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advice for simulation set up or suitable tutorial (3D stress distribution with multiple materials in contact)

April 9, 2013, 9:04 pm
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Hi All,

I am trying to help my fellow Orthodontics to showcase COMSOL's ability to simulate one of his problem. But I am struck and getting inconsistent results. The simulation is very basic and therefore experts here are requested to advice or direct a suitable tutorial for us.

The problem is teeth embedded in bone. when bone is subjected to a force, we want to see the stress distribution that is all. My problem is inexperience in 3D and structural modelling handing multi materials in contact. The 2D cross sectional picture is attached. Some may kindly enlighten us to proceed further?

Thanks in advance
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FSI - vibration study of a cylinder in a fluid flow

April 9, 2013, 10:39 pm
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Hello all,

I am new to Comsol. I am trying to study flow induced vibration of a cylinder fixed at one end and free at other. The cylinder is placed vertically against the flow. Is it possible to find the amplitude and frequency of vibration in the cylinder at the tip.

Please recommend me tutorials similar to this problem
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Cooling of a metal box

April 9, 2013, 11:14 pm
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Hallo to everybody!

I'm trying to realize the simulation of a metal box (fillled with air and including an heat source, and surrounded laterally by other boxes that I consider through the simmetry/boundary condition) that is cooled by a tube of water in contact with the box, but i have problem to set good boundary condition.
If I set the inlet temperature of the tube, and set external convection for the other surfaces of the box, i find that everywhere the temperture is close to the one of the inlet surface of the tube... the temperature boundary condition seem 'stronger' than any other boundary condition.
I find more realistic results if I set a different temperature (taken from experimental results) on one of the surfaces of the box, but I am not sure if that is correct, or I am just adding a new heat source that shouldn't be present.

do you have any suggestion?
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Model couplings: Integration vs. Summation over nodes

April 9, 2013, 11:38 pm
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Hello,

I am working with two modules Structural Mechanics and general form PDE as coupled. I need a model coupling to define an integration. When I choose "Summation over nodes", my model works fine, converges and gives logical results except the fact that it calculates my volume incorrectly, which I think is related to the mesh. When I select "Integration", I see that my model calculates my volume correctly as the initial value; however, my model hits the maximum memory and gives "out of memory" error. I use this integration operator inside the PDE and there are terms like Elastic modulus, strain energy and DiracDelta function inside the operator.

Could any body have a suggestion for me?

Thank you in advance.
Onur
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Buckling Amplitude

April 9, 2013, 11:41 pm
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Hello, everyone

I investigate a buckling of compressed plate and have a trouble. I can't find an amplitude of buckling for different pressure. Comsol doesn't react on a changes of compressive force (buckling amplitude is constant for any pressure).

Thanks you for your time.
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Parallel plate model with magnetorheological fluid under magnetic field

April 9, 2013, 11:43 pm
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Hi,

I am trying to model the flow fields of magnetorheological fluid between non-magnetic parallel plate and permanent magnets under magnetic field produced by permanent magnets in in COMSOL3.5a.

There are two permanent magnets and three non-magnetic parallel plates in the model. The middle plate can move in the x direction at a speed of 0.025m/s. The gaps between two permanent magnets and the middle plate are filled with magnetorheological fluid.

There are adhesive forces between the magnetorheological fluid and the middle plate, so magnetorheological fluid can moves with the middle plate. The magnetostatics, Moving Mesh (ALE) and Non-Newtonian Flow modules have been chosen in my model. I have got the magnetostatic field simulation results which can be used as the initial values to deal with the flow fields.

But I do not know how to deal with the flow fields simulation due to the adhesive forces.

Could anyone give me any hint about this, it would be highly appreciated.

Regards,

Hongliang
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meshvol

April 10, 2013, 12:31 am
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Hello,

I'm looking to extract the area/volume of each mesh element of my model. I then discovered the quantity meshvol. However I'm not exactly sure what this gives me: using meshvol I get a scalar value for each node; what does this value represent actually?

