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Flow and pressure Acoustics models

September 1, 2014, 11:04 pm
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Hai is there any example model of flow and pressure Acoustics, to understand how pressure various when there is a constant flow, or heavy flow of liquids.
thank you,
taraka
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Failed to find consistent initial values on FSI simulation

September 8, 2009, 5:13 pm
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I was trying to simulate a FSI problem by modifying the COMSOL FSI example, trying to see the same effect presented in the following reference:

Zhiyong Li, Simulation of the Interaction between Blood Flow and Atherosclerotic Plaque, Proceedings of the 29th Annual International Conference of the IEEE EMBS Cité Internationale, Lyon, France, August 23-26, 2007.

It creates a plaque with cap and core of different Young's moduli, and computes the interaction of them with the blood flow. The model is shown in the attached picture.

In my modified model, when the simulation starts it reports

Failed to find consistent initial values.
Last time step is not converged.

Any trick to define the boundary conditions? I've tried composite and assembly geometries with no vail.

Thanks.
Lathi.
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error test failures

January 2, 2014, 2:22 am
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hi
i use ccp module for simulation,my time range is range(0,5e-5,0.001) but when i compute model times go 7.579247e-019 to this and report this error
Repeated error test failures. May have reached a singularity.
Time : 7.579247088737066e-019
Last time step is not converged.

how can i solve it?
thanks
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Electron energy in DC Discharge Plasma

February 4, 2014, 10:33 pm
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Hej,
I am working with the DC discharge Plasma interface. In my plasma model electrons are produced due the decay of tritium (T=>e+T+), in the real plasma case the main part of the electrons are produced due to secondary ionization. the secondary electrons have a mean energy of about 100meV. To make the model easier I decided to produce a larger amount of electrons from the T-decay reaction.
And here comes my question, which is the energy the electrons (from the decay reaction) are produced with in COMSOL? (As I would like to set this enegy to 100meV) Is it the mass difference of the involving species?
Would be nice, if somebody can help me.

Thanks
Laura
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Modeling tension and compression in curved blob

June 29, 2014, 5:10 am
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Hi guys,

I have a model of a blob (ellipsoid) that is displaced into a bowl-shape (prescribed displacement driven by a gaussian equation in the z direction). There is no movement in the x or y directions. I would expect to see tension on the convex surface as it is displaced outward, and compression on the concave surface as it is displaced inward, but instead we see only vertical stresses acting throughout the cross-section in the XZ or YZ planes (model attached). I've tried changing the type of stress from von mises to pretty much every other option (including strain, etc.) and can't seem to get anything that looks remotely like tension/compression (horizontal lines in the cross section rather than vertical). Any suggestions?

Thanks!
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Plot of Time Average Electric Field

August 26, 2014, 1:22 am
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Using the optical/RF module, when plotting the variable ewfd.Ex (x componente of electric field), do we see the time averaged value of the field OR a snapshot in time of the field distribution?

Regards,
Rui
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Definition of some parameters in Joule heating module

August 28, 2014, 5:35 pm
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Hi guys,
I am working on a simple geometry to simulate it with Joule heating module. While I am looking through equations in this module, I cann't find description of some of them. I appreciate if someone may help my about them:
1- Under Joule heating model for domains, what is Q_j (and its difference with Q) and J_e and also epsilon_0?
2- Under boundary electromagnetic heat source, what is Q_sh and since we have another boundary condition for electric field such as electric insulation, why we need boundary electromagnetic heat source?
I am sorry if the question looks awkward, but I really need to know what is going on within the fundamental equations of simulation.
Thanks a lot.
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Meshing problem

September 2, 2014, 3:07 am
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Hello
I am currently encountering following Problem.
I have been modelling a cable in ground. In order to calculate my results faster I have been modelling the cable only over a distance of 0.1[m]. Now I am encountering a Problem with the mesh when i am trying to expand the structure to 10 [m] or even more. It say something about:
Components: free tetrahedronmesh1, marginalized layer 1
Mesh couldnt generate for this area
Internal error consindering borders

No idea what i am doing wrong.


Does anyone of you might know how i will be able to solve this Problem?

Thank you very much.
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Kundts Tube with Thermoacoustics, Complex nummbers

September 2, 2014, 4:44 am
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Hi,
I have got a good working comsol model of the kundts tube. To get a value for the reflexion coefficient I need the acoustic pressure at two different points in the middle of the tube. But I also need the phase difference of the two points, or alternativly the acoustic pressure as a complex number.
How will Comsol give this information?
Thanks
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Modeling Traffic Noise with Comsol

September 2, 2014, 6:39 am
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Hello,

I am interested in using Comsol's Acoustics module to simulate the sound propagation from different roadway geometries (elevated, depressed, with(out) wall barriers).

The setup I wish to use would be as follows:
- The noise source be represented as a point or line source depending on domain of the model (2-D or 3-D)
- Infinite elements be used for propagation beyond the complex roadway region
- Terrain/barriers modeled with the potential of absorption and/or reflection

I would also be interested in the Aero-Acoustics part of the Comsol Acoustics Module. This would allow me to insert a background wind flow into the model with possibility of affecting the sound propagation.

Question: Since I am interested in the advanced Acoustics Module license, does Comsol have the potential to model my setup as described above?

Thanks,
Michael
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limiting a dependent variable to a specified range of values

September 2, 2014, 12:17 pm
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Hello,
I am conducting a heat transfer simulation in which I have a dimensionless dependent variable which represents the vapor quality of the coolant fluid.

By definition, vapor quality must take values between zero and one, where a vapor quality of zero represents pure liquid and that of one is pure vapor. Values of less than zero or greater than one have no physical meaning (at least for the purposes of this simulation).

