Quantcast
Channel: Latest Discussions - COMSOL Forums
Viewing all 1884 articles
Browse latest View live
↧

A Swept Quad Mesh Within Free Tet - Quality Concerns

March 17, 2017, 10:00 pm
$
0
0
Hi everyone,

I'm looking for some advice on a meshing problem that I have - I have a heat load imposed on a 3D rectangular beam embedded within a larger beam of the same material; the two beams form a union. The area where the heat load is applied is very finely meshed with a mapped distribution so that I can control the exact number of elements in my area of interest.

This is great but my problem is that in order to cut down on computation time/memory cost - I am converting the boundaries of this swept block (or another swept block around it) to tri's and then putting in free tetrahedral mesh for the large remainder of the geometry. This has the unfortunate effect of creating a region of poor mesh element quality around the swept block where I need my mesh to be the most accurate.

I have attached an image of what the mesh element quality looks like in one iteration of this model. It seems that every time I try a slightly different meshing scheme - my results are significantly different and I have tried many variations. If anyone can suggest a better alternative to my current meshing scheme, or point me in the right direction of increasing the mesh quality, I would greatly appreciate it.

Finally, my heat loads are asymmetric and so unfortunately I cannot exploit any symmetry to cut down on the computational cost.
↧
Search

Simulation of composite laminates

June 21, 2013, 5:57 am
$
0
0
Hi all,

Do you have any idea of modeling (simulation) of laminates , e.g. bi-layer composites having layers with different elastic modulus avoiding the so called 'free edge effect' (a stress singularity at the free edge).

i am using Comsol 4.3b and having this problem while i try to work with modeling creep in bi-layers

thanks for your time
-Tesfaye
↧
↧

2D Axisymmetric and 2D simulation of permanent magnet

January 23, 2015, 4:27 pm
$
0
0
Hi,


I am trying to simulate magnetic fields from a permanent magnet in simple 2D and 2D axisymmetric configuration using magnetic field no current module but COMSOL is erroring out saying that the error is greater than tolerance. The configuration in 2D is a rectangular bar magnet and configuration in 2D axisymmetric is a rectangle offset from the axis (i.e. a ring shaped magnet in 3D). However, I have tested other configurations as well and the error stays the same

3D simulations are working out perfectly for any magnet geometry. I followed the steps for setting up the magnetic field in COMOSL tutorial for a horse-shoe magnet and got perfect results in 3D but when I apply same setup in 2D and 2D axisymmetric COMSOL is erroring out. I am attaching my 2d axisymmetric case (COMSOL V 5.0).

Can anyone please point out if there needs to be a different setup for 2D and 2D axisymmetric?
Any help is greatly appreciated

Thanks and regards,
Souvik.

↧

Acoustics - Large models convergence

August 26, 2015, 10:32 am
$
0
0
Hi,

I'm driving crazy about this subject. I think don't know many things about this model, but regardless how mesh, solver configuration (multigrid, iterative, direct, etc.) or any other thing I change doesn't matters, it can't reach the convergence.

I'm trying to simulate the noise generated by a solid source that emits noise in all frequencies, like a power transformer, in an electrical distribution substation. I'm using the acoustics module in the frequency domain.

I don't know very well how to set the sources pressure (or the pressure level) with the boundary conditions. I'm using the "pressure" boundary condition setting an arbitrary pressure in order to perform a test.

I'm using an iterative solver with multigrid method (2 or 3 levels), with Krylov preconditioning. Then I use SOR or Jacobi methods.

No matter if set or not a parametric sweep (for frequencies), the solver not converge.

There's any "trick" or something that guides me to reach the convergence in these type of models?

Please, see the attached images in order to understand the described above.

Thanks in advance.
↧

Moving Mesh velocity in tpfmm

January 24, 2016, 9:50 pm
$
0
0
Hi,

I'm wondering how COMSOL calculates the mesh velocity (tpfmm.x_free
) in the tpfmm module, as I define a flux in fluid-fluid interface

I want to know it because the velocity is very slow and need to know how can it improve


