Latest Discussions - COMSOL Forums

Issue with Image Resolution When Exporting from COMSOL

Sat, 18 May 2024 10:20:50 +0000

Hi everyone,

I'm currently working on my thesis and need to export high quality images of my COMSOL model. However, whenever I save the images, the resolution seems too low, and the details are not clear enough for publication. I've tried adjusting the settings and I used some online application such as Jpeg compressor and others but haven't had much success.

Has anyone encountered this issue before, and can you suggest the best way to export high-resolution images from COMSOL?

Thanks in advance

Monitoring intermediate results during running time dependent simulation

Sat, 18 May 2024 09:38:24 +0000

Hi all,

I am running time dependent jobs on remote cluster, and need to monitor the results at regular intervals to monitor the progress. Is there a way I can output the solution files at predefined timesteps/intervals, so that I can transfer them to my local and open in GUI. Can the recoveries feature be modified to do this?

Best Regards Amit

Oscillatory Flow

Sat, 18 May 2024 00:15:28 +0000

Hello, community. I have a doubt. I would like to realize a purely oscillatory flow. One of the requirements for this simulation is that, somehow, the mass flow has to be zero so that the wave passes through the medium and does not take the mass of liquid along with it (let's assume a cross section of a cylinder, a rectangle). What options would I have? Would there be a way to do this without importing the Acoustics library into Comsol? How to impose (algebraically) a mass flow condition equal to zero in COMSOL and how to place the wave in the simulation? Would it be worth using the Wave form part of COMSOL?Thank you very much.

Circular Polarization with Gaussian Beam

Fri, 17 May 2024 13:22:48 +0000

The below post is related to an archived discussion

I have been working to get a circularly polarized Gaussian beam. I found that this solution does indeed work for the user defined waves but using the (built in) function for a Gaussian beam, the result is elliptically polarized light. I have combed through the equations and cannot see anything amiss. I have also tried to counteract the ellipticity using various methods, but to no avail. I believe there must be a way to simulate an circularly polarized beam in COMSOL, but thus far I cannot find it. I have attached a simple model which demonstrates the difference in the two methods despite the same inputs.

Planar spiral inductors

Fri, 17 May 2024 11:05:30 +0000

Hi, Im building a planar coil for simulation of inductance. The model consists of many square coils. When im building it, I am getting an error " Numeric coil Coil 1 (coil1) not solved for. Solve it in a Coil Geometry Analysis step. "

Please help me to rectify the error.

Numerical diffusion and unphysical results

Fri, 17 May 2024 08:48:41 +0000

Hi all,

The equations I am solving are simple set of equations just to get a feel for the software as I build more complicated systems. Here, I have a simple diffusion-reaction equation of Zn+2OH->ZnO+2H2O I am solving using equation based modelling since thats what I will be using in the later part of my modelling. Here, in domain 1(centre square) the initial conc of Zn is given and all other species are set to zero. The idea is that OH diffuses from outside (outer annular square) into the inner square, reacts with Zn to give ZnO and H2O. ZnO does not diffues and H2O must diffuse outside. I have formed a union of the system and enforced conituinty at the edges. Now my question is, 1) Although I have given the diffusion coefficient in domain 1 and 2 for Zn and ZnO to be zero, I still see both these species diffusing out of the central square which should not occur? 2) The solution produced negative results for ZnO inside the centre square which can never be the case since ZnO is the species being produced. After being produced the ZnO is not supposed to diffuse since its diffusion coefficient is set to zero. So is it due to numerical diffusion that I see the artifacts here? And how can I avoid them or am I making a mistake in the model? I appreciate any help I can get. I am new to COMSOL and the learning curve is quite high.

