Latest Discussions - COMSOL Forums

SMF 3D Analyzis

Thu, 27 Mar 2025 02:58:20 +0000

Hi all, hope you are doing fine.

I am trying to run a 3D simulation and analyzis using COMSOL 6.3 version, for a SMF. My geometry simulates a real fiber with 10 um core radius and 125 um cladding radius. The idea was to simply see propagation through a short lenght on lam=1550 nm.

On my setup I am using the Wave Optics module > Eletromagnetic Waves > Beam Envelopes, with a Boundary Mode Analysis for both input and output ports, plus a Frequency Domain study.

Inicially, tried to replicate tutorials seen on youtube (https://www.youtube.com/watch?v=kBQCvzn_dxc), that were using COMSOL 5.6. Most of the GUI is the same throughout menus, except for Mode Solver option within Boundary Mode Analysis > Study Settings.

In my setup, I used the ARPACK, but do not know the difference to the "Normal" used on version 5.6. All other parameters are the same.

For my surprise, the propagation seen in my study was quiet different from the original, and not commonly seen on theory. The electric field is pulsing during propagation length, with little concentration on the core and significant in the interface between core and clad.

If someone could please help me understand what I am doing wrong, I would appreciate. I´ve ran 2D simulations in the past, but I´m rookie on 3D.

Thanks!

Two phases flow

Wed, 26 Mar 2025 14:25:00 +0000

Hello,

I'm trying to simulate air injected from a 1.54 mm inlet into 15 * 20 cm water domain and the velocity is 0.045 m/s so bubble would form naturally and the surface tension = 0.072.

I am having problem with both phase field and level set the tuning parameters are not working correctly and also which one of them i use to perfectly capture the bubble diameter (level set or phase field)?

For the wetted wall i assumed pi/2 for all the domain or only the wall were air is flowing next to water?

In the photo the experiment I'm trying to validate

Appreciate any type of help!

Running 2 components in a single time dependent study

Tue, 25 Mar 2025 20:51:41 +0000

I have two components that are coupled in a time-dependent study, but the model is not converging. So, I conducted a test. I simulated each component separately in different studies, and both converged. Then, I simulated both components together in a single time-dependent study without coupling, but it still did not converge. My question is: Why it is not converging without coupling in a single time dependent study? The next step is simulating it with the coupling but I need to make sure that it is converging in single study time dependent firstly without coupling.

The variables converge quickly when I simulate the components separately. The solution error is high during the simulation when it was simulated the 2 components together without coupling.

Heat transfer with surface to surface radiation is not coming under multiphysics

Tue, 25 Mar 2025 17:28:28 +0000

Im relatively new to comsol, im using comsol 5.1 and i want the Heat transfer with surface to surface radiation to come under multiphysics but it does not.

Modeling Flow Boiling in Evaporator Channels with COMSOL

Tue, 25 Mar 2025 16:06:15 +0000

Hello everyone,

I’m working on a flow boiling model in evaporator channels using COMSOL . My goal is to capture vapor phase formation and growth due to heating and the transition between different flow regimes. If you’ve worked on modelling two-phase flow boiling in COMSOL, I’d love to hear your thoughts.

Thank you!

Coupling Chemical Transport Across Porous/Non-Porous Interface

Tue, 25 Mar 2025 01:31:14 +0000

Hello all,

I have a model where I have two regions, one with freely flowing laminar flow and one with flow through porous media (using the free and porous media Brinkman physics). The two regions are touching along an interface.

I would like to model the concentration of a solute convecting and diffusing through both the non-porous and the porous media. I expect to need to use two physics models, the "transport of diluted species" physics for the nonporous region, and the "transport of diluted species in porous media" for the porous region.

I cannot seem to figure out how to match the concentrations and fluxes at the interface between the two regions, as the two physics models have self-defined separate concentration variables (c and c2). Is there a standard practice for equalizing the concentrations and solute fluxes at an interface such as this so that it does not cause the model to break?

I have attached my file. I would be very grateful for any guidance.

Cheers.

