Latest Discussions - COMSOL Forums

Calculation of core losses in a transformer

Fri, 01 May 2026 06:14:09 +0000

After referring the ecore_transformer documentation in the application library, i am trying to calculate the core losses using the Steinmetz equation using the time dependent study followed by time to freq losses.

Using the solid conductors with current excitation at input and External I vs U as coil excitations, the error as "The Current excitation is not supported for Single conductor coils in time dependent studies."

Whereas with External U vs I excitation, the Pardiso and Assembling matrices are keep progressing with the compute and solution progress as constant hence no convergence data is coming. Can you help where I am doing wrong.

Can Parametric Surfaces Be Turned Into Volumes?

Fri, 01 May 2026 02:18:05 +0000

Hello

This question is pretty simple in nature. I am attempting to model a tube with a rectangular transition in the middle. There is a screenshot of the geometry in question below for context. I am working on COMSOL version 5.2a, so to create this geometry, I opted to do so using a parametric surface. I did so using a super ellipse parametric equation, and as it was a surface I wanted to turn it into a volume by unioning endcaps and using the convert to solid function on the union.

This workflow has failed repeatedly. As such I attempted to see if I could get convert to solid to work for more simple cases, and defined a simpler hollow cylinder as a parametric surface and attempted to utilize union and convert to solid to turn it into a volume. This also failed, and subsequent attempts with trying to turn other simple surfaces into volumes like cubes have also not worked.

I have only seen videos of convert to solid being utilized in 2d, so I wanted to ask if utilizing convert to solid on 3d surfaces is fruitless as I have had no successful attempts and cannot find any examples online.

If so, does anyone have any suggestions for creating smooth transitions in 5.2a? I do not have access to a loft function in this version it seems, and I also can only import STL's, rather than another form of CAD file. I have had very poor experiences with the quality of STL imports, so the idea of creating the geometry in Solidworks and importing it also is failing me.

Thank You

Adding a Rotating Wall in the Euler-Euler Interface

Tue, 28 Apr 2026 19:24:23 +0000

Hello all,

I am trying to model a rotary tube reactor, where I am trying to model two phase gas-solid flow inside a rotating domain. I am using Euler-Euler for the two-phase flow and I have added a rotating wall to prescribe the rotary motion of the external wall.

A part of the geometry is as shown in one of the images. I want to rotate the outer wall and solve for the flow in the domain highlighted in blue. However, the Euler-Euler interface's wall setting does not include a place to enter or couple directly from frame the rotational component. Only the translational and sliding components are present.

Does anyone know why this is happening? Am I missing something or is there any other way to solve this?

Thanks!

3D Comsol model Heat transfer is not coming in my cable modelling

Tue, 28 Apr 2026 05:35:15 +0000

In my 3D comsol modelling of power cable file, heat transfer plot is not working properly

Capillary-driven unsaturated flow through layered porous media — Richards' and Two-Phase Darcy both struggle

Mon, 27 Apr 2026 22:33:13 +0000

I'm trying to simulate water wicking through a layered porous medium and need advice on the right physics interface or convergence strategies in COMSOL.

What I want to simulate

A finite water droplet sits on top of a stack of porous layers. Capillary suction pulls water through the layers into a paper channel and absorbent paper region. I need to:

Drive flow with capillary pressure / suction (not forced flux)
Enforce finite water volume (the droplet eventually exhausts)
See saturation evolve over time in each domain (rise, plateau, drop)

Materials have anisotropic permeability in the top layers (columnar pores, vertical permeability higher than lateral) and isotropic permeability in the paper regions.

What I've tried

Richards' Equation with finite reservoir

Added a cylinder domain on top of the porous stack representing the finite droplet
Tried Brooks-Corey and Van Genuchten retention models for the cylinder
With realistic capillary parameters (strong suction), the solver becomes too stiff to converge — timesteps collapse to nanoseconds
With "lighter" parameters that converge, the cylinder doesn't sustain water supply: pressure equilibrates quickly with the porous layers, flow drops by ~100× within seconds, and the top layer never reaches saturation
Tried various outlet drainage BCs — either too aggressive (water passes through without accumulating) or too weak (no convergence)

Two-Phase Darcy's Law

Same convergence stiffness issues, plus 2× more unknowns
Same retention curves (VG, BC), so same endpoint singularity problems near Se=1
Did not solve the source-supply issue

Common failure modes

"Negative power of zero" errors from VG retention near Se=1 (using l=1 helps but doesn't always avoid)

My current diagnosis

The fundamental issue seems to be: with realistic capillary parameters for fine-pore media, the gradients are sharp enough to make the solver stiff, but with milder parameters the cylinder reservoir can't sustain supply long enough to fill the porous layers to saturation.

Questions

Is there a recommended physics interface in COMSOL for capillary-driven wicking through layered porous media with a finite water source? I've considered Moisture Transport in Porous Media but it uses moisture diffusivity rather than direct permeability + retention curves.
Are there standard convergence strategies for stiff Richards' / Two-Phase problems? I've tried lower BDF order, manual time stepping, and regularizing Se with min/max clamps in user-defined retention. Other suggestions?
Is the cylinder reservoir approach the right way to enforce finite water volume, or should I be using something else? Coefficient Form PDE with explicit moving boundary? Moisture Transport with sorption isotherms? Auxiliary domain with custom storage?
Has anyone implemented dynamic capillary pressure (Hassanizadeh-Gray) in COMSOL for fast wetting problems? Is the τ ∂Se/∂t term significant enough to matter here?

Any pointers, papers, or example models would be hugely appreciated. Happy to share more details if useful.

Thanks!

