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How to couple T variables in bluk and thin film

February 2, 2012, 6:36 am
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We are modeling heat transfer in solids that contain a thin film within the bulk. So we have "Heat Transfer in Solids" for the bulk, and "Thin Conductive Shell" for the thin film. The default variable for the former is T and the latter T2. We haven't found a way to specify "T=T2" (it is the same temperature we are trying to solve), except just change T2 to T, i.e. setting the dependent variable in both Physics to T. That seems to work, except we would get Reset History error, see this thread:

http://www.comsol.com/community/forums/general/thread/25804/

What is the correct way to tell COMSOL that T and T2 are the same temperature variable?
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piezo energy harvestor with open circuit voltage to closed circuit voltage?

June 10, 2012, 7:26 pm
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hello freinds,

i construct a piezoelectic energy harvestor in comsol 4.2. this model can give us induced open circuit voltage based on applied force of some frequency.but open circuit voltage is hardly of any use.so,please anybody can tell me how we can obtain closed circuit voltage across some load resistance through this model.i also attached my comsol file.
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Time Dependent Analysis of two Coupled Membranes

June 27, 2012, 8:36 am
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Hi everyone!

I am very new to comsol, so I apologize in advance if my problem is trivial.
I have to perform an acoustical simulation with comsol 4.2a.
My system is made of two elastic circular membranes coupled by an air-filled cavity. I want to apply a uniform (but time dependent) pressure on the two membranes, namely po*cos(w*t) on one membrane and p0*cos(w*(t+dt)) on the other.
As a final result, I want to get the velocity of vibration of the two membranes in the stationary state. However, I cannot understand whether I implemented correctly the time dependent conditions and I actually do not know how to build the study in order to get the velocity of vibration in the stationary state.

Concerning the pressure boundary conditions, I defined two analytical functions in the global definitions:
cos1=cos(w*t)
cos2=cos(w*(t+dt))
with argument t[s]
Then I defined two variables
p1=p0*cos1(t)
p2=p0*cos2(t)
I defined w, dt and p0 as parameters.

I am using an Acoustic-Shell Interaction, Frequency Domain Physics, and I selected a Face Load to apply for example p1 on one of the membranes and p2 on the second one.
Is that the correct way to proceed?
Moreover, how should I proceed in order to perform the time dependent study?

Thank you very much in advance!
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Parameter Estimations by Inverse Analysis using Comsol 4.2.

August 14, 2012, 3:46 am
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Dear Sirs,

I would like to have an opinion by more expert users than me. I am facing a problem of parameter estimation by inverse analysis for structural mechanics. More simply, I have to estimate the values for certain parameters of the constitutive law. The observation variable that I look at in order to understand if the current value of the parameter is correct is the displacement field in the domain.

The mathematical formulation of the problem involves a functional J that should be minimised and the so called primal and dual problems.

Have some of you ever tried to solve this type of problem? If yes, which package of Comsol did you use? I think the best would be to use the Sensitivity module that is in the General PDE module but I would like to have some advice.

Many thanks for the help,

I wish you a nice day,

Paolo Tricerri
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How do I locate specific Vertices, Edges, and Boundaries?

August 22, 2012, 6:11 am
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Occasionally I will get errors like "vertex is adjacent to several outer edges" and it will cite Vertex 263. How can I easily find where this specific vertex is without clicking on every single one? I also have the same issue with edges and boundaries.

-Steve
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Meshing Errors In Small Solenoid Simulation

August 22, 2012, 12:25 pm
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I am having trouble meshing a somewhat simple solenoid in COMSOL, more specifically, solenoids with a small pitch. I have attached a simple solenoid simulation (created in 4.2) which demonstrates the problem I am having. In this file I am trying to calculate/visualize the flux generation of different solenoid models with a specified current input.

When the pitch of the solenoid is small then I COMSOL will give me a mesh warning or error when generating the free tetrahedral mesh around the solenoid. If you look at the model, you can see COMSOL is having trouble generating the mesh at the input/output of the solenoid. COMSOL has no problem creating a mesh when the pitch and minor radius are increased.

