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Optimization of Heat Transfer Parameters using Experimental Data

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Hi there,

I have 6 years of actual temperature data gathered from instrument probes placed within a landfill. There are 5 probes spaced out vertically within the landfill.

I am using a 1D time dependent COMSOL model to predict these landfill temperatures. I use Point Probe Expressions in order to track the temperature at these 5 locations. In the Heat Transfer in Solids physics, I specify factors such as initial temperature, ambient temperature, solar radiation, density, thermal conductivity, heat capacity, heat transfer coefficient, etc., to predict the temperature with time at 5 different locations along the 1D line (which represents a vertical column of the landfill). In the model, I use a best guess approach for specifying the heat capacity and the heat transfer coefficient (that is, I use values from literature because I do not have actual values for the heat capacity and heat transfer coefficient for the municipal solid waste in our landfill).

I would like to use the Optimization tool in order to help predict the heat capacity and heat transfer coefficient of the waste. I would like COMSOL to find the best fit values for heat capacity and heat transfer coefficients by minimizing the error between my actual temperature data, and the point probe expression temperature.

I have added a Global Least Squares Objective in and uploaded a comma separated file with my field data (column 1 = time, column 2 = temperature). However, I am having trouble with the rest. How do I specify that I want COMSOL to take the least squared error between my actual data and the point probe expression temperature? And how can I specify that I want it to do so by changing the variables for heat capacity and heat transfer coefficient?

Any suggestions would be greatly appreciated!

Courtney


cooling of welded bars

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Hi Guys,
I want to appreciate all who have made selfless sacrifices to upload tutorial materials on Comsol which have really helped me to learn the use of the software to this level.

How do I subject a heat transfer problem (Welding precisely) to cooling back to room temperature?
I have tried coupling heat transfer and fluid flow to no avail.

Please, kindly share with me possible solutions.

How to model ambient air for heat transfer

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Hi,

I am very new to using COMSOL. The first thing I am working on is a cylindrical metal wire encapsulated in a polymer jacket surround by ambient room temperature air. The metal wire is set to an initial temperature, and I want to model how quickly the polymer jacket heats up. But the polymer jacket is surrounded by room temperature air. How to I create an essentially infinite air surrounding this wire and jacket that will be acting as a cooling force that is moving convectively and not warming up like a solid. Right now I have an air boundary that is basically a cylinder twice the diameter of the polymer jacket and the outer boundary of the air cylinder is set as a boundary condition to be room temperature, but this is obviously not a real world scenario, and I'm not sure my assumption of the air cylinder being twice the diameter of the polymer jacket is a good assumption, as when I change it to 3 of 4 times the diameter I get pretty different results. I assume there is a very easy setting I'm not aware of to just surround this wire and jacket with air that is essentially supplying convective cooling.

Thanks,

Josh

Optimization RF Module

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Hi
I have a working model of an rf heating example and want to extend it as an optimization problem.
The model works well without optimization in which I want to maximize absorbed power that depends on only one dimension of the heated body geometry.
The absorbed power is evaluated as a derived result (ht.Qtot) in the original model. I tried to use it as an objection function in the Objective expression field but the solution goes on and on for hours and/or gives Out of Memory message, although the range of the chosen design parameter is very small and I using an i7 64-bit Laptop with 4 GHz RAM.
My questions are:
1. Can I use a derived solution directly as an objection function or need to redefine it as a global or local variable and how to define it?
2. which type of objective function is appropriate in this case Integral, probe ... etc.?
3. Is the given error message a genuine error or is due to the program going into empty endless loop?

Some one can HELP? A COMSOL3.3 model cannot to be used in COMSOL5.2 ?~~

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Hello everyone,
I 'm using COMSOL5.2 to simulate a project. Now I meet a problem.
My mentor is using a old version: COMSOL3.3. I want to use his model in my COMSOL5.2, but it says they are not compatible. I read the COMSOL help document and know that a COMSOL 3.5 can be imported into COMSOL5.2 but what if a COMSOL3.3 model?
Now I don't know how to solve the problem and I haven't found some documents about it. It really trouble me for a long time, so I think maybe some people here can help me with it.
Thanks for all of you in advance.
Dustin

How to use result data (temperature, concentration) as initial conditions and then re-run the simulation?

