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Bio-heat Transfer

May 16, 2016, 12:44 pm
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Hi,
As per I know, in Comsol Multiphysics The fraction of necrotic tissue is expressed as θ = 1 – exp(–α).[Application ID: 497].
For my ongoing research I need authentic reference of this Expression.
Can anyone there to help me in this case.
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COMPUTING THE STIFFNESS CONSTANT OF A BEAM

May 16, 2016, 10:04 pm
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I want to compute the stiffness constant of the J-shaped beam using comsol. I have the young's modulus and the density of the beam but I want the stiffness constant. Hope to hear from you soon. Thank you..
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simulating intensity modulated point source

March 16, 2010, 7:54 am
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Hi,
I am working on a project on Diffuse Optical Tomography. We are using COMSOL to simulate lasers irradiating a biological tissue with certain vales of scattering and absorption coefficients. Till now, we had used a constant point source by putting 'u_test' in the weak coefficient of point settings. But now, we want to modulate the intensity(or amplitude) of this point source sinusoidally. I am not able to find any ideas anywhere. Please Help, very urgent.
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constraining the range of dependent variables

December 5, 2012, 8:19 pm
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Hello,

I have implemented an axisymmetric drift-diffusion equation using the equation-based modeling interface in COMSOL 4.3 (incorporating the necessary terms due to the curvilinear coordinates). I have attached a movie of the resulting density profile over time. I am using zero flux boundary conditions. I was wondering if there is a way to define a range (specifically a maximum) for the dependent variable (number density here) so that the peak remains less than a certain value.

Thank you,

Best,
Aryan
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Thin Thermally Resistive Layer on top of Boundary Heat Source

June 3, 2013, 7:17 am
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Hello everybody,


I want to simulate a flat mikroheater on top of a foil that is covered by a liquid. Since the foil has a thickness of about 100µm and the liquid covering the heater has a height of 1mm, the heater's height of about 0,5µm is almost negligible. Additionally the heater is covered with a thin passivation layer with 5µm thickness.

To simulate the temperature increase of the heater I wanted to use "Boundary Heat Source" with a defined "Total boundary power". On top of it I wanted to use a "Thin thermally resistive Layer", but I did not find out how to defne two layers on top of each other.

Is there any possibility to do so?


Many thanks in advance


Bastian
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Coupling heat transfer with an ODE

August 17, 2015, 9:52 pm
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Hi all,

I am working on a problem that involves solving temperature (T)- and a new dimensionless variable called conversion (alpha). These variables need to be solved simultaneously, since T=f(alpha) and alpha=f(T). Here is the ODE for alpha:

dalpha/dt=C*exp(B/T)(1-alpha)

where A,B are constants and T is the Temperature; alpha on the other hand is dimensionless. I used the heat transfer module and I inserted alpha using the global ODE module. My problem is that when I define the new variable alpha as a function of T, COMSOL does not recognize T, and I get the following error:

Undefined variable.
- Variable: comp1.T
- Global scope:
Failed to evaluate expression.
- Expression: comp1.T
- Feature: Time-Dependent Solver 1 (sol1/t1)

Any thoughts on how to couple an ODE that defines a new variable with a variable already defined in COMSOL, in this case Temperature=T. I have attached a simplified version of my problem.

Thank you
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Frequency sweep

April 15, 2016, 8:06 am
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"Hello there

I use HFSS most of the times for frequency sweep and plotting S11 over a range of frequencies to monitor the performance of the antenna and it seems pretty straight forward.

Now in COMSOL I have been trying to frequency sweep it through Frequency-Stationary Study and it takes ages to solve the problem and returns with the following error:

Failed to find a solution.
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.

Considering how simple this operation is, I am missing out on something. Is there any better way to find and plot the S11 against Frequency range?

Can somebody please suggest an alternative or the best way to achieve this?

Cheers
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inertial focusing in microfluidic channel

May 11, 2016, 10:34 pm
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Firstly，I want to modeling inertial focusing in straight and curved microfluidic channels（may the channel geometry seems like more complicated ）,just like
cn.comsol.com/story/download/1...85/Veryst_Mass_Gen_CN2013.pdf;
here is my model scheme:
1、sovle a CFD probelm(steady) without the particle;
2、calculate the force act on the particle induced by the “stress tensor and pressure ”,just like
www.chem.mtu.edu/~fmorriso/cm3...esonSurfacesinComsol5_2015.pdf
(I know there have “drag force” “lift force”etc.,but I CAN NOT find an explict formula of lift force suited complicated channel)
Lift Force(x)=sphint(r,spf.T_stressx); Lift Force(y)=sphint(r,spf.T_stressy);
The sphint(r, expr) operator computes the surface integral of the expression expr on the surface with radius r around the point in which it is evaluated.;r is the radius of the particle.
3、model particle tracing for fluid flow ,and "Force_x" =lift force(x),"Force_y"=lift force(y)

But the force seems like have influence to the particle, as "the particle inserted at a specific location in the straight channel remian at that location"

