Latest Discussions - COMSOL Forums https://www.comsol.com/forum/ Most recent forum discussions Fri, 28 Mar 2025 02:30:50 +0000 COMSOL Forum: Latest Discussions https://www.comsol.com/shared/images/logos/comsol_logo.gif https://www.comsol.com/forum/ Evaluate how much charge deposited on wall https://www.comsol.com/forum/thread/350402/evaluate-how-much-charge-deposited-on-wall?last=2025-03-28T02:30:50Z <p>Hello I see in the documentation of Comsol 6.3 that</p> <p>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.</p> <p>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?</p> Fri, 28 Mar 2025 02:30:50 +0000 4.2025-03-28 02:30:50.350402 Defining port in 2D (not axisymmetric) with microwaves launched from open-ended circular waveguide https://www.comsol.com/forum/thread/350392/defining-port-in-2d-not-axisymmetric-with-microwaves-launched-from-open-ended-circular-waveguide?last=2025-03-28T11:11:10Z <p>Hi COMSOL folks,</p> <p>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.</p> <p>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.</p> <p>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!</p> Thu, 27 Mar 2025 20:28:33 +0000 4.2025-03-27 20:28:33.350392 Transient Induction Heating Simulation with BH Curve Material https://www.comsol.com/forum/thread/350383/transient-induction-heating-simulation-with-bh-curve-material?last=2025-03-28T13:49:21Z <p>Dear respected experts,</p> <p>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.</p> <p>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.</p> <p>Core requirements:</p> <p>Maintain BH curve definition (necessary for accurate hysteresis loss calculation)</p> <p>Perform transient analysis with AC current in U-shaped coil</p> <p>Constraints observed:</p> <p>Relative permeability models cannot replicate measured hysteresis losses</p> <p>Experimental data confirms hysteresis loss dominates over eddy current loss in this heating process</p> <p>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.</p> Thu, 27 Mar 2025 15:18:58 +0000 4.2025-03-27 15:18:58.350383 singular matrix error https://www.comsol.com/forum/thread/350371/singular-matrix-error?last=2025-03-27T10:48:00Z <p>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.</p> <p>Could this be due to boundary conditions or solver settings?</p> <p>I would appreciate any help.</p> Thu, 27 Mar 2025 10:48:00 +0000 4.2025-03-27 10:48:00.350371 Mobility plot of example: mobility model https://www.comsol.com/forum/thread/350362/mobility-plot-of-example-mobility-model?last=2025-03-27T07:38:34Z <p>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.</p> Thu, 27 Mar 2025 07:38:34 +0000 4.2025-03-27 07:38:34.350362 SMF 3D Analysis https://www.comsol.com/forum/thread/350352/smf-3d-analysis?last=2025-03-27T12:27:55Z <p>Hi all, hope you are doing fine.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>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.</p> <p>Thanks!</p> Thu, 27 Mar 2025 02:58:20 +0000 4.2025-03-27 02:58:20.350352 Two phases flow https://www.comsol.com/forum/thread/350351/two-phases-flow?last=2025-03-26T15:49:58Z <p>Hello,</p> <p>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.</p> <p>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)?</p> <p>For the wetted wall i assumed pi/2 for all the domain or only the wall were air is flowing next to water?</p> <p>In the photo the experiment I'm trying to validate</p> <p>Appreciate any type of help!</p> Wed, 26 Mar 2025 14:25:00 +0000 4.2025-03-26 14:25:00.350351 Running 2 components in a single time dependent study https://www.comsol.com/forum/thread/350342/running-2-components-in-a-single-time-dependent-study?last=2025-03-25T20:54:10Z <p>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.</p> <p>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.</p> Tue, 25 Mar 2025 20:51:41 +0000 4.2025-03-25 20:51:41.350342 Heat transfer with surface to surface radiation is not coming under multiphysics https://www.comsol.com/forum/thread/350341/heat-transfer-with-surface-to-surface-radiation-is-not-coming-under-multiphysics?last=2025-03-25T19:32:58Z <p>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.