Latest Discussions - COMSOL Forums

Potential transfer between two electrodes in series

Thu, 31 Oct 2024 12:50:58 +0000

I have an experimental system that contains a copper wire with a potential E. A porous cathode made of Graphite Felt is connected to the wire. The wire is supplying the current to the GF cathode. The goal is to simulate the current density distribution along the cathode and possibly at the connection point of the wire.
For this purpose I have selected a Highly Conductive Porous Electrode to simulate the wire inlet potential connected in series with a porous electrode which simulates the Graphite Felt cathode within a Tertiary Current Distribution module. Both electrodes enable the simulation of the chemical reactions of the cathode and the wire. My problem is how to transfer the potential from the wire to the cathode. I didn't found boundary conditions available to set in the conditions at the boundary between the two electrodes.

I see zero stress and displacement when modelling electromagnetic lorentz force interaction

Wed, 30 Oct 2024 19:37:27 +0000

I am working on a model where I have to simulate the magnetic field around a electrically induced nerve fiber. I see the magnetic field and electric field potential but I notice zero displacement or von stress in the nerve. I am not sure if the boundary is not defined correct or not. Any help would be appreciated.

PCB Import Issue: Missing Via Connections Between Layers in COMSOL

Wed, 30 Oct 2024 18:38:06 +0000

Hello everyone,

I'm currently working on a project involving a 2-layer PCB. I designed it in Altium and exported the 3D model as STEP and DXF files, including all traces, vias, and pads. However, when I import the files into COMSOL, I encounter an issue: while I can see the vias, I don’t see any connection between the top and bottom layers through the vias. It appears as though the vias aren’t establishing connectivity across the layers.

Has anyone experienced this before, or could anyone suggest the best way to ensure the layers connect properly through the vias in COMSOL?

Thanks in advance for any insights!

COMSOL cluster sweep with separated output files from command line

Tue, 29 Oct 2024 18:20:21 +0000

Hi all,

Is it possible in Comsol to set up a distributed parametric sweep on a cluster and get the separated output model files, similar to batch sweeps on local? As I understand, this functionality is available only via the GUI mode, and it's not possible for me to launch cluster jobs this way. The other option is cluster batch calls via command line, which only generates a combined single file and not a separate file for each parameter. Will appreciate if someone can help me on this.

Best Regards Amit

Problem with the imported mesh

Tue, 29 Oct 2024 15:12:12 +0000

Hi everyone,

I am trying to observe to Reflectivity spectrum of an FBG. If i build the correct geometry in one project (Let's call it Project A) and i run the "Boundary Mode Analysis" i get the right results. But if i build the exact same geometry in a second project, study the deformation of the geometry using the "Solid Mechanics" and then import it in a third project for the "Boundary Mode Analisys" (Project C), the results i get are wayyy different.

In the "Solid Mechanics" project i run a "Stationary" study step using a Point Load of 0 Newton. I should get the exact same geometry after the study and thus the exact same results of the Reflectivity spectrum. I dont know if i am doing something wrong, anything can help. Could be an exporting error? The study step for the Mode Analysis in project A and C are the same with the same parameters. :(

I am using COMSOL version 5.3a.

Regarding the faster simulation of mph file through LiveLink for MATLAB

Tue, 29 Oct 2024 06:41:19 +0000

Hello everyone,

I am simulating the behavior of Litz wire using the LiveLink for MATLAB and observe its current, voltage, and resistance. My simulating model is complex (cannot be reduced/simplified/meshed further). after observing the running time, i found the following code takes 95% of time. model.sol('sol').runAll;

can you please give me any alternative code to run the model so that I can execute it fast. I only want to record the current, voltage, and resistance.

Thanks in advance.

Unable to Select Fluid-Fluid Interface for Free Surface Deformation using Moving Mesh

Mon, 28 Oct 2024 23:35:37 +0000

Hi,

I am trying to simulate the physics model mentioned in the paper whose DOI link is here: https://doi.org/10.1016/j.applthermaleng.2024.122562. Specifically the one in section 2.2 the MHD submodel with the moving mesh for the geometry that I have in my mph file.

I am unable to select the Fluid-Fluid Interface between the air and liquid metal domain. I crosschecked to see if my other boundary conditions match with the one given in Table 1 in the paper and they do. Please let me know if I am missing anything there.

Additionally, utang is the tangential velocity that seems to only appear when I choose RANS model. Is there a possibility of getting it by choosing Laminar Flow and simulating free surface deformation using only the Laminar Flow without additional turbulence modelling.

