Latest Discussions - COMSOL Forums

How do i obtain directional Wall Shear Stress in a 3D body?

Fri, 04 Apr 2025 09:46:02 +0000

I've been using COMSOL up till now only for microfluidic channels - for which you can get WSSx and WSSy as (spf.mu * dtang(u,z)) and (spf.mu * dtang(v,z)) respectively. However, for a 3D body or a curved object, the wall shear stress cannot always be determined along cartesian co-ordinates.

Additionally, COMSOL does not let me perform operations to obtain: (spf.mu * dtang(velocity along t1, x) ) Is there another way to do this? I want WSS along t1, WSS along t2 with respect to n.

syntax for absorbed heat

Thu, 03 Apr 2025 17:20:03 +0000

Please I need help i writing the syntax of heat absorbed (attached) and i want to know if it is volume integral or surface integral

Need to change circular planner shape to hexagonal

Thu, 03 Apr 2025 08:17:27 +0000

Hi,

I wish to change the circular coil to hexagonal in 3D. Take a look the 3D design,

Suggest me what to do in Geometry>workplane>plan geometry>rectangular .

Absorption Coefficient

Thu, 03 Apr 2025 00:44:01 +0000

I want the syntax to compute the absorption coefficient and I want to know if it could be calculated from the absorption cross-sectional area

Hollow Fiber Membrane Modeling

Wed, 02 Apr 2025 20:51:12 +0000

Hi,

I am new to COMSOL and I am attempting to recreate the hollow fiber membrane modeling that was performed in this presentation.

https://www.comsol.com/video/modeling-co2-removal-with-hollow-fiber-modules-in-comsol-aug-20-2018

I was able to recreate most of it but when I click compute I get the following error.

Feature: Stationary Solver 1 (sol1/s1) Failed to evaluate initial residual for segregated step 1. Undefined variable.
- Variable: comp1.nirf1.rho
- Geometry: geom1
- Domain: 3 Failed to evaluate variable.
- Variable: comp1.spf.rho
- Defined as: comp1.nirf1.rho Failed to evaluate expression.
- Expression: dvol_spatial(r(pi((-((d(comp1.u,r)comp1.u)+(d(comp1.u,z)comp1.w)))(2*comp1.spf.rho)))) Failed to evaluate Jacobian of expression.
- Expression: (2comp1.spf.rho(-(d(comp1.u,r)comp1.u+d(comp1.u,z)comp1.w)test(comp1.u)-(d(comp1.w,r)comp1.u+d(comp1.w,z)comp1.w)test(comp1.w))pir)*(dvol_spatial)

I attached the mph file any help would be greatly appreciated.

Thanks,

Juan

solvers when there are coupled modules or not

Wed, 02 Apr 2025 05:52:42 +0000

For the same dimension (1d, 2d...), is the solver always the same for all modules?

Does the software always automatically adjust the solver when there are more than one module (even when the modules being solved don't share the same unknows, aren't related or coupled at all)?

How to induce voltage from PZT-5A to copper coil, which is kept at a distance of 40 mm ?

Wed, 02 Apr 2025 05:27:00 +0000

Hey there,

I'm a newbie in comsol and trying to solve one problem. A piezoelectric material, PZT-5A is being applied by an impact force of 1000 N, now due to stress there's some accumulation of charge in PZT, and I've also applied magnetic field in the surrounding, Now I want to check an induced voltage on a copper coil which is kept at 40 mm or less distance by PZT.

I'm trying everything, yet there has been no success, can anyone please help ?

P.S. The geometry is 2d axis symmetric.

About RF MEMS switches in reconfigurable antennas.

Wed, 02 Apr 2025 05:19:05 +0000

Hi all, I am currently doing one project in RF MEMS switches which i can use for Frequency selective surfaces or reconfigurable antennas. The issue is that how we can incorporate this RF MEMS switch in Frequency selective surfaces or reconfigurable antennas in order to observe the mechanical, electrical and electromagnetic properties. I am confused that how all the modules will work together to get the results

Thank you

Inverted mesh element - phase change interface deforming geometry

Tue, 01 Apr 2025 18:47:22 +0000

Hi,

I have been getting this error and this warning:

The following feature has encountered a problem: - Feature: Automatic Remeshing 1 (sol1/t1/ar1) Failed to find consistent initial values. Last time step is not converged.

Inverted mesh element near material frame coordinates (0.0499996, 87998.2). In Material Frame Variables: There was an error message from the linear solver. The relative error (1) is greater than the relative tolerance.

I am trying to create a moving boundary problem so my geometry is deforming, I am assuming this is what may be causing inverted mesh elements.

I have tried adding an automatic re-meshing node and refining my mesh around the deforming boundary.

I am new to COMSOL so any help would be appreciated, thanks.

Transient magnetic field: mimic a wire

Tue, 01 Apr 2025 18:46:45 +0000

Hello, I have built a solid mechanics and magnetic fields multiphysics simulation. At a high level, the simulation includes a current-carrying wire (that generates a magnetic field), and a small, soft-magnet device at some distance from the wire. In the presence of the magnetic field, I study the deformation of the soft magnetic structure.

