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Interpretation of results

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Hi,

what is the difference between "Line Integration", "Line Maximum/Minimum" and "Line Average" under subnode "Derived Values"?
What is calculated specifically? How to interpret the results?
For example, if I want to calculate the reaction forces?

When to choose the linear and when to choose the quadratic discretization as displacement field for Solid Mechanics Model?

parametrize the position of a point in the geometry gives an error message

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Dear Comsolfriends,
I want to do a parameter study for the size of my geometry, but I get the following error when trying to set the position of a POINT using a parameter defined before in MATLAB (directly in comsol this problem does not occur) -- for circles etc everything works fine in matlab, but for points the trouble starts:

model.param.set('cx','1'); model.param.set('px','1');
model.geom.create('geom1', 2);
model.geom('geom1').feature.create('c1', 'Circle');
model.geom('geom1').feature.create('pt1', 'Point');
model.geom('geom1').feature('c1').set('pos', {'1' '1'});
model.geom('geom1').feature('pt1').set('p', {'1'; '1'});

this works fine, as well as
model.geom('geom1').feature('c1').set('pos', {'cx' '1'});

but if I try
model.geom('geom1').feature('pt1').set('p', {'px'; '1'});
I get the error message:

Error using com.comsol.model.impl.GeomFeatureImpl/set
Java exception occurred:
Exception:
com.comsol.util.exceptions.FlException: Unknown variable name
Messages:
Unknown variable name
- Name: px
- Property name: p

Stack trace:
at com.comsol.util.classes.o.a(Unknown Source)
at com.comsol.util.classes.o.a(Unknown Source)
at com.comsol.util.classes.o.b(Unknown Source)
at com.comsol.util.classes.o.a(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.e(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.a(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.a(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.a(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.a(Unknown Source)
at com.comsol.nativeutil.parser.ParseUtil.a(Unknown Source)
at com.comsol.nativeutil.properties.ak.set(Unknown Source)
at com.comsol.model.impl.PropValueImpl.set(Unknown Source)
at com.comsol.model.impl.PropFeatureImpl.c(Unknown Source)
at com.comsol.model.impl.PropFeatureImpl$p.a(Unknown Source)
at com.comsol.model.impl.PropFeatureImpl$p.execute(Unknown Source)
at com.comsol.model.clientserver.ClientManagerImpl$d.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

has anyone an idea why this happens? where is the big difference between a point and a circle? did you try something similar, and, above all, HOW TO SOLVE THIS? I want a geometry with a point at the middle of one boundary, and when I sweep the size of my geometry, the point must move as well of course.

Thanks a lot for any answer!!! :)
Sabine

save the mesh points into a text file

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How can I save the mesh points into a text file or some similar?

Thanks!

Issue importing ipt files from Inventor with the CAD module

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Hi,
I can't seem to import a simple IPT cad file (that has a helix built in) from inventor, the import module gives me an error back saying:
Not a valid ENTITY type for this operation

- Detail: Internal_error_translating_CAD_model
- Detail: File version is not supported
- Filename:...

Is there any version limitation on inventor files or would that be something else?
Thanks in advance,
Matthieu

Scattering boundary conditons for non-normal incident

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Hi all,

I'm wondering, if it possible to use the scattering boundary conditions in the RF module to make a boundary transparent for a plane wave with a known wave-vector (which is different from the wave vector of the incident field at this boundary).

To give a simple example, if I, for example, want to simulate the reflections of a plane wave (with a wave vector given by k=(kx,0,kz) and a polarisation of E=(1,0,-kx/kz)) by a metallic half space (surface given by z=0), I know that the wave vector of the reflected field will be k=(kx,0,-kz). Is there any possible to make this simple simulation using scattering boundary conditions (without using PML) and solving for the full field? (I don't want to solve for the scattered field or use PML, since it would be inconvenient for the simulations I'm interested in. Obviously my final goal is not to calculate the reflection of a plan wave at a metal surface.)