Sensitivity Analysis

Fri, 17 May 2024 07:55:43 +0000

Hello,

I am simulating a capacitive pressure sensor and am stuck with Sensitivity Analysis. I have used Sensitivity analysis under Study 1 and have added Maxwell Capacitance expression comp1.es.C11 as the Objective Function and selected Pressure as my Control Variable. I am unable to understand the process involved in Sensitivity analysis as to whether Change in Capacitance divided by Change in Pressure is being computed or not which is the formula to calculate the Sensitivity. When I check for the sensitivity vs. pressure graph in Results section, I am getting a wrong curve.

Kindly clear my doubt over what is happening behind the COMSOL Sensitivity Analysis process.

Regards, Sourabh

Question in electro-thermal coupled simulation based on electric-field-dependent conductivity

Fri, 17 May 2024 07:02:13 +0000

The conductivity of the insulation materials in my simulation is a function of temperature and the electric field strength. But how I express the electric field strength in the function in COMSOL 6.0? Maybe ec.normE? But it didn't work for me.

Coupling Matrix of Piezoelectric materials

Fri, 17 May 2024 01:19:36 +0000

How to find Coupling matrix of a Piezoelectric materials? I am working with MoS2, and I can't find its properties like coupling marix,elasticity matrix, compliance matrix.

Dispersed phase

Thu, 16 May 2024 19:44:40 +0000

I am trying to couple heat transfer with Euler-Euler flow physics. I have defined solid particles and air in a Euler-Euler physics with respective volume fraction. I have a constant heat source heating a particle so I need heat transfer physics. I am bit confused and trying to figure out how to define dispersed phase in heat transfer physics. Please let me know if there is a way to do so.

Thank You

Divergence on piezoelectric domain

Thu, 16 May 2024 18:15:33 +0000

Hello to all,

I'm trying to create a 2D model of an ultrasonic NDT using Elastic Waves, Time Explicit with Electrostatics. I used the tutorial "Angle Beam Nondestructive Test" (https://www.comsol.com/model/angle-beam-nondestructive-testing-78811) as starting point for my own model, but I'm having some trouble with the Piezoelectric domain.

I assigned an edge as Electric Potential boundary condition and to create a pulse I inserted an Analytic function as voltage input, just like the tutorial. The simulation starts fine, but after a while, the electric potential in the piezoelectric domain grows and I can't figure it out why. I attached a plot of the average electric potential on the edge, in this image is visible the input pulse and how exponentially the voltage grows after some point.

I thought that it could be a mesh problem, so I tried to refine it, but that didn't work. Anyone faced a similar problem?

Thank you in advance,

Rodrigo Pires

How to define an initial current for a coil in magnetic fields physics

Thu, 16 May 2024 14:19:56 +0000

I'm simulating a coil with voltage source. How to define the coil initial current so that I don't need to wait for the transient period to finish? Or how to initiate the time stepping solution with the static (time harmoinc) solution?

Parametric sweep not being made/showing any plots

Thu, 16 May 2024 14:10:25 +0000

Hello,

I encounter an issue when I try to perform a parametric sweep for my meshsize. I am trying to get a plot showing how it changes based on what meshsize one gets for each frequency in my plot (mainly the eigenfrequencies). How come my parametric sweep is not being performed or it is being performed but only showing one constant value? I will attach a picture of my sweep as well as my model file.

Thank you in advance!

Magnetic Force-Based Simulation and Experiment Differ by scaling of (length)^2 for geometries with changing (length)

Thu, 16 May 2024 13:50:10 +0000

My team is trying to 2D model a short (~50um) post (10 x 10 um) with a single cube (sizes from 10-40um) at the top that bends at its fixed base in the presence of slowly rotating (1Hz) magnetic field. The system is also in a fluid medium, so there is fluid structure interaction. The model is compared to experiment and we find that

(exp value) = (Constant) * (sim value) * (L^2)

where "exp value" and "sim value" are the deflection of the cube's leading corner from experiments and simulations, respectively, over a range cube sizes defined by L. "Constant" is a fixed value of 2.5 that was chosen beause it makes the magnitudes of the results agree with minimized R^2 error ~=0.85; the Constant used has the same value no matter what cube size we model.

