Static Current Conduction strange results

Numerical methods and mathematical models of Elmer
TadasK
Posts: 18
Joined: 30 Mar 2021, 20:09
Antispam: Yes

Static Current Conduction strange results

Post by TadasK »

Good day,

I am getting rather unexpected results while calculating the current conduction. The cables (marked in the picture), have different current densities in the beginning and the end. Any reasonable explanation why I can get something like that?
Current conduction.PNG
(116.84 KiB) Not downloaded yet

The shape looks like this:
Shape.PNG
(51.22 KiB) Not downloaded yet
.step file of the case (sorry, the mesh size is simply too large)
Corrected.rar
(121.32 KiB) Downloaded 136 times
.sif file:

Code: Select all

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 = 1
  Output Intervals = 1
  Solver Input File = case.sif
  Post File = case.vtu
End

Constants
  Gravity(4) = 0 -1 0 9.82
  Stefan Boltzmann = 5.670374419e-08
  Permittivity of Vacuum = 8.85418781e-12
  Permeability of Vacuum = 1.25663706e-6
  Boltzmann Constant = 1.380649e-23
  Unit Charge = 1.6021766e-19
End

Body 1
  Name = "Body 1" 
  Equation = 1 
  Material = 3 
End 

Body 2
  Name = "Body 2" 
  Equation = 1 
  Material = 3 
End 

Body 3
  Name = "Body 3" 
  Equation = 1 
  Material = 3 
End 

Body 4
  Name = "Body 4" 
  Equation = 1 
  Material = 4 
End 

Body 5
  Name = "Body 5" 
  Equation = 1 
  Material = 2 
End 

Body 6
  Name = "Body 6" 
  Equation = 1 
  Material = 2 
End 

Body 7
  Name = "Body 7" 
  Equation = 1 
  Material = 2 
End 

Body 8
  Name = "Body 8" 
  Equation = 1 
  Material = 2 
End 

Body 9
  Name = "Body 9" 
  Equation = 1 
  Material = 1 
End 

Body 10
  Name = "Body 10" 
  Equation = 1 
  Material = 1 
End 

Body 11
  Name = "Body 11" 
  Equation = 1 
  Material = 1 
End 

Body 12
  Name = "Body 12" 
  Equation = 1 
  Material = 1 
End 

Body 13
  Name = "Body 13" 
  Equation = 1 
  Material = 1 
End 

Body 14
  Name = "Body 14" 
  Equation = 1 
  Material = 1 
End 

Body 15
  Name = "Body 15" 
  Equation = 1 
  Material = 1 
End 

Body 16
  Name = "Body 16" 
  Equation = 1 
  Material = 1 
End 

Body 17
  Name = "Body 17" 
  Equation = 1 
  Material = 1 
End 

Body 18
  Name = "Body 18" 
  Equation = 1 
  Material = 1 
End 

Body 19
  Name = "Body 19" 
  Equation = 1 
  Material = 1 
End 

Body 20
  Name = "Body 20" 
  Equation = 1 
  Material = 1 
End 

Body 21
  Name = "Body 21" 
  Equation = 1 
  Material = 1 
End 

Body 22
  Name = "Body 22" 
  Equation = 1 
  Material = 1 
End 

Body 23
  Name = "Body 23" 
  Equation = 1 
  Material = 1 
End 

Body 24
  Name = "Body 24" 
  Equation = 1 
  Material = 1 
End 

Body 25
  Name = "Body 25" 
  Equation = 1 
  Material = 1 
End 

Body 26
  Name = "Body 26" 
  Equation = 1 
  Material = 1 
End 

Body 27
  Name = "Body 27" 
  Equation = 1 
  Material = 1 
End 

Body 28
  Name = "Body 28" 
  Equation = 1 
  Material = 1 
End 

Body 29
  Name = "Body 29" 
  Equation = 1 
  Material = 1 
End 

Body 30
  Name = "Body 30" 
  Equation = 1 
  Material = 1 
End 

Body 31
  Name = "Body 31" 
  Equation = 1 
  Material = 1 
End 

Body 32
  Name = "Body 32" 
  Equation = 1 
  Material = 1 
End 

Body 33
  Name = "Body 33" 
  Equation = 1 
  Material = 1 
End 

Body 34
  Name = "Body 34" 
  Equation = 1 
  Material = 1 
End 

Body 35
  Name = "Body 35" 
  Equation = 1 
  Material = 1 
End 

Body 36
  Name = "Body 36" 
  Equation = 1 
  Material = 1 
End 

Body 37
  Name = "Body 37" 
  Equation = 1 
  Material = 1 
End 

Body 38
  Name = "Body 38" 
  Equation = 1 
  Material = 1 
End 

Body 39
  Name = "Body 39" 
  Equation = 1 
  Material = 1 
End 

Body 40
  Name = "Body 40" 
  Equation = 1 
  Material = 1 
End 

Body 41
  Name = "Body 41" 
  Equation = 1 
  Material = 1 
End 

Body 42
  Name = "Body 42" 
  Equation = 1 
  Material = 1 
End 

Body 43
  Name = "Body 43" 
  Equation = 1 
  Material = 1 
End 

Body 44
  Name = "Body 44" 
  Equation = 1 
  Material = 1 
End 

Body 45
