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Re: Wind tower design

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Kevin,
The following are additional references for Vortex Shedding.
1. DNV Classification Notes No. 30.5, Environmental Conditions and Environmental Loads, March 2000              
2.  A Criterion for Assessing Wind Induced Crossflow Vortex Vibrations in Wind Sensitive Structures,     Health and Safety Executive,  Offshore Technology Report, OTH 92 379
regards
Ashraf

 
On 20/11/2007, Kevin Below <kbofoz(--nospam--at)gmail.com> wrote:
Davenport was the wind tunnel expert on the CN Tower project.  I worked on that tower in 1975 and I visited his wind tunnel lab.  We did some research and testing on the tower.  They will almost certainly be consulted on the current project, once we get past the initial stage.

Kevin


On Nov 19, 2007 1:51 PM, Daryl Richardson <h.d.richardson(--nospam--at)shaw.ca> wrote:
Harold,
 
        Actually, to add to what you've written, vortex shedding may become a problem whenever the frequency of vortices shed (a function of the tower diameter and wind speed) matches the natural frequency of the tower.  This will generally occur for one wind speed; but that wind speed could very easily be within the normal operational range of wind speeds.  Vortex shedding, which produces dynamic forces perpendicular to the wind direction, should be considered an extreme wind effect itself; it does not need to coincide with the extreme effect of the wind forces parallel to the wind direction.
 
        There are two (make that three if you wish to consider two different sources for the same information) sources of information on vortex shedding that I am aware of (and probably several others that I am not).  There are
 
1.)  The National Building Code of Canada, Structural Commentaries for any of the past several editions.
This same wind loading procedure are also contained in the Vibration and Shock Handbook (or maybe it's the Shock and Vibration Handbook) of which I do not have a copy.  The name Davenport is associated with both of these publications.
 
2.)  ASME STS-1-2000, Steel Stacks.  There may now be a later edition for this.  This publication has a detailed technical discussion on damping.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Monday, November 19, 2007 10:17 AM
Subject: RE: Wind tower design

 
I doubt that you will find any sort of code or design guide on this topic.  I would suggest that a wind tunnel study be conducted especially if this is for operational wind load characteristics.  If this is for extreme wind effects, I would think that the dominate issue will be the vortex shedding on the mast. 

Regards,
Harold Sprague


Date: Fri, 16 Nov 2007 22:02:19 -0500
From: kbofoz(--nospam--at)gmail.com
To: seaint(--nospam--at)seaint.org
Subject: Wind tower design

Has anybody done any wind tower design work ?  I am doing some preliminary work on a concrete tower design, and I am thinking about the dynamic behaviour
and the effect of the passage of the blade when it passes in front of the tower.  Does anyone have any information or ideas on this ?

The Germans and the Japanese have actually built some concrete towers already.  Apparently steel towers are at about their height limit now, and the way to greater efficiency and bigger turbines leads to higher towers, which will probably be in concrete.




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