Thanks a lot
↧
↧

Unable to evaluate an expression

February 4, 2016, 3:40 am
$
0
0
Excuse me, I am getting an error as

Attempt to evaluate real square root of negative number.
Function: sqrt
Failed to evaluate expression.
Expression: nojac(min(1,(sqrt((comp1.fsi.h2GNS*((comp1.fsi.rho^2)*(((comp1.u fluid-d(r,TIME))^2)+((comp1.w fluid-d(z,TIME))^2)))))/(comp1.fsi.mu*24))))
Failed to evaluate variable.
Variable: comp1.fsi.xi m, Defined as: nojac(min(1,(sqrt((comp1.fsi.h2GNS*((comp1.fsi.rho^2)*(((comp1.u fluid-d(r,TIME))^2)+((comp1.w fluid-d(z,TIME))^2)))))/(comp1.fsi.mu*24))))
Failed to evaluate variable.
Variable: comp1.fsi.vhNS lin, Defined as: ((0.5*sqrt((max((comp1.fsi.tau m*(((comp1.fsi.res u*comp1.fsi.xi m)^2)+((comp1.fsi.res v*comp1.fsi.xi m)^2))),0)*comp1.fsi.B0YigijtauNorm2)))/(comp1.fsi.B0YigijtauNorm2+eps))
Failed to evaluate expression.
Expression: nojac(((1.4142135623730951^(1-shapeorder(comp1.u fluid)))*max((comp1.fsi.vhNS lin-comp1.fsi.vhNS quad),0)))
Failed to evaluate variable.
Variable: comp1.fsi.vhNS, Defined as: nojac(((1.4142135623730951^(1-shapeorder(comp1.u fluid)))*max((comp1.fsi.vhNS lin-comp1.fsi.vhNS quad),0)))
Failed to evaluate temporary symbolic derivative variable.
Variable: comp1.fsi.crosswindnsVDN${test8}, Defined as: ((comp1.fsi.rho*comp1.fsi.vhNS)*((comp1.u fluidr*(-comp1.fsi.gijrr))-(comp1.u fluidz*comp1.fsi.gijrz)))
Failed to evaluate expression.
Expression: d((2*comp1.fsi.crosswindns*pi*r)*(dvol spatial),{test8})
Last time step is not converged.

Can Any one answer this pls
↧

Liquid-Vapor interface drops very fast

March 18, 2016, 11:01 am
$
0
0
Hi

I have encountered a problem in COMSOL when using the “laminar two-phase flow, moving mesh” physic.
A simple model indicating what I am trying to solve is provided in the attachment.

As you can see in the attached file, the liquid evaporates at a very low pressure (300 Pa) with a uniform mass flux of 1e-3 (kg/m2s). When the contact angle is 90, everything goes well. However, as I change the contact angle even a little bit from 90 (i.e. pi/2.1), the interface drops very fast, which is physically meaningless. I have had this problem with both COMSOL 4.3b and 5.1.

I could have been able to improve it by making the contact point meshes extremely fine. However, this gives me weird values of pressure (absolute negative pressures) in these regions.

I appreciate if you could help me sort out this issue.

Amin
↧

The relation between mesh size and time step in time-dependent study on heat transfer problem

May 13, 2016, 8:03 am
$
0
0
Dear all,

I am simulating heat transfer problem and when it comes to set up the mesh, is there a limit on the max mesh size according to the time step I set up? Say I compute the heat transfer and want to see the temperature distribution in the material each 1ms, is there a requirement for the mesh size due to this condition (or the velocity that heat travels)?

Thanks.
↧
Search

Global Size Node in Mesh Tree

April 2, 2017, 3:08 am
$
0
0
Hi everyone, I have a question about the global size node the in the mesh tree that I can't quite figure out. I don't understand how it is still affecting my meshing scheme when every domain in my geometry has a custom mesh with a custom size and all the boxes ticked with my size parameters defined. Despite this setup, if I switch the global size node from normal to finer, there is a small change. The model does include a mapped and swept quad mesh with a conversion on the boundaries so that tets can go in along side it. Any information would really be appreciated, thank you!
↧
↧

Using previous solution as initial values

April 10, 2017, 4:55 am
$
0
0
Dear all,

I am trying to get familiar with how to use results from a previous solution as initial conditions in a new solution. To do this I am using a very simple model (see description down below) but I seem to be unable to get it to work.

In the first part of my model I am using a solid mechanics physics where I have a simple square with roller boundary conditions on the right and lower boundaries. The top boundary has a prescribed displacement that depends linearly on time.

After this I use the "Remesh deformed configuration". I then import this mesh as the geometry for my second physics node, which is also solid mechanics. The new geometry is the same as the solution from the first study, so far so good. I use the same roller boundaries but this time I prescribe a time dependent displacement on the left boundary. In this study I set the "Initial values of variables solved for" to User controlled - Solution - Study 1 - Last. However, the stress at time zero is still much lower that the last time step in Study 1.

I would be very greatful for any help on what I might do wrong or if I can do this another way.

Kind regards,
Lisa
↧

Thermal stresses in Al2O3 cylinder due to laser heating

April 10, 2017, 5:21 am
$
0
0
Hello All,

Thank you in advance for reading this. I have an issue with a solution of a 2D axisymmetric model with coupled heat transfer and solid mechanics effects. A relatively thin cylinder (like a pie chart) is heated with a laser up to temperatures on the order of 2,000 K in a thermo-shock heating profile. COMSOL seems to resolve the heat transfer effects correctly, however I am obtaining strange results for the principal stresses. I have tried changing the mesh and the heating rate, however the issue still persists. It seems that strange structures are forming for different thicknesses. In the attached image one can see the results for thicknesses of 2.05 mm and 14 mm. My question is whether these anomalies are caused by an improper resolution of the physics, or the spatial resolution (mesh), or the temporal resolution (using smaller time steps vs. heating rate), or could it be a solver issue? In the 14 mm case, lines which go through the nodal locations of my mesh are formed, which is why i thought that I had to refine it, but after I did it did not fix the issue. All comments and ideas are welcome.
↧

Stirring tank/Rotating Machinery problem

April 10, 2017, 8:19 am
$
0
0
Dear all,
I was trying to add a 3d barrier inside the stirring tank. However, I'm not familiar with the rotating machinery. I don't know how to set up the boundary condition for the new barrier. The original stirring tank's file was downloaded from the comsol application gallery. I also found out that even I changed the number of baffles into zero. There's still one baffle left.

