Latest Discussions - COMSOL Forums

Unreasonable particle trajectories and invalid wall condition

Wed, 26 Nov 2025 02:59:25 +0000

Hello there,

I encountered some issues while using the charged particle tracing module in COMSOL. I have completed the simulation and obtained the particle trajectories. But some particles don't look very reasonable. A portion of the particles collided with my metal electrode and passed through it, but the surface of electrode was set with the wall condition "Disappear." I used a finer mesh and smaller time steps, but the situation did not improve. What method can be used to solve this problem?

Thank you all in advance.

Custom boundary conditions with identity pair

Tue, 25 Nov 2025 10:21:10 +0000

Hi,

I have a 3D model of a pile which is embedded within a cylinder representing the soil; both are thus modelled as solid mechanics. I have created the model using assembly, meaning I have identity pairs on the boundaries that are in contact.

What I want to achieve is to enforce compatibility and equilibrium only in the horizontal directions, by default continuity enforces all directions. I have not found a way to do so.

I have thought about using contact pair, however I want to remain in the frequency domain; which should be possible.

I did find a seemingly related thread on this discussion form on Google, however that page apparently does not exist anymore.

Thanks in advance!

Line heat source rotating like the handle of a clock

Tue, 25 Nov 2025 08:43:12 +0000

Hello fellow comsol users,

I am trying to model a heat line source rotating about the center of a circle. While I have seen a lot on rotating heat sources (mostly ways to model rotating or moving laser sources); i cannot for my life think of a method to make it work for a rotating line source. Maybe I am thinking too complicated here.

Also, the heat line source feature seems to work only on edges that are fixed in the geometry, so that doesn't work either.

If any of you have faced this problem yourselfs or has an idea on how to implement it, I would be grateful for any advice you can share.

Thank you in advance! André

PS: I only have the basic license and the heat transfer module license available. If your solution requires another method, please mention the module name as well. Thanks!

State Variable in 6.3

Mon, 24 Nov 2025 19:31:03 +0000

I'm trying to define a state variable in 6.3. I have enabled Variable Utilities in the Model Builder, and I can access that ribbon in the Definition branches, global or component. But State Variable does not appear as an option. What am I missing? Thank you!

How to measure the band structure in the linear potential flow frequency domain

Sun, 23 Nov 2025 07:42:07 +0000

In acoustic, linear potential flow frequency domain, measurement of band structures. As a beginner in COMSOL and unable to find relevant cases, the supplementary materials in the literature suggest(To calculate band structures, we set the Floquet periodic boundary conditions by setting ‘Pointwise Constraints’ to introduce the Bloch phase shift to the eigenfields. ) However, I am not yet familiar with the specific operations involved, such as setting expressions

Client PC Cannot Connect To The Host/Server PC

Thu, 20 Nov 2025 05:49:34 +0000

Successfull in installing and run as server, as well as client on host PC. However, cannot connect a new client PC to the server/host PC.

Simulation of Ecoflex 00-30

Wed, 19 Nov 2025 20:09:57 +0000

Hi, I am trying to simulate a solid and a hollow cylinder made of ecoflex 00-30. I have used different hyperelastic material model values i.e. Yeoh, Ogden, Mooney-Rivilin, etc. from different research papers, yet, I failed to converge the solution in COMSOL 6.3 & 6.1 (both version).

I don't know, what boundary conditions and solver settings are missing, the model is 3D and dimensions are in millimeters.

How to know which solver settings and boundary conditions are required to solve the simulation correctly?

Thanks,

PDE for Modeling Liquid Interfaces

Wed, 19 Nov 2025 17:33:38 +0000

Hello!

I would appreciate some help, as I am trying to solve a partial differential equation of a type I have not worked with before. This PDE models the boundary of a liquid as a radius, , which is a function of the 2D plate the liquid is "sitting" on, such that :

where and are constants. The plate is bounded at the ends by circular plates such that .

