Quantcast
Channel: Solving, solving\ - Latest Discussions - COMSOL Forums
Viewing all 3988 articles
Browse latest View live
↧

calculate the electric field near a pylon

March 7, 2014, 1:45 am
$
0
0
Hi everyone,

I just started using COMSOL and I could use some help.

I would like to compute the electric field near a pylon caused by 6 conductors.
I set up the 6 conductors with a potential: u*sin(100*pi*t).
The pylon itself is ground.

A cylindrical geometry is placed over the whole pylon to define the air.

Now I would like to do a time dependent study. This works well until i set up the cylindrical geometrie as a infinite element. I tried a lot of iterative solver, but they all wont converge to one value.

can anyone help me to fix this?

thanks in advance.
↧
Search

Geometry Parametric sweep

July 11, 2013, 7:52 am
$
0
0
Hello,
I want to run a geometry parametric sweep.
Consider the following geometry sweep parameters:
H range(20[mm],10[mm],60[mm])
Z range(0[mm],10[mm],20[mm]+H)

The idea is that Z maximum value is against the height H of the object in the current nested iteration of Z against H.
In the first round (H=20) maximum Z will be 20+H=40. When first round of Z sweep finishes, H will become 30 and the maximum Z will be 50[mm].
This is not happening and ComSol is using the H global defined parameter.
Is it possible to force ComSol to use in the Z parameter sweep range the H value as calculated in the for the current parameter sweep step?

A simple code for that will be
for (H=1 to N)
for (Z= 1 to H)
mesh.....
next Z
next H

Thank you,
Dimitris
↧
↧

Quickly, please: can I set a time delay for a simulation start?

March 7, 2014, 1:50 pm
$
0
0
COMSOL'ers:

I know there is a way to set a timer up to 24 hours on a Batch Sweep; however, is there a way to do so for any other standard solving steps? A parametric sweep, for example? The functionality is obviously already built into COMSOL, so why wouldn't it be available to all solving methods?

I am trying to leave for the weekend, and I do not want to wait until my current sim is finished, and so I am looking for a quick answer! THANKS!!

v/r

Bryan
↧

Cantilever beam fracture

July 31, 2012, 12:38 pm
$
0
0
Hi Everybody

I have a question regarding analysis of deflection of the cantilever beam.
As it is clear, If I apply a small force on tip of the cantilever it will deflect. However in simulation I don't know how I can evaluate if the deflection (or applied force) is small enough to avoid fracture (breaking) of the beam. [beam dimensions are as follow: Length 500 to 100 um , width 30 to 50 um, thickness 0.7 um] and the force is in range of 100 pN
Can anybody give me some idea?


-I went through some mechanical books and they said the maximum stress that a material can tolerate before fracture is equal to yield stress (or fracture strength), but i don't know in my simulation I should compare which parameter with yield stress.
↧

How to put friction in non newtonian fluid?

March 10, 2014, 1:06 am
$
0
0
Hellow, I really wonder the method to use friction function in 3D.
But i couldn't find it... already i did the simulation of friction in 2D.
even if the modelings of 2D and 3D are same, results are different.
I really don't understand that... Why....
So i tried to set the wall was slip and give the equation of friction both 2D and 3D of modeling.
But only 3D has something wrong. Because the result of 3D was same with only slip state.
it doesn't make sense...

If you guys know some ways, let me know. and if you wonder the results of them, leave some
reply.

I really need your help.
↧
↧

Use a solution of a very similar problem as initial values...

December 11, 2013, 8:17 am
$
0
0
Dear all,

I am generating a phononic band diagram of a photonic crystal (mechanics-analogy to photonic bands...) by sweeping the bloch-floquet k vector from Matlab (i.e. a boundary condition - but in general, the same should hole for all small changes to a model).
So in principle, for each k vector, just the boundary conditions change a little, the rest stays the same.
Yet apparently (computation times!), each step costs as much time as the first one.
For direct solvers, I kind of understand this, but at least for iterative solvers, I would like to benefit from my knowledge of the previous solution.
I tried to enforce this with the ...refine.mph-file by setting an iterative solver on the same problem with the initial values being the solutions already, but still, it takes forever to converge.

