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Surface Plot results not correcly moving

April 8, 2013, 11:00 pm
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Hello,

i have a "moving mesh" problem coupled with magnetic fields. I want to let the domain of a magnet move by a prescribed deformation in the ALE-Interface. It's a sinusoidal movement of a mass-spring-damper-system which i calculate by a global ODE and is used for the pescribed deformation.
If i couple the movement of the magnet with the magnetic field interface (mf) and do a time dependent study the magnet is moving by the correct displacement i calculate by the ODE but the result of the magnetic flux density is not moving or only the domain of the magnet is moving while using the spatial frame. I need the whole moving of the magnetic flux desinty in order to compute the inducted voltage of a coil.

Any advice to my problem? Thanks for your suggestions.




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Extrap

April 9, 2013, 12:23 am
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Hello Comsol gurus,

I am doing a CFD simulation in which I need to use the solution of another CFD simulation. I need to take a "slice" of the solution and use it in another geometry. As I understand, there are two ways, one is to import the data and use it in another file and the other way is to couple two models in the same file.

I have tried the second way with satisfactory results but I want to try the other one. I exported the data as a spreadsheet in a .txt file and I used an interpolation function in the new file. I inserted the interpolation function at the inlet of my geometry (in the laminar flow moduel settings: inlet) and tried to solve.

I have an error called "Extrap not supported. Error in multiphysics compilation". So far I have not found any entry or thread about this error. Either the solution is too simple or this error is not so common, I asume is the first one. What can I do? I am sure I missing something but I can't find it

Regards and thank you in advance

Miguel
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Animation depending on distance

April 9, 2013, 12:46 am
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Hello dear Comsol gurus,

I have made a CFD simulation (stationary) which is based on the model library example of the static mixer. I have also generated the slices and surfaces to see how my fluids are being mixed (using concentration results) but I would like to make an animation with them.

Is there a way to make an animation using the slices (or surfaces)? This animation then would depend on the distance (on x for example) and not on time.

Thank you in advance

Best regards

Miguel



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Finding the location of the maximum of a variable

February 21, 2011, 1:17 am
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Dear Comsol Community,

I am looking for a way to find the location of the maximum of a variable. Getting the maximum value is easy, but so far I have not been able to get the coordinates of the maximum, preferably without using Matlab. Does anyone know how to do this?

Best regards!

Christian

Edit: Removed typo in title
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Asynchronous Machine time dependent startup, singularity error

July 21, 2011, 9:00 am
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Hello,

I am trying to simulate a ASM in the rotating machines physics, time dependent.
The Stator slots are coupled to the electrical circuit physics for a Voltage excitation
The rotor slots are also coupled there to define the short circuit resistants.
I am using the ODE Interface for a rotation velocity equation.

When simulating for 20ms, with a timestep of 1ms(or less), everything is fine (rotor slowly starts rotating).
But when I want to calculate for a longer time, the computation stops somewhen in the middle, saying something like:

"Repeated error test failures. May have reached a singularity.
Last time step is not converged."

I choose the mesh as extremely fine and tried a step size of 55us.
As "Maximum Step" and "Initial Step" I'm using the same value as for "Step Size".
But it does not help...

Does anybody have any advice?

Thanks in advance



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Geometric Nonlinearity problem

February 2, 2012, 10:49 am
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I have an odd problem. I am trying to recreate the Large Deformation Beam model (www.comsol.com/showroom/documentation/model/204/) before I start my own project to investigate buckling. I was following along with the model, but when I go to Study 1 > Step 1: Stationary and open Study Settings, I do not see any buttons that say "Include Geometric Nonlinearity". Indeed, I do not see any buttons at all.

When I download the support file for the Large Deformation Beam model, I do see this button.

However, if I delete the stationary solver and add a new one, I do not see the button any more.

It seems like I must be doing something dumb here, but I can't seem to figure out what. Any help would be appreciated.

