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Drag coeifficient over a cylinder

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Hi,

anyone know how to calculate the drag coeifficient by use the post-process mode in COMSOL.

which type of boundary integration I should use? I mean pressure, viscous forces or else.

I used the impressible N-S model.

Thank you!! Please help me.

Error messege : initial guess leads to undefined function value

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Hi,

I encounter,

error : 7043
initial guess leads to undefined function value


I have already clear all meshes and solutions and reset the model using the "reset model" opition inthe file menu, and I've also set the solver manager intit page to " initial value expression evaluated at the current solution".

But there's nothing happened.

does anyone ever encounter the same problem as me? How can I solve this kind of error messege?

Disk error while writing to temporary solution file

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Dear Sir/Madam:

I running five different HT+CFD transient model simultaneously from last Saturday and today morning I noticed the error saying "Disk error while writing to temporary solution file." I never came across this situation before and therefore I need your suggestion. Please also suggest me how to change temporary directory.

Regards,
Hitesh Vora

ERROR: nonlinear solver did not converge, when simulating ball movement in meso-size chamber.

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Hi all,

I have seen several threads about this error and tried to figure it out myself using the sample cases but I still fail to simulate this. Any help will be greatly appreciated.

I am trying to simulate the movement of a 1 mm diameter ball inside a chamber. There is a water flow on the top of chamber, from left to right. I am using fluid structure interaction (FSI).

I keep getting the same error message that says
Nonlinear solver did not converge.
Time : 4.6875e-005
Segregated group 2

Attempt to evaluate real square root of negative number
Function: sqrt ... (and so on)

I also get a list of warning saying that "Inverted mesh element near coordinates ..., ...) that are located inside the ball (which is linear elastic solid material). I am also confused because it supposedly have less deformation compared to fluid area.

Any help or idea will be greatly appreciated. Thanks in advance.

Simulate Fields Outside of Semiconductor Device

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Is it possible to simulate the electric fields outside a solid-state device (such as a PN junction)? In other words, I'd like to create a boundary outside the device representing air and solve Poisson's equation in that region based on the charges and potentials on the surface of the device.

If this is possible, must I use the semiconductor module (to simulate device physics by solving Poisson's and drift-diffusion equation) with the AC/DC module (use the potentials generated from the semiconductor module and apply to boundary of air)?

Is it possible to choose for drift-diffusion + Poisson's equation to be solved inside device and only Poisson's outside of device, thus requiring only the semiconductor module?

Transparency in Comsol

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HI

I am actually modelling and simulating wire sweep on comsol. I have a cavity in which the microprocessor is placed. I will have a glass pane on top of it. I have modelled everything and even added all the materials. What i don't know is how to make the glass surface on top, transparent and leave the rest of the the model opaque.

I'm new to this software so any help would be greatly appreciated.

Thanks and regards
Ahmed

2D-Axisymmetry not considered for domain probes in the calculation "Average" or "Integral"?

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Is the 2D-axisymmetry not considered in the calculation of domain probes?

I learned, that I had to check the checkbox "Compute Integral in revolved geometry" when I wanted to calculate the correct average or integral with Component/Definitions/Component Couplings/Average.

But I didn't find the checkbox "Compute Integral in revolved geometry" in Component/Definitions/Probes/Domain Probes

Photo carrier generation in the Semiconductor Module

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I'm trying to figure out how to achieve photo-carrier generation in a direct band gap semiconductor in the COMSOL 4.4 semiconductor module. The only form of generation I see in the module is Impact Ionization which consists of various a,b,c, and d factors for electrons and holes. I need the equivalent of a photo-excitation signal to analyze the IV characteristics of a semiconductor. How can I model the generation of photo-carriers in the semiconductor module?

Semiconductor photoelectrolysis

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Hello,

I am hoping to model a photoelectrochemical cell in which a semiconductor working electrode (e.g. InP) is used in conjunction with a counter electrode (e.g. Pt) which under the influence of solar irradiation can split water into hydrogen and oxygen.

I'm struggling to think of where to start with this problem; the examples provided in the electrochemistry module are too simplistic as I need to gain an insight into where band edges within the semiconductor sit relative to oxygen- and hydrogen-production potentials in the electrolyte.

A Schottky junction (band bending) is formed at the semiconductor electrode - electrolyte interface and illumination should (in theory) flatten this band bending by the photogeneration of charge carriers in the depletion region formed by said bending. I would ideally like to model the extent of this band bending under varying illumination.

Does anyone have any suggestions as to where to start or ideas/thoughts about the aims in general? Any help greatly appreciated!

