Latest Discussions - COMSOL Forums

Desiccant Cooling System Simulation

Sun, 07 Dec 2025 03:56:27 +0000

Hi, my name is Edward Akpee, a masters student working on a project that requires simulation. i what to ootimize a solar Assisted Desiccant Cooling System. its my first time using comsol, I don't know how to go about it. i need your assistance.

collision between two gases

Sat, 06 Dec 2025 12:05:38 +0000

Hi i want to model the collisions between the particles of a steady gas (distribution is maxwellian) and a moving one with a defined velocity (the distribution is maxwellian but i sum the known velocity in direction z). the model should be axysimmetric. i know the densities of both gas, particles mass and their volume. i want to know how the particles of the first gas change density and i want to mesure the pressure waves that form. how do i do? i'm a beginner but i dont think that would be too hard

Optimization of an electron beam radius

Sat, 06 Dec 2025 11:52:08 +0000

Good morning, I am performing a simulation for an electron accelerator which consists of a cathode, an initial accelerating potential and then the electron beam is guided by six coils on a target which is almost 1m far from the cathode. The simulation itself is ok and I can see the beam.

What I'd like to do next is performing an optimization of the radius of the beam with respect to the currents in the coils. To do so, I defined a boundary probe on the surface of my target with the expression called R_spot, where qy and qz are the position of particles in y and z.

Then I set up an optimization with objective function (spot_target - comp1.R_spot) where spot_target is defined as 1[mm] in my parameters. I ask for a minimization with control variables the six coils currents. But I keep getting this error and I don't understand how to resolve:

Error in sweep. - Parameters: "I_coil_1","20","I_coil_2","20","I_coil_3","20","I_coil_4","20","I_coil_5","20","I_coil_6","20" Cannot evaluate expression. Undefined variable. - Variable: comp1.qy - Geometry: geom1 - Boundary: 87 Failed to evaluate expression. - Expression: sqrt((comp1.qy^2)+(comp1.qz^2)) Failed to evaluate expression. - Expression: comp1.bnd1_operator1(sqrt((comp1.qy^2)+(comp1.qz^2))) Failed to evaluate variable. - Variable: comp1.R_spot - Defined as: comp1.bnd1_operator1(sqrt((comp1.qy^2)+(comp1.qz^2))) Failed to evaluate variable. - Variable: opt.obj1

I also watched the Optimization tutorials in the Learning Center. If someone can help me figuring out what I'm doing wrong I will be grateful since I'm few days into Comsol and I'm learning it by myself. Thank you in advance, Emanuele

How to prevent Model Remeshing while solving after Updating Boundary Selections (No Geometry Change)

Thu, 04 Dec 2025 20:14:42 +0000

Hi,

In my workflow, I use a union of ball selections(created in geometry, after Form Union) to identify and select new boundary surfaces. Then, I update the boundary conditions with these newly created selection sets. Importantly, I do not modify the actual geometry, just create an union of different ball selections to use as boundary.

Here’s a simplified snippet of my code where the BCs are assigned and then the study is run:

model.component('comp1').physics('ec').feature('term1').selection.named('geom1_termUnion'); model.component('comp1').physics('ec').feature('gnd1').selection.named('geom1_groundUnion');

model.study('std2').run;

termUnion and groundUnion are unions of several ball selections.

However, when I run the study, COMSOL remeshes the entire model before solving. I would expect that only the solution should update, there should be no reason to regenerate the mesh if the geometry hasn’t changed. That is the entire idea of using ball selections.

Why does COMSOL trigger a remesh in this situation, even though only boundary selections have changed? Is there a way to prevent unnecessary remeshing when updating boundary conditions via selection sets?

Any tips would be greatly appreciated! Thank you in advance for your help.

Multiple lumped ports with excitation

Thu, 04 Dec 2025 13:54:31 +0000

I want to simulate a chip with 4 independent CPW resonators, each having an input and output lumped port at the end of the respective resonators to calculate the two-port transmission S-parameters. I add "EMW - Frequency Domain" Study and add total 8 lumped ports (4 pairs with excitation ON and OFF) and compute. I expect getting S-parameters in the Results but I don't get it and instead all I can get is "Reflection coefficient with multiple excitation" only for 4 ports which had excitation ON. How can I get S-parameters for 4 CPW like, (S00, S10, S01, S11), (S22, S32, S23, S33), etc.?

