Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

What is the reason that you can only get a picture of one moment from the transient model, and basically there is no change at different times?

Please login with a confirmed email address before reporting spam

What is the reason that you can only get a picture of one moment from the transient model, and basically there is no change at different times?


6 Replies Last Post 15 oct. 2022, 07:05 UTC−4
Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 13 oct. 2022, 10:17 UTC−4

The most likely explaination is that the solution doesn't change much over the range of times you run the model. This could be because the physcics are either much slower or much faster than the time span of your run.

Best,

Jeff

-------------------
Jeff Hiller
The most likely explaination is that the solution doesn't change much over the range of times you run the model. This could be because the physcics are either much slower or much faster than the time span of your run. Best, Jeff

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 13 oct. 2022, 23:34 UTC−4

Thank you.I want to study the dynamic problem of the electric double layer and the induced charge around the metal cylinder. Now the model has been established, which is a transient model. But the final calculation results do not change after I apply different times, and I only get a look of the electric double layer in a stable state. I can't see the change process of the electric double layer establishment.

Thank you.I want to study the dynamic problem of the electric double layer and the induced charge around the metal cylinder. Now the model has been established, which is a transient model. But the final calculation results do not change after I apply different times, and I only get a look of the electric double layer in a stable state. I can't see the change process of the electric double layer establishment.

Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 14 oct. 2022, 08:44 UTC−4
Updated: 2 years ago 14 oct. 2022, 09:07 UTC−4

The symptom you are describing is very consistent with the physics being fast relative to the solution time, so that all the transients are happening before the end of the first stored time. Another possible explanation could be that your initial conditions match the stationary state closely.

Best,

Jeff

-------------------
Jeff Hiller
The symptom you are describing is very consistent with the physics being fast relative to the solution time, so that all the transients are happening before the end of the first stored time. Another possible explanation could be that your initial conditions match the stationary state closely. Best, Jeff

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 14 oct. 2022, 09:47 UTC−4

Thank you.How to solve? Is it necessary to change the time step of the solver or the initial value boundary conditions and initial conditions ?

Thank you.How to solve? Is it necessary to change the time step of the solver or the initial value boundary conditions and initial conditions ?

Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 14 oct. 2022, 10:56 UTC−4

If the issue is the first one I mentioned, then make sure you run your model for a length of time that makes sense for the physics, and that you ask the software to store solutions at times that capture the transients. This requires that you estimate how long those transients are (from experience, or litterature, or non-dimensionlalization of the equations, etc).

If the issue is the second one I mentioned, then you need to make sure your problem is set up so that it is not already at steady-state in its initial conditions.

Best,

Jeff

-------------------
Jeff Hiller
If the issue is the first one I mentioned, then make sure you run your model for a length of time that makes sense for the physics, and that you ask the software to store solutions at times that capture the transients. This requires that you estimate how long those transients are (from experience, or litterature, or non-dimensionlalization of the equations, etc). If the issue is the second one I mentioned, then you need to make sure your problem is set up so that it is not already at steady-state in its initial conditions. Best, Jeff

Please login with a confirmed email address before reporting spam

Posted: 2 years ago 15 oct. 2022, 07:05 UTC−4

Thank you very much. I'll revise it from these two points.

Thank you very much. I'll revise it from these two points.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.