Any help is much appreciated! Thanks! Maruthi

Lumped mechanical module

Mon, 28 Oct 2024 14:16:25 +0000

i want to couple a structure and discrete spring-mass system representing a local resonator defined as: displacement node at the connecting point (where input displacement is computed from multicoupling), a spring, a mass with free end node in lumped mechanical module. my structure is a hollow cylinder excited at the top. in lumped-structure connection i define the direction of the discrete system which it depend on the position along the circumference. when i solve in frequency domain i do not get any difference with/without the presence of discrete system or i got a problem in the segregated solver.
I have tried a 2d simple case and was working fine but when i move to 3d case it seems there is no coupling between the systems. I thought i should add the reaction force of the displacement node as a point load in solid mechanics (-lms.disp1_f) but still no way. I thought maybe i should use external source instead of displacement node but two port are required and each resonator is only connected to one point.

i have tried a different approach using PDE :add global equation, call a function as x, add weak contribution where mass(2pifreq)^2x*test(x) is my cinetic energy of the resonator and add spring-damper with source point defined as connection point and for destination point i prescribed the displacement as x. It works if i'm considering only one direction in the x,y,z which is 1,0,0. the problem arises when the resonator is placed along the circumference (for example theta angle ) of the cylinder where i have to add the x,y contribution but it doesn t work anymore. if you have any suggestion using the first one or the second method please let me know

Interpolation Sweep as a Function of Five Arguments

Mon, 28 Oct 2024 12:00:05 +0000

Good day,

I am working on a model with two steps; in the first model I investigate the eigenmodes and eigenfrequencies of a system and subsequently export the parameters of interest together with these values into a .csv-file.

In the second model I want to import these values using the interpolation function, which is limited to 3 arguments (x, y, z). This works fine in the case of a singular combination of one eigenmode and its corresponding eigenfrequency.

Initially I tried to index both these eigenvalues and interpolate using 5 arguments, but this isn't possible in the current version. I tried working with smaller sets to see whether anything was possible, but all values have to be defined as i.e. frequency(x,y,z) and not frequency(x,y,z,a,b). I also assume that nesting these isn't possible either. But the full .csv file contains a total of 1500 combinations, so how do I sweep over all of those in a single model and extract the results?

How to model the Bragg Wavelength shift caused by an applied load

Mon, 28 Oct 2024 09:42:35 +0000

Hi everyone,

I am trying to simulate the shift of the Bragg Wavelenght in an optic fiber caused by an applied load. I am using COMSOL version 5.3a. I simulate the deformation of the fiber caused by the load using the physics "Solid Mechanics" and the load is applied as "Point Load" on the cladding of fiber. In this simulation i checked the option "Inclued non linearity" to later export the deformed geometry.

Then i export my deformed geometry and i import it in a second project for the optical study using the physics "Beam Envelope". I remesh the geometry, delete the outer cladding (to simply the simulation) and define the PML. I define the refractive indexes of the core, cladding and PML using the equation i found in the COMSOL tutorial "Stress-Optical Effects in a Photonic Waveguide". The stress used in the equations is imported from the "Solid Mechanics" model using 3 interpolation function i called (sx, sy and sz).

The results i obtain (attacched) don't match with the theorical result and with the results i obtain in FBG-SimPlus (also attached). Anyone can tell me what i am doing wrong? Are the equations wrong or is the entirety of the approach?

The projects are too big to be attached sorry.

Also sorry for my english.

Domain and boundary layer mesh generation problem

Mon, 28 Oct 2024 07:29:48 +0000

Hello!?

I am modeling a heat transfer model of a shell and tube heat exchanger. I am trying to simulate only the shell side domain and keep the tube wall temperature constant. On the tube side, I use ribs in a concave shape, which creates an edge.

While meshing the geometry, I used a physics-controlled mesh and faced some difficulty. First of all a notification pops up that the domain has a thinner region than the minimum element size and the second problem is boundary layer stops meshing after two layers for a poor mesh element. I don't know how to resolve this problem!

I hope you can help.

Thank you,

Solving Nonlinear Equations

Sun, 27 Oct 2024 17:26:51 +0000

How can I solve the constraint equation using the arc-length method in COMSOL? I am working on a problem involving non-linear behavior, possibly with snap-back effects, and I need to ensure the solution path remains continuous throughout the analysis. Additionally, what are the recommended solver settings for arc-length control to manage convergence effectively?

