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Applying time derivative as a dirchlet boundary condition

March 1, 2013, 3:11 am
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Hi,

I need to apply the time derivative of a displacement created in a piezomaterial as the velocity for a fluid boundary.....

Could someone please let me know as to how this can be handled in COMSOL....Eagerly waiting for your reply.....

Thanks in advance!!

Regards,
Rahul Kishor
Nanyang Technological University,Singapor
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thermally resistive layer

March 7, 2013, 6:19 pm
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Hi everyone,

I am modeling a pipe with fluid circulating within by coupling heat transfer and fluid flow and the pipe diameter is defined in the geometry section.
i need to define the pipe wall thickness for my pipe as well which i do it with adding a thermally resistive layer in heat transfer physics and define the conductivity as well as the wall thickness.
my question is that considering the pipe wall thickness, is the pipe diameter defined in building the geometry inner diameter or the outer one?

Regards
ASAL
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wireless power transfer by pcb coil

March 10, 2013, 3:48 am
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Dear All,

I want to model and simulate a wireless power transfer module. Its application is in microchip implant.

The model has two 3D microstrip(PCB with substrate) coil. One for transmitter and the other is for receiver. My model has two physics:

1) Magnetic and electric Fields

2) Electrical Circuit

Electrical circuit supplies Sin power to transmitter in 4MHz frequency. The receiver coil is connected to a resistor load. I use terminal in magnetic and electric field to connect the 3D model to circuit.

I want to study electrical field (E) and magnetic field (H) in 3D model. Also, I want to study how much power transfer and how much is the efficiency.

I use frequency domain study and stationary or Time Dependent study, but in frequency domain I got error in convergence and in time dependent the circuit can’t stimulate the 3D model.

How can I solve this problem?

Is there any idea to get my goal results?

I attach this model in this share link you can download it here:
www.4shared.com/file/BHB8du0n/power.html

So Thanks.

Mina
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The ouput voltage of piezoelectric with displacement

March 10, 2013, 4:10 am
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Hello All,

I am new with comsol software, now I am trying to solve the basic problem with piezoelectric device. I try to set 'electric potential ' with voltage value as 0, and set 'boundary load' to get the displacement of each layer.

How could I get the output voltage with the pre-define displacement?


I hope the attachment would help you to understand what kind of problem I faced.

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Air dehumidification via liquid desiccant

March 10, 2013, 5:39 am
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Hi
I want to built a model to simulate air dehumidification via liquid desiccant. In this model wet air is blown toward a tube that desiccant liquid is flowed in it. The tube is made of membrane that moist and heat can diffuse through it so moist in air delivered to inside liquid and therefore the air will dry.
The problem is similar to that describe in paper "Conjugate heat and mass transfer in a cross-flow hollow fiber membrane contactor for liquid desiccant air dehumidification" that I upload it.
I built a model to simulate it, but I not sure wheather multiphysics model should I use and if my built model demonstrate the problem in good manner or not.
Regards

NOTTICE: Since the size of COMSOL file is large (6.38MB) I compress it by Winrar, but COMSOL forum page don't allow to upload a .rar file so, I change the extension of file to .mph and rename it to "compressed dehumidification.mph" and then upload it. After download the file change its extension to .rar and extract it to achieve to COMSOL file.
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What is convergence?

March 10, 2013, 7:37 am
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I'd just like to know what convergence is - in the context of COMSOL.
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Java Runtime Environment error

July 28, 2011, 2:37 am
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Getting following error,

A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x0000003da3efbc6c, pid=6909, tid=46912497239488
#
# JRE version: 6.0_20-b02
# Java VM: Java HotSpot(TM) 64-Bit Server VM (16.3-b01 mixed mode linux-amd64 )
# Problematic frame:
# C [libgtk-x11-2.0.so.0+0xfbc6c] gtk_icon_set_render_icon+0x58c

Does anyone know how to resolve it...

Regards
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RF MEMS swich

July 26, 2012, 9:01 pm
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HI all,
I am new to this software tool.I need some practice on RF MEMS. so if any one have example on RF MEMS switch, please attach here or send to my mail id billalaxman@aol.com
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Multiple-size particle tracing

October 30, 2012, 3:24 am
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Hello everyone

I have a short question on the particle tracing module. Does anyone know that whether it is possible to simulat particles of different sizes in the same model. How to implement this since I could only add one unique particle property?

Many thanks

Yuexia
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COMSOL License Error -15, 570

December 6, 2012, 12:44 am
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Dear COMSOL team,

We purchased a 64 bit COMSOL 4.3 verson of software along with a server license. After installing the software on a Linux (Debian 6 Squeeze) based system. We are encountring the following problem. When I start comsol it starts but generates an error in a window. After i close the error window COMSOL exits.


License Error: -15
Cannot connect to license sewrver system.
The license server manager (lmgrd) has not been started yet,
the wrong port@host or license file is being used, or the
port or hostname in the license file has been changed.
Feature: COMSOLGUI
Servername: xxxxxxxxxx
License path: /usr/local/comsol43/license/license.dat:
FLEXnet Licensing error: -15,570. System Error_ 115 "Operation now in progress"
For further information, go to www.flexerasoftware.com.


Thanks in advance for the coperation and support.


Regards,
Yousuf Khan

Institute of Nanostructure Technologies and Analytics (INA)
Technological Electronics - University of Kassel
M.Sc. Electrical Communication Engr.
Heinrich-Plett-Str- 40
34123 Kassel - Germany
Tel.: +49-561-804-4147; Fax: +49 561 804 - 4488
E-mail: yousuf.khan@ina.uni-kassel.de
Web: www.ina-kassel.de
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particle size and geometric constraint of channel

January 29, 2013, 6:25 am
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Hi,

I designed a microfluidic channel with gaps at 10 um. Of course, particles with diameter at 1 um can go through this gap, but particles with diameter of 15 um still can go through this gap, which is not possible. How can I add geometric constraint besides the different forces for different sized particles?

