Latest Discussions - COMSOL Forums

How to obtain unbalance response plot in COMSOL?

Wed, 07 Jan 2026 11:25:46 +0000

I am working on similar case of "Simply supported rotor", I am unable to plot the unbalance response plot. Kindly help me.

Far‑field radiation from magnetoelectric antenna driven by piezoelectric–piezomagnetic coupling (no electrical port)

Tue, 06 Jan 2026 13:32:35 +0000

Hello everyone, I am working on a magnetoelectric (ME) antenna model in COMSOL Multiphysics and I would appreciate guidance on the correct strategy to compute the far‑field radiation. Model description The antenna is composed of: grounded Mo bottom electrode, piezoelectric AlN layer, magnetostrictive FeGaB layer The surrounding medium is a spherical air domain (inner sphere, and outer pml sphere) The physics interfaces used in the near‑field study are:Electrostatics (ES), Solid Mechanics (SM), Magnetic Fields (MF) with the following multiphysics couplings:Piezoelectricity (ES ↔ SM), Piezomagnetism / magnetostriction (SM ↔ MF) The system is solved in the frequency domain. A harmonic voltage is applied across the piezoelectric layer, generating strain that propagates into the magnetostrictive layer and produces a time‑varying magnetization. An external bias magnetic field is also applied in the air domain. Importantly, this antenna is not electrically fed (no lumped port, wave port, or impressed current), as the source of radiation here is the antenna due to the magentization evolution in FeGaB. My Question: I would like to compute the far‑field radiation pattern of this antenna. I added the Electromagnetic Waves, Frequency Domain (EMW) interface and tried to use COMSOL’s near‑to‑far‑field transformation, but all far‑field quantities (e.g. emw.normEfar) evaluate to zero. I understand that: 1. Far‑field calculations in EMW require a non‑zero electromagnetic near field (E, H) 2. EMW does not directly couple to Magnetic Fields, Solid Mechanics, or Electrostatics 3. Variables such as mf.Mx, mf.Hx, or es.V are not accessible inside EMW as sources I attempted to introduce equivalent magnetic or electric current sources based on the magnetization, but EMW does not recognize variables from the MF interface, even when defined through component variables.

Questions 1. What is the recommended COMSOL workflow to compute far‑field radiation from a mechanically driven magnetoelectric antenna that has no electrical port? 2. Is the correct approach to: Perform a first study to compute the magnetization, then use a second EMW‑only study with an equivalent current (calculate it in matlab based on the output magnetization or field that i wil get due to the near field study)? 3. Are there any built‑in features or best practices in COMSOL for handling radiation from magnetization‑driven sources (e.g., magnetic dipole–type antennas)?

Any guidance, references, or example models would be greatly appreciated. Best regards, Rayan

Defining non-design regions for topology optimization of organic geometries

Mon, 05 Jan 2026 16:58:42 +0000

Good evening,

I am designing an orthopedic, handle-like device intended to be held in the hand, and the final step of my workflow is topology optimization.

The geometry is generated from a 3D scan of the hand; therefore, most of the dimensions are non-parametric and the shape is highly organic. A portion of the device is in direct contact with the hand and its external shape must be preserved for ergonomic reasons.

I would like to perform topology optimization while keeping this contact region unchanged. However, due to its organic shape, this portion cannot be easily isolated using simple geometric primitives such as boxes, cylinders, or spheres. I can select the contact surface itself (I have partitioned the surface were I need), but I am unsure how to correctly partition the volume so that this region is excluded from the design domain.

Is it possible to perform topology optimization while leaving a surface (and an underlying thickness of material) untouched? If so, what is the recommended approach to define the non-design region in this case?

I am attaching a screenshot of the device; the highlighted surface corresponds to the hand–contact area.

Thank you very much in advance for your help.

Error occurs when saving newly created COMSOL models

Thu, 01 Jan 2026 07:19:51 +0000

An error occurs when saving a newly created model in COMSOL. Models created previously can be opened and run without any issues, but saving a new immediately triggers this error. What could be the cause, and how can this issue be resolved? Thank you. The attached picture shows in detail.

