Latest Discussions - COMSOL Forums

Modelling Radial Fans as Flow Control in a Turbulent Flow Component

Thu, 13 Nov 2025 09:02:58 +0000

I am trying to simulate the airflow using the k-epsilon model in a ventilation system that uses radial fans. There are resistances before and after the radial fan, so I cannot simulate inlet path and outlet path separately. These radial fans naturally induce a 90 Degree bend as opposed to axial fans. There is an interior boundary condition called "Interior fan", which seems to be able to simulate axial fans only. Any ideas How I could simulate a radial fan? If I simply put the interior fan next to the intake our exhaust of the radial fan, I would severely underestimate the airflow because then the centrifugal fan space acts as an extreme bend and I also run into convergence issues.

I was thinking about skipping the volume of the fan that spins entirely by connecting an inlet where the fan exhaust, and an outlet where the fan takes in air, with the space between them just not part of the simulation, and the airflow through the outlet (fan intake) is "teleported" to the inlet (fan exhaust). I have so far not been able to figure out how to do this and do not know if it is possible.

Best Regards, David

Undefined value found in the stiffness matrix.

Thu, 13 Nov 2025 06:42:39 +0000

I was simulating the Darcy flow-fracture module and introduced pressure-dependent permeability and porosity. Then, I performed calculations on a two-dimensional rectangular area containing several simple fractures. However, within less than three seconds of computation, the following error popped up:

Undefined value found.

Details: There is an undefined value in the stiffness matrix. There are 229721 equations, and NaN/Inf appears in the matrix rows for the variable comp1.p. At coordinates: (140,60), (139.079,59.1385), (139.586,58.4897), (138.92,58.3842), (137.275,58.76), ... Similarly, NaN/Inf appears in the matrix columns for the degrees of freedom.

Based on this error message, I attempted the following steps:

Adjusted the mesh density.

Handled variables that might result in zero in the denominator. For example, I rewrote "a/p" as "a/max(p, 1e-7[MPa])".

Checked the boundary conditions to ensure no conflicting Dirichlet boundary conditions were applied to two adjacent boundaries. In reality, the external boundaries of the model are all set to no flow, and a pressure condition is only applied at the midpoint of one boundary, using a step function to ensure a smooth transition of the pressure at that point.

After taking these measures, the error still persists. The error coordinates are concentrated in the upper-right and lower-right corners of the rectangle. How can I resolve this issue?

Skin Effect Not Visible in Electric Currents (EC) Frequency Domain Simulation

Tue, 11 Nov 2025 17:50:20 +0000

Hi everyone,

I'm trying to visualize the skin effect in a tungsten cylinder using the Electric Currents (EC) interface in the frequency domain. I’ve added a Terminal and a Ground, and set the excitation frequency to 1 MHz.

I also refined the mesh near the boundaries using Boundary Layers (to capture the skin depth), but the current density distribution still looks uniform it behaves as if it’s a DC simulation.

Could anyone explain:

How to correctly make the skin effect visible in EC (without switching to the Magnetic Fields or EM Waves interface)?
Whether this setup can actually capture the skin effect, or if the EC interface inherently behaves as a low-frequency (quasi-static) solver?

Thanks in advance!

Current in a custom racetrack coil

Tue, 11 Nov 2025 14:52:35 +0000

I have a racetrack coil that is imported from CAD and I am having trouble exciting current in it. I have no error messages but no flux at all.

MoS2 based Transistor

Tue, 11 Nov 2025 10:41:31 +0000

To the COMSOL Community and Experts,

I am writing to request assistance with a convergence issue I am encountering while using the COMSOL Semiconductor Module.

My objective is to replicate a simulation based on a publicly available model of an MoS2 + HfO2 transistor (which I will refer to as the "2nd file"). I have constructed my own project, "MoS2_transistor" (the "1st file"), by carefully transferring the physics, parameters, and mesh settings from the reference model.

A critical problem has arisen: while the reference model (2nd file) computes and converges successfully, my implementation (1st file) consistently fails to converge and terminates with an error.

Given that the reference file functions correctly, I suspect there may be a subtle discrepancy or setup error in my project file that I am overlooking.

I would be extremely grateful if an expert could offer guidance or insights to help diagnose and resolve this convergence failure.

Thank you for your time and consideration.

Sincerely,

2D Fracture Network Generation

Tue, 11 Nov 2025 10:02:42 +0000

I currently working on discrete fracture networks. I wanna analyze via Monte Carlo approach multiple DFN´s. I know that there is the integrated Add-in (Discrete Fracture Network) but it is for me not possible to process the simulation with different networks.

Maybe anyone has a nice idea or work around for that. :)

Greetings Dominik

heat loss and temperature of microantenna structure

Tue, 11 Nov 2025 07:54:39 +0000

I am trying to model a loop antenna of micron dimensions for emitting magnetic field for NV diamonds.

So far, i have used the RF module to understand the strength and homogeneity of magnetic field emitted. I would like to study the the temperature of the antenna in use, to see if it is operable without breaking up, for which i believe the Heat transfer from solids, and microwave heating is the intended modules to be used.

However, no matter what i try, the temperature in the end remains the same, which isnt what i hoped to see.

I figure im new to using the heat transfer module, so id appreciate any kind of help

IDT based piezoelectric magnonics device

Sat, 08 Nov 2025 02:46:39 +0000

Hi there. Is there anyone who is working on piezoelectric, electrostatic and Micromagnetic modules (developed by professor Weichao Yu). I am having issues in coupling the surface acoustic wave developed by IDT device to mmf modules.

