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Iteration Plot - Vanished

August 4, 2014, 11:52 am
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Hello,

Has anyone any idea how to recall the iteration plot? I mistakenly pressed closed and I can now not find it anywhere. I am using COMSOL 4.4

Thanks,
Andi
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Updating COMSOL variables at each time step

August 4, 2014, 3:44 pm
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Hi all,

I am trying to solve a model which requires updating a variable (something like a boundary condition) based on the solution at each TIME STEP. I am planning to use MATLAB LiveLink on order to have a control over COMSOL model solution as it progresses in time. I know there is a function to run the study node (something like Model.sol('xxx').run('xxx')); but it does not work for me, as it starts to solve the whole study. I want to have control over time stepping.

A brief description of what is going to happen in my model is as follows:
1. set initial/boundary conditions and start to solve the model
2. advance one time step
3. evaluate some predefined expression (specifically, a line integral of a solution variable)
4. check if this line integral has the value that you expect (e.g. we want it to be equal to 2)
5. if yes, then advance one time step. If not, do this time step again with updated boundary condition (until criteria are satisfied) and then advance in time.

Thanks!
Ali
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Failed to generate mesh for domain

August 4, 2014, 11:18 pm
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Hi,

I was trying to simulate an object moving in a fluid, the model went well at first. However, when a corner of the object hit the wall, an error occurred, saying

"Failed to build feature 'Couches Limites 1' in sequence 'Mesh 1'.
Failed to generate mesh for domain.
- Domain: 1
Failed to insert point.
- x-coordinate: 1.24959
- y-coordinate: 0
A degenerated triangle was created."

The attached image shows the case. Does anybody know how to fix that? Any help would be appreciated.


Thanks,
Tianhang
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How to export the mesh nodal reaction forces?

August 4, 2014, 11:27 pm
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Hi everyone,

I'm using the comsol to solve the petroleum geomechanical problem. Now I want to use the mesh nodal reaction forces to balance the initial stress. but I don't know how to restrain the mesh nodals and then get the mesh nodals reaction forces value and put in the other model with the same mesh and different boundary conditions.

I give an alternative solution in Modal Exchange（www.cn.comsol.com/community/exchange/243/）, May be through this file you will more clear understand what the problem I meet.

can anyone know how to do this?

Many thanks

Yellow
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ion creation rate does not fit ion outflow in stationary state

August 5, 2014, 1:04 am
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Hej,

I am computing a model with the DC discharge interface. I have a constant Tritium density (background gas). The tritium is decaying to T+ and e-. (There is also recobination). To verify then calculations I tested the continuity equation and if the outgoing ion (electron) current density equals the integral of the generated ions (electrons). I have done this test with convection (flow of the background gas) and without. For electrons in both cases continuity equation as well as outflow equals creation rate is fine. Without convection this is also the case for ions. However implementing convection I have a much to high ion outflow current density (ca. 6.5e-5 A/m^2) compared to the resulting created current density (ca. 1e-5 A/m ^2) althought this is a stationary state...
So it seems there are additional ions created or something like that...
I attached the 1D model of the problem.

I hope somebody can help me.

Thanks
Laura
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regarding laser heating

August 5, 2014, 1:47 am
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hello sir
im also simulating laser heating . i need some help from you sir. can i get your mail id so that we can discuss
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regarding laser surface melting

August 5, 2014, 2:15 am
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Respected sir

This is uma research scholar for national institute of technology warangal india. as part of my work i would like to do laser surface melting simulation. for that i need some some help for you. I had modelled and simulated one model. sir the problem what i'm facing is that i'm not able to find how much metal is melting and temperatures across the solid part. i would like to know the the melt depth and the temperature across the the solid. sir if u give your mail id i will forward the model file

i request you to help and give suggestion in this regard . i will be very great ful for the help sir

thank you
your sincerly
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Eigenvalues from different study steps

July 25, 2014, 5:36 am
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Hi everyone,

I am trying to calculate an overlap integral between two modes of different origin -- a common problem of electrooptics or optomechanics. So I have two physics interfaces (say electromagnetic and structural mechanics) and I need to solve them and compute overlap integrals between all modes.

If I use two distinct studies (one for electric eigenvalues and other for mechanic eigenvalues) I get two different solutions (data sets) that cannot be brought together.
If I use two study steps in one study I again get two data sets. Though the first one has one of the modes of first problem, it looks like there is only one of them. I tried to use the with() operator but I still can't address to other modes.

Is there any way to do the thing?
Thanks.
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I have a question on simulation magnetic field

August 5, 2014, 9:57 pm
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hi everyone,
I am recently using this software and I want to simulate a magnetic field around 200-turn coil with different core
shapes. but there is always an internal error 900 I did with all kinds of mesh normal ,...but this error appears.
in the simplest way I want to simulate just a 200-turn coil without core. but that error still appears.
please help me what I should do to simulate magnetic field around coils with different core shapes.
best regards
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Traction does not converge

August 6, 2014, 1:40 am
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Hallo everyone,

I'm trying to model thermal stress in a glas plate caused by a solder drop with a initial temperature. The problem is that the traction does not converge with finer mesh, it gets bigger and bigger after refining the mesh.
I'm doing a time dependant, 2D axissymmetric study.