I was able to create a swept mesh based on a free triangular pattern but I found I was unable to create a free tetrahedral mesh around the model (for the 'air' box representing the boundary conditions).

Does anyone know why I might be getting these meshing errors and any suggestions as to what I could try next?
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Simulation of balloon gore deformation under inflation.

August 23, 2012, 1:59 am
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Hello,

Im doing analysis on the shaping of balloon gores cut from a polyethlyene/polyester laminate. The shape of the inflated balloon is used as an optical reflector and is therefore crucial to the application.

I want to find via simulation the 2d gore shape that when arrayed and bonded into an inflatable envelope gives the most effective ballon profile curve.

For an idea of the construction method i mean see the old NASA project PAGEOS. http://space.skyrocket.de/doc_sdat/pageos.htm

Any way id like to model the deformation of one or all the gores under inflation but I dont know where to begin in applying the correct constraints and edge forces to my gore section model.

Is this type of analysis possible in the comsol framework?? Any tips or practical suggestions would be hugely appreciated.

Best Regards
Declan
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Current in Induction heating (Peak or RMS)?

August 23, 2012, 3:39 am
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Hello,

When solving using the Induction Heating solver, can anybody confirm if the "Current Excitation" in the "Coil Group Domain" is peak or RMS? I have a suspicion that the value to be specified is the PEAK value, since the expression for the coil power has a factor of 1/2. Can anybody confirm?

Abhishek
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Modeling Acoustic Metamaterial

August 23, 2012, 9:57 am
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Hi,

I want to model an 2D acoustic metamaterial in Comsol. My target is to apply acoustic waves along one side of the geometry and calculate the wave amplitude from opposite face of the geometry. I also want to plot effective mass density and bulk modulus with respect to frequency.

Can anyone help me with step by step procedure?

Regards
Riaz
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Three phase modeling

August 23, 2012, 2:40 pm
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Hi there,

I have a problem with coupling single phase and two phase flow (phase field) physics.

I would like to model ice nucleation inside a water droplet. This droplet, however, is inside a laminar air stream. I have picked two phase flow (phase-field) for the droplet and initial ice inside it, and the ice grows by time.Then the rest of the domain is considered as single phase (air). The problem is that I dont know how to couple these two physics together. In fact, I dont know how to set the boundary condition for the droplet's outer boundary (which is in contact with air) in such a way that air flow changes drop's shape.

If any body could help me I highly appreciate it.

Sean
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frequency analysis

August 23, 2012, 8:00 pm
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Sir,
In frequency analysis how to do it for a particular frequency.where to add a frequency value
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How can I extend the time range?

August 24, 2012, 2:17 am
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I use PDE model to solve time dependent PNP equations coupled with N-S equation. Attached is my model. Please run study 1 and study 2 firstly. Study 1 is for stationary solutions to prepare initial values. Study 2 is for the solution without an external electric field. You can see in the "Global parameter", the value of "ele" is equal to 0, which means I switch off the electric field. After running the study 1 and study 2, then please change the value of "ele" to be "1" , meaning I switch on the electric filed. Last, please choose the solution of time 0.01 in study 2 as initial value for study 3. Finally, run study 3 to get the results I want.

Now my problem is if I extend the time range larger than the present values, the solutions are not converged, saying I change the time range of study 2 from (0, 0.001, 0.01) to (0, 0.1,10), or time range of study 3 from (0.01, 0.01, 0.08) to (0.01, 0.1, 10) or more. I have changed the Jacobian update on every iteration, but get no change to the situation. So, could you help me to treat this problem?Thanks!

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Relative residual is greater than the relative error in heat transfer model

August 24, 2012, 3:18 am
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I have built a model of heat transfer including conduction, convection and radiation. When the model was computed with coarse mesh, it worked well, but when I refine the mesh, solution returns this error message:

Failed to find solution.
The relative residual is greater than the relative tolerance.

