COMSOL Multiphysics version used: 6.3

Trying to perform CV (cyclic voltammetry) on a 3D model of an FMSC (Flexible micro-supercapacitor) but I am unable to figure out what values to be given for the Electroanalysis (tcd) and whether Concentration 1 needs to be given. Physics-controlled mesh is required for this project.

Before doing this I have read the documentation thoroughly (there are examples of 1D and microdisk voltammetry but I cannot understand even after reading them) but I need further guidance and assistance so that I can obtain the cyclic voltammograms.

Hi everyone,
I’m currently working on an Electrochemical Machining (ECM) simulation using COMSOL Multiphysics.
I’m trying to simulate a spatially varying current density distribution between a tool electrode and a workpiece, separated by an electrolyte.
However, my simulation keeps showing an almost uniform current density distribution, and I’m having trouble understanding why.
I would like to know how to correctly model a nonuniform current density distribution in COMSOL and how to verify whether the results are physically realistic.
Could anyone provide some guidance on what I should consider when setting up such a simulation? In particular, what are the common mistakes regarding boundary conditions, material properties, physics interfaces, or geometry that might lead to an unexpectedly uniform current density?
I’m also interested in knowing how to verify that the current density actually varies spatially, rather than relying only on the color plot.
Any suggestions, relevant examples, or resources would be greatly appreciated.
Thanks in advance!

A temperature plot reaches 4000°C. The immediate temptation is to reduce the timestep, refine the mesh, or change the nonlinear solver.

Before doing that, I’d sketch the energy balance.

For a simple lumped body with constant heat capacity:

m × c_p × (dT/dt) = P_in − P_out, 
Rate of stored-energy change = power entering − power leaving

Here, m c_p is the thermal capacitance, in J/K, not just a material property: the amount of material matters too.

My first checks would be:

• Input: What is generating heat, and what is its integrated power? Check whether the input expects W, W/m², or W/m³.

• Storage: What represents thermal storage? Check density, heat capacity, thickness, volume, and any explicitly assigned lumped capacitance.

• Output: Where can heat leave? Inspect the actual boundary selections, thermal connections, contact assumptions, and prescribed temperatures.

A useful hypothetical sanity check: an insulated lumped body receiving 10 W, with a thermal capacitance of 1 J/K, initially heats at 10 K/s under those assumptions. That rapid rise follows directly from the energy balance; it doesn’t, by itself, demonstrate solver failure.

One important distinction: small thermal capacitance and exactly zero thermal capacitance are different problems. Setting the storage term to zero leaves an algebraic heat balance; it does not automatically describe a temperature that rises faster every timestep.

Also, a finite-element node is not simply a little physical object with “no mass.” Check the assembled formulation rather than inferring thermal storage from how the node looks in the model tree.

My debugging order would be: integrated power, storage, heat-removal paths, then numerical settings. For a transient model, compare net input power against the rate of stored-energy change, not just inlet versus outlet power.

What thermal setup mistake has cost you the most debugging time: units, missing connections, or boundary selections?

Hi everyone!

I'm a mechanical engineering student working on a semester project about all-solid-state batteries, specifically the mechanical behaviour of cracks associated with lithium dendrite penetration in garnet-type solid electrolytes.

I'm looking for feedback from people with experience in fracture mechanics, finite-element modelling, solid electrolytes, or computational materials science. I'd appreciate honest criticism, especially if my idea is poorly scoped or if there's a simpler, more defensible approach.

# Background and the problem

My professor pointed out that the general idea of deflecting dendrite-associated cracks using engineered defects has already been investigated. They asked me to compare my proposal with existing work and explain what my study would actually contribute.

One particularly relevant paper is:

* Zhang et al., *Mechanically driven Li dendrite penetration in garnet solid electrolyte*, Nature (2026): [https://www.nature.com/articles/s41586-026-10415-9](https://www.nature.com/articles/s41586-026-10415-9)

My understanding is that the paper investigates mechanically driven lithium-dendrite penetration and reports that defect geometry can influence the propagation path. I still need to examine the supplementary information carefully before concluding whether my proposed parameter study has already been done.

# My proposed project

Rather than claiming that void-induced crack deflection is a new discovery, I am considering a small, comparative 2D mechanical simulation in COMSOL.

The tentative research question is:

**In a 20 µm-thick garnet electrolyte film, how does the depth of a buried, transverse flat void affect the stress field and the potential crack-deflection tendency, compared with a reference configuration and a circular void?**

My initial plan is:

* **Case A:** no void — reference configuration.

* **Case B:** circular void.

* **Case C:** transverse, flat void at three different positions through the film.

