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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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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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COMSOL 5.2 gets stuck after some time

March 9, 2016, 8:35 pm
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From almost two weeks I am facing this problem that whenever I run a simulation that requires long processing time, I find that the program stops responding. I just get a "waiting" cursor and a (Not Responding) message in the title bar.

I thought it might be due to the latest update for COMSOL 5.2 so I uninstalled the COMSOL program and re-installed v5.2 without the update. But, still it gave me the same problem. I also tried installing the update for it, and still I have the same issue.

I am running the program on Windows 10 Pro 64-bit with 32 GB RAM and i7-4790 processor with a 4GB NVidia GeForce GT730 graphics card.

It used to run fine before but now its frustrating me because its impossible for me to run anything. I waste hours and end up with nothing because the program just hangs up.
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extracting results from COMSOL using livelink for matlab

March 21, 2017, 12:23 am
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Hi everyone~
It is trying to do shape optimization involving stationary analysis. The code of optimization method was written by Matlab, and it needs to receive the simulation results from the COMSOL.
For example, in the case study of "Multistudy optimization of bracket", I want to extract the max stress value from the COMSOL using matlab, however I found the result was wrong. Does anyone know why?
Many thanks!


Matlab code :

model = mphload('multistudy_bracket_optimization');%load the model

x=[11.8 2.7 9.0 22.3 9.5 20];% parameters

model.param.set('rC', x(1,1), 'Radius of central hole');
model.param.set('zCo', x(1,2), 'Distance from bend to bottom of central hole');
model.param.set('rO', x(1,3), 'Radius of outer holes');
model.param.set('zOo', x(1,4), 'Distance from bend to bottom of outer hole');
model.param.set('yOo', x(1,5), 'Distance from edge to outer hole');
model.param.set('wInd', x(1,6), 'Width of indentation');
model.hist.disable;

model.sol('sol2').runAll;
Max_Stress = mphglobal(model,{'maxop1(solid.mises)'}); % get the max stress value

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Use of coefficient form PDE with global equation (simple ODE)

March 21, 2017, 3:54 am
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Dear Sir or Madam,
I am trying to solve a coefficient form PDE "dC/dt+ u.dC/dz =D 1/r.d/dt (1/r.(dC/dr)" with a global ODE equation "dCt/dt=constant*(C(t,L) - Ct)" together. I am using 4.1 version so I know that I can not use C(t,L) with ODE so I replaced it with aveop1(C) which is the average operator for C at the location of L. But I am getting a zero answer across the geometry. Could you please someone help me?



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How to plot vorticity

March 21, 2017, 4:12 am
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I can visualize only pressure and velocity.

Do you have any ideas about how to get the vorticity for a 3D problem?
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Time Dependent Study for Loudspeaker Systems

March 21, 2017, 6:27 am
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Hi all,

I am interested in performing a Time Dependent study for loudspeaker systems. As a starting point here, I work with the tutorial model “Loudspeaker Driver in a Vented Enclosure”. Given that I have already studied successfully this model as it is i.e. in the Frequency Domain, I have tried a few things which fail.

(1) I added a second study (Step 1: Time Dependent) to the existing model. Given that this is available only for the Shell interface, I deactivated the Pressure Acoustics Frequency Domain Interface (Study 2 -> Step1: Time Dependent -> Physics and Variables Selection). Then, I ticked "initial values of variables solved for" (Study 2 -> Step1: Time Dependent -> Values of Dependent Variables) and I chose “initial expression” (Method), “Study 1, Frequency Domain” (Study) and a single frequency value from the list (Parameter value (freq(Hz))).

This study cannot be computed because the error “undefined variable, -Variable: shell.u_tz” appears. At this point, I wonder why this variable is also recognized as undefined in the Frequency Domain study of the tutorial model (Component1 -> Definitions -> variables -> av_apex(shell.u_tz)), but for this case, the study is computed successfully.

(2) When I changed further the expression for the electric driving force (Component 1 -> Definitions -> variables -> Fe) by replacing “Vo” with “Vo*sin(omega*t)”, I got the same error.

Is there a way to use the solution from the Frequency Domain study to perform a Time Dependent study?

Could be an alternative approach to work with the Pressure Acoustics Transient Interface? Given that PML layer is not applicable for this Interface, how can outgoing waves be absorbed for this case?

I would highly appreciate a response to these issues.
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Fabry-Perot cavity with metal mirror on one side

March 21, 2017, 6:35 am
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I want to simulate a Fabry-Perot cavity, one mirror is dielectric mirror with multi-stack coatings, but another one is metal mirror. For metal mirror, I need to include Fresnel reflection losses and also attenuation due to imaginary refractive index.

I know there's a tutor example of Fabry-Perot cavity in COMSOL website, it's using geometric optics model, I already build a nice working Farby-Perot model with this model but it's with two dielectric mirror. Now I change one mirror to metal and include the complex refractive index of the metal, but the result is absolutely not right.

If geometric optics model could simulate my case, if yes, how can I correctly set metal mirror and include the losses. And if geometric optics model is not working, what model should I use? Thank you.
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Attempt to evaluate real logarithm of negative number.

March 21, 2017, 8:15 am
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Hi, All

I got this error when I run the simulation:

" Attempt to evaluate real logarithm of negative number.
- Function: log
Failed to evaluate variable.
- Variable: comp1.semi.Efp
- Defined as: comp1.semi.Ev-(comp1.semi.Vth*log(comp1.semi.P/(comp1.semi.gamma_p*comp1.semi.Nv))) "

I tried to calculate the component in log (i.e., comp1.semi.P/(comp1.semi.gamma_p*comp1.semi.Nv) ) in Comsol Results and the result shows that this component indeed a positive number with a order about 10^-4~10^-9. If so, why I still face this error?

Can anybody help?

Best regards
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