Why did it happen? Any idea?

Thanks in advance.
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How to run!

August 24, 2012, 5:11 am
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Dear users,
I just installed the Comsol 4.3 trial version on my mac (OSX) , but I am not able to run it. I don't have any application form file to run the software !
what could be the problem. any guidance appreciated!

M
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point settings (pressure) in bubbly flow mode

August 24, 2012, 5:56 am
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Hi everyone,

I have a question about the point settings in bubbly flow mode in comsol 3.5a.

After I select one point, I am asked to set the pressure value. What is the definition of this pressure? Should it be 1atm, or should it be the difference between the real pressure in the simulation and 1atm?

Similarly, I have a problem in comsol 4.2a. I am asked to set the value of the reference pressure. What is the definition of the reference pressure?

Any help will be greatly appreciated!

Thanks,
Xiaofei
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to find a curvature(or shape) of liquid minisci(hanging from a vertical capillary tube) under the action of electric field

August 24, 2012, 9:14 am
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hello
i want to solve a problem in which there is a capillary which is at very high voltage(capillary at 5000volt and in front of capillary there is a plate at 0 voltage) and there is a droplet of water which is in equilibrium condition under the action of hydrostatic pressure, electrostatic pressure and surface tension.
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How do you disable compressible flow in *Non iso thermal flow*?

August 24, 2012, 10:23 am
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By default the documentation says this is compressible. Why does it assume that? I have a incompressible problem but can't find a way to switch this.

I can easily do it for a regular fluids problem. Am I missing something fundamental here?
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How to export the x,y,z coordinates

August 24, 2012, 11:54 am
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I created 7x7x7 cubical shape and want to export the x,y,z coordinates in the pattern that I want as attached. Please help me.
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Memory problems with mphinterp

August 24, 2010, 3:37 pm
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I have a large RF simulation, and I need to get the value of the electric field on a rather dense rectilinear grid. For this, I have been using mphinterp. However, I have been running into the problem that if I make the grid too large I run out of heap memory.

At first I thought that this was due to evaluating too many points simultaneously, so I split the evaluations up but got the same problem. I played around with this a bit and noticed that ANY call to mphinterp seems to permanently (as far as I can tell) increase the amount of RAM being used by comsolserver.exe. So, even if I call mphinterp at a single point over and over the RAM being used by COMSOL will steadily increase until I hit my heap limit and get an error. At this point, trying to do pretty much anything with my model returns the out of memory error, since there seems to be no way to unallocate this RAM, and I have to quit and restart COMSOL.

This is quite a problem for me, since I do in fact need a large number of points in this grid. I can manually set the heap allocation to be larger, but I'm rather curious why this is occurring in the first place. As far as I can determine from the documentation mphinterp is supposed to interpolate the value of a given expression based on the existing solution vector, so I see no reason why it should need to permanently increase the amount of memory used by the model.

Does anyone know why this is happening? Is this a bug (memory leak, or something else)? If not, is there any way to free up the memory used once I have the interpolated values?
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Variable modifications between solution iterations

May 3, 2011, 7:04 am
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I'm developing a transient model using the Livelink interface. The model first calculates an initial solution for the first time window, then I would like to modify the state variable values due to some external disturbance using MATLAB, then proceed to rerun the model for the next time window using the newly adjusted values of some of the variables, but the other variables should be retained from the previous solution iteration.

When I prescribe the use of the previous solution for subsequent iterations as:

model.sol('sol1').feature('v1').set('initmethod', 'sol');
model.sol('sol1').feature('v1').set('initsol', 'sol1');

it seems that the specification of initial conditions through either

model.variable('var15').set('X0', num2str(X0));

or

model.init('init4').set('position',num2str(X0));

are ignored completely and the unchanged values from the previous solution are retained. Is there a plausible method to effectively update some of the variables this way? Perhaps by modifying the dataset of the previous solution?

Thanks.
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