I would appreciate your help.
Thanks

Max
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Two Phase Flow and Mass Transfer

August 6, 2014, 8:21 am
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Hi,
I was reading one of your answer in COMSOL forum about adjusting phase field variable to see diffusion effect. i have a similar problem and appreciate if you can help with this issue.
I am trying to simulate evaporation of a water film when air is passing over its surface. I am using Laminar Two-Phase Flow, Phase Field(tpf) physics coupled with Transport of Diluted Species(chds). I expect to see the interface movement due to evaporation of water. the only coupling which is available in comsol is the velocity. but interface is also changing with mass exchange. is there any way to change the phase field variable to see effect of diffusion?

thanks in advance,
Rohaldin
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using results from electrostatics module in ODE solver

August 6, 2014, 10:57 am
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I need to integrate two ODEs, in which some of the coefficients depend on spatial derivatives (at one point, at each time step) of an electric field computed using the electrostatics module.

Can someone either tell me how to do this, or refer me to appropriate COMSOL documentation.
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Drag Force on a sand particle

August 6, 2014, 12:10 pm
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Hi,
I’m currently simulating a sand particle flowing within oil in a pipe. I’m required to find the drag force acting on the sand particle during its flow.

With the laminar flow:
To find Total Force: I did a surface integration over the sand particle by choosing it’s boundaries and then for the expression I chose total stress (spf.T_stressx) but this gave me very small values.

I also tried using particle evaluation from the derived values and inserting the drag force, x component, from the particle tracing expressions but it just gave me zero.

Is it best to model only the fluid in the pipe then use the particle tracing to find forces on the sand particle or do I draw the particle as a sphere within the pipe and compute the study? I did both but I can’t seem to work it out.
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Hi

July 26, 2014, 8:26 pm
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I modeled a geometry in matlab, can any one tell me how to import that geometry to comsol
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Condense 3D to 2D temperature field (maximum values)

August 5, 2014, 10:02 pm
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Hi,
I want to find maximal values of a 3D temperature field in a certain direction (condense 3D information to 2D plot).
I managed to integrate (with "General Projection 1" definition) temperature values in the x-direction so that I get a y,z-surface plot with the integrated temperature along one axis. Instead of an integration, I now want to find the maximal values along the x-direction and plot them as a 2D y,z-surface plot. How can I do that?
You can find the mph file of the problem attach.

Best regards and thanks for any help,
Jörg
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4.3b, AC/DC, Material Problem. Different Results on 2 Computer.

August 7, 2014, 2:47 am
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Hello everyone,

iam new to Comsol and iam having some Problems. For my Bachelors Thesis iam looking into the resistivity of Concrete.

I createt a Cone in version 4.3b that exists of Concrete with two electrodes of Steel at the bottom and top.
I also created the exact same Cone in Verion 4.4.

Iam using Surface Average and Volume Integration to get the Current Density and Current. While using V4.4 iam getting the right results. Checked this with hand calculations.
While using comsol 4.3b iam getting really weird results. Very different from what the results should be like.
I made sure both Models wehere created the same.

After this i changed te concrete to Titanium just to see what happens. Again i let Comsol calculate Current Density and Current. Both V4.4 and V4.3b show the same results. Like its supposed to.... i guess.


I suspect the Material Concrete to be the Probleme. I checked all Material Propertys but i could not find any difference.

I would be really nice if someone of you could help me out.

I can post the files here if needed!


Thank you!
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My first PDE

August 7, 2014, 6:16 am
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Hi , we are two undergraduates students who are trying to solve a system of five PDE's in COMSOL.
We have been able to do this in MATLAB but are unable to achieve this in COMSOL. To start of we tried to implement a simple diffusion PDE using the coefficient PDE solver. We have troubles simulating our system. Can someone explain why?
SPECIFICS
-Geometry: 100 mm^2
-Coefficients: C = 4.9*10^-6, da = -1, all other 0.
-intial value: 1*10^7
- boundary: Dirchlets r = 0 for all
- normal mesh, fine
Then we used the study tool (time dependent) and solved for time (0,1,10).
Error: "Differential-algebraic equation encountered. Use Singular mass matrix = Yes.."
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Shaking model to find velocity

August 7, 2014, 12:56 pm
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I want to simulate shaking of my model at different frequencies and find the velocity of the water particles inside the model.

What physics or study or condition can be used to do this?

Thanks for any help!!
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How to calculate photonic band gap, transmission and reflection spectra?

April 10, 2013, 12:54 pm
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We want to get photonic band gap, transmission and reflection spectra of 1D or 2D PC.

Could you help me how can I obtain band gap and Transmission/Reflection spectra of 1D or 2D photonic crystal? Or could you send me instruction about how can I get this?

Thank you for your help
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Regarding floating potential

June 25, 2014, 6:55 am
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Hello,

I came across a reply from you on a post about floating potential. I needed some help if you don't mind.

I made a time-dependent model that has some time varying sources and a medium and a conductor. The sphere conductor in my medium has a floating potential. The problem as you mentioned is that I don't know that potential. So when I set the dirichlet boundary condition for my medium boundary, the potential is unknown. I have two specific questions in this regard:

1) how can I ask comsol to solve for this unknown potential (lets call it Ve)? whats the best way to define the equation for Ve since its not a field variable.

2) whats the best way to impose the zero charge boundary condition on my medium (boundary with conductor)? Currently I define an integral (nx*ux + ny*uy + nz*uz) and set it to be zero in Global Equations but it gives me Singular Matrix error.

I appreciate it.

Farhad
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