Small body

[MattePOLI]

Good afternoon,
I've a problem with small objects in simulation of StatCurrent solver.
i'll explain, I've two conductors cylinders body with 0.01m radius buried in the ground (much bigger than they).
Is possible that Elmer does not recognize the small objects in the simulation?
Because when I plot the potential flow I've a potential hole on the conductors.

[mzenker]

Hi,

it depends on your mesh size. If it is small enough and your settings are correct there should be no problem.

Matthias

[MattePOLI]

Thank you for your quickly reply,
however the same problem with bigger objects not occurs.
We did a mesh with 700000 elements and every conductors are divided into 1000 elements one.
If i post the sif file, do you take a look?
Thank you forward

[mzenker]

I can have a quick look, yes.

[MattePOLI]

Header
CHECK KEYWORDS Warn
Mesh DB "." "."
Include Path ""
Results Directory ""
End

Simulation
Max Output Level = 5
Coordinate System = Cartesian
Coordinate Mapping(3) = 1 2 3
Simulation Type = Steady state
Steady State Max Iterations = 100
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Solver Input File = case.sif
Post File = case.ep
End

Constants
Gravity(4) = 0 -1 0 9.82
Stefan Boltzmann = 5.67e-08
Permittivity of Vacuum = 8.8542e-12
Boltzmann Constant = 1.3807e-23
Unit Charge = 1.602e-19
End

Body 1
Target Bodies(1) = 1
Name = "Body 1"
Equation = 1
Material = 2
Initial condition = 1
End

Body 2
Target Bodies(1) = 2
Name = "Body 2"
Equation = 1
Material = 2
Initial condition = 1
End

Body 3
Target Bodies(1) = 3
Name = "Body 3"
Equation = 1
Material = 1
Initial condition = 1
End

Solver 2
Equation = Static Current Conduction
Calculate Volume Current = True
Procedure = "StatCurrentSolve" "StatCurrentSolver"
Variable = -dofs 1 Potential
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStab
Linear System Max Iterations = 500
Linear System Convergence Tolerance = 1.0e-10
Linear System Preconditioning = ILU0
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End

Solver 1
Equation = Result Output
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output Format = Vtk
Output File Name = case
Exec Solver = After Simulation
End

Equation 1
Name = "EQ"
Active Solvers(2) = 2 1
End

Material 1
Name = "Terra"
Electric Conductivity = 0.01
End

Material 2
Name = "Copper (generic)"
Poisson ratio = 0.34
Heat expansion Coefficient = 16.5e-6
Poisson ratio = 0.34
Electric Conductivity = 59.59e6
Youngs modulus = 115.0e9
Youngs modulus = 115.0e9
Heat Conductivity = 401.0
Sound speed = 3810.0
Heat Capacity = 385.0
Mesh Poisson ratio = 0.34
Density = 8960.0
Poisson ratio = 0.34
Youngs modulus = 115.0e9
End

Initial Condition 1
Name = "InitialCondition 1"
Potential = 0
End

Boundary Condition 1
Target Boundaries(1) = 1
Name = ""
End

Boundary Condition 2
Target Boundaries(1) = 2
Name = "Attivo"
Current Density = 3.176745371
End

Boundary Condition 3
Target Boundaries(1) = 4
Name = "Isolante"
Current Density = 0
End

Boundary Condition 4
Target Boundaries(1) = 7
Name = "Terra"
Potential = 1.5915
Current Density = -0.001591549431
End


Thank you very much

[mzenker]

Hi,

I don't get quite what you are trying to do. Some observations nevertheless:

* Initial conditions don't make sense for a steady state simulation.
* Boundary condition 1 is empty.
* You said that you don't have the problem with bigger objects - are you sure that with exactly the same settings and just a changed geometry, everything is fine? (Note that ElmerGUI forgets the boundary conditions when you load another mesh.)

A sketch of your geometry would be nice to understand better what you want to do.

HTH,

Matthias

P.S.: I will go home soon, so the next post may be for monday...

[MattePOLI]

Thanks..don't worry, we aren't in a hurry
So, i know everything that you said, but the initial conditions are mandatory, otherwise the solver not compute.
I can't set the boundary condition for this body, because i want to study the potential on this conductor while I provide current to upper conductor. I can't set floating potential on the second body (in this case conductor under).Whenever i want to study something i set again the model setup.
The geometry of my project is attached. In this picture i removed the earth upside that is set to non-conducting.

[mzenker]

Hi,

your picture just shows a portion of a spheroid or something like that. I can't see the conductors - or I miss something...

You could start with a VERY easy geometry to see if what you want to do works at all, maybe that way you can find out where the problem is.

Have a nice weekend,

Matthias

[raback]

Hi

I think that the fact that you have no BCs may be the problem. A Poisson equation is not uniquely defined if you haven't defined the potential even in a single point. In fact you are getting a solution only because the Krylov subspace solvers such as BiCGStab are not so picky on these things. A direct solver would never be able to solve it.

To set one point study "Target Coordinates" or "Target Nodes" in conjunction with BCs.

-Peter

[MattePOLI]

Thank you everybody for your help.
I'm an italian student (and i'm sorry for my poor english) and i'm studying how the potential distribuction in the ground when i inject a current in a active copper rod.
So i want to know the potential on another rod under the first. So i can't define the BCs on floating rod because i don't know the potential and i don't know the current density in the rod, but i setted the body without BC with the option 'use as body'. You told me that i should set mandatory the BC on the floating rod, even in only one node, but i don't know how. Can you explain me? thank you very much.
Matteo