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Bend a sheet of metal to cylinder

January 6, 2015, 5:41 am
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Hello,

I would like to bend the following plane structure (attached) and form a cylinder along the x-axis direction. I have tried many several ways, but nothing worked.

Thank you alot in advance.

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Frequencies on a squared plate (membrane)

January 6, 2015, 5:48 am
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Hi guys, i'm sorry if i'm doing this wrong but i'm kinda new on COMSOL and I'd like to know if you guys could help me on this exercise:

i need to see how is the behavior of the frequencies on a squared membrane, like chladni figures experiment. There's a model for circular ones that works pretty well but i can't adapt for myself, because there's data like pre-tensions that i won't need right now. My plate is only fixed on the center by a screw on a base made by me. I just would like to see how would be this behavior on some frequencies (6 is fine).

Plate:
size - 16 cm
thickness - 3 mm
poisson - 0.33
young - 69 GPa
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Warning sign in "Step 2: Time Dependent" node in COMSOL

January 6, 2015, 10:14 am
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Hello guys,

I am solving a ODE in COMSOL which is coupled with AC/DC module through the velocity (Lorentz term) in "Magnetic and Electric fields" interface. When I choose "study controlled" in Equation form of this interface, as shown in picture 1.1 attached, the solver converges quickly and I get good results, at least their trends are reasonable. However, in this case, a "Waning sign" appears in the node "step 1: Time Dependent" which the picture 1.2 shows that. Is there any problem with this "Warning sign" or not?

Could you please tell me the here what does "study controlled" mean? I checked the COMSOL help but did not find related comments about this.

In another case, when I choose "Stationary" in Equation form of "Magnetic and Electric fields" interface, it can be seen in picture 2.1, the "Warning sign" disappear and I can see the "Green tick sign", see picture 2.2 please. But the problem is that my model in this case does not converges !!!

Any help or idea would be appreciated.

Thanks,
Mohsen
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meshing

January 6, 2015, 11:34 pm
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hi

I am new to the comsol 3.5 , I am working on two pass cooling channel with ribs .now what I want is that I want fine meshing of the bottom plate of channel and normal mesh on rest of the geometry ,can anybody tell me how to do different meshing of different parts of geometry.
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high mach number flow simulation (CFD)

January 6, 2015, 11:52 pm
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Hi
i want to simulate an airfoil in high mach flow .
i am using high mach number flow module k-epsilon method .also adaptive mesh method employed to finer meshing near shock wave region .
for the special case of airfoil, simulation for all velocity converged(even for higher than 10 mach number flow) and result are acceptable .but when i change slightly dimension of the airfoil ,simulation cannot be converged,even in very low mach number(nearly 2 mach ). I am really confused.nearly two month i am working on this simulation but i can not identify the problem .
to solve the problem please help me.
best regard
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compilation error

March 19, 2014, 8:49 am
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Hi,

I ran a conjugate gradient model for determine temperature distribution (time domain). Then I added a structural analysis model (steady state) with last solution from conjugate gradient as input (with deselecting fluid from the analysis). However, I get the following error:

"No sequence specified
Error in multiphysis compilation."

I would appreciate if any one can point me to a potential solution.

Regards,
Susant
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Non-Newtonian models in COMSOL

January 3, 2015, 6:48 pm
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HI,

I am re-posting this as I didn't receive a lot of attention last time. I have only seen Carreau and PowerLaw models for non-Newtonian flows in COMSOL. However, I want to implement a different constitutive relation of my own that involves some constants and has it's own unique functional form in the CFD module for non-Newtonian flow! The independent variable is still shear rate (gamma dot) but it is a different function than Carreau.

