Latest Discussions - COMSOL Forums

Running Batch Sweep with Batch commands

Mon, 31 Mar 2025 13:50:01 +0000

Hi All,

Is there a way to run a Batch Sweep using batch commands? I'm trying to execute a huge parametric sweep with Batch Sweep to speed up the overall simulation. I'd like to initiate the simulation with a batch command, but it seems to only perform a parametric simulation. (The simulation took the same amount of time as a normal parameter sweep, and the individual sub-simulations do not appear in the batch folder.)

Persistent error with undefined variable in time dependent solver and stationary solver

Mon, 31 Mar 2025 12:16:06 +0000

Hello Comsol,

I am facing an issue in my COMSOL model that I have been unable to resolve for a few days now, even after multiple attempts and fixes. I am working on a time-dependent simulation of blood flow in the aorta (normal aorta and with coarctation), and I have added Global ODEs (RCR model) to model the pressure changes in the arteries. My Boundary conditions have been set to velocity inlet and outlets with pressure. My main issue is that when I try to run the simulation, I keep encountering the error: "Undefined variable - Variable: comp1.p" This happens both in time-dependent and stationary solvers. How do I fix this issue?

(C_B*comp1.pt + comp1.p/R2_B - Q_B) this is the equation I have used in the global equation in global ODEs and DAEs. where: C_B is the compliance comp1.pt is dp/dt R2_B is distal resistance Q_B is the flow rate. I have defined all these parameters.

Electrical and Thermal Characteristics

Mon, 31 Mar 2025 09:32:08 +0000

Hello everyone! I'm looking for a big guy in Beijing who is proficient in electric heat simulation, and I can pay a consulting fee if I have a question!

keep all plot features in matlab livelink

Mon, 31 Mar 2025 05:08:55 +0000

There's a matlab file (function out = model) that creates a model, solves and postprocesses. All plot features including titles, legends are written within this model m function. Then use mphplot(model,'pg') to plot 'pg'. But this loses all plot features. How to use mphplot while keeping all plot features without rewriting all features?

solvers: solving the same model with various equally suitable modules

Mon, 31 Mar 2025 03:55:06 +0000

The software automatically specifies solvers according to the specific modules used. When solving the same model with various equally suitable modules in one batch within the same mph file, by default only one solver is used for all the modules applied. This solver may be suitable for only one of the modules but not for the rest of the modules. In this case how to make the software use different solvers when solving different modules?

Issue in modeling natural convection to a pot

Mon, 31 Mar 2025 01:54:16 +0000

I am trying to model the heat transfer to a pot in natural convection mode. This is an axisymmetric model, where a stove setup is modeled. The temperature at a bottom boundary (represents the burner) is set to a constant value. There is a pot placed on the stove. There is water (modeled as a solid object with a high thermal conductivity) inside the pot. We are studying the heat transfer to the pot and to the water through conduction and natural convection in this case.

I am using the heat transfer in solids and fluids, turbulent flow, and nonisothermal flow multiphysics coupling with a fully coupled solver to get the solution. The issue is that the bottom surface of the pot is getting heated, however, there is negligible temperature gain at the interior surfaces of the pot and also the water in the pot. What could be be possible issue? I am attaching the model .mph file for your reference.

Thanks!

Electrical and Thermal Characteristics

Mon, 31 Mar 2025 00:39:40 +0000

Hello everyone! Using a porous medium model to simulate Joule heat, it is known that the bed resistance decreases with increasing temperature, and the resistance and temperature data are obtained experimentally, fitted by an equation and then defined inside the material conductivity of comsol, why is the bed temperature change small?

Question about COMSOL tutorial provided

Sat, 29 Mar 2025 20:03:14 +0000

Hello I am trying to understand this tutorial https://www.comsol.com/model/dc-corona-discharge-in-air-in-a-point-to-plane-configuration-100451 I want to change the wall boundary condition to just absorb the electrons and i want to plot it on the wall. I am not able to do so. can you please tell me why. My objective is to determine how much charge got deposited on the wall during the simulation

different time stepping under same 1D plot group

Sat, 29 Mar 2025 04:45:18 +0000

I want to compute the same thing with 2 different time stepping and plot them under the same 1D plot group. The 2 different time stepping are plotted in line graph 1 (sol1) and line graph 2 (sol2) under 1D plot group.

Do I have to use different studies for different time stepping (yielding sol1 and sol2)? Different steps under the same study don't seem to allow different time stepping.

Is there any way of sweeping time steps in the parent node of 1D plot group? sol1 and sol2 are from different studies.

2D Simulation of PDMS Membrane with PEG-PCL-DA Hydrogel Reservoir

Fri, 28 Mar 2025 19:12:13 +0000

Hi,

I am trying to model the stress experienced within a PEG-PCL-DA hydrogel reservoir which will house cells. I am using a 2D, solid mechanics, time-dependent study to do so. I have created a rectangular membrane made of polydimethylsiloxane (PDMS) with a stationary end and a moving end, this end will be stretched at the strain rates 5%, 10%, and 12.5%. Within the rectangular membrane is a rectangular reservoir with the assigned material, PEG-PCL-DA hydrogel. The model is time dependent and is stretched for 0.2 seconds. I want to set up a cyclic time dependent study to include a retraction phase for 0.4 seconds after reaching a distance of 2mm, but am unsure about how to set up a piecewise or interpolation function. Any thoughts or advice? I have attached my .mph file for reference.

Gradient Coil Simulation Data Analysis

Fri, 28 Mar 2025 17:04:53 +0000

I have a simulation where I have created a set of gradient coils along the z-axis, and the coils are to create a gradient magnetic field across the field of view. I want to plot the change in magnetic flux density, and the magnetic field norm in the x-direction, as a function of distance along the z-axis. I have tried both line integration, and plotting of the magnetic flux density w.r.t. distance, and both return 0, which is satisfactory for line integration, but the magnetic flux density always returns a 0 line value. This is incorrect because when I place points along the z-axis, measuring the magnetic flux density in the x-direction, I receive values. How would I go about creating a 1-D plot that gives me the magnetic flux density as a function of distance?

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.