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Defining convergent center-oriented gravity field! please Help me

Hi everybody,
any one know how can I define a convergent (center-oriented) gravity field in OF? I have a sphere that have a convergent gravity field.

Thank you

what is "convergent gravity field"?

Quote:

Originally Posted by nimasam (Post 374084)

what is "convergent gravity field"?

Hi Nima,

Assume we want to solve convection heat transfer in a spherical body that it has a gravity field. for example the earth, the earth gravity vectors are perpendicular to the surface and they are intersecting each other at the center of sphere(earth- a center-oriented field).

Do you know how can I define such gravity field that varies with radius of sphere?

Thank you

it is possible with some pieces of coding:
i have an idea, instead of using a dimensionVector "g" , define a VolVectorField "g"
then, using funkySetField or setField utility to define a non-uniform "g"

Quote:

Originally Posted by nimasam (Post 374101)

thank you, Nima

I will test it.

Dear adam
it seems that your field is constant over time.
the simplest way is to look how the points are written in constant/points. then write a code with a programming language to create a non uniform distribution.

Quote:

Originally Posted by niaz (Post 374149)

hi Niaz,
just now I'm trying!!!!!!!!

thank you

Quote:

Originally Posted by niaz (Post 374149)

hi,
I try but I couldn't do it, I never did it before and I'm pretty a new user of OF.

can you give me more information about defining this field or an example?

thank you

Dear mahmoud
do you use blockmesh. if yes, send me your case to describe you

Quote:

Originally Posted by niaz (Post 374179)

Dear mahmoud
do you use blockmesh. if yes, send me your case to describe you

Dear Niaz,

No, I create it with Gambit (.msh) and I've used fluent3DMeshToFoam. have you any idea???

Thank you
Mostafa Mahmoudi

if you can please show it in the site for better understanding

Quote:

Originally Posted by niaz (Post 374210)

if you can please show it in the site for better understanding

its file size is about 19Mb. so I attach you a picture.
it is similar to the earth, it has a hot core and its surface is at ambient temperature. assume that the mantle of earth is a fluid. I want to solve the convection in mantle.

Thank you niaz
Mostafa Mahmoudi

Dear adam
if you set your center to (0 0 0) you can use your point for creating the fields.
you should define a vector field then use your points to calculate the vector.
gfield=g*(x/R*i+y/R*j+z/R*k)
R=(x2+y2+z2)^1/2

Quote:

Originally Posted by niaz (Post 374223)

thank you niaz for your replies,
Where should I define this field? I never do anything such it before. do I apply it to g file in constant directory? please explain it for me with more details. how can I calculating the vector by using points? at least I have 1 million points.
a new problem is that my gravity is varying with depth!!!! it means that the gravity at 0.5R isn't equal to gravity at R!!!! What should I do????

again thank you niaz

Greetings to all!

This isn't the first time I see someone asking about changing how gravity works in OpenFOAM. But after a quick search, I only found this to be relevant: http://www.cfd-online.com/Forums/ope...tml#post360969 post #23
That particular post has an implementation that might be a good source of information or at least idea on how to do what you're looking for.

Good luck!
Bruno

Quote:

Originally Posted by wyldckat (Post 374235)

Thank you wyldckat,

that was great, I got many ideas from it!
all of posts were about time dependence of gravity, but my problem is varying it with depth. it is independent of time. how can I apply it? of course, after defining my gravity pattern!!!! because I have problems in defining a center-oriented gravity field yet!

Dear adam
please look at your points in constant folder. your points are written in the form of (x y z).
you need to drive a unit vector which I discuss in last post.

Quote:

Originally Posted by niaz (Post 374289)

Dear adam
please look at your points in constant folder. your points are written in the form of (x y z).
you need to drive a unit vector which I discuss in last post.

hi niaz,

this is a portion of points file:

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  2.0.1                                 |

|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       vectorField;

    location    "constant/polyMesh";

    object      points;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //





43003

(

(-0.01847759065 0.007653668647 0)

(-0.01779042759 0.007552721936 0.005143644393)

(-0.01960468925 0.003159255628 0.002382281129)

(0.007679387991 -0.006329673946 -0.01734826296)

(0.01688526706 -0.01020474922 0.003278848865)

(-0.01834319804 0.002810689581 0.007458358384)

(-0.01584939034 0.006818828176 0.01011436642)

(-0.01460689264 0.01135644457 0.007594067049)

(-0.01592745136 0.01184211524 0.002465887277)

(-0.01597723029 0.01167792986 -0.002890340183)

(-0.01295887432 0.01522695429 -0.0004554552274)

(-0.01220887115 0.01514557064 0.004642752982)

(-0.01213174065 0.01012345964 0.01226117587)

(-0.01034525646 0.01425080084 0.009481051856)

(-0.01950515249 0.003259328014 -0.00298760896)

(-0.01772160189 0.007511999119 -0.005432742923)

(-0.01591634427 0.001975366477 0.01194855273)

(-0.01287687011 0.005423605639 0.01430981195)

(-0.01940682589 -0.001585931407 0.004567267278)

(-0.01994415536 -0.00137345384 -0.0005867635026)

(-0.01762641938 -0.001868149175 0.009263873847)

(-0.009026652487 0.01777835472 0.001565135287)

(-0.007606758639 0.01740382727 0.006264504705)

(-0.00769419341 0.01248809659 0.01359583875)

(-0.005493030072 0.01606271423 0.01057430056)

(-0.008817764601 0.008133616155 0.01600285336)

(-0.01261059616 0.0005972273644 0.01551180788)

(-0.009091657511 0.003292598427 0.01750715737)

(-0.01806927596 0.003124101276 -0.007983812223)

(-0.0190956556 -0.001197339263 -0.005824286735)

(-0.01901153672 -0.005970452141 0.001707387688)

(-0.01888850544 -0.005639026881 -0.003380197942)

(-0.01249883992 0.01462668367 -0.005462520073)

.

.

.

.

my problem is how can I do it? how can I establish a relation between g and this points?

thank you

hi dear adam
as my friend niaz told you before, you need a unit vector.
unit vector can be find like that:
(r-r0)/|r-r0|
which r is the position vector in each point and r0 is the position vector of your center,
as i before said i guess you should define a volVectorField instead of dimensionedVector (Burno post give you the idea how to implement it), then you can define easily such a function with funkySetFields or groovyBC

Quote:

Originally Posted by nimasam (Post 374316)

thank you Nima,

I hope that I can do it. I will be here soon!!!!! ;)