Does anyone how to define this function and then how to call it for calculation of the viscosity for a non-Newtonian flow simulation?
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Acoustic-Solid Interaction physic relational problem

January 7, 2015, 3:42 am
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Hi all, can you tell me how can I set the sound attenuation in the solid model?
Someone told me that it is in the damping that is located in linear elastic material.
But I still donot know how to set the parameter for the competition of sound propagation loss.
Looking forward to your replay.
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Laser Heating of a Silicon Wafer Model ID: 13835

January 7, 2015, 5:20 am
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I think I should have written this somewhere else but since it took me at least half a day to understand that something is wrong with this model, I thought it will worth writing here. This model has a fundamental error since the rotational frequency is wrongly accepted as angular velocity. The difference is only a factor of 2pi. What I mean is: in the model v_rotation is defined in terms of rpm and it is converted to Hz by COMSOL automatically. On the other and the rotation is defined in terms of translation vectors (u's in COMSOL) as ux = -y*v_rotation, uy= x*v_rotation, which is in fact should be ux = -2*pi*y*v_rotation, uy= 2*pi*x*v_rotation. Try yourselves and see.. Thanks a lot.
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Assigning material

January 7, 2015, 6:51 am
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How can I assign the Young modulus (E) of the solid material which has different E (in a specified time) over the volume. I tried to use of the interpolation function (spreadsheet) but it dosen't work. The spreadsheet data is E for (x,y,z). The type of erroe it shows is 'failed to evaluate variable Jacobian'. thanks
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heat and mass transport in porous media

January 7, 2015, 6:58 am
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hi
plz . can any one answerme about
if COMSOL can simulate heat and mass transfer in porous media or not ?
witout need to any other programm
best regards
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Diffuse Double Layer Model - Interpretation of results

January 7, 2015, 8:16 am
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I have been trying to recreate this model :

www.comsol.com/model/model-of-a-diffuse-double-layer-13525, which is based on the Paper web.mit.edu/bazant/www/papers/...2005_SIAM_J_Appl_Math_MTF2.pdf .

This might sound like an unusual question, but I'm regarding the dimensionless charge density -Why is the Charge density across the domain asymmetrically distributed? i.e, close to the Cathode, it reaches 0.6, while on the Anode, it reaches -1.8. I'm not really able to understand what is the physical reason behind this. Mathematically, I can see that the distribution of Anions is an exponential curve dependent on Potential, which is inherently asymmetric, but even then, shouldn't the distribution of Cations and the distribution of Anions be 'inverses' of each other? I have attached an image of the plot that I'm referring to.
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How to generate scattered field for multiple angle of incidence ( or sum parametric sweep solutions)

January 7, 2015, 10:56 am
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Hi all,

i'm working on a scattering problem. I need to find the scattered field over a range of angle of incidence.
I know that i can plot the scattered field for each angle of incidence , but i want to plot the total field for all angle of incidence added together. So basically, i want to find out the total scattered field from multiple plane waves. I figured i could join the results for this parametric sweep, i could obtain the total scattered field, but i'm not sure how do to so in comsol, since i don't have a 2nd dataset. Your help is greatly appreciated!

thanks,

Yuchu
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Mikic elastic correlation error in thermal contact node

January 7, 2015, 11:12 am
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I keep getting an error when trying to model thermal contact.

Division by zero.
- Function: /
Failed to evaluate variable.
- Variable: comp1.ht.tc1.Econtact
- Defined as: ((down(comp1.ht.tc1.Eequ)*up(comp1.ht.tc1.Eequ))/(((1-(up(comp1.ht.tc1.nuequ)^2))*down(comp1.ht.tc1.Eequ))+(up(comp1.ht.tc1.Eequ)*(1-(down(comp1.ht.tc1.nuequ)^2)))))
Failed to evaluate expression.
- Expression: if(((comp1.ht.tc1.Tn==0)||(comp1.ht.tc1.Econtact==0)),0,((comp1.ht.tc1.Tn*1.4142135623730951)/(comp1.ht.tc1.m_asp*comp1.ht.tc1.Econtact)))
Failed to evaluate variable.
- Variable: comp1.ht.tc1.TnRel
- Defined as: if(((comp1.ht.tc1.Tn==0)||(comp1.ht.tc1.Econtact==0)),0,((comp1.ht.tc1.Tn*1.4142135623730951)/(comp1.ht.tc1.m_asp*comp1.ht.tc1.Econtact)))
Failed to evaluate operator Jacobian.
- Operator: if
- Geometry: geom1
- Boundary: 93
- Feature: Stationary Solver 1 (sol1/s1)

I don't see anything wrong with my inputs, though. I put in values for E and the Possion ratio for the Weighted Harmonic Mean, but it treats Eup and Edown as 0? I have no idea where to input those values. I would think it pulls the values from the material properties. In any case, what exactly is it that I am filling in when I put in the value for E and the Poisson ratio in that node?

