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constitutive soil - double hardening yield

March 8, 2013, 2:03 am
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Hello!

I'm doing my own constitutive model of soil , then I would like to know, if anybody have gotten to perform double yield surface and hardening isotropic.

Thanks
Mayu
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Ask the question about the particle tracing module.

March 8, 2013, 4:06 am
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I have a question when I have used particle tracing module(fpt). Because I try to utilize the condition of Particle-Particle Interaction. I don’t know how to define the interaction force of particle.

E is electric field, in fact, I have already calculated through AC/DC module. rij is the distance vector between the center of particle i and the center of particle j.

I know the function of dest, but I don’t understand how to combine vector E(Vx,Vy) and position(qx,qy).
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Electrical Circuit and Comsoll

March 8, 2013, 4:55 am
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Dear memebers

I Work with Comsol 4.3 ACDC. I know now how to import a SPICE Netlist to Comsol.But I still have a problem.


I followed the exmaple in ACDC modul called "inductor in a Circuit". So to be able to place the Comsoll Modell to the electrical Circuit you/I have to define it like this " I copied it from the inductor in circuit exmaple"



X1 4 5 inductor
.SUBCKT inductor V_coil I_coil COMSOL: *
.ENDS


-So X1 should be my Comsoll Modell What ist Inductor it is the name of the modell ??? cause the modell is called inductor_in_circuit

-The SUBCIRCUIT defeines <file name>|<physics_interface_name>|*

So what is <physics_interface_name> ..V_coil I_coil and where and how can I declare them in my Modell


I would be really thankfull if any one can give me some tipps esc.


Thanks and greetigs from Germany
Ahmed Hegab
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How to mesh finer in a specific area in 3D

March 8, 2013, 5:45 am
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My model is a insulator in 3D surroundded by air, i added a small water droplet on the insulator to observe the electric field enhancement around the water droplet.
So i need to focus on the small water droplet and need finer or extra fine mesh for the air around the water droplet, but i don t want to make the whole air have finer or extra fine mesh because this will cost me much more longer time to compute it.
My question is that is there a way to mesh the air near water droplet finer but coarser in other part of air domain.
I tried distribution but it seems just make the surface finer but not the 3D space.
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How to update dependent variables manually..

March 8, 2013, 5:48 am
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Hi ,
Is it possible to update the dependent variables in each step manually in COMSOL ?
For example, I want to assign new values for a dependent variable (V) in each step like:
V ..... if (phils<0.5, 0, V)
BUT I always get Duplicate variable error. Because V is already defined in the solver.
Any ideas that how this is possible in COMSOL?

Thanks
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couple 2D solid and 1D beam

March 8, 2013, 7:55 am
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hi, how can i couple a 1D beam and 2D solid. I want to link these on a point which is located in the same position geometrically. the beam is a cantilever.
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Why conservation of mass is violated in Comsol - Laminar flow?

February 7, 2011, 3:09 pm
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The model is simple, I use rectangle as my geometry(0.1505m*0.006m) ,and chose laminar flow as my module, then assign inlet boundary condition, which is pressure boundary,10[Pa], outlet condition is 0[Pa], other two boundaries are no slip boundaries. Initial value(velocity and pressure) are specified with 0. After running model, I found outlet flux(1.4441e-6m^2/s) is not equals to inlet flux(1.4491e-6 m^2/s). How does this happen even though I refine the mesh of model? Is this due to resolution of Comsol? Any help will be appreciated. Thanks a lot.

By the way, if I use a more complex geometry, then the outlet flux will more than up to 17% of inlet flux in spite of very finer mesh.
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Two phase flow moving mesh + Electrostatics

June 21, 2012, 3:26 am
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Hello,

I am trying to model a contact angle change by maxwell stress tensor using the moving mesh module coupled with the electrostatic (from where the electric field is calculated).

The modules work fine taken separately, but when coupled with the body force, or even without coupling but solved at the same time, the contact angle doesn't change, in fact the system doesn't converge.


Can you tell me if there is any problem in this coupling?


VdV
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Marangoni Stirring / Phase Change: Weak Contribution Settings

February 28, 2013, 9:06 pm
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Hi

I have a problem with a weak contribution in a laser surface melting model:

My model takes into account solid-liquid phase change using an enthalpy-porosity technique and liquid phase volume forces using the Boussinesque Approximation (as in the Continuous Casting tutorial). The model also takes into account Marangoni Forces on the top surface of the material via a weak contribution boundary condition with an expression:

test(u)*gamma*Tx

where u is the velocity x component, gamma is a surface tension/ temperature gradient (a constant) and Tx is the Temperature in the x direction.

The resistive volume force term in the domain beneath the top surface serves to brake the fluid motion down to that of the material (the model is Eularian, meaning the material moves rather than the laser spot) when the material is solid, and allowing additional fluid motion within the molten area.

The trouble is, when the weak contribution is added to the top surface, it seems to allow additional fluid motion in areas where the material is supposed to be solid.

How can I tie the volume force term to the Marangoni weak contribution on the surface to ensure that any additional fluid motion is only allowed within the liquid phase of the material?

Many thanks in advance for your help

Dan




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how to control the temperature?

