Latest Discussions - COMSOL Forums

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.

Structural Simulation with CTE: Multiple Solid and Shell Interfaces

Tue, 10 Mar 2026 04:53:52 +0000

Hello,

<Geometry> I am trying to simulate a geometry which comprises of multiple stacks of rectangular cross section layers composed of 3D solids (~20 to 40 microns) and shells (~2 microns). There are various interfaces in this geometry across its thickness, which connect solid to shell, shell to shell, solid to solid & shell to solid. The width for all entire geometry is 4 mm and length is 20 mm.

<Problem Statement> I am trying to simulating thermal stress and strain between the various layers as per CTE. I have set the fixed constraint for the bottom most layer. I have also used Rigid Motion Suppression on solid and shell domains.

<Issue> While computing the stress, in the results the corner points exhibit exceptionally high concentrations.

Regards,

Homogenized Multiturn causing tolerance issues

Mon, 09 Mar 2026 05:58:50 +0000

Hello,

I am currently simulating my model using the Coil Geometry Analysis study in COMSOL. When I select the Single Conductor option for the coil, the analysis runs successfully.

However, I would like to proceed with a Time-Dependent study, which requires using the Homogenized Multiturn coil model. Since I have already modeled all the turns explicitly in the geometry, I set N = 1. But when I switch to the homogenized multiturn option and run the Coil Geometry Analysis, the solver returns the error “Failed to find a solution.”

Could you please suggest how to resolve this issue?

Thank you for your support.

Energy calculation with PML boundary condition

Fri, 06 Mar 2026 18:12:36 +0000

Hi,

I am working on a 2D finite element analysis of a thin rectangular piezo to analyze frequency response. On the left and right boundaries of the piezo, I have used PML boundary condition. Now, I want to know when COMSOL calculates the stored energy in the piezo, does it calculate and add the energy in the PML domain? Please give reference supporting your answer.

Regards

electrostatic film actuator

Fri, 06 Mar 2026 08:40:52 +0000

I want to perform a simulation using COMSOL Multiphysics 6.3: It is a 2D model with nine thin electrodes embedded in a thin resin layer, and a small water droplet is placed on the resin. The electrodes are 0.1 mm wide with a 0.1 mm gap between them. Every three electrodes form one group. Within each group, the electrodes are connected to three‑phase sinusoidal AC with a 120° phase difference; all groups use the same phase sequence. The time‑varying electric field forms a traveling wave, which induces charges inside the water droplet. Under the action of the electric force, the water droplet is driven to move in one direction. I don’t know how to implement this. I have tried coupling Electrostatics (ES) with laminar flow and two‑phase flow, but I cannot get the results I want.

Modelling Shell and Tube Heat Exchanger

Wed, 04 Mar 2026 14:32:03 +0000

Good day everyone. I am an undergraduate chemical engineering student in my final year. For my final year project I am to design and simulate a shell and tube heat exchanger. the point of the capstone is to vary baffle angle and cut to increase heat transfer and reduce pressure drop. While running a parametric sweep i have encountered many errors. one of the errors is pasted below:

