Latest Discussions - COMSOL Forums

swept mesh problem in branched tube

Tue, 15 Sep 2026 16:53:17 +0000

i have branched tube y shape and has hexahedral mesh done by swept mesh in horizontal tube but i have problem in creating hexahedral mesh in branched tube it is showing unsuported topology . how to mesh branched tube branched tube is at 25 cm from inlet and length of horizontal tube is 50 cm and branched tube is 25 cm

Nonsymmetric matrix

Tue, 15 Sep 2026 13:59:39 +0000

In a simulation I am running, two coils wound on separate cores separated by an air gap are connected in series (Coils 1 and 3 are in series, and Coils 2 and 4 in series as well). When I run, I see the following in my log with almost no progress:

Nonsymmetric matrix found. Scales for dependent variables: Magnetic vector potential (comp1.A): 1.7e-05 Divergence condition variable (comp1.mf.psi): 1

The physics I use is similar to that in the ecore_transformer tutorial.

Mismatch Between Bandgap Calculated by Eigenfrequency Study and Transmission Loss Spectrum from Frequency-Domain Study in the Solid Mechanics Module

Mon, 14 Sep 2026 16:12:15 +0000

I am using the Solid Mechanics module in COMSOL Multiphysics 6.3 to study in-plane elastic wave propagation in a periodic acrylic plate with holes. From the eigenfrequency study with Floquet periodic boundary conditions, the dispersion curve shows a bandgap between the 3rd and 4th bands, approximately from 133 kHz to 154 kHz.

To verify this bandgap, I performed a frequency-domain study on a finite structure with PML layers, I gave prescribed displacement of 1mm in x direction and calculated the transmission loss spectrum. However, the transmission results do not fully agree with the eigenfrequency analysis. The transmission loss is not consistently high throughout the predicted bandgap range, and noticeable attenuation also appears near 118 kHz, where no bandgap is observed in the dispersion curve.

Could you please explain the possible reason for this discrepancy? How can I determine whether the bandgap given by the eigenfrequency study is a true complete bandgap for in-plane elastic waves, and what is the recommended COMSOL procedure for validating it using a frequency-domain transmission loss analysis?

Flow electrodes modeling

Sat, 12 Sep 2026 10:39:21 +0000

I want to model a flow electrode where the fluid is a mixture of water and activated carbon with 1M Na2SO4. Can any one help me ? The two electrodes are separated with a nafion 114 membrane.

Level set variable no longer maintaining values between 0 and 1 after ~3 s

Fri, 11 Sep 2026 09:43:21 +0000

Hello,

I am using the Two-Phase Flow, Level Set approach in COMSOL for a transient simulation. The model converges successfully until the end of the simulation time. However, after approximately 3 s, the level set variable no longer maintains the expected values close to 0 and 1.

In particular, the maximum value of the level set variable gradually decreases to around 0.7–0.6, instead of remaining close to 1.

Initially, I suspected that this was related to the mesh, so I refined the mesh, but the problem still persisted. I also adjusted the parameter controlling interface thickness and the reinitialization parameter. These changes improved the behavior to some extent, but did not completely resolve the issue.

Has anyone experienced a similar problem with the Level Set method? I would appreciate any suggestions regarding mesh resolution, reinitialization, interface thickness, solver settings, or any other parameters that may help maintain the level set variable closer to its expected range.

Thanks in advance.

Comsol 6.4 on Linux w/ multiple GPUs

Tue, 08 Sep 2026 08:49:54 +0000

Hi,

I've recently been trying to make Comsol use multiple GPUs on a Linux-based supercomputer. Both CPU-only and single GPU configurations work fine.

The machine has 4 GPUs, and given the same CUDA-related variable values, Python manages to use all 4 while Comsol only uses 1. My study uses the cuDSS solver, and I've ticked the option to use multiple GPUs in the solver config menu, to no avail...

Anyone facing the same issue or having thoughts on the matter ?

Cheers

Request a Trial Passcode

Mon, 07 Sep 2026 16:59:27 +0000

Hello Team, need a trial passcode to evaluate the software for my research work in wearable sensors on Human Body.

trial passcode

Mon, 07 Sep 2026 13:28:36 +0000

Hello COMSOL team i need a trial passcode please,

Thank you

Manel A

Phase specific turbulence on Euler Euler Interphase

Fri, 04 Sep 2026 12:03:59 +0000

How can I use k epsilon turbulence model only on the continuous phase on the Euler Euler Turbulence interface.

