Quantcast
Channel: Solving, solving\ - Latest Discussions - COMSOL Forums
Viewing all 3988 articles
Browse latest View live
↧

Prolonged error with "Last Time Step Not Converged"

March 12, 2013, 8:40 pm
$
0
0
Dear sir,

We were trying out "PIPE FLOW MODULE" as you have suggested. And thanks for the advice, as it has reduced the number of mesh elements to a larger extent. But, we were getting a consistent error message namely,

"Error:

Failed to find consistent initial values.
Segregated group 2

COMSOL assertion failure.
Last time step is not converged.

Warning:

SOR line did not find any lines. "

I would like you to verify our model and help us if any errors made in the modeling.

Basic parameters are that, the heat flux will take place in walls through inner air, atmospheric air and water in pipes as in the model. I would be so grateful, if our prolonged error is sorted out.
↧
Search

How can I find the flow velocity of a specific coordinate point

March 13, 2013, 7:44 am
$
0
0
Dear all,

I would like to ask how can I find the flow velocity of a specific point (x=105, y=2.5) in my channel (it is shown in the picture). In the graph, if I click at any random point I got 3 values: on the x axis I got the channel's length, on the y axis the height and the different colours represent the flow velocity profile and hence, I got 3 values for x,y and u.

But I would like to find my velocity at a specific point, so could you pleqse help me how can I do that?

Thank you a lot beforehand.

Regards

Dimitrios
↧
↧

Automatically parameter increasing

March 13, 2013, 8:26 am
$
0
0
Dear friends,
I have a simple 2D rectangular model, I want to measure some acoustic properties in my desired frequency range, for specific height of model it's easy, but I want to check a range of heights for example 0.1 mm to 10 mm, with 0.1 increment, how can I set COMSOL to do this and save data automatically?
Regards
↧

Convergence behaviour in a stationary solver

March 14, 2013, 9:06 am
$
0
0
Dear Comsol gurus,

I have been dealing with a CFD/transport of diluted species (TDS) simulation for a while and I was hoping you could bring some light to the subject.

I am simulating a flow in a micro mixer (related to example: www.comsol.com/showroom/gallery/320/) using laminar flow and transport of diluted species. I want to emulate the behaviour of the so called "chaotic mixers" in which a laminar flow with an initial concentration of a specie "c" is "streched and bent" in order to mix "c" in the entire volume. The chaotic mixer is used in small channels (µm and mm) due to the lack of turbulent forces.

I am not having any results so far. I have uploaded the convergence plots for both step 1: laminar flow, step 2: TDS and my model. At the beginning I wanted to define a lateral (zx in this case) boundary as symmetric boundary for then mirror it. The latter was unsuccessful and I defined it as a wall without results. I have used the default iterative solver and direct solver, I have change the mesh from coarser to fine, I also changed the multigrid mesh coarsening factor from 2 to 1.5 and increase the relative tolerance, all of them at the same time or each one separatelly without any success.

My first guess is that the large "turbulence" made by the bending and streching of the flow might increase each time the error in each iteration leading to a never ending iterative process. But the people involved in the original article was successful in their simulation using periodic boundary conditions but I dont know how to use them.

Sorry for the long post but I wanted to give you a better picture of my situation. Your ideas are more than welcome

My best regards

Miguel
↧

"Reinitializing GUI" for a long time

March 14, 2013, 1:35 pm
$
0
0
Hi, when I solve a PDE, it takes a lot of time. I closed the programme with task manager of windows. When I reopen the file, the programme is "reinitializing GUI" . I wait for almost an hour and nothing changed. At this time I cann't do anything else in the software. How can I solve this problem?
↧
↧

Solve PDE on 1D domain?

March 15, 2013, 4:33 am
$
0
0
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.
↧

Time dependent simulation

March 15, 2013, 6:43 am
$
0
0
Hello Ivar,

I need a big favor from you.
Its a request since my model is giving weird results. I have worked on it but I need to get the physics right.

So I decided to try the time dependent study which should give the instantaneous current values which are then used in the stationary study, that is my thinking.

