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Mesh

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Hello, I need your help please ! I have the following geometry : a box with some disks surrounded by an interphase layer. I couldn't mesh this layer with "physics controlled mesh", however it mentions for me the following error : "Edge is much shorter than the specified minimum element size." and "Face is (or has a narrow region that is) much smaller than the specified minimum element size."
Please find attached an exemple of what i'm talking about, the blue part is the layer. I will be grateful if anyone could help me to build my mesh for my entire geometry.
Thanks

Simulation of a floor heating

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Hi all,

I want to simulate a floor heating in a 2D modell. Floor heating systems release about 90 % of heat in the form of radiation and about 10 % in the form of convection. So is it possible to take this situation on one boundary? I tried this with heat-flux and surface-to-surface radiation. But there i can't divided the heat transfer in 10 % heat flux and 90% radiation. I also don't understand the equation in surface-to-surface radiation, what does mean "G".

I hope somebody can help me.

Thanking you in anticipation.

Markus

Far field of dipole antenna on substrate

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Dear COMSOL community

I try to model a nanodipole antenna on glass substrate , first I create a model for a nanodipole in air and the far field seems good to me ( the tours shape typical for dipole antenna ) , where the far field calculation is made by a surface surround the dipole and placed lamb/2 far away from the dipole.

Now I placed the dipole on the top of a glass substrate , while the far field domain this time will be half air and half substrate , unfortunately the shape of the far field seems to me incorrect , I read on the thread that the far field domain has to be homogeneous, but how to calculate the far field in the case of antenna placed on substrate

Thanks in advance

M.H.Elshorbagy

UCM , Spain

Why does an example on comsol website use 13W power for a cellphone?

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Hello all,
I'm new to comsol, i have been learning it by internet, i have started solving some examples available on comsol website. The link of the example is mentioned below-

www.comsol.com/model/absorbed-...on-sar-in-the-human-brain-2190

and i have also attached the pdf file for this example. One thing that is bugging me is in the lumped port section (page no.15 of pdf), they put v= 45.5 and Z= 75 ohm that means p= 13W, but the maximum power that a cell phone can radiate is 2W so why are they using 13W?


Thanks in advance!

Amplitude response of beam in frequency study

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I am tying to obtain the amplitude response of a MEMS bridge (model attached) with the structural mechanics module, I obtained the resonant frequency of the bridge via Eigen studies. I was trying to obtain the amplitude response of the bridge via frequency studies around the resonant frequency I obtained via Eigen studies. However, my displacement is always zero all across my frequency sweep. Can somebody let me know what I am doing wrong or missing in my model. It seems like a straightforward problem to me.

Thank you.

Point plotting within a volume

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Hello, thanks for looking at this,

I want to get tabled results at a certain point within my model. I create my multiphysics simulation by first importing a mesh from NASTRAN, and then simulating (so I normally can't create points from geometry this way).

Is it possible to take the geometry I get from a mesh import, select a point in 3D, and then get a output value (in my case: pressure)? I can view the volume and surface normally, but this is for some post processing.

Thanks for your help!

COMSOL Design of Membrane Deformation using FSI

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Hello!

We are currently doing research that models deformation of a membrane, and we are using COMSOL Microfluidics 5.2a. We want to know the feasibility of our design we present, as well as feedback on the configuration of our solution. Please find attached a sketch of the diagram we plan to implement (not drawn to scale). We use a large rectangle with dimensions 30 μm (width) by 300 μm (height) to represent a fluid channel, through which air passes. We then created a membrane with dimensions 0.1 μm (width) by 100 μm (height), in the middle of and bordering the left side of the channel. The material used for the membrane is PDMS (Polydimethylsiloxane). Two fillets are added to the top and bottom of the membrane to create smoothness to those sides. We want to measure the deformation of the membrane using a time-dependent study. We have based our simulation on that presented in the FSI handout, and we would like to create similar results (see link below for handout):

www.comsol.com/model/download/...luid_structure_interaction.pdf

We have used the same settings for inlet and outlet as in the handout, with parameters and variables defined accordingly. Because the structure of our channel is vertical as opposed to horizontal, we changed the input velocity so that H (height) was changed to W (width). Other than that, no other modifications were made to the inputs. The output was given pressure with the default of 0 Pa. We applied fixed constraints to the fillets, a free boundary condition to the left side of the membrane, and a fluid-solid interface boundary to the right side of the membrane. In addition, we have included an extremely coarse mesh to decrease runtime, as well as a free triangular condition and size to the mesh as explained in the FSI handout. Finally, in the solver configuration, we have set the range of times from 0 s to 4 s in 0.1 s increments.

