Adding weight inside the tube will do nothing for vortex shedding. The
mass loading will change the mechanical resonance properties, perhaps
avoiding the natural frequencies excited by the vortex shedding. A rope
adds mass and an energy absorbent quality (inelastic collision sort of
situation with frictional losses.)
Attacking the vortex shedding directly is a different approach. One
approach is to put a spiral wrap of UV resistant cordage on the outside
of the element. (Fishing department at Walmart has UV resistant black
cordage in various diameters.) Interior measures last much better than
exterior ones. Dampening the effects of vortex shedding can be as good
as eliminating the vortex shedding itself.
See also...
https://en.wikipedia.org/wiki/Vortex_shedding#Mitigation_of_vortex_shedding_effects
http://www.spartaengineering.com/vortex-shedding-and-tall-structures/
Note the picture of a tall chimney at the first of the above URLs. It
shows the spiral wrap solution clearly.
The cause and effect are the same for a vertical or horizontal cylinder
(element.)
I'm just guessing at how cable inside an element dampens oscillations
but I put my money on friction between the cable and the ID of the
tubing in addition to mass loading that lowers the frequency of the
mechanical resonance of the element, perhaps moving the resonant
frequency of the mass loaded element away from the natural frequency of
the vortex shedding.
Any mechanical engineer vortex shedding experts out there care to
comment. I'm just guessing from a physicist point of view with what I
hope makes some sense.
Patrick
On 6/22/2017 8:10 AM, Jim Thomson wrote:
You need a bit of weight to kill the vortex shedding.
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