How to extract data from Layered Shell dataset to matlab

Sat, 29 Aug 2026 06:13:05 +0000

The mpheval and mphinterp functions fail to extract localized variables (such as r_llmat1_xdim) when querying standard evaluation datasets directly in memory. I need help on how to export this data into MATLAB. lshl1_eval = mpheval(model, {'T'}, 'dataset', 'lshl1'); 错误使用 mpheval mpheval (0): Java exception occurred: Exception: com.comsol.util.exceptions.FlException: 数据集类型无效。 Messages: 数据集类型无效。 - 标记: lshl1

lshl1_eval = mpheval(model, {'T','r','r_llmat1_xdim'}, 'dataset', 'dset1', 'selection', 3, 'edim', 1);

错误使用 mpheval mpheval (0): Java exception occurred: Exception: com.comsol.util.exceptions.FlException: 无法计算表达式。 Messages: 无法计算表达式。

未定义变量。
- 变量: r_llmat1_xdim
- 几何: geom1
- 边界: 3

无法计算表达式。
- 表达式: 1000*r_llmat1_xdim
- 特征: 计算

Difference in Results Depending on the Journal Velocity Setting in Multibody Dynamics–Hydrodynamic Bearing Coupling

Thu, 20 Aug 2026 05:38:13 +0000

I am modeling a rotating shaft using Multibody Dynamics (MBD) and a Hydrodynamic Bearing (HDB).

In MBD, I applied Prescribed Rotational Motion to the shaft and specified a constant angular velocity, omega.

I then defined the journal bearing surface using the HDB interface. I tested two different settings for the Journal Velocity:

Multiphysics-coupled velocity: The Journal Velocity is automatically obtained from the MBD interface through the Multiphysics coupling.
Manually specified velocity: The Journal Velocity is directly set to the same constant angular velocity, omega.

Since the shaft is prescribed to rotate at the same angular velocity omega in both cases, I expected the HDB results to be identical. However, I am obtaining different results between the two cases, such as differences in pressure distribution and other bearing characteristics.

Why can these two Journal Velocity settings produce different HDB results even though the shaft is rotating at the same prescribed angular velocity omega in both cases?

I would appreciate any explanation of what velocity is actually being passed to the HDB interface through the Multiphysics coupling.

COMSOL 6.4 "Operation not supported" Error

Wed, 19 Aug 2026 16:42:31 +0000

My workplace just migrated to COMSOL 6.4. All of the models I developed in 6.3 are not working because of an error in several Electrical Circuit (cir) elements.

I have five elements in my model: Ground Node 1, Voltage Source 1, Resistor 1, Inductor 1 and External I-Terminal 1. The Ground Node 1, and External I-Terminal 1 work as normal, when I click on them the GUI displays their settings. Clicking on Voltage Source 1, Resistor 1, or Inductor 1 produces a pop-up Error box with the text "Operation not supported" and a single OK button. Clicking OK closes the box but the Settings window is empty.

I have recreated the Error in multiple old model files.

I created a new model in COMSOL 6.4, added Electrical Circuit (cir) physics, and then added a Voltage Source. The Error was present in the new model as well so its not simply back compatibility, something is not working with the Electrical Circuit (cir) elements themselves.

Please help,

David

Invalid XML character (Unicode: 0x1)

Sat, 15 Aug 2026 13:42:03 +0000

Hello,

I ran a COMSOL simulation and saved .mph file with all the data preserved to be able to use it again in future. I opened the same file again and got this error.

"An invalid XML character (Unicode: 0x1) was found in the element content of the document."

Is this error solvable? How can I recover my .mph file?

Regards,

Zain

Fluid Structure Interaction simulation fails at constriction with inverted mesh and ALE errors

Tue, 04 Aug 2026 09:33:52 +0000

Hello Team COMSOL,

I'm working on a 2D FSI model using Laminar Flow + Solid Mechanics (Neo-Hookean hyperelastic) + Moving Mesh with a fully coupled solver with automatic remeshing.

The model contains a deformable hyperelastic object moving through a microchannel with a constriction. The simulation runs normally until the object reaches the constriction, where it consistently fails with errors such as:

Inverted mesh element
Undefined value found in the stiffness matrix
NaN in comp1.spatial.u and comp1.spatial.v
Failed to find consistent initial values
Last time step is not converged

I've already tried:

Refining the mesh near the constriction
Adding fillets to the constriction
Automatic remeshing
Different Newton solver options
Verifying mesh and boundary conditions

The failure always occurs at the constriction.

Has anyone encountered a similar issue? Are there any recommended ALE/remeshing settings or solver strategies for large-deformation Fluid Structure Interaction in narrow constrictions?

I have attached the design for reference. Any suggestions would be greatly appreciated.

Thank you.

Modeling heat transfer in geothermal using grid cell values

Mon, 03 Aug 2026 14:58:24 +0000

Hi, I have 3D array with permeability properties and binary label indicating faults. In this tutorial, it seems the objects (fracture/faults, layers, etc) are defined thru different format and values are assigned uniformly for each objects. https://www.comsol.com/video/modeling-heat-transfer-in-porous-media-using-comsol-multiphysics How to use my data format for geothermal heat transfer simulation? I have 3D array with permeability values and 3D array with binary label where 1 is fracture and 0 is not-fracture.

"Content is not allowed in prolog". Message regarding a recovery file

Mon, 03 Aug 2026 13:40:14 +0000

Hello,

My computer crashed when editing a new file without ant previous saves. The existing recovery file does not open and instantly gives me this error message "Content is not allowed in prolog". Also when appearing in the recovery file window it has a blank name.

