Q. Wind Induced Vibration of Vertical Vessels?

Vertical vessels having a height-to-diameter ratio (h/D) (does not include insulation thickness but does include skirt height) greater than 15, may vibrate due to vortex-excited resonance, unless sufficient external appurtenances or wind spoilers are present to disrupt the airflow over the vessel, thereby preventing the generation of the vortices with the undesirable predominant frequency. (In general, the addition of spoilers is typically more feasible than changing the natural frequency of the vessel, or by providing supplementary damping). In case of cylindrical pressure vessels that have been determined to be candidates for wind-induced vibration, it has been found that spoilers are only required for the top third of the vessel height, and that normal attachments in this region, such as ladders and piping, will be effective as spoilers, provided the maximum circumferential distance between them is 108^o (30% of the vessel circumference).