Latest Discussions - COMSOL Forums

Wall Deposition

2025年10月23日 15:22:05 +0000

Hello,

I’m currently trying to visualize aerosol deposition in the laminar flow regime using Particle Tracing for Fluid Flow in COMSOL, aiming to validate experimental results from a nebulizer-based setup.

My model consists of a cylindrical pipe (radius = 1 mm, length = 6.7 mm) with air flow velocity = 0.03 m/s. I’m simulating 0.5 μm particles with Stokes drag and Brownian motion enabled. However, I’m unable to observe significant deposition under these conditions. Interestingly, deposition increases sharply when gravity is included.

Has anyone successfully modeled nebulizer-like aerosol deposition in a laminar airflow field? Are there recommended settings or modeling approaches to better capture near-wall deposition without relying solely on gravity?

I’m also considering switching to the Transport of Diluted Species interface for a continuum approach to diffusion and deposition, and I’d appreciate any insights or comparisons from others who have tried this.

Ultimately, my goal is to compare cylindrical vs. rectangular channels to understand how geometry affects deposition patterns.

Thank you in advance for your suggestions and experiences!

Concrete plastic deformations without Geomechanics Module

2025年10月23日 09:56:34 +0000

Hello, I’m new to COMSOL and currently trying to perform a flexural analysis of a concrete beam. I would like to ask whether it is possible to accurately model the plastic (nonlinear) behavior of concrete without having access to the Geomechanics Module. From what I have read, the Smeared Crack Model and Damaged Concrete Model are available only through the Geomechanics Module, while the default material models such as von Mises or Tresca seem to be more suitable for metals, not brittle materials like concrete. Is it possible to simulate plastic deformations or cracking in concrete using only the Structural Mechanics Module, or is the Geomechanics Module required?

Thank you for your help

Minor Dataset issue

2025年10月22日 20:23:54 +0000

I have a minor dataset issue:

I am running the same model in COMSOL 6.2 on 2 machines running the same OS. On one machine, when I compute a new study it makes a new dataset in the results. With the other, the study overwrites the previous dataset with the new results. Where is the preference that controls this behavior? I prefer a new dataset with each study.

Geometric Optics Imaging through medium

2025年10月22日 16:22:29 +0000

Very new to COMSOL geometric optics, trying to model how an image looks after a cross grating / scattering medium / absorption layer domain or boundary. At first I want to keep it as simple as possible and looking for insight to support my challenges. All of my Multiphysics experience thus far has been in wave optics module.

To keep it as simple as possible for now the optical train would be image plane -> medium -> lens -> ray detector. I was able to compute ray trajectories previously, but some troubleshooting change i made to the physics broke things and now am getting an error each run time that prevents ray trajectories from being plotted. Advice / insight / applicable models to point to and learn from are all helpful. I already tried adapting the double gaussian lens for my purpose by adding an additional film domain right in front of the image plane but that seemed to have broken things.

Objective: Input scattering medium or cross grating parameters to model image formation through the medium. Idealistically similar to the double gauss lens tutorial results where the image and formation are next to each other.

Branch Flow Statistics in Fluid Simulation

2025年10月22日 08:47:54 +0000

In fluid simulation, the model has one inlet and one outlet, with 90 branch pipes in the middle. How can I quickly calculate the flow rate of each branch pipe in the middle? Thank you for your help.

S parameter extraction from 3D model + external circuits

2025年10月20日 19:00:11 +0000

Hi everyone,

I’m modeling a two-port piezoelectric resonator that functions as a transformer (per the mBVD representation). I’ve connected the device to an external matching network with a series inductor at the output to cancel Cout, and I’d like to extract the S-parameters of the combined device.

So far: Using Terminal (power) with Terminated boundaries on the 3D structure gives me S-parameters for the bare 3D model only, not the coupled device-and-circuit.

I also tried an Electromagnetic Waves, Frequency Domain (EMW) study, but I’m not confident this is appropriate for a primarily lumped, electromechanical two-port with an external circuit.

Question: What is the recommended workflow to obtain S-parameters when a 3D piezoelectric resonator is connected to external circuitry?

Thank you for any guidance.

induction heating

2025年10月19日 06:52:30 +0000

Why, during the process of conducting the simulation of workpiece induction heating, as the workpiece moves, the temperature of the induction heating part of the coil keeps rising continuously, and it fails to reach a state where the heat input and output are balanced, thus preventing the temperature at the heating location from remaining constant.The 2-D rotational modeling that I use.Set up heat radiation and heat flux for heat dissipation. Thanks for help!

