Latest Discussions - COMSOL Forums

Mode Shape Suppression After Adding Molybdenum Layers to AlN Resonator

Tue, 15 Jul 2025 19:17:42 +0000

Hello,

I am currently working on building a 3D piezoelectric resonator model.

As a starting point, I simulated a 1 μm-thick AlN layer on its own and was able to observe a well-defined thickness-extensional mode in the expected frequency range.

However, after adding 200 nm molybdenum (Mo) layers on both the top and bottom surfaces of the AlN to represent electrodes, I noticed a significant change. The thickness mode appears to be heavily suppressed, and the resulting mode shapes do not resemble those from the initial AlN-only configuration. Additionally, the output response is much weaker, and the resonant frequency appears to shift outside the previously observed range.

Could anyone advise why this behavior occurs? I expected a moderate frequency shift due to the added mass and acoustic impedance of the Mo layers, but not such a drastic change in the mode shape or suppression of the thickness mode altogether.

Any guidance or insight would be greatly appreciated.

3D dispersion graph AMMs

Tue, 15 Jul 2025 13:16:26 +0000

I am simulating a unit cell of a supposedly acoustic lieb structure in acpr module. I have my 1D band diagram where it is a plot of k vs freq and k is swept between 0 to 3. Now for illustrative purposes I wanted to plot a 3D dispersion diagram but I haven't been able to do it via COMSOL. How can i sweep kx and ky and a 3D surface?

solver issue

Tue, 15 Jul 2025 11:59:30 +0000

for PCM +Air hybrid cooling of battery pack, i enabled conjugate heat transfer module where turbulence physics defined for Air domain and under Heat Transfer in solids and fluids battery defined as solid and pcm as a fluid..selected phase change material under PCM(not sure about PCM setup as i asked earlier doubt.) we are getting results only for the stationary study and getting error for time dependent study.

but we require time dependent simulations only...kindly give idea

PCM simulation setup in COMSOL Multiphysics.

Tue, 15 Jul 2025 05:25:56 +0000

How to do PCM simulation setup in COMSOL Multiphysics. https://drive.google.com/file/d/1QJDjC4hOGsd8K3qDd_vl-luYoqq_sv8j/view?usp=drive_link

My study is cooling of battery cell by using both PCM and air.The cell is covered with cylinder PCM and again it is covered with aluminium casing cylinder.The aluminum casing is cooled by blowing air at some velocities. Here heat transfer takes place from cell to PCM,PCM to alumnium casing and alumiumuin casing to air.I have doubt about PCM simulation setup. Since when PCM melts its density changes and also other property changes with temperature. How to setup the simulation in COMSOL for a natural convection of PCM. when PCM melts, it converts solid into liquid.How to set physics for above problem.

Ion tracing through solids

Mon, 14 Jul 2025 17:17:15 +0000

Hi I am replicating an example in from the https://www.comsol.com/particle-tracing-module. and I want to simulate it with multiple sheets instead of a solid block. So i make the walls transparent and did the simulation but no output waveforms are seen. so can anyone help to let me know if how to do simulation with multiple sheets where charged ions or electrons will pass through it.

How to write variables in proper syantax ?

Sat, 12 Jul 2025 17:25:37 +0000

Respected professor, I am using COMSOL M version 6.0 for my work ,Topology optimization of Heat sink. As I am not expert facing some problems while inputting the parameters. Problems 1} While using Brinkman's equation for topology optimization of heat sink, what are the physics I have to select ? 2] Inverse Permeability, how to write ?

α (ρ) = α_min + (α_max - α_min) q(1-ρ)/q+ρ   

As a variable how can I write in proper syntax

α_simp = α_min + (α_max - α_min) comp1.dtopo1(k_simp*ht. q(1-theta^n)/(q+theta^n)

Is it correct ? if not please suggest me.I tried but showing error.

Thanks

Export Results->DerivedValues->System Matrix

Sat, 12 Jul 2025 13:10:32 +0000

Hello!

In Study I used Assemble to store or save the Stiffness Matrix in the Solution. In Results->Derived Values->System Matrix the Stiffness Matrix is to big to evaluate it into a Table.

Can I directly save or export the Stiffness Matrix into a text-file? I also would try it via Java.

A simple Yes would be enough to know that it is possible; I then figure out by myself.

Nice Greetings

Time-Dependent Heat Transfer/Convection Simulation of a building: Singularity failure

Sat, 12 Jul 2025 12:27:56 +0000

Hello everyone,

I'm currently trying to simulate the heating of a building with particular focus on its surroundings, throughout an entire summer day. For this, I am using a 24 hours time-dependent study, including the heat transfer and the laminar flow physics modules. When first approaching this project, I focused on the building heating up due to the sun's irradiation, making use of the heat transfer and the surface-to-surface radiation modules and omitting the laminar flow module. This has worked out fine and yielded usable results.

