Latest Discussions - COMSOL Forums

Far field calculation in metasurface

Tue, 16 Sep 2025 22:35:08 +0000

Hi guys. Now I am facing a problem of getting far field from an array. When calculating the near field, periodic condition is applied and only a single unit is calculated. But when I tried to apply far field node in the model, I think COMSOL only do stratton-chu equation on the single unit but not the whole array. Since I want to calculate the far field from the whole array, I think I need the integral on the whole surface of the whole array. Is there a solution for this problem now? Thanks!

Partition an Imported Face into Circular/Rectangular Regions in COMSOL?

Tue, 16 Sep 2025 13:44:19 +0000

Hello everyone,

I’m working with imported geometries in COMSOL (typically STL/MPHTXT files), and I would like to partition specific faces into smaller circular or rectangular regions of defined size. The ultimate goal is to assign different boundary conditions on these partitions later in my simulation workflow.

Here’s what I’m aiming for:

Workflow: Import the geometry. Partition a selected face (for example, Face 2/3 in my attached geometry) into circular or rectangular regions (e.g., a circle of 1mm radius centered on a certain point on Face 2). Use these partitions to define boundary conditions in the physics modules and mesh them separately. Ideally, automate or repeat this sequence via MATLAB.

Challenge: I’m able to find the “Partition Faces” operation in the Geometry module, but it only seems to offer splitting via work planes, extended edges, or curves between existing vertices. I don’t see an option to directly create arbitrary-shaped partitions (like circles or rectangles) purely on an existing face, especially on imported surfaces.

Is there a way to do this?

Thank you very much for your time and assistance!

Force and torque change with displacement

Tue, 16 Sep 2025 08:19:54 +0000

What I want to achieve in a simulation (multibody dynamics) is to apply a certain external force and torque to an object, where the magnitude of the applied external force and torque varies continuously with displacement. Specifically, when the change in displacement is less than 1 [mm], I want the displacement value to 'revert' or 'hold' at the last achieved value that meets the conditions (for example, the last whole millimeter point). In other words, I want the forces and torques I apply to exactly result in a 1 [mm] change in displacement. I have tried many different settings, but nothing has worked, so I would like to know how to configure it properly.

Help with Free flow and Porous Media Flow (Brinkman)

Tue, 16 Sep 2025 01:58:12 +0000

Hi all,

NOTE: I tried uploading to the forum earlier today, but once I finished writing and click "submit" it disappeared and I couldn't figure out if it was under review? or some sort of process before posting, or if it was discarded entirely. If you see a similar post by me that looks like this one, my apologies.

I am having trouble modeling using the Free flow and porous media flow (Brinkman). I am trying to model hyporheic flow by simply creating a 2D box, made of 2 layers (sediment and water). I apply velocity or pressure from the left boundary and create a lateral flow that partially seeps into the sediment bed (mimicing hyporheic flow). However, the issue I'm having is that the model will not find a solution and/or the solver won't converge unless I use very low velocities or pressure values (0.001 Pa or 0.001 m/s). I am trying to run the model using larger values of velocity, not extremely large but something around the values of 0.5-5 m/s velocity values.

I tried using another physics component, which was the free and porous media flow (Darcy), but to no avail. I tried making the cross section larger (it is 1m by 0.5 m), and again the model wont give out results unless the boundary condition is very small.

Can someone please help me figure out why the model wont let me use larger values, and how do I fix this issue? Thank you.

Exporting 3D shape without Its mesh

Mon, 15 Sep 2025 04:07:36 +0000

Hello, everyone! I am relatively new in COMSOL. What I've understood is when I export an expression under "volume" result, I will get cube coordinate as well as the expression value in .txt format (for example). Then when I visualize It, there will appear a volumed shape together with Its mesh.

However, I just want to export any volumed shape without any mesh. Anyone please help me. Can I get this from COMSOL? Many thanks in advice

How to Export Mode Shapes (Vertical Displacement) in COMSOL 5.2

Sat, 13 Sep 2025 02:44:48 +0000

Hi everyone,

I’m currently modeling a plate because I want to obtain its mode shapes and corresponding natural frequencies. I’ve been able to get those results, but now I’d like to export the mode shapes (specifically the vertical displacement ? as a function of ? and ?) and I’m not sure how to do it.

In the Results tab, I see Surface 1, and under that, I have Deformation, but I can’t find a way to export the data. I’m using version 5.2.

Any guidance would be greatly appreciated.

Thanks in advance

Why does 2D static deformation plot show displacement magnitude smaller than the Y-axis displacement?

Fri, 12 Sep 2025 17:09:34 +0000

In this model, the color-scale (displacement magnitude, ~0.1mm) deformation does not match the XY spatial deformation of the plot (~20mm). Can someone help me understand how the displacement magnitude is different from what is plotted in XY space?