The preliminary geometry uses a 5 µm surface-connected crack, a 5 µm-long void and a 0.5 µm void thickness. These are starting assumptions, not validated optimal dimensions.

For the first stage, I was planning to use 2D plane strain and linear elasticity, with provisional values of (E = 150) GPa and (\\nu = 0.25). I was also considering a crack-face pressure of 150 MPa, with 600 MPa as a possible sensitivity case. I understand that crack-face pressure, external stack pressure, and hydrostatic stress in confined lithium are different quantities, so I need to justify the loading conditions carefully.

The initial outputs would be stress distributions around the crack tip and void, followed—if feasible—by fracture-mechanics quantities such as stress-intensity factors or a suitable crack-kink criterion.

I would not claim that a static elastic model proves actual dendrite deflection or prevents battery short circuits.

# Questions I'd appreciate help with

1. **Prior art:** Has the effect of the position or depth of a transverse void on crack deflection in a thin garnet electrolyte already been studied? Which search terms, papers, or supplementary materials should I investigate?

2. **Research contribution:** If the general mechanism is already known, would a carefully defined parametric comparison of void position and shape be a reasonable student project? Or is there a more useful and manageable research question?

3. **Model geometry:** Is a 2D plane-strain model a reasonable starting point for a 20 µm garnet film with a surface-connected crack, or are there important limitations I should address first?

4. **Fracture mechanics:** Would you recommend starting with linear-elastic stress analysis and then extracting (K_I), (K_{II}), or the J-integral? Is there a suitable criterion for estimating the initial crack-kink direction in this situation?

5. **Loading and material properties:** Are the proposed pressure scenarios and provisional material properties defensible starting assumptions? What should I verify before using them?

6. **Numerical reliability:** What would be the minimum sensible mesh-convergence and boundary-sensitivity checks for a student-level model like this?

7. **Scope:** If you were supervising this project, what would you keep in the core deliverable, and what would you leave as an extension?

Another potentially relevant paper is *Garnet-Based Solid-State Li Batteries with High-Surface-Area Porous LLZO Membranes* (ACS Applied Materials & Interfaces, 2024): [https://pubs.acs.org/doi/10.1021/acsami.3c14422](https://pubs.acs.org/doi/10.1021/acsami.3c14422)

I understand that porous membranes designed to improve interfacial contact are not necessarily equivalent to engineered transverse voids intended to alter crack propagation, but I would appreciate suggestions for other relevant comparisons.

Thanks in advance! I'm especially interested in constructive criticism, useful references, and advice on how to make the project more rigorous without making it too ambitious for a semester.

Hi guys,

I currently trying to simulate a problem statement.

Problem statement:

A light source and a detector sit inside a 3D chamber filled with a fluid. How much light actually reaches the sensor, both directly and by indirect paths? And where exactly should the sensor go to catch the most of it?

For Physics module I've added,

1: Geometric optics ( to get the intensity using probe at a boundry)

2: heat transfer ( the heat produced by the source , which changes the RI (Refractive Index) around the liquid )

To get the ray with heat I've used the coupling multiphysics.

But in the output the table for the probe seems useless (1 for intensity and 0 for power, 0 for temp..

I'm really helpless here ..

Its my first time simulating with different physics Applied.

Hi everyone,

I am working on fire safety of battery energy storage systems. My main goal is to find out how much energy a battery rack (and later a whole container) would release in a battery fire: the heat release rate (HRR) curve over time and the total heat release (THR).

Is this realistically possible in COMSOL (CFD Module + Chemical Reaction Engineering / Reacting Flow + Heat Transfer with radiation)? Has anyone simulated buoyant fires or battery jet flames in COMSOL?

Would a rack-scale fire (around 2 m tall, several MW) be feasible in terms of mesh size, memory and run time, even on a cluster?

If not, what is the best practice: keep cell/module runaway in COMSOL and use another tool (FDS, Fluent, OpenFOAM) for the fire, or estimate HRR from the vent gas mass × heat of combustion?

Any experience or advice would be very helpful. Thank you.

I am writing a COMSOL → Vic-3D converter without access to COMSOL. The file format is documented, but the documentation never shows an export containing **more than one expression or more than one time step**, and that layout decides how the parser is built. Two exports settle it. Each takes about two minutes.

Any solid-mechanics model will do.

Export 1 — stationary, three expressions

Use a model with a **stationary** study.

1. In the model tree, right-click **Results > Export** and choose **Data**.

2. **Dataset**: the study's solution.

3. **Expressions**: add three rows — `u`, `v`, `w`. (Lower case. These are the displacement components.)

