Latest Discussions - COMSOL Forums

Antenna calculation Frequency combination

Tue, 22 Apr 2025 13:07:01 +0000

I would like to consult regarding a technical issue concerning dual-band antenna simulation using COMSOL's RF Module. Currently, I'm modeling an antenna that needs to operate simultaneously across two frequency bands: 0.6-1.0GHz and 1.6-2.0GHz, with the goal of obtaining composite simulation results.

Specifically, I need to:

Apply a single excitation source that simultaneously covers both frequency bands

Analyze the antenna's radiation characteristics under this dual-band operation

Acquire the superimposed field distribution results

Could you please advise on the proper configuration for implementing this multi-frequency analysis in COMSOL? Your guidance on the setup methodology would be greatly appreciated.

Thank you very much for your assistance!

Polypropylene PP material library

Tue, 22 Apr 2025 07:29:01 +0000

Hello, I am looking for polypropylene in the material library but can not find it. How to have it ? Thanks

How to Export Stiffness and Mass Matrices in COMSOL Eigenfrequency Study

Tue, 22 Apr 2025 01:52:51 +0000

Hello,

I'm using COMSOL Multiphysics to perform an eigenfrequency analysis of a cryogenic suspension beam for a gravitational-wave detector project. I want to export the stiffness matrix (K) and mass matrix (M) for each mode, so I can compute the energy using the quadratic form:

externally.

Issue: I followed these steps:

Created an Eigenfrequency study (with or without prestress).
Added a Matrix Export node under "Derived Values."
Selected “Stiffness Matrix” and “Mass Matrix” with options "Global" and "Sparse."

However, when I try to export, COMSOL gives the error:

"K is not stored."

I’ve also tried switching to frequency-domain or stationary studies and adding Input Matrix nodes under the solver configuration, but nothing has worked so far.

My Questions:

Is there a correct way to configure the eigenfrequency study so that the stiffness and mass matrices are stored and exportable?
Does this feature require enabling something before solving?
Is there any workaround if I don’t have LiveLink for MATLAB or Java API access?

Any guidance would be very appreciated

Can COMSOL prestressed Eigenfrequency Analysis Provide Valid Elastic Energy Estimates for Mode Shapes?

Tue, 22 Apr 2025 01:40:56 +0000

Hello,

I'm working on a cryogenic suspension design for a gravitational wave detector and using COMSOL Multiphysics to study internal vibration modes. I'm trying to determine whether the elastic strain energy reported in an Prestress Eigenfrequency Study can be reliably used to estimate the thermal motion of modes at cryogenic temperatures using energy scaling — for example, by scaling mode shapes such that the total energy equals

A senior collaborator raised this concern:

“Eigenvalue analysis is a frequency-domain calculation, and energy is not properly defined because initial conditions are not included. Therefore, the energy returned by COMSOL may not be meaningful.”

I understand that eigenfrequency mode shapes in COMSOL are arbitrarily normalized. However, COMSOL does internally compute the strain energy density and integrates it over the domain to report a total elastic energy per mode. I have already exported this using a volume integral of:

My questions:

Does this computed strain energy in COMSOL prestress eigenfrequency studies represent the actual mechanical energy stored in the mode shape (up to normalization)?
Is it valid to rescale the eigenmode displacements using:

If not, what is the rigorous way to obtain mechanical energy or displacement amplitudes from eigenmode simulations?
Are there COMSOL resources, papers, or documentation that clarify the assumptions and limits of using eigenmode strain energy for physical interpretations?

I understand that damping, Q-factor, and time-domain dynamics are not included in the eigenfrequency solver, but I’m only interested in using the elastic energy to scale the displacement fields to match thermal energy at 4 K.

Thank you for any help or guidance!

COMSOL simulation issue — power extraction from PN junction using Electric Circuit interface

Mon, 21 Apr 2025 11:22:03 +0000

Hello everyone,

I’m currently working on a project in COMSOL where I simulate multiple PN junctions connected in a serpentine layout. I apply a thermal gradient (Seebeck effect) and successfully generate a voltage (~70 mV), but I’m struggling to calculate the extracted power.