Thanks.
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extrude from 2d to 3d

April 10, 2013, 1:27 am
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Hi,
i have successfully extrude from 2d geometry to 3d but how to add the thickness/depth on z -plane as right now the geometry drawn in x-y plane .
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Is there a way to do a temperature dependent heat source in Conjugated Heat Transfer?

April 10, 2013, 1:42 am
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Hi

I'm working in the conjugated heat transfer physics and I'm hoping/wondering if there is a way to make the heat source temperature dependent.

I have a cable that is covered with different materials at different areas so the temperature in the copper wire fluctuates. Since the heat source is copper where the resistivity changes with the temperature and thus gives an uneven load across the length of the cable. I'm thinking that the option "general source" doesn't account for thìs?

I might be working in the wrong physics, but the thing is, I'm interested in is to improve the cooling of the cable. So I thought this would be the correct physics.

Any help would be much appreciated..


And by the way thanks for a brilliant forum.

Rógvi Østerø
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List expressions and predefined quantities in Maltab or Java

April 10, 2013, 4:11 am
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Hello everyone,
I'm looking for a way to find the "expressions and predefined quantities" a model offers within matlab or java.

Via COMSOL-GUI, this is simply possible by clicking one of the two buttons "Replace Expression" and "Insert Expression" within a plot - but how to get this Information within a maltab or Java application?

Any help would be great.

Thanks

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About FBAR（BAW）Filter

April 10, 2013, 4:41 am
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Hi everyone

Is there anyone who has used comsol to simulate FBAR/BAW filters? I want to simulate FBAR filters. But I have some problems on simulation. Is there anyone could give me sonme advice on that?

Thanks
Rick
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Poisson-continuity coupled equation

February 19, 2011, 11:50 pm
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Hello,
I try to model the corona discharge in wire-cylinder geometry governed by the equations:

nabla (V) =- rho/epsilon0 (Poisson equation) and

grad (rho) * grad (V) = rho ^ 2/epsilon0 (equation of current continuity)

with boundary conditions:
V_w = V0 (on the wire)
V_cyl = 0 (on the cylinder)

As rho is unknown, I should compile until the electric field on the wire is equal to a given value Es.

knowing that I can give an initial estimate for rho on the wire --> rho_w.

My problem is I dont know how to solve these two coupled equations.
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CFD Boundary Conditions for Journal Bearings

September 29, 2011, 3:29 am
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Hi all,

I have recently started working with Comsol. It seems very easy to use and so far I was able to build my model and have the basic physics working. I am trying to build a journal bearing model which gives me a realistic fluid film pressure distribution for different shaft speeds and loads. Using the pressure I would then like to calculate the fluid friction and with that the heat distribution within the bearing.

The journal bearing tutorial was very helpful, however it does not solve gaseous effects such as cavition. Comsol support told me that they are working on that but it will not be available any time soon. There are many ways to simulate journal bearings without calculation cavitation, one is be setting the right boundary conditions such as Reynolds, Gümbel, etc. as explained by Schweizer (Schweizer B., "ALE formulation of Reynolds fluid film equation", 2008).

The question is: How/Where do I set these boundary conditions? By using global equations? I have tried to set up global equations but did not succeed - maybe I did it wrong? I have included the model I am working on. The fluid streamlines and most parts of the pressure seems right.

Can anyone help?
Thanks,
Toan
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Thds Electrostatics coupled convergance problem

January 12, 2012, 7:59 am
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Hi everyone!

I try to simulate a 3D microstructure of a lithium ion battery (just of the anode). I simulate the electrolyte with ionic transport of 2 ion species c_el, c_elA with c_el as positive and c_elA as negative ions. I do that with transport of diluted species with migration in electric field. The source of the electric field is the voltage V_ES which is from an Electrostatics, defined also in the electrolyte region. In this electrostatics I define a space charge density with the value: (c_el-c_elA)*F (F=Faraday constant). That should create my V_ES.
I also define initial values for the 2 concentrations c_el0 = c_elA0 = 1000 mol/m^3 and for the voltage V_ES = 0V
At the open (not to the electrode bordering) side, I define a constant concentration of the positive ions c_el = c_el0 to simulate the constant inflow of that one species of ions (the Li-Ions), and a constant electric potential 0V.