Even more interesting, the exp results are parabolic (the deflection peaks at an intermediate value of L and drops by ~30 and 70 % at the low and high cube sizes) which this particular scaling matches suprisingly very well. It would seem very odd that this particular scaling matches the data so closely over the wide range of L without some underlying reason since the parabolic nature is tied to simulation geometry. The required Constant could come form material property measurements, or experimetnal field values being off due to fixed machine calibrations and is not seen as a major issue (although 2.5 is an oddly round number).

We've sat with this for months doing hand calculations and simpler models to tease out whether this is an issue with the 2D sim, our application of the Force calculation, Comsols force calculation itself, experimental data collection, some thickness effect that is/not acounted for, and the list goes on.

Anyone have any ideas or threads to pull to help us figure this out? All thoughts are appreiated.

Electric field due to dipole in Comsol RF. Difference between closed form solution and comsol results

Thu, 16 May 2024 11:38:56 +0000

The field produced by the electric point dipole in COMSOL RF differs from that of the closed-form solution.

Simulation details:

Simulation domain is a square region of side length 2.2m with 0.1m allocated for PML along all six sides
Electric Dipole is located at the origin
Dipole moment is 0.001Am along the Z direction.
Frequency is 433 MHz

The closed-form expression is evaluated using the attached Matlab code, which implements the equations in the attached image in spherical coordinates and transforms the fields to cartesian coordinates. The absolute value of the field along the Z direction is plotted for the 2D slice at z=0.

Problem: The absolute values of electric fields are drastically different.

Question: Why is there a considerable deviation in the amplitude of electric fields? Is there anything wrong with the Comsol settings or the code implemented?

Can any one of you point out the issue?

Obtain the coordinates of faces

Thu, 16 May 2024 11:18:14 +0000

Hello!

I'm using COMSOL with MATLAB, and I need to get the coordinates of the faces of my model. I'm using the following code: [info1, data1] = mphgeominfo(model, 'geom1', 'entity', 'face');

However, I'm encountering a problem because the geometry comes from an imported mesh, which results in the following error:

Error using mphgeominfo DATA output is not supported when the geometric model is defined by a mesh and entity is a face

Error in TestSelecAuto (line 72) [info1, data1] = mphgeominfo(model, 'geom1', 'entity', 'face');

How can I obtain the face data in this situation?

Thank you, Vassili

1D transient conduction problem

Thu, 16 May 2024 09:39:59 +0000

Hi there

In a 1D transient conduction problem we are trying to validation the fig 11 in this paper and I set all BCs and equations but I cant get the results, can someone have a look and help me ? Im using Comsol V6

Thanks alot Abraham

Crossover from capacitive to inductive electromagnetic responses in near selfcomplementary metallic checkerboard patterns

Wed, 15 May 2024 23:47:30 +0000

Hi,

I am new to comsol and trying to simulate this article using the COMSOL software. It's about metallic checkboard pattern response to THz. I am not getting results as the paper suggests. In the paper, simulation, were done on Poynting for Optics, Fujitsu. I have used periodic boundary condition (Floquet) and PEC for checkboard pattern. I have also tried using material specified in the paper by using refractive index and transition boundary condition. I am still not getting any reliable data.

Kindly let me know what mistake I am doing.

Variable definition

Wed, 15 May 2024 16:35:22 +0000

I'm having a problem and I don't know how to go around it. I'm trying to solve the equation (du/dt)+(du/dx)+(dP/dx)=(d2u/dx^2) using the coefficient form PDE maths physics.I used u as my dependent variable. but P is also another dependent variable here and I'm not able to define it in the physics setting because its unit is different from u. How do I define P as a variable? I tried to define it as a global variable but I don't have data on how P changes with x and don't know how P depends on x. Any help? Thank you.

MR fluid simulation

Wed, 15 May 2024 14:24:31 +0000

What are the necessary modules and BCs needed for MR fluids simulation?