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Thermal stress in a multilayer object

March 14, 2013, 2:25 am
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Hi.
Im trying to simulate the residual stress in a multimaterial sandwich structure and I have done it with the thermal stress module and with a time-dependant study.
I put all my doamins at an initial temperature of 100 °c, then I leave cool down by convection at 0°C. Every ten second I have the result for the Von Mises stress within my structure, in order to understand whether this stress reach the strenght of materials themselves.
Instead of finding that the stress increase as the temperature lowers (due to different thermal contraction), it results that the stress decreases in all layers.

1)Why?

2) What for, in case of a stationary study with steady temperature (T_initial=T_final), the stress is not zero?

Thanks to them can help me.
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Crack propagation with COMSOL

March 14, 2013, 4:14 am
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Hello,
I am studying the possibility of acquiring COMSOL and I need to know if it is possible to solve problems of cracks propagation using cohesive elements, or if there are specific modules to solve these problems?
Thank you for your help in advance

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COMSOL in parallel mode: a speedup of 20% using 4 cores?

September 23, 2009, 1:01 am
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Hello everyone,

I have performed the following experiment. Using the command -np #cores, I have forced COMSOL Multiphysics to use 1, 2, 4 or 8 of the available cores on my computer. I also used the default configuration of COMSOL Multiphysics, i.e, without the command -np. I performed the experiment using two models comprising two drift-diffusion equations coupled with the Poisson equation - one is quasi-linear, the other is highly non-linear. The solver used was Pardiso. The results are in the attached file.

I have obtained a speed-up of about 20% when I activated 4 cores, as compared with the duration of calculations using only 1 core. Do you believe that this improvement of 20% is the typical speedup that can be obtained? Does anyone have some more data or experience on this issue?

Thank you for your help.

Kind regards,
Pedro
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Velocity gradient expression in 2D-axisymmetric

April 28, 2012, 7:59 am
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Hello,

the velocity gradient tensor for a 2D-axisymmetric problem presents, for the phiphi component, the following expression

chns.graduDGphiphi = if(abs(r)<0.0010*h,d(u,r),u/r)

does anyone know the meaning? I can guess that is introduced to avoid spurious effects at the axisymmetric boundary but still it is not totally clear to me.

Best,

J
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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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Electromagnet modeling in 3D BH curve&relative permeability

January 17, 2013, 4:40 am
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Hi all,
at start let me say I am new in Comsol. I am using v 4.0a AC/DC Magnetic Fields. What I am trying to model is type of a magnetic brake. It`s geometry is very similar to plain electromagnet, consisting out of single cylindrical coil and a single (or mere) solid cylindrical iron (or other materials) solenoid. I have successfully modeled this geometry, defined all parameters and got results in 3D Plot Group 2/Slice 1/Arrow Volume 1/ etc. See attachment.
The thing that troubles me is how to define VARIABLE RELATIVE PERMEABILITY as a B-H curve function. i have modeled this geometry entering a number in relative permeability field but that is not want I want. I want to enter a r. permeability as a B&H curve function for specific material. I have data for B-H curves for materials of interest. I tried to type mu0*(normB/normH) as a equation in material`s relative permeability field and Comsol accepted this but I still do not see how or where to define B-H curve.
The main reason for doing this, correct me if I am wrong, is that I think I should enter relative permeability as a function not as a fixed number in case if I decide to make a solenoid out of two very different materials.
I know I haven`t presented my situation as best as it should, but I think You get the picture.
So, to summarize, should I enter relative permeability for certain material as a fixed number of as a B-H curve function and if so, how to do it?
Thank You all.
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Moving mesh ALE

February 28, 2013, 10:27 pm
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Hi,

I am simulating a moving boundary with ALE method.

My program is working fine with a certain geometry, mesh and time, but if I would like to change the geometry or set a larger time, then I get a message: "last time step is not converged".

I attached the model that is not working and the good one.
Please let me know what I am doing wrong.

best regards


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Gravity volume force in non-isothermal laminar flow

March 12, 2013, 1:29 am
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Hello

I'm trying to simulate non-isothermal laminar flow through a tube, and I use 2D-axisymmetrical to decrease the computing time. The model works fine with laminar flow and heat transfer, but when I add gravity, volume force, in the laminar flow interface (-g_const*spf.rho) a solution cannot be found. I get the following error:

- - -

Failed to find a solution.
Singular matrix.