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Hi Everyone :)

I need to use the result of a simulation (the temperature and concentration result) as initial conditions and then re-run the simulation.

Basically I'm trying to input text files (.txt) as an initial value. I am currently modeling time dependent heat and mass transfer simultaneously and my model is working fine (2D geometry). What I would like to do is to

1. run the model for a certain time (600s)
2. export the temperature and concentration results as a text file,
3. Make changes to the (x,y) coordinates of the text file
4. Input the new temperature and concentration text file as initial value for another 600s simulation which contains the exact geometry and mesh

Could someone please help me on how to go about? I have been trying to achieve this for quite a long time now

Thank you

3D Schottky diode

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Hi,
I am working on 3D Schottky simulation using COMSOL 5.1, but I have a problem; every time I press compute to do the study, the following message appears:
"Invalid field variable in property Llimitfivar"
what can I do to solve this problem?
Thanks.

2D Axisymmetric Schottky diode

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Hi,
I am working on 2D axisymmetric Schottky simulation using COMSOL 5.1, but I have a problem with the results, after changing the doping concentration from n-type (donor doping concentration) to p-type (acceptor doping concentration), the J-V plot gave a non-rational result and the plot of y-axis was the same with or without log-scale which is too strange.

Do you have any idea about the reason? because I did this study before with no problems for n-type but when I change the doping to p-type too many errors appear.

Thanks.

Stuck in calculation of Force

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Hi,

I downloaded a model that "Permanent Magnet Application ID: 78" and it's reated by COMSOL engineers. They used a compose model to decrease the computational time of the whole system. When I change the symmetry axis of the model, I'm able to obtain almost same force on the rod according to symmetry ratio that I applied. However, when I remove out the "compose" property and analyze the whole system once again, the obtained force is non-stable depending on block size(air) of the model. The obtained force should have been around 6.11 N but it's changing in the range of 3-8.3 (N) according to analysis result. Thus, could you please tell me what the point i missed and how to solve. And also, could you share the solved problem for whole system not for (1/4 model) ?

All the best

"Add Study" button not working...

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Its blowing my mind. It was working 2 days ago, then I decided to make a new model. Now across ALL my COMSOL files, the "Add Study" button is not bringing up the menu when I clicking. This is the same for "Add Physics" and other such buttons.

Why is this happening please?

Thanks for help.

I'm running windows 10 64-bit if that means anything. Button/program was perfectly fine 2 days ago. Also, even when I make a brand new file, trying to add a study still doesn't work.

Did I accidentally delete the menu or something?

Magnetic field of current passing through a 2D sheet

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Hi all

I modeled a magnetic field of current passing through 2D sheet, the theoretical solution gives positive magnetic field on one side and negative magnetic field on the other side. Note that the magnetic field outside the sheet is constant, independent of the distance from the sheet.

I verified the magnetic field value by comsol however in comsol both sides of sheet magnetic field is positive ?!

can someone help me why magnetic field is positive on both side ? what is it missing here?

Regards
Abraham

Modelling Room Air Environment in COMSOL

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Hi Everyone,

I need to define a Room Air Environment in COMSOL, in which I need to measure a Air Pressure at a specific point on the object plane.

I am not sure how can I define the Physics for Air Environment, and how to measure a Air pressure or flow at a specific point, any help would be appreciated.

