COMSOL Exchange

Another Pandulum (3d truss element)

Wed, 18 Apr 2012 15:00:11 +0000

Pandulum model using 3d truss element.
initial position is from (0,0,0) to (0,2,10).
(0,2,10) end is pinned.
(0,0,0) end has 10kg mass.
gravity is applied in -z direction.

analitical solution is approximated very well:
period =sqrt(Length/gravity)

the model image shows the y displacement vs time.

1D resonant quantum tunneling

Tue, 28 Feb 2012 10:44:03 +0000

The model sets up boundary conditions for the Schrödinger equation
in order to achive tunneling solutions. A resonant barrier potential is created with 1nm separation-width and 0.2nm oxide thickness barriers of 4eV. The result is plotted as the transmission coefficient t^2 vs. the energy (parametric solver). The resosnances are close to to the quantized levels for a particle in a box.

Zernike Polynomial extraction of deformed optical surface

Tue, 28 Feb 2012 07:43:00 +0000

You will find hereby a COMSOL Multiphysics v4.2a Solid + Optimisation model extracting the first dozen Zernike polynomials from a deformed circular surface, expressed in RMS values.

In optics, the expressions of the deformations of an optical surface, such as a mirror under gravity or pressure loads, are often decomposed in Zernike orthogonal polynomial coefficients.

Unfortunately, there are several normalisation of these polynomials, the different optical programmes uses each there own normalisation, so the results should be carefully benchmarked against each particular softeware you use. And pls be aware of the loong formulas, these might still contain typos ;)

The present normalisation is the one from J.C.Wyant, 2003, "ZernikePolonymialsForTheWeb" that can be found under www.mpia.de /AO/...

Have fun COMSOLING

Pyramidal Horn Antenna

Thu, 09 Feb 2012 02:48:32 +0000

We provide a convenient 3D RF model of a generic pyramidal microwave horn, with a simple user-adjustable (parameterized) geometry. The model was prepared with Comsol Multiphysics v4.2a with the RF module. The user may specify the input waveguide size (width and height), horn flare length, horn aperture dimensions, and some other useful settings, all as global definitions. Computational region, meshes, and frequency range are then defined automatically (but can also be modified by the user). Two symmetry planes are employed to speed up the computation. The model computes the gain, VSWR, and E-plane and H-plane far-field beam patterns.

2D transient pressure field from a boundary

Tue, 17 Jan 2012 11:13:07 +0000

This very simple 2D transient model uses the Acoustic Module to show how a pressure wave propagates in time.

The scenario is a simple 2D rectangle with one boundary acting as the source of the pressure field and the other 3 are given wave radiation boundaries so that there is minimum reflection.

The model is made up so that you can define:

1) The frequency of the pulse
2) How many pulses you wish to simulate

The model is handy as it shows you how to create a boundary condition which varies in time.

Also, the model has been made so that the mesh (which is frequency dependant) is generated automatically. I think its quite nice and should help with some basic models of acoustics.

This model is similar to the Gauss explosion model.

Also, please note that the time stepping has been defined in the global definitions> parameters along with other values.

Thanks goes to Glenston Miranda for the function.

Rob

ps, Check Pressure 1 for the function which defines the BC.

Loudspeaker Driver Electromagnetic v4.1

Fri, 27 May 2011 05:59:31 +0000

This model is the electromagnetic part of the Loudspeaker Driver model (http://www.comsol.com/showroom/gallery/1369/). The acoustic module is NOT required to open this model.

Low Reynold's k-epsilon model for Comsol v3.5

Wed, 30 Mar 2011 18:56:52 +0000

This implemented Low-Re k-epsilon Comsol model is based on the Launder-Sharma damping functions as described in Wilcox's Turbulence modeling for CFD book. Model implementation was in 2D under steady state situation but it can be extended to 3D with relative ease.

The variables solved in the model are U,V,P,k, and epsilt (epsilon tilde) using equation based modelling in general form.

The model also includes a k-e model from the chemical engineering module for comparison.

Hints: go to options-> expressions -> scaler or subdomain expressions to learn more about its implementation.

CoBoGUI - An open source graphical user interface for two dimensional solar cell simulations with Comsol Multiphysics v3.5 and Matlab

Sun, 13 Mar 2011 16:27:34 +0000

CoBoGUI is a freely available collection of MATLAB scripts for

two dimensional solar cell simulations with COMSOL Multiphysics and MATLAB.

It proviedes a flexible graphical user interface and can be

downloaded from the ISFH-website:

http://www.isfh.de/institut_solarforschung/software.php?dm=1&&_l=1

It can also be seen as a multi purpose batch GUI, since it can be used to batch any feasible Matlab function.

If you want to cite the CoBoGUI, please use following publication:
http://www.isfh.de/institut_solarforschung/files/25eupvsec_eidelloth.pdf

The CoBoGUI was created for Comsol v3.5a.

Edit: There is a new version for Comsol v4.1 available (in alpha state).

SPICE RCL-circuit with initial conditions

Tue, 05 Oct 2010 13:39:04 +0000

This model shows how to set up a SPICE model of a RCL-circuit in COMSOL4.0a with other initial conditions than default.

