Latest Discussions - COMSOL Forums

Frequency study not converging

Sun, 11 Jan 2026 18:06:48 +0000

Coil geometry analysis and stationary analysis is being done and coming correctly. While doing the frequency study the solution is not converging, is there any problem in the geometry or some settings i have to change.

Modeling radiative loss to the ambient environment for a system operating in vacuum conditions

Sun, 11 Jan 2026 17:48:54 +0000

Hi,

I am modeling the temperature distribution in a Hall Thruster, to be operated in vacuum conditions (either in space or in a vac chamber). I am using Surface-to-Surface radiation to model radiative transfer between various thruster interfaces. However, the thruster has a radiator that is meant to radiate heat into the ambient environment. My question is, does S2S radiation account for this or do I need to separately define Surface-to-Ambient radiation at the external boundaries of the thruster?

Thank you in advance :-)

Thermal expansion for cryostat model

Sun, 11 Jan 2026 17:44:09 +0000

Hi there,

I am new to using COMSOL and I am setting up a simulation to test the cooling capabilities of my cryostat. I have built up the model slowly, starting with a basic simulation to model the cooling power of my cryostat then making it more advanced to incorporate radiation and other sources of loss.

The final step that I am trying to incorporate into the model is thermal expansion specifically to test whether our sample will contract away from some surfaces due to thermal expansion. I have run an initial simulation however the results showed that every part of my model was connected together so they all contracted together, rather then showing whether the sample contracts away from other parts. From looking online, I think the issue is that I used "form union" rather than "form assembly". I have tried again to run the simulation using form assembly however it is not progressing past t = 0 in the time dependant study.

I am wanting help to set up this simulation properly to incorporate thermal expansion of the parts, and allow them to contract away from each other. Since the simulation is working properly when I use "form union" I am wanting to learn how to change the model to the "form assembly" situation. I am also curious to know if there is a way I can see what is causing my simulation to stall at t = 0 without waiting for hours to get an error message.

I am using COMSOL 6.3 on Ubuntu 24.04. I am happy to provide as much detail about the system as needed.

Material data ordering in Solid Mechanics simulations: Voigt vs. Standard

Fri, 09 Jan 2026 20:56:29 +0000

I'm simulating mechanical resonators made of anisotropic materials and am struggling to understand COMSOL's expected input for the material's elasticity tensor.

Under the Linear Elastic Material node, there's a dropdown to choose "Material data ordering" and can be toggled to select either "Standard" or "Voigt". Under the Materials node, you can either specify a material's "Elasticity matrix", or its "Elasticity matrix, Voigt notation."

I ran the same study on the same component 4 times with all possible permutations of the toggles above, and I'm not understanding how to interpret the results.

Study 1: "Standard" ordering and "Elasticity matrix." Study 2: "Standard" ordering and "Elasticity matrix, Voigt notation." Study 3: "Voigt" ordering and "Elasticity matrix." Study 4: "Voigt" ordering and "Elasticity matrix, Voigt notation."

Studies 1 and 3 gave identical results, while studies 2 and 4 also gave identical results. This makes it seem like the "Material data ordering" toggle has no effect on simulations, so what does it do? I understand that changing between "Elasticity matrix" and "Elasticity matrix, Voigt notation" while inputting the same tensor values changes the order of the shear terms, so seeing different results between those studies was expected.

In each case, I set the elasticity matrix to be assigned from the material rather than choosing "User defined." Is the toggle really only necessary when inputting "User defined" material properties?

I compared these 4 studies with a study where the "Material symmetry" was set to "Crystal" and inputted the c_ij values for the elasticity tensor (in Voigt notation); and this study gave identical results to studies 2 and 4.

What is the "proper" way to set the "Material data ordering" and input elasticity tensors in these simulations?

Thanks!