So I created current variables in the parameters section, ix and iy. These currents are dependent on time, t. So I thought the parameters will be able to access the variable t, but ????

I defined the current in a coil as -ix on one coil-side and +ix on the other coil-side, is this right in the multi-turn coil domain under MF.

The other difficulty I faced is defining relative permeability which will change depending on the H and B values for non-linear material, since mu_r = 1/mu_0 * B/H, where B and H are from the BH curve.
So how do you go about this issue. I was not able to define relative permeability as defined above.
I also Imported with both the 1st and 3rd quadrant, you can check a plot to see how it looks like and I hope its OK.

From the plots of the magnetic vector component, it can be seen that the flux is not penetrating the silicon steel sections ????

Regards and thanks in advance
NB: I attached an m-file by mistake but the model is as attached.
I also submitted the same to the technical support.

Wanjiku
↧

How to combine the Frequency Domain and Coil Current Calculation

March 15, 2013, 7:33 am
$
0
0
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
↧
Search

why are my solutions the same as initial values?

March 18, 2013, 12:39 am
$
0
0
Hi. I build a 1D time-dependent model (transport of diluted species).

using conservative form.
convection transport mechanism
D=0;
u=-k/x^m; (k is a constant)
R=0;
no flux

iniitlal distribution: 1/(x^4*sqrt(2*pi)*log(sigma))*exp(-0.5*((log(x)-log(r_m))/(log(sigma)))^2)
k=4.92*10^(-14)/3600
m=3
sigma=1.2
r_m=0.034

But when I solve it, the solutions at all time are the same as initial values.

I also solve this problem with matlab, the solutions should be in the same shape but different values.

I don't know what had happened. The mph file is too big to be uploaded.

Would you please help me? Thanks very much.
↧
↧

how to define Heat source?

March 18, 2013, 3:36 am
$
0
0
Hi,

I use COMSOL to simulate a microheater to heat the polymer waveguide on Silicon substrate.

The model is 2D. Silicon substrate serve as the heat sink at 25 degrees. When I set the microheater to 300 degrees, I can get a right a temperature distribution.

But now I want to set the microheater as the Heat source,and use the general source as 1000 W/m3. I set Bottom boundary at 25 degrees, and other boundaries as the Thermal Insulation. I can't get a right temperature distribution.

Can any experts on COMSOL tell me the reasons? Very urgent! Than you!

The version is Comsol 4.2.
↧

how to simulate a permanent magnet with vertical movement toward a coil ?

March 18, 2013, 2:51 pm
$
0
0
Hello everybody, i want to simulate a permanent magnet with vertical movement toward a coil
i've used magnetostatics and moving mesh in comsol 3.5
i defined a constant Br(remanent flux) and a prescribed displacement in y direction for the magnet,but B(flux density) doesn't change in the surrounding area and the coil, with the displacement of the magnet.
if i have to use assembly how can i do that??
i send a picture of my simulation for you.(the area between coil and magnet is filled with air)
tnx
↧

Difficulties with #985 Peristaltic Pump Model

March 18, 2013, 6:05 pm
$
0
0
Hi All

(bear with me; I'm new)

Working my way through the peristaltic pump tutorial and all has been a-okay thus far but once I get to the plot of the total volume (bottom of pg. 14) when I try to evaluate the surface integration for the volume it says no solution exists. I am sure that all the boundary conditions are properly defined. Hoping someone has had a similar issue..

Any ideas?

Thanks,

Alexis
↧

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

September 23, 2009, 7:01 am
$
0
0
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
↧
↧

Java Runtime Environment error

July 28, 2011, 8:37 am
$
0
0
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
↧

negative concentrations with high reaction terms in biokinetic models

September 26, 2011, 10:46 am
$
0
0
Hi,

I am using a biokinetic model based on the ASM (activated sludge models) to simulate water contaminant removal in a gravel filter. This kind of models consider the degradation of the influent solute components by several species of microorganisms. As a result of the degradation, this microorganisms also grow.