So now my question: How can I make, for this and similar problems, use of the fact that I almost know the solution already? In principle it would be sufficient even if I could just follow inly one eigenfrequency by its way through k-space...
And is the comsol internal sweep doing something different from what I tried (I would prefer not to use it since steering from Matlab is more comfortable...)?

Obviously either my understanding of iterative solvers or my try to use them is quite wrong - but why exactly?

Thanks for any help and/or comments...

Wolfgang
↧

Hi, I wonder how to set the solvers.

March 14, 2014, 2:09 am
$
0
0
Hi, I got the mail box following
Error:
Failed to find a solution:
Maximum number of Newton iterations reached.
Returned solution has not converged.

So I wonder what the set of solver is suitable.

This is my setting.

GMRES
Incomplete LU 5E-4

Relative tolerance 1.0E-2
Maximum number of iterations 800

If you know the proper setting of the solver for computation,
Let me know, please.

Thanks
↧

TEHL-Simulation

March 15, 2014, 7:34 am
$
0
0
Dear Mr. Aksoy,

I saw your post on LiveLink to Matlab, where you ask for the mpheval-command and thought that you might be working also on EHL-Simulations like I do. I tried to set up two models: one for the pressure distribution and film thickness, and the other for solving the energy equations in order to obtain a temperature distribution. Where I struggle right now is the coupling of both models via MATLAB. Have you solved your problem in obtaining the computed solution by mpheval-command yet? How did you do it? I appreciate your help and am looking forward to hearing from you!

Best regards,
Enzo Maier
↧
Search

Error: 7161 The mass matrix is zero - resolve

March 12, 2013, 6:59 am
$
0
0
Respected sir/ma'am,

I am trying to simulate a Nano ElectroMechanical Switch(NEMS) using the following modules:a)solid, stress-strain, b) Moving Mesh, and c)Electrostatics.
When i run the solver, it shows an error message:'Error: 7161 The mass matrix is zero' along with a warning: 'Not all domains are meshed'.
The sizes are in nano domain. Model is attached for your kind reference.
For meshing i used Mapped Meshing to reduce number of elements.
I am using Version 3.5a on Pentium processor with 32 bit and 2 GB RAM.

Thank You in advance
↧
↧

comsol generates a reduced mesh when starting second step in conjugate heat transfer

March 16, 2014, 6:57 am
$
0
0
after building the corresponding model and its mesh which has pretty high resolution 1.5m elements i click on solve, however the solver fails stating that boundaries could not be respected, examining the model after that i realized that a new mesh with very low resolution was created and that that one was being used for the computation i didn't find a way to avoid that
has anyone got that problem too?
↧

To demonstrate a "sieve" at the particle tracing module

February 26, 2014, 7:14 pm
$
0
0
Hi all, now I'm trying to demonstrate a particle sieve using the particle tracing module.
I expected that the particles bigger than the pore size of the sieve could be filtered and stuck on the sieve surface.
But it seems that the particle tracing module cannot demonstrate such effect because every particle can pass through the pores even which are much smaller than those particles!

Do you think that I have to set up a sort of force equation or "if-condition" which can describe the sieve effect by the size difference??

Thanks!!

Dukwoo
↧

Checking continuity equation

March 17, 2014, 2:48 pm
$
0
0
Hello,

I'm currently modeling incompressible flow with the Navier-Stokes equations in a Y-shaped pipe with newtonian properties (a fluid similar to water). My problem emerges when I try to check the continuity equation -> div u = 0. I export the data for the first derivatives ( du/dx, dv/dy, and dw/dz) and for each node the sum should be near 0 but it gives a value of the 10^2 order.

Is there something failing with COMSOL? Or did I defined something wrong? Am I exporting the correct data?

Thank you!
↧

Set tolerance for continuity - help!

March 18, 2014, 1:48 pm
$
0
0
Hello,

I've written previously with no success. My model uses the Laminar Flow module to solve the Navier-Stokes equation. One of the equations is a constraint, the continuity equation that states that div(u) = 0. However, when I plot the divergence of the velocity field, not all values are zero which implies that the velocity field must be corrected. In the dependent variables of the model there are the corrected velocity field components but apparently it is not possible to export those, so there is my first problem. But even if I'm not able to export the corrected velocities, is it possible to set a tolerance for the divergence value as a constratint to the equations?

