Latest Discussions - COMSOL Forums

surface impedance and sound absorption coefficient

Mon, 09 Jun 2025 11:51:30 +0000

How to calculate surface impedance and sound absorption coefficient for a two cavity parallel MPP system.

Expression for 2nd moment of area for domain probe?

Sun, 08 Jun 2025 12:30:51 +0000

Hi to all,

I was wondering if there is any built-in expression for calculating the second moment of area (area moment of inertia) using the Expression Tool. I’ve tried searching with keywords such as "inertia", "second moment", and "moment of inertia", but haven’t been able to find a suitable expression so far.

Any guidance on how to access or define such an expression would be greatly appreciated.

Best regards, Mirhan

Coupling physics, H-A formulation

Sat, 07 Jun 2025 11:49:45 +0000

Hello, i am trying to link two physics, applying the H-A formulation. My objective it to induce current in an hts, superconductor, pickup coil, using a copper coil. I wanted to use the H formulation for the hts coil, using COMSOL Magnetic Fields Formulation, mfh, and the rest (air+copper coil) solved with A, using Magnetic Fields Formulation, in a 2D axisymetrical model.

My question is how the linking/coupling of the two physics should be done, so there is continuity in the electromagnetic properties. I'm guessing that is should be done via boundary conditions, but i am a bit lost where, what should be done in each side (mf and mfh), and using what parameters/values.

Thanks

Fiber to Waveguide

Fri, 06 Jun 2025 16:55:56 +0000

Hi I am having trouble figuring out how to couple a fiber optic to a waveguide. I keep getting an error of having an undefined value in a residual vector and I don't know how to resolve it. I have attached my model. Any advice will be welcome!

Convective Flow

Fri, 06 Jun 2025 12:58:30 +0000

I am working on a coupled heat and water flow. The physics involved are Richard's equation for water flow and heat transfer in porous media for heat flow. In my model setup, I applied free drainage (pressure head equal 0) at the bottom boundary which means water is leaving the system. This is confirmed from the total velocity result however for the convective flow the values are negative and the sign convection is upward. Since water is leaving the system, convective flow should have arrow downward add to the heat loss from the system via water removal in addition to the heat removed via conduction.

Please see the attached for more details.

Lumped port question

Thu, 05 Jun 2025 13:32:25 +0000

Hello,

I am trying to model a simple 3D wire with MHz AC current running through it using the magnetic fields interface with lumped ports.

I am printing out the parameters that the solution gives me for the lumped port, and I am a bit confused as to how to interpret them. I get an impedance, is this the impedance of just the region of the lumped port itself, or everything that is attached to the lumped port. Same for the power and voltage, is this for the whole system or only the lumped port itself?

Thanks

How to Plot Effective Relative Permittivity (Tensor Form) vs Wavelength

Thu, 05 Jun 2025 12:48:09 +0000

Hi, I am working on a metamaterial structure and have determined the effective relative permittivity components along the x, y, and z directions. However, I am unsure how to properly plot the real and imaginary parts of these permittivity components as a function of wavelength in COMSOL.

I attempted to define the anisotropic permittivity as a tensor in the Materials node, but after simulation, I am unable to access the material function to generate a plot of effective permittivity versus wavelength.

I would appreciate guidance on how to correctly define and visualize the wavelength-dependent effective permittivity components (both real and imaginary parts) in COMSOL.

Area moment of inertia (2nd moment of area) calculation

Wed, 04 Jun 2025 14:31:59 +0000

Hi everyone,

I’m trying to calculate the area moment of inertia (Ixx and Iyy) for an arbitrary 2D shape. As a simple example, consider a cross-section composed of two circles—I'd like to determine the area moment of inertia for this small circle.

Since the geometry can be arbitrary in other cases, I’m looking for a general method to compute Ixx and Iyy. I’ve noticed that COMSOL (e.g., through the "mass properties" function) provide mass-related properties like mass moment of inertia, but what I need are the area moments of inertia.

