[FLASH-BUGS] "minor" glitch in flatten.F90

[Markus Gross]

Hi!

I was scratching my head about this for the last couple of days and finally 
found a reason for it.

Situation:

assuming 1d, hydro, ppm, split. you have two blocks with identical data, the 
only difference is that the one block is an exact mirror copy of the other. 
ie:

p_block1(:)u_block1(:)=-u_block2(16:1:-1)

for pressure and velocity.

Expecting the same results for block1 and block2 would be reasonable but 
leads to suprises and a lot of scratching of the head.

The reason for this was in the flattening which has a bias towards one 
direction if the pressure gradient is zero in a small section. There seems to 
be a similar bias in the monotonizing, just didn't get around to investigate 
it yet.

The problem is:

!this is the original
!!$       if (dp(i) .LT. 0.e0) then
!!$          scrch2(i) !!$       else
!!$          scrch2(i) !!$       endif

I replaced it with:

!
!
! this is the at.hoc modification
       if (dp(i) .LT. 0.e0) scrch2(i)        if (dp(i) .GT. 0.e0) scrch2(i)        if (dp(i) .eq. 0.e0) scrch2(i) 
I didn't check if it is reasonable yet, because my Colella & 
Woodward is buried here somewere at the moment and I cannot find it ...

I attached an example with hardcoded values for pressure and velocity. This 
small programm runs twice, for the original and the mirror data.

What do you think? Is a special case somewhat of course, but some bc's (as 
mine) or ic's may produce this sort of data and error subsequently.


Markus.






-- 
_______________________________________________________________

Markus Gross AMIMechE BEng (Hons.) Mechanical Engineering

Heriot Watt University Edinburgh
School of Engineering and Physical Sciences
James Nasmyth Building
Edinburgh
EH14 4AS
UK

Member of  IMechE, SPIE, CSME and VDI
_______________________________________________________________

further contact:

Phone   : +44 (0) 131 451 4737

UNiX talk: talk markus at lasersim.mce.hw.ac.uk

_______________________________________________________________

"Plans are a place to begin," Grove said. "They rarely deliver
you to where you expect. Make your plans knowing you are going
to throw them away."

_______________________________________________________________




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