Recovery after power failure

Mon, 24 Mar 2025 20:16:16 +0000

Hello. I recovered a static, parametric study which failed after a power cut. I could see the parametric solutions and wanted to continue the study after the power came back on. I recovered the mph file from the Comsol sidebar the opened the parametric study and pressed the 'Continue' button with the option to keep the existing solutions. After the resumed parametric study had completed, the 'Parametric Solutions' only contains the solutions after when the continue button was pressed.

I can see the original solutions in the parametric study, however, in the parametric list, only the ones after the continue button was pressed can be accessed as a parametric solution.

Is there a way to combine the studies inside a Parametric Solution so I may plot the data?

Thanks,

Neil Pearson

Boundary conditions when a pde degenerates to lower order

Mon, 24 Mar 2025 13:41:22 +0000

In a pde module, suppose the default form has a second derivative in space. In the boundary conditions, there are terms related to the first derivatives in space. What if the user sets the coefficient in front of the second derivative in space in the bulk to be zero, then the first derivatives boundary conditions are redundant. How will the software deal with this situation?

Heat Transfer

Mon, 24 Mar 2025 00:52:16 +0000

Hi every one I would like to inqure how i can cancel the thermal insulation that construct automatically between two different physics in COMSOL for heat transfer

periodic BCs in heat transfer with convection in infinite space

Sun, 23 Mar 2025 10:13:30 +0000

Consider 1D (x=0~1) heat transfer with a fixed convection velocity. To mimic infinite space, what periodic boundary conditions should be set upon x=0 and x=1?

In the heat transfer in solids module, thermal insulation boundary conditions will be overridden by periodic boundary conditions on the same boundaries. But when writing a heat transfer equation in a PDE module, thermal insulation boundary conditions won't be overridden. Why?

When is Runge-Kutta not applicable?

Sun, 23 Mar 2025 09:39:00 +0000

In time stepping, there's BDF, generalized alpha and Runge-Kutta. When is Runge-Kutta not applicable, showing an error message?

Surface area problem for 3D

Sun, 23 Mar 2025 03:53:06 +0000

Dear Researchers, After Topology optimization, I am getting less surface area of optimized geometry for 3D than original object.I am working on the topics of topology optimization of heat sink and I expect more surface area for high heat rate. I am using COMSOL Multiphysics of version 6.0 Thank you,sir

Infrared detection of internal and surface defects in materials

Sat, 22 Mar 2025 14:02:23 +0000

I want to make an object made of carbon brazing material with defects, internal bubbles, and surface scratches. I want to heat the object with some kind of excitation source, and finally use infrared imaging to make the defects visible. Can you simulate it with COMSOL, experienced ladies and gentlemen

Plotting unmeshed/unused geometry into the results

Fri, 21 Mar 2025 21:14:56 +0000

Let's say I want to mesh only part of an entire geometry and run a laminar flow simulation in domains 1-3, but do not want to include domains 4-6 in the laminar flow simulation. Is there a way to add domains 4-6 into the final postprocessing results (i.e., plotting a 3D velocity contour slice with domains 1-6) after the laminar flow simulation ends?

Thanks.

Radiative Heat Transfer with Implemented Temperature Condition

Fri, 21 Mar 2025 21:11:00 +0000

I am trying to find radiative heat fluxes based on a temperature profile that is not realistic and violates an energy balance. Is there a way to utilize the RTE by implementing a temperature profile across an entire geometry?

Convergence issues with electromagnetic simulations based on the specific input parameters

Fri, 21 Mar 2025 16:48:06 +0000

Hi everyone,

I'm performing some simulations with the efwd module, to see the effects of nonlinear phenomena on the optical properties of infinitely periodic electromagnetic scatterers, but I'm encountering issues with the convergence of the solver under specific conditions. Unfortunately, for a matter of secrecy I cannot upload the models or some screenshots, but I'll try to be the most precise possible in describing the situation.

The workflow I'm trying to implement is the following: the model has two components, one that does not consider the nonlinear effects on the refractive index (let's call it "unperturbed"), and another for the nonlinear phenomena (let's call it "perturbed"). The second component must use the solutions of the first component (more precisely the electric field) to modify the refractive index of the materials, and then compute basically the same physical quantities of the first component. The key point is that this "perturbation" depends, of course, on the intensity of the incident light, which is one of the input parameters of the model.