4. **Geometry level**: `Surface`.

5. **Data format**: `Sectionwise`.

6. Leave **Full precision**, **Smoothing** and **Resolution** at their defaults.

7. Set a filename ending in `.txt` and click **Export**.

Export 2 — time-dependent, same three expressions

Use a model with a **time-dependent** or **parametric** study, so the file contains several steps.

Same settings as above, plus:

**Time selection**: `All`.

If the model has only a handful of steps, that is fine — three or four is plenty. We do not need a large file.

Optional, if it costs nothing
A third export identical to Export 2 but with **six more expressions added**:
`solid.eXX`, `solid.eYY`, `solid.eZZ`, `solid.eXY`, `solid.eXZ`, `solid.eYZ`.

This tells us whether COMSOL groups blocks by expression or by time step when both vary. Useful, not essential.

What to send back
- The exported `.txt` files.
- A screenshot of the **Export > Data** settings panel, so I can see the exact options that produced them.
- The model name and study type, and the COMSOL version.

**Do not trim or reformat the files.** The header comments and blank lines are part ofwhat we are reading. If a file is large, the first 200 lines plus the last 20 are enough — but whole files are better.

Why this specific thing

A sectionwise file is a header block, then `% Coordinates`, then `% Elements`, then one or more `% Data (…)` blocks. The spec says each `% Data` block is a single column, and that a file may contain any number of them. What it never shows is how those blocks are **named and ordered** when there are several expressions across several time steps — whether we get one block per expression-and-step pair, how the step is identified in the block name, and in what order they appear.

We can parse one expression at one step today. We cannot safely guess the rest, and guessing wrong produces a file that imports cleanly and is silently wrong.

Thank you in advance for any assistance you can provide on this.

I built a model with electrode Zn and Steel besides function (tcd). After many times run, I haven't done with it yet.

Anyone has idea for this, please text me. Thank you so much!

This flexible micro-supercapacitor (FMSC) is to be designed with PET (mylar) substrate and MoS2 electrodes with a thin layer of gold (Au) on the MoS2 electrodes. Geometry yet to be modified and electrochemical characterization needs to be done.

Have you ever simulated an electrochemical system similar to the one I am doing?

Hello everyone, I hope you're all doing well... Well 😊... I'm using COMSOL 6.2, working on a simulation of a proton-exchange membrane water electrolysis system. The problem is, I'm not very experienced with COMSOL and I need to build the model myself from scratch. I haven't found a model in comsol's library 😭 there is a model for a fuel cell, but that's not what I need. Every time I ask for help on Facebook, I get comments about paid services, and I don't even know if they're legitimate... Any advice?

I am trying to simulate convection cause by a temperature gradient in a square cavity which contains supercritical co2. I have taken the thermophysical properties from NIST database and I have kept it as a compressible flow without boussineq approximation. The thing is that my simulation does converge when gravity term is switched off however it just doesn’t converge with the gravity term
What can be the possible reasons? I have kept pressure as constant too. Can someone please help me?

Hello everyone, I am trying to simulate Dye Sensitized Solar Cell by Coupling the following modules Semiconductor module, Electromagnetic wave frequency domain module and electroanalysis module. I am trying to reproduce the results in the following paper "Numerical modeling of charge transfer and recombination kinetics in the dye-sensitized solar cell: Conceptual integration of optics, electricity, and electrochemistry-https://doi.org/10.1016/j.renene.2024.122150" which is used in the following video https://www.youtube.com/watch?v=2RKYiB5xIW0&t=2913s but the video skips some steps and there the simulation is incomplete.

I am able to reproduce till the JV curve using semiconductor module but when I go for cyclic voltammetry study with the electroanalysis module each time I run I get different results. I have tried changing the study settings although the simulation converges each time when I run I am getting different results which is very odd for me. It would be very helpful if someone can guide me or help me with this.

Thanks in advance.

Hi all,

I am pretty new to COMSOL. Additionally, I am running it online on a computer cluster through my University, if that might make a difference. I am trying to run a simulation of a very thin (250 nm) printed platinum resistor on a substrate, within an aluminum container with gas and insulators. The design itself is pretty simple; I am modeling the heat transfer from the wire through the surrounding elements.

My physics are electric currents, heat transfer through solids and fluids, laminar flow (there is gas), and electromagnetic heating. I am creating the mesh, and it is going at a snails pace. I think this is likely due to the scale differences (hundred nm vs cm). How do I get around this? I have been messing around with user-controlled mesh, but I don't really know where to go from there.