Efficient Selection of Multiple surfaces as boundaries

Tue, 02 Dec 2025 22:17:19 +0000

Hello everyone,

I’m modeling a system in COMSOL where two rectangular boundary regions must be dynamically moved across a surface, as guided by an optimization algorithm. My current method updates rectangle coordinates on a workplane for each optimization step, but this requires running form union and remeshing every time boundaries change, which is very computationally expensive.

As an alternative, I’m considering pre-generating hundreds of small rectangles on the surface as potential boundary areas. For each optimization iteration, I would simply select subsets of these rectangles to define "terminal" and "ground" regions for electric current physics, without touching the geometry or mesh modules.

To clarify:

Geometry and mesh remain unchanged; only boundary conditions are reassigned among rectangles. I need an efficient way to programmatically select which rectangles to use at each step, ideally automated via MATLAB LiveLink. Currently, I reference rectangles by their surface numbers, which works for a simple test case, but managing hundreds will quickly become unwieldy. I’d like to avoid manually tracking indices.

My main questions:

Is this approach feasible for avoiding repeated form union and remeshing while constantly changing boundary conditions? Is there a robust way in COMSOL to tag or systematically reference large numbers of geometric entities for flexible boundary condition management, especially with MATLAB automation?

I've attached a sample model showcasing this approach, with hundreds of small rectangles and the previous large-rectangle method for reference. For this model, my optimization algorithm will guide me to shit my terminal and based on that I want to select another set of rectangles.

Thank you in advance for any insights!

Optical generation rate

Tue, 02 Dec 2025 16:23:51 +0000

i have computed total generation rate from ewfd module in a varialbe named G_tot that is wavelength dependent and is a spacial data. now i want to integrate the data over wavelength. so the data remains only spatial non dependent on lemda. but when i am usign the integrate operator it just reduces a dimension. as a result the unit of generstion rate becomes (1/m2.s) instead of (1/m3.s) l. what is the solution .

Silver faces and material assignment crisis

Tue, 02 Dec 2025 15:46:42 +0000

Hello, I am struggling with a simple modulator 3D structure. I tried to create the geometry in many different ways but the cleanup wizard always appears to bother me. I tried to extrude a 2D surface, or directly create the 3D blocks, but I always encounter problems such as silver faces, and I experience a constant struggle with material assignment (many boundaries are not correctly assigned). I had a 2D model with the identical structure, and never encountered these kind of problems. WIth the 3D, it is a mess. Please help me understand how to cope with this. I want to compute the S parameters and characteristic impedance. I've also tried to insert some boundary conditions such as impedance boundary condition but I am not even able to select the correct faces! This model is simple, there is nothing sketchy about it. Please help me. Thank you

Inconsistency in Theory manual 6.0 and 6.2 - Multiplicative plasticity

Tue, 02 Dec 2025 14:25:51 +0000

Dear Community and Moderators,

I am seeking clarification on the flow rule for finite plastic strain with multiplicative decomposition. In COMSOL 6.0 documentation, the flow rule is:

and in COMSOL 6.2 documentation, the flow rule is:

I am confused about which one COMSOL actually uses. Or are they equivalent? Any help will be useful, thank you. Please see the attached screenshots as well.

How to store result files at the end of each time step in a transient analysis?

Sat, 29 Nov 2025 08:33:38 +0000

Hello, Is it possible to make COMSOL store the results at the end of each time step to hard disk? In this way, even if the job gets interupted before the final time step is reached, the partial results can still be seen. Regards Abhishek Basak

Flow noise in the time domain

Fri, 28 Nov 2025 03:38:03 +0000

Hello there,

I noticed that COMSOL provides a case study on flow noise (Cavity Flow Noise Application ID: 105021), but the noise results obtained are all analyzed in the frequency domain. Can we obtain the noise results in the time domain at a certain monitoring point?

Thank you all in advance.

Unreasonable particle trajectories and invalid wall condition

Wed, 26 Nov 2025 02:59:25 +0000

Hello there,

I encountered some issues while using the charged particle tracing module in COMSOL. I have completed the simulation and obtained the particle trajectories. But some particles don't look very reasonable. A portion of the particles collided with my metal electrode and passed through it, but the surface of electrode was set with the wall condition "Disappear." I used a finer mesh and smaller time steps, but the situation did not improve. What method can be used to solve this problem?

Thank you all in advance.

