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March 3, 2004, 15:38 
Delta form of equations.

#1 
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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. 

March 3, 2004, 22:01 
Re: Delta form of equations.

#2 
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Dear Unknown...
Please inform us what equation do you mean? 

March 4, 2004, 01:29 
Re: Delta form of equations.

#3 
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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.


March 4, 2004, 02:16 
Re: Delta form of equations.

#4 
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Delta form... Is this Dirac deltafunction or something else?


March 4, 2004, 10:05 
Re: Delta form of equations.

#5 
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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 secondorder time difference as
du/dt = (3u(n+1  4u(n) + u(n1)/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(n1). 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. 

March 4, 2004, 12:30 
Re: Delta form of equations.

#6 
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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 SIMPLEmethod.


March 8, 2004, 08:46 
Re: Delta form of equations.

#7 
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Hi,
Can you provide some reference. Thanks Apurva 

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