I’ve tried adding the Electrical Circuit interface and connected a resistive load, but COMSOL won’t compile. I suspect that the circuit isn’t properly linked to the 3D physics, or I may be missing a terminal or an external connection setup.

Has anyone worked on a similar model or could point me to a tutorial/example showing how to connect a terminal from a thermo-electric model to an external circuit and extract power?

Any help or guidance would be greatly appreciated.

Thank you!

matlab live link: mphplot produces no legend

Mon, 21 Apr 2025 10:46:32 +0000

The following code with mphplot(model,'pg1') plots 2 lines in a figure properly but doesn't show the legend. What's the problem?

model.result.create('pg1', 'PlotGroup1D'); model.result('pg1').create('lngr1', 'LineGraph'); model.result('pg1').feature('lngr1').set('xdata', 'expr'); model.result('pg1').feature('lngr1').selection.set([1]);

model.result('pg1').set('looplevelinput', {'manual'}); model.result('pg1').set('looplevel', {'1, 101'}); model.result('pg1').set('xlabel', 'x-coordinate (m)'); model.result('pg1').set('ylabel', 'Dependent variable u (1)'); model.result('pg1').set('legendpos', 'lowermiddle'); model.result('pg1').set('xlabelactive', false); model.result('pg1').set('ylabelactive', false); model.result('pg1').feature('lngr1').label('Line Graph'); model.result('pg1').feature('lngr1').set('xdataexpr', 'x'); model.result('pg1').feature('lngr1').set('xdataunit', 'm'); model.result('pg1').feature('lngr1').set('xdatadescr', 'x-coordinate'); model.result('pg1').feature('lngr1').set('linemarker', 'point'); model.result('pg1').feature('lngr1').set('markerpos', 'datapoints'); model.result('pg1').feature('lngr1').set('legend', true); model.result('pg1').feature('lngr1').set('resolution', 'norefine');

Non linear solver does not converge, and simulation is very very slow

Thu, 17 Apr 2025 11:48:26 +0000

Simulation is very very slow also non linear solver convergence error. When i try to increase the time for simulation, then i often encounter "non linear solver does not converge" error. I modified some things in segregated solver but that is making simulation very very slow. How can i solve that problem.

Handling Geometry or Meshing Failures in MATLAB-COMSOL Model

Wed, 16 Apr 2025 20:42:02 +0000

Hi all,

I’m running a MATLAB-COMSOL model where I update my design variables using a command like:

% Set the variables nPoints = size(xy, 1); % Number of point pairs for i = 1:nPoints xi = xy(i,1); % x-coordinate yi = xy(i,2); % y-coordinate

model.param.set(sprintf('x%d', i), sprintf('%0.4f [mm]', xi));
model.param.set(sprintf('y%d', i), sprintf('%0.4f [mm]', yi));

end

However, in some cases, certain combinations of design variables lead to non-viable geometries. As a result, the model fails either during geometry generation or meshing, and I get an error when trying to evaluate:'

mphglobal(model, 'solid.LFcrit');

To handle this, I would like to check whether the geometry and mesh were successfully generated before calling mphglobal. If they weren’t, I want to skip that part so that MATLAB can continue iterating without crashing the whole optimization loop.

Is there a recommended way to check the status of geometry and mesh generation in COMSOL via the MATLAB API?

Any suggestions would be much appreciated!

Best regards, Mirhan

Can Global Equations (ODEs) effect boundary conditions?

Wed, 16 Apr 2025 20:36:56 +0000

Hello!

Can Global Equations (ODEs) effect boundary conditions??

In 1D (time-dependent): I have a (pointwise constraint) boundary condition, which sets the dependent variable V to zero. (It's grounding or short-circuiting, because its an electric context.) But this boundary condition doesn't work anymore. V takes values unequal to 0.

I have to add a second equation in ODE, where the value is unequal to zero or the change dt or dt² must be zero, to make the boundary condition work again. This second equation is not used somewhere, but helps. Kind of workaround.