It is my understanding that this equation cannot be put into divergence form, which is required by the Coefficient Form PDE interface. As such, I am wondering if there is another COMSOL interface which is best equipped to solve this kind of PDE or if there is another way to still use Coefficient Form PDE.

Thank you in advance for any assistance.

Plate displacement and force due to halbach array

Wed, 19 Nov 2025 10:43:04 +0000

I am working on a problem, where the circular permanent magnets halbach array is rotating using external motors over a Aluminium plate. Due to the flux of time-varying magnetic field, a electromagnetic force is experienced by the halbach array, making it levitate. I am trying to simulate this situation, to calculate the forces acting and the steady-state levitation height of the halbach array. I have tried to simulate it in two ways, first case in which the halbach array is fixed and the aluminium plate rotating with the surrounding region is taken as deformable zone and account for the forces and displacement of plate, and second case in which the plate is rotating at a fixed location and the halbach array inside a deformable region with the forces and displacement of the array. Currently, I have taken the reference from a example problem from application libraries named "electrodynamic_levitation_device". My simulation is running but getting stuck at 4-5% progress. Kindly guide me, I have the attached the .mph files for the both cases.

Modeling the vibration of microbubbles in Thermoviscous Acoustics

Wed, 19 Nov 2025 09:19:15 +0000

Hello,

I am trying to simulate the acoustic streaming around a microbubble under acoustic actuation. To do so, I coupled Pressure Acoustics with Thermoviscous Acoustics and defined surface tension at the bubble interface. First, I did Eigen study and found the resonant frequency. Then, I did frequency domain study at the resonant frequency I found, and use the results of the frequency domain study in a stationary study for Laminar flow to see the acoustic streaming. The problem is that the simulation result doesn't match the experiments. When I check the mode shapes of the bubble interface in Eigen study and Frequency domain study, they are not the same, while I think they must be the same because they are at the same frequency.

Can somebody help me with this contradiction?

Best, Ali

Transport of Concentrated species & Laminar flow

Wed, 19 Nov 2025 02:44:16 +0000

Hello,

I am a Nuclear science and technology doctoral student and I wish to simulate hydrogen & Helium mixture separation by palladium membrane. (Tube shaped) Here is the question.

Case Overview: This study involves helium-hydrogen mixture transport through a pipeline lined with a palladium (Pd) membrane. Hydrogen is able to permeate through the membrane walls, while helium remains confined and flows only within the pipeline.

Boundary Conditions: Constant inlet mass flow rate, Constant outlet pressure, Uniform temperature along the entire pipeline

Model Setup: A coupled model: using the Transport of Concentrated Speciesand Laminar Flow interfaces. Strong coupling between mass transfer and fluid flow is achieved via the Reaction Engineering functionality.

However, the simulation yields unphysical results, as described below. Observed Anomaly: As the He–H₂ mixture flows through the pipeline, hydrogen permeates outward through the Pd membrane. The total mass flow rate of the mixture is expected to decrease along the flow path, and the mass flow rate of helium should remain constant across any cross-section of the pipeline. However, the current model shows a constant flow velocity along the pipeline, while the mass flow rate of helium increases toward the outlet. This results in a higher helium mass flow at the outlet than at the inlet—indicating a clear violation of mass conservation. Visually, it appears that the model artificially compensates for the loss of hydrogen by increasing the helium content.

Objective: Identify the root cause of the mass non-conservation and adjust the model such that the flow velocity decreases gradually along the pipeline, consistent with physical expectations.

It would be of a great help if anybody could guide me on these.

Thanks, Leopold Jiang

COMSOL Multiphysics® Version 6.4 is now available!

Tue, 18 Nov 2025 15:29:12 +0000

We're pleased to announce the release of COMSOL Multiphysics^® version 6.4.

