dynamic wind analysis

[bothul]

Hello, I am trying to analyse a cable structure. They are affected very much by the wind. I would like to simulate a dynamic wind load. If anyone has documentation about wind action and method of introducing dynamic wind load in FEM software, i would appreciate it.Thanks in advance!

 

[btrueblood]

Distributed force, acting in direction of wind, with periodic (sinusoidal) time variation at roughly:

freq (Hz) = 0.2 V/d;

Where V is flow speed, d is wire diameter.

Google Strouhal number, or see

http://en.wikipedia.org/wiki/Strouhal_number

for starters.

 

[jhardy1]

@btrueblood:

The oscillations which occur with a frequency of 0.2xV/d actually occur transverse to the wind direction, not along the wind direction, and can generte cross-wind vibrations. (Do a Google search for "vortex street".)

There are also along-wind dynamic effects due to buffeting etc, but this effect is a function of wind turbulence, etc, and is not particularly associated with the Strouhal Number.

(To the OP - this is a very complex subject, for which I am not competent to provide a useful response!)

 

[bothul]

Thank you for the replies

 

[btrueblood]

jhardy,

Well, to be pedantic, the center of pressure oscillates about the aft face of the body, thru an angle that is dependent on the Reynolds number. The drag force is higher than the lateral force, with a sinusoidal term superimposed that is roughly equivalent to the lateral forces. The OP asked "how to model" the force, and a simple answer is the one given - it will give a sinusoid input to a model that will cause it to vibrate at about the right frequency. A more complex model would add the lateral oscillation at a 90 degree phase shift relative to drag forces, and an even more complex model would attempt to actually predict what the magnitudes of those forces are, something that gets fuzzy quickly.

 

[davidosterberg]

Wind engineering is a complex subject. A good reference is the book Wind loading of structures by Holmes.

Regards
David

http://www.durotec.se

 

[utkk]

do you have ASME Code.? Wind force is in section design of force.

Rubber engineering

 

[IDS]

There has been a recent (within the past 2 years or so) issue of the ICE Buildings and Structures Journal covering this issue which would be worth reading. It is a complex problem, with much recent research, so I doubt if a text book would cover it adequately (but I haven't seen the one recommended, so it may do).

If you have any contacts in any of the big suppliers of cable stays for bridges you could also try picking their brains.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/