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# Re: More on vortex shedding

• To: seaint(--nospam--at)seaint.org
• Subject: Re: More on vortex shedding
• From: Juan Enrique Justo <jjusto(--nospam--at)copime.org.ar>
• Date: Sat, 25 Jul 1998 22:43:09 -0700

```jjusto wrote:

Important is not only the natural frecuency of the column/tower/stack but
the way to evaluate the dynamic action of von karman vortex.
As I mentioned in my very first post, some literature, and aparently some
codes too, considers the wind acting only on the top third of the stack,
while for example, the argentinian code (that for the dynamic analisis is
just a recomendation) considers the full height of the structure.
Does for example UBC, or the canadian or new zelander code say something
Thanks

Fountain Conner wrote:
>
> BE CAREFUL WITH REFERENCE 2, BELOW!!!
>
> 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?
>
> Thanx,
> Fountain
>
> ----------
> > From: Fountain Conner <fconner(--nospam--at)gulf.net>
> > To: seaint(--nospam--at)seaint.org; rajendra(--nospam--at)edumaster.net
> > 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
> can
> > get from ASME
> > 1-800-843-2763.  You will probably have to call ASME after you get
> started,
> > 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
> (50
> > 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,
> "Section
> > 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).
> They're
> > 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
> into
> > 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)edumaster.net>
> > > To: seaint(--nospam--at)seaint.org
> > > 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)edumaster.net.
> > >
> > > Thanks
> > >
> > > Rajendran
> >
>

```