Many thanks,
Sam

*Now Available* COMSOL Multiphysics 5.0 with the New Application Builder

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Hello COMSOL Community,

COMSOL Multiphysics(R) 5.0 with the Application Builder was released on Friday October 31. With the new and revolutionary Application Builder, you can easily build apps based on your COMSOL(R) models to be shared with colleagues and customers throughout the world.

COMSOL Multiphysics 5.0 can be downloaded at:
www.comsol.com/support/download

Read the release highlights:
www.comsol.com/release/5.0

*News in COMSOL Multiphysics*
- Application Builder: Provides you with an automated way to build a powerful yet simplified interface for any COMSOL model, which can then be shared with your colleagues and customers. Included with the Windows(R) version of COMSOL Multiphysics 5.0, the Application Builder provides all the tools needed to build and run simulation applications.

*News in add-on products*
- Drastically improved handling of large arrays and CAD assemblies where hanging nodes are allowed.

- The Multiphysics node, introduced in COMSOL 4.4, has been greatly expanded to cover additional multiphysics couplings.

- Mechanical: Model geometrically nonlinear beams, nonlinear elastic materials, and elasticity in joints using the products for modeling structural mechanics. In the Heat Transfer Module, thin layer, film, fracture, and rod as well as cryogenic damage and parallelized radiation have been added. The Acoustics Module has two new methods for modeling high frequency or geometrical acoustics (Ray Acoustics and Acoustic Diffusion Equation).

- Electrical: The AC/DC Module, RF Module, and Wave Optics Module now contain a frequency- and material-controlled auto mesh suggestion that offers the easy, one-click meshing of infinite elements and periodic conditions. The Plasma Module now contains interfaces for modeling equilibrium discharges.

- Fluid: Create automatic pipe connections to 3D flow domains in the Pipe Flow Module. The CFD Module is expanded with two new algebraic turbulence models, as well as turbulent fans and grilles.

- Chemical: The Chemical Reaction Engineering Module now contains a new Chemistry interface that can be used as a Material node for chemical reactions.

*New products*
- Ray Optics Module: Industry-leading simulation tool for analyzing systems in which the electromagnetic wavelength is smaller than the smallest geometric detail in the model. Includes the ability to compute the trajectory of rays in graded and ungraded media, and the modeling of polychromatic, unpolarized, and partially coherent light.

- Design Module: Expands the available toolset of CAD functionalities in the COMSOL product suite. The module includes the following 3D CAD operations: loft, fillet, chamfer, midsurface, and thicken, in addition to CAD import and geometry repair functionality.

- LiveLink(TM) for Revit(R): Allows COMSOL users to interface with the building information modeling software from Autodesk(R) and seamlessly synchronize a geometry between Autodesk(R) Revit(R) Architecture and COMSOL, allowing multiphysics simulations to be brought into the architectural design workflow.

COMSOL Multiphysics 5.0 can be downloaded at:
www.comsol.com/support/download

Read the release highlights:
www.comsol.com/release/5.0

Enjoy COMSOL Multiphysics 5.0 and the Application Builder!
Valerio

--
Valerio Marra, Ph.D.
Technical Marketing Manager
COMSOL, Inc.
+1-781-273-3322
valerio@comsol.com

Defining prescribed mesh velocity in Deformed Geometry physics

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I am modeling the dissolution rate of a particular particle inside water using both the Transport of Dilute Species and Deformed Geometry physics.

There's only one dependent variable in "Transport of Dilute Species" physics (c). I do have a relation for the prescribed normal mesh velocity section in "Deformed Geometry" physics. But, this relation contains the partial derivative of "c" (from transport of dilute species) with respect to time ON the surface boundary of the particle! this is the tricky part I do not know how to approach.
I want to know how to use the variable "c" calculated in one physics and use it and its derivatives in other physics involved.
I'd appreciate it if you could help me with that.
Thank You,
--
SY

Extracting Eigenvalues and Eigenvector using Eigenfrequency study

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Hello,

I was successfully able to extract the first N (~ 50) eigenvalues, using Eigenfrequency study and Solid Mechanics physics setup. I use the export option to write out the frequencies and eigenvalues (lambda).
However, now I also need the corresponding Eigenvectors. I am not able to do the same, since the exporter does not show Eigenvectors in the export list.

Pls let me know how I can export the first N eigenvalue and eigenvectors pairs. Is there is a simpler way to do this using Matlab LiveLink?

Thanks,
Gaurav

Force transfer between surfaces

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I have a question and I hope the answer will be an easy one. I have tried to figure this out in the program and looked around through the forums but was unable to find a solution. Here is my problem:

In axi-symmetric space I have a coil with a radially outward Lorentz force on it. The coil supports itself mechanically but also transfers some of the Lorentz force to an adjacent support structure. How can I determine the amount of force that is transferred onto the support structure through the surface?

