First passage time as an analysis tool in experimental wind engineering

The first passage time is the time required for a system to evolve from an initial configuration to a certain target state. This concept is of high interest for the study of transient regimes which are widely represented in wind engineering. Although the concept has been widely studied from theoretical and numerical standpoints, there are very few practical or experimental applications where the results are seen from this angle. This work is a first attempt at bringing first passage times of stochastic systems into wind engineering by suggesting the use of a first passage time map as a standard analysis tool in experimental wind engineering. The wind tunnel data related to the spinning dynamics of a rotating square cylinder in turbulent flow is processed under the frame suggested by a theoretical model for a simple linear oscillator. A specific algorithm is developed for the determination of the average first passage time as a function of initial and target conditions based on the experimental measurements. It is shown that the simple theoretical model is able to capture the different regimes of the experimental setup, so that an equivalent linear Mathieu oscillator, presenting the same evolution of energy, from a first passage time point of view, was identified. This experimental investigation provides a first link between an analytical but simplified result and a more complex reality.