The model I've built in this way works perfectly fine, as long that the incident intensity is not too high. Above a certain threshold, however, the model stops working, and it gives the following error: "Maximum number of Newton iterations reached. Returned solution is not converged. Not all parameter steps returned". After reading several articles and forum posts, I've tried many alternative approaches (including finer meshes, greater distances of the two ports from the scatterer, load ramping), but none of these actually worked. The last approach I've tried, which seemed to work at first, is to change the kind of stationary solver: the default setting uses a Fully Coupled solver, but now I've tried setting up a Segregated Solver with two different steps, one for each of the components (I followed the instructions reported here: https://www.comsol.com/support/knowledgebase/1258). With this new approach, the model now runs also for higher incident intensities, but it gives me a result that physically makes no sense at all.

Does anybody have any idea of what's going on? Is this "segregated approach" way the right one, or am I missing something else? And if it is correct, why isn't it giving me the correct result?

Thank you in advance,

Pietro

Unexpected Magnetic Force Calculation Between Two Magnetic Objects – Seeking Guidance

Fri, 21 Mar 2025 08:29:58 +0000

Dear COMSOL Community,

I am working on a magnetic force simulation involving two magnetic objects placed above an iron-core coil (using the Magnetic Fields physics interface). Despite their different distances from the coil, the calculated magnetic forces on both objects are nearly equal, which contradicts my expectations. I would greatly appreciate your insights to help identify potential issues in my setup.

Model Overview:

A coil with an iron core generates the magnetic field. Two magnetic objects (identical material properties) are placed at different vertical distances above the coil (one close, one far). Stationary study with default solver settings. Observations:

The magnetic flux density (B-field) decreases with distance, as expected. However, the total magnetic force (mfnc.ForceZ_0 via Maxwell Stress Tensor) on both objects is almost identical. Any suggestions or references to relevant documentation would be immensely helpful. Thank you in advance for your time and expertise!

Best regards,

Magnetic Field Simulation : Difference in Inductance Values

Fri, 21 Mar 2025 06:56:09 +0000

Hi All, I have modeled a Transformer 2D as shown in below image in COMSOL AC/DC Module to find the leakage inductance.

I'm using version COMSOL Multiphysics 6.0 (Build: 405). I have used homogenized, numeric, coil group feature for the windings. The LV_a and LV_b constitutes one coil group for the LV winding, with LV_b having reversed current direction. Similarly, the HV_a and HV_b constitutes one coil group of HV Winding (having opposite current direction than LV winding). The LV winding is applied with 5V and HV winding short-circuited (0V). For a Magnetic Field physics study with frequency of 20kHz, the simulation results are as follows:

LV Coil current (A) : 0.037315-4.3362i
LV Coil inductance (H): 9.1752E-06
LV Coil concatenated flux (Wb): 0.00000015255-0.000039787i
Total magnetic energy (J): 0.000043133

Now, as per the above results, the LV coil inductance calculated by using the formula,

[L = 2*Total Magnetic Energy / (LV Coil Current)^2]

is 4.587E-06, which is exactly half of the inductance value in the COMSOL results shown above.

So, which value of LV Coil Inductance is correct? And why is the difference? Can someone throw some light on the above issue please?

Heat a block between parallel copper plate

Thu, 20 Mar 2025 22:45:06 +0000

Hello experts,

I am trying to heat a block (bone) between parallel copper plate. The plate is 5 cm in diameter and 0.2 cm in height. The block dimension 1x1x0.2 cm. I read a research paper who solved similar problem (attached). They mentioned using EM Waves, frequency domain and heat transfer modules. For the power input 100 W for 50 ohm impedance. Peak voltage input 100 V. They also mentioned using lumped port. Which surface should I select as lump port? Should I select uniform lump port? How can I solve the problem based on your opinion? Source file attached. Thanks in advance.

Heating Cuvette in Microwave Oven

Thu, 20 Mar 2025 22:38:36 +0000

Hello everyone,

I am trying to heat a cuvette in a Microwave oven. I have set the port and power source. When I tried to run the file it shows Undefined variable. I have attached the source file. Can anyone help me solve the problem?