Latest Discussions - COMSOL Forums

Laminar Flow Not Affecting Electroanalysis Results — Dean Flow Not Observed

Wed, 01 Apr 2026 14:58:52 +0000

I am modeling a microfluidic electrochemical system in COMSOL using a two-step study: (1) a stationary Laminar Flow (spf) solution to obtain the velocity field, followed by (2) a time-dependent Electroanalysis (tcd) study for cyclic voltammetry (CV). The intention is for the velocity field from the laminar flow solution to be used in the electroanalysis step so that convection influences species transport and, consequently, the electrochemical response.

However, I am not observing any change in the CV results when varying flow rate or channel curvature (including geometries where Dean flow is clearly present in the velocity field). The concentration profiles at the working electrode appear unchanged across different flow conditions, suggesting that convection is not being accounted for in the electroanalysis solution.

In the time-dependent study step, Laminar Flow is unchecked (not solved), and I have set “Values of variables not solved for” to use the solution from the stationary study. Despite this, the electroanalysis results remain insensitive to flow.

Is there something I may be missing in properly coupling the laminar flow solution to the electroanalysis physics (e.g., enabling convection in species transport, required multiphysics coupling, or solver configuration)? Any guidance would be greatly appreciated.

Explicitly Modeling Reference Electrode

Wed, 01 Apr 2026 14:43:12 +0000

Hello everyone,

I am attempting to model a three electrode Microfluidic Electrochemical Sensor (MES). I am able to model the working and counter electrodes and get some results, but I believe they are incorrect. One reason I am thinking is because I am not explicitly assigning a boundary condition to the reference electrode. Is there a way to explicitly assign a boundary for the reference electrode and assign the correct physics? Any help would be greatly appreciated. I am using the electroanalysis physics.

How to extract the stiffness matrix K in multi-body dynamics (mbd) Transient simulation using MATLAB?

Wed, 01 Apr 2026 08:49:15 +0000

As the title indicates, when I attempted to use the mphmatrix function, I encountered an error: "The solution does not contain an active Variables node"

How are global evaluations of the displacement field done in a solid mechanics simulation?

Wed, 01 Apr 2026 07:57:16 +0000

I am doing an eigenfrequency study of a solid mechanics system. I have defined some variables, let's call them A and B, which depend on the "solid.disp" variable from the "Solid Mechanics>Linear Elastic Material" node (that is to say, the mechanical displacement magnitude) and the "displacement field", the dependent variable in the "solid mechanics" node. I then evaluate A and B under a "results>derived values>global evaluations" node. Now my question is, how will A and B be evaluated? The mechanical displacement should change as the mechanical system resonates, right? So is the solid.disp used in the global evaluation the maximum of the displacement magnitude or is it something else?

I am asking because I expect A > B and instead get A < B so maybe I am missunderstanding something about how the variables are evaluated. For both variables, A and B, involves an integral over the same spatial domain and B involves a derivative of the "displacement field".

RF Magnetron sputtering solving errors

Tue, 31 Mar 2026 10:44:14 +0000

Facing the following errors while solving, I need help with this.

Failed to find a solution. Singular matrix. Returned solution is not converged. Not all parameter steps returned.

"Divergence error" when simulating EM interaction between a Hall plate and a coil

Tue, 31 Mar 2026 06:05:59 +0000

Hello everyone,

I am currently working on simulating the electromagnetic interaction between a Hall plate and a surrounding coil in an IC, and I have run into a persistent convergence issue.

My coil model contains very small gaps (typically < 0.5 μm), and the coil itself is made of wide, thin metal (width ~30 μm, thickness ~0.5 μm). Because of this high aspect ratio, my simulation consistently fails with a Maxwell divergence error (e.g., divergence cleaning failed). Increasing the mesh density did not solve the problem; it only led to a severe out-of-memory (OOM) issue.

I have tried the following troubleshooting steps, but none of them resolved the error:

Using a Custom Mesh Sequence: I applied a "Free Triangular" mesh to the coil surfaces and used a "Swept" mesh across its thickness. For the remaining domains (the spherical air domain and the Hall plate), I used a "Free Tetrahedral" mesh.

