Latest Discussions - COMSOL Forums

Reg- Microbalance sensor

Tue, 14 Oct 2025 03:05:34 +0000

Dear Staff, Good morning, I would like to simulate Mass sensor based on graphene. Could you assist me or send any related model to start.

thank you

TFLN rib waveguide - optical field results not showing

Mon, 13 Oct 2025 10:08:50 +0000

Hello everyone, I am trying to simulate the optical field of a rib waveguide in lithium niobate. I attached an image of the cross section, together with the mph file. I first defined a work plane and extruded it to create the structure. I defined the materials and inserted a diagonal refractive index for the lithium niobate since it is an asymmetrical material. In the end I defined the ports and inserted the mesh, and launched everything.

The problem is that the program runs and ends the simulation, without any shown error, but at the same time it doesn't compute the electrical field. In fact, the electrical field section under "Results" doesn't exist. Why is that?

Solver Convergence Issue in 2D Brinkman Flow through Anisotropic Porous Medium (Wavy Channel)

Mon, 13 Oct 2025 05:07:18 +0000

Hello,

I’m simulating steady-state flow in a 2D wavy channel using the Brinkman Equations interface (COMSOL Multiphysics 6.0). The flow domain is an anisotropic porous medium confined between two impermeable wavy walls.

MODEL SUMMARY: * consists of a wavy bottom that i defined using parametric curve * upper top plate is a moving plate with velocity lets say U0 in x direction and 0 in y * the left and right walls are not moving * No slip condition is applied for all * Physics used is brinkaman equation where the porous matrix is set to be a diagonal matrix where the diagonal entries were already defined in the parameters under global definitions. * Physics controlled mesh is used. * stationary study is added.

ERROR:

Failed to find a solution. Maximum number of Newton iterations reached. There was an error message from the linear solver. The relative residual (0.041) is greater than the relative tolerance. Returned solution is not converged. Not all parameter steps returned.

TRIED SO FAR: * Adjusted tolerances and damping * switched between direct solvers * increased iteration limits

QUESTIONS: * Recommended solver setup (Fully Coupled vs Segregated) for Brinkman flow? * Tips for stabilizing convergence in anisotropic, wavy porous domains? * Any scaling or nondimensionalization suggestions?

Any help to stabilize or improve convergence for this steady Brinkman model would be appreciated.

Regards!

Regarding the issue of the presence of both the paranoid coil and the incentive coil simultaneously

Sat, 11 Oct 2025 09:30:41 +0000

I want to conduct a simulation of a transducer. The overall structure is a cylinder. The coil part consists of an inner bias coil and an outer excitation coil. The bias coil provides a constant bias magnetic field, while the excitation coil provides an alternating magnetic field. How should I set up the bias coil to be energized by direct current, and the excitation coil to be energized by alternating current of a certain frequency?

How to add multiphase material in COMSOL 6.0

Sat, 11 Oct 2025 08:30:07 +0000

I am trying to replicate the capillary filling model for two phase field in COMSOL 6.0. How to add a multiphase material? If we add from material library, how to specify the phases?

Potential Field in Electro-osmotic Flow

Fri, 10 Oct 2025 09:19:25 +0000

Hi all,

Currently I was trying to reproduce results from a research paper titled from Choi et al. (2011), (attached below). In that paper, two boundary conditions are used at the interface for electric potential. These are (i) potential jump and (ii) simplified gauss law at the interface. Now, while modeling using the 'es' physics in COMSOL, I am not able to see how to model both the conditions at the interface.

I have attached my trial file, in which when I tried putting these conditions at the identity pair, the surface charge condition (gauss law) was getting overridden or fallback-ed due to the potential jump condition. From my understanding, COMSOL isn't letting me put both at the same time. I tried using a coefficient-form PDE to solve it too but it had the same issues with the interface conditions.

What could be a potential fix to this? Is there another way to model the system as given in the paper?

Dual gate MOSFET design

Wed, 08 Oct 2025 05:08:55 +0000

Can anyone give any guideline regarding the design of dual gate MOSFET in COMSOL?

