atmospheric wind study
 

Hi all i am tryng to model an atmospheric wind over an off shore platform with a K-Epsilon model. when i run simpleFoam im getting a pointstack error as below :_


anyone has got any idea on whats the problem

noone has an asnwer to this??

atmospheric wind study
 

How are you specifying your boundary conditions?

Goncalo

currently my boundry condition is a cylindrical control volume. ive specified the top and the sides to be an inlet the bottom of the control volume which represent the sea and my geometry(offshore plateform) to be walls.

i am trying to run a simple kepsilon turbulence model.

i need help in setting up the case, i am trying to replicate a CFX run to validate results.

no offense but even in CFX:
-if its a cylinder and you have one wall and 2 inlets where shall the flow go too?
-the platform is @ the axis of the cylinder?

in cfx i specified it as an opening. i am trying to figure out how to replicate that. does the inletOutlet type the same as opening type in CFX?

Since i know that from CFX, you can cut the entire domain in half, depending on the wind dir. and specify one half as inlet and the other half as a inletOutlet (no backflow) with 0Pa rel.Pressure and the top as zeroGradient for the vel. and a desired pressure level for p.

If you really have an pressure/velocity-atmospheric profile you should think about using grovvybc to set everything depending on the height of your domain.

i am trying to setup this boundary condition on my domain but cant seem to figure out a way to define it.

this is a CEL script from CFX

AirDensity = 1 [atm] / (287.06 [J kg^-1 C^-1] *AirTemperature)
AirTemperature = 10[C]
ak=0.41[]
cmu=0.090000004[]
cmuhalf=cmu^0.5
dir=0[]
dira=dir*pi180
ed1=(ustarnew^3)/(ak*(zabs-zref))
eps=30.0 *z0
pi180=pi/180
speed =(ustarnew*loge((zabs-zref)/z0)/ak)*step((z-z0)/1[m])
te1=ustarnew^2)/cmuhalf
thetaa=dira+(pi/2.0)
u1=speed*cos(thetaa)
uref=2[m s^-1]
ustarnew=al*uref/loge((zuref-zref)/z0)
v1=-speed*sin(theetaa)
w1=0.0[ms^-1]
z0=0.001[m]
zabs=abs(z+1E-007[m])
zref=0[m]
zuref=10[m]

anyone knows how to do this??

Did you took a look at atmBoundaryLayerInletVelocity?

i just found out about its existance it openFoam1.7.1 i am installing it right now. will try it out

i am trying to use theatmBoundaryLayerInletEpsilon boundary condition but when i run potentialFoam it says its an invalid patch type.

DOMAIN
{
type atmBoundaryLayerInletEpsilon;
Ustar $Ustar;
z $zDirection;
z0 $z0;
value $internalField;
zGround $zGround;
}

this is how i've set my boundary condition.

when i run simpleFoam this is what i am getting

hello,

try to take a look in the tutorial of simpleWindFoam. you can find it in tutorials/incompresible/simpleWindFoam. there you have a case, which maybe close to your problem.

Best,
Ovidiu

I followed the tutorial but importing in myown mesh from icem. it runs perfectly without turbulence, but when i turn on turbulence it crashed out after 2 iterations as below : - please advice on the following issues

apreciate any help

thank yo

Hello,

Maybe the problem is in your mesh. Have you tried to run checkMesh and see if it find any problem in your mesh?

I am certainly not sure this is work. But I had similar problems and I tried to give low values for relaxation factors for p,U,k,epsilon in the
system/fvSchemes like :

relaxationFactors
{
p 0.01;
U 0.02;
k 0.02;
epsilon 0.02;
}

This is because the values of k and epsilon blows up very high that they exceed machine precision like 1.5e200 etc.. This very low relaxation factor will avoid such blow up.

You may need to run more than twice the number of iterations as the convergence will be very slow, but it worked for me.

Also you can give higher number for nOrthogonal Correctors like
SIMPLE
{
nNonOrthogonalCorrectors 5;
}

This will also increase computational time but hopefully will try to get better convergence.

Let me know if this helps..

Bala