Thanks,
-jfb
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materials of a surface mesh element

February 6, 2012, 9:05 am
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Hi everyone ,
I’m looking for a possibility to distinguish the different materials that belong to a single surface-mash-element (for example: a triangle) in matlab? For better understanding - my problem in a second way. Starting from a model containing a single meshed surface. Each mesh-element is now between two materials. So how do I get knowledge about the two materials/groups/… the element is between?
Thanks for help!
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Stop condition in Electromechanics(emi)

September 12, 2012, 11:42 pm
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I would like to implement a stop condition similar to what is described for a moving mesh problem.

The parametric study would stop when the mesh quality is lower than a certain value, inorder to prevent an inverted mesh.

For a moving mesh problem you add a stop condition with the following term:
mod1.ale.relVolMin-0.01

But what term should I use for an electromechanics simulation?
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Maxwell Stress Tensor

April 2, 2013, 10:30 pm
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Hello all,

I'm new to Comsol and Im having a little difficulty getting my head around how the Maxwell Stress Tensor operates. I understand its operation when applied to parallel wires (Like in the example given in Comsol) but when I try to use it for my own model I don't understand it's behaviour.

I'm currently using Comsol to look at the scattering of electromagnetic waves from a dielectric sphere. I also want to look at the forces on the sphere.

All I've tried to do is to add a line integration, with the surface of the sphere chosen as the line, and then there is an option to get the upward and downward Maxwell Stress Tensor.

This gives me a complex result which doesn't make sense to me. Perhaps my understanding of the problem isn't complete? Is there a better way to work out the force on the particle?

Any help would be greatly appreciated!

Thanks,
Mark.

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Problem with Mesh when sweeping a geometric parameter

April 9, 2013, 2:54 pm
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I am making a model of an optical device that is composed of a metal grating, with an air gap below, a dielectric layer below that and a metal ground plane below. All of the geometry is defined with parameters. I am using a frequency domain study.

I have been able to sweep the wavelength with a parametric sweep to get a nice spectrum for the device. I now want to sweep the height of the air gap and the wavelength at the same time by adding it to the same parametric sweep as the wavelength. When I try to this, I get the error "You must specify the destination."

I've traced this back to the mesh node. I've used the Copy Edge feature to match the mesh at the edge of my model where I have periodic boundary conditions. Apparently, trying to sweep the geometry in this way depopulates the selections used in Copy Edge. To repair the model, I then have to revert to the last saved state. Whenever I change the air gap manually, my geometry and my mesh both update correctly. Is there a way I can make this work properly using a parameter sweep?

Thank,

Will Streyer
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advice for simulation set up or suitable tutorial (3D stress distribution with multiple materials in contact)

April 9, 2013, 9:04 pm
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Hi All,

I am trying to help my fellow Orthodontics to showcase COMSOL's ability to simulate one of his problem. But I am struck and getting inconsistent results. The simulation is very basic and therefore experts here are requested to advice or direct a suitable tutorial for us.

The problem is teeth embedded in bone. when bone is subjected to a force, we want to see the stress distribution that is all. My problem is inexperience in 3D and structural modelling handing multi materials in contact. The 2D cross sectional picture is attached. Some may kindly enlighten us to proceed further?

Thanks in advance
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FSI - vibration study of a cylinder in a fluid flow

April 9, 2013, 10:39 pm
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Hello all,

I am new to Comsol. I am trying to study flow induced vibration of a cylinder fixed at one end and free at other. The cylinder is placed vertically against the flow. Is it possible to find the amplitude and frequency of vibration in the cylinder at the tip.

Please recommend me tutorials similar to this problem
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Cooling of a metal box

April 9, 2013, 11:14 pm
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Hallo to everybody!

