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"No frame is defined for 0D applications"

February 22, 2013, 2:58 am
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Hello again.

I am trying to simulate an E-core transformer. When I click the study 1 and select the show default solver there is an error occurs "No frame is defined for 0D applications" . What is it mean?

Thanks

Asli
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Surface impedance

February 23, 2013, 11:53 am
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Hello everyone,

I want to plot the surface impedance of my simulation. Can I do it in COMSOL? How I do it?

Thanks

Gustavo
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Error Jacobi with user-defined function

February 23, 2013, 1:53 pm
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I defined a function in Global Definition to describe the graded-index. However, when I used the Solve-Modal Analysis, the COMSOL popped a window to warn error in Jacobi matrix.

Plus, I suppose my function was working well, I am not sure whether it can be a assignment in Material dialog.

If I replace my function with a constant in index value setting, the model works well.

Thank you.
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biosensor

February 23, 2013, 6:11 pm
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hi sir,i am currently working on microcantilever beam based biosensor,and i want to know about the piezoelectric module and how to incorporate BC in microcantilever,



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How to Improve Convergence in Natural Convection

February 23, 2013, 6:34 pm
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I am wondering how I can improve convergence in my natural convection model. It is a simple model; an isothermal aluminum plate in water.

The model starts out fine but as the run continues (transient model), the plume begins to lose stability causing the problem to reduce its time stepping. I have tried re-meshing as much as my PC can handle (3 mil elements).
I am wondering what else I can do to solve this problem. Should I change tolerances, crosswind or streamline parameters. I am running out of ideas. Any help would be greatly appreciated ( as I have been stuck on this problem for several days now). I have attached the model (with no mesh or solution). Typically, the model solves the first 20-30 seconds, then the solution becomes very strange and results become unreasonable.
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Comsol doesn't keep initial values

February 24, 2013, 1:28 am
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Hi
Now, I work on a Comsol model describing a spouted bed apparatus (spouted bed is a kind of fluidized bed, when the apparatus has a conical bottom). I use Comsol 4.3 with Euler-Euler model, laminar flow. Because I had stability problems with the stationary solver, I was forced to use the time dependent solver. I noticed, that it had convergence problems when I "turned on" the gravity, so first I ran the simulation without the gravity in the range from 0 to 3 s with the step 0.1 s. After that I selected the results from one time step as a initial value for the simulation with the gravity. In this moment I observed a problem with Comsol. When I wanted to use as the initial values the results not from the last time step for instance from 2 s Comsol always set up this option during calculation to "Automatic"
(the branch in the model: Study 1/Step 1:Time Dependent/ Solver Configuration/ Solver 1/Dependent Variables 1/Initial Values of Variables Solved for/
Method: Solution
Solution: Solver 1
Time: Automatic.)
Now, I can't use as initial values the results from any time step but only from the last one. Can anybody help me ?
By the way, I have a little question to Comsol producers. Are You going to add Euler-Euler model with turbulent flow to the CFD module ?

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Properties of model

February 24, 2013, 3:53 am
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Hey.

How can I check the properties of the model object?
For example, the current in the coil, or the radius of the circle, the properties of the materials.

Thank you.
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Problems related to relative tolerance and relative error

February 24, 2013, 9:36 am
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Hello

I want to reproduce a model in which there are two spheres in contact one upon the other along the z axis, and then i has applied two forces, one on the top (point or boundary region of the sphere above) with -z direction and other force on the bottom (point or boundary region of the sphere below) with z direction. In summary the idea is to confront the two spheres subject for the forces and will see the results corresponding to the stress and displacement of both spheres. Unfortunately when I solve and compute it, appear the following messages:

Failed to find a solution.
The relative residual (55) is greater than the relative tolerance.
Returned solution is not converged.

Failed to find a solution.
The relative error (2.2e2) is greater than the relative tolerance.
Returned solution is not converged.

What is the meaning of this? the reason is because the problem isn't configure correctly and therefore cannot converged? How can I avoid this problem and resolve it succesfully?