So， can anyone give some advises？
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modeling a 3d electromagnet in a stationary study

May 17, 2016, 7:38 am
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Hey i am having som trouble.

it is giving me this error:
and i can't figure out why!
i tried to use and modify the "Multi_Turn Coil Winding around a Rectangular Ferromagnet cleared.mph" to help me make it. i modified the size and use it in a stationary rather than frequency domain so it fits my needs. but i can't seem to compute it.

im new in comsol, so it might just be a brain fart.

the error i get is:
Division by zero.
- Function: /
Failed to evaluate variable.
- Variable: comp1.mf.Jey
- Defined as: ((comp1.mf.ICoil_1*comp1.mf.mtcd1.eCoily)*N)/comp1.mf.mtcd1.area
Failed to evaluate variable.
- Variable: comp1.mf.Jy
- Defined as: comp1.mf.Jiy+comp1.mf.Jey
Failed to evaluate expression.
- Expression: d((comp1.mf.d*(-comp1.mf.Hx*comp1.mf.testcurlAx-comp1.mf.Hy*comp1.mf.testcurlAy-comp1.mf.Hz*comp1.mf.testcurlAz+comp1.mf.Jx*test(comp1.mf.Adepx)+comp1.mf.Jy*test(comp1.mf.Adepy)+comp1.mf.Jz*test(comp1.mf.Adepz)))*(dvol),{test@24})

the file is to large to upload it here. so i put it in my google drive at:
drive.google.com/open?id=0B52pVuxc2-oFU1FDNnZXV19aTms

thank you in advance.
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Large Virtual Memory after Derived Value Calculation

May 17, 2016, 8:04 am
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Hello,

I've recently been calculating some surface integrals over a wide range of parameters. I have successfully run a parametric solution with 21x4 parameter combinations, and now I'm trying to calculate a few different surface integrals for each parameter combo.

Fortunately, the surface integrals only yield a single value, so after all is set and done, I should only be generating a few kilobytes worth of table data.

Here's the problem- COMSOL seems to be stacking up more and more virtual memory as it goes along. I made it through about 80% of my surface integrals before my computer ran out of virtual memory on the hard drive at 45 GB.

So how can I get COMSOL to clear out that 45 GB? Sometimes I've noticed that if I ask COMSOL to do another calculation, sometimes it reclaims the VM. So I did a dummy study but it only dropped to 40 GB. Is there a node I can delete to reclaim this memory? I've already saved all 24kb of the table output that was successfully generated.
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How to set a max and min to the main variable in General form PDE

May 17, 2016, 1:19 pm
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Hi,
I really need somebody help me. How can I set a max and min value to the main variable in General form PDE?

Thanks,
Arezoo
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water flow and heat transfer

May 17, 2016, 4:47 pm
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Hi,

There are some error in my model? someone can help me to check it, please?

It is a coupled heat transfer and water flow model.

Please see attachment.

Thanks.
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COMSOL JAVA API to Control Camera

May 18, 2016, 12:10 am
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Hi,

I am using COMSOL 4.4 JAVA API to export a series of group plots images. However, the model is ugly aligned in the output image. I am wondering is there any way to control the camera attributions using JAVA API?
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Flow Separation in fluid flow around a sphere

May 18, 2016, 2:37 am
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I am new to COMSOL MULTIPHYSICS. I want to find out at which Reynolds number the flow separation starts in laminar flow.How can I exactly find the point of separation ?
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Dye sensitized solar cell (DSSC) simulation

June 25, 2012, 8:09 am
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I want to simulate the electrical behavior of a DSSC.

This kind of solar cell is made in a sandwich like structure.

First of all, there is a FTO glass like electrode. On this glass it is deposed a TiO2 layer, a dye layer is adsoberd on the TiO2, a liquid electrolyte is in contact with these two layers, and at the end a counter electrode close the system. The counter electrode is a platinized FTO glass.

I would like someone tell me how to start the model and how to register the electrical parameters (voltage and current).
What model do I have to use?

Thank you.
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Strange boundary artifacts for two phase level set model

January 20, 2015, 3:30 pm
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I built a model to investigate the case that viscous fluid from a pipe deforms on a horizontal surface. In the 2D axisymmetric model modified from the level set nozzle inkjet model, viscous fluid from a pipe enters a large cylinder which was all air. The inlet fluid velocity has a parabolic profile. The right vertical boundary is an outlet with constant pressure, and other boundaries are no slip walls. I attached two plots, where the red region is the fluid, and the blue region is air. The fluid puddle evolves fine, but at the right boundary, strange artifacts develop at later time, and will be more serious as time goes. I want to know how I can eliminate this artifact. I tried fixed mesh and adaptive mesh, but it does not help. Thanks.
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Electrostatic and transport of diluted species coupling to an IPMC sensor model

June 14, 2015, 10:34 pm
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Dear community,

I am trying to build a simulation of an Ionic Polymer Metal Composite (IPMC) strip sensor, a thin membrane of polymer ionic on witch too thin gold electrodes are plated. It is a 2D time depending model, which output the difference in potential among the surface according to the force applied on its tip.