Running COMSOL server on Linux cluster, LiveLink for MATLAB on local Windows machine

Fri, 09 Jan 2026 10:08:10 +0000

Dear all, my system is configured as follow:

I work on a windows laptop, I access a UNIX workstation via native windows Remote Desktop. I do not have access to the folders there from windows (I tried to map the workstation to windows with popd and net, with no success, maybe it would work installing Samba on the workstation, but I cannot). Can I access the files on the workstation with a Comsol Livelink Matlab command?

I tried as follows:

on the workstation I start the comsol server

 ./comsol mphserver -user myself -passwd mypwd

on the laptop I start matlab&Livelink and I connect to the comsol server
```
 mphstart("the.correct.ip", thecorrectport, "myself", "mypwd")
```

I can mphload a model from the local laptop, for example with

model=mphload('myModelwithResults.mph');

and for example re run solutions on the comsol server, but I would like to have the model located on the workstation and loaded it from there, for example

model=mphload('//the.correct.ip/home/myself/myModelwithResults.mph');

but it does not work. What is the correct syntax for mphload (and then I assume is the same for mphsave, I would like to be able to save the model on the workstation, too).

I can run matlab directly on the workstation, but I am interested in the specific configuration I mention here.

Thanks,

How to couple the built-in PID controller with the induction heating?

Thu, 08 Jan 2026 22:30:53 +0000

Hi All,

I am trying to add the built-in PID controller to my induction heating system. I chose a domain point probe and monitored this probe's temperature as my PID controller's input. Then, I got an output whose unit is "volt" as the input of the induction coil. However, no matter what the target temperature that I set, the model always cut off the output at the very first beginning no matter I set "big" or "small" time step.

I also checked with the convergence plot and found that it didn't seem to be converged over time. I also downloaded the COMSOL's official induction heating demo and tried to add the PID controller into it and replace the input of the coil with the output of the controller, but it failed too.

I really have no idea how to address it and really appreciate any suggestions you give to me.

Thanks.

Convert an image into geometry

Thu, 08 Jan 2026 16:53:43 +0000

Dear all,

I have a question regarding the possibility to convert an image of a steel microstructure in a geometry. How can I do that ? Is it needed to use an Add-in ?

thank you.

triboelectric nanogenerators

Thu, 08 Jan 2026 15:25:15 +0000

Hello everyone, I'm currently researching triboelectric nanogenerators. Their principle involves a PTFE film fixed at one end oscillating vertically under wind energy at a certain wind speed. This periodic flapping against fixed copper plates at the top and bottom generates charge transfer, thereby producing electricity. In COMSOL, I first attempted a fluid-structure interaction simulation by replicating the oscillating beam case from the COMSOL library. However, the calculation consistently diverges. Does anyone know how to configure this correctly? Kindly help me, thanks！

How to obtain unbalance response plot in COMSOL?

Wed, 07 Jan 2026 11:25:46 +0000

I am working on similar case of "Simply supported rotor", I am unable to plot the unbalance response plot. Kindly help me.

Far‑field radiation from magnetoelectric antenna driven by piezoelectric–piezomagnetic coupling (no electrical port)

Tue, 06 Jan 2026 13:32:35 +0000

Hello everyone, I am working on a magnetoelectric (ME) antenna model in COMSOL Multiphysics and I would appreciate guidance on the correct strategy to compute the far‑field radiation. Model description The antenna is composed of: grounded Mo bottom electrode, piezoelectric AlN layer, magnetostrictive FeGaB layer The surrounding medium is a spherical air domain (inner sphere, and outer pml sphere) The physics interfaces used in the near‑field study are:Electrostatics (ES), Solid Mechanics (SM), Magnetic Fields (MF) with the following multiphysics couplings:Piezoelectricity (ES ↔ SM), Piezomagnetism / magnetostriction (SM ↔ MF) The system is solved in the frequency domain. A harmonic voltage is applied across the piezoelectric layer, generating strain that propagates into the magnetostrictive layer and produces a time‑varying magnetization. An external bias magnetic field is also applied in the air domain. Importantly, this antenna is not electrically fed (no lumped port, wave port, or impressed current), as the source of radiation here is the antenna due to the magentization evolution in FeGaB. My Question: I would like to compute the far‑field radiation pattern of this antenna. I added the Electromagnetic Waves, Frequency Domain (EMW) interface and tried to use COMSOL’s near‑to‑far‑field transformation, but all far‑field quantities (e.g. emw.normEfar) evaluate to zero. I understand that: 1. Far‑field calculations in EMW require a non‑zero electromagnetic near field (E, H) 2. EMW does not directly couple to Magnetic Fields, Solid Mechanics, or Electrostatics 3. Variables such as mf.Mx, mf.Hx, or es.V are not accessible inside EMW as sources I attempted to introduce equivalent magnetic or electric current sources based on the magnetization, but EMW does not recognize variables from the MF interface, even when defined through component variables.