The SPICE (Electric Circuit, "cir") in COMSOL does not allow you to specify initial voltage of a capacitor or an initial current through an inductor.

This is a way of walking around this problem, using sub-circuits (External IvsU and UvsI) in combination with the equations of state for C and L in an "ODEs and DAEs"-node in COMSOL.

The tricky part is to find out what the variable name for the voltage across the inductor (mod1.cir.UvsI1_v) and the current through the capacitor (mod1.cir.X1_i) are, as these enters in the ODE's. One could find out these from the plot-menu: Results->1D Plot Group 1->Global 1->Expressions->(+)->Electrical Circuit->Voltage across device UvsI1 (mod1.cir.UvsI1_v).

Parallel plate capacitor COMSOL 4.0

Thu, 29 Jul 2010 09:45:46 +0000

This example show the electrostatic potential and electric fields in parallel plate capacitor with air gap.
.
Model by Michal Jedrzej Radziwon

Non parallel plate capacitor COMSOL 4.0

Thu, 29 Jul 2010 09:45:30 +0000

This example show the electrostatic potential and electric fields in capacitor which plates are tilted and separated with air gap.
.
Model by Michal Jedrzej Radziwon

[SM v3.5a] Rotation constraints in structural module. With complements

Fri, 30 Apr 2010 14:53:05 +0000

There are different boundary constraints in COMSOL structural, but in 2D/3D structural (smpn, smsld ...) there are no angular variables predefined, hence no easy way, as in the Euler beam modules, to enforce angles.

The present model (BeamRotz_4) illustrates 2 ways to constrain the rotation of a gravity loaded beam (by comparing Euler beams and SMPN beam results).

These are either by constrining the angles (which gives very wrong reaction forces) and a cleaner way by applying an external torque until the angle is restrained, through an optimisation approach, as per smeug.pdf p69 v3.5a.

Note:
I use reacf() reaction forces in there for the Torque calculations, so if you need the weak constraints you might get an error message, these reaction forces could be replaced by, albeit supposed to be less accurate, traction forces, or just the lm's.

Further explanations are given in the model properties.

I have added a second "PN" (BeamDispForce_1) and a third "SMPN" (BeamDispForce_smpn_1) example comparing displacement constraints and coupled force & moment load adapted by COMSOL to obtain the same constrained displacement, all on a fixed-free beam in 2D. Further explanations are given in the model properties. THe cntact case is active in the SMPN model. Porting to 3D is almost trivial ;)

Have fun COMSOLing
Ivar

[SM 3.5a] 3D Euler Beam Properties Calculations

Fri, 30 Apr 2010 14:52:43 +0000

3D Euler Beam based FEM models calculate quickly and are very usefull for design otimisation and conctual design phases.

In COMSOL, as most FEM codes, 3D Euler Beams require the input of quite some beam properties data to calculate correctly. But in fact all of them can be solved by COMSOL once the geometry section is correctly sketched in a 2D geometry. In particular "J" the "Torsional Constant", or often called St. Venenat Torsion Constant, can be quite tricky to assess and is often confused wrongly with the polar moment.

Please note that "warping" effects are not explicitely considered herein.

A general procedure and a few COMSOL model examples are given for full and hollow beam sections, on how to use COMSOL to calculate these theoretical torsion constant values.

The pdf presentation is closing with a summary slide, mentioning a few possible improvements for COMSOL to sped up the use of 3D Beam model set-up.

I wish you a pleasant reading,
and pls do not hesitate to report back any errors or possible improvements

A MatLAB-based tool for handling Tessellated Free Shape Objects with a Morphing Mesh Procedure

Mon, 08 Feb 2010 16:59:23 +0000

Description:
This is a fully MatLAB-based tool, called ProMESH, allowing to handle tessellated models (in .STL ASCII file format). Open imported tessellated model may be thickened.
Geometry shape may be modified through a morphing approach.
MatLAB’s GUI allows to pick any control point belonging to the imported geometry and set the relative influence hull, by controlling its sizes and orientation.
The influence hull is assumed as an ellipsoid. The morphed shape may be easily tuned and controlled by modifying any control points of the piece-wise Bezier curve (weight function).
Once the tessellated model is ready, EXPORT button creates the Comsol geometry object (and it is saved into MatLAB workspace), ready to be processed.

Implementation:
ProMESH was developed under MatLAB 2007b and it seems to work well also with MatLAB 2009b.
Comsol Multiphysics must be run with MatLAB.
See [Franciosa, P., Gerbino S., Handling Tessellated Free Shape Objects with a Morphing Mesh Procedure in Comsol Multiphysics®, in Proc. of COMSOL Conference’09, Milano (Italy), October 14-16, 2009].

How to use:
Unzip “Matlab functions.rar” file and run “MainGUI.m”. Model “demofile.stl” may be used just to begin.
A video example, related to the application described in the above paper, is also provided.

