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Using simulated potential to simulate magnetic field.

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I have a simple 5 domain model, composed of roughly concentric spheres. I am modeling a transmembrane potential on the 3rd domain using the General Form PDE physics. This part is working correctly. I am then trying to use that potential to compute the magnetic and electric fields at the inner boundary of the outermost domain.

This was implemented pretty simply in COMSOL 3.5, using Conductive Media DC and QuasiStatics to find the electric and magnetic fields sequentially. The only inputs were the conductivities and the external current density from the PDE simulation. I'm not having any luck reimplementing it in 4.3.

With COMSOL 4.3, I'm using the Magnetic and Electric Fields physics. The transmembrane potential is used in the MEF physics in the expression for the external current density on the 3rd domain. I have a study with two steps - a time-dependent and a stationary step. The PDE physics are active in the first, the MEF physics in the second. For the stationary step, I tell it to use all the solutions from the time-dependent step for the variables not solved for.

My most recent error message is:
Failed to find a solution.
Divergence of the linear iterations.
Returned solution is not converged.

When I look at the convergence plot, the error steadily decreases until it hits a floor, and then it stays constant until COMSOL gives up after 10000 iterations.

Any suggestions on what's causing this?

(As a side note, these ask for permittivities and permeabilities that I didn't need before - why? Is there a way around this?)

about solving

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thank a lot for my last question the answered..
and now i will ask again about solving...
there are many menu in solving.. and what the meaning about in submenu 'solve parameter'
thare are general-stationary-......-advanced
in general there are menu linear system solver that it will also include many sub-menus i still not understand about submenus of that.. can help me to explain about that?
as well as submenu advanced..

Drift-diffusion solution wihtout using Plasma module

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I want to use comsol to solve drift-diffusion and Poisson equation in a coupled manner for a wire that has variable resistance (or charge density) across it. Charge density at each location depends on the potential that is present at that point. I need the solution in a 2D-axisymetric geometry. Currently, I can do the Poisson part easily using the comsol 4.3a that we have in our lab. However, our version does not have the Plasma module that I need for solving Drift-Diffusion.

In such case, please suggest me alternate ways of solving drift-diffusion without using the plasma module.

Coupled PDEs, Last time step is not converged

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Hi,
I am new to COMSOL, and what I encountered is about coupled PDEs. I have two coupled PDEs in one physics model in general form. One is about heat transfer (T), the other is an ODE used for the source term of the heat transfer (T). The ODE looks like du/dt=f(u,T), namely du/dt is a function of u and T.

When I ignore the T, like du/dt=f(u), COMSOL works. But it doesn't work when I consider the T. As follows.

Repeated error test failures. May have reached a singularity.
Time : 0.334945980028302
Last time step is not converged.

Thanks,
Du

Coupling Poisson and Transport

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Hi,

I am using Comsol 4.3a and want to couple Poisson and transport for determining the flow of charge (or electrical current) within an wire due to application of voltage across it. Now, the output variable for Poisson is "u", while the input variable for "Transport using diluted species" is "V".

How can I couple these two modules (i.e., Poisson and Transport using diluted species) by feeding output of Poisson "u" into the input of transport as "V", because "u" is used in the transport equation for defining a different quantity "velocity field". Can I redefine the variables for either Poisson or Transport module?

- Ahmad

Parametric sweep : Can I bypass (ignore)the error occuring for a particular parameter?

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In coupled MEMS electrostatic study, I defined two parameters: Vdc and InitialGap.

These two parameters were used for parametric sweep on the electromechanics module of Comsol 4.3.

Now Comsol runs my model for these parameters one by one , as in nested loop. Total number of parameter combination equals (number of Vdc values)x(number of InitialGap values).

Whenever instability occurs, Comsol cannot converge and returns and error.This is fine. But the error which comes terminates the computational progress once the error occurs, further combinations of the parameters are not evaluated, because the error was returned.

Is there any way to sort out this because the alternative to this will be running seperate Comsol simulations in parallel for individual InitialGap values which will be tiresome. Is there an option which bypasses(or ignores) errors during parametric sweep, so that rest of the parameter combinations are evaluated?

Speed up a Computational Problem in COMSOL involving parametric sweep

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Consider the general parametric sweep case:
When I set up a non-linear FEM problem, it takes considerably more time than a Linear FEM case. The reason for this extra time taken is the extra effort by COMSOL which involves :
1. COMSOL takes the step as specified by the user in the parametric sweep section and if cannot converge, takes smaller steps to go as far as possible. SO many step sizes are tried by COMSOL.
2. COMSOL tries different solver strategies and tries to converge for each step.

For my problem, probably the last of 1 and 2 efforts are successful which involves a total of 4 hours to solve. I can see in the progress section that the parametric sweep goes very fast from 1V to 26V and then it takes at least 3 hours near 26V. I have specified parametric sweeping limits from 1V to 50V in steps of 1V. It is fantastic that the error comes at 26V stating inverted mesh elements (owing to system instabilities) retaining the previous solutions of 1V to 26V.

