Latest Discussions - COMSOL Forums

can extract such kind of coordinations to build the model?

Thu, 09 Feb 2012 01:25:20 +0000

Hi, everyone,

I’m building a heat transfer model, so the dependent variable is the temperature T. During the model, I want to obtain the location or coordination (x,y) where the temperature is equal to a specified value, for instance, T=3425[K]. I actually known the contour plot in the result node, and I can extract the data into a .txt file (contain the x,y coordination and the corresponding value of contour). However, as far as I known, the kind of process “postprocessing” can’t be used in the model automatically (am I wrong?).

what I want is
1. obtain the data of the contour (x,y coordination);
2. do some calculation with or without Matlab using the data of the contour;
3. return value(s) after the above-mentioned calculation to the COMSOL to continue the study.
The data of the contour is supervised and extracted at each time-step, and after the specified calculation, the resultant value is imported into the COMSOL though function or something similar.

Is there any accessible way to do this?
Thanks in advance for your advice and guidance.
Best wishes to you and your family.

Time-dependent problem-convergence issues

Wed, 08 Feb 2012 22:32:33 +0000

I am working on a time-dependent FSI problem. The problem converges well when I model the solid as a linear elastic material. However I end up with convergence issues and inverted mesh elements when I use a hyperelastic material model to represent the solid.

I am wondering if someone can explain why this is happening and how do I fix this?

Thanks,
Sirisha

Defining Geometry Domains

Wed, 08 Feb 2012 21:24:12 +0000

Hi,
I've made a closed loop with 4 different Bezier Polygon line segments. I'm able to select them as a group of boundaries but I can't find a way to define them as a domain to add later physics.
Thanks
LoongYi

Mesh question

Wed, 08 Feb 2012 18:13:27 +0000

I've been working with Comsol for a while now (currently we have version 4.2) and my mesh problem doesn't make sense to me. I'm simply trying to get a Gaussian Beam to travel in a box of air surrounded by PML. To do so, I have set up a port on the left side of the box and set up the equations accordingly (at least to my knowledge).

I have noticed that if I set my mesh size to "finer" or larger, I have no problem and the produced wavefronts look like what I would expect, but if my mesh gets any finer than that ("extra fine" or "extremely fine") I get a lot of stuff that doesn't resemble a gaussian beam.

Is there a such thing as a mesh that is too fine? That doesn't seem plausible to me, but it's happening here.

I'm also trying to attach my model to this board and getting an error "file extension error". Why is everything concerning Comsol so clunky :)?

Using stationary computational results as the initial condition for time-dependant solution

Wed, 08 Feb 2012 17:40:44 +0000

Hi, I'm kind of new to transient analysis in COMSOL and I have a few questions.

Is it possible to use the reults of a stationary study as the initial conditions for transient analysis?

For example, in my current model(using the joule heating and optimization module), I have system heating up to a steady state temperature through a defined current density and boundary heat source. I want to know how long it will take for all parts of the system to cool down to room temperature if the heater and current are turned off.

So far, I've tried introduce a stationary solver as step one, and then a time-dependant solver as step two. However, this just gives me a time dependant solution of the system heating up (not cooling down). I have also tried to use the "Store Solution 2" option in the solver configurations by
- right clicking on the "Store Solution" option and selecting "compute to selected"
- manually changing the heat source and current density to 0
- deleting the optimization solver
- selecting "use store solution 2" under solver configurations--> dependant variables 2 --> Initial values of variables solved for
- and finally right clicking on the "Store Solution" option and selecting "compute from selected"

But, this method just gave me a solution of everything at room temperature.

Can you please help me with this problem?

Identity Mapping question

Wed, 08 Feb 2012 13:33:35 +0000

Hi

In source and destination frames options of Identity mapping there is Mesh , Spatial, Material and Geometry.

What is the meaning of "Geometry" here?

thanks

David

Time-step dependent reaction rates

Wed, 08 Feb 2012 10:51:31 +0000

Hi,

Help me how to set a "time-step" dependent "reaction-rate constant" for a time-dependent solver.

Regards,

Attempting to find total drag force on an object

Wed, 08 Feb 2012 00:42:28 +0000

I'm fairly new to COMSOL and haven't been able to find any really detailed guides on how to go about this. I've currently got two problems that I can't figure out how to solve.

1) When I solve the simulation, I get an error reading:

"Cannot evaluate expression.
Failed to evaluate variable.
- Variable: mod1.fsi.mises
- Geometry: 1
- Boundary: 22
Failed to evaluate expression.
- Expression: mod1.fsi.mises
- Plot: surf1 (Surface)"

Boundary 22 is my inlet flow. I'm not sure how big of a deal this is because I don't believe I need the von mises stress for what I'm trying to solve for. What I'm trying to figure out is how to get...

2) The reaction forces. How can I find the forces on the solid part of my model? And how do I go about integrating them to find the total drag force?

Thanks a ton

How to calcualte capacitance between two parallel plates

Tue, 07 Feb 2012 23:37:19 +0000

I tried to calculate the capacitance between two parallel plates. I set one plate as floating and another as electrode with 5V. When I used global evaluation to calculate capacitance. It calculated the self capcaitance for the electrode. How can I caluclate the capacitance between this two plate.

Thanks

How to calculate/record peak value of T variable?

Tue, 07 Feb 2012 18:08:20 +0000

I have a Heat Transfer in Solids model. I would like to know the peak temperature (highest T during the model time) at each (x, y, z) location. Is it possible to add an equation, something like

Tpk = (T>Tpk) * (Tpk-T) + T

?

I tried a few items under Mathematics without any luck. What's the correct method to do it?

How to draw a block with rounded corner in geometry?

