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Old   March 3, 2004, 15:38
Default Delta form of equations.
  #1
unknown
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What is the advantage of using a delta form of equation and where could I find more information on this.

thanks.
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Old   March 3, 2004, 22:01
Default Re: Delta form of equations.
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Michail
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Dear Unknown...

Please inform us what equation do you mean?
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Old   March 4, 2004, 01:29
Default Re: Delta form of equations.
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versi
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I remeber that the advance of a delta form discrete matrix equation is the independence of steady state solution on time step. T. H. Pulliam's book may contain it as well as in other CFD books.
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Old   March 4, 2004, 02:16
Default Re: Delta form of equations.
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ZZ
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Delta form... Is this Dirac delta-function or something else?
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Old   March 4, 2004, 10:05
Default Re: Delta form of equations.
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ag
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In the delta form of the equations you are solving for the incremental change of the dependent variables. For example you can write a second-order time difference as

du/dt = (3u(n+1 - 4u(n) + u(n-1)/2dt

or

du/dt = 1.5*(du(n+1) - (1/3)*du(n))/dt

where du(n+1) = u(n+1) - u(n), du(n) = u(n) - u(n-1).

It's the same equation, but the delta form is better behaved because typically the delta quantities are small changes and the resulting equations are more robust.
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Old   March 4, 2004, 12:30
Default Re: Delta form of equations.
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ZZ
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Thanks. I probably used such delta form when solved Poisson's equation for increment of pressure. This is one of steps in SIMPLE-method.
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Old   March 8, 2004, 08:46
Default Re: Delta form of equations.
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Apurva
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Hi,

Can you provide some reference.

Thanks

Apurva
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