Custom boundary conditions with identity pair

Tue, 25 Nov 2025 10:21:10 +0000

Hi,

I have a 3D model of a pile which is embedded within a cylinder representing the soil; both are thus modelled as solid mechanics. I have created the model using assembly, meaning I have identity pairs on the boundaries that are in contact.

What I want to achieve is to enforce compatibility and equilibrium only in the horizontal directions, by default continuity enforces all directions. I have not found a way to do so.

I have thought about using contact pair, however I want to remain in the frequency domain; which should be possible.

I did find a seemingly related thread on this discussion form on Google, however that page apparently does not exist anymore.

Thanks in advance!

Line heat source rotating like the handle of a clock

Tue, 25 Nov 2025 08:43:12 +0000

Hello fellow comsol users,

I am trying to model a heat line source rotating about the center of a circle. While I have seen a lot on rotating heat sources (mostly ways to model rotating or moving laser sources); i cannot for my life think of a method to make it work for a rotating line source. Maybe I am thinking too complicated here.

Also, the heat line source feature seems to work only on edges that are fixed in the geometry, so that doesn't work either.

If any of you have faced this problem yourselfs or has an idea on how to implement it, I would be grateful for any advice you can share.

Thank you in advance! André

PS: I only have the basic license and the heat transfer module license available. If your solution requires another method, please mention the module name as well. Thanks!

State Variable in 6.3

Mon, 24 Nov 2025 19:31:03 +0000

I'm trying to define a state variable in 6.3. I have enabled Variable Utilities in the Model Builder, and I can access that ribbon in the Definition branches, global or component. But State Variable does not appear as an option. What am I missing? Thank you!

How to measure the band structure in the linear potential flow frequency domain

Sun, 23 Nov 2025 07:42:07 +0000

In acoustic, linear potential flow frequency domain, measurement of band structures. As a beginner in COMSOL and unable to find relevant cases, the supplementary materials in the literature suggest(To calculate band structures, we set the Floquet periodic boundary conditions by setting ‘Pointwise Constraints’ to introduce the Bloch phase shift to the eigenfields. ) However, I am not yet familiar with the specific operations involved, such as setting expressions

Client PC Cannot Connect To The Host/Server PC

Thu, 20 Nov 2025 05:49:34 +0000

Successfull in installing and run as server, as well as client on host PC. However, cannot connect a new client PC to the server/host PC.

Simulation of Ecoflex 00-30

Wed, 19 Nov 2025 20:09:57 +0000

Hi, I am trying to simulate a solid and a hollow cylinder made of ecoflex 00-30. I have used different hyperelastic material model values i.e. Yeoh, Ogden, Mooney-Rivilin, etc. from different research papers, yet, I failed to converge the solution in COMSOL 6.3 & 6.1 (both version).

I don't know, what boundary conditions and solver settings are missing, the model is 3D and dimensions are in millimeters.

How to know which solver settings and boundary conditions are required to solve the simulation correctly?

Thanks,

PDE for Modeling Liquid Interfaces

Wed, 19 Nov 2025 17:33:38 +0000

Hello!

I would appreciate some help, as I am trying to solve a partial differential equation of a type I have not worked with before. This PDE models the boundary of a liquid as a radius, , which is a function of the 2D plate the liquid is "sitting" on, such that :

where and are constants. The plate is bounded at the ends by circular plates such that .

It is my understanding that this equation cannot be put into divergence form, which is required by the Coefficient Form PDE interface. As such, I am wondering if there is another COMSOL interface which is best equipped to solve this kind of PDE or if there is another way to still use Coefficient Form PDE.

Thank you in advance for any assistance.

Plate displacement and force due to halbach array

Wed, 19 Nov 2025 10:43:04 +0000

I am working on a problem, where the circular permanent magnets halbach array is rotating using external motors over a Aluminium plate. Due to the flux of time-varying magnetic field, a electromagnetic force is experienced by the halbach array, making it levitate. I am trying to simulate this situation, to calculate the forces acting and the steady-state levitation height of the halbach array. I have tried to simulate it in two ways, first case in which the halbach array is fixed and the aluminium plate rotating with the surrounding region is taken as deformable zone and account for the forces and displacement of plate, and second case in which the plate is rotating at a fixed location and the halbach array inside a deformable region with the forces and displacement of the array. Currently, I have taken the reference from a example problem from application libraries named "electrodynamic_levitation_device". My simulation is running but getting stuck at 4-5% progress. Kindly guide me, I have the attached the .mph files for the both cases.