Latest Discussions - COMSOL Forums

complex band structure

Mon, 13 Apr 2026 17:32:16 +0000

I am studying complex band structure of a 1D two-layer periodic unit cell consisting of:

One elastic layer One viscoelastic layer (with damping)

My goal is to compute and plot:

Real part of wavenumber (Re(k)) vs frequency Imaginary part of wavenumber (Im(k)) vs frequency

to identify attenuation regions (band gaps).

state space extraction from heat transfer models

Mon, 13 Apr 2026 14:54:41 +0000

Hello

I am trying to extract state space models of a 2D heat transfer models with phase change and radiation boundary condition, my input is laser beam and output is a pyrometer defined as a Gaussian weighted integration over an oval area on the surface.

the issue is that while extracting state space model with pyrometer the deviation between state space and FEM is very large while when using a point probe for extraction the deviation is not much, can you please help me have a better state space for pyrometer?

I use mphstate for model extraction

Electromagnetic simulation on non reciprocal magneto plasmonic material

Mon, 13 Apr 2026 11:17:39 +0000

Hello everyone,

I am positing on this forum because I am new to COMSOL software and I am actually working on meta surfaces. The article I work on is about magneto plasmonic where they use a dielectric material in which they put a ring of MO material in which there is a silver disk inside.

The thing is even though I understand and know the physics concepts behind I have no idea on how to simulate it on COMSOL so I tried to be helped with some tutorial and GPT but it is actually way too difficult since I think it's already advanced simulations.

I tried to create the structure in 2D but, after that, I have absolutely no idea what type of physics, study and mesh I should use and why.

Can someone help me with that or give me some examples or link to tutorial to that type of study?

The article name is "Nonreciprocal isolator based on a plasmonic magneto-optical resonator" if that could help.

I also attach my model file.

Thanks.

simulation of a Steam Generator

Fri, 10 Apr 2026 18:55:35 +0000

Good Evening all,

Me and my team have been perfecting this geometry from a year, and have finally arrived at this model for a steam generator (SG).

The SG is a straight shell and tube type heat exchanger, where water enters into the SG via the central inlet and exits out as steam.

The water stream is pressurised to 80bars. The water is heated through natural convection with the help of lead.

While, the appropriate physics have been added, while trying to simulate it with stationary, and time-dependant studies, our workstation runs out of memory due to the high number of DOFs that are being created even at the coarsest level.

Kindly help us regarding this, on how to simplify this model, or simulate this. We need the heat transfer and fluid profiles for this SG.

The file for this SG model has been attached below:

the mph file is 29MB even with the physics removed (it was 1.9GB with the physics and extra-coarse mesh) ...... what do I do?

Pressure Field - CFD

Fri, 10 Apr 2026 02:38:54 +0000

Are the pressure field results from the CFD simulation static pressure or total pressure?

Compression plots

Thu, 09 Apr 2026 18:19:54 +0000

Hello,

I am simulating a model to see the interaction of electric field of a tip (like AFM tips) on a electrostriction substrate surface. In the model, I am trying to insert a defect in the material. I need a plot of the strain or compression the surface suffers when the tip is polarized, which characterizes a electrostriction effect. But in the plot I could not find a way to plot the strain in 2D, just the stress. How can I plot the plot equivalent a compression effect in th results?

I have another question regarding the electrostriction effect: how can I add this effect? I used the coupling for electrostriction and added the Q electrostriction tensor, is this enough? It seems to me that I am missing something.

I am sending a printscreen of the physics I am aplying to my model, as the geometry of my problem too.

Hope someone can help, thank you. Hugs, TMV

Message (plus 1 internal DOFs)

Thu, 09 Apr 2026 15:57:12 +0000

What is the meaning of the message "(plus 1 internal DOFs)" ? Is it something I should be concerned about?

Plasma time periodic

Thu, 09 Apr 2026 14:28:39 +0000

Hello,

I am trying to simulate a CCP plasma, I looked into the COMSOL examples and they use cross sections for evaluating the coefficient rates, but instead I want to use rate constants which are dependents from the electron temperature. I tried to put directly in the equation space for the rate constant as ptp.Te, but I am having problems with division by zero. I am trying to see where is the zero problem, but I am not finding, can someone help me?

