Latest Discussions - COMSOL Forums

Geometry

Thu, 06 Mar 2025 23:08:40 +0000

I have the coordinates for my spherical nanoparticle in .xyz mol file and i want to import without the bond length showing and also forming a cluster. Thank you

Error while attempting to perform frequency domain study

Thu, 06 Mar 2025 19:00:30 +0000

Hi there,

I'm very green to COMSOL and am encountering this monster of an error while trying to run frequency domain study, does anyone know how I'd go about fixing it?

I can't upload a copy of the file without permission from my supervisor, but any help would be appreciated.

Feature: Stationary Solver 1 (sol1/s1) Division by zero.
Function: / Failed to evaluate variable.
Variable: comp1.solid.D13
Defined as: (comp1.solid.Ecomp1.solid.nu)/((1+comp1.solid.nu)(1-(2*comp1.solid.nu))) Failed to evaluate variable.
Variable: comp1.solid.Seli33
Defined as: ((comp1.solid.eel11comp1.solid.D13)+(comp1.solid.eel22comp1.solid.D23))+(comp1.solid.eel33*comp1.solid.D33) Failed to evaluate variable.
Variable: comp1.solid.Sel33
Defined as: comp1.solid.Seli33 Failed to evaluate variable.
Variable: comp1.solid.Sl33
Defined as: comp1.solid.Sel33 Failed to evaluate expression.
Expression: dvol*(-comp1.solid.Sl33) Failed to evaluate Jacobian of expression.
Expression: (-comp1.solid.Sl11test(comp1.solid.el11)-2comp1.solid.Sl12test(comp1.solid.el12)-2comp1.solid.Sl13test(comp1.solid.el13)-comp1.solid.Sl22test(comp1.solid.el22)-2comp1.solid.Sl23test(comp1.solid.el23)-comp1.solid.Sl33test(comp1.solid.el33))(dvol)

Struggling to understand error thresholds for COMSOL iterative solvers

Thu, 06 Mar 2025 15:55:02 +0000

Hi, I have a question and I am wondering if anyone can help?

I am fairly new to COMSOL, although I have a fair bit of prior experience with CFD/numerical methods. I am trying to run a stationary EM wave, frequency domain simulation of microwaves heating some dielectric material. However, I am struggling to understand how the error threshold settings work for the iterative linear solvers.

I am using COMSOL v5.5. For the stationary linear solver, I am using GMRES with a geometric multigrid preconditioner. For the pre- and post-smoothers, I am using SOR Vector and for the coarse solver, I am solving direct (using Pardiso).

In the 'Stationary Solver' node, I have 'Relative tolerance' set to 0.001. In the 'Iterative' sub-node, I have 'Residual tolerance' set to 0.1 and 'Factor in error estimate' set to 2. However, when I solve, the error convergence (according to the convergence plot) is getting down to around 3e-7 (and flatlining around there), but the solver won't terminate. This seems to be significantly lower than the requested error thresholds.

Can someone please help me to understand how the specified residual thresholds translate into an error threshold that will cause the solver to terminate? It seems quite confusing.

Understanding COMSOL parameters, equations and dropdowns

Thu, 06 Mar 2025 10:50:47 +0000

Hi all,

I have an interesting conundrum. What is the best way to understand the relationship between COMSOL and real life parameters? For example, in packed bed model there is a drop down which can choose between reaction terms being either "Pore volume" or "Total volume". This choice will be influenced by how the reaction rate parameters are defined by the user, whether it is per unit volume of pore or per unit volume of catalyst. These choices will yield very different results if one is not careful and I notice that the model workings and how to couple can be understood well from model library but how does understand the physical significance of the model to the real life values of the model parameters and the different choices COMSOL has to offer?

Regards, Anish

Import file, Mesh generation

Thu, 06 Mar 2025 06:16:35 +0000

Hello, I am using an electromagnetic module to calculate the impact on human tissues and encountered an issue while importing a specific tissue. I would like to seek some advice. The specific details are as follows:

After importing the tissue, I am unable to perform the 'Physics-Controlled Mesh' operation. When attempting to use the 'User-Controlled Mesh', an error message appears: unable to generate a mesh for this domain, and surface intersections are not supported, among other issues. How should I proceed with mesh partitioning in this situation?!
To better align with other models I have constructed, I would like to adjust a certain surface of the kidney model to make it more rounded, specifically by bulging a particular part. How can I achieve this?
After importing the kidney model, I noticed that the relative positions of the two kidney tissues are fixed. If I need to adjust their positions individually — for example, if the distance between the two kidneys is too large and I want to bring them closer together — how can I do this? Alternatively, if the position of a kidney is too low relative to the coordinate system and I want to adjust its position, how should I proceed?