"""TA"",""0.34907"",""cut"",""0.4""" "Error in sweep.⏎ - Parameters: ""TA"",""0.34907"",""cut"",""0.4""⏎The following feature has encountered a problem:⏎ - Feature: Time-Dependent Solver 1 (sol1/t1)⏎Failed to find consistent initial values.⏎Temperature⏎Attempt to evaluate real square root of negative number.⏎Function: sqrt⏎Failed to evaluate operator.⏎Operator: nif, Geometry: geom1, Boundary: 30⏎Failed to evaluate expression.⏎Expression: nif(comp1.spf.d w plus u<(10/(up(comp1.nitf1.Pr)^0.33333333333333331483)),nojac(comp1.spf.d w plus uup(comp1.nitf1.Pr)),comp1.spf.d w plus u<sqrt((comp1.spf.kappav1000)/up(comp1.nitf1.Prt)),nojac((15(up(comp1.nitf1.Pr)^0.66666666666666662966))-(500/(comp1.spf.d w plus u^2))),nojac(((15(up(comp1.nitf1.Pr)^0.66666666666666662966))+((up(comp1.nitf1.Prt)log(comp1.spf.d w plus u))/comp1.spf.kappav))-(((0.5up(comp1.nitf1.Prt))(1+log((comp1.spf.kappav1000)/up(comp1.nitf1.Prt))))/comp1.spf.kappav)))⏎Failed to evaluate expression.⏎Expression: if(comp1.spf.hasWF u,nif(comp1.spf.d w plus u<(10/(up(comp1.nitf1.Pr)^0.33333333333333331483)),nojac(comp1.spf.d w plus uup(comp1.nitf1.Pr)),comp1.spf.d w plus u<sqrt((comp1.spf.kappav1000)/up(comp1.nitf1.Prt)),nojac((15(up(comp1.nitf1.Pr)^0.66666666666666662966))-(500/(comp1.spf.d w plus u^2))),nojac(((15(up(comp1.nitf1.Pr)^0.66666666666666662966))+((up(comp1.nitf1.Prt)log(comp1.spf.d w plus u))/comp1.spf.kappav))-(((0.5up(comp1.nitf1.Prt))(1+log((comp1.spf....1000)/up(comp1.nitf1.Prt))))/comp1.spf.kappav))),0)⏎Failed to evaluate variable.⏎Variable: comp1.nitf1.Tplus u, Defined as: if(comp1.spf.hasWF u,nif(comp1.spf.d w plus u<(10/(up(comp1.nitf1.Pr)^0.33333333333333331483)),nojac(comp1.spf.d w plus uup(comp1.nitf1.Pr)),comp1.spf.d w plus u<sqrt((comp1.spf.kappav1000)/up(comp1.nitf1.Prt)),nojac((15(up(comp1.nitf1.Pr)^0.66666666666666662966))-(500/(comp1.spf.d w plus u^2))),nojac(((15(up(comp1.nitf1.Pr)^0.66666666666666662966))+((up(comp1.nitf1.Prt)log(comp1.spf.d w plus u))/comp1.spf.kappav))-(((0.5up(comp1.nitf1.Prt))(1+log((comp1.spf.kappav1000)/up(comp1.nitf1.Prt))))/comp1.spf.kappav))),0)⏎Failed to evaluate expression.⏎Expression: if(comp1.spf.hasWF u,(((-comp1.nitf1.qwfc u)up(comp1.ht.Cp))(comp1.ht.Tu-comp1.nitf1.TuWF))/sqrt(1.0E-6+(max(comp1.nitf1.Tplus u,0)^2)),0)⏎Failed to evaluate variable.⏎Variable: comp1.nitf1.qwf u, Defined as: if(comp1.spf.hasWF u,(((-comp1.nitf1.qwfc u)up(comp1.ht.Cp))(comp1.ht.Tu-comp1.nitf1.TuWF))/sqrt(1.0E-6+(max(comp1.nitf1.Tplus u,0)^2)),0)⏎Failed to evaluate expression.⏎Expression: (-comp1.nitf1.qwf u)comp1.ht.d⏎Failed to evaluate Jacobian of expression.⏎Expression: ((-comp1.nitf1.qwf u)test(comp1.nitf1.TuWF-comp1.ht.Tu))comp1.ht.d⏎Failed to evaluate Jacobian of expression.⏎Expression: (if(comp1.spf.hasWF u,-comp1.nitf1.qwf utest(comp1.nitf1.TuWF-comp1.ht.Tu)comp1.ht.d,0))(dvol spatial)⏎Last time step is not converged."

I do not understand what i am doing wrong, so i am asking for some guidance from anyone who is willing.

Modeling a Rotary Tube Reactor

Tue, 03 Mar 2026 19:11:47 +0000

Hi all,

I want to develop a 3D model of a rotary tube reactor, where there is an input feed coming from one end of the reactor along with some gas. The reactor is externally heated, and the heat drives some reactions in the input feed. My main question is the approach to use for simulating this.

To develop a complete model, I need to account for the flow, heat transfer, and the reactions. The general way of initiating this from the literature is as follows (see attached image for some more clarity): 1) Based on the experimental parameters such as the reactor dimensions, reactor tilt, feed rate, etc., compute the bed height and the angle of the chord subtended by the solid bed. 2) Develop a geometry based on this including the reactor shell, a domain for the bed, and a domain for the freeboard (gas) region.

In this case, the bed consisting of powdered solids still moves so the flow of the solid bed should be accounted for. Additionally, the things to take care of are: the flow in the freeboard region, heat transfer (conduction+convection+radiation), and chemical reactions either through species transport modules or defining our own ODEs.

I wanted to know: 1) If I assume the bed height/angle of the chord through the analytical equation and make a geometry based off of it (note that there will be the solid bed in the geometry but in reality, initially there will only be air in the tube), what functionality does COMSOL have to model the flow of the bed? 2) Assuming I do not use the analytical equations and I use Euler-Euler model to model the flow, how can I include the boundary conditions from the heat transfer/species transport/ODEs interfaces as I will not be having a geometry defined for the solid bed (because in Euler-Euler, I will be treating the whole region inside the tube as a multiphase material but specified volume fractions)?

Thank you! I understand that my description might not be very clear. In this case, I am happy to discuss further.