For simplification, I modeled two (outer) walls of a building, a ground floor and the air above. Note that the ground floor and the air are supposed represent the outside of the building.

Sadly I encountered severe problems when trying to simulate the convection of the air outside the building. The computation of my current model fails with the error Repeated error test failures. May have reached a singularity.. The error occurs as soon as the temperature of the building walls diverges from its initial values; however given that the building walls "must" heat up over time, I do not know what I need to change in my model to solve this error.

I wasn't able to reduce my .mph file to the required < 5 MB in order to upload it. If someone here would like to look at it anyway, I will gladly find another way to upload it somewhere else. For now, I will list the most relevant information below and include another screen shot of my model tree to give a basic idea of my physics module usage.

I would be very happy to receive some pointers to where exactly my problems stem from and what I could do to solve them. If someone here has more experience with modeling heating and convection, I finally would like to ask if my particular simulation case could also be approached with the "indirect" convection modeling techniques from Modeling Natural and Forced Convection in COMSOL Multiphysics® or through the One-Way Coupled Studies for Nonisothermal Flow.

Thank you very much and best regards

Luca

=============== Additional information: * Irradiated surface temperature: From my previous model using only the ht and rad modules, I recorded the resulting average wall and ground floor surface temperatures throughout the simulated day duration to a table. In my current model, I use this table to statically set the surface temperature for each simulated point of day. I do this over the ht > Boundary Temperature node. The range is from 12 °C to 55 °C. * Distant air temperature: In order to represent the temperature of the surrounding air, I similarly set the surface temperature of the air at the outer edges of my model through a simple diurnal cycle ranging from 12 °C to 27°C. * Mesh: I use a physics-controlled finer mesh. * Study: I use a time-dependent study with the following output times, in seconds except where specified differently: range(0,0.1,1), range(1,1,10) range(10, 30min, 23.5h)

Can I change the percentage of the contribution of the plastic strain in phase field damage?

Sat, 12 Jul 2025 09:22:32 +0000

I am trying to build a model to simulate the fracture of a ductile metal. I am trying to use the phase field damage models under solid mechanics interface. When I was checking the user's mannual, I found this description:

"By selecting Total strain energy density, additional contributions from dissipative material features, such as creep, plasticity, and viscoelasticity, are added. Select the Calculate energy dissipation checkbox in the parent material model to compute these variables."

For the problem I want to solve, I do need some plastic contribution in the driving force for the phase field interface evolution. However, usually only 10% of the plastic work is considered to be stored in the material and is available for creating new surfaces, the rest of it is considered dissipated through heat.

I am wondering if I select the* Total strain energy density*, and select the Calculate energy dissipation checkbox, the how much of the plastic contribution is taken into account by COMSOL? Is it all of it? If so, how could I regulate the model to have only 10% of the total plastic work to contribute in the phase field damage driving force?

best wishes Runzi

Ignoring or excluding mesh in some regions while being able to simulate

Fri, 11 Jul 2025 17:58:27 +0000

I wanted to ask if it is possible to exclude some regions when modeling the mesh for a large or complex system.

For example, modeling a micro antenna with centimeter-size wires is too dense a mesh to model. Along with the air region around.

So i wanted to see if one could ignore some regions that are unimportant, so as to save space and time, whilst still simulating somehow.

Update version from 6.2 to 6.3

Fri, 11 Jul 2025 14:07:53 +0000

Hello,

I cant install the version 6.3 of Comsol, when i attach the .dat file as a license path, an error appears saying:

The license could not be validated, please contact support@comsol.com for assistance and include the error message below and a copy of the license file.

License file does not support this version. Feature: SERIAL Application version > License version: 6.3 > 6.2 License path: C:\Users\Mattia\AppData\Local\Temp\cscomsol84494\comsol18049980329219368361.dat; FlexNet Licensing error:-21,126

Phase change from powder to liquid and back to solid

Fri, 11 Jul 2025 13:16:47 +0000

Hi everyone, I am simulating Laser Powder Bed Fusion (LPBF) process and have modelled powder layer as a continuous-scale. I have coupled heat transfer in solid and fluids with laminar flow. I want to know how I can model the phase change for powder as it will first melt to liquid and then will solidify into solid. I want to know how to do this in COMSOL. Using phase change would convert back it to the same material. So, how to make it one way such that it first converts the powder into liquid and later liquid is converted to solid. More information: Properties like density, thermal conductivity and specific heat capacity of powder layer properties is defined as an average of air and solid based on volume fraction.

Computing second-order derivative of Temperature field

Fri, 11 Jul 2025 11:52:58 +0000

I am working on a circular domain defined in 2D. I need to compute the angular derivative of the temperature, basically I want to compute:.

For this, I have used the following transformation from Cartesian to Polar coordinates:

I have tried to:

Change the frame from spatial to Material
Change the shape function for discretization.
refine the curvature factor.

But I still do not get the accurate result. Can somebody explain me how can I fix this?

Thanks in advance!

