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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 l.jpg
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.


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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.


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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 .


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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.


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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.


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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.


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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.



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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.



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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.


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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.


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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.


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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.

    ------------ The End -------------------------


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