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Heat loss in hydraulic hose

February 9, 2013, 2:10 pm
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Hi,

I'm working on an project where it's in my interest to find the heat loss to the surroundings, from the hydraulic fluid
inside a hose. I have access to Comsol Multiphysics 4.3 through my work and school, but has only used it with
mechanical simulations before.

If someone could help me get started, I would be greateful. Also, if somone has made an simulation like this and have
the .mph file, it would be very glad if you could share this with me?!

I have attached an image of an simple straight forward hose that I want to simulate.


I will be grateful for any help you can provide.
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Scaling of motional mass

February 10, 2013, 1:06 am
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Hello everyone,

Thanks to this forum I have found out how to calculate the motional mass for different vibrational structures. The calculation of (MPF_mod1.u^2)/(TotalMass) and for v and w gives a nice distribution of motional masses, and taking enough eigenmodes sums up to the total mass. However I think there must be a further normalization I do not understand because for the clamped membrane case I find a participation factor of a half the total mass instead of the 1/4 it is in reality. The same is the case for a clamped wire/beam where the motional mass should be half the total but instead is about 0.7 of the total mass. I attach this case.

Am I just confusing the normalization?

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Problems with boundary layer meshing

February 10, 2013, 5:24 am
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I am trying to mesh a k-epsilon model and cannot generate a boundary layer mesh. My model has a very narrow region and I expect that that is the problem area. The error I get most often is: Could not shift boundary node at all. The first screen shot attached is a view of the narrow region. The second shot shows the internals.
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SPIRAL HEAT MODEL

February 10, 2013, 7:07 am
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HI,
Just i want to know howl can i change the height of the COSOL spiral heat model, it's around 6mm, and i want to make it at 60 mm
thanks
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How to analysis a muffler(decibel & Frequency rate of outlet)? please help!!!!

February 10, 2013, 8:07 am
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Hi guys!
I have a model muffler of an exhaust that will to analysis. i will to measure Sound intensity(db)
& frequency of outlet. i show a picture of my muffler in this picture(I show inlet & outlet,too):

upload.tehran98.com/img1/f9pdgyt0f3szwoo43k5v.jpg

I have several question:

1- Which calculator should I use(which interfaces?(pressure acoustics(frequency domain(acpr)) or...))?
2- How to meshing?

My Assumptions is on inlet:
frequency range: 1000hz to 20000hz
Sound intensity range: 30db to 130db

Now, I will calculate sound intensity & frequency of outlet. I will to know that my muffler how Reduced the sound intensity & frequency of outlet.
How to do this job?
please help me!
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Problems about Periodic Conditions in the tutorial model “Periodic Boundary Condition”

February 10, 2013, 11:10 am
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Hi all,

Recently I confront one confusion about periodic conditions in the tutorial model - Periodic Boundary Condition. In Periodic Condition, it selects only boundaries 1 and 6 which are parallel with the yz-plane. As you know in the model, the cube should be a repeated cell and certainly repeated on the xy-plane both in the x direction and in the y direction. However, boundaries 1 and 6 only correspond to x direction. So what about repetition in the y direction?

Then I try to select both boundary 1, 6 parallel with yz-plane and boundary 2, 5 parallel with xz-plane in the Periodic Condition. But some problem occurs just as follows:

Errors during multiphysics.
Failed to find destination boundaries or destination selection empty
- Feature: Periodic Condition 1 (pc1)

I don't know why this happens and how to set Periodic Condition that means a repeated cell in the xy-plane both in the x direction and in the y direction.

Thank you so much.
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How to define AC voltage and the direction of AC current in comsol

February 10, 2013, 2:40 pm
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Hello, guys:
I am a new user to Comsol and I am currently doing electromagnetic single phase power transformer model using comsol. The Physics i am using is Electric Currents (ec), Magnetic and Fields (mef). I am using comsol version 4.2.
The problem i am facing is that when i trying to define the AC voltage for the winding of the transformer, the Electric potential shows only Vo. And I cannot find out any of the defines of the Electric Currents contains Vac that ask me to define the frequency and amplitude.
The other problem is that how do you define the direction of the AC current in Comsol.
Can anyone provides some hit.
Thanks
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Error: Unknown property: funcname

August 22, 2011, 9:58 am
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Hi,

I have defined a MATLAB function which is called by COMSOL. I get an error message such as:

Undefined value found.
- Detail: Undefined value found in the equation residual vector.
There are 2128 degrees of freedom giving NaN/Inf in the vector for the variable mod1.solid.pw
at coordinates: (0.452,0), (0. 448,0), ….

In the meantime, when I try to get a Report from my model in Results/Report, I receive such an error:

Unknown Property
Property: funcname

I think I have properly implemented the MATLAB function (regardless of how it calculates the things for me, because I get the above error).

