Latest Discussions - COMSOL Forums

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?

error message of Singular matrix in nitsche contact

Wed, 15 May 2024 13:55:24 +0000

When the same problem is solved by penalty and augmented Lagrangian there is no error. But with nitsche, there's the following error:

Feature: Stationary Solver 1 (sol17/s1) Failed to find a solution for the initial parameter. Singular matrix.

There are 264 void equations (empty rows in matrix) for the variable comp1.solid.Wfric_p1. at coordinates: (2.65789e-18,0.0248165,-0.0434066), (2.16489e-18,0.0353553,-0.0353553), (1.51957e-18,0.0434066,-0.0248165), (7.86146e-19,0.0483235,-0.0128387), (1.8747e-34,0.05,-3.06162e-18), ...

and similarly for the degrees of freedom (empty columns in matrix). Returned solution is not converged. Not all parameter steps returned.

Magnetic Force Calculation

Wed, 15 May 2024 13:08:44 +0000

Hello everyone.

I am a new user of COMSOL. I have a project for my school. I need to calculate magnetic force. I have a cylindical magnet with a hole. Also cylindrical carbon steel top and the bottom of the magnet. Magnet radius is 80 and carbon steels are 90mm. It is a magnetic wheel in total. I have flat plate which is also carbon steel. I just wanna calculate the magnetic force between magnet and the flat plate. Carbon steel is also magnetized so i want to include all the factor for magnetic force.

Can you please tell me step by step about that calculations?

Thank you for all

Premixed Combustion

Wed, 15 May 2024 03:42:48 +0000

Hi,

So Im trying to build the methanol laminar premixed combustion in COMSOL. I used several physics interface like heat transfer in fluids, chemistry, transport concentrated species, and laminar flow. I used a single formula reaction rate (Arhenius reaction)

r = kexp(-E/RT)C_CH3OH^1.4

Eventhough, the temperature increase a lot, however the flame does not appear. Is anyone here can solve my prblem? or anyone knows about the setting in laminar premixed combustion in COMSOL?

I would really need help on this problem. I attached my file here

Rizky Kusumastuti

Scaling down issue in COMSOL Multiphysics from millimeter to micro meter

Tue, 14 May 2024 16:00:38 +0000

Hi Experts,

I have a model created and defined dimensions as parameters in millimeter range and I want to scale it down to micrometer dimension. I used the scaling option under geometry and add 1000 as scaling factor with isotropic option selected but after I clicked the build option, it processed the image and didnt show anything in the right hand side and sometimes it throws error saying "the object to be scaled must be selected".

I did select the CAD image as can be seen in the below screenshots image 2,image 3.

Am i doing some mistake in the whole scaling down process? could you please advise .I use COMSOL 2024 version. Is there any other way to scale down the parameters in comsol from millimeter to micrometer?

Image 2.png below is the inital image to be scaled but Image 3.png is the scaled image that vanishes when i click build all.

Kind reg Amit

A question about fluid-structure interaction

Tue, 14 May 2024 12:55:09 +0000

Why is the minimum temperature change in my FMI heat transfer simulation 5K, I want a more accurate temperature change, how should I do this, how should I implement the effect of microfluidic velocity on the FSI module

How to utilize Temperature Data for Complex Rolled Foil Geometry

Tue, 14 May 2024 12:53:24 +0000

Hello everyone,

I conducted a flow simulation (2D-axisymmetric) to obtain temperature data within a specific system. Now, I would like to utilize this temperature data for a separate study where the geometry is significantly more complex (a coated, rolled-up foil with over 3000 layers and layer thicknesses ranging from 5-60 µm).

Is there a way to directly transfer the temperature data from my flow simulation into a new study with the modified geometry? I am not particularly experienced with COMSOL. How would you suggest proceeding? Especially the thin and numerous layers are posing challenges for me.

Thank you!

Luis

Temperature difference boundary condition

Mon, 13 May 2024 12:47:26 +0000

Hello everyone,

I want to define a boundary condition in which there is a constant value for the temperature difference of two surfaces. How can I define such boundary condition?

Livelink for MATLAB taking too much time to simulate

Mon, 13 May 2024 11:46:57 +0000

Dear all,

    I am simulating coil strands to know its AC resistance. i am using LiveLink for MATLAB to automate this task. however, for 10 turns coil with 100 strands, the total simulation time goes to 5 hours while for 10 turns with 300 strands, the total simulation time goes 50+ hours.
    by profiler code checking, i found that *** model.sol('sol').runAll;*** is taking 95% of overall simulation time. can you please suggests me to reduce the time duration of simulations.
I am using regular mesh with minimal complexity. 

best regards
thanks