Gaussian Beam Plane Wave Expansion

Tue, 07 Oct 2025 21:21:26 +0000

Hi, I just recently learnt that the paraxial gaussian beam equation is not really effective for a scatterer surrounded by inhomogeneous domains when using the scattered field formulation. it was proposed I use the plane wave expansion approach. for a 3D model, has anyone used the plane wave expansion approach using equations. I have attached my model of the paraxial approach. you can edit my model to suit the plane wave expansion method or if you have any example. That will be great.

NaN/inf value error

Mon, 06 Oct 2025 08:40:48 +0000

I'm trying to simulate a cylindrical gas bearing with a sort of foil "floating" on it but I keep getting the same error: Undefined value found. - Detail: Undefined value found in the equation residual vector. There are 7 degrees of freedom giving NaN/Inf in the vector for the variable comp1.spatial.u. at coordinates: (1.94255,-0.112035,0.0920496), (1.94284,-0.111364,0.09286), (1.94356,-0.111577,0.092605), (1.94329,-0.111264,0.0930404), (1.9433,-0.111842,0.0923323), ...

I don't think my mesh is the problem as well as my boundary conditions. I suspect it is something to do with my geometry although I also have the feeling that is correct as well. The model was working when I used the fluid-structure interaction model but I wanted to model smaller thickness of the foil and decided to change to fluid-shell interaction but then it did not work anymore whilst the boundary conditions basically have not changed compared to the previous model that did work. To get a surface from my previous model I have used the tool "Convert to surface" where I had a finite thickness ring around the gas bearing. What could be the problem here and where should I be looking to solve this problem?

Issue With Object Contact

Sun, 05 Oct 2025 22:49:07 +0000

Hi everyone,

I have been trying to model a basic piezoelectric compression model involving two domains. I have one block on top which represents a steel mass and another block on the bottom which is meant to model piezoelectric paper.

I am very new to using COMSOL and am currently having trouble getting the two blocks to connect. When I apply a boundary load to the piezoelectric paper block and perform a stationary study, it works just as intended. However, when I place the block on top (in the assembly) and apply a Continuity to both domains of the Identity Boundary Pair (the two touching faces), I can't seem to get a solution that converges. I also apply gravity to both objects and put a fixed constraint of the bottom face on the paper.

I can imagine this issue is likely due to the meshing as I am currently trying to use the Normal, Physics-controlled mesh. I wanted to try to build a User-controlled mesh in which the mesh gets finer when it is close to the point of contact for both objects. However, when ever I try to build a User-controlled mesh it never seems to work (the mesh is not physically displayed).

I can't imagine that the fix is too challenging, but I have been stuck on this problem for quite some time. If anyone has any suggestions or ideas, that would be greatly appreciated!

Implementation of Weak Form PDE from PDE interface for battery charging discharging cycle

Thu, 02 Oct 2025 14:00:04 +0000

Hello,

I'm trying to build a Lithium-ion Battery model using Weak Form PDE from PDE interface in mathematics module, not using the lithium ion battery physics in Batteries module.

I want to implement a charge-discharge cycling condition using Weak Form PDE from PDE interface in mathematics module, but I don't know how to do this.

I know the way to applying the charge-discharge cycle in Lithium Ion Battery Physics, but I want to know the way to applying the charge-discharge cycle using Weak Form PDE from PDE interface Physics.

Please provide the way, how can i Implement this?

Thanks for reading,

Prakash

Plot of temperature along a line inside of a thin layer

Wed, 01 Oct 2025 16:20:37 +0000

Hello

How can we plot the temperature along a line inside a thin layer? The line is parallel to the thin layer surface. I manage to do the surface graph of the temperature on the layer, but I would like to do the plot of the temperature only on a line. I've tried several approaches with the command atxd but they didn't succeed.

Thank you

Mass conservation in COMSOL

Tue, 30 Sep 2025 20:32:41 +0000

Hi! I am using Heat transfer in solid and fluids module where phase changes from solid to fluid with larger density difference. I have integrated Laminar flow too to account for fluid movement. The phase change is working and the mesh size remains the same. How is it possible as the Laminar Flow module uses mass conservation equation too without any change in mesh shape? Thanks in advance.