There are 16 void equations (empty rows in matrix) for the variable mod1.p.
There are 1 void equation (empty rows in matrix) for the variable mod1.spf.pmfinl1.
Returned solution not converged.
- Feature: Stationary solver 1 (sol2/s1)
- Error: Failed to find a solution.

- - -

A finer mesh made no difference, but decreasing the gravity to "-0.1*g_const*spf.rho" returned a converged solution.

Any ideas to what might be the problem would be appreciated.

/Simon Tågerud
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Thermal stress analysis

March 14, 2013, 7:34 am
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Hi sir,

i have analysed thermal stress by passing the laser beam on rectangular plate (through structural mechanics module).i used stainless steel temp dependent material properties to my simulation. i used elasto plastic properties yield and tangent modulus. i have attached the properties also.i satisfied with results of deformation of plate and temperature profile. but my major problem is von mises stress exceed the ultimate stress level.

how can i reduce the stress value??

is there any possible to use smooth function.

please help me genius.
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Resistivity change vs deflection

March 14, 2013, 9:41 am
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dear all,

How to plot the resistivity change of a simple piezoresistor vs deflection of a membrane in a MEMS sensor?

thanks
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Fluid flow channel in cantilever beam

March 14, 2013, 11:15 am
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Hello,

My model is the following: a cantilever beam has one longitudinal channel containing a fluid flow. My goal is to find the effects of the fluid flow (viscosity, velocity, size of the channel) on the damping of the beam.

Until now, I was using "Solid Mechanics" looking at the frequency response of the beam around its eigenfrequencies (to estimate damping). But when I add a laminar flow, the results do not change. I have changed the parameters of the fluid, but still no changes.

I would like to know:
1) How to make sure the 2 physics are solved.
2) Am I right to use these 2 physics (Solid mechanics + Laminar flow) over Fluid-flow interaction.

Thanks for your help,

Matthias
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Save soltution at stop condition

March 14, 2013, 8:06 pm
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Hi!
How can I force COMSOL to save the solution for the time instant when the stop condition is satisfied?
Thank you,
Miroslav
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How to find temperature variation for a single element in my model

March 15, 2013, 2:11 am
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My model has 7 elements as a whole. I am able to plot the temperature variations of the whole model but not for any separate element in the model. I request if somebody helps me know how to plot the variation of temperature of a single solid or a variation along a plane in a solid.

Further, In my model, I wish to know the temperature variation across a curved line and plot it in a graph. As the dimensions vary along, either x-y or y-z or z-x, can you give me an idea how to plot the temperature variations??
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Problem with air as a fluid ;-)

March 15, 2013, 2:14 am
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Dear sir,

While solving my model, I am getting an error that the "Last time step is not converged" if the air is taken as a fluid whereas it is showing the results when air is taken as a solid.

What should I do to get the solution with air as a fluid??
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Tem analysis-Joule Heating and Thermal expansion of wire

March 15, 2013, 2:35 am
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Tem analysis

Hello,

I was using Joule Heating and Thermal Expansion Analysis of Wire Bond.

Basically, I would like to apply 2.1 Voltage to the wire and see displacement . However, I am not sure that i am on the right truck. My experimental results are somehow different ...like 2 times more displacement ...

Another thing is about reading result..why is the displacement on -y axis looks like downward ? It just does not make sense to me.

Can you please help me about it ?

Best
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How to set a compliance current

March 15, 2013, 3:08 am
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Hi,
I'm relatively new at Comsol. I am working on an electronic model of a NVRAM. I would like to clamp the current within my cell. But I cannot find a easier way than create a transistor that will set a compliance current.
Is there a another way to set a compliance current in Comsol?

Thanks in advance
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Solve PDE on 1D domain?

March 15, 2013, 4:33 am
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Hy guys, I have a problem with solving a PDE based model defined by me, it is not a default template in COMSOL.

My problem is that the equation is solved for the time domain, but not for the geometry specified. ( Interval )

Does the solver automatically solve with respect to 'x axis' ( it represents the height of a reactor x=[0,20] m )?