Does anyone know what this error means?

Thanks,
Jessica
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Plasticity

February 4, 2013, 6:40 am
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Whats the difference between Small Plastic Strain and Large plastic strain?
How is a model with contact and friction to simulate? What is important?
My models usually have convergence errors when I expect friction. What am I doing wrong?
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Continuing Modeling Issues with 2D & 3D piezoelectric SAW model

February 7, 2013, 6:22 am
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Hello all,
I’m in desperate need of help with my model. The initial model setup is a 2D cross-sectional SAW device where I have silicon, a metallic electrode as my ground, a buffer layer, a piezoelectric layer (PZT-5), and gold electrodes. The current physics I have defined is with piezoelectric devices (with COMSOL version 4.2.0) with the silicon and buffer/protective layer (SrTiO3) as my linear elastic material model, the metallic electrodes and metallic layer as my electrical material layer, and piezoelectric material model with the PZT. I have defined parameters most of the materials in terms of elastic matrix D, Young’s Modulus, Bulk modulus, permittivity, and so forth. My main issue is when I run a frequency domain analysis; I consistently get the error of:
Failed to find a solution for the initial parameter. Singular matrix. There are 3906 void equations (empty rows in matrix) for…etc.
I have looked through the discussion forum consistently to see why I continue to get the errors I received and I thought it was simply a matter of fixing my boundary conditions but I thought I had accounted for all constraints for this simplified model. I do not know at this point where I have been going wrong for the past couple of months now. I’m attaching the current model. Any suggestions or comments would be greatly appreciated. Thank you.


--
Sarah
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Particles traveling through boundaries

February 7, 2013, 5:16 pm
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Hello All,

I am attempting to use the particle tracing function on a laminar flow in a small channel with obstructions in the channel. I modeled the design after the lunchtime seminar on the particle tracing on comsol's youtube channel. The velocity profile comes out fantastic and feasible, which means the boundary exists for the obstructions for fluid. When I begin a second physics and try to find particle paths through these obstructions they simply travel directly through the boundaries straight for the exit. I've attached the .mph file for any so kind as to help me with this problem. I should probably mention that I am new to this version of comsol so it might be something obvious. Thanks in advance!
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Eigenfrequency seems right, but displacement units are totally wrong.

February 7, 2013, 7:18 pm
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Dear Comsol Community,

in the model attached I have a 20 micron long beam using the Solid Mechanics module to get the Eigenfrequencies. I calculated them manually using Euler-Beam theory and the first Eigenfrequency should be around 5 MHz.. Comsol calculates 4.8 MHz. I thought great result, but if you look carefully at the screenshot, you will notice that Comsol claims the displacement is on the order of meters, which is totally wrong (it is rather pico meters). I feel I am missing something fundamentally, but I cannot get Comsol to spit out the correct displacement as well. (Scaling or anything of that sort is disabled).

Thanks for advices!

Erik
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Preparation of figures for papers/thesis?

February 10, 2013, 8:19 pm
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If it has been written somewhere, can someone point me to where there is a guide to producing figures from 2D plots?

I am using COMSOL 4.2a, and want to use some surface plots alongside legends of the colour tables used. It is bizarre that COMSOL does not provide vector graphics export. I have tried to generate a decent image using the png export (via the 'snapshot' button -- is there any other way?), but it is horrible.

How I am doing it is:
1. Use highest 'Quality' settings in each component of the plot group that has such a setting (e.g. Surface; Contour)
2. Set export resolution to 1200 DPI
3. Set image dimensions to highest possible (for me it seems 4096 pixels is the upper limit?).
4. First generate a snapshot without any includes (i.e. no title, legend, axes. etc)
5. Then generate a snapshot with the legend included.
6. In GIMP cut and paste and scale as required.

See attached file for example of trying to export a surface plot with two colour legends. The model image part of the figure is tiny, and the legends huge.

If anyone has any tips or a separate set of routines in python/matplotlib or similar already in place I would love to see it!
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RF Source

February 11, 2013, 3:54 am
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Hi,

I want to apply a current or a voltage source to a rectangular surface in a COMSOL RF module problem. Would you please let me know how I can do that?

Regards,
Elham
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must i compute the whole programe again?

February 11, 2013, 4:15 am
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Hello,

I am a beginner of comsol. Most of the time, i made mistakes and got different solution from references. Then i changed Model settings and tried to find the right solution. But usually it take 1-2 hours to complete the computation again. I wonder is it possible to only compute the small part which i have changed? Any tips are welcome! Thank you!
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Modelling Metallic Diaphragm

February 11, 2013, 5:39 am
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I am a novice COMSOL user using the software for a student project so apologies if my problem below seems simple.