  Name = "Body 45" 
  Equation = 1 
  Material = 1 
End 

Body 46
  Name = "Body 46" 
  Equation = 1 
  Material = 1 
End 

Body 47
  Name = "Body 47" 
  Equation = 1 
  Material = 1 
End 

Body 48
  Name = "Body 48" 
  Equation = 1 
  Material = 1 
End 

Body 49
  Name = "Body 49" 
  Equation = 1 
  Material = 1 
End 

Body 50
  Name = "Body 50" 
  Equation = 1 
  Material = 1 
End 

Body 51
  Name = "Body 51" 
  Equation = 1 
  Material = 1 
End 

Body 52
  Name = "Body 52" 
  Equation = 1 
  Material = 1 
End 

Body 53
  Name = "Body 53" 
  Equation = 1 
  Material = 1 
End 

Body 54
  Name = "Body 54" 
  Equation = 1 
  Material = 1 
End 

Body 55
  Name = "Body 55" 
  Equation = 1 
  Material = 1 
End 

Body 56
  Name = "Body 56" 
  Equation = 1 
  Material = 1 
End 

Body 57
  Name = "Body 57" 
  Equation = 1 
  Material = 1 
End 

Body 58
  Name = "Body 58" 
  Equation = 1 
  Material = 1 
End 

Body 59
  Name = "Body 59" 
  Equation = 1 
  Material = 1 
End 

Body 60
  Name = "Body 60" 
  Equation = 1 
  Material = 1 
End 

Body 61
  Name = "Body 61" 
  Equation = 1 
  Material = 1 
End 

Body 62
  Name = "Body 62" 
  Equation = 1 
  Material = 1 
End 

Body 63
  Name = "Body 63" 
  Equation = 1 
  Material = 1 
End 

Body 64
  Name = "Body 64" 
  Equation = 1 
  Material = 1 
End 

Body 65
  Name = "Body 65" 
  Equation = 1 
  Material = 1 
End 

Body 66
  Name = "Body 66" 
  Equation = 1 
  Material = 1 
End 

Body 67
  Name = "Body 67" 
  Equation = 1 
  Material = 1 
End 

Body 68
  Name = "Body 68" 
  Equation = 1 
  Material = 1 
End 

Body 69
  Name = "Body 69" 
  Equation = 1 
  Material = 1 
End 

Body 70
  Name = "Body 70" 
  Equation = 1 
  Material = 1 
End 

Body 71
  Name = "Body 71" 
  Equation = 1 
  Material = 3 
End 

Body 72
  Name = "Body 72" 
  Equation = 1 
  Material = 1 
End

Body 73
  Name = "Body 73" 
  Equation = 1 
  Material = 2 
End 

Solver 1
  Equation = Static Current Conduction
  Procedure = "StatCurrentSolve" "StatCurrentSolver"
  Variable = Potential
  Calculate Volume Current = True
  Exec Solver = Always
  Stabilize = True
  Optimize Bandwidth = True
  Steady State Convergence Tolerance = 1.0e-5
  Nonlinear System Convergence Tolerance = 1.0e-7
  Nonlinear System Max Iterations = 200
  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 = 1000
  Linear System Convergence Tolerance = 1.0e-10
  BiCGstabl polynomial degree = 4
  Linear System Preconditioning = none
  Linear System ILUT Tolerance = 1.0e-3
  Linear System Abort Not Converged = False
  Linear System Residual Output = 10
  Linear System Precondition Recompute = 1
End

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

Material 1
  Name = "Copper (generic)"
  Poisson ratio = 0.34
  Density = 8960.0
  Youngs modulus = 115.0e9
  Electric Conductivity = 59.59e6
  Heat Capacity = 385.0
  Heat expansion Coefficient = 16.5e-6
  Sound speed = 3810.0
  Heat Conductivity = 401.0
End

Material 2
  Name = "Steel (stainless - generic)"
  Poisson ratio = 0.285
  Youngs modulus = 200.0e9
  Heat Capacity = 460.0
  Heat Conductivity = 24.0
  Heat expansion Coefficient = 14.9e-6
  Electric Conductivity = 1.824e6
  Density = 7925.0
  Sound speed = 5100.0
End

Material 3
  Name = "Vapour"
  Electric Conductivity = 2.17e-11
End

Material 4
  Name = "IG"
  Electric Conductivity = 5e-9
End

Boundary Condition 1
  Target Boundaries(4) = 462 464 466 468       
  Name = "Ground"
  Potential = 0
End

Boundary Condition 2
  Target Boundaries(186) = 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443  
  Name = "120kV"
  Potential = 120000
End
Thanks.
Ted.
kevinarden
Posts: 2237
Joined: 25 Jan 2019, 01:28
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Re: Static Current Conduction strange results

Post by kevinarden »

Is there a reason there are so many bodies? Usually 1 per material. Are there coincident nodes at the boundaries between the bodies? In Elmer they should share nodes. With what tool did you mesh the step file and convert it to Elmer?