Thanks beforehand.
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The relative error is greater than the relative tolerance..Error!!!

February 24, 2013, 12:09 pm
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Iam a newbie to comsol. And Iam learning comsol for my research. I simulated my first simulation and I got the below mentioned errors.

Failed to find a solution.
The relative error (4.6e+004) is greater than the relative tolerance.
Returned solution is not converged.

Later I did some modifications and the error was

'Failed to find a solution.
The relative residual (0.0036) is greater than the relative tolerance.
Returned solution is not converged.

and a warning-->New constraint force nodes detected: These are not stored.

Can anyone help me to eliminate this errors.
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Limiting simulations-Dynamic Pull-in Cantilever

March 3, 2011, 7:58 am
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Hi everyone,

I have a quick question, Can I tell comsol to simulate till it reaches some theoretical value and the stop? I mean, what I'm trying to do is Simulate the dynamic behaviour of a cantilever beam under an applied voltage, so, when I solve the Static model, the coupled Physics(es and solid) work good cause I'm able to reach the Pull-In voltage as the value when the system fails to converge. Theoretically speaking, that's the point were the Electrostatic force equates the Elastic restoration force. Till here everything works logically, however, when I go to stationary study and simulate, there is no reaction, I mean there isn't even a convergence error or something, It just goes through the contact material, so I'm not able to get a Dynamic Pull in Voltage (which should be slightly different to the static). The point is that as comsol is not letting me obtain the dynamic pull in, I-m trying to do the following: Calculate the value of the force at which the system fails to converge in stationary study and then tell comsol in the time-dependent study to simulate just till it reaches that force value. I know it isn't the best approach but if it lts me extrapolate the dyamic pull in I'll live with it. Any help would be greatly appreciated.

Regards
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Geometric nonlinearity

February 1, 2012, 12:39 am
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Hi,

I have used structural mechanics to simulate an indenting sphere on a half space polymer film. I am changing the elastic modulus of the polymer film to go from hard material to soft material.
I am trying to reach a certain force using weak constraints. When I use the elastic moduli from some GPa to around 80 MPa for indentation of 100- 400 nm, very well I can use linear elastic physics without selecting the box "consider geometry nonlinearity".

However, as long as I choose the elastic modulus 60 MPa or less with indention between 500 nm to 600 nm (I want to reach to a certain force and as the material is soft indentation is high), the simulation fails. It does not stop but a big triangular max pick appears at around 500 nm. However if I turn on "consider nonlinear geometry " and change the poission ratios, it works. but then I reach to a force at much lower indentation that I cannot compare the results with the previous calculations.

I would like to know why do that happens? and how can I fix it?


Yours,
Marjan
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HEAT TRANSFER IN A BITUMEN TANKER

September 27, 2012, 8:38 am
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Hi, I am a new Comsol modeler and I am trying to model a steel tanker filled with molten bitumen. The tanker is insulated and the bitumen is heated by two propane burners ( in form of U) located at the bottom. For the bitumen I have Non-isothermal Flow-Laminar , for the propane I guess Non-isothermal Flow (flow in a pipe) and also I have Heat transfer in solids for all solid structure and convection to the exterior.

I have tried many times to do my model and always I have some kind of message error.
Someone could give some directions to do this model. I am using Comsol 4.2a.

Thanks
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Creating a region with a constant gradient field

February 18, 2013, 4:54 am
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I want to create a region of air with a static magnetic field in the z direction that has a constant slope (gradient) in that direction as well, for example H(x,y,z)=(0,0,1+z/10). Once I have this, I'm planning to put an object in it, but thus far I've not figured out to to make this sort of initial field. I tried creating a cube with the H field on the boundaries set to 0,0,1+z/10, but the calculated result within the cube wobbles away. It's even different along the boundaries! Very puzzling.

