huangyhg

resonance (vibration) of tall flare stacks
i am working on a wind assessment of tall flare stacks and i am trying to check the sensitivity of these structures to vortex vibration (resonance).
i am using a document entitled "a criterion for assessing wind induced crossflow vortex vibrations in wind sensitive structures" (by rw robinson and j hamilton) but i am having difficulties with calculating the amplitude of the vibration because the relation in the document contains errors.
the formula for the amplitude is
a/d=(3.82*cl*γ)/(1+0.19(2π*ks*(st^2)*cl)^355
obviously this 355 is not correct. is it 3.35 or 35.5?
has anybody used this document before? if yes can you tell me what is the expression for the amplitude?
any recommendations for other documents that deal with the same problem are more than welcomed.
thanks.

some time ago i had the experience of working out details of a tall chemical process column. my ce opposite no. was concerned that this column was exposed to high temp excursions and how to handle guy wire support. we agreed on the following:
- select the number of guy wire sets based on the mode and desired frequency. karman vortex formula predicted x cps, and we chose support nodes to far exceed this frequency. we had two levels of guy wires. the mode was fixed on the bottom, supported on two levels, and the shape of the deflected column was an s, free at top.
- allow the column to slide within a structural cage, which was guy wire supported on two levels. worked fine.
do you know for sure that it's not right? i ask, because that exponent seems to be repeated on two different equations on that page.
if it is wrong, you might try hunting up the references he gives.
to plasgears
how to retrofit the flare stack is not the problem – the problem is proving there is something wrong with it. the fact that it will vibrate due to vortex induced resonance is not sufficient proof because you have to verify that the order of magnitude of the vibration will cause problems (max stresses too high or fatigue failure)
to jstephen
at the end of the document there is an example – again in the example the reference the same formula, but when you actually try to verify the number, using 355 yields results of different order.

working backwards through the equation in table 4.2, i get the exponent as 3.35.

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