Thank you,

TMV

Wrong Q factor

Thu, 09 Apr 2026 10:27:00 +0000

I am simulating 1/4 of a SiN membrane suspended with 4 thin arms and clamped to the surrounding substrate, the membrane is very thin (100nm) but very wide and long (high aspect ratio managed using Swept function in the mesh) and the entire structure has an isotropic damping equal to 1/Q where Q is set to 100.

Performing an eigenfrequency study, I am expecting to find for all the modes a value of Q (that COMSOL evaluates automatically) equal to the value I set (100). Unfortunately, for the fundamental mode this doesn't happen; precisely, the Q of the fundamental mode is sometimes higher (120,130,150) and sometimes smaller (70, 80) than 100. In addition, every time I launch a new simulation run (even though I do not change nothing) the value of Q (and consequently the Real and Imaginary parts of the eigenfrequency) changes.

Is it normal? Is it a big issue?

Installation problem COMSOL Multiphysics 6.3

Mon, 06 Apr 2026 13:50:32 +0000

When I am installing COMSOL Multiphysics 6.3, I face these kinds of error: for reference I am attaching the screenshoot of an error.

COMSOL 6.4 Error

Sun, 05 Apr 2026 10:47:39 +0000

Cannot set up file java error java.lang runtime.exception.invalidroot directory cd : c

component variables and global parameters for this .mph file

Thu, 02 Apr 2026 21:34:37 +0000

I have access to v6.2, and this simuulation is uploaded to the COMSOL application gallery only as 6.4. I can still use the .txt file containing all of the formatted equations for rpi model phase change at the wall and in the 3d space as well as corresponding heat transfer equations. The phase change is modeled in the formatted equations that are defined in the parameters and in the variables.

Can someone using v6.4 send a .txt export of all of the parameters and variables?

This is the simulation i am referencing from the application gallery: https://www.comsol.com/model/subcooled-nucleate-boiling-with-extended-rpi-model-113081

Laminar Flow Not Affecting Electroanalysis Results — Dean Flow Not Observed

Wed, 01 Apr 2026 14:58:52 +0000

I am modeling a microfluidic electrochemical system in COMSOL using a two-step study: (1) a stationary Laminar Flow (spf) solution to obtain the velocity field, followed by (2) a time-dependent Electroanalysis (tcd) study for cyclic voltammetry (CV). The intention is for the velocity field from the laminar flow solution to be used in the electroanalysis step so that convection influences species transport and, consequently, the electrochemical response.

However, I am not observing any change in the CV results when varying flow rate or channel curvature (including geometries where Dean flow is clearly present in the velocity field). The concentration profiles at the working electrode appear unchanged across different flow conditions, suggesting that convection is not being accounted for in the electroanalysis solution.

In the time-dependent study step, Laminar Flow is unchecked (not solved), and I have set “Values of variables not solved for” to use the solution from the stationary study. Despite this, the electroanalysis results remain insensitive to flow.

Is there something I may be missing in properly coupling the laminar flow solution to the electroanalysis physics (e.g., enabling convection in species transport, required multiphysics coupling, or solver configuration)? Any guidance would be greatly appreciated.

Explicitly Modeling Reference Electrode

Wed, 01 Apr 2026 14:43:12 +0000

Hello everyone,

I am attempting to model a three electrode Microfluidic Electrochemical Sensor (MES). I am able to model the working and counter electrodes and get some results, but I believe they are incorrect. One reason I am thinking is because I am not explicitly assigning a boundary condition to the reference electrode. Is there a way to explicitly assign a boundary for the reference electrode and assign the correct physics? Any help would be greatly appreciated. I am using the electroanalysis physics.

How to extract the stiffness matrix K in multi-body dynamics (mbd) Transient simulation using MATLAB?

Wed, 01 Apr 2026 08:49:15 +0000

As the title indicates, when I attempted to use the mphmatrix function, I encountered an error: "The solution does not contain an active Variables node"

How are global evaluations of the displacement field done in a solid mechanics simulation?