Overall, we would like to display signs of deformation and receive results similar to those in the handout, except with deformation in our model happening horizontally. We would also like to see deformation displacement values, as well as measure flow rate and pressure (also, create plots) from the deformation. We have been running the simulation for 2 days, and it will most likely take some more time before computation completely finishes. We would appreciate any input on our design. Is this the correct approach? What modifications would make the model more efficient? How can we fix the design so we can receive results as intended, and what should we change to increase efficiency and decrease runtime?

Please feel free to ask me for any clarifications on our design. Thank you!

Eddy current simulation not converging when velocity increases

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My simulation simulates an array of magnets moving over an aluminum plate at a fixed height and a given velocity, and while it computes and yields results similar to those of a numerical analysis, it won't compute at high velocities--which in this case refers to speeds greater than 50 m/s; I need to be able to simulate the system up to 115 m/s, so this is a big issue.

When I say that the simulation doesn't converge, I don't mean that I get a non-convergence error, I mean that the computation time approaches infinity and the convergence plot levels out and won't decrease any further. since skin depth becomes a more significant factor at higher velocity I've tried to make the mesh size a function of the velocity so that the mesh elements will always be smaller than the skin depth so that it can be resolved, however the number of mesh elements gets so large that the computation time is still excessively long, and since I'm using a parametric sweep the computation time becomes even longer.

I'm wondering if there are any meshing methods or techniques to make this work/work faster; this is under the assumption that the only source of this issue is that at high velocity the skin depth becomes smaller than the minimum element size and thus can't be resolved and COMSOL can't compute a solution, hopefully there isn't anything else wrong with the model that I haven't caught yet.

Does anyone have any insight into this type of simulation and can help me out with this issue? The file is too large to attach to this post (6.31 MB) but I can email it to anyone who's willing to take a look at it.

Electromagnetic Waves, Axial Symmetry

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Can one specify a linearly polarized incoming (plane) wave for a geometry based on axial symmetry?
For instance if the incoming wave enters along the z-axis through a surface in the x-y plane . The polarization needs to be orthogonal to the z-axis. The only options are radial polarization and azimuthal (phi) polarization, and linear combinations. Neither represents the right physics - a linear polarized beam. (Radial polarization implies a line charge, azimuthal polarization a changing magnetic field in the z-direction).

Put another way - the linearly polarized field would break the axial symmetry; to represent a linear polarization as a sum of azimuthal and radial polarizations, the components must depend on the azimuthal coordinate (phi).

Is the only solution then a full three-dimensional geometry? We are hoping to avoid this.

Mass Spring Damper system with excited base

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Hi,

I'm trying to simulate with COMSOL 3D the behavior of a mass-spring-damper system applied on a plate that it's excited and moves.
The goal is to see how the mass-spring-damper system affect the displacement of the plate.
I was thinking to implement the forces with boundary load BC.

The force equation is the following:

mx'' + bx' + kx = F + by' + ky

The problem is that I don't have access to the displacement x, the velocity x' and the acceleration x'' of the mass of the actuator.
Can anyone help me with it?

You can find attached my COMSOL model and a picture that describe the system.
Thank you,

Mattia

Importing ASCII Geometry

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I am completely new to Comsol so I really am struggling.

Can anybody explain how I can import some flat panel polygons I have defined as a series of x, y, z position vectors in ASCII into a Comsol file geometry.

I have used Matlab to create some CAD dfx files and tried doing an import. Everything looks like it is going fine then just get a "no geometry imported" error message. (See attached screenshot)

I also have Matlab LiveLink.

Any suggestions would be greatly appreciated,

Shearing of Rocks

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Hello,

I have created a rectangular (solid) object with material properties of a sandstone. How can I subject it to simple shearing in comsol?

Bistable beam simulation

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Hello,

I wanted to ask that is it possible to model the behavior of electrostatically actuated bistable beam (curved beam) in COMSOl. As I tried to do it using electromechanical physics but unable to find out snap-through and pull-in instability.


Regards,
Vasudha

Incompressible Yeoh Model - Solid Mechanics

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Hello,


I'm relatively new working on Solid Mechanics with hyperelastic materials in COMSOL Multiphysics.

I'm using Yeoh model. How can I simulate incompressibility conditions in this model? I have the 3 model parameters:

c1 = 17005.903 Pa
c2 = -73429.379 Pa
c3 = 414952.313 Pa

But I'm having problems to determine the initial bulk modulus in order to simulate incompressibility.

Any help would be appreciate!

Best regards,

Javier

Convergence problems

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Hi everyone.

