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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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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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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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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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Coaxial Probe in Concrete

March 19, 2017, 8:55 pm
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Hi,

I am very new to COMSOL I was wondering how you would model a coaxial probe in concrete sample and see the wave propagation through the concrete?

Thanks a lot!
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Implementing integral across time using analytic temperature-based function

March 19, 2017, 9:00 pm
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Hello,

I have defined a global analytic function f(T) which is dependent on temperature. I need to integrate this function across time for a cut point in the model. The bounds of the integral are temperature values (where the temperature is itself a function of time, evaluated at a single spatial point in the model). Is there any way to have Comsol evaluate this?

Thank you!
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How to insert hard differential equations (containing two variables) in COMSOL 5.2a

March 20, 2017, 12:42 am
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Hi Everyone,

I attempt to program new physics in my two-phase flow + phase field model. I search since several days how to inserts my partial equations in COMSOL 5.2a.
The concentrated form of my dimensionless equation is:

1- d(xi*F)/dt+Nabla(xi*F*u)=(1/Pe)*Nabla(xi*Nabla(F))-h*delta*J(F,f)
2- d(delta*F)/dt+Nabla(delta*F*u)=(1/pe)*Nabla(delta*Nabla(F))+h*J(F,f)
Where :
u is velocity so dependent variable of Laminar two phase flow
xi=1-c WITH c is an dependent variable of another physic (phase field)
delta=(3*sqrt(2)/a)*c^2*(1-c)^2
J(F,f)= Bi*(k*F*((1-l*c)/l)-f)
Bi is "0" when xi=1 and "1" when xi=0. Bi can take 0 and 1 only
k,h,pe,Pe and l are all constant.

when I try to do differentiation by part, I get:

1- xi*dF/dt + F*dxi/dt + F*u*Nabla(xi) + xi*Nabla(F*u) – (xi/Pe)*Nabla(Nabla F) - (1/Pe)*Nabla F * Nabla (xi) = – h*delta*J
2- delta*dF/dt + F*d(delta)/dt + F*u*Nabla(delta) + delta*Nabla(F*u) – (delta/pe)*Nabla(Nabla F) - (1/Pe)*Nabla F * Nabla(delta) = h*J

Dividing eq.1 by x1 and eq.2 by delta, I get:

1- dF/dt + Nabla(F*u) – (1/Pe)*Nabla(Nabla F) + F*a + beta* Nabla F = FRIGHT
where
a = (1/xi)*dxi/dt + (1/xi)*u*Nabla(xi)
beta = (1/xi)*(1/Pe)*Nabla xi
FRIGHT= – (1/xi)*h*delta*J

2- df/dt + Nabla(f*u) – (1/Pe)*Nabla(Nabla f) + f*b + gama* Nabla f = fRIGHT
where
b = (1/delta)*d(delta)/dt + (1/delta)*u*Nabla(delta)
gama = (1/delta)*(1/pe)*Nabla(delta)
fRIGHT= (1/delta)*h*J

Is it correct ?
how to translate in COMSOL 5.2 language ?
And finally, In what option, insert these equations which govern my additional physics ?

Thanks for your response.
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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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Loudspeaker Dodecahedron

March 20, 2017, 6:21 am
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Good night.
I want to get a directivity of dodecahedron loudspeaker with Comsol simulation. My simulation model is set up using a combination of the Magnetic Fields interface and the Acoustic-Structure Interaction multiphysics interface. And, I import file from Solidworks ( for geometry). For an information, dodecahedron loudspeaker is 12 driver ( loudspeaker) in the dodecahedron shape. When I meshing this geometry, I have an error "out of memory in mesh memory ". Maybe, anyone can help me to discuss or show me how to simulate it ?
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Inductances AC vs DC

March 20, 2017, 6:51 am
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Hello everybody!

I've discovered that coil with iron core has different inductance values depending on a study type.

Stationary study produces higher inductance value compared to frequency domain one. Field distribution is also different. DC has more homogeneous magnetic field within iron core while AC has all the field concentrated in a thin surface layer.

So now I have 2 questions:
1. Which of the two inductances is the correct one?
2. As far as I know, maximum achievable magnetic field in iron core lies around 2 T. In AC model I got magnetic flux density up to 5 T within iron core. Since inductance is derived from total magnetic energy and that energy is calculated by integrating all those flux density values, does it mean that I'm getting incorrect inductance values as well?
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Parameter settings

March 20, 2017, 7:51 am
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Hey !! How could i set a parameter which is increasing with an exponential step??
Thank you
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Acceleration missed in the transient modal analysis

March 20, 2017, 9:28 am
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Hi all,

I've got a little issue with comsol during the modellation of a relative simple problem.

I have a plate, impacted in the middle of its surface. I would like to make a simulation in two phases. The solid part of the plate, and the air around 20mm from the surface. In this way, I would like to simulate the acceleration of the plate, due to the impact, and the acoustic pressure in its prossimity.

What I particullary care is the damping of the material (5%), and the modal interaction due to materials, geometry and boundary conditions.

I tried the transient modal analysis, but for some reason that I miss, it gives me the displacemente and the velocity of the plate, but not the acceleration. Now, this is not a big issue, since I could derive the velocity plot in time to have the acceleration. The problem is about the acoustci pressure, that seems is not calculated as well as the acceleration.

I tried the only transient analysis too, but in this case the modal shapes neither the damping factor are considered. It returns acceleration and acoustic pressure, but they are strongly affected by the modal and damping errors.

Could someone help me and suggest the best way to simulate a problem relatively simple such this one?

Thank you very much in advance.
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Magnetic Fields-No Current, for Permanent Magnets

March 20, 2017, 9:35 am
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I am doing magnetic analysis for 16 magnets arranged in linear halbach configuration. i am having difficulty in understanding if COMSOL calculates the flux density by averaging all the flux from magnets separately?? or some other method. Kindly some one guide me.

Hassan
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Linearized Navier Stokes Model for Aeroacoustics Simulation

March 20, 2017, 10:08 am
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Hi all,

I'm trying to use the linearized NS to model the acoustics modes of a rectangular shape duct .

Could anyone help me on how to use it in COMSOL 5.2a?

I would really appreciate any kind of help

Best,
Mohammad Ghulam
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importing from solid works

March 20, 2017, 1:18 pm
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first of all hi ,

i am new to this so i could use all the help i could get .

i watched a tutorial of how to design a wind turbine to solidworks .

I try to import said geometry to comsol . The problem i face is that it is imported as one item thus , i cannot mess around afterwards with the materials etc.

I have thought of taking each part of the turbine and importing it piece by piece , but if you have a quicker solution , much appreciated
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