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More on vortex shedding

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Watch out for the units in some of the equations.  I calculated natural
frequency of a uniform stack, using Refs 1, 3, and RISA 2D, as well as
reference 2.  Ref 2 calls for E to be in psf, and Weight to be in pounds
per vertical foot of the stack.  Correlation is fairly good if you use E in
psi, and weight in pounds per vertical inch of the stack.  Otherwise the
fundamental natural frequency differs by a factor of 35.

Likewise for the natural frequency for ovalling.  Ref 2 calls for thickness
of shell in ft; I believe inches should be used instead.

 If I'm wrong, will someone let me know?


> From: Fountain Conner <fconner(--nospam--at)>
> To: seaint(--nospam--at); rajendra(--nospam--at)
> Subject: Re: vortex shedding
> Date: Saturday, July 25, 1998 2:27 PM
> 1.  ASME STS-1-1992 (May be a later revision now) -- Steel Stacks.  You
> get from ASME 
> 1-800-843-2763.  You will probably have to call ASME after you get
> because there are some  points which are not clear.
> 2.  I just got a reference which has a chapter on self supporting stacks.

> "Tubular Steel Structures, Theory and Design" by M.S. Troitsky, D.Sc.,
> Published by Lincoln Arc Welding Foundation -- I ordered mine from Brown
> Book Shop in Houston, 1-800-423-1825.  There's lots of material in this
> pages, plus 2 1/2 pages of references), and it looks pretty good.  
> 3.  I also have a copy from somewhere (I don't remember) entitled,
> 26, Chimneys", by Max Zar and Shih-Lung Chu of Sargent & Lundy.  
> About spoilers -- They increase wind forces/moments, because they add a
> large area near the top.  And stack constructors hate them (especially if
> they have to be stainless steel), because they are very costly, both in
> material and fabrication.  A possible alternate is to use a shroud to
> control the natural frequency of the stack to stay out of the resonant
> range.  
> There are also mechanical damping systems available (One supplier, Warren
> Engineering, Inc., Atlanta, Ga., 404-843-8333, FAX 404-843-0089). 
> pretty pricey, but sometimes there's no other way, especially on an
> existing stack.
> Vortex shedding forces are not impossibly large, but it's easy to get
> a resonant condition with much lower wind velocities than you would
> normally use for design.
> BTW, I'm not a stack designer.  I get just enough stack work to keep me
> challenged.  And I apologize for being long-winded.
> Fountain E. Conner, P.E.
> Gulf Breeze, Fl. 32561
> ----------
> > From: P.Rajendran <rajendra(--nospam--at)>
> > To: seaint(--nospam--at)
> > Subject: Re: vortex shedding
> > Date: Saturday, July 25, 1998 8:09 AM
> > 
> > I have been trying find some reference material for designing spoilers
> > on tall stacks.  Your participation in discussing "vortex shedding"
> > makes me believe that you may have some leads to the information I am
> > seeking.  If you have such information, please respond to my email
> > address which is: rajendra(--nospam--at)
> > 
> > Thanks
> > 
> > Rajendran