Highlights include:

Enhanced solver performance with the new NVIDIA CUDA® direct sparse solver (cuDSS) for NVIDIA^® GPUs for single-physics and multiphysics simulation
Structural explicit dynamics including support for nonlinear materials, for simulating impacts, blasts, and drop tests
Granular Flow Module: a new product that can be used to simulate the motion and interaction of solid particles in bulk processes, for applications such as conveying, mixing, and additive manufacturing
Support for OpenAI API-compatible models within the Chatbot window
Improved workflows for geometry and meshing

See the complete list of new features and download version 6.4 here: https://www.comsol.com/release/6.4

Issue with wave optics simulation

Tue, 18 Nov 2025 12:38:01 +0000

Hi say i am creating a box(air domain). n=0,k=0 (Refractive index) .

Using two port1 and port2 at opposite face and on other face i am assigning periodic boundary condition. Now i am getting 100% reflection and 0 % transmission. But if i am doing the same thing with microwave frequency range (RF module) i am getting 100 % transmission but not reflection which is correct. But why i am getting unusual results for infrared.

PCM Material based metasurface Phase graph re-simulation

Tue, 18 Nov 2025 04:23:40 +0000

Hello everyone, I am a student working on a PCM-based metasurface for amplitude and Phase modulation in COMSOL in ewfd. I am re-simulating the Fractional crystallisation of GST's amplitude and Phase from the paper "Reconfigurable multifunctional metasurfaces employing hybrid phase-change plasmonic architecture".
I have almost obtained the amplitude modulation, but the problem is the phase modulation, which is totally opposite to it. I have used Arg function and mod function, but the result is still not the same. I would be thankful if someone has the solution for this in Comsol.

Modelling Inflation

Mon, 17 Nov 2025 15:29:38 +0000

Hello, I am hoping to model how an air bladder inflates and how pressure changes. I am trying to create a weight-bearing inflatable and need a way to model this process. I am super lost with where to start so any help or advice would be greatly appreciated.

Correction in the theory manual: Nonlocal Plasticity Equation

Mon, 17 Nov 2025 14:34:34 +0000

Dear Community and Moderators,

I think I have found a mistake in the COMSOL documentation of nonlocal plasticity: https://doc.comsol.com/6.0/doc/com.comsol.help.sme/sme_ug_theory.06.30.html#4121532

Please see the first strong form equation there which I have quoted below:

In the equation, I think the term should not appear as it makes the equations dimensionally inconsistent.

Please let me know if I am wrong. Happy to hear counter arguments and discussions.

Cheers, Ratul

Object stacking problem

Mon, 17 Nov 2025 08:30:05 +0000

For a single object, I applied a 'prescribed displacement' to achieve compression, but after stacking multiple objects axially, using 'prescribed displacement' only compresses the bottom object, while the objects above it do not change at all, causing the simulation to fail.

Parametric Scan

Sun, 16 Nov 2025 07:56:08 +0000

I want to perform a parametric scan on three parameters a, b, and c. a scans from 0 to 30 with a step of 1. After a reaches 30, b starts scanning from 0 to 30 with a step of 1. After b reaches 30, c starts scanning from 0 to 30 with a step of 1.

Making Kymograph plot?

Sat, 15 Nov 2025 15:44:33 +0000

I'm fairly new to Comsol and have difficulties with the following: I have a time-dependent simulation that gives me a concentration as a function of space and time. The geometry and simulation is axially symmetric. I'd like to make a kymograph plot where one axis is time and the other is r, with color coding of the concentration. How can I make this happen? Thank you!

Simulation Times Increasing with LiveLink for MATLAB

Thu, 13 Nov 2025 14:36:45 +0000

I've been running automated simulations with LiveLink for MATLAB, where each run makes small geometry changes, remeshes, and solves. I’ve noticed that while early simulations take ~45 minutes, after 20–30 runs, the simulation time increases a lot (more than twice), even though the problem size stays the same.

Has anyone else experienced this slowdown?

Are there best practices for preventing resource issues or memory leaks when using LiveLink for MATLAB for multiple runs? Is it helpful to restart the COMSOL server periodically, and if so, how do you safely restart it without physically clicking from the start menu?

Would appreciate any advice!