Latest Discussions - COMSOL Forums

Acceleration time history data for seismic analysis

Fri, 16 Nov 2018 07:40:19 +0000

Hi all,

Can somebody explain how to apply acceleration time history load for seismic analysis of buildings?

Maximum deformation expression

Fri, 16 Nov 2018 05:03:59 +0000

I want to apply inequality constraints for optimization module that max deformation of component is smaller than 1mm.

So I need expression for max deformation.

How can I express that?

Simulating Ice Melting from -20 degC to room temperature 25 degC in a tank under vibration

Thu, 15 Nov 2018 22:39:01 +0000

I would like to simulate the metling dynamics of ice in a tank under environmental vibration (eg. 2 Hz, 1 g).

I need to consider the phase change process and also the free convection in the situation where a tank with ice (initial temperature: -20 degC) is held in the air (25 degC).

Can anyone give me some suggestions and some examples on this? I am new to comsol, just did some toturial examples using this software.

Please let me know any of your thoughts.

Thanks,

Hai

Flow through metal grate

Thu, 15 Nov 2018 19:17:02 +0000

Hi all,

I do not have much experience in CFD simulation.

I would like you to clarify to me about the simulation of flow through metal grates. I read some scientific articles on this type of simulation, in which they considered the grid to be a thin porous medium. I know there is the porous media module in Comsol. However, a question arises: My model has a turbulent flow (I intend to apply the k-e turbulence model), but I do not know which flow model is used internally by the porous media module (whether it is laminar or turbulent).

I also tried to conjugate the porous media module with the k-e turbulence module. However, in doing so, I noticed that the constructed model did not change its behavior with the alteration of thin porous medium parameters (porosity and permeability), it seems that the conjunction of the two models was not successful.

It is important to note that I do not have the equivalent values of porosity and permeability of the metal grate, I was only doing tests to verify the possibility of using the porous media module.

Attached is the illustration of the geometry of the model (axissimetric geometry of a dryer) and the 3D geometry.

Thanks

Using Non-Spherical Particles in Particle Tracing

Thu, 15 Nov 2018 17:23:21 +0000

Hello All,

Is there any way to change the shape of the particles in the various Particle Tracing modules? I am trying to model the flow of cylindrical and disc shaped particles. I want to examine their different characteristics under the action of magnetophoresis and electrophoresis.

Both of these forces have, in the literature, different force equations from than those acting on the default spherical particles. I do see a way to choose Drag to compensate for non-spherical shapes, but I see no way to make a similar modification for the -phoreses.

Is there a way to do this? I've worked through all of the Particle Tracing tutorials to no end.

If there isn't a built in way to solve this, is there a way to add the necessary physics? For example, can I open the Particle Tracing module in Physics Builder and add the necessary variables to create cylinders and discs? And do so again to the -phoreses modules and modify the forces there?

Thanks

Frequency domain prescribed velocity profile

Thu, 15 Nov 2018 14:29:33 +0000

Hi, I have a model that I have investigated previous by using the velocity of the vibrating surface for excitation (determined experimentally) to view the sound pressure directivity both near and far field and interactions. However, I have the velocity profile for the vibrating structure and want to use that instead of just the maximum value. I know it can be applied with FSI in time by linking the time step to a constant known velocity , but my study is frequency domain and I am not tatolly sure of how to go about it.

Thanks....

Gradient in axisymmetric mode

Thu, 15 Nov 2018 12:06:00 +0000

Hello, I'm solving Heat Transfer in 2D axisymmetric space dimension. I want to export gradient of temperature in cartesian coordinate system. So I tried to write Tx, d(T, x), d(T, X), it didn't work (Tr and d(T, r) works). I also tried to make 2D Revolution and use space variables from it d(T, rev4x), it didn't work too. Does anybody know, how to write it correctly to export gradient?

General

Thu, 15 Nov 2018 11:30:27 +0000

Dear all,

I am trying to simulate a droplet breakup with a level set model , as a part of my project. I have used capillary number and initial length for giving the boundary condition at the inlet. I calculated velocity with capillary number formula and then , gave a uniform velocity at the inlet for continuous phase plus a zero pressure at the outlet, then I would like to give a zero pressure gradient at the inlet and a zero velocity gradient at the outlet but I don't know how I can do this I would be glad if there is a solution for the problem. I also attached the basic model here. Aabha

How to simulate flow with really close multiple rotating parts

Wed, 14 Nov 2018 19:10:51 +0000

Hi !

I want to simulate the gas flow inside a non-existing rotary engine. Please see the picture for better understanding.

It has 3 rotors, where the central one has teeth-like parts that compress the gas in the cavities of the side rotors. So it appears that the rotating domains will overlap. I want to simulate this model to see where is the best places for inlet and outlet locations.

However, I'm new to consol so even the 2d simulation is giving me trouble. how should I configurate the rotating domains, and meshing ? Is there a tutorial with a similar example ? Because I haven't found a example that uses interchanging teeth with flow between them.

Obs.: I use Solidworks for the Geometry.

Thank you very much !

Variable

Wed, 14 Nov 2018 17:51:36 +0000

I want to creat a temperature dependent variable for reaction module. Could anyone please guide me?

Piecewise funtion to determine voltage pulse

Wed, 14 Nov 2018 17:16:09 +0000

Hello all,

I have a simple thermoelectric simulation I want to run. I want to create a voltage pulse across a coil and calculate the coil temp over time. I cannot define my piecewise voltage function correctly in the definitions. I keep getting an undefined variable error when I try and run the simulation

Thanks in advance Sami

Defining Electric Field with X or Y polarization in 2-D axisymmetric case in RF (wave Optics) module

Wed, 14 Nov 2018 16:18:51 +0000

I was using the 2-D axisymmetric electromagnetic module to simulate a 3-D case. I can see that all fields are defined as Er, Ephi, Ez in this axisymmetric case in both "port" and "electric field". I want to define a wave with y polarization or x polarization. How can I do that? Also, clearly I can not express my desired x or y polarization base on R and Phi components since it involves sin(phi) and cos(phi) which are not recognizable by this module.