The PDE I'm trying to solve is the following:
dT/dt=-VL*dT/dx-constant

where VL and constant are known.

Could you help me with this,

Thank you.
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Convergence error using batch command line

March 15, 2013, 4:46 am
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Hello,

I want to solve a single phase fluid flow, turbulent low Reynolds k-epsilon model in batch mode. This works fine when trying to run from the COMSOL desktop (i.e. with GUI). However when I try to enter batch mode using command prompt I get a convergence error. I use the following command:

comsol batch -inputfile TurbulentPipeFlow_k-e-lowRe.mph -study std1 -batchlog batchlog.log

The error part of the log:

-----------------------------------------------------------------------------------------------------------

Segregated solver iteration 5.
Substep 1, for group 1.
Current Progress: 5 %
Memory: 899/900 2411/2411
Iter Damping Stepsize #Res #Jac #Sol LinIt LinErr LinRes
1 0.5000000 0.46 5 5 5 43 0.00083 0.14
Substep 2, for group 2.
Scales for dependent variables:
mod1.k: 0.9
mod1.ep: 95
Iter Damping Stepsize #Res #Jac #Sol LinIt LinErr LinRes
1 0.3000000 0.62 17 17 17 220 0.00098 9.7e-05
2 0.3000000 0.52 18 18 18 238 0.00061 0.00012
3 0.3000000 0.41 19 19 19 269 0.00089 0.001
4 0.3000000 0.32 20 20 20 469 0.044 0.94
Stationary Solver 2 in Solver 1: Solution time: 50 s.
The_following_feature_has_encountered_a_problem
Exception:
com.comsol.util.exceptions.FlException: Failed to find a solution
(rethrown as com.comsol.util.exceptions.FlException)
Messages:
The following feature has encountered a problem

Failed to find a solution

In segregated group X#2

Divergence of the linear iterations

Returned solution is not converged
- Feature: Stationary Solver 2 (sol1/s2)
- Error: Failed to find a solution.

-----------------------------------------------------------------------------------------------------------

Doing multiple tries, the error always occurs at the same time and the logs are identical. The other turbulence models (k-eps and k-omega) work just fine.

The only reason for this that I can think of is that the comsol batch command starts the batch run with other convergence criteria than a 'normal' run from the COMSOL GUI, but that seems very odd to me. All help is appreciated.

Thanks in advance,

Thomas van der Meer
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How to combine the Frequency Domain and Coil Current Calculation

March 15, 2013, 7:33 am
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Hello everyone,

i´m trying to simulate an numerical coil with alternating current. The coil is built with the "Multi-Turn Coil Domain". My coil type is numeric wich requires an additional "Coil Current Calculation" step before my "Frequency Domain" step in my study. I solved it for 50,500,5000 Hz and looked at the coil paramters. My coil excitation is set to 0.15A wich should be the coil current for all frequencies. The "Coil voltage" and "Coil resistance" should be different for each frequency which is not, if i do a global evaluation for those two parameters.
Anyone got an idea how i can solve my problem? I´m attaching my modelfile, if someone is willing to take a look at it.


Best wishes,
Andreas Schneider
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Thermal Stress Analysis

March 15, 2013, 10:32 am
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Dear all,

I am trying to model and analyze thermal stress in a solid block sandwiched inside a Steel-press. The model is attached. As I used to work on CFD and I am fairly new to the FEA, there is a big chance that I made mistakes on boundary condition settings.

So I designed the geometry, and as can be seen a Copper object (block) is pressed between a two Steel blocks. At this point, I kept the boundary force very small (200 N) applied only over the upper steel-part, while I kept the lower steel-part to be fixed. the Copper block must be heated up to 800 degree F, and then will be inserted into the press steel-parts, while they are also preheated to 460 degree F, and I took care of these settings in the inital conditions. The whole system is thermally isolated, and only the Copper block faces convective cooling.

This process must take long for 60s. Unfortunately, the model is incapable for converging for time-dependent solver! and as I turned the solver into stationary (which is not the case) as can be seen from the results of "Study 1" in the attached model, the Copper block penetrates into the lower steel-part of the press. And also, the tempreture distribution as a result of Heat transfer in the solids does not seem to be correct.

Could you please take a look into the model, and help me to set it up correctly?

Regards,

Shawn
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