Result: This effectively reduced the total number of mesh elements and memory load, but the divergence error still occurred.

2.Using "Remove Details" in Geometry: I tried using the Remove Details operation to eliminate small geometrical features in the air gap region.

Result: The divergence error persists.

These are the approaches I could think of so far, but I am certain I must be overlooking a critical setting (perhaps a specific boundary condition for thin structures?). Has anyone encountered a similar issue or can point me in the right direction to debug this?

Thank you very much for your help!

Implementing the floquet periodic condition in lshell

Mon, 30 Mar 2026 08:17:24 +0000

Hello, I have been trying to draw the dispersion curves of a layered composite material using the shell interface, which includes the floquet boundary condition, and I have obtained some results. But, it seems that the layered shell interface is better suited for this purpose, the problem am facing is that there is no implemented floquet boundary condition in lshell. Is there a way i can implement it easily. Thank you very much

Fixing Divergence Caused by Modeling Ambient Air Heated by Furnace

Mon, 30 Mar 2026 05:54:16 +0000

Hello All

I am a research intern who is attempting to model the effects of boring a hole into a furnace utilized at our lab as we wish to know how hot the surroundings will become due to this hole. I have had no issues creating the geometry, and the simulation converges and behaves just fine when it is just the furnace with the bored hole, but once I add a block of air above the furnace to model the ambient air around this bored hole my simulation consistently diverges.

To help picture the study I have attached a screen-shot of the model in question. The rectangle on top is the block of air causing divergence.

I am running a stationary multi-physics study of heat transfer in fluids and laminar flow. For physics, the air in question is assigned laminar flow and ambient initial conditions. Gravity is on, and as the air is a boundary of the simulation, I have assigned it the boundary condition of heat flux just like the rest of outer layer of the model to simulate convective cooling of this block of air from the ambient air around it thats not being explicitly included in the geometry.

To preface I am not well versed in FEA nor PDE's, so I am sorry if my question seems trivial or foolish. This problem also seemed quite simple to me but I cannot get anything to converge for the life of me so I am hoping someone who knows anything could potentially help. If any more information is needed, please ask and I will specify.

Thank you

Modeling Temperature Stability for Vaccine Transportation Using Dry Ice

Wed, 25 Mar 2026 13:41:15 +0000

Hello everyone,

I am interested in modeling temperature distribution for vaccine transportation using dry ice in insulated containers. Since vaccines require strict cold chain conditions, maintaining a consistent low temperature during transit is critical.

I would like to understand how we can simulate:

Heat transfer inside an insulated box Sublimation effect of dry ice (CO₂ phase change) External temperature impact during transportation

Is it possible in COMSOL Multiphysics to couple heat transfer with phase change for dry ice cooling? If yes, which physics interface or module would be most suitable for this type of simulation?

Additionally, if anyone has experience with real-world cold chain applications (such as pharmaceutical logistics), I would appreciate insights on practical parameters to consider.

From a practical perspective, reliable dry ice supply and proper insulation are commonly used in the industry to maintain temperature stability during transport.

Looking forward to your suggestions and guidance.

Thank you.

Electrostriction simulation

Wed, 25 Mar 2026 13:40:50 +0000

Hello,

I am trying to simulate the compressive strain caused by an electric field, but I am having problems to have the strain plotted in 2D graphs. I think I am doing wrong at somepoint in the plot, because I am getting the opposite I was expecting for a strain graphs in 2D. Could someone help me with this? What is the variable name for strain when I am plotting it?

Modeling 3-phase Toluene (LNAPL) transport and biodegradation across vadose and saturated zones: Physics interface selection

Thu, 19 Mar 2026 13:06:40 +0000

Hi everyone,

I am developing a model to simulate 3-phase Toluene (LNAPL) transport and natural attenuation—including volatilization and Monod-based biodegradation—across both vadose and saturated zones.

