Von Karman vortex shedding strakes on stacks

[pacamengineers]

Does anyone have a source of the article : Mahajan, Kanti H., “Tall Stack Design Simplified,” Hydrocarbon Processing, p. 217, September 1975 on stack design or some other treatise on stack frequency response and damping

 

[plasgears]

I once worked with a CE to develop supports based on the selected modes of vibration. Karman vortex frequency is a function of stack size and air velocity. The stack will have a set of natural frequencies as a beam starting with no supports above (cantilever), to 1 set of guys, 2 sets of guys, etc. Knowing what these natural frequencies are, the guy scheme can be selected so that the natural frequency is comfortably above the forcing frequency from Karman vortices at the worst velocity case.

Choose the guy scheme, and add 10% high spiral fins to further dampen the vibes.

 

[pacamengineers]

The stack in question is an unsupported cantilever type but fitted with staggered vertical strakes as per API 560 Clause 9.5.4 (1) rather than spiral (helical) spoilers Clause 9.5.4 (2) but there seems to still be an unexplained driving frequency that causes a larger amplitude in the sway than was expected. The stack is mass damped to remove natural frequency response problems.

 

[aybee]

did you ever get a source for this Paper?

Aybee