Thank you very much for your assistance!

S11 calculations

Thu, 06 Mar 2025 02:52:38 +0000

Hello, when calculating the S11 of the antenna placed in the chamber using Comsol, is it calculated directly from the port or indirectly through other means?

How to connect two different material layers? Continuity Boundary Condition not showing

Wed, 05 Mar 2025 16:04:51 +0000

I am using COMSOL 6.3 Multiphysics and I am trying to model a composite material following COMSOL webinar "COMSOL Webinar: Simulation of Composite Materials". But I am facing two problems as stated in the video he selects layered shell from the structural mechanics tab but in my structural mechanics no layered shell is available. So I selected shell and proceeded. But in the middle he tries to connect the two layers by using continuity boundary equation. But in my case I am not able to see where is the boundary condition.

Kindly help me out with this.

Thank You.

White light laser reflectance

Wed, 05 Mar 2025 09:11:57 +0000

Hello, I would like to ask about the reflectivity for broadband coherent light. Can I use the ewfd module to analyze each band separately? Because I think that if we discuss the reflectance of individual wavelengths, we do not need to consider the issue of interference, or will the interference of light of different wavelengths actually affect the original intensity? If it does, how should I calculate the reflectance of each wavelength? Thank you.

Undefined variable error

Wed, 05 Mar 2025 06:18:41 +0000

Hello,

I am getting this error when running a model.

Undefined variable. - Variable: comp1.plas.ndotE_wAr_1p - Geometry: geom1 - Boundary: 9 Failed to evaluate Jacobian of expression. - Expression: (comp1.plas.M_wArcomp1.plas.Rsurf_3_wAr)dvol_spatial Failed to evaluate Jacobian of expression. - Expression: (comp1.plas.M_wArcomp1.plas.Rsurf_3_wArtest(WAr))*(dvol_spatial)

Unable to find the variable.

Please share any insights on what the issue might be. Thanks!

Vibration analysis due to Magnetostriction

Wed, 05 Mar 2025 05:12:52 +0000

Problem Statement: There is a core (Ferromagnetic/Steel) placed horizontally with one end fixed and other end free. A coil is wounded on the core, and given AC supply to it. Due to alternating flux generation in core, Magnetostriction phenomenon will be observed, and eventually the core will vibrate. I want to analyze frequency of vibration of the core.

I am new to COMSOL. Can someone please help me out to simulate this problem statement, any references, examples? Thanks in Advance !!

User-defined Young's modulus

Wed, 05 Mar 2025 05:08:04 +0000

I have a flexible tape like material with varying cross section and therefore varying flexural rigidity as well (EI, E= Young's modulus and I= Moment of Inertia). I have the data of its flexural rigidity as a function of its length (something along the line of EI= A*exp(-B*y/L); where y=the position where I want to calculate EI, A,B = coefficients and L= length of the tape). How should I incorporate it in to the material property as an user-defined function?

Link part of model to experimental temperature data

Tue, 04 Mar 2025 21:07:22 +0000

Hi All,

I am trying to have one part of my model follow some temperature data I have from a test. I have the data as a .csv with one column as time and the other as temperature in Kelvin. I created a global interpolation function and imported the data. When I plot the function it looks as expected.

I created a parameter and set its value as the function (I called the function temp so I put temp(t)). I then created a Temperature boundary condition in the Heat Transfer section of the model builder and set the temperature value there to that of the parameter.

When I run the model (I have it as being time dependent), the boundaries I selected remain the temperature of the first entry in the data for the whole simulation. The default initial temperature I have set for the entire domain is different, so I know that it is somehow reading in the first value, just not stepping through the rest of them. I ran a smaller time step set sometime in the middle of the data I have and the boundary temperature was still the temperature in the first time step, not even the temperature at the beginning of the smaller temperature range.

Thus far I have tried setting the temperature in my boundary to the function directly (i.e. not using the parameter) which had no discernible effect. I also tried using a .txt file instead of a .csv with the same data, and nothing changed.

Any advice/help would be greatly appreciated! Thanks

Computing View Factor

Tue, 04 Mar 2025 15:57:17 +0000

Hello, I have performed simulations of surface-to-surface radiation using solar and ambient settings to account for the wavelength dependence of the radiative properties. I would like to verify the view factor between two surfaces. I have already obtained great information from this: https://www.comsol.com/blogs/computing-view-factors-with-the-heat-transfer-module, being able to verify the view factors for the constant wavelength dependence of the radiative properties using the rad.radopd and rad.radopu operators. I tried to do the same using the operators rad.radopB1u or rad.radopB2u but always got an unknown operator error message. I have also tried using a different syntax based on the definition of other variables within COMSOL getting the same result. I thank in advance anyone who can help me solve this problem.