Thanks in advance

dipole moment calculation issue

Wed, 14 Nov 2018 10:19:18 +0000

Hi I have used electric current physics in AC/DC module to compute dipole moment of a spherical dielectric particle in external E field. Once I determined the type of particles and medium and their electrical properties in this physics, after running the program, I could obtain polarization vector explicitly at any point using comsol. on the other hand, I computed this parameter in another way. I set the whole system as medium and then computed electric field in every point of the medium .then by calculating manually the dipole moment of a spherical dielectric particle, I expected that the results will be same but the result from manually calculation overestimate this parameter nearly 2 order magnitude higher than that of comsol value. I would very much appreciate if you anybody know about the differences?

a cantilever beam 50 mm immersed in liquid

Wed, 14 Nov 2018 07:25:28 +0000

i want to extract the frequencies of a cantilever beam of length 300 mm and immersed in liquid the one sixth part of the cantilever length but when i excute the compute in comsol multiphysics it returns an error of the following. so kindly please share me how to fix these errors and warning.

Seeking help for Solid State Li battery modeling

Tue, 13 Nov 2018 20:33:49 +0000

I'm working on a project for my master thesis. I need to simulate a solid state li battery but unfortunatly our school doen't provide the liscence for the battery simulation. Therefore, I'm doing it with equetion based modeling. The problem that I face with is that I cannot cuople the DAE for current with the other two PDEs since the variables are unknown for the DAE.

I would be really grateful if you have any suggestion with my modeling as my thesis depends on it.

Also the sample of what I'm doing can be found in comsol website: https://www.comsol.com/model/all-solid-state-lithium-ion-battery-12451

Exporting from Matlab back to Comsol and plotting in Comsol

Tue, 13 Nov 2018 19:48:39 +0000

Hello,

I want to export a variable from Matlab back into Comsol to plot it after some processing has been performed on it.

Initially I exported an electric field distribution (the x,y,z components Ex, Ey, Ez) from Comsol to Matlab. I did some calculations on it, and now want to export it back to Comsol. The original format was a 1-by-n matrix with length n equal to the number of position (x,y) pairs in the mesh (this is how Comsol exports it), and the output is still a 1-by-n matrix.

For argument's sake, let's just pretend I took that original matrix and multiplied it by 2, and now am trying to import it back into Comsol to plot. Thus all values are still in the same order, to be used with the original (x,y) points in the original mesh. If I did this in Comsol, it would obviously just be 2 ewfd.Ex, for example. But I want to do this in Matlab and export to Comsol, because I am doing more than just multiplying by 2.

How do I go about doing that? Thank you for any help you can provide.

MPHPLOT: Figure Resolution

Tue, 13 Nov 2018 17:49:50 +0000

Hi Everyone,

I am using mphplot to display contour plots within Matlab using the color table "Rainbow". The resolution of the resultant figure is really low compared wth how it looks within Comsol Multiphysics. I tried to look for any properties I could change to fix it but no luck so far.

Does anyone know any solution to this problem?

What I am planning to do right now is either: - Extract the plot from Comsol Muliphysics as png for example then displaying it in Matlab hoping it would have a better resolution. - Extract the raw plot data (as in a spreadsheet of values for example) from COMSOL Multiphysics then plot it using Matlab itself.

Any help is highly appreciated, many thanks. Mohamed Abdelhamid

Failure to create correct Temperature profile

Tue, 13 Nov 2018 16:02:23 +0000

Hello,

I am new user of COMSOL and I would like to explain my problem. I have a pellet of magnetite, where I try to heating up with Joule effect. The pellet has 13mm diameter and height of 2mm. Below the pellet I design two small boxes 0.27mm0.27mm0.27mm that I use them as electrodes from copper, and they are placed in a symmetric distance of 4.13mm from the pellet's center of the lower surface. The outer surface of the first electrode, is my (Terminal) Electric Potential where with V=V0=21V and the symmetric place of the other electrode to be my ground. The Tref and the Tamb=500K and I used a Temperature boundary condition where the wall temperature of the pellet is constant T=500K. The upper and lower surface of the pellet within electrodes to be characterized with the default boundary condition of thermal Insulation. My first question is why the temperature profile doesn't give me the expected one. I mean to have a hot zone between the electrodes, and the only hot zone is two half spheres above the electrodes (one and one). The Second question that I want to quote is, why changing the electrodes' dimentions with the same V I have different Q when the material properties is the same.

Thanks in advance.

COMSOL 5.4 "Graphics" window doesn't fill entire window (Ubuntu 16.04)

Tue, 13 Nov 2018 15:32:33 +0000

I recently installed COMSOL 5.4 on my Ubuntu 16.04 workstation with NVIDIA Quadro K2200 graphics card. Unfortunately, the Graphics window in COMSOL doesn't fill the entire space reserved for it. Another (probably) artifact is that mouse clicks are terribly calibrated within the Graphics window such that when you drag to choose boundaries, the dragging box is offset both in x and y directions by 500 pixels or so. Here's how the Graphics window looks like (see attached).

Warning: Identifier: root is not serializable

Tue, 13 Nov 2018 12:41:56 +0000

The below post is related to an archived discussion

[start here] Warning: Identifier: root is not serializable I have exactly the same problem. But I am running additional jave stuff. Anyone has an answer.

Regards