I now want to do this simulation in a transient domain, however I would like to eliminate the need to simulate the field from the wire. Instead, I would like to specify or easily generate a field with the same exact profile as the wire. The reason for this is that COMSOL is giving me trouble when I attempt to study the coupled physics involving the current carrying wire while in a transient domain. If I can instead specify a transient magnetic field (not coming from a wire, just a "magic" field, if you'd like), then I can avoid this problem.

I have made this field already by using the MFNC module and specifying the Hx Hy and Hz. It runs fine. However, I am wondering if there is/are better ways to do this?

Thank you.

prism based SPR sensors simulation

Tue, 01 Apr 2025 09:02:20 +0000

Hello, I am doing the SPR sensor design on COMSOL, i have done my structure(Upside down the prism, and other layers onto the prism), assigned the materials, and properties also. Now I have to give the ports and Scattering Boundary Conditions. Can you help?

Problem With ODE Time Dependent Study

Mon, 31 Mar 2025 21:03:02 +0000

I have in my simulation some variables. They are converging correctly but when I add a ODE that is not coupled with those other variables, my solver doesn't converge anymore. All variables is not converging. Someone could explain to me what is happening? I'm using segregated solver, so, in theory this variable doesn't affect the other because they are uncoupled.

Running Batch Sweep with Batch commands

Mon, 31 Mar 2025 13:50:01 +0000

Hi All,

Is there a way to run a Batch Sweep using batch commands? I'm trying to execute a huge parametric sweep with Batch Sweep to speed up the overall simulation. I'd like to initiate the simulation with a batch command, but it seems to only perform a parametric simulation. (The simulation took the same amount of time as a normal parameter sweep, and the individual sub-simulations do not appear in the batch folder.)

Persistent error with undefined variable in time dependent solver and stationary solver

Mon, 31 Mar 2025 12:16:06 +0000

Hello Comsol,

I am facing an issue in my COMSOL model that I have been unable to resolve for a few days now, even after multiple attempts and fixes. I am working on a time-dependent simulation of blood flow in the aorta (normal aorta and with coarctation), and I have added Global ODEs (RCR model) to model the pressure changes in the arteries. My Boundary conditions have been set to velocity inlet and outlets with pressure. My main issue is that when I try to run the simulation, I keep encountering the error: "Undefined variable - Variable: comp1.p" This happens both in time-dependent and stationary solvers. How do I fix this issue?

(C_B*comp1.pt + comp1.p/R2_B - Q_B) this is the equation I have used in the global equation in global ODEs and DAEs. where: C_B is the compliance comp1.pt is dp/dt R2_B is distal resistance Q_B is the flow rate. I have defined all these parameters.

Electrical and Thermal Characteristics

Mon, 31 Mar 2025 09:32:08 +0000

Hello everyone! I'm looking for a big guy in Beijing who is proficient in electric heat simulation, and I can pay a consulting fee if I have a question!

keep all plot features in matlab livelink

Mon, 31 Mar 2025 05:08:55 +0000

There's a matlab file (function out = model) that creates a model, solves and postprocesses. All plot features including titles, legends are written within this model m function. Then use mphplot(model,'pg') to plot 'pg'. But this loses all plot features. How to use mphplot while keeping all plot features without rewriting all features?

solvers: solving the same model with various equally suitable modules

Mon, 31 Mar 2025 03:55:06 +0000

The software automatically specifies solvers according to the specific modules used. When solving the same model with various equally suitable modules in one batch within the same mph file, by default only one solver is used for all the modules applied. This solver may be suitable for only one of the modules but not for the rest of the modules. In this case how to make the software use different solvers when solving different modules?

Issue in modeling natural convection to a pot

Mon, 31 Mar 2025 01:54:16 +0000

I am trying to model the heat transfer to a pot in natural convection mode. This is an axisymmetric model, where a stove setup is modeled. The temperature at a bottom boundary (represents the burner) is set to a constant value. There is a pot placed on the stove. There is water (modeled as a solid object with a high thermal conductivity) inside the pot. We are studying the heat transfer to the pot and to the water through conduction and natural convection in this case.

I am using the heat transfer in solids and fluids, turbulent flow, and nonisothermal flow multiphysics coupling with a fully coupled solver to get the solution. The issue is that the bottom surface of the pot is getting heated, however, there is negligible temperature gain at the interior surfaces of the pot and also the water in the pot. What could be be possible issue? I am attaching the model .mph file for your reference.

Thanks!

Electrical and Thermal Characteristics

Mon, 31 Mar 2025 00:39:40 +0000

Hello everyone! Using a porous medium model to simulate Joule heat, it is known that the bed resistance decreases with increasing temperature, and the resistance and temperature data are obtained experimentally, fitted by an equation and then defined inside the material conductivity of comsol, why is the bed temperature change small?

Question about COMSOL tutorial provided

Sat, 29 Mar 2025 20:03:14 +0000

Hello I am trying to understand this tutorial https://www.comsol.com/model/dc-corona-discharge-in-air-in-a-point-to-plane-configuration-100451 I want to change the wall boundary condition to just absorb the electrons and i want to plot it on the wall. I am not able to do so. can you please tell me why. My objective is to determine how much charge got deposited on the wall during the simulation