Latest Discussions - COMSOL Forums

Difference between MEF and EMW frequency study

Sun, 16 Jun 2019 21:16:55 +0000

There are two different physics interfaces Magnetic and Electric fields interface in ACDC module and Electromagnetic Fields, Frequency domain interface in RF module.

As I understood from the manual, both interfaces work without any static assumptions in frequency domain analysis.

MEF interface uses Maxwell-Ampère's law with displacement current included. And using the constitutive relations and equation of continuity it obtains two equations in terms of A and V and solves for these variables.

EMW interface solves for the wave equation.

These two methods seems equivalent to me. Are there any difference between them when used with a frequency domain study?

Matlab function

Sat, 15 Jun 2019 11:41:39 +0000

I have a couple of question;

1-Is it necessary that the input arguments of MATLAB function should be equal in size? and also output argument when using Livelink Matlab

In this case, the sizes of the arguments are ;

c = 100

cavg=1

MI =1

.................................................................

function MI = MixingIndex(c,cavg)

sumc=0;

for n=1: length(c)

a=(((c(n)-cavg/cavg)^2));

sumc=sumc+a;

end

MI=(1-sqrt((1/length(c))sumc))100;

...................................................................

2- How can I use this external function as a stop condition?

for example;

MixingIndex(c,aeop1(c))<0.5

aeop1(c) is the surface average on a boundry .

what is your suggestion to seek these goals?**

How to get Capacitance matrix from Stationary Source Sweep?

Fri, 14 Jun 2019 23:13:29 +0000

Hi,

I am trying to find capacitance matrix for a simple 2D geometry of conductors. Using the Stationary Source Sweep study, I got the electric potential plot for the individual terminals.

But in the results node, it shows no values for capacitance matrix. What setting do we need to extract capacitance matrix from Stationary Source Sweep?

Thanks.

Meshing interpolated curves

Fri, 14 Jun 2019 15:21:47 +0000

I have a simulation where my geometry is an interpolated curve. The meshing for that feature is really fine and detailed:

https://i.imgur.com/V8RDmKw.png

zoomed in:

https://i.imgur.com/o7YLIr8.png

Are there any tricks I can use to reduce the required meshing? Even if it lowers the simulation accuracy, I'm willing to do quicker runs and then more thorough simulations once I'm in the ballpark.

I'm running 5.3 by the way.

Thanks!

Elecromagnet

Fri, 14 Jun 2019 10:11:38 +0000

I built one coil in Сomsol 5.2a as the Helmholtz coil and inserted an iron core in the middle of circle, but after starting the Study the magnetic lines do not pass through the core. How to include the core in this process?

laser

Fri, 14 Jun 2019 09:32:08 +0000

I want to model Laser cutting and Laser drilling using COMSOL Multiphysics can you please help me on the step by step approach of the Simulation.

Specific absorption rate in comsol

Fri, 14 Jun 2019 01:38:08 +0000

Hello everyone,

Please see attached file and help me to understand how should i calculate SAR for 1 gram or 10 gram like in CST (shown in the file) in COMSOL?

Any help would be appreciated

Thankyou

Difficulty in selecting geometry for boundary condition in a magnetostrictive model.

Thu, 13 Jun 2019 19:31:25 +0000

Hello everyone, I am working on a magnetostrictive model which is a solid cube and I want to apply periodicity as a boundary condition to vertex to the opposite vertex, edge to opposite edge, and face to opposite face. When I select periodicity as boundary condition it just allows me to select boundaries of the model which are basically faces of the cube. I could apply this boundary conditions in ABAQUS by using a matlab code but I am unable to do it in COMSOL. Is there any way I can select geometry according to my requirement mentioned above??

Two phase flow using phase filed method : filling of liquid through different widths channel

Thu, 13 Jun 2019 18:08:32 +0000

Hello, I am simulating the channel filling of water . The channel dimension starts with 600 micron in width and reduces to 200 microns and then again increases to original dimension of 600 micron. I need to track the interface at the front. unable to solve the model . please help.I have attached the model.