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PDE solving or defining force in terms of displacement

February 18, 2013, 7:56 am
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Hi,
I hope you are doing well,
I am a new user of Comsol.
At this moment, I am trying to model a cantilever beam with an applied force on its edge as a function of displacement.
So, what I need is either:
define the force on the boundary as a function of displacement. I am trying to do this in equation view but it seems that it does not take expression and it asks me just values in x and y directions.
or:
write a PDE and try to solve it. The equation is derived from the Euler-Bernoulli theory as:
EI uxxxx=F(u)
I tried to find a predefined PDE and change the coefficients but I could not to do it.
Could you please help me on this issue?
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Thermal expansion of a liquid

February 19, 2013, 12:15 pm
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Hi all,

I’m am trying to produce a model of a fluid enclosed on all sides except one by fixed constraints(walls), on the remaining face a thin diaphragm is in contact with the fluid. As such this is a closed system with no flow.

I would like to model the deflection and stress of the diaphragm wrt the temperature of the enclosed fluid. Clearly as temp increases thermal expansion will deform the diaphragm

I have tried to model the situation using the fluid-structure interface option on 4.2 however I can’t find a tutorial that features a stationary fluid?

Which interface should I be using?

Any help would be greatly appreciated!

Thanks,
Matt
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Gas Pipe Flow

February 25, 2013, 7:51 am
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Hello , I have a simple question. What module should I use to simulate a gas flow in a pipe.Something like the Pipeline Insulation in the Model Library but with a gas.

Thanks,


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HEAT TRANSFER IN A BITUMEN TANKER

February 25, 2013, 8:21 am
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I am trying to model a steel tanker filled with molten bitumen. The tanker is insulated and the bitumen is heated by two propane burners ( in form of U) located at the bottom.

For the bitumen I have Non-isothermal Flow-Laminar ,

For the gaseous phase above the bitumen: Non-isothermal Flow-Laminar (not sure).

For the propane: Pipe Flow module (I am not sure if I can use it for a gas)

Also I have Heat transfer in solids for all solid structure with convection to the exterior.

I need to simulate the propane because my goal is to analyze the different configurations of heaters and their impact in the temperature profiles , specifically , the risk of reaching ignition conditions at the interface bitumen/gaseous phase.

Are the modules ok for this simulation ? I always have some kind of error message.

Thanks,
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Call For Papers

February 25, 2013, 8:23 am
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We are pleased to invite you to present your work at the COMSOL Conference 2013. The user oral and poster presentations at the Conference highlight achievements in multiphysics modeling and simulations using COMSOL. Presenting at the conference not only provides a unique venue in which to showcase your accomplishments; additionally your work will be published on the Conference online proceedings, which reaches an audience of over 150,000 people worldwide.

You can submit your paper or abstract on the COMSOL Conference 2013 webpage: www.comsol.com/conference2013/usa/papers/.

Abstracts and papers will be reviewed by the COMSOL Conference Program Committee—a panel composed of multiphysics modeling and simulation experts in a variety of fields.

Visit the Conference 2012 Highlights page to see photos, videos and more from the COMSOL Conferences in Boston, Milan and Bangalore last year: www.comsol.com/conference2013/usa/highlights2012/


Valerio
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How to get final dimensions i.e. outer profile in COMSOL?

February 25, 2013, 8:38 am
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Dear friends
i want a help in this part. Here, i'm explaining the full problem.
# i got the co ordinates of a biological part from image analysis in MATLAB . I plotted those points in the COMSOL ( solid mechanics ) by help of interpolation curve. All the conditions were applied like body load, angular velocity, B.C etc. And finally i got the stresses. Till this point i got good results.
But i want the final dimensions i.e. co ordinates from this as i have to do another analysis based on the dimensions.

So, I tried to grt the final co ordinates in the result section of model builder, but can't succeed.
Could anybody help me in this matter.
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Unable to create mesh : Error Free Tetrahedral 1

February 25, 2013, 12:31 pm
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Hi everybody,

I am having this error when I try to mesh a 3D structure :

The following features have problems :
Features : Free Tetrahedral 1


I don't find a way to have more information about this error.
My geometry is really complex, with many points/edges. I cannot make it simpler.
I still have the same error when I change the element size to be 'Extremely coarse'.

Does someone have an idea to fix this error ?

Thanks.
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