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Syntax error

March 17, 2017, 9:28 am
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Hi
I get following error in static study and also in a dynamic study. Any suggesstion about the solution would be appreciated.

Syntax error in expression.
- Expression: comp1.pdom1()
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Normal current into cross section of 2D geometry

December 7, 2016, 3:06 am
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Hi,

I'm doing a thermal simulation of electric power cables with the "Joule Heating Physics" module.
Till now I'm assuming a constant heat source to model the conduction losses.
I'm trying to use the "electric currents" node for defining a current that generates heat instead of
using a constant heat source till now. Maybe there is some way to insert a formula for conduction losses dependent on the flowing current and temperature?

I want to define a normal current into the cross section of the conductor.
So I'm working at the "x-y-plane" (the cross section) and I want to let the current flow through that cross section in z direction.

If anybody knows a way to do that please let me know.

Thanks !

Jan
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multiple eigenvalue study steps

March 17, 2017, 10:40 am
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I am running amodel in which I have three study steps. The first step is a stationary step which solves for a poptential profile to be used in the eigenvalue step. Thesecond step is an eigenvalue step should take the potential from the stationary step and compute eigenvalues. The third step is a different eigenvalue step which should again tae he potentials from the first step and compute a new set of eigenvlues.

The problem is that the output only has a single variable named "lambda" which lumps all the eigenvalues for both steps into one array. I would like for the solver to solve one eigenvalue step with eigenvalues named lamda1 and the second with eigenvalues named lambda2. Is this possible?
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A Swept Quad Mesh Within Free Tet - Quality Concerns

March 17, 2017, 10:00 pm
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Hi everyone,

I'm looking for some advice on a meshing problem that I have - I have a heat load imposed on a 3D rectangular beam embedded within a larger beam of the same material; the two beams form a union. The area where the heat load is applied is very finely meshed with a mapped distribution so that I can control the exact number of elements in my area of interest.

This is great but my problem is that in order to cut down on computation time/memory cost - I am converting the boundaries of this swept block (or another swept block around it) to tri's and then putting in free tetrahedral mesh for the large remainder of the geometry. This has the unfortunate effect of creating a region of poor mesh element quality around the swept block where I need my mesh to be the most accurate.

I have attached an image of what the mesh element quality looks like in one iteration of this model. It seems that every time I try a slightly different meshing scheme - my results are significantly different and I have tried many variations. If anyone can suggest a better alternative to my current meshing scheme, or point me in the right direction of increasing the mesh quality, I would greatly appreciate it.

Finally, my heat loads are asymmetric and so unfortunately I cannot exploit any symmetry to cut down on the computational cost.
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Simple parametric sweep

March 18, 2017, 2:28 am
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Hello! How to set parametric calculation, so that on the 1D graph I can imagine the sound pressure from the parameter value?
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Solving Poisson's equation in Electrostatics module with potential-dependent charge

March 18, 2017, 3:24 am
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Hi, I would like to approximate a 2D electron gas by solving Poisson's equation as shown in the attachment. Basically, the charge everywhere is initially zero, unless somewhere the potential becomes larger than E_0. A charge then appears which we derive from the Thomas-Fermi approximation and this has to be plugged back in to find a self-consistent solution.

Could anyone give me a pointer on how to achieve this? Thanks!
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The compression simulation, and the material "exploded" during simulation, why?

March 18, 2017, 8:05 am
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Hello everyone,
I am just using Comsol to simulate the process of compressing PMMA with the indented shape.
I followed the similar example from the Comsol examples, and set the PMMA as a viscoelastic material instead of hyperelastic material. But during the simulation process, the material began to 'explode' instead of being compressed.
The simulation is stationary, parametric sweep in time to simulate the compressing process on different moments.
So I am wondering what is the reason for this failure.
Is it because of the material setting? Boundary setting? Solver setting? Or others? Thanks a lot!
I posted the compressing processes on different time:
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Error using Polarization in Transient EM wave problems

March 18, 2017, 8:06 am
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Hello,

I cannot understand the reason for the following error.
The following simple 2D transient EM problem (temw) is solved with COMSOL 4.3:
a pulse enters a rectangular domain from left (boundary condition = scattering, plane wave) and proceeds towards right (BC = scattering).
Top and bottom of the rectangle are PEC.
If I use Relative Permittivity = 1 in the Electric Displacement Field of the Wave Equation box, the solution is correct.
If I use Remanent Electric Displacement = 0, the solution is (correctly) identical.
If I use Polarization = 0, the solution should be the same (in my opinion) but instead I get an error connected to the variable temw.epsilonrxx (Failed to evaluate variable Jacobian).

Any idea of the reason for that behavior?

Thanks,
Roberto
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Transmission line and scattering parameters

March 18, 2017, 8:10 am
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Hello. I want to model a transmission line and put some solutions above and compute the s-parameter variations.
Can anybody help me if there are any PDF and applications that are useful?