Thank you!
↧
↧

How to plot the S11 plot of the patch antenna

March 18, 2014, 7:26 pm
$
0
0
I want to know how to plot the S11 plot for the patch antenna
↧

Video plot

March 18, 2014, 7:28 pm
$
0
0
I have designed a patch antenna. I want to change the substrates permeability values from 1 to 100 in multiples of 10 and want to view the plot at once in the form of the video. Please help me, how can it be done?
↧
Search

Difficulty in simulating simple H-Cell

March 18, 2014, 8:03 pm
$
0
0
Dear All

I m new to comsol. I started to design a very simple H-cell as demonstrated in Video

www.comsol.com/video/video-239

But when I try to simulate i get this error:

Failed to find a solution.
Maximum number of Newton iterations reached.
Returned solution has not converged.
Can anyone help me in this regard..I did exactly the same way as demonstrated in video.Pls help

Regards
Yousuf
↧

Comsol convergence problem!!!

March 19, 2014, 2:00 am
$
0
0
Hi
I am trying a 1D flow module. I use: "coefficient Form PDE" but it gives me error "Nonlinear solver did not converge.
Time : 0.001
Last time step is not converged." during Time dependent solver.
In this model, my coeffients are very coupled.
Any idea why this is happening?
Thanks in advance
↧
↧

weak form PDE

March 19, 2014, 8:02 am
$
0
0
Can anyone help me solve a differential equation (solve for x) using time dependent weak form boundary PDE module. The equation is dx/dt = a(1-x)-b(x). I tried to write expressions x_test*(a*(1-x)-b*x) in weak form PDE and the expression x_test*x_time in weak contribution steps. I dont know if it is right or not. I also tried to change the expressions test(x)*(a*(1-x)-b*x) and test(x)*d(x,t) instead of above two. I have values for a and b. I appreciate your help.
↧

Solver start and end time

March 19, 2014, 11:46 am
$
0
0
Hello all,

I am trying to define the start and the end time of a time dependent simulation using a MATLAB function. This is necessary because the start and end time will be different for each simulation during a parametric sweep that I wish to do. I have tried to implement this, but it gives an error:
Failed to evaluate expression. Function: ... Property name: tlist.
I am using this function somewhere else in the model as well, where it is working fine. So the problem isn't that COMSOL can't find or use the function properly.
Is it even possible to actually using a function here, or do you think I am doing something wrong?


thank you,
Gert
↧

3D AC Coils with Moving Mesh

March 19, 2014, 3:32 pm
$
0
0
Hi guys,

I'm trying to model a pair of coils, one active with a varying AC current and a parallel passive coil that is suppose to act like a sensor. In this model I'm sending a metallic object through the centre of the two coil and then measuring the induced current on the passive coil.

At the moment I'm having some trouble simulating the study as it's taking 5+ hours to run and I'm not sure whether the model is behaving correctly. If someone could take a look at my model and let me know if the following is correctly implemented, or if there is an easier alternative:

The AC input
The external current density, I want to apply 30A so the equation written in the parameters is I/A where is the area of the coil
The Moving Mesh physics, where the air domain and metallic object are included, with the metallic object set to have a prescribed deformation

I'm also unsure whether to apply a copper material to the coils, as I've seen in the Helmholtz tutorial, it states that the external current defines the coil, however I have one coil without anything current applied. When I do run the study without material I get the correct magnetic flux density, and when I apply copper the values are incorrect.

The study has to be time dependent as I have to observe the change in induced current in the passive coil as the object passes through the magnetic field. Also which is the best way to observe this change in induced current? using a domain point probe or evaluating a surface or volume integral in the derived values?

Thanks,
--
Ryan Mulheron
↧
Viewing all 3988 articles
Browse latest View live
Search
<script src="https://jsc.adskeeper.com/r/s/rssing.com.1596347.js" async> </script>