<img src="http://" alt="" /></p> Tue, 25 Mar 2025 17:28:28 +0000 4.2025-03-25 17:28:28.350341 Modeling Flow Boiling in Evaporator Channels with COMSOL https://www.comsol.com/forum/thread/350332/modeling-flow-boiling-in-evaporator-channels-with-comsol?last=2025-03-25T16:06:15Z <p>Hello everyone,</p> <p>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.</p> <p>Thank you!</p> Tue, 25 Mar 2025 16:06:15 +0000 4.2025-03-25 16:06:15.350332 Coupling Chemical Transport Across Porous/Non-Porous Interface https://www.comsol.com/forum/thread/350322/coupling-chemical-transport-across-porousnon-porous-interface?last=2025-03-25T22:09:30Z <p>Hello all,</p> <p>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.</p> <p>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.</p> <p><strong>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).</strong> 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?</p> <p>I have attached my file. I would be very grateful for any guidance.</p> <p>Cheers.</p> Tue, 25 Mar 2025 01:31:14 +0000 4.2025-03-25 01:31:14.350322 Recovery after power failure https://www.comsol.com/forum/thread/350321/recovery-after-power-failure?last=2025-03-24T20:16:16Z <p>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.</p> <p>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.</p> <p>Is there a way to combine the studies inside a Parametric Solution so I may plot the data?</p> <p>Thanks,</p> <p>Neil Pearson</p> Mon, 24 Mar 2025 20:16:16 +0000 4.2025-03-24 20:16:16.350321 Boundary conditions when a pde degenerates to lower order https://www.comsol.com/forum/thread/350313/boundary-conditions-when-a-pde-degenerates-to-lower-order?last=2025-03-24T17:20:02Z <p>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?</p> Mon, 24 Mar 2025 13:41:22 +0000 4.2025-03-24 13:41:22.350313 Heat Transfer https://www.comsol.com/forum/thread/350291/heat-transfer?last=2025-03-24T12:07:55Z <p>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</p> Mon, 24 Mar 2025 00:52:16 +0000 4.2025-03-24 00:52:16.350291 periodic BCs in heat transfer with convection in infinite space https://www.comsol.com/forum/thread/350273/periodic-bcs-in-heat-transfer-with-convection-in-infinite-space?last=2025-03-23T10:14:23Z <p>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?</p> <p>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?</p> Sun, 23 Mar 2025 10:13:30 +0000 4.2025-03-23 10:13:30.350273 When is Runge-Kutta not applicable? https://www.comsol.com/forum/thread/350263/when-is-runge-kutta-not-applicable?last=2025-03-28T14:09:22Z <p>In time stepping, there's BDF, generalized alpha and Runge-Kutta. When is Runge-Kutta not applicable, showing an error message?</p> Sun, 23 Mar 2025 09:39:00 +0000 4.2025-03-23 09:39:00.350263 Surface area problem for 3D https://www.comsol.com/forum/thread/350261/surface-area-problem-for-3d?last=2025-03-27T07:06:53Z <p>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</p> Sun, 23 Mar 2025 03:53:06 +0000 4.2025-03-23 03:53:06.350261 Infrared detection of internal and surface defects in materials https://www.comsol.com/forum/thread/350253/infrared-detection-of-internal-and-surface-defects-in-materials?last=2025-03-23T09:32:27Z <p>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</p> Sat, 22 Mar 2025 14:02:23 +0000 4.2025-03-22 14:02:23.350253 Plotting unmeshed/unused geometry into the results https://www.comsol.com/forum/thread/350212/plotting-unmeshedunused-geometry-into-the-results?last=2025-03-22T12:30:12Z <p>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?</p> <p>Thanks.</p> Fri, 21 Mar 2025 21:14:56 +0000 4.2025-03-21 21:14:56.350212 Radiative Heat Transfer with Implemented Temperature Condition https://www.comsol.com/forum/thread/350202/radiative-heat-transfer-with-implemented-temperature-condition?last=2025-03-21T21:11:00Z <p>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?</p> Fri, 21 Mar 2025 21:11:00 +0000 4.2025-03-21 21:11:00.350202