The boundaries I'm defining are simple -- just a rectangle against another rectangle.
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limiting the maximum value of concentration

January 7, 2015, 3:23 pm
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Hello,

I am solving a 1D convection-diffusion equation using the Classical PDE set up. My equation has a source term. The left BC has a zero flux, while the right BC has a dirichlet condition of u = 0. Since the left BC has zero flux, the concentration u will increase with time due to the source term. How can I limit the concentration on the left boundary to a specified value so that as time increases, the concentration there is capped at the threshold?

Thanks.


Best wishes,

EH
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Ultrasonic Non Destructive Testing

January 7, 2015, 3:27 pm
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Hello Everyone,

It's about my graduate thesis, I ve been trying to make an analysis which is NDT. There is a specimen, transducer, and cylinder( for showing to cracks-voids)

I can't send a sound from transducer to specimen. That's why I can't see the result as a [db] and [f]

I'm so pleased whether anyone help me

thanks
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How to add a continuous pulse with a frequence from 25THz to 100THz?

January 7, 2015, 5:47 pm
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How to add a continuous pulse with a frequence from 25THz to 100THz in RF moudle? I want to let the pulse be a source to irradiate a structure,but i don't how to do it .I hope you can give me a hand.Thank you very much.
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From modal participation factor to modal mass

January 8, 2015, 12:57 am
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Hi everyone,

I read all the posts about Modal Participation Factor. I understood that for one direction the sum of all the MPF will give us the total mass thanks Ivar.
The fact is that I'd like to get the modal mass for one mode and can't manage to do it. I mean, how from the 3 MPF (MPF_u, MPF_v & MPF_w) for one mode I can get the effective (modal) mass for this mode?
I don't know if it's really clear, I can precise my question if necessary.

Thank you to everyone who could help me,

Jean
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Phase Change + Flow

May 8, 2011, 6:48 am
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Dear All,

I need to simulate a tank filled with Phase Change Material that is heated by circulating hot water through a pipe inside it.
I am using COMSOL 4.1. What kind of physics would you recommend me to use?

Thank you!
Paul
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Parallel Computing with MATLAB Livelink and COMSOL

July 20, 2013, 8:37 am
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Hi everyone,
I am currently trying to use Matlab's Global Optimization tool (specifically using genetic algorithms) with my function. Every time my function evaluates, it loads a model file, modifies some parameters in it, does the calculation and sends it back to the Matlab program. In order to speed up this process, I intend to parallelize my code. The Matlab part of this is easy, as I simply have to start a pool of MATLAB workers and turn the parallelization option in the optimization tool. However, for the COMSOL part, I think that I need an independent COMSOL server for every worker/core. How does one go about doing this?

I have tried the solution outlined in this thread (www.comsol.com/community/forums/general/thread/33446/). Specifically what I tried to do was write the following code to initialize multiple COMSOL servers:

matlabpool open 3
comsolPort = 2036;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

comsolPort = 2037;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

comsolPort = 2038;
system( ['comsol -np 1 server -silent -port ' num2str(comsolPort) ' &'] );
pause( 6 )

Then after this I start the Matlab genetic algorithm, which calls upon my function.

Within my function, I add an mphstart(portno), with the portno depending on the MATLAB worker ID.

What happens when I run this code is that at first three COMSOL servers seem to come up (with three splash screens etc.). Initially each worker seems to be able to start accessing the model. However after a few seconds (while the workers are modifying the model) the COMSOL servers shut down and only one worker is left doing its job. What is the cause of this? Is it that COMSOL doesn't allow more than one server operating?

On the other hand, when I tried to make all workers simply connect to the same COMSOL server, a "java.lang.NullPointerException" occurs, which led me to believe that I need three independent servers.

If anyone has any pointers on how to execute this task (running a parallel operation on MATLAB livelink where each worker has access to a COMSOL server, or perhaps do this without needing multiple COMSOL servers), that would be great!

Thanks in advance for any help given.
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