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Re: Vortex Shedding

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Ghassem:

The Wind Load Commentary to the National Building Code of Canada 1995 has a
couple of pages on Vortex Shedding. A couple of highlights:

"Slender free standing cylindrical structures ......... should be designed
to resist the dynamic effect of vortex shedding. ........A structure may be
considered slender in this context if the ratio of height to diameter
exceeds 5."

"Slender structures with cross-sections other than circular may also give
rise to vortex shedding, but data are limited and other forms of across-wind
motion may develop if the wind speed, VH, is greater than about 7nD, where D
is the across-wind breadth. In such cases wind tunnel tests provide the most
satisfactory method of estimating the likely response."

The article includes calculations to determine the wind speed which will
cause vortex shedding at the natural frequency, n, of the structure. Plus
approximate methods to calculate a static equivalent to the dynamic effect
of vortex shedding. If you'd like me to fax you a copy of the two pages send
me an email offline.

Cheers,
John MacLean