I'm trying to realize the simulation of a metal box (fillled with air and including an heat source, and surrounded laterally by other boxes that I consider through the simmetry/boundary condition) that is cooled by a tube of water in contact with the box, but i have problem to set good boundary condition.
If I set the inlet temperature of the tube, and set external convection for the other surfaces of the box, i find that everywhere the temperture is close to the one of the inlet surface of the tube... the temperature boundary condition seem 'stronger' than any other boundary condition.
I find more realistic results if I set a different temperature (taken from experimental results) on one of the surfaces of the box, but I am not sure if that is correct, or I am just adding a new heat source that shouldn't be present.

do you have any suggestion?
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Model couplings: Integration vs. Summation over nodes

April 9, 2013, 11:38 pm
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Hello,

I am working with two modules Structural Mechanics and general form PDE as coupled. I need a model coupling to define an integration. When I choose "Summation over nodes", my model works fine, converges and gives logical results except the fact that it calculates my volume incorrectly, which I think is related to the mesh. When I select "Integration", I see that my model calculates my volume correctly as the initial value; however, my model hits the maximum memory and gives "out of memory" error. I use this integration operator inside the PDE and there are terms like Elastic modulus, strain energy and DiracDelta function inside the operator.

Could any body have a suggestion for me?

Thank you in advance.
Onur
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Buckling Amplitude

April 9, 2013, 11:41 pm
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Hello, everyone

I investigate a buckling of compressed plate and have a trouble. I can't find an amplitude of buckling for different pressure. Comsol doesn't react on a changes of compressive force (buckling amplitude is constant for any pressure).

Thanks you for your time.
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Parallel plate model with magnetorheological fluid under magnetic field

April 9, 2013, 11:43 pm
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Hi,

I am trying to model the flow fields of magnetorheological fluid between non-magnetic parallel plate and permanent magnets under magnetic field produced by permanent magnets in in COMSOL3.5a.

There are two permanent magnets and three non-magnetic parallel plates in the model. The middle plate can move in the x direction at a speed of 0.025m/s. The gaps between two permanent magnets and the middle plate are filled with magnetorheological fluid.

There are adhesive forces between the magnetorheological fluid and the middle plate, so magnetorheological fluid can moves with the middle plate. The magnetostatics, Moving Mesh (ALE) and Non-Newtonian Flow modules have been chosen in my model. I have got the magnetostatic field simulation results which can be used as the initial values to deal with the flow fields.

But I do not know how to deal with the flow fields simulation due to the adhesive forces.

Could anyone give me any hint about this, it would be highly appreciated.

Regards,

Hongliang
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meshvol

April 10, 2013, 12:31 am
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Hello,

I'm looking to extract the area/volume of each mesh element of my model. I then discovered the quantity meshvol. However I'm not exactly sure what this gives me: using meshvol I get a scalar value for each node; what does this value represent actually?

Thanks.
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extrude from 2d to 3d

April 10, 2013, 1:27 am
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Hi,
i have successfully extrude from 2d geometry to 3d but how to add the thickness/depth on z -plane as right now the geometry drawn in x-y plane .
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Is there a way to do a temperature dependent heat source in Conjugated Heat Transfer?

April 10, 2013, 1:42 am
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Hi

I'm working in the conjugated heat transfer physics and I'm hoping/wondering if there is a way to make the heat source temperature dependent.

I have a cable that is covered with different materials at different areas so the temperature in the copper wire fluctuates. Since the heat source is copper where the resistivity changes with the temperature and thus gives an uneven load across the length of the cable. I'm thinking that the option "general source" doesn't account for thìs?

I might be working in the wrong physics, but the thing is, I'm interested in is to improve the cooling of the cable. So I thought this would be the correct physics.

Any help would be much appreciated..


And by the way thanks for a brilliant forum.

Rógvi Østerø
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Poisson-continuity coupled equation

February 19, 2011, 11:50 pm
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Hello,
I try to model the corona discharge in wire-cylinder geometry governed by the equations:

nabla (V) =- rho/epsilon0 (Poisson equation) and

grad (rho) * grad (V) = rho ^ 2/epsilon0 (equation of current continuity)

with boundary conditions:
V_w = V0 (on the wire)
V_cyl = 0 (on the cylinder)

As rho is unknown, I should compile until the electric field on the wire is equal to a given value Es.

knowing that I can give an initial estimate for rho on the wire --> rho_w.

My problem is I dont know how to solve these two coupled equations.
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