Thanks,

accoustic lens

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hi guys
i am just about to finish my degree and i am working on a project in which i am trying to acquire a acoustic image using accoustic len and a matrix of microphones.
now i am trying to run a simulation of the accoustic len in comsol and i would realy appriciate if someone can help me
thank you very much

Pyroelectric response

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I have a piezoelectric buzzer (material unknown but presumed to be PZT) I am testing as a possible low frequency pressure sensor. I have the buzzer connected to a charge amplifier I built to have a very large time constant. While this allows me to measure very low frequency pressure signals, the long time constant means that the pyroelectric effect is significant allowing use as a temperature sensor. I am however puzzled that an increase in temperature produces a signal with the opposite polarity of that produced by a compressive force. Since the d33 of PZT (and other piezo-ceramics) is positive, I would have expected both an increase in temperature and a compressive force to produce an output signal of the same polarity since both compressive forces and increases in temperature produce a reduction in the remanent polarisation in the poled piezoelectric. If anyone can help explain this anomaly I would be eternally grateful!

mems based capacitive type humidity sensor

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Hello
I am working on capacitive type humidity sensor in which I've to model diffusion of humidity in polymide layer that will change the permittivity of polymide hence changing the capacitance between electrodes in which polymide layer was sandwiched but I don't know which physics to use i'm new to comsol . I guess it's gonna be a complex structure so I decided to model diffusion in polymide first but again i don't know which physics to use and which material to use for humidity( should i use a material named "HumidAir" in COMSOL 4.3 ? would i be able to change it's parameters ?)

Thanks.

I am trying to model a perforated panel in impedance tube.

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Hello,

My name is Hwa Young, Song, I'm a Korea student in acoustics (from seoul national university of science and technology)

I am trying to model a perforated panel in impedance tube. (refer to attached file).
But i have the problems with the absorption coefficient(alpha) and reflection coefficient(R).

I have defined the variables in below
p_i : 1[Pa]*exp(-i*acpr.k*x)
p_r : p - p_i
R : p_r / p_i
alpha : 1-abs(R)^2

But my results don't look like as absorption coefficient

I also tried different variables and i still got different results..
Could someone check the correct variables?
and did someone tried something similar and help me?
I hope you will have time to answer and to help me to solve the problem.

Thanks in advance.

Why the same program sometime need 4000 secs and sometimes 300 secs

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May I ask if anyone know why the same comsol program sometime need 4000 secs and sometimes 300 secs to solve? Exactly the same one, I didn't change any parameters, mesh, solver, just run it

Curvature radius of thick plate

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Hello everyone. I would like to simulate tensile stress on some thick plates with different hardness under the same curvature radius. I'm using COMSOL 5.2a.
(Actually materials are the same, but patterning is different)

I could simulate under the same force so far, but could not under the same curvature radius.
I would like to bend plates one direction, I mean it is like surface of the cylinder, not like surface of the ball.

I hope somebody help me.
Thanks in advance for any help.

Default parameters from Modules

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Hiii all,

I need to know the way to figure out the available by default output values from different modules which can be used in COMSOL.

To make my statement clear, I am using the magnetic field no current interface and I saw from the code of my senior that he used the value of the field Hx and Hy for calculating magnetic volume force and in the variable section, called these Hx and Hy as mfnc.Hx and mfnc.Hy.

My query is how can I know that Hx and Hy is the output variable from this interface. Where can I see the possible outcomes of a particular module?? Similarly, for heat transfer module, how can I figure out the value of the parameters that I can call further in my code.

Thanks,
Subhasish
NTU Singapore

Doubt regarding default parameters in COMSOL

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Hiii all,

I need to know the way to figure out the available by default output values from different modules which can be used in COMSOL.

To make my statement clear, I am using the magnetic field no current interface and I saw from the code of my senior that he used the value of the field Hx and Hy for calculating magnetic volume force and in the variable section, called these Hx and Hy as mfnc.Hx and mfnc.Hy.

My query is how can I know that Hx and Hy is the output variable from this interface. Where can I see the possible outcomes of a particular module?? Similarly, for heat transfer module, how can I figure out the value of the parameters that I can call further in my code.

How to figure out the default parameters that we can get from different modules in COMSOL and call that later for defining another function?? - ResearchGate. Available from: www.researchgate.net/post/How_..._for_defining_another_function [accessed Jan 9, 2017].
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