The original file is here: www.comsol.com/model/modular-m...turbulent-mixing-k-omega-16903
(modular_mixer.mph)

1. How to set up the boundary condition for the new barrier.
2. How to eliminate all the baffles.

Thank you
↧

Laminar two phase flow, moving mesh

April 10, 2017, 6:06 pm
$
0
0
Hi,
I am going to model a vapor bubble that is growing in the liquid inside a 2D channel. liquid has an inlet velocity that drag the bubble downstream and also bubble is growing due to the mass flux of evaporation that is going to bubble. I am using the "laminar two phase flow moving mesh". I noticed a warning "inverted mesh element " and then it diverges before even the first time step. can anyone help me to fix this?
Thank you in advance.
↧
↧

Problem with meshing my geometry in the corner

April 10, 2017, 7:42 pm
$
0
0
Hi
Can anyone help me get my desired mesh in the corner of the curved surface found in the attachment?
This is a 3D model and I used tetrahedral meshes. As I decrease the mesh size, I still get one element in the corner. I need to get two or more.
Is there any way to do this?
Amin,
↧

Mesh equation

April 12, 2017, 10:54 am
$
0
0
Hi,
Does anyone know the form of equation for creating mesh?

I can´t find it in the system´s help.

Thank you
↧
Search

Using symmetry to create a heat sink

April 13, 2017, 1:39 pm
$
0
0
Hi guys,

I am looking to design a heat sink with pin fins however I'm finding that if I make a full design it takes ages to compute. How can I use some form of symmetry so that the software only has to compute a small part of the array, rather than the whole thing? I have a small heat source in the centre of my sink (the sink sits on a chip that dissipates heat). Would that change anything?

Thank you very much
↧

Memory Problems with Magnetic Field Shielding Simulation

April 17, 2017, 6:13 am
$
0
0
Hello everyone,

I am working currently on a simulation designed to test the effectiveness of a magnetic shielding system. The simulation has the following elements:
• Simulation volume: cylinder with a diameter of 805 mm and a height of 1645 mm
• Magnetic dipole
• Two paramagnetic concentric cylindrical shells of height 470 mm, inner diameters of 85 mm and 92 mm respectively, and 0.5 mm thickness, with magnetic permeability mur = 250000
The dipole is the source of the field and the paramagnetic shells constitute the shielding system. The solver calculates the magnetic field in the entire simulation region. The problem does not have a rotation symmetry due to the chose dipole position and orientation.

The problem I am having is that the computer is running out of memory as I am conducting a mesh convergence test. In an attempt to solve this, I tried to roughly calculate how much memory on average an element would take in an attempt to calculate the ram I would need to run my simulations. I ran one test with 1.5e6 total domain elements and 8.5e6 degrees of freedom. This simulation seemed to peak at around 14-15 GB when the meshing was being created. That would mean that on average each tetrahedron would need around ~1000 bytes per degree of freedom.

I am confused as to why this number is so high per degree of freedom.

Any insight on this issue would be much appreciated,
Thank you
↧
↧

Warning: relative tolerance error

April 20, 2017, 3:19 am
$
0
0
Hi
We implemented some simulations about our project 'comb-drive'.
After compute, it showed warning 'There was an error message from the linear solver . The relative error (0.081) is greater than the relative tolerance. '.
Even, we set the all mash size. But we cannot solve the problem.
We want to remove the warning sign. How can we do that?
↧

Weather Conditions on a Plant

April 21, 2017, 8:57 am
$
0
0
I'm working on a project, which i am making a study about the interaction of sunlight with a plant at a specific weather conditions.

The problem that i am facing is that i don't know how to input the hourly weather conditions data that i have which they are the temperature, wind speed, humidity, solar radiation and pressure for a specific day.

Also how to make Comsol understand that these are weather conditions data.

↧

Moving Mesh (ale) with magnetic fields

April 25, 2017, 1:38 pm
$
0
0
Hello,

I am working on a simulation to use a magnet to pull another magnet. My model couples the Structural Mechanics Module (solid), the Moving Mesh Module (ale), and the Magnetic field Module ( mf). I was expecting that when first magnets pulls the second magnet, then the magnetic field of the second magnet should move with the material. However, the magnet fields from the mf physics seemed immobile. Can somebody kindly explain what is wrong with my model (please find attached).

Thank you.
↧
Viewing all 1884 articles
Browse latest View live
Search
<script src="https://jsc.adskeeper.com/r/s/rssing.com.1596347.js" async> </script>