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Novice question - Deforming a mesh according to a solution

September 22, 2014, 2:35 pm
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Hi,

Let me begin that I am new to COMSOL.

Using COMSOL 4.4, I have created a model for poroelasticity based on mixture theory. The COMSOL model uses the Weak Form PDE and things seem to work fine in terms of obtaining solutions.

Since my simulations involve the motion of fluids within deformable media I am trying to post process my solution so that the fluid flow is shown on the deformed shape of the body. So my question is: How do I get the mesh or the geometry to deform according to one of the displacement vector field that I compute?

This is not a moving mesh problem. The mesh or geometry motion I am talking about is simply a post-processing operation. Any help would be appreciated.
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Moving heat plate comes in contact with surface

September 30, 2014, 11:32 am
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Hi, I have a model using the Heat Transfer module and the Deformed Geometry module. I have a heating plate at a fixed temperature and a long sheet initially at ambient temperature. Both entities are initially separated. The plate moves at a constant speed and comes in contact with the sheet. According to the geometry of my model and the trajectory of the heating plate, both entities should come in contact (they should just brush against each other).

When solving the model, even tough the plate clearly comes in contact with the sheet, it doesn't heat it.

What should I do so the plate heat the sheet as it moves along?

Thank you.
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Defining prescribed mesh velocity in Deformed Geometry physics

November 14, 2014, 3:24 pm
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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
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A problem about exporting data on deformed mesh

February 19, 2015, 5:18 pm
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I am trying to export the data on a deformed domain at different times. However, the export file only contains Coordinates information of the first time frame I chose. If there is 10 time steps, I have to export the data on each time step one by one. Is this a bug of Comsol I did something wrong?
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Deformed geometry : How to use the coordinates of a boundary in the deformed geometry as a variable?

April 27, 2015, 9:55 am
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Hi

In my model, I am using the Weak form PDE module and I require to use the at() operator for a source term.
For the first argument of the operator, I require the coordinates of one of the boundaries of my model, but it is deformed by a prescribed mesh velocity and is not stationary.
I could integrate the velocity over time and figure out the displacement, but I think there should be a straightforward way to get the displacement. Can someone shed any light on this?

(My model is 1D, so I'm using the at1 operator.)

Thanks
George
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Applying Boundary Conditions Based on Deformed Geometry

May 15, 2015, 12:50 pm
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Hello everyone,

Right now, I am trying to solve a coupled physics problem involving deformation and electric current. In essence, what I want to do is correlate electrical resistance between two spheres for varying applied loads. Based on previous work, we know that altering the applied force changes the spheres' contact area and, hence, the final electric resistance. TO implement this in COMSOL, however, there are a few issues I'm running into. Now, as you can imagine, there is an insulation boundary condition along the surface outside of the contact region. However, inside the contact region, current should be able to run freely between the spheres.

When trying to implement this insulation BC, there's a major issue in COMSOL. If I start with the undeformed geometry, then there is no contact region, and the entire surface is set as an insulation boundary. What I need to do is apply this boundary condition ONCE the deformation has taken place, but there is no way to do this at all. I have tried many suggestions before. Of those suggestions, one is to use the moving mesh (ALE) module to use the deformed geometry in the electric current module. Unfortunately, this does not work - since the entire surface is treated as insulated. Similarly, I also tried to export the deformed mesh into a new geometry via the "remesh deformed configuration" option. Again, this does not seem to work; the mesh is deformed inside the simulation, but the exported geometry is no different than the original geometry. The only difference is that the contact point is shifted vertically; the surface deformation is NOT exported. Is there any way that I could run the elasticity module and THEN apply this insulation boundary condition - such that current may run freely between the spheres? ANy suggestions are GREATLY APPRECIATED; this has been beyond frustrating....
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Deformed geometry under concentration

