Latest Discussions - COMSOL Forums

Evaluate how much charge deposited on wall

Fri, 28 Mar 2025 02:30:50 +0000

Hello I see in the documentation of Comsol 6.3 that

This text bellow is from documentation Electron Density Wall Settings The Use wall for electron density checkbox is selected by default and deactivates the wall boundary condition for the electron density only. When activated, the flux of electrons lost to the wall is self-consistently computed based on the electron temperature and electron density adjacent to the wall. When this is deactivated, the flux term is no longer applied for the corresponding equation, and the software will impose a zero flux boundary condition for that dependent variable. Select or enter a value for the Secondary emission flux (SI unit: 1/m2·s)). The secondary emission flux can either be a user-defined expression or come from another physics interface, typically The Heavy Species Transport Interface. When using this boundary condition in the Plasma interface, this setting is not editable, and the secondary emission flux comes from the surface reactions.

My question is this Please tell me if this understanding is correct. Suppose i do a electrostatic discharge and give wall boundary condition i can estimate how much electrons got deposited on the wall? If so how can i visualize it?

Defining port in 2D (not axisymmetric) with microwaves launched from open-ended circular waveguide

Thu, 27 Mar 2025 20:28:33 +0000

Hi COMSOL folks,

Here is my problem: I am trying to focus microwaves launched from an open-ended circular waveguide at 2.45 GHz to the inside of a small diverging nozzle (essentially a cone with metal walls). I am working inside of a vacuum chamber, so I am limited in space, therefore I am trying to implement a custom off-axis parabolic (OAP) mirror, assuming a mostly collimated incident beam which will be reflected and focused to a point, at which location I'd place the nozzle.

In the image attached, I have the OAP, section of circular waveguide, and the conical nozzle modeled in the domain. I would like to put this setup into a 2D simulation, but I am having a hard time knowing how to correctly define the port as there is no circular port option. I don't have the strongest EM background, but I believe I would need the e-field distribution for TE11 mode with a circular waveguide.

I would really appreciate any advice, comments, or guidance on how to approach this simulation or improve the setup as a whole. Thanks in advance!

Transient Induction Heating Simulation with BH Curve Material

Thu, 27 Mar 2025 15:18:58 +0000

Dear respected experts,

I am encountering difficulties in simulating an induction heating process and would appreciate your guidance. The configuration consists of a U-shaped single-turn coil carrying AC current to heat a soft magnetic material plate via induction.

The key technical issue is: When defining the soft magnetic material's constitutive relation using a BH curve, frequency-domain analysis becomes unavailable. However, when switching to transient calculation, I cannot apply current excitation to the single-turn coil. Attempting voltage excitation results in severe convergence issues.

Core requirements:

Maintain BH curve definition (necessary for accurate hysteresis loss calculation)

Perform transient analysis with AC current in U-shaped coil

Constraints observed:

Relative permeability models cannot replicate measured hysteresis losses

Experimental data confirms hysteresis loss dominates over eddy current loss in this heating process

Has anyone successfully implemented such a combination (BH curve material + transient AC current excitation for single-turn coils)? Any suggestions on solver settings/excitation implementation would be highly valuable.

singular matrix error

Thu, 27 Mar 2025 10:48:00 +0000

Hello, I am having trouble computing the multiphysics of multiphase flow in porous media for a water electrolyzer. The geometry is configured as a half-cell. Upon reviewing the conditions, I didn't find any issues, but I keep encountering a singular matrix error.

Could this be due to boundary conditions or solver settings?

I would appreciate any help.

Mobility plot of example: mobility model

Thu, 27 Mar 2025 07:38:34 +0000

Hello, I tried to do semiconductor MOSFET mobility model. When I plotted 2D mobility value, I found there is specific depth layer where mobility decreased. I can't understand why there is situation occurs.

SMF 3D Analysis

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

Hi all, hope you are doing fine.

I am trying to run a 3D simulation and analysis 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 quite 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?