Thanks in advance.

Streamlines

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Hi All,

I am working on a micropump and trying to have a plot of the flow. How can I generate a plot just like the attached picture? I tried streamlines, but I could not get the direction of the streamlines.

Thank you so much.
Marwan

Virtual Work (convert work in force)

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Hi@All,

I'm trying to compute a magnetic force with the principle of virtual work. Therefore I have created a simulation with a cylindrical coil and a ball-permanent magnet. The ball has a remanent magnetization Br of about 1.3T and the current of the coil is calculated separately, the resistance is approx 32 Ohm withe 1200 turns and the current is about 3A at 100V.
For the calculation of the force on the ball, I moved the coil (x_coil: range(10[mm],02[mm],20[mm])) and determine the total magnetic energy: mf.intWm in [J].
For the calculation of the force i try "Work = Force x Distance" but i thing it does not work right.
It would be great if someone here could look at my simulator and give me a hint for calculation of the force can be (in the x axis).

thx @ all
cya Thomas

fsi flexible splitter plate

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Hi,There is an example of Fluid-Structure interaction problem given in Comsol model library which is an oscillating beam. I tried to give some change to that model. I separated the beam from the cylinder to investigate the detached splitter plate, removed the Gaussian pulse function and the point load, and applied a fixed displacement constraint to the plate's edge opposite the cylinder. The solution diverged. even when I assumed that the plate is rigid; the solution did diverge . If I run this simulation for an splitter plate attached to the cylinder without point load and Gaussian pulse function, the solution is convergent. Can anyone suggest why my simulation is not convergent in the other two cases?
Thanks,
Bryan

Ivar Kjelberg- Problem on Joule Heating analysis over a thin geometry

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Dear Ivar,
(After patient waiting I had to direct the query to you,sir! ;) Dont mind)

I am trying to simulate Joule Heating analysis for a very thin geometry (description- 4 domains over each other with different materials respecectively,each have certain thickness) Please check the the attached file, you would get a clear picture of the problem!
In Joule heating module, I am assigning HEat flux to respective boundaries of interest. (Basically a heat transfer problem) The physics and mesh is all set.
However when it starts computing it shows the following error at a certain time step.
"Nonlinear solver did not converge.
In segregated group 1:
Time : 0.8
Size of vector and sparse matrix disagree.
Last time step is not converged."

May I know how can I resolve this issue?

Many thanks!!

About damping in Solid mechanics

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Dear all,

Hi, I have a question about the damping in Solid mechanics module.
I want to simulate a piece of metal drive by Force=F0cos(wt); So I choose frequency domain and do it.
But at beginning I didn't set any damping. It means under linear elastic material node, I didn't add any sub-node. But still I can see the damping in spectrum figure. Why? Is it because computer gives a random damping as default value?
Secondly, I want to know if I want to add a right damping in my simulation system, which type of damping I need? Rayleigh or isotropic or anisotropic?
Is there any one can help me distinguish these 3 type of damping? Which type of damping should I use in my system?

Thank you.
Mingkang

bapa mana bapa di jonggol WAKWAAWWW

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Calculation of normal vectors on surface

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Hi,

I need to calculate normal vectors on a 3D geometry surface to calculate boundary conditions from that (it's a rather complex matlab code). I took the postinterp help to get a starting point and tried to calculate the normal vectors in the center of each element. I used postinterp and tried to determine nx, ny and nz, but, whatever I do, I only get NaNs. In the postinterp help, a parameter s was used to do that, this also works fine in 3D, but I am not sure how I would transform certain points to that parameter... Here's my code:

% Create sphere surface geometry
clear fem
fem.geom=geomcoerce('face',sphere3(1,'pos',[0,0,0]));
geomplot(fem,'edgelabels','on'), axis equal
% Generate mesh
fem.mesh = meshinit(fem);
fem.shape = 2;
fem.xmesh = meshextend(fem);
% Get element triangulation
a=get(fem.mesh,'el');
tri=a{3}.elem;
p=fem.mesh.p;
% Calculate center point of each triangle
pn=(p(:,tri(1,:))+p(:,tri(2,:))+p(:,tri(3,:)))/3;
% Calculate normal vectors
nx=postinterp(fem,'nx',pn)
% this gives only NaNs, why?

Any ideas? Also the interpolation in the mesh points does not work,

nx=postinterp(fem,'nx',fem.mesh.p)

gives me the same NaNs...

Nils
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