Which physics interfaces should I use to best capture this process? Specifically, is it better to couple "Multiphase Flow in Porous Media" with "Transport of Diluted Species in Porous Media", or is there a more numerically efficient approach to handle the air-water-oil distribution and phase-specific reaction kinetics?

I am particularly concerned with correctly representing the capillary fringe and the transition of toluene from a separate liquid phase to dissolved and gaseous phases. Any advice or relevant examples from the Application Gallery would be greatly appreciated.

Exposure to an RF Electromagnetic Pulse

Thu, 19 Mar 2026 09:37:45 +0000

Hello there!

I am a newcomer to COMSOL Multiphysics and I am currently attempting to set up a simulation involving the exposure of a object to a radiofrequency (RF) electromagnetic pulse. The primary objective is to study the thermal and electromagnetic physical parameters (temperature, EF distribution). I am aware that the appropriate tool for this type of problem is the RF Module; however, I remain uncertain as to which of its physics interfaces best suits my case. Having briefly reviewed the available options, I have identified interfaces such as Electromagnetic Waves, Frequency Domain (emw) and Electromagnetic Waves, Time Explicit, among others, but I lack the background to determine which most accurately captures the physics of RF pulse propagation. I am also encountering difficulties in correctly defining the boundary conditions. Specifically, I am unsure how to set up the RF pulse excitation source and how to handle the outer boundaries of the computational domain. I have come across conditions such as Scattering Boundary Conditions and Perfectly Matched Layers (PML), which appear to be relevant for suppressing spurious reflections at the domain boundaries, but I have not yet been able to understand how to apply them correctly within the context of my model.

In light of the above, I would be most grateful if members of this community could direct me towards:

Official COMSOL tutorials or Application Library models addressing RF exposure. Should any member of the community have already addressed a similar problem and be willing to share a worked example or provide direct guidance, I would be most grateful for their contribution;
Guidance on which physics interface within the RF Module is most suitable for this class of problems;
Introductory documentation or methodological references appropriate for users approaching coupled electromagnetic–thermal modelling for the first time.

Any guidance, even of a general or preliminary nature, would be of considerable value at this stage. Thank you in advance for your time and expertise.

Kind regards

Mass conservation violation in a stirred reactor

Wed, 18 Mar 2026 16:01:55 +0000

Hi,

I would like to simulate a stirred reactor for an aqueous reaction. The stirrer is a huge plate, and the reaction occurs on the surface of this plate. For the flow regime, first, I solve the Frozen Rotor problem. Then, I use the Frozen Rotor solution as the initial condition for a time-dependent study. To study mixing and reaction, I use the flow field obtained from the time-dependent simulation, and I solve another time-dependent study

I am considering an irreversible reaction, for example: A → B. At some point, the concentration of A starts to accumulate inside the reactor, while the concentration of B begins to decrease (which is physically impossible). The trends appear to be very symmetrical. If I disable the reaction, the concentrations becomes stable. There is no accumulation in this case.

I asked ChatGPT about possible reasons for this behavior. I have tried changing the mesh density, adjusting the time steps, and switching the convective term to conservative form (which led to a numerical instability/explosion), and none of these worked for me.

Therefore, I would like to ask whether you have encountered this type of problem before, and what the possible causes or solutions might be.

Thank you for your time and support.

Trial passcode

Mon, 16 Mar 2026 09:48:52 +0000

Can you provide me with a trial code so I can test it out and see if it's suitable for my project?

Problem about Deformation of a Biomedical Stent with Simulation

Sat, 14 Mar 2026 16:19:20 +0000

Hello guys, I encountered a problem when conducting the mechanical simulation of a bracket and would like to seek advice from everyone. In the reference case, due to the symmetry of the bracket, only a 1/24 model was established for calculation; however, my own bracket structure is not completely symmetrical, so I hope to directly establish and calculate the entire bracket model. But when using the complete model, an error occurs during the solution process: "The iteration for finding the elastic-plastic strain variable did not converge." I would like to ask what usually causes this situation? Is it a problem with material parameters, boundary conditions, contact settings, or mesh/solver settings? If you have similar experience, please share some troubleshooting ideas. Thank you very much.

