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Calculate the effective thermal conductivity

June 16, 2014, 1:05 am
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Hi,
im very new in Comsol and its my first post here, so if you need more information for saving my problem just let me know.

I want to calculate the effective thermal conductivity of a tank containing insulation materials. The tank should be heated below and I want to determine the temperature at the top and bottom. With this information, I could then calculate the effective thermal conductivity of the complete tanks.

Now i created my geometry and filled the tank first with air.
But my simulation does not work. I think its due to the physics settings. Because im not sure if i did it right. In the most posts here there is written something about the heat flux. But if i dont know how to set it up.

I've attached my Comsol-file

I hope you can help me.

Greetings
Kevin
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Restricted Solution Set

June 16, 2014, 9:08 am
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Hello All,

I'm trying to fit parameters to my model (using some known experimental values), the thing is that it's not computationally cheap to evaluate. I have a voltage source and all the model does is to calculate the distribution of the potential in space. I was wondering if it's possible to restrict the calculations to only solving at the points where the experimental values are defined, and if that would even speed it up to any degree?

Thanks,
Aaron R. Shifman
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3D conduction with heat flux

June 17, 2014, 3:00 am
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Hello,

I am trying to build a simple model of a channel in 3D.
I set a physic "Heat transfer in solids" and I stablished the following boundary conditions:
- heat flux of 800W/m2 in one of the faces
- Initial values 800 degC in the all faces of the channel
- Temperature in all faces of the channel except the face with the heat flux

It is giving me an error and I can not see the problem.
"Failed to evaluate variable.
- Variable: nitf2.U
- Geometry: 1
- Domain: 1
Failed to evaluate expression.
- Expression: nitf2.U
- Plot: slc1 (Slice)"

I hope you can help me.
Best regards and thank you,

Ana Tostao
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Finding mesh volumes for volume integral

June 18, 2014, 4:35 pm
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Hi all,

I have calculated an energy density (per volume). Now, I am trying to find total energy by integrating this energy density. I have a list of (x, y, z) coordinates and each point's energy density. I know that in the triangular mesh, the volumes are not always equal, so I'd like to get a list of volumes corresponding to the points, so that I can multiply by the respective densities and add them to integrate. I am using 4.4, and I have looked under mesh statistics, but I haven't found what I need.

Does anyone know a way that I can do this, or an alternative method for calculating this integral? Thanks!
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Constraint found for variables in different Segregated groups. Try to merge these groups.

June 19, 2014, 1:46 am
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I am trying to solve for the emf induced in array of coils placed above an array of magnets orgranised with opposite polarity. Here the magnet array is vibrated in x-direction and coils are stationary. I am using magnetic field and moving mesh as physics.

When I am computing the model for the time dependent study, I am getting the following error message:
Constraint found for variables in different Segregated groups. Try to merge these groups.

I am not able to attach file due to file size. Can anyone please help asap.
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Particle Trace Value

June 19, 2014, 8:53 am
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Hello All,

This might be a bit of a trivial question, but I'm not sure how to do it. I solve for an electric field in space and everything is fine. I know about the particle trace graph where I can drop a "particle" and trace it's trajectory along the electric field. I'm wondering if there is a way to plot some variable over the trajectory of the particle?

Thanks,
Aaron R. Shifman
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Shape optimization on loaded knee (L-sock)

June 20, 2014, 12:29 am
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Hi everybody
I'm doing shape optimization on the loaded knee. I've made the geometry similar to the image posted, instead I've just put a fixed constraint on the upper boundary and the force is working in the -y direction instead. I've made the geometry by creating two rectangles and using the difference tool. I've also added a fillet with radius=5.
I'm using the Deformed Geomtry module in order to make the shape optimization. I've attached my module, so you can see the Prescribed Mesh Displacements. I'm using the total elastic strain energy as my objective function
My problem is that shape optimization doesn't work properly, I want my result to look something like result.png (attached), but instead it looks like result2.png

I hope you can help!
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Heat Generation in a Disc Brake with 4 brake pad

June 21, 2014, 4:46 pm
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I'm newbie on simulations, I would like to know how do I resolve some issues I'm finding my style. I want to make a simulation of heat transfer with four brake pads on a disk. I took the model that has the library and imported the geometry of the ventilated disc I'm using, and the brake pads.

