Latest Discussions - COMSOL Forums Most recent forum discussions Sat, 01 Apr 2023 04:54:41 +0000 COMSOL Forum: Latest Discussions Entering mixed derivatives in coefficient form PDE <p>Hi,</p> <p>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.</p> Sat, 01 Apr 2023 04:54:41 +0000 4.2023-04-01 04:54:41.322181 Heat transfer phase change model <p>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 <a href="http://"></a></p> Fri, 31 Mar 2023 17:50:15 +0000 4.2023-03-31 17:50:15.322162 Joule Heat in porous media <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>Electric currents: effective media - how it works with porous media?</p> Fri, 31 Mar 2023 17:23:50 +0000 4.2023-03-31 17:23:50.322161 How to apply Uniform Variable load <p>i need to Apply UVL load along Height of Column in soil Mechanics. can anyone please help me on this</p> Fri, 31 Mar 2023 11:01:48 +0000 4.2023-03-31 11:01:48.322151 Nonlinear solver did not converge <p>Hello.</p> <p>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:</p> <p>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.</p> <p>Does anyone know how I could solve this issue?</p> <p>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?</p> <p>Thanks in advance for the help.</p> Thu, 30 Mar 2023 21:57:44 +0000 4.2023-03-30 21:57:44.322141 Objective function missing after computing optimization <p>Hi all,</p> <p>I am trying to optimize (topology optimization) a plate structure, in order to maximize the lowest eigenfrequency.</p> <p>When selecting my objective function in Study > Topology optimization, I am able to choose comp1.plate.freq , as well as "maximization".</p> <p>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).</p> <p>Does anyone know what could be the cause of this?</p> <p>Kind Regards,</p> Thu, 30 Mar 2023 12:30:30 +0000 4.2023-03-30 12:30:30.322131 Air expansion during electrical arc <p>Hi, I want to simulate air expansion during electrical arc. Can I simulate that. If I can, can u send some resoueces about it.</p> Wed, 29 Mar 2023 16:35:20 +0000 4.2023-03-29 16:35:20.322121 How Can I Change The Positon Of A Imported Model In Comsol? <p>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.</p> <p>Thanks</p> Wed, 29 Mar 2023 15:50:29 +0000 4.2023-03-29 15:50:29.322111 Misleading advice in tutorial <p>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),</p> <p>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:</p> <ol> <li>Disable Periodic conditions 2 and 4 in Electromagnetic Waves, Frequency Domain.</li> <li>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.</li> <li>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.</li> </ol> <p>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!</p> Wed, 29 Mar 2023 11:43:46 +0000 4.2023-03-29 11:43:46.322081 Comsol Error when trying to compute <p>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!</p> Tue, 28 Mar 2023 21:48:18 +0000 4.2023-03-28 21:48:18.322042 importing and compiling multiple custom Java classes to use with COMSOL Java API code <p>Hello,</p> <p>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 <code>comsol compile</code> in the documentation.</p> <p>I would like to ask for further clarification about how to do this.</p> <p>Let's say I have two files, and The first file has the main and the COMSOL model. The second file implements a simple class Pair the works similarly to tuple.</p> <p>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 <code>comsol compile</code> to compile?</p> <p>In the <code>comsol compile -help</code> there is the classpathadd &lt;classpath> option to provide an additional classpath. However, it's not clear how to use it. Could you provide examples of usage please?</p> <p>Many thanks, Francisco</p> Tue, 28 Mar 2023 15:14:51 +0000 4.2023-03-28 15:14:51.322041 Comsol Error When compiling Equations <p>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</p> Tue, 28 Mar 2023 15:02:55 +0000 4.2023-03-28 15:02:55.322032 frequency dependent thermal strain <p>Hi,</p> <p>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)</p> <p>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?)</p> Tue, 28 Mar 2023 14:41:59 +0000 4.2023-03-28 14:41:59.322021 Fracture mechanics <p>How to realize the bar tensile fracture model</p> Tue, 28 Mar 2023 10:34:00 +0000 4.2023-03-28 10:34:00.322013 How can I express free outflow boundary in Classical PDEs module? <p>Hi</p> <p>I'm trying to couple new physics to Darcy's law by using Convection-Diffusion Equation in Classical PDEs.</p> <p>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'.</p> <p>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.</p> <p>I attached some pictures about my situation.</p> <p>Thanks.</p> Tue, 28 Mar 2023 10:26:11 +0000 4.2023-03-28 10:26:11.322011 File version <p>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.</p> Tue, 28 Mar 2023 08:03:44 +0000 4.2023-03-28 08:03:44.322001 How can I get this trial pass code? <p>How can I get this trial pass code?</p> Tue, 28 Mar 2023 06:55:17 +0000 4.2023-03-28 06:55:17.321991 How to model the Selective laser melting process in COMSOL? <p>I am trying to model the SLM process from powder to solid metal formation, please provide the developing steps.</p> Tue, 28 Mar 2023 05:19:01 +0000 4.2023-03-28 05:19:01.321982 About the nodes sequence in the global stiffness and mass matrix <p>Dear all,</p> <p>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?</p> <p>I appreciate your help,</p> <p>Regards, Yexi</p> Mon, 27 Mar 2023 16:31:49 +0000 4.2023-03-27 16:31:49.321953 dynamic viscosity of a solid?? <p>what value should I give for dynamic viscosity of a piezoelectric material??</p> Mon, 27 Mar 2023 14:37:47 +0000 4.2023-03-27 14:37:47.321951