How to Model Two-Photon Absorption

Wed, 31 Dec 2025 08:02:27 +0000

Hi, I am trying to model the two-photon absorption (TPA) process in a nanostructure using COMSOL Multiphysics. For describing light propagation, I am using the Wave Optics Module.

My main question is how many physics interfaces are required to properly model this process .

I would greatly appreciate any guidance on the choice of appropriate physics interfaces and the practical steps needed to implement two-photon absorption in COMSOL.

In addition, if anyone could point me to an example model or a COMSOL application that demonstrates two-photon absorption, or more generally multiphoton absorption, I would be very grateful.

Memory Issue

Wed, 31 Dec 2025 05:19:25 +0000

I am doing 3D simulation that is not symmetric, using the mf physics , coil geometry analysis and stationary study. Coil geometry analysis have 2,192,126 DOF and Stationary study have 19,338,394 DOF.

I have used domain wise mesh maximum upto fine and with a total of around 12 GB physical memory.

I am using segregated and iterative solver of stationary study. But my simulation is stucking. I am doing the simulation using i5 processor and 16 GB RAM. Further I have to do frequency analysis.

Can you tell is this the memory issue? If yes, how much is recommendable memory for this much DOF.

There is no Option for "Hide for Physics" in View under Definitions in COMSOL-6.3.

Sat, 27 Dec 2025 14:31:01 +0000

Hi COMSOL users !

I am using COMSOL 6.3 version.

I want to hide some edges in the geometry for the visualization purposes to plot the contour plots.

In model builder in the definition section under the view option , there is option for 'hide for geometry' but there is no option for 'hide for physics'.

How can I enable this option for better contour plots in post processing without intermittent lines/edges ?

Thanks.

modeling aid

Mon, 22 Dec 2025 15:50:01 +0000

Hello, I need your help with a model. I want to model a polystyrene nanoparticle (d=20 nm) in water on Comsol.

What are the vibration effects?
The medium should be water.
The excitation type is opto-thermal/light excitation.
Particle point/average displacement vs. time.
Maximum RMS displacement vs. time.
Q-factor / damping extraction.
Pressure field p(x,t) in fluid.
Fourier transform (FFT) of pressure/potential time series → spectrum.
Mode shape snapshots (in time or from modal analysis).
Acoustic energy flow / power.
Phase vs. time or vs. frequency
Parameter scans (sensitivity plots)
Spatial cross-sections / field maps (p(x,t) or u(x,t))
If optothermal: Temperature(t) at particle & fluid + thermoelastic stress.

How do I model these and visualize the vibration and time-dependent relationships in graphs? Thank you very much for your help...

Create Diffraction order using Livelink for matlab

Mon, 22 Dec 2025 09:32:11 +0000

Hello, I want to create a diffraction order in using livelink in matlab. I could not find a command that describe how to create it. pasted bellow my lines of code in matlab:

%%%%% Assign Boundary Variables%%%%%% bL = 1; % left boundary -> inpot port bR = 12; % right boundary -> output port bB = 2; % bottom boundary -> periodic (Floquet) bT = 3; % top boundary -> periodic (Floquet)

%%%% Floquet periodic BC (y-direction) %%%%

pc1 = ewfd.create('pc1','PeriodicCondition',1); pc1.selection.set([bB, bT]); pc1.set('PeriodicType','Floquet'); pc1.set('kFloquet', {'k0cos(theta)', 'k0sin(theta)', '0'});

%%% input port (left) %%% port1 = ewfd.create('port1','Port',1); port1.selection.set(bL); port1.set('PortType','Periodic'); % port1.set('ModeType','PlaneWave'); port1.set('PortExcitation','on'); port1.set('E0', {'0','1','0'}); % Ey polarization doR1 = port2.create('doR1','DiffractionOrder',1); doR1.set('m',1); doR1.set('n', 0);