Electric field not reaching material across air gap (Electric Currents, Frequency Domain)

2025年10月18日 04:01:01 +0000

Hello everyone,

I’m currently working on a model in COMSOL Multiphysics (AC/DC Module – Electric Currents, Frequency Domain) and I’m facing an issue where the electric field does not seem to penetrate the material located across a small air gap.

Here is the setup: -Two planar electrodes (terminal and ground) placed side by side on a PCB substrate. -Above the electrodes, there is a thin polymer layer, then a 2 mm air layer, and finally a block of bone material. -Everything is enclosed by a cylindrical air domain. -Excitation: 3.3 V at 32 kHz (frequency domain study).

When the air layer is present between the electrodes and the bone, the electric field and current density completely vanish inside the bone, only the region in the air shows nonzero values. If I replace the air layer by the bone (so there’s direct contact), then I see the expected electric field inside the bone and i can see changes in capacitance, even when changing bone properties and material.

The strange part is that if I artificially set the air conductivity to something like 0.001 S/m, the field appears inside the bone again. But with σ_air = 0 S/m, it disappears entirely and capacitance dont change.

Thanks in advance for any advice or insight, I’ve been stuck on this for a while and would really appreciate any suggestions on how to make the field correctly propagate through the air and into the bone layer.

Best regards, Diogo Pires

Shape changes with Temperature in COMSOL using Joule heating

2025年10月16日 22:02:26 +0000

The below post is related to an archived discussion

[start here] Hi, Sorry to follow up now after a long time. I could not work with the model. I am not actually looking for thermal expansion. My problem is a little different. Let me explain- My model starts with a regular octagonal shape, with side marked as 1,2,3,4,5,6, 7 and 8. After modeling, I am expecting the shape to convert to a rectangular shape. Considering both shapes will have same volume, after modeling side 3 and 7 will move to -x and +x respectively. The change in length of the sides will be function of domain temperature. I am attaching an image here. Can anyone please guide where to start with this problem?

Transient study - Convergence issues

2025年10月16日 11:47:48 +0000

Dear all,

I am experiencing an issue with the model attached to this request. My goal is to analyze the behavior and response of a superconducting tape under the action of an external field generated by appropriately applying currents in the system’s exciter.

When I modeled the superconducting region by approximating it as a line, I did not encounter any problems. However, now that I am treating it as a rectangular domain (also because I plan to include additional non-superconducting layers in the future), the model shows convergence issues.

I am fairly confident that the formulation is correct as implemented, since I have verified it against several references in the literature, and it is consistent with those sources.

Could you please help me resolve the issue related to Study 2 – Transient? I have tried setting the stationary Study 1 as the initial condition and tested various solvers, but without any positive results.

Thank you very much for your support.

Geometry Repair

2025年10月15日 14:13:32 +0000

Hi all

Could you explain an effective procedure to repair a geometry (files: *.stl or step) in order not to produce errors such as "intersection faces", and reduce elements or size of the geometry to improve compilation time ?. I've tried already several strategies as reparation in Meshlab and Freecad platforms, but not succefull so far. I attached the geometry file for consideration... Thanks

Reg- Microbalance sensor

2025年10月14日 03:05:34 +0000

Dear Staff, Good morning, I would like to simulate Mass sensor based on graphene. Could you assist me or send any related model to start.

thank you

TFLN rib waveguide - optical field results not showing

2025年10月13日 10:08:50 +0000

Hello everyone, I am trying to simulate the optical field of a rib waveguide in lithium niobate. I attached an image of the cross section, together with the mph file. I first defined a work plane and extruded it to create the structure. I defined the materials and inserted a diagonal refractive index for the lithium niobate since it is an asymmetrical material. In the end I defined the ports and inserted the mesh, and launched everything.

The problem is that the program runs and ends the simulation, without any shown error, but at the same time it doesn't compute the electrical field. In fact, the electrical field section under "Results" doesn't exist. Why is that?

Solver Convergence Issue in 2D Brinkman Flow through Anisotropic Porous Medium (Wavy Channel)

2025年10月13日 05:07:18 +0000

Hello,

I’m simulating steady-state flow in a 2D wavy channel using the Brinkman Equations interface (COMSOL Multiphysics 6.0). The flow domain is an anisotropic porous medium confined between two impermeable wavy walls.