Fluid structure interaction for a membrane

Thu, 13 Jun 2019 18:07:07 +0000

Hello, Iam trying to simulate a expansion of the membrane with both end fixed Iam facing following issues in solving the model. 1) If i give inlet boundary condition as velocity /discharge /mass flow rate it doesnt solve with the follwoing error. Failed to find consistent initial values. Last time step is not converged. Iam not able to get the expansion of the membrane.

Failed to form solid object

Thu, 13 Jun 2019 17:43:54 +0000

Dear All, does anyone can help me with the following issue,

I imported stl file (rock sample) into Mesh Part, then into geometry and when I try to convert to solid form I faced the following error - "Failed to form solid object."

How to solve it? or can I leave it and simulate (laminar flow) without forming solid object?

Screenshot is attached (mph size exceed the limit)

Compute Error: "No Such File or Directory"

Thu, 13 Jun 2019 16:16:37 +0000

I am tyring to compute a model and getting the error "No Such File or Directory". The model was built in COMSOL 5.2 and I am running 5.4. I am not sure where this directory issue is coming from. Thank you.

Where to find COMSOL 5.4 variable description with details?

Thu, 13 Jun 2019 14:53:44 +0000

Hi Everyone,

I am trying to modify some predefined equations in COMSOL 5.4 using the equation view, but there are a lot more variables than I expected. I don't know what many do and the short description in equation view does not help much.

For example, in the Semiconductor module, the Metal Contact has a variable called semi.bcAn with the description "SG exponential term for electrons at the boundaries ". I have no idea what that means. One could try and figure out by analyzing the way the variables are connected to one another. But with hundreds of them in the whole model, it's very time consuming.

Is there some document where can I find some more details on the variables? The COMSOL documentation doesn't seem to include anything beyond basic stuff. Thank you!

Completely wetted or non-wetted wall with phase field

Thu, 13 Jun 2019 13:11:22 +0000

Hey !

I've been trying to make a simulation of completely wetted or non-wetted walls (theta_w=0 or theta_w=pi) with phase field but it's always diverging. Have you ever tried and/or manage to do so ? How would you implement that plz ?

Thx in advance Joseph

Dielectric slab

Thu, 13 Jun 2019 12:24:50 +0000

Dears, I am biginner of COMSOL. I have some queries about dielectric slab. I am able to produce electomagnetic wave in 2D dielectric slab but unable to propagate in 3D dielectric slab. For reference i am attaching files.

Combination of Computational Fluid Dynamics and Chemical Reaction

Thu, 13 Jun 2019 08:51:05 +0000

Hello guys,

I am studying about microfluidic technology, so I would like to use the simulation for it.

I want to handle two types of model - Computational fluid dynamics (CFD), especially Multi-phase case - Chemical Reaction, especially Cross-linking case for a polymer.

Is there any study about it? Please give me some opinion. It is possible or impossible? Do we have any tutorial about the combination of them?

Thank you so much!

Directivity at a Certain Direction

Thu, 13 Jun 2019 08:37:34 +0000

Hi all,

For a far field domain antenna study, I can achieve the maximum directivity by typing emw.maxDdB in the expression of a global evaluation, which is in the and direction. But I need to get the directivity value (or gain value) at a certain direction such as and .

By the way, I can get the all values manually by copying plot data of 2D or 1D far field radiation plots but it is not practical for me because I will use that single directivity value in the application builder. How can I obtain a directivity value at a certain direction?

Thank you.

The file increases in size every each run

Wed, 12 Jun 2019 18:00:49 +0000

I made one model and only change few parameters every time I run this model. I clear the solution from the previous study every time, but I noticed the file is taking more space. Why?

Set solution of previous time step as initial condition

Wed, 12 Jun 2019 16:44:55 +0000

I want to export the Temperature solution of my model onto Matlab and set the entire Temperature matrix containing temperatures of all the domains as initial condition for next iteration. But I see that I can only set 1 value for the initial temperature condition. What do I do with it?

Continue calculation with a single value from a sweep

Wed, 12 Jun 2019 16:02:55 +0000

Hi All,

Here is a situation that occures very often in my optimization problems. I want to do a simulation in two steps:

Step 1: A parametric sweep over the parameter f, where I probe the energy E. Step 2: A single calculation (not a sweep) with f set to the value, where E was largest in the sweep of Step 1.

Is that possible?

Best, Jacob