Exporting data from COMSOL while computing electric field magnitude and direction in an electrospinning machine

Thu, 10 Jul 2025 14:49:05 +0000

I am building a simulation of an electrospinning machine on COMSOL, and my objective is to study the electric field magnitude and direction within the machine. I would like to export the magnitude data that shows on a 1D plot. Is there a way to obtain a table of values that I can open in Microsoft Word, Excel, or another similar platform?

COMSOL not using all memory available

Thu, 10 Jul 2025 14:27:36 +0000

Hello,

I was trying to run a COMSOL simulation and it would always go over the available amount of RAM and start using Virtual Memory, which was extremely slow. Therefore, I bought more RAM (went from 64gb to 128gb), but COMSOL doesn't seem to want to use the full amount it has available. Indeed, once it reaches 64gb, it starts to write on the disk again even though there is still twice as much RAM available. Thinking that this was because COMSOL didn't "recognize" that there is more RAM, a clean install was done of COMSOL MultiPhysics, but this didn't solve the problem. Furthermore, I also tried to disable the use of Virtual Memory to force COMSOL to use the available RAM, but the simulation ends when COMSOL reaches the 64gb mark, with an error saying that there wasn't enough memory.

Why does COMSOL not use the full amount of RAM available?

Thanks in advance for your help!

Marek

Failed to evaluate negative error for Heat Transfer in Porous Media

Thu, 10 Jul 2025 02:17:20 +0000

HI, I am trying to simulate a flow through packed bed and transfer between the fluid and porous bed using thermal non equilibrium case, but I am getting this error it is because of the model input in the Fluid section, when I enter a number then the error is not coming, but when I set the default ht/porous/fluid/T value then it is giving error, i have coupled the Brinkmans equation with the HTPM using Non Isothermal Flow Multiphysics

Choice between Transport of Diluted Species and Transport of Concentrated Species

Wed, 09 Jul 2025 02:50:07 +0000

My physical scenario is as follows: At room temperature and atmospheric pressure, a gas mixture of 80% Ar and 20% CO₂ is introduced at a flow rate of 500 sccm through two small inlets (each with a diameter of 1 cm) into a metal enclosure filled with air. The enclosure has dimensions of 3.14 m × 1.76 m × 0.24 m, and there are two outlet holes (also 1 cm in diameter) on the opposite side.

My question is: Given this setup, should I choose the "Transport of Diluted Species" or the "Transport of Concentrated Species" physics interface in COMSOL?

Thank you in advance for your guidance!

Continuity between two domains with different physics

Tue, 08 Jul 2025 17:21:48 +0000

Hello all,

I am developing a model for the combustion of a fuel pellet placed inside a furnace. There is air flow enabled in the furnace, which I would think "seeps" oxygen inside the porous pellet. Before I went into the complete heat, mass and reaction coupling, I just wanted to to run a study with just fluid flow interfaces defined. I am using the laminar flow interface for the furnace domain and brinkman equations for the porous pellet domain.

Since I defined the geometry as a union, I would assume that COMSOL automatically treats internal boundaries with continuity conditions, however, when I checked the results I see that the continuity is not maintained.

Currently, the interfaces between the pellet and the furnace are defined as walls, which I assumed would be overridden automatically. Now I think I need to add some additional B.Cs to let COMSOL know that there is an interface between the pellet and the furnace where continuity needs to be maintained. Or do I need to define identity pairs? Or is there anything else that I am missing. I am also having some trouble determining the source and destination boundaries while defining identity pairs.

I am attaching an annotated image with some information that might be useful.

Any help is much appreciated, thank you!

'Results While Solving' in Iterativ Stationary Solver

Mon, 07 Jul 2025 16:30:34 +0000

Hello!

Is it possible in an Iterativ Stationary solver calculation to see the successive converging results due to 'Results While Solving' every iteration or every few iterations??

I tried activating 'Results While Solving' in 'Fully Coupled' node or changing 'Update at', but I don't see any converging behaviour, though it's definitely there. I just see the graphical result of the previous calculation, though I know there is a noticable converging behaviour by testing with different 'Maximum number of iterations.'

Is such or anything like that possible???

A simple 'Yes' would be enough; then I figure out for myself.

Nice greetings

Eddy Simulation as Inspection

Mon, 07 Jul 2025 00:26:23 +0000

Hi, I'm a doctoral student using the License number COMSOL® 6.3, in my thesis. So, my objective is to simulate an eddy current inspection for a heat exchanger tube. You can understand this kind of test by watching the video on the YouTube link (https://youtu.be/MYd92lzhsX8?si=mtOjR_rgwhkP2LJP). How can I assemble this kind of model in COMSOL? Could you please help me? Basically, I need to insert a bobbin coil sensor probe inside a tube, where the probe should be moving inside the tube along time. In the end, I want to see the impedance plan for each step, XL versus XR, and all steps as voltage versus amplitude versus probe displacement. Please, I need your help!!!