I have a 2D axisymetric model of a thin metallic diaphragm (approx 25mm di and 0.025mm in thickness).
The diaphragm is deformed by a uniform pressure load and fixed around its perimeter.

To begin I have used a simple flat diaphragm and the model produces deflection results that agree well with theory for small deflections (up to approx 2xthickness)

When a greater pressure differential is applied the model appears to become over "stiff" and the predicted deflection is significantly below that given by theoretical results.

Currently I have tried varying the mesh size and shape (quad/tri) with no significant change in the result. I have also trialled both linear and quadratic elements with no significant improvement (the element quality is always extremely high due to the simple geometry).

I am using a linear elastic model with non-linear geometry enabled. Is this Ok to use when there is considerable strain in the model?

I would be great full if anybody has any feedback on how to improve the model / experience with a similar model or ideas on why it may be differing from theory?

Thanks in advance!

Matt
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Limiting simulation volume/area or displacement for mechanical model

February 11, 2013, 6:33 am
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Hey,

while doing a buckling study of an optical fiber I tried including a fixed box around the fiber to constrain the movement of the fiber within this box. Sadly this increases the required simulation time a lot so I replaced the box with 'beams' that would effectively constrain the fiber between the beams.
When converging (the model seems quite unstable for certain parameter values) I noticed that, eventhough I specified contact pairs between the fiber and the inner boundaries of the constraining beams, the simulation tends to give me a result where the fiber ignores the beams and buckles in another direction.
It seems the fiber ignored it's contact pairs with the beams and somehow went through them.

So I was wondering if there is a way to limit the displacement/deformation of an object, in a 3D stationary mechanical model.
If this "box-approach" is the only way to do this: is there a way to either reduce the simulation time by telling COMSOL that you're not interested at all in what happens with the objects that form this constraining box, or make sure the contact pairs are respected during a deformation.


thanks

Evert


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Heavyside-Function and Divison by Zero

February 11, 2013, 10:13 am
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Hi

I stumble realising a Gaussian-beam like in the tutorial model "Nanorods" (using RF-module).

Problem:
Part of the wave function has a singularity: constant/z
Solution in tutorial:
Define a piecewise-function covering the singularity like:
z<-z0 : constant/z
-z0<z<z0 : constant/z0
z0<z : constant/z

But in contrary to the example I need frequency-dependent borders respectively frequency-dependent z0 [Z0(freq)].
As this is not possible with piecewise-function (i guess) i tried a sum of Haevyside-functions (like recommended in several forum-posts):
(constant/z)*flc2hs(-z-Z0(freq),range)
+(constant/z0)*flc2hs(z+Z0(freq),range)*flc2hs(-z+Z0(freq),range)
+(constant/z)*flc2hs(z-Z0(freq),range)

Does the same when being plotted from the Global_Definition/Anayltics-Node. Produces also no error when the model is being computed. But trying to plot from Solution1-Node producing the error:
Evaluation of result expression failed
Error in user-defined function
Failed to evaluate expression

This error does not occur if the (constant/z)-function is replaced by a non-singularity-function. So plotting after computing messes somehow with the Heavyside-function.

Any idea or experience how to get that work? This starts to erode my self-confidence.

Thanks for any help


edit: Problem was, i think, not the above expression but the fact that inside of the wave-function something gets divided by that expression. And i think the smoothening of the heavyside-function leads to a zero at the singularity. And then again divided by zero ^.^ -> error
Though i am not sure.

But in this case using the inverse function just works fine : )
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How to implement a biphasic asymmetric waveform?

February 11, 2013, 1:39 pm
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Hello everyone. I'm trying to figure out how to implement a biphasic asymmetric waveform in Comsol 4.3a. I need to be able to use the following electrical simulator settings in order to stimulate an array of electrodes. Does anyone know how to do such a thing in Comsol? Your help would be greatly appreciated. Thanks.

Here is the information for the 4 channel electrical stimulator settings:

Channels 1+2 output as one biphasic waveform:
Channel 1:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = 10 V
Channel 2:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = -0.32 V

Channels 3+4 output as one biphasic waveform:
Channel 3:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = 0.32 V
Channel 4:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = -10 V

I look forward to hearing from anyone who may be of some help for me on this topic. Thanks again!
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Adding a Faxen Force on Stokes drag force in Particle Tracing Module

February 11, 2013, 4:13 pm
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Hi everyone,

I am trying to use the particle tracing module with a non-uniform laminar flow in a channel. I am using "Drag Force" to trace the particles' motion. However, the Stokes force is defined without the Faxen Force in Comsol.
(oi46.tinypic.com/28c33nl.jpg)

I am wondering how I can add the Faxen Force on the equation. Is there already built-in physics module for Faxen Force?

Thanks a lot,
Damla
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