Thank you.
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Running FSI examples, "undefined value found"

March 7, 2013, 3:13 am
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Hi!,
i am trying to run an fluid-structure example with use of the MEMS module, byt anytime i get the error "undefined value found..." for the variable mod1.v_solid.
So i even downloaded the 2d fsi example from the comsol page and changed there only the geometry (i adapted the boundary condition to this new geometry but i took the same type of bc) I again get the above listed error.
I checked the bc several times....
I wonder, because the undefined values for u_solid apper in such a (x,y) coordinate, which is not involved in the domain for linear elastic model. Is that a problem? Or what i am doing wrong? I spent a lot of time with this.


I have another question. It is poissible to split the structural equation (i.e. the linear elastic model) to several step (something like operator splitting)?
I am trying to overcome this using Laplace equations instead of solid mechanics and solve them together with laminar flow and deformed geometry (ALE) . I take segregated solver, hereby i need inputs from one segregated step to different one. By this approach i have a problem with the FSI-interface condition ( i chose "moving wall") u_wall=u_laplace, where u_laplace is a solution from different segregated solver. The segregated solver for laminar flow does not know the variable u_laplace . Solving both problems in one segregated steps, or using coupled solver helps, but this is not, what i want to. How can i store the solution from one segregated solver and use it (for example as boundary, or initial condition) in the next timestep in another segregated solver?

Thanks for your help!
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How to apply polarized E-field?

March 10, 2013, 8:39 pm
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My question is simply "how to apply polarized E-field to z-axis?"
I mean the incident wave should be polarized Ex or Ey.

p.s how can i fix below problem?

Failed to find a solution.
Singular matrix.

For mesh-case 0 there are 1 void equations (empty rows in matrix) for the variable mod1.emw.S1x.
at coordinates: (0,0,0), ...
and similarly for the degrees of freedom (empty columns in matrix).
Returned solution is not converged.
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Extruding a hexagon polygon

March 11, 2013, 4:22 am
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I want build a prism with a hexagon cross section but am having some issues. I have drawn a hexagon polygon and tried to extrude this but it doesn't seem to be working. Any suggestions would be greatly appreciated.
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hyperelastic material in contact with a rigid material

March 11, 2013, 8:36 am
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I'm trying to model the stresses in a hyperelastic material as it's removed from a highly rigid material (which is acting as a mold). I've set up a time-dependent model with the two materials, a contact pair with friction between them, and prescribed a velocity at the top of the hyperelastic material, but am having convergence problems.

I've tried playing with the meshing (mapped works best), the material properties, the initial values (mod1.u should be initial-value based) and several other things. For the lowest-strain cases (the first value in the parametric sweep in the attached file) the simulation runs fine, but for the higher-strain cases (all other values), the simulation fails before completion.

I'd appreciate any suggestions you have as to how I could improve this!

Kind regards,
Allison
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helix with rectangular cross section 2

March 11, 2013, 9:48 am
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Hi,

I was following the thread re: helix with rectangular cross section and downloaded the file helix.mph.

By fudging the parametric values, I almost get what I need except the the major radius appears to be 1mm.

I need a major radius of 2.5mm but don't see how to adjust any of the parameters to get this.

Also, the resolution of the swept helix appears quite coarse.

If anyone in the forum can help to fix these two items, it would be greatly appreciated.

Thanks,

Art
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Failed to find a solution for the initial parameter. Multigrid canceled. Returned solution is not converged.

March 11, 2013, 3:47 pm
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Hello everyone,

I'm having a problem in my simulation, where it does not converge and return me this menssage when I cancel the simulation.
"Failed to find a solution for the initial parameter.
Multigrid canceled.
Returned solution is not converged.
"
What do I have to do to fix it?

Thanks

Gustavo
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Eigenfrequency Problem

March 12, 2013, 4:49 am
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Good evening,


I'd like to know if there's a way to find the highest, maximum , eigerfrequency of a structure using COMSOL.
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changing boundary cond. with time

March 12, 2013, 5:00 am
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Hello,
I want to ask for advice how to change boundary condition in time. E.g. I have exact temperature on boundary for 3600 sec. and after this time, I want to change this boundary to insulation. I've tried using Convective cooling function with very high and low user definied heat transfer coefficient as a function of time.

But now, I want to have one boundary that is insulated and after some amout of time it will become Convective cooling (Internal forced convection), so I can't change the heat transfer coef. I've tried to set velocity of external fluid to zero, but it didn't work quite well (still some heat fluxes through boundary).

I've also tried to make more study steps that will continue one after other, but than it's hard to manage with results. Time series results doesn't make continuous solutions, i cant export animations, etc..

I hope, there's some great solution for this, that i've missed.

Best regards, Jan.
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Problem with meshing in a microfluidic channel.

March 12, 2013, 5:07 am
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Hey all,

I am trying to simulate the deflection of a half-sphere, with ALE Fluid-structure interaction, stuck on the bottom surface of a microfluidic channel (height = 50 um and width = 300 um) and it works fine with mean inlet flow velocity 10 cm/sec (I see the sphere deflecting), but when I try to increase it to 15 cm/sec, for example, I got an error, stating:

"Non-linear solver didnt converge. Attempt to evaluate real square root of negative number..."

And then a huge mesage follows...

I tried to make the mesh finer, to use adaptive mess, or to use auto-meshing, but every time I had the same error.

So, what do you suggest me to do in order to have higher velocities?


I am also trying to attach the file, but it says it is too big for attaching...

Thank you alot in advance.
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