Questions 1. What is the recommended COMSOL workflow to compute far‑field radiation from a mechanically driven magnetoelectric antenna that has no electrical port? 2. Is the correct approach to: Perform a first study to compute the magnetization, then use a second EMW‑only study with an equivalent current (calculate it in matlab based on the output magnetization or field that i wil get due to the near field study)? 3. Are there any built‑in features or best practices in COMSOL for handling radiation from magnetization‑driven sources (e.g., magnetic dipole–type antennas)?

Any guidance, references, or example models would be greatly appreciated. Best regards, Rayan

Defining non-design regions for topology optimization of organic geometries

Mon, 05 Jan 2026 16:58:42 +0000

Good evening,

I am designing an orthopedic, handle-like device intended to be held in the hand, and the final step of my workflow is topology optimization.

The geometry is generated from a 3D scan of the hand; therefore, most of the dimensions are non-parametric and the shape is highly organic. A portion of the device is in direct contact with the hand and its external shape must be preserved for ergonomic reasons.

I would like to perform topology optimization while keeping this contact region unchanged. However, due to its organic shape, this portion cannot be easily isolated using simple geometric primitives such as boxes, cylinders, or spheres. I can select the contact surface itself (I have partitioned the surface were I need), but I am unsure how to correctly partition the volume so that this region is excluded from the design domain.

Is it possible to perform topology optimization while leaving a surface (and an underlying thickness of material) untouched? If so, what is the recommended approach to define the non-design region in this case?

I am attaching a screenshot of the device; the highlighted surface corresponds to the hand–contact area.

Thank you very much in advance for your help.

Error occurs when saving newly created COMSOL models

Thu, 01 Jan 2026 07:19:51 +0000

An error occurs when saving a newly created model in COMSOL. Models created previously can be opened and run without any issues, but saving a new immediately triggers this error. What could be the cause, and how can this issue be resolved? Thank you. The attached picture shows in detail.

How to Model Two-Photon Absorption

Wed, 31 Dec 2025 08:02:27 +0000

Hi, I am trying to model the two-photon absorption (TPA) process in a nanostructure using COMSOL Multiphysics. For describing light propagation, I am using the Wave Optics Module.

My main question is how many physics interfaces are required to properly model this process .

I would greatly appreciate any guidance on the choice of appropriate physics interfaces and the practical steps needed to implement two-photon absorption in COMSOL.

In addition, if anyone could point me to an example model or a COMSOL application that demonstrates two-photon absorption, or more generally multiphoton absorption, I would be very grateful.

Memory Issue

Wed, 31 Dec 2025 05:19:25 +0000

I am doing 3D simulation that is not symmetric, using the mf physics , coil geometry analysis and stationary study. Coil geometry analysis have 2,192,126 DOF and Stationary study have 19,338,394 DOF.

I have used domain wise mesh maximum upto fine and with a total of around 12 GB physical memory.

I am using segregated and iterative solver of stationary study. But my simulation is stucking. I am doing the simulation using i5 processor and 16 GB RAM. Further I have to do frequency analysis.

Can you tell is this the memory issue? If yes, how much is recommendable memory for this much DOF.

There is no Option for "Hide for Physics" in View under Definitions in COMSOL-6.3.

Sat, 27 Dec 2025 14:31:01 +0000

Hi COMSOL users !

I am using COMSOL 6.3 version.

