Safety analysis on a vibrating prismatic body: A data-mining approach

In this paper, the flow-induced oscillation of a prismatic body, viz., a square section cylinder (test cylinder) under interference conditions is analysed considering it as representing a typical building structure. The analysis is carried out using a data-mining tool called 'Decision Tree' mainly in view of assessing the safety of the structure (test cylinder) with respect to the vibratory amplitude. To achieve this aim, wind tunnel studies have been conducted on the vibratory response of the test cylinder when it is vibrating in the vicinity of another square cylinder (interfering cylinder) which is placed at various locations relative to the test cylinder. The amplitude data thus obtained is suitably classified to carry out the safety analysis. All the data gathered pertains to at a single value of reduced velocity (10.0). Experiments have been carried out for various size ratios (b/B) of the test cylinder (upstream structure) and the interfering cylinder with values of 0.5, 1.0, 1.5 and 2.0. The results indicate that, for certain combinations of the parameters - relative position (L/B, T/B) and size ratio (b/B), the upstream structure could vibrate with high amplitudes making the structural environment 'critical' (unsafe). In practical situations (such as in the case of tall buildings), the critical combinations of these parameters could be identified and eliminated for ensuring structural safety. Parametric combinations ensuring safe structural condition are also identified. Decision Tree also brings out the order of importance of various parameters influencing the interference excitation of the structure (test cylinder); L/B is shown to be the most influencing parameter. The results also show that, for L/B > 3.0, there is a higher possibility for the structure to become unsafe when compared to the conditions at L/B ≤ 3.0.