Any idea if this can be fixed and I can gain access to the file.

Best regards

Solution not Converging

Fri, 31 Jul 2026 20:56:26 +0000

Hello,

I'm pretty new to COMSOL, and I'm trying to simulate airflow through a diffuser (diverging duct), with gauze screens to prevent separation. I've tried using multiple models, including k-epsilon, k-omega, and SST. The convergence is rather quick when no screens are introduced. However, as soon as I introduce one screen, the error keeps oscillating and the solution never converges.

The boundary conditions are: Inlet: 5 m/s Outlet: 0 Pa Walls: no-slip Inner boundary: wire gauze screen with 0.5 solidity and 0.001m wire diameter

I've attached screenshots of the mesh and the convergence plot using k-epsilon model.

Any recommendations would be greatly appreciated!

Identification of critical surface

Fri, 31 Jul 2026 11:02:42 +0000

Hello everyone, I would like to know if any of you can help me with a post-processing option of COMSOL. I have a flow field in which I want to identify the critical surface of the capture zone of a single well in a uniform regional gradient, isotropic , homogeneous medium. I know the coordinates of the stagnation point and I know that this critical surface I am looking for is the stream surface passing through the stagnation point. Can you suggest me what types of commands could I use to visualize this critical stream surface? This would be really helpful to me. Thanks a lot.

ABH and power law curve in the TL audio duct

Thu, 30 Jul 2026 14:17:22 +0000

Hello everyone, I would like some opinion on the correct physical interpretation of a system that combines an Acoustic Black Hole (ABH) profile, a power-law curve, with a progressively increasing cross-sectional area filled with fiber or foam. I've read about this topic, but I'm not sure if it can also be applied in the audio field to the first part of a transmission line duct (after the woofer and before the 180-degree bend) of a speaker enclosure. I'll briefly summarize what I understand: 1. A duct in which the air cross-sectional area decreases towards the end following a power law (curve with exponent ≥ 2). From theory, this profile should progressively slow the phase velocity of the wave to values close to zero, reducing reflection at the end. 2. In the terminal area of the duct (where the air cross-sectional area is now very small), the space is almost completely filled by a wedge of porous material (fiber) with progressive density (increasing towards the tip). **Note: I thought about applying the power-law curve and the wedge of porous material to opposing panels (one facing the other). I've attached an image.

Does anyone have experience with this? Any explanations are welcome, even simple ones, because I'm still a beginner.

Thanks to anyone who can respond.

References - ABH/SBH theory for ducts: ScienceDirect - A plug-in sonic black hole for duct terminations - Rectangular ABHs for air absorption: ScienceDirect - Numerical study of rectangular acoustic black holes - Distinction of mechanisms in SBH: ScienceDirect - Sonic black holes without rainbow trapping

Combining Explicit trap distribution with Lombardi mobility in 2D MOSFET

Tue, 28 Jul 2026 10:48:14 +0000

I am working on a 2D nMOSFET stationary study in COMSOL 6.3 (Build 420) using the Semiconductor Module. I am trying to combine two features that each work individually but fail when used together:

Trap-Assisted Surface Recombination (boundary, Boundary 5) with Explicit trap distribution, Continuous Energy Level sub-node, Gaussian σ=0.1 eV, midgap centred
Arora + Lombardi + Caughey-Thomas mobility model chain with continuation parameter cp

WHAT WORKS SEPARATELY: - Explicit trap distribution alone converges using a three-step sequence: trap-free solve at subthreshold → ramp Nt at fixed Vg → sweep Vg forward ✓ - Lombardi + Caughey-Thomas alone converges using the auto-generated Segregated solver ✓

THE PROBLEM: When combining both, the auto-generated Segregated solver computes this scale for the trap occupancy variable at the start of the solve:

Trap Occupancy (comp1.semi.tasr1.ctb1.ft): 2.3e+35

This is clearly wrong — ft is a dimensionless occupancy fraction bounded between 0 and 1, so its scale should be ~1. The incorrect scale of 2.3e+35 makes the Newton step sizes completely wrong and the solver diverges.

WHAT I HAVE TRIED: - Setting manual scale of ft = 1 in Dependent Variables node — this is reset when Show Default Solver regenerates the configuration - Fully Coupled solver instead of Segregated — also fails, same root cause - Lower/Upper bounds on ft (0 to 1) added to Segregated node — helps slightly but does not resolve the scaling issue - Various Nt/cp ramp orderings — the system converges up to Nt = 1×10¹² m⁻² but fails consistently at Nt = 1×10¹³ m⁻² with residual stalling at ~7×10²

SPECIFIC QUESTION: How can I permanently set the scale of comp1.semi.tasr1.ctb1.ft to ~1 in the auto-generated Segregated solver for Lombardi, so that it persists and is not reset by Show Default Solver? Is there a known approach for combining Explicit trap distribution with field-dependent mobility models in a 2D stationary semiconductor study?

I am attaching the log file showing the incorrect scale. Any suggestions welcome.