I want to hide some edges in the geometry for the visualization purposes to plot the contour plots.

In model builder in the definition section under the view option , there is option for 'hide for geometry' but there is no option for 'hide for physics'.

How can I enable this option for better contour plots in post processing without intermittent lines/edges ?

Thanks.

modeling aid

Mon, 22 Dec 2025 15:50:01 +0000

Hello, I need your help with a model. I want to model a polystyrene nanoparticle (d=20 nm) in water on Comsol.

What are the vibration effects?
The medium should be water.
The excitation type is opto-thermal/light excitation.
Particle point/average displacement vs. time.
Maximum RMS displacement vs. time.
Q-factor / damping extraction.
Pressure field p(x,t) in fluid.
Fourier transform (FFT) of pressure/potential time series → spectrum.
Mode shape snapshots (in time or from modal analysis).
Acoustic energy flow / power.
Phase vs. time or vs. frequency
Parameter scans (sensitivity plots)
Spatial cross-sections / field maps (p(x,t) or u(x,t))
If optothermal: Temperature(t) at particle & fluid + thermoelastic stress.

How do I model these and visualize the vibration and time-dependent relationships in graphs? Thank you very much for your help...

Create Diffraction order using Livelink for matlab

Mon, 22 Dec 2025 09:32:11 +0000

Hello, I want to create a diffraction order in using livelink in matlab. I could not find a command that describe how to create it. pasted bellow my lines of code in matlab:

%%%%% Assign Boundary Variables%%%%%% bL = 1; % left boundary -> inpot port bR = 12; % right boundary -> output port bB = 2; % bottom boundary -> periodic (Floquet) bT = 3; % top boundary -> periodic (Floquet)

%%%% Floquet periodic BC (y-direction) %%%%

pc1 = ewfd.create('pc1','PeriodicCondition',1); pc1.selection.set([bB, bT]); pc1.set('PeriodicType','Floquet'); pc1.set('kFloquet', {'k0cos(theta)', 'k0sin(theta)', '0'});

%%% input port (left) %%% port1 = ewfd.create('port1','Port',1); port1.selection.set(bL); port1.set('PortType','Periodic'); % port1.set('ModeType','PlaneWave'); port1.set('PortExcitation','on'); port1.set('E0', {'0','1','0'}); % Ey polarization doR1 = port2.create('doR1','DiffractionOrder',1); doR1.set('m',1); doR1.set('n', 0);

%%% output port (right) %%% port2 = ewfd.create('port2','Port',1); port2.selection.set(bR); port2.set('PortType','Periodic'); port2.set('ModeType','PlaneWave'); port2.set('PortExcitation','on'); doT1 = port2.create('doT1','DiffractionOrder',2); doT1.set('m', 1); doT1.set('n', 0);

Regards Hammam

Modelling of carbonate dissolution

Sat, 20 Dec 2025 20:31:30 +0000

Hi all,

Thank you for your assistance. I am trying to model moving of boundaries as a result of carbonate dissolution in COMSOL. Is it possible anyone can help me with a file to get started with or a step by step approach to get a simple model (single pore model) done?

Sincerely, E.A

Union/Assembly

Fri, 19 Dec 2025 07:48:30 +0000

I am doing magnetic field study and made one U structure rectangular coil with an Air Domain. When I am forming a union, current is flowing is 1 or 2 legs of the coil and not in all 3,and forming magnetic field according to those conductors. When I am forming assembly, magnetic field is not being generated in Air but current is flowing in every conductor, How to resolve this issue!!!

The symmetry precision problem

Thu, 18 Dec 2025 01:52:20 +0000

Recently I'm using Comsol for BEM of static electric field. I found when the geometry is symmetric, there will always be a ~0.0001V asymmetry of the calculation results when the voltage of a specific electrode is set 1V. It remains even if I set the physical field as a symmetric one, and I also tried to reduce relative tolerance from 1e-3 to 1e-4, and it failed to fix that as well. Is this inherent to Comsol? I'll appreciate it if someone could help me with that.