A question about time resolution in the acoustic simulation (High frequency)

Sun, 27 Oct 2024 09:10:30 +0000

I did a simulation of thermo-ultrasound (thermoelastic). But the time resolution is not high. In my experience, when the convergence value is not high, the resolution will be very low. I'm curious how we can improve the time resolution.

the output curve doesn't smoothe properly

Fri, 25 Oct 2024 16:28:16 +0000

Hi,

I have a problem when solving a solar radiation on a surface. The input data period is 10 min, both for temperature and solar radiation. But when a make a 1D plot, it seems not to follow this period, or smoothing is not going. Can anybody tell me what can be happening? In the image attached, dot-dashed are real data. continuous line is the simulated surfaces temperature. Time dependent is configurated to (1,10,1430). Each every 10 min.

thanks in advance!

Borja

direction in lumped-structure connection

Fri, 25 Oct 2024 14:26:10 +0000

How is it define the direction under lumped-structure interaction in user defined x,y,z? I thought it was normalized direction so it could have -1 to 1 value depending on the position. For example: if I'm considering a cylinder with radius r=2 centered at 0,0,0 where I attach some mass-spring system in the circumference. This mean that given a point with angle theta has x,y component depending on cos(theta) and sin(theta). This point should depend on its position like x=rcos(theta), y=rsin(theta) and z=z_point, or only its direction as x=cos(theta), y=sin(theta), z=0; (i thought this one) when i m computing I get or no influence of my mass-spring system or a problem in the solver. I have tried to a simple case in 2D but I still do not understand. I attach file.

Seeking Help with Capacitive Sensor Modeling in COMSOL

Thu, 24 Oct 2024 18:11:43 +0000

Hello everyone! I’m working on modeling a capacitive sensor using COMSOL. The sensor I’m studying consists of an FR4 substrate with 15 pairs of copper interdigital electrodes. The measurements I took with the sensor showed capacitance values ranging from 6 pF to 100 pF (using air, water, and ethanol as test media). My goal is to model this sensor using the Finite Element Method (FEM).

Initially, I developed a reduced model, the RVE (which represents only one pair of electrodes). By proportionally multiplying the results, I obtained values relatively close to the measured ones, with errors ranging from 1% to 17%.

Currently, I’m working on a full model that aims to represent all the geometric characteristics of the real sensor. Although I haven’t been able to fully replicate all the feed lines, the model seems fairly accurate. However, the errors are even larger than in the reduced model.

Does anyone have suggestions on how I can improve the model? Is there any way to import the .gerber file used in the sensor’s fabrication directly into COMSOL? Or could this be a mesh adjustment issue?

I’m feeling a bit lost, so any help would be greatly appreciated. I’ll attach some images that illustrate the problem. If anyone is interested, I can also share my current model file.

Heat transfer in porous media - boundaries for infinite aquifer

Thu, 24 Oct 2024 10:10:26 +0000

Hello! ?

I am modeling heat transfer in an aquifer, which I have represented as a 3D block. There is a heat source within the porous media, and I aim to simulate how heat propagates through this medium. There is water flow through the domain.

I am uncertain about how to establish the boundaries for my model. I want to simulate heat propagation in an infinite aquifer, which means I need to account for the effects of the boundaries. Ideally, I would like the heat to the domain as if the porous media surrounding the block were infinite. If I use thermal insulation, the injected heat remains trapped within the domain, leading to results that are inconsistent with a naturally infinite domain.

I hope you can help.

Thank you,

CO2-water two-phase flow in fractured reservoirs

Thu, 24 Oct 2024 02:19:53 +0000

Hi, I want to simulate the process of injecting CO2 into an aquifer to form bubbles. I added Darcy's law, porous media heat transfer and porous media phase transfer to the 3D model, and achieved coupling through the multiphase flow of porous media. In addition, three two-dimensional planes were added to characterize artificial fractures after fracturing, and a "fracture" model was added to Darcy's law and porous medium heat transfer fields, but I could not find the fracture interface in the phase transfer field. When CO2 continues to be injected into the aquifer and does not reach the end of the fracture, the model converges well. However, when some CO2 reaches the end of the fracture and needs to enter the reservoir, it is difficult to converge. I don't know where the problem lies, nor do I know how to deal with this situation. Thank you in advance!

Find the normal gradient of field variable at domain edges

Wed, 23 Oct 2024 17:31:57 +0000

Dear all,

How can I find the gradient of a field variable on the edge of the domain. Example I am trying to find the gradient of gas saturation (s_g) to formulate an outflow boundary condition at the exit of a porous domain, and I cannot use the d-operator as it is not well defined, and I use the dtang operator as suggested. Here, the operator gives a finite value to x comp of gradient which is tangential to the edge but 0 to the y comp of gradient. I know s_g has a normal gradient to the boundary. Which operator will give me this value at the edge?

Best Regards Amit

How to simulate the Joule Thomson effect?

Wed, 23 Oct 2024 07:43:54 +0000

There is a reference here, but it doesn't mention the detailed parameterization process.