Question 1: Is there a way to find out which solver strategy was successful in the first run and in subsequent runs force the same strategy so that the simulation is sped up in subsequent runs?
Question 2: Can the 3 hours be saved in which nothing useful was done except returning the error, provided that I dont know that the system instability occurs near 26V at the beginning of running the simulation?

error test failures

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hi
i use ccp module for simulation,my time range is range(0,5e-5,0.001) but when i compute model times go 7.579247e-019 to this and report this error
Repeated error test failures. May have reached a singularity.
Time : 7.579247088737066e-019
Last time step is not converged.

how can i solve it?
thanks

Gaussian Distribution of Particle Size

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Hi folks,

does anyone know if it's possible to use a Gaussian Distribution of Particle Size function for the particle diameter in the Mixture Model interface? If so, can you provide an example?

Best Regards,

Rui

Absolute tolerance convergence criteria for flow simulations.

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Hey.

Normally convergence criteria are divided into a relative and an absolute.
Where can I find and set the absolute tolerance for my transient flow simulation.

Thank you for your time

Fluid structure interaction

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Hi all! I have some problems simulating a "Fluid structure interaction". I start from this model www.comsol.com/showroom/documentation/model/361/ . I have tosimulate the mitral valve of te heart so l have changed the structure of internal rectangle. Then l define the boundary condition as in the reference model but Comsol 4.2 return this error:

The following feature has encounteres a problem:
-Feature:Time Dependent Solver 1(sol1/t1)
-Error: Nonlinear solver did not converge.

I already tried to use the smallest mash but i receive the same error

Any ideas?
Thanks

Convergence problem with Comsol 4.3b

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Hi Everyone

When I run the model in the 4.3a, it can work very well. The convergence firstly is about 1e4 to 1e5. When the comsol software is updated from 4.3a to 4.3b, the convergence becomes 8e8 and cannot work. Does anybody have the same problem? or Does anyone have the idea how to deal with it?

Best wish
Di

singularity. error

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Hello,
Does anyboday know why I encounter the below error message in Comsol 3.5a?


Error:
Time 7.86913096623935e-007:
Repeated error test failures. May have reached a
Last time step is not converged.


Thanks.

singularity. error

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Hello,
Does anyboday know why I encounter the below error message in Comsol 3.5a?


Error:
Time 7.86913096623935e-007:
Repeated error test failures. May have reached a
Last time step is not converged.


Thanks.

COMSOL Error for Initial Values(RF Module)

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I am defining a model with different concentrations of oil and water and trying to measure the heat distribution by using the microwaves. But I obtained the error mentioning Initial values:

THE FOLLOWING FEATURE HAS ENCOUNTERED A PROBLEM
-FEATURE:TIME DEPENDENT SOLVER
-ERROR:FAILED TO FIND CONSISTENT INITIAL VALUES

Failed to find consistent initial values.
Undefined value found.
NaN or Inf found when solving linear system using SOR.

Although the initial values defined are by default and I did not change any thing.Please see the attached file.

Can anybody suggest me some solution of these problems?

Thanks in advance.

Java Runtime Environment error

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Getting following error,

A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x0000003da3efbc6c, pid=6909, tid=46912497239488
#
# JRE version: 6.0_20-b02
# Java VM: Java HotSpot(TM) 64-Bit Server VM (16.3-b01 mixed mode linux-amd64 )
# Problematic frame:
# C [libgtk-x11-2.0.so.0+0xfbc6c] gtk_icon_set_render_icon+0x58c

Does anyone know how to resolve it...

Regards

Fluid structure interaction

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Hi all! I have some problems simulating a "Fluid structure interaction". I start from this model www.comsol.com/showroom/documentation/model/361/ . I have tosimulate the mitral valve of te heart so l have changed the structure of internal rectangle. Then l define the boundary condition as in the reference model but Comsol 4.2 return this error:

The following feature has encounteres a problem:
-Feature:Time Dependent Solver 1(sol1/t1)
-Error: Nonlinear solver did not converge.

I already tried to use the smallest mash but i receive the same error

Any ideas?
Thanks

magnetic field gradient in 3D return zero!

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Hi everybody

If anybody knows that why the gradient of magnetic field in 3D models is always zero? I checked the different methods. for example I wrote d(Bx,x) or different component of B and H. Even d(d(Ax,x),x) is always zero! I am using the quadratic discretization. It is OK when I simulating in 2D or 2D axisymmetric, However the similar geometry in 3D give the zero for gradient of magnetic field.

could somebody help me?

Convergence problem with Comsol 4.3b

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Hi Everyone

When I run the model in the 4.3a, it can work very well. The convergence firstly is about 1e4 to 1e5. When the comsol software is updated from 4.3a to 4.3b, the convergence becomes 8e8 and cannot work. Does anybody have the same problem? or Does anyone have the idea how to deal with it?

Best wish
Di

Unidirectional coupling of a time dependent study to a stationary study

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Hello,

I am using structural mechanics module and a stationary study to calculate stresses and strains in a simple 2D axi-symmetrical model. The model has a thermal expansion node.

I have another study step, which is a time-dependent one. This step has a heat transfer module and I am calculating the temperature distribution in the domains for the times from 0 to 24 hours.

I am trying to couple the temperatures calculated in the time-dependent study to the thermal expansion node in my stationary analysis. I can do this for only a certain time, using the 'Values of variables not solved for' option under the 'Values of dependent variables' section in the Study settings.

Instead, I want to be able to use a continuation parameter in the stationary analysis and in each sweep, I would like to get the temperatures at a certain time, say starting from 0 to 1h, 2h... (25 steps).

I hope I could state the problem clearly. Is this possible? I'd appreciate it if anyone could guide me.

Thanks,
--
Tolga
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