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Domain partitioning; ‘exporting’ and ‘importing’ . Domain-partitioning reduces a large calculation to a succession of smaller ones

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domain partitioning exporting and importing
Domain partitioning; ‘exporting’ and ‘importing’

. Domain-partitioning reduces a large calculation to a succession of smaller ones

  • It is useful for computer simulation of flow phenomena. characterised by a predominant direction of flow, as for example when several chemical-plant vessels are connected in series.
  • A similar situation arises when it is necessary to simulate the flow over an extensive tract of terrain, for example a complete city or a wide forest. Partitioning is then possible because usually the direction of wind varies little from place to place.
  • Upstream partitions are simulated first; their results are ‘dumped’ as ‘export objects’ which are treated as ‘import objects’ by the next-downstream partitions.
  • The computations are carried out successively.
  • How this can be done with PHOENICS will now be explained.
using transfer objects for import and export
Using transfer objects for import and export
  • The idea is simple to understand; but implementation has to be made easy for users.
  • Therefore ‘Transfer Objects’ have been introduced into PHOENICS by providing two new keywords for In-Form, namely:(EXPORT and

(IMPORT

  • The first causes the PHOENICS solver module, EARTH, to write a transfer-object file at the end of its run; and the second causes EARTH to read such a file at the start of its run.
  • Transfer objects can be created by placing in the Q1 file an In-Form statement such as:

(EXPORT in NAME_OF_TRANSFER_OBJECT at PATCH_NAME) , or

(EXPORT in NAME_OF_TRANSFER_OBJECT at OBJECT_NAME)

.

  • Some tests now follow.
transfer object tests 1
Transfer-object tests, 1
  • This 2D test of steady laminar convective flow shows how one gets the same answer whether one partitions the domain (B) or not (A) when the flow is uni-directional, and the Reynolds number is much larger than 1.
  • This is Library case 856 .
  • The variable is H1 .
transfer object tests 2
Transfer-object tests, 2
  • This 3D example shows partitioning in two directions.
  • It represents a steady atmospheric boundary layer with a point source of pollutant.
  • The results with (i.e. B) and without (i.e. A) partitioning are in close agreement.
  • Library case 858.
transfer object tests 3
Transfer-object tests, 3
  • This example concerns unsteady spread of a finite release of pollutant into the atmosphere.
  • With (bottom) and without (top) partitioning, the concentration distribution at a fixed time is much the same,
  • Library case 859.
transfer object tests 4
Transfer-object tests, 4
  • The partitions may be connected in more complex ways.
  • For example, the first might be used to compute the flow and heat transfer within, and the output from, a computer cabinet; then the second might comprise a computer room with several identical computers within it,
  • Or the first might be a room with a smoke-producing fire in it, the second the space around the building, and the third another room into which smoke enters through open windows.
  • Both of these will be illustrated in what follows.
transfer object tests 5
Transfer-object tests, 5
  • Here is the result of computing the temperature distribution within, and the heat output from, a (highly idealised) computer cabinet.
  • Its output is ‘exported’ to its environment via transfer objects at its fan inlets and outlets.
  • The library case is 863.
transfer object tests 6
Transfer-object tests, 6
  • This is the result of the subsequent simulation of the temperature distribution in a room containing several identical computers.
  • Their effects are ‘imported’ via the ‘export’ objects of the previous calculation,
  • This is library case 864.
transfer object tests 7
Transfer-object tests, 7
  • Now for the smoke-producing fire in a room.
  • It ‘exports its smoke through open windows.
  • This is library case 860.
  • It is treated as steady, which is not realistic; but it suffices to show how transfer objects can be used.
transfer object tests 8
Transfer-object tests, 8
  • The second computation shows how the smoke is ‘imported’ into the surroundings which ‘export’ some of it to other rooms in the building’.
  • This is library case 861.
transfer object tests 9
Transfer-object tests, 9
  • Simulation number 3 shows how the adjoining room ‘imports’ smoke through its open windows.
  • This is library case 862.
  • Of course, the simulation could have been carried out in a time-dependent manner;
  • And all the rooms in the building could have been treated in the same way.
  • Finally, if two-way interactions between rooms are suspected, it is necessary to iterate.
how to learn about transfer objects
How to learn abouttransfer objects
  • Look in the PHOENICS Encyclopaedia.
  • Try the tutorial (It’s quite good).
  • Look in the library (you won’t find any, because the search engine has not yet been told what to look for!)
  • Create some examples for yourself.
  • Send them to CHAM for use by all.

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