Many thanks and kindest,

Aniello

RF Module Antenna Calculation

Tue, 04 Mar 2025 03:28:11 +0000

Hello, I would like to ask for some advice. I am currently using the Electromagnetic Waves, Frequency Domain (RF Module) to build an antenna, with the frequency range set to 0.7 GHz - 5.1 GHz and a step size of 0.6. The calculation process is very slow, but it eventually results in an error. I hope that the S11 parameters and voltage standing wave ratio (VSWR) of this model can be calculated up to 5.0 GHz and above, and I also need to observe whether the S11 parameter values are less than -10. I previously consulted with you and received your response, and indeed, I made a mistake. After recalculating according to the solutions you provided, the error still persists. The error message is: "Feature: Stationary Solver 1, failed to find a solution. The linear iteration diverged. The returned solution does not converge. Not all parameter steps were returned." Could you please tell me what might be causing this? Is it an issue with the model? How can this problem be resolved? Thank you very much for your assistance!

Calculating volumetric mean shear stress, mean shear rate and mean turbulence kinetic energy in the Mixer Module

Mon, 03 Mar 2025 19:21:20 +0000

Hello,

I am trying to optimize impeller compositions and get better flow regimes for my project and I am trying to learn COMSOL by the other side. The default mixer module creates eddy diffusivity and logarithmic shear rate graphs after the simulation in the results section.

But I need some numerical datas about volumetric mean shear stress, mean shear rate and mean turbulence kinetic energy in the mixer reactor. It would be better if I could add these calculation on study and results sections to be calculate automatically at the end of all simulations I'll do in the future studies.

Can anybody help me about how I integrate these math calculations onto the module to get?

If any other way to calculate these values inside of the mixer reactor mathematically, I will be open different ideas also.

Thank you.

Problem with Adaptive Mesh Refinement in Phase Field Simulation

Mon, 03 Mar 2025 06:16:54 +0000

Hi,

I have been trying to simulation a phase field equation coupled with temperature which are essentially two heat equation (parabolic) form with coupling in the form of having their respective variables in the other physics. I have used Weak Form for both the equations on COMSOL 6.2 and tried automatic mesh refinement to make the mesh finer around the interface as the interface grows in a time dependent study.

Unfortunately, there seems to be not much of detailed blogs here explaining the mesh refinement module and where to apply its respective options. I am not sure how i am getting the result I am or how to troubleshoot it. I have attached the mph filed for reference and also the equations I am using to simulate. Any help is highly appreciated.

Thank you so much!

Antenna calculation

Mon, 03 Mar 2025 05:03:50 +0000

dew point evaporative cooler

Mon, 03 Mar 2025 05:01:45 +0000

I am trying to simulate dew point evaporative cooler which is having dry and wet air channel separated by thin material wet air channel which is coated with porous material. What are the physics involved in this, and how are they coupled? Please guide me.

MEMS Bistable Switch

Mon, 03 Mar 2025 04:25:53 +0000

Hi guys,

I am trying to build a MEMS bistable switch using curved beam. In stationary study, the graph of reaction force vs. displacement has shown a bistable behaviour. In time-dependent study, I apply the prescribed displacement to a block which is meant to push the bistable structure but keeps getting error message like "Nonlinear solver did not converge. Maximum number of Newton iterations reached. There was an error message from the linear solver."

Is it possible to see the bistable structure snap-through process in comsol since I never see an example? If so, what should I do to fix the problem.

Thank you.

Antenna calculation

Sun, 02 Mar 2025 09:11:35 +0000

Hello, I would like to ask for some advice. I am currently using the Electromagnetic Waves, Frequency Domain (RF Module) to build an antenna, with frequency ranges set to 0.7 GHz - 4.9 GHz and 0.7 GHz - 5.1 GHz, and a step size of 0.5 for both. In these two frequency ranges, the calculated results for the S11 parameter and voltage standing wave ratio (VSWR) can only be computed up to 4.7 GHz. Additionally, the resonant points calculated in both frequency ranges are the same, and the values corresponding to each resonant point are also identical. Could you please tell me what might be causing this? Is it only possible to compute up to 4.7 GHz, or is it an issue with my designed model? Thank you very much!