I already sucdeed (I think, the result looks consistent) to calculate the concentration of cation inside the sample, coupling the solid mechanic module and the transport of diluted species (tds) interface. Now using this concentration, I would like to know the difference in potential coupling the tds and the electrostatics interface (es).
For that I added to the es a surface charge condition in the entire domain:
rho = -z_cation*e*NA_const*C_cation+z_a*e*NA_const*C_0
Where C_0 is the initial concentration, anion being fixed, C_cation the concentration in cation from the tds and Z_cation and Z_anion the valence of cation and anion respectively.
I also added a surface charge density condition on the electrode, because I assume the ipmc strip works as a diffuse double layer:
rho= -epsilon0_const*deltaV/lambdaS
Where deltaV is the difference in potential between the metal phase and the stern compact Layer and lambdaS the Stern layer thickness.

At this point my problem is the following:
The model doesn't compute, "Failed to find consistent initial value, last time step is not converged". I have ever had a look at some other model from this forum and the COMSOL model Gallery (most of time the output is the ionic concentration according an input voltage using the Nerst-Planck and Poisson equations). I would like to do the reverse and I think I could use those equations, couldn’t I? I can't find the problem.
I am a beginner in COMSOL and in electrochemistry so maybe I don’t use these equations correctly. If someone could somehow give me some food for thought...

Thank you very much for any help.

Marie
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API java class error

June 30, 2015, 5:17 am
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Dear COMSOL,

I am coupling a COMSOL heat transport model with the universal parameter estimation software PEST in Windows. I realize there is an optimization module for COMSOL but it's performance is far superseded by PEST. To achieve the coupling I need the model to read an input file with parameter values (that PEST can modify prior to the model being run) and to write state variables to an output file (for PEST to calculate the objective function and its derivatives). Also, I need to be able to trigger a model run, with the API modifications, from the command line.
To the best of my knowledge, the coupling must be done by the COMSOL API. I have experience with the FEFLOW and Minecraft APIs which are both easy to use, in particular the former. Unexpectedly, I am struggling a lot with the COMSOL API.
Here is what I have done so far:
I have exported the cylinder_conduction example model to a java file and compiled it with Eclipse as a sort of proof of concept (the feeder_clamp model is nowhere to be found). The code runs perfectly in Eclipse and makes a connection to the COMSOL server that I have set up (which can be checked in the server log). I use the server connection to check that the model code is actually being run.
However, loading the class file directly into COMSOL produces an error:

Error running Java Class
-Detail: Error_running_java_class

If I run the class file from the command line I receive an identical error. I have included the installation paths of the jdk and the COMSOL home directory in the Windows path variable.

On a sidenote: If I use the standalone option (ModelUtil.initStandalone(true)) as suggested in the API reference, I get the following error: "Input length must be multiple of 16 when decrypting with padded cipher".

I am at my wits end here. I can run the code in Eclipse which is some sort of workaround because I can trigger it from the command line but it is definitely not an optimal way of implementing the API module. Can anyone help me here?

Best regards,
Søren

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Problem with Automatic Remeshing / MUMPS allocation factor increased to 1.44.

January 14, 2016, 5:41 pm
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Hi there,

I have built a COMSOL 2D model that uses deformed geometry, where the geometry movement is non uniform. I need to use Automatic Remeshing to update the mesh elements. But after some time (t = 0.29s) it fails.
I tried using moving mesh, mesh refinement as well as segregated solver, but I am unable to get rid of this error. I need to know why this error keeps popping up, and whether there is something that I am missing.
I have given the error, as well as the warning below, and also attached the wireframe and surface plots of the concentration before the error.

Any help would be appreciated.
Thanks.

Warning:
MUMPS allocation factor increased to 1.44.

Error:
The following feature has encountered a problem:
Nonlinear solver did not converge.
In Segregated Step 1
:
Time : 0.2924214449879353
Segregated Step 1
Singular_matrix

There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 14 comp1.cH_1p
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...
There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 14 comp1.cOH_1m
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...
There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 10 comp1.npe.Ceq_eqreac1
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...


Last time step is not converged.
- Feature: Automatic Remeshing 1 (sol1/t1/ar1)
- Feature: Time-Dependent Solver 1 (sol1/t1)
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SAR plots of the brain, No results

February 11, 2016, 1:27 pm
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Hi all,

I was going through the tutorial for Absorbed radiation (SAR) in human brain

www.comsol.com/model/absorbed-...on-sar-in-the-human-brain-2190

I am not sure if anyone else tried this one but I am struggling to gather results for both the SAR distribution and heating. The only change I did to the model and the instructions provided in the link above was the lumped port setup as suggested by Edgar here:

www.comsol.com/community/forums/general/thread/20391/

I have attached the project file (not computed version as it was too big to attach) and the pictures of the results which show no interaction with the study. It seems that I am missing out on something. Can anyone suggest some pathway on this please?

Thanks very much


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