Latest Discussions - COMSOL Forums

Entering mixed derivatives in coefficient form PDE

Sat, 01 Apr 2023 04:54:41 +0000

Hi,

I am trying to enter a mixed derivative of the form d3c/d2xdy in coefficient form PDE. Any help in this regard is highly appreciated.

Heat transfer phase change model

Fri, 31 Mar 2023 17:50:15 +0000

How are the theta1 and theta2 modeled? They look like logistic functions but if so what is the growth rate and how does it relate to the temperature range? reference pic is attached

Joule Heat in porous media

Fri, 31 Mar 2023 17:23:50 +0000

The below post is related to an archived discussion

Electric currents: effective media - how it works with porous media?

How to apply Uniform Variable load

Fri, 31 Mar 2023 11:01:48 +0000

i need to Apply UVL load along Height of Column in soil Mechanics. can anyone please help me on this

Nonlinear solver did not converge

Thu, 30 Mar 2023 21:57:44 +0000

Hello.

I am trying to create a system where I cool lithium-ion batteries using phase change material. The program was computing for 9 hours and I was getting good results, but in the end I got the following error:

Nonlinear solver did not converge. In Velocity u, Pressure p: Divergence of the linear iterations. There was an error message from the linear solver. Very ill-conditioned preconditioner. Time: 640.74034002309429 s. Last time step is not converged.

Does anyone know how I could solve this issue?

Also, I noticed that the error happened close as the temperature of the phase change material approached the melting point. Might this have an effect on the error?

Thanks in advance for the help.

Objective function missing after computing optimization

Thu, 30 Mar 2023 12:30:30 +0000

Hi all,

I am trying to optimize (topology optimization) a plate structure, in order to maximize the lowest eigenfrequency.

When selecting my objective function in Study > Topology optimization, I am able to choose comp1.plate.freq , as well as "maximization".

However, right after running the study, it says the variable is undefined. After this, the variable also has disappeared from the list of variables (model>plate>global).

Does anyone know what could be the cause of this?

Kind Regards,

Air expansion during electrical arc

Wed, 29 Mar 2023 16:35:20 +0000

Hi, I want to simulate air expansion during electrical arc. Can I simulate that. If I can, can u send some resoueces about it.

How Can I Change The Positon Of A Imported Model In Comsol?

Wed, 29 Mar 2023 15:50:29 +0000

Hi, How can i change the position of a imported model? I have to modify a file with 4 imported parts in it but I have to space them more from each other. I cannot find any way to move anyone of them.

Thanks

Misleading advice in tutorial

Wed, 29 Mar 2023 11:43:46 +0000

Hello, I would like to propose a small correction to your tutorial - it is about model Frequency Selective Surface, Periodic Complementary Split Ring Resonator (Application ID: 78011), https://www.comsol.com/model/frequency-selective-surface-periodic-complementary-split-ring-resonator-78011

I believe, PMLs on both sides are not needed at all there - both ports will deal with it. Here is how one can modify the current model to check my assumption:

Disable Periodic conditions 2 and 4 in Electromagnetic Waves, Frequency Domain.
In the main node, Electromagnetic Waves, Frequency Domain, uncheck domains 1 and 5 (which are currently PML). Then the remaining domain selection list will be just 2, 3, and 4.
For Port 1 and Port 2 in Electromagnetic Waves, Frequency Domain, uncheck Activate slit condition on interior port. This is because these ports are no longer internal - they are at external boundaries of the simulation domain.

That's it, one can run the same studies - with smaller and a bit faster model :) Otherwise - thanks a lot for your tutorials and demos, it really helps a lot!

Comsol Error when trying to compute

Tue, 28 Mar 2023 21:48:18 +0000

Hello, I am working on a project for my electromagnetic fields class and I am trying to compute the low pass filter response in the frequency domain. I have attatched my project and the error I am receiving. any help would be appreciated. Thank you, Nicole!

importing and compiling multiple custom Java classes to use with COMSOL Java API code

Tue, 28 Mar 2023 15:14:51 +0000

Hello,

I would like to integrate custom Java classes with my COMSOL Java API code. However, I cannot find any recommendation about how to do it using the comsol compile in the documentation.

I would like to ask for further clarification about how to do this.

Let's say I have two files, Main.java and Pair.java. The first file has the main and the COMSOL model. The second file implements a simple class Pair the works similarly to tuple.

Should I compile multiple .java files at once? Should I make a package using a directory containing classes and import them from the main file? Or should make a JAR files? How should I organise file structure and how to use comsol compile to compile?

In the comsol compile -help there is the classpathadd <classpath> option to provide an additional classpath. However, it's not clear how to use it. Could you provide examples of usage please?

Many thanks, Francisco

Comsol Error When compiling Equations

Tue, 28 Mar 2023 15:02:55 +0000

Hello, I am currently working on a project for my electromagnetics class where we have to design a low pass filter. I am trying to compute the frequency domain plot. When I try to compile I get the error "Uniform lumped ports should be placed between two conductive boundaries. Feature: lumped port 2 (lport2) Feature: lumped port 1 (lport1)". I am not sure how to fix this since I have the lumped ports between two conductive boundaries. I have attatched my project file and I would appreciate any help. Thank you, Nicole

frequency dependent thermal strain

Tue, 28 Mar 2023 14:41:59 +0000

Hi,

I am trying to model frequency dependent thermal strain system with the form e_th(w) = a*(T(w)-T_ref) (e_th : thermal strain , frequency dependent T(w) : induced tempereture, frequency dependent a : coefficient of thermal expansion)

Could you please give me an advise how to start? Is it right to only using solid mechanics or do I have to use Multiphysics(Thermal Stress?)

Fracture mechanics

Tue, 28 Mar 2023 10:34:00 +0000

How to realize the bar tensile fracture model

How can I express free outflow boundary in Classical PDEs module?

Tue, 28 Mar 2023 10:26:11 +0000

I'm trying to couple new physics to Darcy's law by using Convection-Diffusion Equation in Classical PDEs.

Since there is no predefined outflow boundary condition in this physics, I have to define the free outlet boundary which satisfy 'normal flux equals zero'.

I've tried to define this by using Constraint node, but I was not able to find out how to define it. I'll be appreciated for any information about solving this problem.

I attached some pictures about my situation.

Thanks.

File version

Tue, 28 Mar 2023 08:03:44 +0000

Hi, Is that possible to open un file vesion 5.6 in version 6.1? beacuse when I tray to opent it the application refused.

How can I get this trial pass code?

Tue, 28 Mar 2023 06:55:17 +0000

How can I get this trial pass code?

How to model the Selective laser melting process in COMSOL?

Tue, 28 Mar 2023 05:19:01 +0000

I am trying to model the SLM process from powder to solid metal formation, please provide the developing steps.

About the nodes sequence in the global stiffness and mass matrix

Mon, 27 Mar 2023 16:31:49 +0000

Dear all,

Hi. When I got the stiffness and mass matrix using the 'mphmatrix' with matlab, and got the nodes and elements sequence of the model from DATA.vertex and DATA.elem using '[STATS,DATA]=mphmeshstats(model)', I found that the sequence of nodes corresponding to each row in the stiffness or mass matrix is not consistent with the sequence of nodes in DATA.vertex. For example, the third row in the stiffness may be not corresponding to the third node in the DATA.vertex. So my question is what is the sequence of nodes in the matrix?

I appreciate your help,

Regards, Yexi

dynamic viscosity of a solid??

Mon, 27 Mar 2023 14:37:47 +0000

what value should I give for dynamic viscosity of a piezoelectric material??