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Relaxation and convergence

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Old   March 20, 2008, 04:32
Default Relaxation and convergence
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sammi
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Dear Sir,

It's me again. I read some posts said that the speed of convergence depends much on relaxation setting. And which relaxation setting should be used depends on experience.

I know the following questions sounds stupid, but I need help...

1)What is the actual meaning of linear relaxation and false time step? What is the different between them? (I only known a negative value means linear relaxation, but I don't actually understand what the meaning of them is.)

2)What is the effect of tighter and looser the relaxation, when should I make it tightr/looser?

3)I found an equation calculating relaxation: (smallest cell distance in main direction of flow)/(fastest velocity) So, if I ran a model using 16 wind directions, does it means that all 16 directions should have different relaxation? If I ran NE direction wind, how should I determain the cell distance. If the smallest cell distance is at 2.5m while the fastest velocity is at 596m, is the different of height improtant?

Regards, Sammi
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