I tried to repeat all the data from the model library in my model. However some items went wrong.
1st Error: swepts not work, ask to set something that I do not know what is. So I created a mesh without them.

Error 2: The model library has global equations, however in my model I can not add these equations. Not appear in the list.

I tried to simulate without these items. I let simulating 24 hours and still had not finished. Once the simulation has ended, the results were not expected, the model was the same temperature in all parts. So I wonder, what's wrong with this model?
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waveguide to microstrip Measure s-parameter

June 21, 2014, 7:59 pm
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Hi,
I am designing simple rectangular waveguide of some 50x100. Then i try to catch microwave signal from waveguide to microstrip with 50 ohm strip line. I used FR-4 as material and copper , rectangular waveguide as alumnium.

I got error whenever i try to simulate. I want to know how i will see S-parameters.

Moreover, when i design rectangular waveguide structure you will see the part of microstrip inside rectangular waveguide divided into two part and i have to define two times wave port 32 & 36. this i feel is not correct.
i am new user can anyone explain or download my comsol file , make it correct and send me.

I will be thankfull to you

I have attached the comsol file and also one image file to show what i want to design.

best regards,
Mehdi Khan
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Import S-parameters of Transistor or diode in comsol from Agilent ADS simulate in comsol

June 22, 2014, 3:05 am
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hi,
How i can import S-parameters of transistor or diode (active component) from Agilent ADS and then simulate in COMSOL.

I have one microstrip coupler which is connected with diode. i want to import Diode s-parameter in COMSOL and then want to see response
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How to Couple Free and Porous Media Flow with Heat Transfer In Solids

March 11, 2012, 4:01 pm
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Hi Everyone,

I am new to COMSOL and I am trying to simulate a solar panel cooling system. I am trying to simulate in 2D the heat transfer between a thin rectangular layer (the photovoltaic cell), another thin rectangular layer (thermal paste), and finally a porous layer through which water is flowing. Ultimately, I want specify a heat flux and initial temperature on the top layer (PV cell) and obtain the heat removed and temperature change achieved by using the porous media as a heat sink. I can couple the heat transfer between the 2 solid layers easily, however, I am having trouble simulating the heat transfer between all three layers (i.e. PV cell, thermal paste, and porous media).

Currently, I am using the following physics packages:

"Free and Porous Media Flow" - Models water flow through porous media
"Heat Transfer in Porous Media" - Models heat transfer in porous media layer
"Heat Transfer in Solids" - Models heat transfer in top two layers

My problem is that I can't get the top layers to "talk to" the porous media layer.

Any help would be greatly appreciated.

Thank you,
Brad
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Laminar flow without outlet (mixing with sliding wall) does not find solution

June 6, 2014, 6:39 am
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Hey,

I have been trying to simulate a system where a sliding wall is causing convection in a closed box.

In brief, the system is a box with one wall sliding at a rate of 0.01 m/s. The other walls are No slip.

The solver seems to solve the problem quite fine, and the result looks reasonable. However, I get the following error message:

Failed to find a solution.
Maximum number of Newton iterations reached.
There was an error message from the linear solver.
The relative error (4e+002) is greater than the relative tolerance.
Returned solution is not converged.