June 25, 2015, 7:43 am
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I’m trying to solve a 2D coupled biological problem where the concentration of diluted species inside a body sunk in water is calculated by a diffusion problem (to simplify). The most important part of the model is that the concentration of the diluted species determines the area of the body. To simplify, [Area = x*Concentration + Initial area]. This means that somehow the body swells when concentration increases.
The body is an “infinite” layer stuck to a fixed boundary (wall), so there is only one free side. The transient concentration is spatially heterogeneous in the two dimensions. Because the concentration is local the growth/swelling of the body is anisotropic.
1- First, I tried to compute the moving boundary by using the mesh velocity tool (in Mathematics > Deformed mesh > Deformed geometry). I set the mesh velocity equal to the change in concentrations. I could obtain nice results but I think that this command only computes the deformation from the concentration measured in the boundary (interface body-water). I’m not sure about this. Maybe it accounts for the local deformation of all the nodes but I don’t think so.
2- Second and instead of following the steps in 1, I divided all the body in many smaller domains. I used surface integration (in Derived values) to estimate the mass in each sub-domain and I repeated the steps in 1 using these values. To capture the whole heterogeneity it is necessary to create sub-domains as small as the mesh elements.
3- Finally, I recalculated the concentrations both in 1 and 2 solving the conservative form of the transport equation by setting the convection term equal to mesh velocity.
Results using 1-3 and 2-3 are completely different. I don’t know which approach is best. Maybe any of them. Any advice is welcome. Thanks
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PDE system and deformed geometry

December 17, 2015, 12:39 pm
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Hello,

I have a very simple geometry: segment with a point in the middle. I pretend to simulate the diffusion process of three components by introducing the PDEs in a math interface. The PDE system solves the concentrations of two of the components (the third one must satisfy xA+xB+xC=1). The diffusion process also modifies the geometry. To compute that, I add a deformed geometry interface. I have two main questions:

- I define 0 flux in the edges. I define constant concentration of one of the components in one of the edge points (boundary). The Dirichlet boundary condition node I use to do that, allows me to define the condition for one of the variables or both variables. If I choose only one, the other one should satisfy 0 flux, but such node appears as overriden. Why the 0 flux cannot be defined independent to each variable too?

- Then, in that node I have an external flux for the variable that I want to keep constant. Such flux is used to define the displacement of the node. I define a velocity in the node. But then, I cannot define 0 displacement (fixed) in the middle point! However I can fix the point in the other edge. Why I cannot fix the middle point when one of the edges is moving? (both semi-segments are defined as free deformation)


Thank you

--
M. Sc. Oscar Banos

TU Dresden (Germany)
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Problem with Automatic Remeshing / MUMPS allocation factor increased to 1.44.

January 14, 2016, 5:41 pm
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Hi there,

I have built a COMSOL 2D model that uses deformed geometry, where the geometry movement is non uniform. I need to use Automatic Remeshing to update the mesh elements. But after some time (t = 0.29s) it fails.
I tried using moving mesh, mesh refinement as well as segregated solver, but I am unable to get rid of this error. I need to know why this error keeps popping up, and whether there is something that I am missing.
I have given the error, as well as the warning below, and also attached the wireframe and surface plots of the concentration before the error.

Any help would be appreciated.
Thanks.

Warning:
MUMPS allocation factor increased to 1.44.

Error:
The following feature has encountered a problem:
Nonlinear solver did not converge.
In Segregated Step 1
:
Time : 0.2924214449879353
Segregated Step 1
Singular_matrix

There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 14 comp1.cH_1p
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...
There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 14 comp1.cOH_1m
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...
There_are x_void_equations_(empty_rows_in_matrix)_for_the_variable_x 10 comp1.npe.Ceq_eqreac1
at_coordinates (-1e-007,2e-007), (-1e-007,1.5e-007), (-1e-007,1e-007), (-1e-007,5e-008), (-1e-007,-3.08102e-020), ...