I'm simulating a conjugate problem (heat transfer and laminar flow), where my domain correspons to a microchannel with ribs. I have been developed a paramteric analysis of the mesh from 100.000 to 3.200.000 DoFs. When I evaluete the convergence at the inlet of the domain, where I have imposed a boundary condition (normal inflow velocity), the velocity changes at the points of that part of the domain, mostly close to the boundary layer.

I think that the values of velocity at the points at of inlet are undepended or of the DoF and the values should be equal to the velocity inlet considering as boundary condition. Could this situation be related with two boundaries condition (inlet velocity and no-slip condition) are applying at the same region????

Thanks.
MDH

Methane/Air Combustion

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Hello all,

I am trying to recreate the OpenFOAM methane air combustion tutorial for reactingFoam and seem to be having some trouble starting the reaction. Any help would be great.

How to choose right conditions

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Hello, i have been trying do that this couple of months and i cant solve this problem by my own.
I dont know , how and which conditions i need to choose to get all worked up.
My main topic is to calculate the displacement of my metal sheet, by changing body load on upper axis, and whole mechanism suppose to be in rotation. Upper roller have to be the one which makes all system move. Please help me with this asap.

modelling of wrap around gate using FEM in COMSOL

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Hii
we are doing a project on "modelling of wrap around gate using FEM in COMSOL we found a few problems regarding the simulation.
Can somebody please help us with this.
we completed the part of geometry and assigning of the materials and analytic doping models, metal contacts and assigning the mesh with the reference of 2d characteristics of MOSFET
Thank you

Undefined variable.
- Variable: T
- Geometry: geom1
- Domain: 2
Failed to evaluate variable.
- Variable: comp1.semi.Nc
- Defined as: (((T/(unit_K_cf*300))^1.5)*28000000000000000000)/(unit_cm_cf^3)
Failed to evaluate expression.
- Expression: subst(comp1.semi.Nc,comp1.semi.Tl,comp1.semi.T0)
Failed to evaluate variable.
- Variable: comp1.semi.Nc_init
- Defined as: eps+subst(comp1.semi.Nc,comp1.semi.Tl,comp1.semi.T0)
Failed to evaluate variable.
- Variable: comp1.semi.ni_init
- Defined as: sqrt(comp1.semi.Nc_init*comp1.semi.Nv_init)*exp(((-0.5)*comp1.semi.Eg_init)/comp1.semi.Vth_init)
Failed to evaluate variable.
- Variable: comp1.semi.n_init
- Defined as: ((comp1.semi.Ndoping_init>=0)*((0.5*abs(comp1.semi.Ndoping_init))+sqrt(((0.5*comp1.semi.Ndoping_init)^2)+(comp1.semi.ni_init^2))))+(((comp1.semi.ni_init^2)*(comp1.semi.Ndoping_init<0))/((0.5*abs(comp1.semi.Ndoping_init))+sqrt(((0.5*comp1.semi.Ndoping_init)^2)+(comp1.semi.ni_init^2))))
Failed to evaluate variable.
- Variable: comp1.semi.V_init
- Defined as: (((comp1.semi.Vth_init*(((comp1.semi.Ndoping_init>=0)*log(comp1.semi.n_init/comp1.semi.ni_init))+((-log(comp1.semi.p_init/comp1.semi.ni_init))*(comp1.semi.Ndoping_init<0))))-comp1.semi.chi_init)-(comp1.semi.Eg_init*0.5))+((comp1.semi.Vth_init*0.5)*log(comp1.semi.Nv_init/comp1.semi.Nc_init))
Failed to evaluate expression.
- Expression: comp1.semi.V_init
- Feature: Dependent Variables 1 (sol1/v1)

“influence of current flow in different wire geometry and their effects”

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Hi, we are doing research in “influence of current flow in different wire geometry and their effects”. The main application, we want adapt to mechanical field. We need to analysis experimental also with some minimum distance. We were trying with comsol 4.2 version as per tutorial follows. We did not… if anyone can help us. We use 1.2 mm wire diameter and 12 cm length.

Sheet metal bending - spring back effect

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Hi

I am trying to make an elastoplastic 2D simulation of sheet metal bending to observe different spring back in various materials. I want to use V-bending proccess since we have a fixture to do the same experiment in the future to check for validity.

I would like to keep it as simple as possible. I am using some data that I have from tensile experiments for different materials and setting simple stress-strain curves with 3 points to vary the hardening. I also set the load/load removal along with auxiliary sweep for the load stepping so the spring back could be observed after the removal of the load.

I am not sure how I should define the contact between the parts. I tried to use contact pairs but I don't know if it is correct. Unfortunately cannot find much about this specific topic on the internet or in this forum (tried to use 3 point bending that someone used which could be similar but didn't succeed much)
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