The Solver log looks like this:

============================================================
Number of vertex elements: 4
Number of boundary elements: 462
Number of elements: 10532
Minimum element quality: 0.8176
Number of vertex elements: 4
Minimum element quality: 0.1194
Stationary Solver 1 in Solver 1 started at 6-juin-2014 17:26:14.
Nonlinear solver
Number of degrees of freedom solved for: 19266.
Nonsymmetric matrix found.
Scales for dependent variables:
Pressure (comp2.p8): 0.27
Velocity field (comp2.u8): 1
Iter ErrEst Damping Stepsize #Res #Jac #Sol LinErr LinRes
1 0.034 0.0100000 0.034 2 1 2 0.053 1.2e-015
2 0.032 0.1000000 0.036 3 2 4 0.0055 3e-016
3 0.031 0.2297586 0.038 4 3 6 0.0031 2.4e-016
4 0.035 0.3012911 0.047 5 4 8 0.0029 3.2e-016
5 0.026 0.5186614 0.047 6 5 10 0.0054 5.1e-016
6 0.0033 1.0000000 0.033 7 6 12 0.025 4.4e-014
7 0.00033 1.0000000 0.0037 8 7 14 0.54 1.7e-012
8 9.7e-006 1.0000000 0.00035 9 8 16 9.2 1.6e-011
9 9.2e-007 1.0000000 1e-005 10 9 18 1.8e+002 3.3e-010
10 1.1e-007 1.0000000 7e-007 11 10 20 4.2e+002 9e-010
11 3.3e-007 0.7500000 1.4e-007 20 11 30 3.9e+002 8.1e-009
12 2.3e-007 0.1128516 3.5e-007 23 12 34 3.9e+002 5.8e-009
13 2.6e-007 0.7500000 2.3e-007 32 13 44 4e+002 2e-008
14 2e-007 0.0049796 2.7e-007 37 14 50 4e+002 1.5e-008
15 3.5e-007 0.7500000 2e-007 44 15 58 4e+002 7.6e-008
16 3.5e-007 1.0000000 3.7e-007 45 16 60 4e+002 5.6e-007
17 2.1e-007 0.0798715 3.7e-007 48 17 64 4e+002 3.4e-007
18 1.3e-007 0.2229211 2.2e-007 50 18 67 4e+002 2.5e-007
19 4.7e-007 0.7500000 1.3e-007 59 19 77 4e+002 2.6e-006
20 2.3e-007 0.1053436 4.9e-007 60 20 79 4e+002 1.3e-006
21 1.2e-007 0.0112598 2.4e-007 62 21 82 4e+002 6.6e-007
22 5.6e-007 0.7500000 1.2e-007 70 22 91 4e+002 8.8e-006
23 3.6e-007 1.0000000 5.9e-007 71 23 93 4e+002 4e-005
24 3.3e-007 0.7500000 3.6e-007 80 24 103 4e+002 0.00011
25 2.7e-007 0.0751680 3.5e-007 83 25 107 4e+002 8.9e-005
Stationary Solver 1 in Solver 1: Solution time: 20 s
Physical memory: 1.18 GB
Virtual memory: 1.23 GB

So for some reason ErrEst goes down but LinErr goes up.

Is this just a problem of COMSOL even though the solution is reached, and more importantly, can I trust the result?

Thanks for any comments and suggestions!

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Drop Test Simulation

June 22, 2014, 7:44 pm
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Hello,

I am a Mechanical Engineering graduate student and I wish to simulate drop test of a human head form.

I have a few questions which I have enlisted below:
Can this kind of explicit dynamic simulation be carried out in COMSOL?
Which package supports this kind of simulation?
Is any specific license (Research/Academic, etc.) required?
Can we import a meshed geometry (model is meshed in Hypermesh) directly into COMSOL for analysis?

It would be of a great help if anybody could guide me on these.

Thanks,
Chandrika
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I wonder why the result is changed?

June 23, 2014, 12:20 am
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Hello. I have a problem.
I simulate lots of time with same geometry and same condition.
But when i open new Comsol and set same way before, but the result from new one is
different from previous one.

I don't understand how to do that?
I didn't change all of conditions. such as mesh and boundary and so on.
But i got another result...
I'm very confused...
What happen to this simulation?...

If you have same problem and resolve or know the reason, let me know please...