Last time step is not converged.
- Feature: Automatic Remeshing 1 (sol1/t1/ar1)
- Feature: Time-Dependent Solver 1 (sol1/t1)
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Cannot use Prescribed mesh velocity in Frequency-Transient Study

April 22, 2016, 8:48 am
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I'm setting up a microwave heating model with a deformed geometry.
The microwave field is solved in the frequency domain, and the other physics (e.g. heating) in the time domain. This is accomplished with the so called Frequency - Transient study, which works like a normal time dependent study, except that it allows to enter the frequency.
The additional 'physics' of the deformed mesh contains a prediscribed mesh velocity. It does what it should do in a time dpendent study. However when I combine it with the microwave using the above mentioned frequency-transient step, then I recieve the error:

Prescribed mesh velocity is only applicable for transient studies.
- Feature: Compile Equations: Frequency-Transient

But I do have a transient study, So? This seems unintended behaviour to me. Any suggestions ?

Food & Biobased Research
Wageningen University
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Studies Loop with Comsol or Matlab?

April 26, 2016, 12:41 pm
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Hello colleagues,

i want so simulate the material removal which includes two big different time scales.
My approach is to simulate in the first study the fast physical phenomena (electrical pulse + vibration, timescale is about 0.02 s) and in the second study a slower physical process (removal, timescale about 10s)

In my first study i simulate an electrical pulse and an oszillating cathode and from that i can compute an average removal speed at the anode within the very short time (0.02s)

Then i start my second study with a deformed geometry (displacement = average speed*time) and after e.g. 10s i have a new geometry as a result of the electrochemical machining.

And now my problem:
How to implement an automatic loop/sequence in Comsol which solves the problem (Studiy1-->Study2-->Study1 with new geometry --> Study2 --> Study 1--> and so on) for a defined number of steps?
Or is it only possible to do it with using of Matlab?

I hope somebody of you have experience in such multiscale/ multitime problems and can hap me.

Thanks and greetings
Ingo
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Remeshing a Deformed Mesh in 4.0a

March 9, 2011, 2:46 pm
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Hi,
I am simulating the heat transfer in biological tissue that has been compressed. First I apply a gravitational load, and next I want to run the heat transfer calculations on the deformed geometry. If I want to run the heat transfer part in a separate study, how do I specify the study to use the deformed geometry from the first study (structural mechanics)? Any help would be greatly appreciated!

Austin R
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Moving boundary

June 27, 2012, 6:33 am
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HI

The attachment is a simple model of my problem, first I solve a Poisson's equation on the circles and secondly I would like to move the boundaries with the velocity field (ux/2,uy/2). After the movement I would like to extract the new geometry and do the same steps till the gradient vanishes on the boundary but these two circles are fixed in all steps. I have tried moving mesh(ale), deform geometry(dg) and level set but have got stuck. I wonder which method is better?
Any suggestion?
You can also consider the two fixed balls as the injection of two fluids(same fluid, or even two heat sources) and we desire to follow the boundary of occupied region after the fluids meet each other.
For more information see pdf file.

Best, Reza
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Shape optimization of radiating plate

April 16, 2013, 2:07 pm
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Dear all,

I'm currently optimizing the shape of a vibrating plate in an closed hollow cylinder filled with air to get an as straight as possible wavefront. I model it 2D axisymmetric and make use of solid mechanics and pressure acoustics in the frequency domain.

My plate is drawn as an rectangle and I only want the top line of the rectangle to be optimized, however now my whole shape (top and bottom line) of the rectangle are changed equally. Which is logic because I set a prescribed mesh displacement in z direction, but I don't know how to do it another way. I tried an parametric curve, but then the geometry and mesh aren't updated.

What I did:
- Build my geometry, add material and configure the pressure acoustics and solid mechanics module correctly
** The geometry of the plate, which I try to optimize, is a rectangle created with 4 linear Bézier polygons.

- Next I defined an displacement of the plate in z direction as a variable.
** Name: dz, expression: q1*sc1*sin(2*pi*s). Here q1(defined later) is the optimization variable and sc1 (defined as global parameter) is a scaling factor (in this case sc1=2)

- I also defined an objective function, which I tested by changing some variables and shape by hand.