How can I set up the simulation so that the vapor quality is limited to values between 0 and 1? For example, if the simulation, for whatever reason, calculates a vapor quality less than zero, I want the vapor quality to be rewritten as equal to zero. On the other hand, if the simulation calculates a vapor quality greater than one, I want the vapor quality to be written as equal to one.

I want to do this to avoid numerical instability that appears to be caused by vapor quality taking on values less than zero.

Thanks!
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Any Introdution materials on Semiconductor Module

September 2, 2014, 5:18 pm
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I have been doing simulation with semiconductor module . But I don't know what the parameter in the governing equaitons mean. So , is there any one have some guide materials on Semiconductor module?
Thank you very much!
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Coding: Geometric Parameter Sweep

September 2, 2014, 11:44 pm
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Hi everyone,

I designed a relatively complicated model where the 3D temperature distribution (with Joule heating) was simulated.

The model consists of a PCB, some wires and some electronic components.

My main concern is to find the maximum temperature on the whole structure, I want to write a script where COMSOL automatically moves the components (and the wires accordingly) around and computes the temp. distribution for each case. Ideally, it should also save results (plots or date).

My idea (strategy proposal): The components are rigid bodies but are composed of several shapes and functions (blocks, extrude, work planes...). I would combine these shapes into a "group" and name them (eg. resistance1, resistance2..). Each "group"s center would have a specific coordinate. By using this center`s coordinate, I will write for-loops and try to achieve the goal.

I did a similar approach in Lumerical, but don`t know if it is applicable to COMSOL.

Would really appreciate if you could help me on this. A similar tutorial would also be very helpful.

Thank you,
Bartu
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Real and Imaginary parts of S11 and S21

September 3, 2014, 2:32 am
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Please tell me how can i obtain real and imaginary parts of S11 and S21 .I plotted a curve between S11, S21 (dB)vs frequency(Hz), but the algorithm which i am going to use requires real and imaginary parts of S11 and S21.If anyone knows please help me.








Regards
Ranu Pal
Ph.D
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USE of Ambient Temperature in AC/DC module

September 3, 2014, 8:21 am
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Hello everyone,
I am new in this forum. I have built a AC/DC module model. Now I want to analyze the changes in different parameters for a certain ambient temperature range. Do I need to add any more physics. If yes, then which physics?
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how to define unit of dependent variable?

September 3, 2014, 8:32 am
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Hello

I am using COMSOL 4.2 for "coefficient form PDE" multiphysics.

How to define the unit of the dependent variable in the equation?

Because, there is no section in the equation for defining the unit.


Thanking you in advance


Anup
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How do I calculate volume flow rate with a thin channel approximation?

September 3, 2014, 8:39 am
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Hi,

I have tried several ways posted in the forum to calculate flow rate in a microfluidic channel simulation. I can not get the right answer so I think I must be missing a detail.

The model is attached, the inlet is the circle on the left, and the outlet is the circle on the right. The flow is driven by gravity, so I used a small pressure difference at the inlet and outlets to drive flow.

I used a thin channel approximation with a depth of .00004m. I am not sure how COMSOL uses this in the integration and average calculations.

What is the easiest way to calculate the flow rate through the device?
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How to compute time-averaged power in a frequency domain solution?

September 3, 2014, 9:29 am
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I am attempting to compute the time-averaged power delivered to a resistive load domain but cannot figure out a reliable way to do so. Any help would be appreciated.

I am modeling inductive coupling between two coils of wire in the Magnetic & Electric Fields interface. The bottom coil is driven by a voltage source imposed by terminals. The top coil is connected to a resistor, where that resistor is simply modeled as a domain with lower conductivity. I'm solving my model in the frequency domain and would like to compute the time-averaged power delivered to that load resistor. I cannot attach my full model, but a toy model is attached to illustrate the situation.

I've tried multiple tactics to compute the power delivered to the load, but none quite work. Here are a few of my attempts:

1) Compute the voltage across the load by averaging the voltage on each boundary and computing the difference. Compute the current through the load by integrating the surface current through a boundary. Compute power delivered to the load as (1/2)*real(conj(V)*I). This gives an okay estimate sometimes, but often has significant error due to varying voltage and current distributions on the load boundaries. In many cases, this can even report more power going into the load than is being provided by the source.

2) Integrate the resistive losses (mef.Qrh) within the load domain. This gives a much more accurate estimate of power delivered to the load, but only at a specific instant in time (i.e., at phase = 0 degrees). If there is a way to compute the time average of these resistive losses, then that'd be perfect, but I cannot find a way to compute the time average for a frequency domain solution.

3) Utilize the time-averaged power flow variables (mef.Pox). Unfortunately, these essentially average to zero on any given boundary and thus appear useless to me.

So how does one go about computing the average power delivered to a resistive load domain? I've been struggling with this question and would appreciate any advice.

Thank you.
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Conditional Statements within an Expression

August 17, 2009, 9:35 am
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Hi,

I was wondering whether it is possible to incorporate conditional statements within an expression?

For example,

if ( t > 6 ) then Zeta = 5

In this example I test the simulation time and if it is greater than 6 then I change a boundary condition.

This is possible in MATLAB, but can it be incorporated into an Expression within COMSOL?

Regards,
Tom
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finite volume, volume of fluid, boundary integral method

August 13, 2012, 5:00 pm
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Hello,

I'm trying to model a cavitation air-bubble in water under ultrasound waves. For that I need to use a Boundary integral method to solve the Laplace equation. The finite element method I try to use until now is not stable for my problem.

Is there any boundary integral method (using Greens function) module for Laplace equation in Comsol 4.2 or 4.3 available?

Thanks for your answer!

Karl
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