Latest Discussions - COMSOL Forums

Scattering by a half-plane

Fri, 18 Jul 2025 15:18:20 +0000

Hello,

I am simulating the scattering of acoustic waves by a half-plane. The domain consists of a rectangular box with the half-plane at the bottom. The box is surrounded by PMLs shown in purple in the image below. Periodic boundary conditions are used in the front and back faces and the background field is a plane wave in the x-direction. I am using the pressure acoustics, frequency domain module and I would like to add a background mean flow in the x-direction.

I have thought of two possibilities:

1) Use the linearized Euler Equations first just to add the mean flow, and then use the acoustics module, but I didn't manage to couple the two things.

2) Modify the wave equation to go from the Helmholtz equation: to a convected Helmholtz equation

I tried using the dipole source as this will give the first order partial derivative, but the results I got don't seem to agree with the analytical model I have.

Is there any better way to include the effect of the background flow?

Thanks

Exporting mesh outline

Fri, 18 Jul 2025 13:49:43 +0000

For context, i have plotted a heatmap of the magnetic field of an antenna on the XY plane. I would like to obtain the outline of the antenna mesh to overlap on the heatmap to show the antenna position.

However, i am only able to obtain the coordinates and not the outline as shown in the graphics view.

I would appreciate any help.

How to force a non-solid truss to activate with solid surface displacement

Fri, 18 Jul 2025 12:15:37 +0000

In COMSOL, the truss element (non-solid line segment) and the geometry point of the solid surface have coincided exactly, but the truss has no displacement and no stress after applying the surface compression displacement, so how can I force the effective mechanical connection between the truss and the solid surface?

Meshing a volume

Thu, 17 Jul 2025 09:34:46 +0000

Hi,

I'm new to Comsol and maybe this issue is actually trivial... Anyway, I am modeling a probe between two electrodes to see how the electric field produced is behaving inside the probe. The thing is that I need to consider the electrodes and the probe to be inside air, the first solution I used is to put my electrodes + probe inside a cylinder and then form an union. Nevertheless, the mesh looks to be only applied on the surface of the cylinder (and on the electrodes and probe). So the question is : How can i consider the space inside my cylinder to be "Air" and how can I put a proper mesh ?

Best, Benoist

P.S.: I am running the simulation on COMSOL 5.3

Classic case of Capillary-Wave in time domain. How to plot a amplitude vs time graph from its wave?

Thu, 17 Jul 2025 06:28:26 +0000

Hello experts,

I am trying to replicate the classical test case for capillary waves using COMSOL. I based the idea on the Basilisk CFD simulation, where surface tension acts as the restoring force between two immiscible fluids, creating a standing wave.

My goal is to extract a graph of amplitude vs time at the fluid interface. I’ve attempted using parametric probes, line probes, and cut lines, but haven’t yet achieved the desired result.

Could someone please guide me on how to: 1. Track the wave crest or interface height over time. 2. Extract and plot a relative amplitude vs time graph like in classical validation studies (e.g., Prosperetti, Popinet papers)? 3. Use phi (level set function) or Volume Fraction data effectively for this?

Any help or similar COMSOL examples would be appreciated!

TL;DR: How to extract amplitude vs time data from a capillary wave simulation in COMSOL?

Here is my current setup and results: ![https://drive.google.com/file/d/15cP3eWpdQfI2-Tr8aSJL_d_dJZVS8MO8/view?usp=drive_link]

Mode Shape Suppression After Adding Molybdenum Layers to AlN Resonator

Tue, 15 Jul 2025 19:17:42 +0000

Hello,

I am currently working on building a 3D piezoelectric resonator model.

As a starting point, I simulated a 1 μm-thick AlN layer on its own and was able to observe a well-defined thickness-extensional mode in the expected frequency range.

However, after adding 200 nm molybdenum (Mo) layers on both the top and bottom surfaces of the AlN to represent electrodes, I noticed a significant change. The thickness mode appears to be heavily suppressed, and the resulting mode shapes do not resemble those from the initial AlN-only configuration. Additionally, the output response is much weaker, and the resonant frequency appears to shift outside the previously observed range.

Could anyone advise why this behavior occurs? I expected a moderate frequency shift due to the added mass and acoustic impedance of the Mo layers, but not such a drastic change in the mode shape or suppression of the thickness mode altogether.

Any guidance or insight would be greatly appreciated.