Is there a more complex relationship between ODEs and boundary conditions (or constraints or constraint forces) in the background, even if the ODE equation and the boundary condition is not direct or not handedly (by hand) coupled?? Has such a background relationship maybe something to do with "Apply reactions terms on: All physics"??

For now it seems like a bug.

Nice Greetings

Update parameters from a file or a database in JAVA code, through COMSOL java API

Wed, 16 Apr 2025 16:18:48 +0000

I have a Java file for a sample model and would like to develop a process that allows me to update the model parameters directly in the Java code. I want to load the input model parameters either from a file or by connecting to a database. While I see this functionality is available in the UI, I’m interested in achieving this through the Java API.

commands similar to the following be appropriate?

comsolcompile sample_test.java comsolbatch -inputfile sample_test.java -paramfile sample_file.txt | (db_string)

import com.comsol.model.*; import com.comsol.model.util.*;

/** Model exported on Apr 15 2025, 11:34 by COMSOL 6.3.0.335. */ public class runSeriesOfModels {

public static Model run() { Model model = ModelUtil.create("Model");

model.modelPath("C:\Users\fs9357\comsol\temp_files");

//model.label("runSeriesOfModels.mph");

model.param().set("L", "21", "Length"); model.param().set("W", "7", "Width"); model.param().set("rho0", "1140[kg/m^3]", "Density"); model.param().set("E0", "2.13[GPa]", "Young's modulus"); } }

Infinite Element Domain is not Working in 2D domain

Wed, 16 Apr 2025 08:10:34 +0000

Hello everyone,

I am simulating a simple long conductor in COMSOL 2D in a magnetic field (mf) to observe its inductance value. However, its inductance values do not converge as I increase the domain size. I used the parametric sweep option. (Please see attached File_1)

Then, I tried to add the infinite element domain to find the inductance value, but it is still not working (File_2)

Finally, inductance value convergences when I perform the exact simulation in the 2D-axisymmetric domain (File_3). Most of the avaialble tutorial on COMSOL focuses on 2D axi-symmetric simulation.

In summary, 2D = not convergence, 2D axisymmetric = converges.

Please help me solve this issue for the 2D domain. Note that I am not asking about the values but about the convergence of inductance values.

Convergence problem

Tue, 15 Apr 2025 12:45:40 +0000

Hello,

I have a Comsol license within the company Framatome. I am currently working on a topic related to the simulation of fluid flow within a test loop section (inlet d = 3mm + rack + 4 titanium steam generator tubes with a diameter of 17mm) and I am encountering a problem with the simulation.

The chosen physics:

Laminar flow (Re = 9 / Velocity = 2.36 * 1E-03)

Steady-state study (solver, tolerance, error; all left as default)

Mesh: Normal (Defined by the physics)

Temperature: 25°C

However, in the end, the solution does not converge, displaying the following message: "Failed to find a solution. Divergence in the iterations of the linear solver. The linear solver/preconditioner is ill-conditioned. The relative residual is more than 1000 times larger than the tolerance. The returned solution did not converge properly."

I would greatly appreciate any clarification regarding this type of error and a possible solution.

Best regards,

homogenization in COMSOL simulation

Tue, 15 Apr 2025 11:26:21 +0000

Dear community members,

My question is about homogenization consideration of COMSOL. Does COMSOL follow some built in homogenization rules as it uses finite element method for simulation? In case of simulation for reflectance in far infrared scale from metasurfaces consisting of metastructures in micron sizes, do one need to care about the homogenization or COMSOL does it by itself as one defines the mesh during modeling COMSOL modeling?

I hope you got my question.

regards,

Shahban

Getting errors while importing Solidworks geometry (step file) into COMSOL Multiphysics

Tue, 15 Apr 2025 11:13:49 +0000

Error Could not obtain license for CAD Import Module.