Thanks a lot in advance for any advises,
Felix

"Undefined value found" Error when simulating EM-Wave on imported 3D Pyramid

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Hey all,

I am trying to simulate the E-Field enhancements on a micro-pyramid structure for which I imported a pyramid with rounded corners from AutoCAD as a .sat file. I set up everything the way I wanted an used the normal mesh size. After the simulation runs for several minutes I receive the error: "Undefined value found - Detail: NaN or Inf found when solving linear system using SOR".
I am sorry but I have absolutely no clue what to change or where to look for to make the simulation running. It would be very important to get this simulation running therefore I would be very thankful if anyone could point out to me what could be the reason for the error. Here is the dropbox link to my file (as 18MB are too large to attach it here):
dl.dropbox.com/u/11950301/3D_pyramid_import_periodic.mph

One thing I could think of is the size of the imported pyramid structure as it is impossible for me to import it in the right dimensions I had to scale it with an empiric value to make it fit into my geometry. Could that be the reason or is there maybe a way to be able to import the .sat file with exact size and dimensions?

Thanks so much for any help with this,
Best Regards,
Max

PML does not work during wavelength sweep

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I was simulating the scattering from a nanodisk by normal incidence.

With a spherical PML, the scattering field should be basically symmetric below and above the disk plane. It is indeed so when I simulate 400 nm and 430 nm.

However when I start to sweep the wavelength, 400 nm to 430 nm, the 430 nm case behave very unexpectedly with the PML. Field penetrates half of the PML and a very strong reflection is observed.

I start to think this is a bug of the comsol 4.3, where the PML somehow did not recognize the new wavelength during sweeping. Maybe I did something stupid, I don't know anyone else experienced this before?

Store solution and use as a boundary condition for the next run

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Hi

Does anybody knows how to apply the results obtained at the outlet of first run back to the inlet as an inlet bounrady condition? Actually the objective is to study a flow in a long clyinder by making it in small cylinders and repeating the BCs from solution back to the inlet. This will save the memory and help in reducing the size of geometry while getting the same results which would actually be obtained in a long clyinder simulation.

Any ideas will be highly appreciated.

regards
Naveed

Problem related to imported mesh file

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I was trying to import a mesh flle (mphtxt) file from Simpleware Scan FE software. However when I import this mesh file in COMSOL and throw all the physics on it, following error appear : Can you please help me to solve this problem

"Problem setting up multigrid.
Multigrid not supported on imported mesh."

Regards,
Zeeshan

Fuel tank simulation

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Hi,

I have a project about fuel tank simulation. The thing that I try is similar to the sloshing tank example. However, since the fuel tanks are closed [ :) ] I need to limit the deforming mesh. Has anyone got any idea how to simulate a fuel tank?

So far I have put another rectangle on the existing rectangle and defined air for the properties. But program did not allow me to use the boundary between two rectangles. Thus, I could not define any thing for that boundary and the simulation crashed.

I need to put an upper boundary for the system to stop floating :)

specifying varing coefficient - interpolation function

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Hi all,

I would like to specify varing htc via interpolation function and apply it to a heat flux boundary condition. I am attaching a sample file.

- Model: 2D-axisymetric (i.e.cylinder, mm), heat transfer in solids, and s-s case
- Features: a heat flux boundary condition with heat transfer coefficient varing along line (not as constant). assigned via interpolation function
- Error: Wrong number of function arguments, Number of arguments expected: 1'

I built a simple 2D axisymetric, heat transfer in solids, and s-s case and added a heat flux boundary condition with heat transfer coefficient which is varing along line. An external htc data set was imported using interpolation function under Global Parameters.

t f(t)
1 50
2 52
3 54
.. ..
399 52
400 50

1) I can see a plot without assiging units, but with units (argument: mm, function: W/(m^2*K)) a horizontal line is only appeared. What should I consider?

2) I am facing the same error message 'wrong number of function arguments' when running the simulation. I believe the number is ok but it repeatedly says it.

Any advice and help will be appreciated,

mg

How to use user defined functions as physics's input? Thanks!

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Hello, every one!
I am learnging to use COMSOL4.2 and want to add AC signal as my device's input.

Just as Eric told me to write an equation as the input.

(www.comsol.com/community/forums/general/thread/34060/#p94106)

I want to try another way.

Because there is a way to define a function( Model bulider--> Global Definition-->Function),

I can define a funciton (name wv1) as wv1= 5 *sin( 50*pi* t ).