March 5, 2013, 3:06 am
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hello

after heating,then entering the cooling stage,when t=20s,i want to get the whole model T=20°C with temperature suddenly jumped
i know the way with ANSYS,but how to set with COMSOL

what should i do??

any help, thanks
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Failed to find a solution. The relative error (35) is greater than the relative tolerance. Returned solution is not converged

March 8, 2013, 2:40 pm
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hi, im writing this mail because im stuck with my thesis simulation. this happened when i change the value of the electrical conductivity for silicon. i change for 1.6 e-3 s/m instead 1e-12 that had before ( the simulation works with this parameter).

i dont have any idea what can be wrong because the real parameter is 1.6e-3 s/m and the error that comsol is telling me each time i run the simulation is Failed to find a solution.
The relative error (46) is greater than the relative tolerance.
Returned solution is not converged.

another doubt is that i need to obtain the voltage on the perpendicular contacts. i put the boundaries like floating potential and i did a graph using thedifference of both contacts but i would make sure if im doing right.

i really appreciate any help to solve this problem

thanks
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element quadrilateral quadratic 8 nodes

March 8, 2013, 4:06 pm
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Hi!

How can i to do a mesh with element quadrilateral quadratic 8 nodes?

Thanks!

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How to create the material characteristic (conductivity) as a function of electric field

March 9, 2013, 12:34 am
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Can somebody help us?
We cannot create characteristic in COMSOL. In our model we want to use the electric field as input parameter and as output we want to obtain conductivity.

Please answer as soon as possible.
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grating reflection & transmission spectrum

March 9, 2013, 3:00 am
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Hi,

I am trying to simulate a grating structure a get the reflection & transmission spectrum of that , I have tried S-parameter but no field propagate in the structure .Is S-parameter the correct method? I don't know how to model the source?

Thanks,
sara
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Simulation filament formation Laminar two phase flow (level set)

March 9, 2013, 3:38 am
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Dear all,

I wonder if someone can help me.

I would like to make a simulation using the Laminar two phase flow method (level set) coupled to an electrostatic simulation (ec module). Basically the idea is to simulate the formation of metallic filaments inside a semiconductor matrix for resistive memories.

The device (simulation 2D) is divided in two regions with different material (a metallic part with on top a semiconducting layer). It has two contacts one at the bottom (in contact with the metal layer) and one on the top (in contact with the semiconductor).

The interface between the two materials is not completely smooth and posses some "bumps" or tips. Those tips should be the seeds of the metallic filament.

When a bias is applied current flows and an electric field establish. The electric field is stronger at the tips along the interface between the two materials. This electric field should be the driving force to grow a metallic filament which crosses the semiconductor until does not touch the other contact establishing the short-circuit of the low conducting semicondcutor.

I am trying to model this with level set + EC modules within COMSOL 4.2. However, I have problems in coupling the two simulations, especially how to define the inlet and outlet of such a problem. Or do you think it would be better to directly define some "volume" force linked to the electrostatic simulation to get the force map across the system?

Any advice is very welcome.

Cheers

Alessio
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PDEs expressed in Weak Form Coupled to ODEs

March 9, 2013, 8:43 am
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Hello,

I am currently using COMSOL 4.3a.

I am solving a problem constituted by a set of coupled PDEs (depending on time and space), defined in a domain.
To solve this, I used the Weak Form.

In addition, coupled to the PDEs, I have 2 ODEs (only depending on time). I implemented the ODEs, in the same fashion of the PDEs, using the Weak Form.

However, I wonder if there is any alternative way to include the ODEs different from what I did. For instance, is there the possibility of introducing the ODEs as expressions that apply to the entire domain.

Has anybody an idea if this is possible and how?
thanks
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One way coupling- A reasonable approximation?

March 9, 2013, 8:59 am
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In the tutorial for FSI in a network of blood vessels, it has been narrated at the end in the results and discussion section for Figure 5.

" The displacements are in the order of 10um, which suggest that the one- way coupling is a reasonable approximation."

Please if any one can explain to me what would be criterion for a reasonable approximation for one-way coupling?

Is their any other evidence or reference for such kind of approximation available?
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Current not flowing across boundaries

March 9, 2013, 10:38 am
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I'm new to COMSOL and having some trouble getting current to flow across material boundaries in my model using the Joule Heating physics.

I have a semiconductor wire with metal contacts on each end and set a potential on one side and a ground on the other. I created 3 rectangles side by side in one plane geometry and then assigned different materials to each. There is also a form union node at the end of the geometry node.

There is no temperature change from the Joule heating. Everything is in equilibrium with the ambient.

Looking at the current density, I only see variation in the metal contact attached to the potential. There is no current flowing into the semiconductor wire or the grounded metal contact.

Does anyone know what the problem could be?

Thanks
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Metal film with subwavelength size hole: Transmmittance and reflectance study

December 23, 2012, 1:26 pm
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Hi


I'm novice in comsol RF simulation. I'm trying to simulate transmittace and reflectance throught metal film with subwavelength size hole. My structure will consists of Air/metal/semiconductor interface. I'm not sure but I think transmittance is governed by surface plasmon polariton. I tried to find some Model on this topic but could not. I'm looking for models that fits best with mine as well as any suggestion how I should go. I'm trying to understand what is the phenomena that governs the transmittance. Thank you
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streamline problem

February 16, 2013, 11:36 am
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Hey, i am having some problems creating the steamlines for my Helmholtz coil. I followed the steps for the one of the model on comsol website for Helmholtz coil except other than revolve to create the coils i did extrusion instead. Now i am getting something really weird for my streamline and I compared with the Helmholtz coil file i downloaded from the website and i looks like I did the exact same thing with the example. I couldn't figure out what might possibly go wrong. I have attached a picture of the streamline I have now. Can you tell me what I did wrong and help me fix it? Thank you.
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