Wed, 01 Apr 2026 07:57:16 +0000

I am doing an eigenfrequency study of a solid mechanics system. I have defined some variables, let's call them A and B, which depend on the "solid.disp" variable from the "Solid Mechanics>Linear Elastic Material" node (that is to say, the mechanical displacement magnitude) and the "displacement field", the dependent variable in the "solid mechanics" node. I then evaluate A and B under a "results>derived values>global evaluations" node. Now my question is, how will A and B be evaluated? The mechanical displacement should change as the mechanical system resonates, right? So is the solid.disp used in the global evaluation the maximum of the displacement magnitude or is it something else?

I am asking because I expect A > B and instead get A < B so maybe I am missunderstanding something about how the variables are evaluated. For both variables, A and B, involves an integral over the same spatial domain and B involves a derivative of the "displacement field".

RF Magnetron sputtering solving errors

Tue, 31 Mar 2026 10:44:14 +0000

Facing the following errors while solving, I need help with this.

Failed to find a solution. Singular matrix. Returned solution is not converged. Not all parameter steps returned.

"Divergence error" when simulating EM interaction between a Hall plate and a coil

Tue, 31 Mar 2026 06:05:59 +0000

Hello everyone,

I am currently working on simulating the electromagnetic interaction between a Hall plate and a surrounding coil in an IC, and I have run into a persistent convergence issue.

My coil model contains very small gaps (typically < 0.5 μm), and the coil itself is made of wide, thin metal (width ~30 μm, thickness ~0.5 μm). Because of this high aspect ratio, my simulation consistently fails with a Maxwell divergence error (e.g., divergence cleaning failed). Increasing the mesh density did not solve the problem; it only led to a severe out-of-memory (OOM) issue.

I have tried the following troubleshooting steps, but none of them resolved the error:

Using a Custom Mesh Sequence: I applied a "Free Triangular" mesh to the coil surfaces and used a "Swept" mesh across its thickness. For the remaining domains (the spherical air domain and the Hall plate), I used a "Free Tetrahedral" mesh.

Result: This effectively reduced the total number of mesh elements and memory load, but the divergence error still occurred.

2.Using "Remove Details" in Geometry: I tried using the Remove Details operation to eliminate small geometrical features in the air gap region.

Result: The divergence error persists.

These are the approaches I could think of so far, but I am certain I must be overlooking a critical setting (perhaps a specific boundary condition for thin structures?). Has anyone encountered a similar issue or can point me in the right direction to debug this?

Thank you very much for your help!

Implementing the floquet periodic condition in lshell

Mon, 30 Mar 2026 08:17:24 +0000

Hello, I have been trying to draw the dispersion curves of a layered composite material using the shell interface, which includes the floquet boundary condition, and I have obtained some results. But, it seems that the layered shell interface is better suited for this purpose, the problem am facing is that there is no implemented floquet boundary condition in lshell. Is there a way i can implement it easily. Thank you very much

Fixing Divergence Caused by Modeling Ambient Air Heated by Furnace

Mon, 30 Mar 2026 05:54:16 +0000

Hello All

I am a research intern who is attempting to model the effects of boring a hole into a furnace utilized at our lab as we wish to know how hot the surroundings will become due to this hole. I have had no issues creating the geometry, and the simulation converges and behaves just fine when it is just the furnace with the bored hole, but once I add a block of air above the furnace to model the ambient air around this bored hole my simulation consistently diverges.

To help picture the study I have attached a screen-shot of the model in question. The rectangle on top is the block of air causing divergence.

I am running a stationary multi-physics study of heat transfer in fluids and laminar flow. For physics, the air in question is assigned laminar flow and ambient initial conditions. Gravity is on, and as the air is a boundary of the simulation, I have assigned it the boundary condition of heat flux just like the rest of outer layer of the model to simulate convective cooling of this block of air from the ambient air around it thats not being explicitly included in the geometry.

To preface I am not well versed in FEA nor PDE's, so I am sorry if my question seems trivial or foolish. This problem also seemed quite simple to me but I cannot get anything to converge for the life of me so I am hoping someone who knows anything could potentially help. If any more information is needed, please ask and I will specify.

Thank you