KenMcWatters
EF1
In the interest of weather analysis, I have attached an engineering estimation of the wind speed required to blow over an empty oil drum. As an engineer, I have actually wanted to make such an analysis for years since I saw this happen personally in a thunderstorm downburst event. Where I worked then in Houston, they used empty 55 gallon steel oil drums as waste cans in our parking lot. One day we had a wet downburst (including small hail) so intense that I couldn't see more than 20 feet outside the windows. When it was over, all the empty oil drums were laying on their sides and rolled around the parking lot. At the time I wondered if there was a way to estimate the wind speed based on an engineering analysis of air flow around the cylinder shape of these drums.
Several years later, I took my PE (Professional Engineer) exam and in studying for it, I found a sample problem that made a similar analysis. Based on this problem, I made calculations to estimate the wind speed during the downburst. As seen in the attached calculations, my estimate of the minimum horizontal wind speed during this downburst event is 76 mph.
I would be interested to get any feedback on the accuracy of this method from others who pursue such analysis, such as Tim Marshall and others in his field. In particular, I'd like to know their opinions on how much inaccuracy results from the fact that my analysis is based on dry air. The actual downburst was wet with copious rain and embedded small hail. At the very least this should effectively increase the density of the "air" in my calculations, which would then lower the estimated wind speed. Is there a way to estimate the effective density of a wet downburst, or for that matter, air full of debris for a tornadic event? Please share your thoughts and comments.
Ken McWatters, P.E.
Tulsa, OK
Several years later, I took my PE (Professional Engineer) exam and in studying for it, I found a sample problem that made a similar analysis. Based on this problem, I made calculations to estimate the wind speed during the downburst. As seen in the attached calculations, my estimate of the minimum horizontal wind speed during this downburst event is 76 mph.
I would be interested to get any feedback on the accuracy of this method from others who pursue such analysis, such as Tim Marshall and others in his field. In particular, I'd like to know their opinions on how much inaccuracy results from the fact that my analysis is based on dry air. The actual downburst was wet with copious rain and embedded small hail. At the very least this should effectively increase the density of the "air" in my calculations, which would then lower the estimated wind speed. Is there a way to estimate the effective density of a wet downburst, or for that matter, air full of debris for a tornadic event? Please share your thoughts and comments.
Ken McWatters, P.E.
Tulsa, OK