Local Drug Delivery by Infusion through a Multi-hole Sprinkler – 3D Model for a Prototype Bioartificial Pancreas Device

Tue, 08 Dec 2009 21:59:51 +0000

This is a fully scaled 3D model built to explore the feasibility of localized drug delivery by infusion through a central sprinkler with multiple, non-axial-symmetric holes into a rodent prototype biohybrid device intended for islet transplantation. It uses a combination of COMSOL’s convection & diffusion and incompressible Navier-Stokes fluid dynamics application modes to obtain an approximate description of drug distribution due to both convective and diffusive fluxes. It served to obtain first estimates of the doses and inflow rates required to achieve and maintain concentrations that are within the expected therapeutic range for most of the volume of the cylindrical device so that localized immunosuppression might be achievable. The model is for a steroid-sized drug (D = 6x10-10 m2/s) delivered at a concentration of 20 microM with a constant influx rate (0.25 microL/h) that can be achieved, for example, with implantable Alzet® osmotic mini-pumps. Details of the model are described in the Proceeding of the COMSOL Conference 2007 Boston as well as in a related paper in Pharmazie 2008, 63, 226. This is a time-dependent model (transient analysis); the stationary solution can be obtained by using the solution from a large enough time (t > 10 h) as starting point.

Square drop oscillation under surface tension – 2D axi-symmetric model

Wed, 18 Nov 2009 16:19:35 +0000

This model is concerned with the simulation of incompressible Newtonian fluid flow problems with surface tension. An initially cubic drop of water is oscillating under surface tension forces. This model is developed for a 2D axi-symmetric transient analysis. The movement and deformation of the computational domain are accounted for by employing the Arbitrary Lagrangian-Eulerian (ALE) description of the fluid kinematics.
The implementation of the model is detailled step by step in the pdf file. To visualize the solution, you need to solve the model (click the solve button).

Deformation of free surface under pressure– 2D model with surface tension

Wed, 18 Nov 2009 11:48:15 +0000

This model is concerned with the simulation of incompressible Newtonian fluid flow problems with surface tension. The fluid is initially at rest in a square tank. A Gaussian pressure is applied on the free surface which deformed the initially flat surface. This model is developed for a 2D transient analysis. The movement and deformation of the computational domain are accounted for by employing the Arbitrary Lagrangian-Eulerian (ALE) description of the fluid kinematics.
To visualize the results, you need to solve the comsol file.

[AC/DC V3.5a] Maxwell Stress Tensor "pitfall" example

Thu, 08 Oct 2009 08:38:10 +0000

The Maxwell Stress Tensor is handy to use to calculate forces on magnets, but the method is very very sensitive to meshing symmetry. This example show the effect of surrounding a square magnet by a circle (GEOM1) and mesh rather fine with triangular free mesh.

The maxwell Stress Tensor calulation is rather wrong.

In GEOM2 the same model is meshed with a rough square mesh and the result is coherent to > 10 digits !

Why ?
The stress tensor aproach derives the force by integrating the divergence of the field along the edges of the Magnet (in this case), the resulting force can be rather large per edge side (try selecting separately left and right vertical edge for your Boundary Edge integrations), but often the force cancel out by an opposite value on the other symmetric edge.
However, it is well known that the numerical error winds up when one do differences of two large numbers almost identical in value.

Conclusions for me: use only square meshes and rely on symmetry when dealing with the Maxwell Stress Tensor.

And as usual: carefully check your models, verify and validate them

For more on the theory on Maxwell Stress Tensor: take a look at the COMSOL documentation or i.e.: "Introduction to Electrodynamics", 3rd Ed, D.J. Griffiths, PrenticeHall 1981, ISBN 0-13-805326-X

Various Mode Heat Transfer

Tue, 07 Jul 2009 16:43:41 +0000

Consider an array of heated tubes submerged in a vessel with fluid flowing past them. Neglecting end effects, the flowfield can be assumed 2-D in planes with normals parallel to the tube axes. Further, for modest fluid onset velocity, a steady state solution can be sought.

This example comes from the textbook "The Computational Engineering Sciences" by A.J. Baker.

Objectives of this problem:

1. Become familiar with the COMSOL Multiphysics environment and its graphical user interface.
2. Appreciate the role of the Reynolds and Nusselt non-dimensional groups on heat transfer characterization.
3. Generate simulations for natural, mixed and forced convection heat transfer by adjusting the Reynolds number Re.
4. Perform a mesh refinement study for each class of heat exchange, solution-adapted if necessary, hence estimate the mesh required for each solution to be engineering accurate.
5. Detail the generated heat transfer mode differences graphically and quantitatively and report the results.

Plane Stress in a Plate With a Hole

Tue, 07 Jul 2009 16:39:16 +0000

The plane stress analysis of a square plate with a hole at the center subjected to tension is performed using COMSOL Multiphysics.

Objectives of this simulation:

1. Evaluate the use of COMSOL Multiphysics for an analysis of a square plate with a hole at the center subjected to tension.
2. Verify the base problem solution on the given mesh and observe the von Mises stress concentration distribution.
3. Refine the base mesh and check the accuracy of this solution.
4. Via computational experiment, determine the shape of the non-circular hole of the same area as the circle that generates the minimum stress concentration in the plate. Use solution-adapted mesh refinement in areas predicted to exhibit extremum von Mises stress concentrations.