It is shown in the HELP of PVElite, see below:
Consider Vortex Shedding
Select to perform vortex shedding calculations on tall, slender vertical vessels susceptible to wind-induced oscillations. This method is documented in the National Building Code of Canada and in texts on wind engineering. The software calculates fatigue stresses based on loads generated by wind vibration and the number of hours of safe operation remaining under vibration conditions. The software calculates the likelihood of this occurrence based on the research of Zorilla and Mahajan. If there is no possibility of wind vibration and you have this option selected, the software warns you that unrealistically high stresses will result and gives you the option to turn this calculation off.
For vertical vessels in which the height to diameter ration is less than 15, select the No Vortex Shedding for H/D <= 15 field to not perform vortex shedding calculations.