3D dispersion graph AMMs

Tue, 15 Jul 2025 13:16:26 +0000

I am simulating a unit cell of a supposedly acoustic lieb structure in acpr module. I have my 1D band diagram where it is a plot of k vs freq and k is swept between 0 to 3. Now for illustrative purposes I wanted to plot a 3D dispersion diagram but I haven't been able to do it via COMSOL. How can i sweep kx and ky and a 3D surface?

solver issue

Tue, 15 Jul 2025 11:59:30 +0000

for PCM +Air hybrid cooling of battery pack, i enabled conjugate heat transfer module where turbulence physics defined for Air domain and under Heat Transfer in solids and fluids battery defined as solid and pcm as a fluid..selected phase change material under PCM(not sure about PCM setup as i asked earlier doubt.) we are getting results only for the stationary study and getting error for time dependent study.

but we require time dependent simulations only...kindly give idea

PCM simulation setup in COMSOL Multiphysics.

Tue, 15 Jul 2025 05:25:56 +0000

How to do PCM simulation setup in COMSOL Multiphysics. https://drive.google.com/file/d/1QJDjC4hOGsd8K3qDd_vl-luYoqq_sv8j/view?usp=drive_link

My study is cooling of battery cell by using both PCM and air.The cell is covered with cylinder PCM and again it is covered with aluminium casing cylinder.The aluminum casing is cooled by blowing air at some velocities. Here heat transfer takes place from cell to PCM,PCM to alumnium casing and alumiumuin casing to air.I have doubt about PCM simulation setup. Since when PCM melts its density changes and also other property changes with temperature. How to setup the simulation in COMSOL for a natural convection of PCM. when PCM melts, it converts solid into liquid.How to set physics for above problem.

Ion tracing through solids

Mon, 14 Jul 2025 17:17:15 +0000

Hi I am replicating an example in from the https://www.comsol.com/particle-tracing-module. and I want to simulate it with multiple sheets instead of a solid block. So i make the walls transparent and did the simulation but no output waveforms are seen. so can anyone help to let me know if how to do simulation with multiple sheets where charged ions or electrons will pass through it.

How to write variables in proper syantax ?

Sat, 12 Jul 2025 17:25:37 +0000

Respected professor, I am using COMSOL M version 6.0 for my work ,Topology optimization of Heat sink. As I am not expert facing some problems while inputting the parameters. Problems 1} While using Brinkman's equation for topology optimization of heat sink, what are the physics I have to select ? 2] Inverse Permeability, how to write ?

α (ρ) = α_min + (α_max - α_min) q(1-ρ)/q+ρ   

As a variable how can I write in proper syntax

α_simp = α_min + (α_max - α_min) comp1.dtopo1(k_simp*ht. q(1-theta^n)/(q+theta^n)

Is it correct ? if not please suggest me.I tried but showing error.

Thanks

Export Results->DerivedValues->System Matrix

Sat, 12 Jul 2025 13:10:32 +0000

Hello!

In Study I used Assemble to store or save the Stiffness Matrix in the Solution. In Results->Derived Values->System Matrix the Stiffness Matrix is to big to evaluate it into a Table.

Can I directly save or export the Stiffness Matrix into a text-file? I also would try it via Java.

A simple Yes would be enough to know that it is possible; I then figure out by myself.

Nice Greetings

Time-Dependent Heat Transfer/Convection Simulation of a building: Singularity failure

Sat, 12 Jul 2025 12:27:56 +0000

Hello everyone,

I'm currently trying to simulate the heating of a building with particular focus on its surroundings, throughout an entire summer day. For this, I am using a 24 hours time-dependent study, including the heat transfer and the laminar flow physics modules. When first approaching this project, I focused on the building heating up due to the sun's irradiation, making use of the heat transfer and the surface-to-surface radiation modules and omitting the laminar flow module. This has worked out fine and yielded usable results.

For simplification, I modeled two (outer) walls of a building, a ground floor and the air above. Note that the ground floor and the air are supposed represent the outside of the building.

Sadly I encountered severe problems when trying to simulate the convection of the air outside the building. The computation of my current model fails with the error Repeated error test failures. May have reached a singularity.. The error occurs as soon as the temperature of the building walls diverges from its initial values; however given that the building walls "must" heat up over time, I do not know what I need to change in my model to solve this error.

I wasn't able to reduce my .mph file to the required < 5 MB in order to upload it. If someone here would like to look at it anyway, I will gladly find another way to upload it somewhere else. For now, I will list the most relevant information below and include another screen shot of my model tree to give a basic idea of my physics module usage.

I would be very happy to receive some pointers to where exactly my problems stem from and what I could do to solve them. If someone here has more experience with modeling heating and convection, I finally would like to ask if my particular simulation case could also be approached with the "indirect" convection modeling techniques from Modeling Natural and Forced Convection in COMSOL Multiphysics® or through the One-Way Coupled Studies for Nonisothermal Flow.