- Next I added the optimization module to my model. I added my objective function as global objective. For global control variables I defined q1 with an lower (-1) and upper bound(1) and an initial value of 0.

- After that I added Deformed Geometry to my model. I selected all the solid mechanics. I added "Free deformation" to the part I want to optimize. To the boundaries of the part that I want to optimize I added "Prescribed mesh displacement" with dz as prescribed mesh displacement in z direction.

- At last I added a frequency domain study where I disabled the stationary solver and added an optimization solver.

Can someone explain me how to optimize only the top line of the rectangle and keep the bottom and sides fixed?

Thanks in advance.

Greetings Nick

PS the attachment is an overview of the geometry and the materials.

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Melting Front and Free Surface

January 29, 2014, 2:54 am
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Dear all,

I'm currently attempting to build a model similar to the "Tin Melting Front" in the model library. This model describes the melting of a metal through the Stefan problem and models the movement of the melting front using the Deformed Geometry interface. In my particular problem I wish to model this melting front but also the movement of the free surface of the liquid metal (this is a similar problem to metal welding).

It is my understanding that the solid/liquid front should be modeled with the Deformed Geometry interface, but the movement of the free surface of liquids is modeled with the Moving Mesh interface.

Is it possible to use both interfaces in the same model to describe the two different interfaces or is there another way to do this?

Thanks for the help.
Helena
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Deformed geometry model converges until I try to use the lagrange multiplier

June 18, 2014, 1:59 pm
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Hi all,

I'm trying to model the growth of a cavity in a block of ice in response to a flow of hot air. I have a model that works fairly well, with conjugate heat transfer and a deformed geometry to track the air / ice interface as melting progresses. At least, it works fine as long as I prescribe the melting rate at a fixed value of 0.001 m/s. In order to simulate melting I followed the approach of the Tin Melting Front example "Stefan problem" model: set the boundary temperature as a weak constraint, and use the lagrange multiplier as input to a prescribed normal deformation on that boundary.

The problem is that whenever I switch from the fixed value to the "Stefan problem" expression for the Prescribed Normal Mesh Velocity, my model no longer converges -- it says:

Nonlinear solver did not converge.
Time: 0
Attempt to evaluate real square root of negative number.

The model is attached. Thanks in advance for any advice!

Aaron
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Novice question - Deforming a mesh according to a solution

September 22, 2014, 9:35 am
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Hi,

Let me begin that I am new to COMSOL.

Using COMSOL 4.4, I have created a model for poroelasticity based on mixture theory. The COMSOL model uses the Weak Form PDE and things seem to work fine in terms of obtaining solutions.

Since my simulations involve the motion of fluids within deformable media I am trying to post process my solution so that the fluid flow is shown on the deformed shape of the body. So my question is: How do I get the mesh or the geometry to deform according to one of the displacement vector field that I compute?

This is not a moving mesh problem. The mesh or geometry motion I am talking about is simply a post-processing operation. Any help would be appreciated.
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Moving heat plate comes in contact with surface

September 30, 2014, 6:32 am
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Hi, I have a model using the Heat Transfer module and the Deformed Geometry module. I have a heating plate at a fixed temperature and a long sheet initially at ambient temperature. Both entities are initially separated. The plate moves at a constant speed and comes in contact with the sheet. According to the geometry of my model and the trajectory of the heating plate, both entities should come in contact (they should just brush against each other).

When solving the model, even tough the plate clearly comes in contact with the sheet, it doesn't heat it.

What should I do so the plate heat the sheet as it moves along?

Thank you.
↧

Defining prescribed mesh velocity in Deformed Geometry physics

November 14, 2014, 11:24 am
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0
0
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
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A problem about exporting data on deformed mesh

February 19, 2015, 1:18 pm
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I am trying to export the data on a deformed domain at different times. However, the export file only contains Coordinates information of the first time frame I chose. If there is 10 time steps, I have to export the data on each time step one by one. Is this a bug of Comsol I did something wrong?
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