Simulation on a MO material

Wed, 22 Apr 2026 13:04:52 +0000

Hello,

Im asking for your help because recently, I have been trying to do simulation on a Magneto optic material , which is defined by an antisymetric permitivitty tensor where epsilon_{xy} = -epsilon_{yx} . my structure is rectangular with Air (domain 3 on top) +MO material (domain 2) +Silver (domain 1)

I did a mode analysis at a certain frequency but i would like to understand if its possible to identify the modes that have forward incidence to the modes that have backward incidence to see the difference between the two propagation constants of my structure.

Do u know how to do it ?

Thank you.

Magnetostriction

Sat, 18 Apr 2026 19:37:43 +0000

I am designing a magnetoelectric antenna and need to apply a 20 mT background field to establish a bias point for AC simulation. However, the simulation will not converge in COMSOL 6.0 , resulting in various errors and preventing me from achieving any meaningful solution. I don't realize any kind of magnetostriction as well.

2D balloon being inflated with liquid, inside pipe

Sat, 18 Apr 2026 15:24:08 +0000

Hello!

I'm very new to COMSOL so I can only ask this question in simple terms.

I have a 2D cross-section of a circular balloon thats filled with liquid, the balloon is inside a rigid pipe that's marginally larger in diameter than the balloon and has some irregularities across the surface, and the pipe itself is also filled with a liquid. What is the simplest/most lightweight method of simulating the balloon expanding from a uniform inflow of more liquid/uniform increase in pressure, until it is pressing against the pipe and deforming around the irregularities?

Eventually I'd also like to divide the balloon into four quadrants with interior walls of the same material. Could I apply the same method to that case too?

laminar flow: a variable in a certain solid domain is undefined

Fri, 17 Apr 2026 13:57:03 +0000

I am conducting heat transfer simulations in a microchannel. The fluid domain is represented by a rectangular block, and the material is water, while the solid domain is made of copper. Using the laminar flow module, after specifying the inlet velocity, the solver returns the following error message:

Undefined variable. - Variable: comp1.spf.U - Geometry: geom1 - Domain: 80 Cannot compute expression. - Expression: comp1.spf.U - Plot: Volume 1

After that, I looked for domain: 80, which points to a fin, but I don't understand why this fin would cause the laminar flow module to fail. Moreover, the fluid properties and the fluid domain in the laminar flow module do not involve this fin. How should I troubleshoot this error?

Flow Boiling Simulation Convergence Problems

Fri, 17 Apr 2026 13:36:17 +0000

I am trying to adapt the extended RPI flow boiling model to my own expiramental setup where i have liquid nitrogen flowing through two channels in a metal test piece, with known heat flux applied to the bottom side. I have replicated the exact setup as the published application. The convergence has failed consistently. I have tried auxillary sweep on the boiling and heat flux, running fully coupled and segregated studies, putting a solver limit on the volume fraction, to no result.

This is how it has been failing:

Undefined value found. - Detail: Undefined value found in the stiffness matrix. There are 111 equations giving NaN/Inf in the matrix rows for the variable comp1.T. at coordinates: (0.0369032,0.029986,0.0268232), (0.0377371,0.0311923,0.026833), (0.0370727,0.0323953,0.0268382), (0.0348952,0.0336535,0.0268406), (0.0341695,0.0347622,0.0268414), ...

and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

here is the application, and screenshots of my own model in an expirament that converged using water, as a reference: https://www.comsol.com/model/subcooled-nucleate-boiling-with-extended-rpi-model-113081

Any advice for convergence with phase change?

The file is too large to send here, but happy to provide more detail to anyone who is willing to help.

thanks!

Cut plane function for AC/DC/charged particle tracing

Thu, 16 Apr 2026 06:49:09 +0000

Hi, I am using the charged particle tracing module from the AC/DC module to simulate an Einzel lens. To get the beam shape i want to have the x and y positions of all my particles for several z values (propagation direction). When i export all data the particles are sorted after time, but do not feature the same z coordinates. I tried to do it with "cut plane", but that didnt work out. How could I do that? I would be very grateful for any help!

Exterior field sum

Wed, 15 Apr 2026 09:52:47 +0000

Hi,

I'm trying to optimize the far-field pattern of multiple acoustic sources (an array of sorts) by tweaking their phases. Rather than simulating the whole thing over and over, I think it could be smart to calculate the radiation of each source individually at first, and then simply calculating the exterior field based on the sum of these with various phases applied. Is this possible?

Carry Over of pre stress for parametric optimisation while using Livelink for Solidworks

Tue, 14 Apr 2026 17:58:50 +0000

I aim to perform a simulation that involves compliant mechanisms (mechanisms that achieve their motion due to their elasticity). Specifically, I am interested in orthoplanar mechanisms. These are flat sheets that have specific cuts to enable motion in perpendicular to plane direction. I have created a Livelink for Solidworks to allow ease of modelling and parametrization.

I have 4 layers of orthoplanar flexure mechanisms. I want to perform a simulation in 2 phases. Phase 1 involves the assembly of orthoplanar flexures. But the catch is the top most orthoplanar flexure and the bottom most orthoplanar flexure are to be pre deflected. The other 2 flexures in the middle are in neutral position. Phase 2 is analysis phase for which I want to connect all four orthoplanar flexures. That is the top most connects to the middle, middle connects to lower middle, lower middle flexure connects to lower most. But for me in phase 2 it is important that the top most and bottom most are pre deflected and pre stressed. So at end of this phase two of my flexures are deflected and two are not deflected. But they are all connected together at the end of this phase.

How can I do this in the most effective way. Keep in mind I am using Livelink for Solidworks and am aiming to perform optimisation on design parameters. I have tried to use remesh deformed configuration but realised that this would not contain the pre stress that I would need. It would be great if you could provide a simple easy-to- implement solution that would integrate in my current workflow with minimal changes.

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?