Thank you very much and best regards

Luca

=============== Additional information: * Irradiated surface temperature: From my previous model using only the ht and rad modules, I recorded the resulting average wall and ground floor surface temperatures throughout the simulated day duration to a table. In my current model, I use this table to statically set the surface temperature for each simulated point of day. I do this over the ht > Boundary Temperature node. The range is from 12 °C to 55 °C. * Distant air temperature: In order to represent the temperature of the surrounding air, I similarly set the surface temperature of the air at the outer edges of my model through a simple diurnal cycle ranging from 12 °C to 27°C. * Mesh: I use a physics-controlled finer mesh. * Study: I use a time-dependent study with the following output times, in seconds except where specified differently: range(0,0.1,1), range(1,1,10) range(10, 30min, 23.5h)

Can I change the percentage of the contribution of the plastic strain in phase field damage?

Sat, 12 Jul 2025 09:22:32 +0000

I am trying to build a model to simulate the fracture of a ductile metal. I am trying to use the phase field damage models under solid mechanics interface. When I was checking the user's mannual, I found this description:

"By selecting Total strain energy density, additional contributions from dissipative material features, such as creep, plasticity, and viscoelasticity, are added. Select the Calculate energy dissipation checkbox in the parent material model to compute these variables."

For the problem I want to solve, I do need some plastic contribution in the driving force for the phase field interface evolution. However, usually only 10% of the plastic work is considered to be stored in the material and is available for creating new surfaces, the rest of it is considered dissipated through heat.

I am wondering if I select the* Total strain energy density*, and select the Calculate energy dissipation checkbox, the how much of the plastic contribution is taken into account by COMSOL? Is it all of it? If so, how could I regulate the model to have only 10% of the total plastic work to contribute in the phase field damage driving force?

best wishes Runzi

Ignoring or excluding mesh in some regions while being able to simulate

Fri, 11 Jul 2025 17:58:27 +0000

I wanted to ask if it is possible to exclude some regions when modeling the mesh for a large or complex system.

For example, modeling a micro antenna with centimeter-size wires is too dense a mesh to model. Along with the air region around.

So i wanted to see if one could ignore some regions that are unimportant, so as to save space and time, whilst still simulating somehow.

Update version from 6.2 to 6.3

Fri, 11 Jul 2025 14:07:53 +0000

Hello,

I cant install the version 6.3 of Comsol, when i attach the .dat file as a license path, an error appears saying:

The license could not be validated, please contact support@comsol.com for assistance and include the error message below and a copy of the license file.

License file does not support this version. Feature: SERIAL Application version > License version: 6.3 > 6.2 License path: C:\Users\Mattia\AppData\Local\Temp\cscomsol84494\comsol18049980329219368361.dat; FlexNet Licensing error:-21,126

Phase change from powder to liquid and back to solid

Fri, 11 Jul 2025 13:16:47 +0000

Hi everyone, I am simulating Laser Powder Bed Fusion (LPBF) process and have modelled powder layer as a continuous-scale. I have coupled heat transfer in solid and fluids with laminar flow. I want to know how I can model the phase change for powder as it will first melt to liquid and then will solidify into solid. I want to know how to do this in COMSOL. Using phase change would convert back it to the same material. So, how to make it one way such that it first converts the powder into liquid and later liquid is converted to solid. More information: Properties like density, thermal conductivity and specific heat capacity of powder layer properties is defined as an average of air and solid based on volume fraction.

Computing second-order derivative of Temperature field

Fri, 11 Jul 2025 11:52:58 +0000

I am working on a circular domain defined in 2D. I need to compute the angular derivative of the temperature, basically I want to compute:.

For this, I have used the following transformation from Cartesian to Polar coordinates:

I have tried to:

Change the frame from spatial to Material
Change the shape function for discretization.
refine the curvature factor.

But I still do not get the accurate result. Can somebody explain me how can I fix this?

Thanks in advance!

Exporting data from COMSOL while computing electric field magnitude and direction in an electrospinning machine

Thu, 10 Jul 2025 14:49:05 +0000

I am building a simulation of an electrospinning machine on COMSOL, and my objective is to study the electric field magnitude and direction within the machine. I would like to export the magnitude data that shows on a 1D plot. Is there a way to obtain a table of values that I can open in Microsoft Word, Excel, or another similar platform?

COMSOL not using all memory available

Thu, 10 Jul 2025 14:27:36 +0000

Hello,

I was trying to run a COMSOL simulation and it would always go over the available amount of RAM and start using Virtual Memory, which was extremely slow. Therefore, I bought more RAM (went from 64gb to 128gb), but COMSOL doesn't seem to want to use the full amount it has available. Indeed, once it reaches 64gb, it starts to write on the disk again even though there is still twice as much RAM available. Thinking that this was because COMSOL didn't "recognize" that there is more RAM, a clean install was done of COMSOL MultiPhysics, but this didn't solve the problem. Furthermore, I also tried to disable the use of Virtual Memory to force COMSOL to use the available RAM, but the simulation ends when COMSOL reaches the 64gb mark, with an error saying that there wasn't enough memory.

Why does COMSOL not use the full amount of RAM available?

Thanks in advance for your help!

Marek