If anyone has suggestions or knows how to extract these values, I’d really appreciate your help.

Best regards, Mirhan

Flow Cycle in Pipe System – Cycle Duration Twice as Long as Defined

Wed, 04 Jun 2025 08:31:52 +0000

Hi everyone

I'm trying to simulate a flow cycle through a pipe system that runs through cold ground.

Goal: The pipes should be flushed with a warm fluid for 0.5 hours, then remain in the ground for 3.5 hours to release heat into the surrounding soil. I’ve implemented the flow cycle using both an Analytic Function and a Piecewise Function. The cycles appear to be defined correctly in both cases.

However, the inlet and outlet plots of the pipes clearly show that the cycle only repeats three times over the full simulation period – effectively running on an 8-hour rhythm instead of the intended 4-hour cycle. Model is in the Swisstransfer Link below because the attachment would have been too large: https://www.swisstransfer.com/d/647ba0ab-3e0b-4bcd-ae1c-d7beda8dff2d

What am I doing wrong?

Thanks for your help!

modelling induced currents

Tue, 03 Jun 2025 18:14:54 +0000

Hello,

I am trying to find the induced current/voltage/power of a coil from the magnetic fields generated by another coil.

I am using the magnetic and electric fields interface, and I have defined my primary coil using a terminal and ground boundary condition on either end of the coil, under the magnetic insulation boundary condition.

I want to make the other coil passive and simply read out what gets induced in that coil, but I am not sure how. If I use another terminal, I need to set the voltage/power, but I don't want to excite this coil too, I just want to see what it feels from the other coil.

How could I go about doing this? Thanks.

Topology Optimization: Comsol 6.3 vs Comsol 5.6 solution issue

Tue, 03 Jun 2025 10:50:09 +0000

Hi Everyone, I am working on a Topology Optimization setup of model (that consists of two materials) that undergoes Induction Heating(Physics involved: electromagnetic heating) in two step study ( Step1: Coil Geometry analysis, Step2: Frequency-Transient Solver, the optimization is applied for step 2). At first, I was having trouble running the above topology optimization in COMSOL 5.6 as I would repeatedly get "Warning: Forward solution failed, requesting reduced step." message and I was able to solve the issue by upgrading to COMSOL 6.3 But now I am facing a new problem, I am trying to run the same study in stationary solver instead of transient solver and I am not able to perform the optimization in COMSOL 6.3 as it keeps giving me an error. I don't face this issue when I run the same study in COMSOL 5.6, so I have been trying to modify the solver config to replicate the solver configs of COMSOL 5.6 but I keep getting the error.

I would really grateful any help to solve this and please let me know if you need any further information regarding this.

Best, Ashok

P.S. Please go through this link for more context on previous issue.

COMSOL–MATLAB Livelink Export Issue

Tue, 03 Jun 2025 10:08:49 +0000

Dear all,

I am using the student version of COMSOL Multiphysics 6.3 and am encountering some issues when trying to run a COMSOL model exported as a .m file in MATLAB.

Specifically, the model (which includes heat transfer and surface-to-surface radiation in a 3D geometry) runs perfectly within COMSOL. However, when I export it as a .m file and attempt to run it in MATLAB, I encounter an error during the physics definition step, particularly when boundary selections are being set.

The error suggests that some of the boundary indices being referenced do not exist.

Java exception occurred: Exception:

com.comsol.util.exceptions.UnexpectedServerException: com.comsol.model.data.SelectionOutOfBoundsException: Illegal input vector illegal entity
number
(rethrown as com.comsol.util.exceptions.FlException)

Messages:

com.comsol.model.data.SelectionOutOfBoundsException: Illegal input vector illegal entity number

This is the incriminated matlab line that gives error but in realty this happen for any selection boundary in the code:

model.component('comp1').physics('ht').feature('hf1').selection.set([41 42 46 49 50 51 53 54 56 57 66 67 68 69 71 72 74 75 83 84 89 90 107 110 127 128 130 131 133 134 141 142 148 149 150 153]);

However, I am unable to understand what is causing the issue, as the model runs flawlessly within COMSOL. The selection indices appear to match those used in the COMSOL model and therefore should exists.

