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-   -   Forces for a sloshing case (http://www.cfd-online.com/Forums/openfoam-solving/59368-forces-sloshing-case.html)

ogloth October 8, 2007 13:22

Dear all, I have the follow
 
Dear all,

I have the following problem which I would also like to present at the OpenFOAM conference in November:

A satellite tank is filled to about 50% and the liquid is all gathered at the bottom of the tank (spherical tank with a cylindrical section in the middle), although there is no acceleration acting on the liquid. At t=0s the system is accelerated downwards and hence the liquid will start to move upwards. At t=15s the acceleration stops and the whole system is left in a zero gravity condition again. I would like to extract the forces acting on the tank in order to compare them with actual flight data (Sloshsat FLEVO). Unfortunately I have no idea how to treat the pressure, since the pressure used in interFoam does not contain hydrostatic pressure, as far as I understood it. I have been scanning the forum forwards and backwards but haven't found anything. I'd be happy if someone could point me in the right direction.

Oliver

ogloth October 10, 2007 03:13

I guess my posts must be reall
 
I guess my posts must be really stupid, since they seem to never get answered. Well - I am fully aware that OpenFOAM is open-source and that all replies and support is voluntarily and that of course nobody has any right to his or her problems being answered. Still, I was hoping to get some support, especially since I am actually trying to validate OpenFOAM against some experimental data.

Anyway, I have implemented a dirty workaround: I simply take the highest point of liquid and set the hydrostatic pressure to zero at that level. All other cells (and boundary faces) get a hydrostatic pressure according to the y-difference to that highest cell. Obviously this will be wrong for isolated regions of liquid.

Somebody must have a similar problem I would assume!

Oliver

gschaider October 10, 2007 07:14

Hi Oliver! This might, or m
 
Hi Oliver!

This might, or might not help you. In Hrv's dev version there is an utility applications/utilities/postProcessing/stressField/interFoamPressure/ that calculates the static pressure from interFoam-results.

I just stumbled on it. I never tried it. I didn't have too close a look at it. You're on your own from here on, I'm afraid.

Bernhard

PS: Just get it with
svn checkout https://openfoam-extend.svn.sourceforge.net/svnroot/openfoam-extend/trunk/Core/O penFOAM-1.4.1-dev/applications/utilities/postProcessing/stressField/interFoamPre ssure/
It compiles with a standard-OpenFOAM-1.4.1-installation (just take care: the above URL usually gets mutilated by the MessageBoard-software)

ogloth October 10, 2007 07:45

Thanks a lot for the link! I h
 
Thanks a lot for the link! I have downloaded the sources and at a first glance it seems to work well. That was exactly what I was looking for; so far I have used a modified version of the liftDrag tool with the crude approximation, which I described above.

Thanks!!!
Oliver

hjasak October 10, 2007 07:54

Careful with the boundary cond
 
Careful with the boundary conditions on p - if you are getting trouble (i.e. pressure distriution that does not look right), the tool now allows you to set the pressure b.c.-s rather than the code trying to guess it.

Hrv

ogloth October 10, 2007 08:18

The pressure looks ok to me. H
 
The pressure looks ok to me. How does the tool guess the BCs? Basically that should be the same as those for pd - from my understanding at least ... Btw, how does it work? I assume you take the gravity and the velocity field and then you compute the pressure field that matches these, is this correct?

Another question: Do you recon it is possible to compute flow with a varying gravity field? By varying I mean spatially - a change in time I am already using in the simulation. I guess it could be done by modifying the ghf field in interFoam. This can be important for acceleration fields that are created by spinning.

Oliver

ogloth October 10, 2007 08:20

just found a flaw in my line o
 
just found a flaw in my line of thinking - BC for pressure should be a gradient in y-direction ...

girogirozakk October 22, 2007 20:12

> Another question: Do you rec
 
> Another question: Do you recon it is possible to compute flow with a varying gravity field?
> I guess it could be done by modifying the ghf field in interFoam. This can be important for acceleration fields that are created by spinning.

Hi,Oliver.
I tried that approach & code is opened at this URL.
http://members.jcom.home.ne.jp/issa_.../sloshing.html


May be , It's OK....I think(hope).
If I made mistakes, please teach me.


> compare them with actual flight data (Sloshsat FLEVO).

I want to try , too.
Where the URL I must check?
If no problem, please tell me.


thanks

Giro

paka October 22, 2007 22:15

I don't understand the followi
 
I don't understand the following sentence by Dr. Jasak:
"Careful with the boundary conditions on p - if you are getting trouble (i.e. pressure distriution that does not look right), the tool now allows you to set the pressure b.c.-s rather than the code trying to guess it."

I figured out the only way to "set" the b.c. for interFoamPressure is to define the "p" dictionary in 0 sec. time directory. Is it right?

I obtained results for defined "p" b.c. and for undefined "p" b.c. Both results look exactly the same. So how to define those b.c.?

Initially, somehow I missed that topic, so if you would like to help me with verifying my results using interFoamPressure tool please follow the following conversation:
http://www.cfd-online.com/OpenFOAM_D...tml?1192152325

Regards,
Krystian


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