For the connection to the electrode I define a current density j_ct (charge transfer) after the Butler-Volmer equation, with which the charged ions leave the electrolyte and with which uncharged particles enter the electrode material. Therfore I simulate the Electrode material with a transport of diluted species (only one sort of particles now and without migration in an electric field, so uncharged) and an electric current, which leaves the electrode on the other side with a current density of j_L. So j_L should control the running of the battery.
I start the j_L with a step function from 0.1s to 1s.

The problem now is, that the progam starts but the convergence goes up to a scale of 1E8, when the current j_L starts to rise. And it has something to do with the coupling of the transport of diluted species and the electrostatics in the electrolyte. If I deactivate the electrical migration or the space charge density, the program goes through.

Hope somebody can help me

Cheers,
Chris!

By the way I use 4.2a.
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PML for SAW interdigital transducer

March 12, 2012, 7:19 pm
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Hi, i'm trying to simulate an interdigital transducer for SAW on a lithium niobate substrate but i have a lot of problems adding PML. I have previously simulated using periodic conditions but now i'm trying to simulate the transducer with the actual measures, to avoid the reflections on the material frontiers i'm using PML.

I have created 2 semicircular geometries on each side of the substrate and one rectangular on the bottom in order for the wave to propagate and dissapear along them. I included PML in definitions as is the new method in version 4.2 and linear elastic material (with LiNbO3 elasticity) for these geometries but when i try to simulate it gives error about the coordinates in the semicircular PMLs.

I tried rectangular and cylindrical (with center in the origin and in what would be the center of the circle) and nothing. Tried different PMLs for each geometry which didn't work and just one for all which simulates but doesn't work as it should (no attenuation in the semicircles).

Please has anyone worked with PMLs in acoustics in version 4.2 and is able to help me with this? i can upload the file if it's necessary.

Thanks!
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NACA 0012 Airfoil with Spalart-Allmaras turbulence model

October 17, 2012, 1:11 am
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Hello,

I am new to COMSOL and I thought I would start with a relatively simple model: a NACA 0012 airfoil at 0 angle of attack.

The domain is small and the mesh resolution is relatively coarse to get faster solutions. (Once it works I will try a larger domain and finer mesh)

I chose the Spalart-Allmaras Turbulence model given its robustness and accuracy in these conditions.

Unfortunately, the simulation always exits prematurely with an error:
Segregated group 2
Expression evaluates to NaN.
- Expression: (((mod1.spf.cb1*mod1.spf.Stilde)*mod1.nutilde)-((mod1.spf.fw*mod1.spf.cw1)*((mod1.nutilde/mod1.spf.l_w)^2)))

I have played with different boundary conditions, mesh densities, solvers. Nothing seems to work.

Any help on this would be greatly appreciated!
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Multiple-size particle tracing

October 30, 2012, 3:24 am
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Hello everyone

I have a short question on the particle tracing module. Does anyone know that whether it is possible to simulat particles of different sizes in the same model. How to implement this since I could only add one unique particle property?

Many thanks

Yuexia
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Coupling between PDE and Electrostatics

November 21, 2012, 8:32 pm
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Dear All,

Does any one have any experience of solving a steady general form of PDE with steady electrostaics module. I am trying to solve a PDE [ Div(DuE) = 0] where D is the mobility coefficient and E is the electric field vector that is obtained from the solution of [Lap(V) = 0] in order to solve for the space charge distribution (u) within the domain, however I am not getting any meaningful results at all and in some cases not even a solution. I am using the default UMFPACK solver.

Regards
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windings providing regarding

April 10, 2013, 10:41 pm
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Sir/madam,
I am doing my m.tech project in modeling of motor using COMSOL.3.5a in 2D. I would like to know the way in which i can provide my three phase windings in the stator slots.
Thanking you and expecting your kind support
Kiran George
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not function COMSOL

April 11, 2013, 12:11 am
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I study university of tre ( Italy)
I gave program
I bought the computer in iran
after that I put license can not go next
I would like to help
thanks
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