For the flow simulation I am using Darcy's Law. The contaminant removal is modeled using the solute transport module with a reaction term, in which monod-like expressions are deffined. These reaction expressions are also multiplied by the concentration of the different species of microorganisms that consume each solute component (the higher the concentration of microorganisms the more they consume).
The growth of bacteria is modeled using PDE general form expressions.

This works just fine for short periods of time (e.g. 1 day), but when bacteria start to grow considerably, the reaction terms become very big and negative (consumption), and thus the concentrations of the solutes become also negative. I've tackled this by deffinig variables s=max(eps^2,S), were S is the concentration of the solute. So when S becomes negative, in the next time step it is seen as a 0 instead of a negative value. If I don't do this, a part from getting negative solute concentrations, the growth of bacteria also gets corrupted (as it depends on S), and therefore this error impacts the whole model. I also tried to add expressions such as *(S>0) in the reaction term of S, but I have not been successful either.

I have checked the solutions suggested in this link, www.comsol.com/support/knowledgebase/952/ but it did not help much.

Could anyone tell me how to make the reaction rate 0 when the concentration of the substrate becomes zero? I do not understand where exactly should I introduce the term max(eps^2,Q).

Hope I made myself clear.

Thank you in advance
↧
Search

Piezoresistive modeling

May 29, 2012, 2:26 pm
$
0
0
Hello all

I want to simulate a piezoresistive beam with Comsol.
I was looking to find an example of piezoresistive modeling to find out what module they usually use and how are the settings but i didn't find any
It seems there was an example of "piezoresistive elevator button" before for old version of Comsol. But it is not avail;able anymore.
Can anyone send me this example or any other helpful link about piezoresistive simulation by Comsol?

Best
Bahar

↧

Error: 7161 The mass matrix is zero - resolve

March 12, 2013, 11:59 am
$
0
0
Respected sir/ma'am,

I am trying to simulate a Nano ElectroMechanical Switch(NEMS) using the following modules:a)solid, stress-strain, b) Moving Mesh, and c)Electrostatics.
When i run the solver, it shows an error message:'Error: 7161 The mass matrix is zero' along with a warning: 'Not all domains are meshed'.
The sizes are in nano domain. Model is attached for your kind reference.
For meshing i used Mapped Meshing to reduce number of elements.
I am using Version 3.5a on Pentium processor with 32 bit and 2 GB RAM.

Thank You in advance
↧
↧

Prolonged error with "Last Time Step Not Converged"

March 13, 2013, 1:40 am
$
0
0
Dear sir,

We were trying out "PIPE FLOW MODULE" as you have suggested. And thanks for the advice, as it has reduced the number of mesh elements to a larger extent. But, we were getting a consistent error message namely,

"Error:

Failed to find consistent initial values.
Segregated group 2

COMSOL assertion failure.
Last time step is not converged.

Warning:

SOR line did not find any lines. "

I would like you to verify our model and help us if any errors made in the modeling.

Basic parameters are that, the heat flux will take place in walls through inner air, atmospheric air and water in pipes as in the model. I would be so grateful, if our prolonged error is sorted out.
↧

How can I find the flow velocity of a specific coordinate point

March 13, 2013, 12:44 pm
$
0
0
Dear all,

I would like to ask how can I find the flow velocity of a specific point (x=105, y=2.5) in my channel (it is shown in the picture). In the graph, if I click at any random point I got 3 values: on the x axis I got the channel's length, on the y axis the height and the different colours represent the flow velocity profile and hence, I got 3 values for x,y and u.

But I would like to find my velocity at a specific point, so could you pleqse help me how can I do that?

Thank you a lot beforehand.

Regards

Dimitrios
↧

Automatically parameter increasing

March 13, 2013, 1:26 pm
$
0
0
Dear friends,
I have a simple 2D rectangular model, I want to measure some acoustic properties in my desired frequency range, for specific height of model it's easy, but I want to check a range of heights for example 0.1 mm to 10 mm, with 0.1 increment, how can I set COMSOL to do this and save data automatically?
Regards
↧
Viewing all 3988 articles
Browse latest View live
Search
<script src="https://jsc.adskeeper.com/r/s/rssing.com.1596347.js" async> </script>