🚀 go-pugleaf

In article <1993Jan21.115722.29874@dutrun2.tudelft.nl>, rcpshdb@dutrun2.tudelft.nl (Han de Bruijn) writes:
|> In article <1993Jan20.120623.18611@dutrun2.tudelft.nl>, I wrote:
|> > Wouldn't it help if people first _unify_ F.V. (fluid) and F.E. (solid) 
|> > methods? 
|> 
|> In article <1993Jan20.162622@roper.mc.ti.com> W. Donald Rolph (hi, Don!):
|> > ................... (pardon Han!) the requirement here is that the shape or
|> > trial functiosa [ he means: functions ] across the interface be compatible.
|> > Under these conditions (oh well here we go again) the FV for the fluid
|> > becomes essentially indistinguishable from FEA for the fluid, certainly at
|> > the boundaries at least, and the problem easily reduces to a tractable form.
|> 
|> Oh yeah? Let's take a combustion engine as an example. I have a the solid parts
|> modeled with MARC, and the fluid parts modeled with PHOENICS. According to Don,
|> it would be a "tractable" matter now to roast the beef. 
|> 
|> Or else, let's start from the basics: take some F.E. ingredients for the solid
|> parts, take some F.V ingredients for the fluid parts. Then ... take a BIG MAMA,
|> and "the problem easily reduces to a tractable form".
|> 
|> One world or no world. Once F.V. and F.E. have been unified into ONE universal
|> numerical method, the true practical problems will remain hard enough to solve.
|> -- 
|> * Han de Bruijn; Applications&Graphics | "A little bit of Physics * No
|> * TUD Computing Centre; P.O. Box 354   | would be NO idleness in  * Oil
|> * 2600 AJ  Delft; The Netherlands.     | Mathematics" (HdB).      * for
|> * E-mail: Han.deBruijn@RC.TUDelft.NL --| Fax: +31 15 78 37 87 ----* Blood

I agree completely with Han.  I pose however, that at least at first pass, the fv
formulation could be established for the fluid matched by trial functions to the
solid with fea and in one single program solve the problem.  Since as posed the
variables would be continuous accross the boundary, the problem is indeed
tractable, as for example Olsen and Bathe Journal of Computer and Structures 21,
1985.

I still pose further, however,  that properly posed the fea equations for the
fluids themselves become indistinguishable form the fv equations for thes fluid
themselves.  Han you have brought up upwind differencing for the convective term
before.  I reference Zienkiewicz 1977 starting on page 633 where he discusses
applying upwind differencing for the convective term using fea procedures.  If
these equations are consistent with your fv upwind differencing, then since you
already conceded that for the pure diffusion problem fea and fv can reduce to the
same form, a common ground would appear to exist.

If the above paragraph sustains critical review, then my position is an even more
optimistic one than yours, that is to say yes we need a merging of the two
techniques - I agree completely, but further that the math to merge the two
techniques already exists.  ONE universal numercal method can be achieved today!

You thoughts Han?

-- 

Regards.
 
Don Rolph  a722756@pan.mc.ti.com WD3 MS10-13 (508)-699-1263

 
Han de Bruijn writes :

>Oh yeah? Let's take a combustion engine as an example. I have a the solid parts
>modeled with MARC, and the fluid parts modeled with PHOENICS. According to Don,
>it would be a "tractable" matter now to roast the beef.

 I'm not sure, but I don't think in that case the shape of the solid part
will be changed by the fluid. And if it does. In my case you need to couple
the Navier-Stokes and the dynamic (?) equations, with all the problems you
will get on the interface.

 I beleive the aeroelasticity is what I was looking for, even if I don't
need compressible equations in my case. Now I have to look the articles
concerning this field.


				Thanks for all,

		
						Olivier.


ps : I'm still curious if you have more informations :)

The proposed method of either Han or myself will couple the navier-stokes
(actually the energy equation is more general I think - comments Han), and the 
dynamic equations of the solid.  It was exactly the elasticity of the fluid 
acting against the dynamic behavior of the soldi which Olsen writes about.
-- 

Regards.
 
Don Rolph  a722756@pan.mc.ti.com WD3 MS10-13 (508)-699-1263

In article <1993Jan21.154511@roper.mc.ti.com> a722756@roper.mc.ti.com (W. Donald Rolph) writes:
>
>The proposed method of either Han or myself will couple the navier-stokes
>(actually the energy equation is more general I think - comments Han), and the 
>dynamic equations of the solid.  It was exactly the elasticity of the fluid 
>acting against the dynamic behavior of the soldi which Olsen writes about.
>-- 
>
>Regards.
> 
>Don Rolph  a722756@pan.mc.ti.com WD3 MS10-13 (508)-699-1263

If my memory serves me correctly (and it often doesn't), the 1985 
Olsen-Bathe paper considers a linear solid and a stationary, inviscid 
fluid. The governing equation of the fluid is then the wave equation, 
while the solid is described by Navier's elastodynamics equations. 
Such problems arise in the study of structural acoustics, in which one 
is interested in the scattering and radiation of pressure waves from 
an elastic body. However, this problem is not really one of aeroelasticity 
(about which Olivier asked), since the fluid domain is not affected by 
solid deformations. 

Don is right is saying that the general nonlinear equations of both media 
can be coupled, and the problem solved (in principle) straightforwardly. 
In fact, we are developing a variationally-based FEM approach to the 
solution of finite elasticty--viscous flow interaction problems. I hope 
to have a paper ready by Spring; drop me a line if you're interested in 
receiving a copy.

Cheers,
Omar

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Omar Ghattas                                 ghattas@cmu.edu
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