Best regards

Jihwan
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Fluid flow in a heated flux media porous

June 23, 2014, 2:43 am
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Hello,

I pretend to built a model where I simulate the heat transfer to air flow through a porous media (in a channel with an inlet and outlet).
My fluid is the air and the porous structure is the SiC.

I stablished the following physics and boundary conditions:
- Brinkman equation: all structure
fluid and flow matrix properties: all structure and properties from the material
wall: no slip, u=0
inlet: velocity u=0,03 m/s
outlet: pressure without viscous stress, p=0,01 Pa

- Heat transfer in solids: porous structure (outer channel)
heat transfer in solids: properties from material (SiC)
thermal insulation: outside surfaces
initial values: 800°C (outer channel)
surface to surface radiation: emissivity 0,4; Tamb=20°C (describes the absorbed radiation on the front boundary of the structure)

- Heat transfer in Fluids: inner channel (air area)
heat transfer in fluids: properties from the material
thermal insulation: no tehrmal insulation
initial values: temperature=20°C (inner channel)
temperature : inlet T=100°C
outflow: outlet, convective flow
temperature: on the boundary cup-air T=800°C

After compute, an error appears:

"Failed to find a solution.
In segregated group 1:
Divergence of the linear iterations.
There was an error message from the linear solver.
Very ill-conditioned preconditioner.
The relative residual is more than 1000 times larger than the relative tolerance.
Returned solution is not converged.
- Feature: Stationary Solver 1 (sol1/s1)"

Please could you give any tipp or advice about what I should do?

I hope you can help me.
Thank you very much,

Ana

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Surface Reactions in a Biosensor (model ID: 10428) Failed to evaluate jacobian

June 23, 2014, 11:49 am
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I'm following the model instructions exactly but getting this error:
Failed to evaluate variable Jacobian.
- Variable: chsr.theta_i_cs_P
- Geometry: 1
- Boundary: 12 13 19 20

Please advise.
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model coupling between different dimensions

June 23, 2014, 11:51 am
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Hi everyone,

I am trying to do a coupling between a 1D component and a 2D component. What I am trying to do is I solve a 1D transport equation. At one boundary (point), I want to evaluate the flux. The I want to put this flux as a boundary condition to one of the boundaries of my 2D model (hence a line). It sounds trivial and I tried to use a component coupling feature (such as a general extrusion) to do it. But all my efforts seem to be in vain as COMSOL complains about unable to evaluate the mapping between a point and a line.

Does someone know how to do it conveniently in COMSOL? Any hint would be very much appreciated.

Sincerely,
Mao
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general question about mass fractions/transport

June 23, 2014, 11:54 am
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I have a basic question,
I have two reactors in contact with each other, both starting with the same initial conditions (equal amounts);
compound#1: solvent
Compund#2: A
compound#3: B
while in one of the reactors A is going to B and vice versa in the other reactor. I would assume that when I run the simulation, compounds A & B would diffuse ( the only physics added to the model being diffusion, no convection) and eventually reach a steady state. but when I run the simulation I get a negative mass fraction. how is that even possible?
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about 'undefined value found'

June 24, 2014, 10:57 am
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I was running a coupled laminar flow and species transport model perfectly fine. But after I scaled the geometry to be isotropically 10 times larger, COMSOL came up with error 'undefined value found'.

I searched the forum, but the solver management which seems to solve the problem before has changed a lot.

Anyone can help?
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How accurate is Comsol compared to FDTD

June 25, 2014, 5:33 am
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Hi:
I am a comsol user. My supervisor asked me to re simulate a design that was done in FDTD using Comsol.
The problem I got is that my solution was not the same as the FDTD solution!!. I am sure I have no error but I have to check with you (comsol community) in case someone can help me figure out what is going on.
I solved for RF (MODE ANALYSIS) and the effective index I got was 3.81. However, the FDTD solution was 3.88.
The shape of the mode I got with Comsol is clearly different from the one done with FDTD.

Any help?. Should I give you the two files to see them?
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