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rc2v07 July 8, 2008 15:33

Orbital velocity Inlet expressions

Im trying to simulate a wave in water on CFX, I have the following expressions for the X and Z velocity components:

U = w*a*Exp(k*z)*sin(wt-kz) W = w*a*Exp(k*z)*sin(wt-kz)

w = ang. freq.(rads/s) a = apm.(m) t = time(s) k = wave no.

Im not sure as to how to specify the x and z distances in CEL expressions, do I create a local co-ord frame in Pre at the inlet boundary? Also the time, do I use 't' or 'atstep' or neither.

The domain is a 2D rectangle with a foil at the centre, it is 3 (long) by 1.5 (wide) meters with openings at top and bottom and symmetry on front and back.

Currently my results with both t and atstep with and without creating a co-ord frame show almost parallel flow to the inlet and vertical flow thoughout the domain!

Thanks for the help!

MAB July 11, 2008 07:14

Re: Orbital velocity Inlet expressions
are you working in deep water scenario. Your equations for velocity components are wrong. it should be U= w*a*exp(k*z)*sin(w*t-k*x) and W=w*a*exp(k*z)*sin(w*t-k*x)

this expression is only true for deep water.

rc2v07 July 11, 2008 07:45

Re: Orbital velocity Inlet expressions
yeah sorry mis-typed them the second z is x. but your eqtns are both the same the W components should be Cos. yeah Im doing deep water alright.

MAB July 11, 2008 08:51

Re: Orbital velocity Inlet expressions
yes it should be cos. just leave it as x , z and time as t , the velocities should work.

rc2v07 July 11, 2008 10:43

Re: Orbital velocity Inlet expressions
yeah but where are x and z measured from?

MAB July 11, 2008 11:47

Re: Orbital velocity Inlet expressions
examine your geometry file in design modeller. you can note where the origin of these coordinate was. for example if you have created your wave tank with the left bottom corner at the origin (0,0,0) than thats where these coordinates are measured from. i hope it helps.

rc2v07 July 11, 2008 14:21

Re: Orbital velocity Inlet expressions
yeah great thanks!

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