Force and torque change with conditions

Fri, 12 Sep 2025 13:51:44 +0000

One type of simulation (multibody dynamics) I want to achieve is to apply a certain external force and torque on an object, with the requirement that the magnitude of the applied external force and torque changes continuously with displacement. It should be such that the magnitude of the force and torque is just enough to cause displacement. How should I set this up?

Material Properties Reference

Fri, 12 Sep 2025 13:24:37 +0000

Hello,

I am working COMSOL Multiphysics 6.3 for quiet a while now and would say I have quiet a bit of experience.

However I have one big issue. I can not get the references for material properties from the COMSOL library. I tried multiple approaches to get that information:

1) As described in the Material Library User guide: In Materials -> Browse Materials -> Select Material and Property. The property reference window just displays no text at all for any material or property I select.

2) Checking in File -> help -> documentation -> Comsol Multiphysics -> Reference Manual -> Materials -> Module-Specific Material Libraries: The source listed here for the piezoelectric materials is the efunda website, which in itself has some books listed but not property specific and non of the books seems to have matching properties to the one COMSOL uses. Some values may be the same but never the set of values I list below. That applies for the CRC Handbook, the MEMS handbook and the Macmillan properties.

3) Checking the online reference manual -> materials -> module specific material databases. There are no sources named for piezoelectric materials and the ones for MEMS are the same as on the efunda webpage but as I said they do not match the values in COMSOL. For example youngs modulus for gold is 70e9 in COMSOL but in the books listed 78e9.

I want references for Youngs Modulus, Poisson ratio and density for: Au, Pd, SiO2 I want references for Coupling matrix, elasticity matric, relative permittivity and density for: Lithium Niobate and Gallium Arsenide

How do I obtain proper sources? Is there a bug in the first option I list? That seems to be the way one is supposed to get that information.

Thanks for any help.

Lumped port problem (Element 1 should be placed between two conductive boundaries)

Thu, 11 Sep 2025 13:53:51 +0000

When I placed the lumped port in the CPW design the error showed - "Subfeature Uniform Element 1 should be placed between two conductive boundaries. - Feature: Uniform Element 1 (ue1) " - I placed the lamped port in between the perfect electric conductor boundary, still this error message came and stopped the process. Can anyone check the file attached and give me the advise to correct this? I already go through the examples COMSOL provide, but can not understand the problem. Also the ground and ports are not connected to each other (separated by a air gap).

1D-Plot the Deformation of a Line / Edge

Thu, 11 Sep 2025 12:18:02 +0000

Hi again,

I wanna plot the deformation (shape) of an outer edge / line of a 3D-structure before and after applying an external load. The undeformed shape I obtain via a 1D-plot using the expression z over x or the arc-length out of an edge 3d node under results. The displacement I obtain via a 3D-cut line. But how can I obtain the position z over the length x in the deformed state? I´m only able to get the undeformed state. But the information about these coordinates must be available in the results, since the 3D-Plot shows the deformation. Maybe one can use the mesh nodes along that line/edge? Pls give me a hint, I´m dealing with that topic for 4 days now.

Thanks,

BR Sven

Comsol Multiphysics 4.2a for Windows

Tue, 09 Sep 2025 17:47:38 +0000

Good afternoon everyone. I hope you are all well.

I have a permanent license for Comsol Multiphysics version 4.2a, but I can't find the installation CD for this version.

This version isn't available on the Comsol website. Can anyone help me? Thank you in advance. Best regards;

Automated Mesh-Based Reassignment of surface Boundaries in COMSOL

Mon, 08 Sep 2025 16:36:02 +0000

Hi all,

I’m working on a AC/DC COMSOL model where I need to move the terminal and ground boundaries to different spots along a specific surface in my geometry. Right now, I pre-define several possible boundaries and manually assign the conditions for each run, but this gets unwieldy for automated or parametric studies.

I’m looking for a more automated (or programmatic) way to do this, ideally using outputs from each simulation to update the positions of these boundaries for the next iteration.

Specifically, I’m interested in any method that allows me to reassign boundaries based on the mesh. The boundaries themselves don’t have to “move” geometrically, as long as I can programmatically select new mesh nodes or elements as the new terminal or ground (using the initial surfaces as a reference and translating the assignment from there), that would be perfect.

Has anyone done something similar, or does anyone know of features, best practices, or scripting approaches (using MATLAB/LiveLink, Java API, etc.) that could help? My current model uses manual pre-tagged surfaces, but I’d love to streamline this process.

I have attached my current model where the surfaces are pre-defined and assigned manually. Right now, I pre-define several possible circular surfaces and manually assign the terminal and ground to the top two circular surfaces. For each new simulation, I want these boundaries to shift to the next two circles, and continue in this way. I would greatly appreciate any guidance or resources to help automate this process.

Thanks in advance for any ideas or suggestions!