Thanks,
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Urgent: oil displacement by surfactant solution, problem of solver-PDEs-Failed to find solution

March 18, 2017, 8:47 am
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Hi everyone
Help me please, I am at the end of the abyss. I work on: influence of the addition of surfactant on the displacement of the oil by the water-view of wettability changind and interface tracking. I made the simple model on comsol with functions, variables and equations all well defined.
When I run the simulation, it appears: "Failed to find a solution. Maximum number of Newton iterations reached. Returned solution is not converged."
The problem is probably in PDEs because the coefficients are also dependent on the main variables so incorrect Jacobian matrix I think.
To explain a little bit, I have 4 system of general equation governing:
1 - Naviers stokes equations to describe the flow in my channel (I choose Laminar flow-two phase flow)
     Variable dependent is U (velocity)
2- Cahn hilliard equation to track interface for two immiscible fluid (choose phase field)
     variable dependent is phipf
3- surfactant transport into water phase during injection (I choose coefficient form PDEs)
     Here, main variable is F interface force or volume force related to equation of naviers stockes, but X is also function of phipf which is dependant in time and space
4- surfactant concentration evolution (I choose also coefficient form PDEs)
    In the same case, main variable is f which traduced surfactant concentration, but we have delta which is   function of "phipf".
Please do something for me (solve my problem please!!! I have to present soon). I am enclosing my model and The governing equations are also attached.
You can see also my model and governing equation on the link below.

filex.univ-lorraine.fr/get?k=67Gu6XQy1fFLl1BOBXR

Thanks in advance, have a good week end
Marc Felix
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Subdomain Settings - Equation system

September 1, 2010, 1:44 am
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When I double Telegraph Equation Model Gallery #28 for voltage and for current,
I notice TWO ways to input Coefficients of the equations that do not necessarily match but may be contradictory:

1 F8 Via Physics - Subdomain settings - Coefficients
2 CTRL+F8 Via Physics - Equation system - Subdomain settings

What is the right or prevalent place?
What is the risk of contradictions between both Coefficient sets?
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Recoverable error in residual, but solver could not recover.

October 17, 2011, 7:20 pm
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Recoverable error in residual, but solver could not recover.

What is the meaning of this error ?
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Setting exhaust fan for exhaust air

June 26, 2013, 11:43 pm
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Can I set the exhaust fan with constant velocity to exhaust air in laminar flow module?
It is just set up the outlet with velocity boundary condition?
Is this boundary setting will let the air go out like a exhaust fan, and let the air has a air exchange process?
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How to transform Pressure boundary condition to No Flow condition during simulation?

March 18, 2017, 12:32 pm
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Dear all

I want to transform Pressure boundary condition to No Flow condition for a porous media during simulation. How can I achieve that? Thank you.
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Double Gate MOSFET

September 7, 2011, 9:09 pm
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hello,

Mr. gidon designed a double gate mosfet and simulated it using comsol and had plotted the charge carrier density succesfully.
I wanted to know whether the model file i.e is .mph file can be accesed beacuse i wanted to repeat his work in a 3-d model with nanodimensions.

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How to import concentration text data in comsol and run with it?

June 26, 2015, 4:21 pm
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Hi,

I am using COMSOL to run a chemical reaction for more than 80days whose data is pretty big and alway run out of memory.

So I want to run it 10 days by 10 days seperately. In this way, I plan to export the concentration data every time, then import the concentration file to a new comsol file and run with the distribution of concentration as the initial point.

How could I achive that?

Thanks!!!!!!!!!
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Problem with laminar fluid

March 19, 2017, 5:37 pm
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Hi, i doing a work, that a need to build a sistem to cooler down. So i am using the model in fluid and termal. The problem is when i try to creaty a problem in 2D, I have no trouble, but when I try to do the same in 3D, appear somes trouble, about the fluid part.
Some one can help me to understante how to deal with fluid laminar flow in 3D, in 5,1 version?
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Out of memory during out-of-core LU factorization

March 19, 2017, 5:42 pm
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Hi

I have a CFD model with 1056,2892 degrees of freedom and a server with 128GB memory. I assume this memory size is enough for computing the matrix I have now. But I keep getting a error:

Failed to find a solution.
Segregated Step 1
Out of memory during out-of-core LU factorization.
In Segregated Step 1:
Returned solution is not converged.

Even after I checked "out-of-core", it still returns me this error.

Any one has some advice for this please?

Thank you so much!


Best,
Chang
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how to calculate curvature in 2D solid mechanics?

March 19, 2017, 8:01 pm
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Hi, I use 2D solid mechanics model
I want to know how to calculate the curvature of line in comsol.
In the result, there are variable curv_spatial, but i don't know the equation of the predefined variable.
please help me.
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Laminar Two phase flow:Interface height

March 19, 2017, 8:45 pm
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I want to add a volume force in the Laminar two phase flow, phase field/level set module which is a function of the height of the interface of the two phase at a every time step and coordinate. How do I add this force as an extra volume force?
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