MODEL SUMMARY: * consists of a wavy bottom that i defined using parametric curve * upper top plate is a moving plate with velocity lets say U0 in x direction and 0 in y * the left and right walls are not moving * No slip condition is applied for all * Physics used is brinkaman equation where the porous matrix is set to be a diagonal matrix where the diagonal entries were already defined in the parameters under global definitions. * Physics controlled mesh is used. * stationary study is added.

ERROR:

Failed to find a solution. Maximum number of Newton iterations reached. There was an error message from the linear solver. The relative residual (0.041) is greater than the relative tolerance. Returned solution is not converged. Not all parameter steps returned.

TRIED SO FAR: * Adjusted tolerances and damping * switched between direct solvers * increased iteration limits

QUESTIONS: * Recommended solver setup (Fully Coupled vs Segregated) for Brinkman flow? * Tips for stabilizing convergence in anisotropic, wavy porous domains? * Any scaling or nondimensionalization suggestions?

Any help to stabilize or improve convergence for this steady Brinkman model would be appreciated.

Regards!

Regarding the issue of the presence of both the paranoid coil and the incentive coil simultaneously

2025年10月11日 09:30:41 +0000

I want to conduct a simulation of a transducer. The overall structure is a cylinder. The coil part consists of an inner bias coil and an outer excitation coil. The bias coil provides a constant bias magnetic field, while the excitation coil provides an alternating magnetic field. How should I set up the bias coil to be energized by direct current, and the excitation coil to be energized by alternating current of a certain frequency?

How to add multiphase material in COMSOL 6.0

2025年10月11日 08:30:07 +0000

I am trying to replicate the capillary filling model for two phase field in COMSOL 6.0. How to add a multiphase material? If we add from material library, how to specify the phases?

Potential Field in Electro-osmotic Flow

2025年10月10日 09:19:25 +0000

Hi all,

Currently I was trying to reproduce results from a research paper titled from Choi et al. (2011), (attached below). In that paper, two boundary conditions are used at the interface for electric potential. These are (i) potential jump and (ii) simplified gauss law at the interface. Now, while modeling using the 'es' physics in COMSOL, I am not able to see how to model both the conditions at the interface.

I have attached my trial file, in which when I tried putting these conditions at the identity pair, the surface charge condition (gauss law) was getting overridden or fallback-ed due to the potential jump condition. From my understanding, COMSOL isn't letting me put both at the same time. I tried using a coefficient-form PDE to solve it too but it had the same issues with the interface conditions.

What could be a potential fix to this? Is there another way to model the system as given in the paper?

Dual gate MOSFET design

2025年10月08日 05:08:55 +0000

Can anyone give any guideline regarding the design of dual gate MOSFET in COMSOL?

Gaussian Beam Plane Wave Expansion

2025年10月07日 21:21:26 +0000

Hi, I just recently learnt that the paraxial gaussian beam equation is not really effective for a scatterer surrounded by inhomogeneous domains when using the scattered field formulation. it was proposed I use the plane wave expansion approach. for a 3D model, has anyone used the plane wave expansion approach using equations. I have attached my model of the paraxial approach. you can edit my model to suit the plane wave expansion method or if you have any example. That will be great.

NaN/inf value error

2025年10月06日 08:40:48 +0000

I'm trying to simulate a cylindrical gas bearing with a sort of foil "floating" on it but I keep getting the same error: Undefined value found. - Detail: Undefined value found in the equation residual vector. There are 7 degrees of freedom giving NaN/Inf in the vector for the variable comp1.spatial.u. at coordinates: (1.94255,-0.112035,0.0920496), (1.94284,-0.111364,0.09286), (1.94356,-0.111577,0.092605), (1.94329,-0.111264,0.0930404), (1.9433,-0.111842,0.0923323), ...

I don't think my mesh is the problem as well as my boundary conditions. I suspect it is something to do with my geometry although I also have the feeling that is correct as well. The model was working when I used the fluid-structure interaction model but I wanted to model smaller thickness of the foil and decided to change to fluid-shell interaction but then it did not work anymore whilst the boundary conditions basically have not changed compared to the previous model that did work. To get a surface from my previous model I have used the tool "Convert to surface" where I had a finite thickness ring around the gas bearing. What could be the problem here and where should I be looking to solve this problem?