Conditional parametric sweep

Tue, 30 Sep 2025 16:03:11 +0000

I'd like to run a parametric sweep with a couple of conditions. Here is an example of what I'm trying to do.

a = range(1:1:10) b = range(1:1:10)

The condition I want to add is a+b<15

Can I do this directly in COMSOL?

Alternatively I generated the combination on MATLAB but when I am having the file read by COMSOL through a saved text file. It is saying Failure reading file. '1' is not a valid variable name.

Could you please help me troubleshoot either of my methods. I'm wondering if the way the data is output from MATLAB is not compatible with COMSOL.

Thanks and regards VK

Error in geometry modelling

Tue, 30 Sep 2025 12:49:42 +0000

Im trying to model geometry to simulate an antenna, but i find that the difference operation shows that the object is empty. Furthermore, when applying materials to the geometry, some of the shapes cant be selected despite what ive tried.

In comparison, when using an older version of COMSOL 5.3, this error doesnt seem to happen. Kidly let me know if there is anything i am missing, or is this a software issue.

I have added the file for reference.

Import fractures of porous media as STL file

Tue, 30 Sep 2025 12:44:04 +0000

I want to import fractures set in STL format from Fracman software, however, It cant be recognized as fractures in COMSOL and It does not appear in Darcy's law. Is there any different options for that as DFN network from COMSOL can be recognized and proceed with the simulations.

Its really important for me as I'm stucked in this step.

Error for LiveLink with MATLAB

Mon, 29 Sep 2025 10:50:33 +0000

Dear all,

I convert the COMSOL simulation model file to run with LiveLink in MATLAB. When I run the .m file, the import commands work, but the command ModelUtil.crate does not.

The command window gives:

Unable to resolve the name 'ModelUtil.create'

Error in (line 10) model = ModelUtil.create('Model')

I am using COMSOL 5.6, Matlab 2022b on Ubuntu 18.04.6 LTS

How can I fix this?

Thank you in advance.

Coupling of 1D and 3D Pipe Flow (nonisothermal flow)

Fri, 26 Sep 2025 16:58:13 +0000

Greetings: I am attempting to transfer flow conditions from a 1D nipfl (nonisothermal pipe flow) outlet to a 3D nonisothermal flow (nitf) domain inlet, however, I have been having trouble making this work.

The idea is simple: use the 1D mass flow rate (or pressure/velocity conditions) and outlet temperature and then use this data to produce an averaged value across the 2D fluid face for a 3D domain and continue analysis from there.

I understand normally you can use features like "pipe connection" for coupling 1D to 3D features, but I'm reasonably sure that nipfl is not supported for this, as I cannot apply this multiphysics feature with the current physics present.

Supposedly this can be done with general extrusion (1D point to 2D face projection), however, I have not successfully figured out how to make this work from the documentation I have read.

Current simple test model is attached. It is meant to be a continuous uniform ID pipe with a thermal condition on the 1D length for testing purposes of this concept. Thanks.

Calculating Leakage and Magnetizing Inductance in a Simple Transformer Model

Wed, 24 Sep 2025 18:11:15 +0000

Hello.

I am making a COMSOL model of a simple transformer with a primary 4 turn coil and a secondary single turn coil around a ferrite core. I was wondering if it was possible to calculate leakage and magnetic inductances in COMSOL with the model I have setup. Currently the only inductance values I can find are those of the individual coils.

My MPH file is attached below. Is the model I made too simple to undergo such analysis?

Thank you

Regarding contact - transient - impact

Wed, 24 Sep 2025 05:33:32 +0000

Now I have a problem with simulating the "stopper" structure (that is, one movable and one fixed constraint). The main small exploration is whether the structure will fail after the movable structure hits the stopper, such as damage or stress exceeding the limit. Assuming the gap between the movable and fixed is 2um, then I apply a load to the movable part, and the displacement of the movable part exceeds the gap, for example, the simulation result shows that the displacement of the movable part is 20um. However, through stress extraction, it is found that the stress has not exceeded the limit, and there is also a contact force in the contact setting. So I'm wondering if increasing the penalty factor is feasible, that is, will it prevent the displacement from being so large? Or are there any other suggested methods?!!