%%% output port (right) %%% port2 = ewfd.create('port2','Port',1); port2.selection.set(bR); port2.set('PortType','Periodic'); port2.set('ModeType','PlaneWave'); port2.set('PortExcitation','on'); doT1 = port2.create('doT1','DiffractionOrder',2); doT1.set('m', 1); doT1.set('n', 0);

Regards Hammam

Modelling of carbonate dissolution

Sat, 20 Dec 2025 20:31:30 +0000

Hi all,

Thank you for your assistance. I am trying to model moving of boundaries as a result of carbonate dissolution in COMSOL. Is it possible anyone can help me with a file to get started with or a step by step approach to get a simple model (single pore model) done?

Sincerely, E.A

Union/Assembly

Fri, 19 Dec 2025 07:48:30 +0000

I am doing magnetic field study and made one U structure rectangular coil with an Air Domain. When I am forming a union, current is flowing is 1 or 2 legs of the coil and not in all 3,and forming magnetic field according to those conductors. When I am forming assembly, magnetic field is not being generated in Air but current is flowing in every conductor, How to resolve this issue!!!

The symmetry precision problem

Thu, 18 Dec 2025 01:52:20 +0000

Recently I'm using Comsol for BEM of static electric field. I found when the geometry is symmetric, there will always be a ~0.0001V asymmetry of the calculation results when the voltage of a specific electrode is set 1V. It remains even if I set the physical field as a symmetric one, and I also tried to reduce relative tolerance from 1e-3 to 1e-4, and it failed to fix that as well. Is this inherent to Comsol? I'll appreciate it if someone could help me with that.

Stationary study of rotating thrust magnetic bearing

Wed, 17 Dec 2025 10:04:22 +0000

Hi Everyone, I have been working on a simulation of a typical active thrust magnetic bearing trying to simulate the losses in such bearing. All physics was modeled using Magnetic and Electric field module. The stationary study worked well until I began to introduce rotation to the thrust disc, using velocity Lorentz term, above the RPM of 5 the solution doesn't converge. I tried several approaches to fix this issue and none of the succeeded:

Increasing mesh progressively
Changing non linear magnetic material to linear
Replacing physical air gap with thin low permeability gap
Changing iterative solver from GMRES to FGMRES
Changing Iterative solver to direct solver (MUMPS)

Unfortunately, none of these approaches worked. Do you maybe have an idea for another approach to solve this convergence problem? I have atatched my current model as reference.

RF Module (emw): Frequency-domain spectroscopy of a single biological cell

Wed, 17 Dec 2025 09:07:24 +0000

Hello, I am working with COMSOL Multiphysics (v. 6.4) – RF Module (Electromagnetic Waves, Frequency Domain) because my frequency of interest is 2.45 GHz. My model consists of a single biological cell, with a realistic geometry imported from CAD. The objective is to study the electromagnetic response of the cell (e.g. transmembrane electric field, SAR, polarization) when exposed to an RF field at 2.45 GHz. I am trying to understand how to properly “deliver” or excite the electromagnetic field on the cell using the RF Module, in a way conceptually similar to how Terminal conditions are used in the AC/DC Module. In other words, I would like the field to be present, but without explicitly modeling a physical RF source (antenna, waveguide, coaxial cable, etc.) and without imposing boundary conditions directly on the cell membrane. I have considered the following approach: * Electromagnetic Waves, Frequency Domain (emw); * Scattered field formulation; * Background electric field (plane wave excitation); However, I am still unsure how to correctly apply and interpret this excitation in practice, especially with respect to the physical meaning of the background field and how it relates to a real RF exposure at 2.45 GHz. An alternative idea I initially had was the following: * Surround the cell with a box representing the extracellular medium * Apply a Port condition on one face of the box * Apply Perfect Electric Conductor boundary conditions on the other faces The intention was to generate a propagating electromagnetic field inside the box and expose the cell to it. However, I am not sure whether this setup is physically correct or recommended, and whether Ports can be used in this way when no actual transmission line or waveguide is modeled. Therefore, my questions are: 1. What is the recommended way to excite an RF field at 2.45 GHz on a single cell using the RF Module, without explicitly modeling an RF source? 2. Is scattered field formulation with background electric field the correct approach for this type of problem, and if so, how should it be properly implemented? 3. Is the idea of using a box with a Port on one face and Perfect Electric Conductor on the others physically meaningful in this context, or should Ports only be used when modeling real waveguides or transmission lines?