Exporting the results of a simulation and using it as boundary conditions for a new simulation

Fri, 07 Nov 2025 12:44:47 +0000

Hi, I have made a simulation of magnetic field in 2D axisymmetric model and I would like to use the 3D result of magnetic field of that simulation as boundary conditions for a new 3D simulation where I would like to add other features. Is there a way to implement that?

Unknown expression in Random Vibration example model

Thu, 06 Nov 2025 11:40:08 +0000

I'm trying to replicate one of COMSOL's example models, called "Random Vibration Test of a Motherboard". I'm following this example to learn how to apply this study in another simple mode. The the motherboard example there is an expression that I have been unable to identify its origin or definition.

In Component1>Definitions>Variables1 there are three variables called a_absX, a_absY and a_absZ, they are defined by an average function aveop1() and an expression solid.a_abs_rvX, solid.a_abs_rvY and solid.a_abs_rvZ. Where each is described as an Acceleration in each direction.

I have been unable to find/identify where solid.a_absX(YZ) is defined. If I use it in my own model, when I try to evaluate the 'Global Evaluation Sweep' that contains this variable as rvib1.psd(a_absZ) I get an error saying thet solid.a_abs_rvZ is an undefined variable.

Could someone please explain where/how the solid.a_abs_rvZ(XY) expression is defined? Best regards.

natural frequency

Thu, 06 Nov 2025 07:52:20 +0000

hi i am simulating a cylinder shape cavity to find the natural frequency. we did the experiment before in the laboratory but by simulating i can not get the exact result. i am wondering if i have applied the right boundary conditions to the model. the cavity put on the foam on the table during the experiment but in the simulation i have just drawn the cavity without foam underneath and applying fixed constraint boundary condition to the walls. what is the problem with my simulation and how can i get the exact result.

Request a trial passcode

Thu, 06 Nov 2025 06:04:40 +0000

Hello,

I would like to request a trial access code for COMSOL Multiphysics to evaluate its capabilities for my research/work/project. Please let me know if any additional information is required.

Thank you for your assistance.

Best regards, Lakshmi B M S Ramaiah Institute of technology

Adding Sheet Resistance

Tue, 04 Nov 2025 14:45:42 +0000

Hi, I want to add sheet resistance to my simulation. The thickness of substrate 1mm and above which there is printed ink structure having a sheet resistance value say R_s. I want to obtain the microwave reflection characteristics of the FSS. There is no option to add sheet resistance. (In impedance boundary condition or in transition boundary condition there is only option to add conductivity (S/m)) not sheet conductivity(S).) The thickness of the ink layer is unknown to me and it is very small compared to the thickness of substrate. Is there any way to add sheet resistance. (may be through some boundary condition or structure or any other way)

Use solution of one study as initial particle position for another without exporting

Tue, 04 Nov 2025 10:06:49 +0000

Hello there,

I am currently working with the Mathematical Particle Tracing module, although this question extends to at least the Charged Particle Tracing module.

Is it possible to use the final particle positions from one study as initial positions in another study without using the "Release from Data File" function?

I have an assembly split in two because one features rotating parts and uses the Rotating Frame domain while the other half does not. I will have to run this simulation for different values, maybe with a parametric sweep, so having the workflow a bit more streamlined would be a great time saver.

Thank you all in advance.

Request for Trial Access — Electrochemistry / Electrolyzer Module

Mon, 03 Nov 2025 17:49:53 +0000

Hi COMSOL Team,

I am a PhD scholar (Chemical Engineering) at IIT Kharagpur. Our group currently uses a COMSOL license but we do not have the Electrochemistry / Electrolyzer Module. We are evaluating purchase of this module and would like temporary trial access to test our models and confirm fit before buying.

Could you please provide details on trial availability and the process to enable the Electrochemistry / Electrolyzer Module for our license?

Thank you, Rajeev Ranjan PhD Scholar, Dept. of Chemical Engineering IIT Kharagpur

excessive virtual memory on macOS on Apple Silicon Macs

Mon, 03 Nov 2025 12:42:10 +0000

I'm running Comsol Multiphysics on macOS, tested on two Apple Silicon Macs: an M1 Air with 8 GB RAM and an M3 Air with 16 GB RAM. In both cases, Comsol reports around 450 GB of virtual memory available, while the actual physical RAM is correctly recognized.

So far, I haven’t encountered any simulation errors or crashes - everything runs normally. It seems the reported value represents the addressable virtual memory rather than real physical memory, which might be misleading but does not appear to affect performance.

Is it possible to introduce an abrupt potential change at an interior boundary?

Mon, 03 Nov 2025 07:41:22 +0000

Hi all, when I handle an electrostatic double layer, i.e., a thin dipole layer, the potential would abruptly change across the interior boundary, is it possible to handle such a discontinuity for the classical PDEs or the electrostatics module? Thanks.

seismic aquifer response

Mon, 03 Nov 2025 07:25:19 +0000

Hello, I want to simulate the subsurface temperature changes caused by earthquakes. I suppose the approach is to first simulate the equilibrium state of the study area under natural conditions in Study 1, then add the influence of earthquakes in Study 2 to observe the evolution of subsurface temperature. However, I have encountered some troubles with the simple initial state. Should the initial flow field be relatively stationary on a large scale? But there is always an initial flow field in my simulation.How to build a sample well-aquifer model with a stable state?

Integral of a distance field over domain as boundary condition

Fri, 31 Oct 2025 06:58:45 +0000

I'm dealing with a Laplace problem on a domain with a Dirichlet boundary condition. And the boundary value is given by , where is the distance between the points and ( may be a subset of ). Any hints on the solution? Thanks.

Photonics Research

Thu, 30 Oct 2025 15:05:35 +0000

Hi, I am a Ph.D. student. How to learn COMSOL Multiphysics for photonics research?