Mon, 06 Feb 2012 23:40:37 +0000

Hi All,

I am trying to draw a round corner cuboid in Comsol 4.2, it will be like a geometry between a cylinder and a block.

I saw somewhere saied "round the corner with fillet radius", but do not know how to actually make it. I tried making several cylinders and a block, and make boolean calculation, but it does not come out a satisfied result. Can anybody give me a way out, let me know the specific procedure of doing this?

Thanks!!

materials of a surface mesh element

Mon, 06 Feb 2012 17:05:20 +0000

Hi everyone ,
I’m looking for a possibility to distinguish the different materials that belong to a single surface-mash-element (for example: a triangle) in matlab? For better understanding - my problem in a second way. Starting from a model containing a single meshed surface. Each mesh-element is now between two materials. So how do I get knowledge about the two materials/groups/… the element is between?
Thanks for help!

animation vieweing from different reference frame

Mon, 06 Feb 2012 11:43:53 +0000

Hi.
I have used 2d spf cfd flow simulation. I have solved and found velocity of a moving wall BC. Is it possible to change this body-fitted movies/animations to view through other frame?
I mean I solved simulations from boat and I want to see the solution from water. Is that possible?
Thanks in advance
Siva

Thermal Resonators

Sun, 22 Jan 2012 22:40:41 +0000

Hi,

I'm looking to model thermal resonators using COMSOL. The structure basically needs to do the following couplings: Run a current through it, account for joule heating and therefore displacement. The stress due to the displacement leads to change in the conductivity and therefore the current, via piezoresistance.

I finally need to do eigenfrequency analysis on the structural resonance and also do transient analysis of the displacement.

Can anyone suggest which are the suitable physics' to add? I tried "Joule Heating and Thermal Expansion" but I'm unable to do the mechanical eigenfrequency analysis of my structure.

General questions about Transient Acoustics and Solid Interaction

Thu, 12 Jan 2012 11:09:27 +0000

Hello fellow Comsol users,

I would very much like to ask a few relatively simple questions regarding transient acoustic models with some regarding transient solid interaction.

In essence my models are looking at how a membrane found in animal ear's behaves to incoming sound pressure, I am only looking to model the membrane not the ear itself. As you can imagine the membranes are very thin (around 1um in thickness and 2000um in diameter). I am doing the models in 3D and am looking at how the membrane deforms in the presence of a sound pressure wave.

I have adapted the Gauss Pulse model to a 3D one. I am modelling the source of the sound as a point Gauss Pulse.

My questions?

1)
Is there a better way to model an incoming sound field? The problem is that I need to place the Gauss Pulse relatively far from the membrane such that the incoming wave has a relatively flat wave front as it comes into contact with the membrane. This however creates relatively large models.

Is there perhaps a plate that I could use as the source of the pulse?

2)
Does anyone know of any other models which I could look at? There are not that many models in Comsol that look at Acoustic-Solid interaction.

3)
Any thoughts or suggestions on how to make the model more efficient.

I have included an image of the model so make things a little clearer.

Thanks very much, I hope there is some discussion to build on the knowledge base on acoustics in Comsol.

Rob

Error: Failed to find a solution. Divergence of the linear iterations. Returned solution is not converged.

Mon, 28 Nov 2011 20:36:30 +0000

Hello All,

I am trying to simulate the inductance of a 10 turn solenoid.
The geometry was drawn using extrudes and revolves in COMSOL 4.2(didn't use the Helix primitive).
I used free tetrahedral mesh for the geometry.
The mesh doesn't show any error.
But when I try to solve the model I get the following message :

Failed to find a solution.
Divergence of the linear iterations.
Returned solution is not converged.

Any help regarding this will be highly appreciated.
Interestingly, when I reduce the radius of the solenoid to half, it solves without any error.

Regards
Hasan

Error in multiphysics compilation

Wed, 23 Nov 2011 06:27:21 +0000

I got error message "Error in multiphysics compilation"

I am working with Heat transfer in solid module.

Can you help?

Thanks

RF Mode Analysis Normalization Convention

Fri, 18 Nov 2011 20:34:08 +0000

Hi all,

This question is in regards to: RF Module > Electromagnetic Waves > Mode Analysis

Does anybody know the normalization convention that is used in the solutions? For example, part of the solution are surface plots of the electric field. The shape of the field distribution is dictated by the specific eigenvalue problem; however, the actual values given by COMSOL are quite arbitrary (i.e. you can always include a multiplicative constant with impunity). How then, does COMSOL determine what numbers to give in the solution for field components, power, etc.?

My first thought was that the integrated power flow would be normalized to 1 W, but, as far as I can tell, this isn't the case. Other obvious integrals over E^2 or H^2 don't seem to indicate any type of obvious normalization either.

Magnetic field of permanent magnet

Sun, 27 Feb 2011 23:34:49 +0000

Hi, I'm trying to create a cylindrical neodymium magnet and visualize the magnetic field generated by the magnet on a normal plane. Anybody knows how to do this? Later on I intended to visualize the interaction between said magnet and a cylindrical coil.

Exporting Comsol data to Matlab?

Wed, 18 Nov 2009 11:00:06 +0000

Hello everybody,

I want to postprocess Comsol data in Matlab. Since Ascii files blow up in size and I get "out of memory error", I'm looking for some other way. I've no experience with Comsol-Matlab interface and it seems to me that this interface is not working in my system.

Could someone please tell me, how to export Postprocessing data in some Matlab-compatible format (not Ascii)?

I've converted a Comsol model (after executing) into an m-file and wanted to run it in Matlab (running separately from Comsol) but Matlab is probably not able to read the flbinaryfile (*.mphm). Any suggestion, what could be wrong here?

Thanks.
Daniel