License error: -5. No such product exists. Note: CAD Import Module functionality is included in the Design Module and the LiveLink products for CAD. No such feature exists. Feature: CADIMPORTCKL License path: C:\Program Files\COMSOL\COMSOL60\Multiphysics\license\license.dat; FlexNet Licensing error: -5,414

Error This feature requires the CAD kernel.

Feature: Import 1 Change 'Geometry representation' to 'CAD kernel' in the Settings window of the Geometry 1 node. Change permanently in the Preferences dialog box

PWM

Tue, 15 Apr 2025 10:48:40 +0000

The temperature regulation module employs high-frequency pulse-width modulation (PWM) combined with soft-switching IGBT inverter control technology. This system dynamically adjusts the DC voltage and current output of the power module to precisely control the thermal ramp rate of the bed layer during heating processes. How to perform numerical simulations using COMSOL Multiphysics®

Epoxy Modelling

Mon, 14 Apr 2025 17:43:55 +0000

Correct approach to model epoxy bonding using thin elastic layer? Do we need to model epoxy or not and define TEL between substrate and epoxy & PZT and epoxy? How to determine value of Ka?

Iron losses over simulation time

Mon, 14 Apr 2025 06:46:46 +0000

Hello everyone, I'd like to analyze the transient behavior of iron losses in order to determine the duration of the settling process. Coming from an ANSYS Maxwell background, I'm still getting used to COMSOL. I'm currently modeling a motor similar to the one shown in the following example: https://www.comsol.com/model/analyzing-electric-motor-and-generator-designs-97091

My first study is a stationary analysis that provides me with the magnetic flux density and torque values. This is followed by a "Time to Frequency Losses" study using the "Rotating Machinery, Magnetic" physics interface. From this, I obtain the parameter rmm.Qh, which represents the volumetric loss density in W/m³. By integrating this quantity and multiplying by the length, I calculate the total iron losses in watts. The file is in the attachment.

Am I correct in assuming that this value represents an average over all computed time steps? When I look at the dataset from the "Time to Frequency Losses" study and export the rmm.Qh value, I only see X, Y, rmm.Qh (see attachment). Which leads me to conclude that rmm.Qh is only a one-dimensional vector. This leads me to believe that the iron losses calculated in this study are not time-dependent—is that correct?

That brings me to my question, how do I plot the iron losses over the simulation time?

Another question that comes to mind: when calculating losses using the Steinmetz equation, are the results already based on a steady-state condition? In other words, do I even need to consider the transient behavior or settling time in that case?

Best regards

Heat Exchanger streamline velocity plot

Sun, 13 Apr 2025 17:26:40 +0000

Hello,

For my transport II class we had to create the boundary conditions (hydrodynamic and thermal) for a 1,4 heat exchanger. I completed and rendered the model with no issues, and for this project in particular we have to show 3 plots, 1 for the temperature, and the other two for the hydrodynamics.

To save time for rendering, we were only making half a heat exchanger and then using the mirror 3D model section of the model builder to create the other half for the hydrodynamic plots.

For whatever reason, under the model builder section, the subsections for More Datasets and 3D Plot Group are not here. To plot the last two graphs, I will need this function.

Can anyone help me with this?

Surface area

Sun, 13 Apr 2025 05:05:16 +0000

Dear Researchers/Faculty

After topology optimization why it showing less surface area for heat transfer optimization problem ? It supposed to be maximum surface area to increase heat rate after topology optimization. How can resolve it ?

Thank you

mesh generation

Sun, 13 Apr 2025 03:20:23 +0000

Hello, I encountered some technical issues while conducting simulation calculations using the electromagnetic module and would like to consult you. Currently, I am using the user-controlled mesh generation method. However, when the calculation reaches approximately 70%, the calculation speed significantly slows down, and the convergence curve becomes a horizontal straight line, failing to meet the convergence criteria. Due to the large scale of the model, if I were to switch to the physics-controlled mesh, it would result in an excessively high memory requirement, exceeding the capacity of the current computer configuration. I would like to ask if you have any suggestions for optimizing the mesh generation settings in this situation. Thank you very much for your guidance!