Thank you in advance to anyone who might be able to help.

Best regards, Federico

Can Magnetic Fields, mf, and Magnetic Fields Formulation, mfh, work together?

Mon, 02 Jun 2025 20:44:01 +0000

Hello, I am working on a WPT 2D-axisymmetric model, using a copper coil as primary and an HTS coil, as secondary, pick up coil. My question is if i can use the mf interface, with the coil domain for the copper coil, and the mfh interface for the secondary, HTS, superconductor, coil? Can the two interfaces work together, where the magnetic field generated from copper coil, in mf interface, can be seen in the hts coil, inducing current?

Thanks, Vitor

Adding a module

Mon, 02 Jun 2025 19:49:10 +0000

I already installed the COMSOL with the license and now want to add a module and I already added in my license but i need to install it, Should I reinstall all software again or I can added on the existing software ?

Radiation shielding using lamellar micro/nano-structured materials

Mon, 02 Jun 2025 04:21:06 +0000

I am new to using COMSOL and am currently exploring simulations to evaluate the shielding performance of lamellar or composite materials against ionising radiation, specifically X-rays and neutrons.

I would greatly appreciate any recommendations for relevant references, seminars, tutorials, or experts in this area who could provide guidance or insights.

Thank you for your time and support.

Best regards,

About: The Electromagnetic Waves, Time Explicit Interface

Sun, 01 Jun 2025 12:25:29 +0000

The below post is related to an archived discussion

[start here]

By 2025, there are still no applications or cases concerning this physical field.

Mass additionally while building geometry from topology optimized product

Sun, 01 Jun 2025 04:04:35 +0000

Hello! Please help me how to know the mass of the actual topology optimized part because after i conducted topology optimization of a product (heat sink in my case) and then import mesh from database and create the geometry, the mass/volume that i can measure from geometry of this part is more than expected. For example in one case of very low mass of 0.1kg even though topology optimization was conducted successfully the end mass was showing more than 0.1 kg whereas I kept the constraint to keep only 70% of the original mass and even mass was removed from the geometry. Please let me know how we can avoid the thresholding error that adds more mass while creating the geometry of the topology optimized part. I am using the "measure" from geometry to know the volume of the product and multiplying it with density to know the mass.

Angle of incident laser

Sat, 31 May 2025 10:46:32 +0000

Hi everyone, I'm beginner in simulation with COMSOL software. I'm very curious in someone's 2015 article about deposited beam power on heat transfer in solid, they filled in 3 parameters about beam origin point, beam orientation but currently my COMSOL software can only change the z parameter of that. So can someone guide me in detail how to use this, because in the article I followed it used that equation?

Long Simulation Time for Time-Dependent Solver

Sat, 31 May 2025 04:03:31 +0000

Hi,

I am modeling an electromagnet with DC input at a constant voltage with the aim to understand the time-dependent changes in the conductivity, flux density, temperature and pull force of the equipment.

The target cycle time is 0-24 hours with steps of 1 hour. The core is soft iron with a CRGO block domain at its center.

I am unable to attach the .mph file since it is currently still running.

The time-solver is progressing time in "seconds" and not "hours" and the simulation for every 5 seconds is taking 30 seconds in real time.

The same applies for studies without CRGO that I have done for 0-8 hour results which have spanned for 12-14 hours in real time.

I need all the results mentioned before, but I need to understand how I can bring down the simulation time drastically since the real time consumed is too long.

Thank you.

How to Simulate Series-Parallel Thermoelectric Generator in COMSOL?

Fri, 30 May 2025 13:53:02 +0000

I need to simulate an electrical circuit where Peltier cells operate as generators using the Seebeck effect. I would like to connect three cells in series and then place them in parallel with another set of three cells, also connected in series. How can I set up this kind of configuration in COMSOL? Thanks a lot for your help!