Photodetector Simulation

Fri, 13 Mar 2026 13:34:01 +0000

I am modelling photodetector and I want to define the refractive index (nk file) for the material but after adding the file in the interpolation when ever i add to the material it is not working

Coaxial cavity resonator

Fri, 13 Mar 2026 05:24:42 +0000

I am trying to model a coaxial RF resonator cavity. It consists of hollow outer and inner cylindrical conductors (copper) and are shorted on the two ends by a copper caps. I added impedence boundary conditions to include the losses. I have added Eigenfrequency study. The issue is, when I "compute", I am getting this error: Undefined variable.

Variable: comp1.emw.Qfactor
Global scope

Failed to evaluate expression.

Expression: comp1.emw.Qfactor
Feature: Eigenfrequencies (emw)

Can you please explain me what am I missing? Also, apart from this error, how should I proceed with this modeling?

Charge Particle Tracing Module

Tue, 10 Mar 2026 16:09:59 +0000

Hi everyone, I’m working on an electron discharge model using the Electrostatics and CPT modules. The setup involves two particles with opposite polarity approaching each other in vacuum and before contact, a field emission‑driven discharge begins between them. I want to model a continuous electron discharge in CPT. At the moment, I need to manually specify the emission time steps, but ideally I want the particle generation and release to be determined automatically by the local electric field strength on each small element. Since the discharge current density depends on the field intensity, I would like the solver to create particles based on this field‑dependent emission rate, using whatever time steps the solver naturally takes. Is there a way to set up CPT so that emission is continuous and governed directly by the evolving electric field, rather than prescribing fixed release times?

High-Velocity Single Particle Impact and Shear instability

Tue, 10 Mar 2026 15:58:00 +0000

Hi everyone, I'm currently working on a high‑velocity impact simulation using the Solid Mechanics interface with the Johnson–Cook plasticity model. I keep running into repeated failures in the elastoplastic update.

Here is a summary of the situation:

Material model: Johnson–Cook A = 90 MPa B = 292 MPa n = 0.31 C = 0.025 m = 1.09

Mesh: ~0.25 µm element size (≈ d/100 for a 25 µm particle) Loading: the particle starts with an initial velocity and travels across a small gap before contacting the substrate Time stepping: explicit, Δt ≈ 3×10⁻14 Local method: Backward Euler (Damped) Mass matrix: lumped Explicit time stepping - Verlet Method with Adams-Bashforth 2 Auxiliary solver. Steps taken by solver: Manual - ts.

Parameter estimation - Results which yield physically meaningful information

Tue, 10 Mar 2026 11:06:22 +0000

Hi COMSOL community!

I have an issue I am sure several others have experienced, where I use COMSOL to model a physical system, though the numerical output does not necessarily make any sense.

Specifically, I use the PDE interface to define my equations and the parameter estimation option to model my experimental data. This is a diffusion problem, where I have time dependent diffusion data (loss/gain of concentration [mol/m^3] over time [s]) for several temperatures. I can model this data with Fick's second law, with the diffusion coefficient as the fitting variable, though it will naturally change with temperature.

My goal is to model these data sets simultaneously, with a global objective function describing the Arrhenius relationship between the diffusion coefficient and the temperature. This way, all the individual diffusion coefficients will change such that they change linearly based on the temperature change. My current model only allows to do one temperature at a time, after which I must change settings to another temperature, and so on. This can yield odd diffusion coefficients, which do not necessarily follow the expected Arrhenius behaviour, hence my wish to circumvent the issue.

A main issue is that I cannot seem to "access" the final value of the diffusion coefficient (from the parameter estimation). I cannot say e.g.: D_trend = [sol1.conpar10 sol2.conpar10 sol3.conpar10]; %where conpar10 is a name for the diffusion coefficient

and that this vector should change linearly with temperature.

This issue is also applicable to other issues, such as heat conduction, structural or fluid mechanics, or any problem where several fitting results should follow a trend with respect to either a temperature, pressure, or any other parameter.

Thank you for any and all input.