My question is, how can I use this function as an AC input to a capacitor's input?

Thanks!

Importing a file from AutoCAD to COMSOL

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I have created a 3D building model on AutoCAD and wish to import it to COMSOL for CFD analysis. Can I know the process for importing?

Velocity of solution

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Hi,

Since it depends what speed calculations?
I created two identical geometry.
One in 2D it is counted in minutes.
Second in 3D it is counted for 30 minutes to 1 hour.

It is possible to calculate the 3D somehow accelerate?

Thank you.

Absolute pressure sensor

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I'm working on simulation of absolute pressure sensor. I want to know that when i compute the result for stress it shows the total stress. I want the longitudinal and transverse both stress at particular point. How I get this?...

Second is that i want to use doped poly silicon pizeoresisstors and through this i want to get change in resistance.
But i dont get this options in Comsol 4.2a. no option for doping poly silicon pizeoresistors and no option for measuring resistance.

electrostatic force cause displacement in parallel plate capacitor in COMSOL

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Hi,

I have been designed a parallel-plate capacitor in COMSOL. Where one plate is connect to voltage of 10V and other one is connected to GND. and a air box is around the parallel plate capacitor.

As I know, if I applied a voltage in plate 1 then there will displace in plate one. I want to know how can I measure and plot this displacement of the plate. I have been stooped here for couple of week.

Would any one please help me in this regard.

Thank in Advance.

-Suzan

Undefined value found in the stiffness matrix, requested mesh quality cannot be achieved, and obstacle in the fluid channel

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Dear All,

I am simulating a sphere flowing in a microchannel with solid traps (2D for simplification). Automatic re-meshing is activated. Two scenarios are considered: Scenario 1, the sphere will encounter a solid trap and get immobilized. Scenario 2, the sphere will flow in the channel beside the trap.

However, for Scenario 1, the simulation cannot go on (or get crushed) when the sphere draws near to the trap. The problem is 'requested mesh quality cannot be achieved', because the mesh near the trap changes so dramatically?

Moreover, how can I set a stop for the simulation, when the sphere achieves to hit the trap (obstacle)? or change the boundary condition?

For Scenario 2, the sphere cannot get through the narrow channel between the traps around it. The problem is 'Undefined value found in the stiffness matrix'. I guess this is also due to the mesh crushing? If I put the sphere at the crushed place and run the simulation again, the sphere can move again and get crushed at the next trap.

Could anybody find a way to solve these problem? Thanks a lot.

The files for scenario 1: www.dropbox.com/s/id9rp4l6ykuc2ba/Scenario1.mph
and for scenario 2: www.dropbox.com/s/fo2u3j4350nukv9/Scenario2.mph

Zimeng

Difference between two modules in comsol

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What is the difference between module " Structural mechanics--->Poroelasticity(poro)" and module "Fluid flow---->Porous Media and Surface Flow"?

Anybody knows?

I was gonna implement solid liquid coupling in porous materials, which module I should use?
Thanks

Some questions about one example in model library

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I am redoing the example of "Terzaghi Compaction", and I have some questions or confusions:

1) In the "Darcy's law----> storage model" section after part "Definition", we just need to set K as K_s, but not point out specific K_s, K_s in "variable" or "Variable 2"? How to distinguish the two when computing?

2) In the "Darcy's law----> storage model" section after part "Materials", we should follow "From the Fluid material list, choose fluid", that means the fluid properties in storage model should come from "Material----->fluid", but we didn't set the properties of solid particles, and set it default as "domain materials", why?

What physic need for SQUEEZED-FILM DAMPING MODELS FOR MEMS in COMSOL

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Hi all,

I am working on SQUEEZED-FILM DAMPING MODELS FOR MEMS in COMSOL. Where one of the plate(1) is fixed and other plate(2) is movable when applying pressure. Whole structure should be inside the vacuum box or gas.

So i need to calculate damping coefficient (b) . I need to give fixed constrain on one side of plate(2) and other side is movable. For fixed constrain I need to assign SOLID MECHANICS physics but when I assigned materials for vacuum or gas ,its required Young's Modulus and Poisson ratio but as we know for gas or liquid don't have these value.

Please help me in this regard.

BR
Suzan
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