1D-Plot from 3D Symmetry Data

Mon, 08 Sep 2025 14:45:53 +0000

Hi,

I got a simple model of a roller under load. Due to the symmetry along the length of the roller, just the half is simulated via a symmetry node and visualized via a 3d mirror node and a 3d edge in the results data set. That works as it should for the 3d evaluation. But if i wanna evaluate (plot) the displacement (shape) of the outer body edge of the roller, I just can pick the one half of the original split half geometry model. So now the question: Is it possible to "copy" or "mirror" also the symmetric displacement (shape) data to show the whole geometry's displacement (shape) at the 1d-Plot? Btw, a 3d line doesn´t work, since the outer shape of the roller is not straight but curved.

Thanks for any recommendations,

BR Sven

Measuring Interface position as a function of Time in COMSOL (Two-Phase Flow, Level Set)

Mon, 08 Sep 2025 11:31:55 +0000

Hello everyone,

I am modeling a wicking phenomenon in COMSOL Multiphysics using the Two-Phase Flow, Level Set method with Laminar Flow. My main challenge is extracting the wicking height (or interface position) as a function of time.

I have attempted to use the Cut Line method to track the fluid-fluid interface (phils = 0.5), but so far I have not been able to properly obtain the wicking height vs. time.

If anyone has experience with this or knows a reliable way to correlate the interface position with time in COMSOL, I would greatly appreciate your guidance.

Thank you in advance for your help!

Convergence issue using Richard's equation

Tue, 02 Sep 2025 16:48:09 +0000

Hi everyone,

I am working on a hydraulic model. The geometry of my model is shown in the attached Figure. I am using Richard's equation. There are host rock that occupies most of the model, a fault shown as the narrow pipe, and other formations at the top right.

The general water flow process is that the inflow is through the top boundary with topography and outflow is through right boundary and top boundary when water table intercepts the surface, which means that pressure head at the top is higher than zero.

For boundary conditions, a constant precipitation was applied at the top boundary with topography, which is in green in the figure. A pressure head of 0 Pa was applied at the top of fault. For the rest top part, a previous layer was applied and it will be applied a big conductance when pressure head is higher than zero. Otherwise, a conductance of 0 will be applied.

The main object of these settings was to ensure that the location of the water table can be dynamic determined by the precipitation rate and permeability instead of applying a constant head at the top.

However, when I use Time-dependent solver for cases that don't have a steady state, the solver does not converge/converges slowly. The solving progress usually stays at 4% and does not move on. If anyone has any insights about how to make it converge or improve my model, i would really appreciate it! Please let me know if more information is needed. Thank you!

Best, Zihao

Implementing Direction-Dependent Etching Velocity in COMSOL Deformed Geometry

Sat, 30 Aug 2025 16:29:07 +0000

Hi everyone,

I am trying to reproduce the chemical etching tutorial from COMSOL (link: https://www.comsol.com/model/chemical-etching-44481 ). In the tutorial, they used Prescribed Normal Mesh Velocity in Deformed Geometry to describe the etching velocity, where the velocity value is constant. In my case, I would like to define a non-uniform etching velocity, meaning that the velocity in the x-direction is different from the velocity in the y-direction. I tried some approaches, but they didn’t work. Could you please give me some suggestions on how to implement this?

Thank you so much!

Color legend

Sat, 30 Aug 2025 03:36:53 +0000

I wanted to change the height and position of the color legend, but I couldn't find it

Undefined Value in Temperature Field (NaN/Inf in comp1.T)

Fri, 29 Aug 2025 10:01:39 +0000

I am currently working on a numerical simulation of a plasma torch using COMSOL Multiphysics. The goal of the simulation is to model the behavior of a plasma jet generated by an electric arc discharge between an anode and a cathode. As part of the setup, argon gas is injected through the torch, which becomes ionized due to the high-temperature environment created by the electric discharge. This ionized gas forms a plasma jet that exits the torch and interacts with an open boundary, representing ambient surroundings or downstream flow.

The simulation includes the following coupled physics:

Electric currents to model the arc discharge.

Laminar or turbulent fluid flow for argon gas transport.

Heat transfer to capture thermal effects and plasma temperature distribution.

Open boundary conditions to allow outflow of plasma without artificial reflections.

However, when I run the model using the Stationary Solver, I encounter the following error message:

Feature: Stationary Solver 1 (sol1/s1) Undefined value found. Detail: Undefined value found in the equation residual vector. There are 2590 degrees of freedom giving NaN/Inf in the vector for the variable comp1.T. At coordinates: (0.0176092, 0.298922), (0.0143478, 0.3), (0.0163046, 0.298921), ...

Extracting data in 3d format

Thu, 28 Aug 2025 15:59:56 +0000

So far, I have been extracting abs(emwHz) values for given parameter in a 2D cutplane in my loop antenna model. I would like to extract it in a 3D grid format.

However, most methods of trying a grid 3D dataset has resulted in errors, where Hz is an undefined variable, like as shown below.

"Undefined variable. - Variable: comp1.emw.Hz - Global scope Failed to evaluate expression. - Expression: comp1.emw.Hz"

Is there a way to overcome this error, or if not, to obtain Hz values in a 3d format?