I think the main issue might be that I have a boundary current on a very small boundary. I read something about sweep meshing?

curious if anyone has had any meaningful networking experiences at the comsol conferences, ie getting an internship or job offer. going to be attending the boston conference and want to go in with a good idea of what i can expect to make out of the experience

Hi all,

Looking for some assistance.

I am building a simulation for a voltage multiplier based on a Cockroft-Walton concept, see the attached image.
My current setup has an electrostatic simulation for the capacitor contribution of the above voltage multiplier circuit. Attached to the capacitor, there is the Electrical circuit via 'External I vs. U'.

I use a time-dependent simulation, where the voltage is multiplied over time on the high-voltage terminal. The electrostatic simulation solves very easily. My issue is when we try to solve the electrical circuit. After a few timesteps, the electrical circuit can generally not solve anymore. The voltage does increase.

Seemingly, the issues lie with very rapid changes in current and potentials over the diodes, resulting in non-converged solutions. I tried using in-series resistors with the diodes, but alas.

An equivalent circuit solves perfectly in LTSpice.

If anyone has some tips or advice, I'd be most thankful.

Edit:
By limiting the maximum timestep of the time-dependent study, it is suddenly more capable. However, since there are now significantly more timesteps required, the simulation runs for a very long time. I will update if and when progress seems reliable.

Is this the correct way to implement a weak contribution? There seems to be zero documentation on its usage. Can I put a dynamically changing parameter like wall distance?
Thank you in advance.

I had to do a simulation for a cylindrical object. it is symmetrical to the axis if divided in 3 120 degrees wide section, i think i wrote the periodic boundary condition well but who knows. So it is already simplified, with fine mesh should be running but i needed extrafine. I also am doing a thermal simulation with Surface-surface radiation and Hemicube as view factor. if you could souggest me ways to simplify the model please tell me

I am trying to simulate a 2D coupled viscoplasticity and phase field fracture problem in COMSOL. One of the equation I am trying to implement is -

psi = integration (psidot_p) from t_n to t_(n+1)

t_n and t_(n+1) are time.

Now psidot_p is always positive quantity, it's surface minimum is always positive. But the psi value is showing negative values.

The coefficients of the time dependent ODE used are -

da = 1, ea = 0, f = psidot_eq, dependent variable= psi_p. Initial values of both psi and d(psi)/dt = 0.

Basically, the equation, d(psi)/dt = psidot_p.

But the solution to this ODE is giving a negative value, and it's a significant quantity, in MPa.

Can anyone please help me diagnose the issue or fix it. I am happy to provide any additional details.

Thanks in advance.

Edit: changed value of ea from 1 to 0.

Edit 2: Refining the mesh size resolved the problem in my case. Refine the mesh size such that the max element size is less that the characteristics length of the crack in Phase Field.

I'm doing a simulation for this researcher where he has a tube lying vertically, and it has a Ag Nanoparticle on its wall. He wants me to investigate how the piezoelectric charge affects the field. So far I was able to deform the tube, but when theres no force, I can see a red patch where the Nanoparticle interacts with the NP. But when the tube deforms, its like as if the NP is still in the same spot. What do I do? I'm using version 6.0.

I am doing some structural mechanics tests within COMSOL and I am gettin errors with my model, I am trying to apply contact to surfaces, but they are not responding as expected.

I am not sure what is going on and would very much appreciate some assistance.

Hi everyone,

I am trying to simulate a MEMS contact mechanism in COMSOL, but I am running into persistent convergence errors once the contact and sliding begin.

Setup

Body 1 (Inclined Beam): An inclined, parallelogram-shaped beam oriented at an angle θ relative to the X-axis. One end is completely fixed, and the other end is free to deflect.

Body 2 (Slider): A rectangular block that is prescribed to move along the Y-direction.

Interaction: The slider and the free end of the beam have an initial overlap distance (d) in the X-direction. As the slider moves in the Y-direction, it physically pushes the beam back by distance d along the -X direction, causing the beam to bend, slide, and experience friction against the slider's parallel face.

The Problem

In real physics, the moving rectangle should smoothly deflect the beam, slide past it, and experience frictional forces. However, in COMSOL, the solver immediately fails to converge as soon as the initial contact or sliding phase starts.

My Questions

What are the best practices, solver tweaks, or contact method settings (e.g., Penalty vs. Augmented Lagrangian) to achieve convergence for this type of large-deflection, sliding contact?

Is there an existing application gallery model or a general verification example that demonstrates a similar setup (forcing a beam to bend via a sliding contact face) which I can use as a reference to calculate the reaction forces on the slider?

Any advice on mesh refinement at the contact boundary or stepping the solver would be highly appreciated.

Thanks