Also the dimensional units in the step file are quite large, they should be in SI units which is meters. The Elmer solver is non-dimensional but the constants and the material constants are in SI units, so the dimensions also need to be in meters.
raback
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Re: Static Current Conduction strange results

Post by raback »

Hi,

Maybe you could also plot a close-up of the mesh of the wire. This kind of problems with huge differences in scale tend to be challenging to mesh. Standard algorithms easily through just one or two tets on the wire width and that is not enough.

-Peter
TadasK
Posts: 18
Joined: 30 Mar 2021, 20:09
Antispam: Yes

Re: Static Current Conduction strange results

Post by TadasK »

kevinarden wrote: 07 Jun 2021, 23:28 Is there a reason there are so many bodies? Usually 1 per material. Are there coincident nodes at the boundaries between the bodies? In Elmer they should share nodes. With what tool did you mesh the step file and convert it to Elmer?

Also the dimensional units in the step file are quite large, they should be in SI units which is meters. The Elmer solver is non-dimensional but the constants and the material constants are in SI units, so the dimensions also need to be in meters.
Hi Kevin,

Regarding bodies, no particular reason, the main answer is my inexperience in FEM calculations.

Regarding Coincident nodes, the interface between cable and larger cylinder should be coincident. The whole model has been built using FreeCad. Before exporting the model to .step file, I have done some boolean fragment actions and used the compound filter. Please find the FreeCad file attached.
More_accurate_v5.rar
(545.74 KiB) Downloaded 136 times
The mesh has been generated using gmsh and exported as a .unv file.

Regarding the dimensions, might be an issue, everything has been done assuming millimeters, thus the whole model is rather huge. Should I redesign everything assuming meters instead of millimeters? (Millimeters is the default option in FreeCad).
raback
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Re: Static Current Conduction strange results

Post by raback »

Hi

The equation is linear & Elmer by default scales the linear system such that the diagonal is ~1. So your results may be off by some factor but the mm->m scaling does not resolve your original problem.

I think this is a meshing issue. Your variation in aspect ratio is so extreme. Also it could be a convergence issue if you're using iterative solvers. They might stop too early. Does changing tolerances affect the results?

-Peter
TadasK
Posts: 18
Joined: 30 Mar 2021, 20:09
Antispam: Yes

Re: Static Current Conduction strange results

Post by TadasK »

raback wrote: 08 Jun 2021, 00:42 Hi,

Maybe you could also plot a close-up of the mesh of the wire. This kind of problems with huge differences in scale tend to be challenging to mesh. Standard algorithms easily through just one or two tets on the wire width and that is not enough.

-Peter
Hi Peter,

I used a quite dense mesh, gmsh was not capable to mesh the model if the element size was larger than 40. If that makes any difference the size of the mesh is ~1.3gb.
mesh.png
(487.05 KiB) Not downloaded yet
mesh_v2.png
(524.9 KiB) Not downloaded yet
raback
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Joined: 22 Aug 2009, 11:57
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Re: Static Current Conduction strange results

Post by raback »

Hi,

Unfortunately both meshes are too coarse. Particularly in the region where the wire joins the container you should have a fine mesh. On the other hand having a uniform mesh in the whole container is a little waste.

If you take a back a step. What is the question you're trying to solve?

-Peter
TadasK
Posts: 18
Joined: 30 Mar 2021, 20:09
Antispam: Yes

Re: Static Current Conduction strange results

Post by TadasK »

raback wrote: 08 Jun 2021, 12:48 Hi,

Unfortunately both meshes are too coarse. Particularly in the region where the wire joins the container you should have a fine mesh. On the other hand having a uniform mesh in the whole container is a little waste.

If you take a back a step. What is the question you're trying to solve?

-Peter
Peter, thanks for the comments. In some way, I received an answer to my question, It seems that I need to go back to the meshing. Although I am still curious, at the moment I am using gmsh to generating a mesh, do you have any recommendations on what should I use for this action?

Ted.
kevinarden
Posts: 2237
Joined: 25 Jan 2019, 01:28
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Re: Static Current Conduction strange results

Post by kevinarden »

in Gmsh the coherence command is used to resolve coincident nodes. Also in Elmer there is a
Coordinate Scaling command to convert to meters prior to entering the solver.
TadasK
Posts: 18
Joined: 30 Mar 2021, 20:09
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Re: Static Current Conduction strange results

Post by TadasK »

Hi,

I have simplified the model, fixed the mesh and I am still getting the same results. I am wondering can it be a numerical thing?

I am adding two figures for reference
calcs.png
(196.07 KiB) Not downloaded yet
mesh.PNG
(93.77 KiB) Not downloaded yet
P.S. ran an additional test just to see whether the same issue occurs if I only have a cylinder and a wire connected. Under this case it seems that the current is uniform, as expected.
calcs2.png
(102.24 KiB) Not downloaded yet
Thank you very much.
Tadas
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