjoy,

Also, you say cA (concentration) which is time-dependent affects the thermal conductivity which is involved in a steady-state form of the equations. How would this work conceptually? I think part of the issue is that you would have to decide what time instance value of cA is meant to be plugged into the stead-state form of the thermal equations? I believe there is a conceptual issue here.

From your description, I believe both sets of equations need to be solved in the time-domain in order for them to be properly coupled as you've described.

Best,
Josh

Hi Josh

Thanks for your comment. you're right. the stationary solid mechanic equations does not affect transient magnetic field equations.
By the way, My major problem is plasticity deformation. as the stress increases and reaches the initial yield stress, because of severe nonlinearity, the solver does not converge.
I was wondering if you could introduce me an example of plasticity deformation in time domain?

Best regards
Behrooz

Sanjoy,

Also, you say cA (concentration) which is time-dependent affects the thermal conductivity which is involved in a steady-state form of the equations. How would this work conceptually? I think part of the issue is that you would have to decide what time instance value of cA is meant to be plugged into the stead-state form of the thermal equations? I believe there is a conceptual issue here.

From your description, I believe both sets of equations need to be solved in the time-domain in order for them to be properly coupled as you've described.

Best,
Josh

Hi Josh,
Thanks you for reply. There were some problems in defining physics. Now, I can run two time independent or dependent together. But I want to keep the Joule heating module time independent. As time dependent part of Joule heating just contributes temperature increasing rate. I tried to use specific heat zero make it time independent. Is there any to run time independent and time dependent module together?

Thanks,
Sanjoy