Any guidance, best practices, or references to similar models would be greatly appreciated.

Defects extending along the z-direction in BEM of static electric filed simulation

Tue, 16 Dec 2025 04:16:55 +0000

I'm trying to use BEM to calculate the Spatial electric potential field distribution of specific electrodes design, and applied that to trap some charged particles. However, I found that there seems to be some defects of the field that results in extension of the particle arrays in z-direction, which is not physical. And these defects will appear at specific sites, so I suppose it's caused by the defects of field calculation by Comsol. I used user-specified grid, and the grid looks regular, and I calculated the spatial potential distribution, found that there is a 0.001V error for symmetric positions. Are there any solutions to this problem? Thank you!

phase field method

Sun, 14 Dec 2025 07:18:37 +0000

I am a master's student currently studying the fracture phase field method. I plan to use COMSOL to simulate phase field fracture. I have read some papers on phase field fracture and some case studies, and noticed that the Solid Mechanics module, Poisson Equation module, Helmholtz Equation module, etc. were used. However, I find many of the settings difficult to understand. Therefore, I would like to know if your company has any operation documentation specifically explaining the use of COMSOL for phase field fracture analysis? If it's possible to create such an operation document, I would be extremely grateful! Thank you！

Certification

Sat, 13 Dec 2025 19:54:48 +0000

I know in the past, COMSOL had certifications for consultants and individuals.

What is the status of that now and are there any references. I tried to search before posting but I couldn't find any so that's why I'm posting in the discussion forum now.

Thanks in advance for your comments.

Skin effect not appearing with union of two cylinders in COMSOL

Thu, 11 Dec 2025 11:09:08 +0000

I am modeling a conductive disk in COMSOL under AC conditions (14 GHz and 80 GHz) with the following setup.

Geometry and Physical Setup

Geometry: The conductor consists of two thin cylinders stacked on top of each other and merged using the Form Union geometry operation. Radius (per cylinder): 0.015 m Height (per cylinder): 0.0005 m Total Geometry: A disk with R=0.015 m and total height 1×10^−3 m.

Current direction: The current flows radially across the disk (from one side of the diameter to the opposite side, i.e., perpendicular to the stacking direction).

Physics: Coupled interfaces: Magnetic Fields (mf) and Electrical Circuit (cir). Coupling: The mf interface uses Lumped Ports for input and output, coupled to the cir interface via the External I vs. U node. The components in the cir circuit are connected in series.

Problem / Observation

When analyzing the current density ? in a cross section: - With the Union of the two cylinders: The expected skin effect (concentration of current at the outer edges of the disk, parallel to the current direction) is not visible. The current density is uniform across the cross section.

As a control, using only one cylinder (R=0.015 m and total height 0.001 m): The skin effect is observed correctly.

Question I don’t understand why, even though I apply a union to the two cylinders, I don’t get the expected skin effect, just like with a single cylinder?

Inclination Flow

Mon, 08 Dec 2025 02:18:38 +0000

Hi, I have a some problem to do the inclination in my geometry. I already put all the parameters and I run the program. But the result error.

Flow splitting at Comsol 6.2 Version

Sun, 07 Dec 2025 21:15:00 +0000

Hello Everyone,

I have a COMSOL Multiphysics geometry as shown in the figure below. The model consists of a main pipe with an inlet at the upstream end and an outlet at the downstream end.

The inlet flow rate is set to 40 L/h. At the first junction, where a U-shaped branch begins, I would like to split the flow such that half of the inlet flow rate is diverted into the U-shaped pipe (20 L/h).

Could you please advise how this flow split can be defined or enforced in COMSOL?

An image of the complete setup is also attached.