Random lock-in intervals for tubular structural elements subject to simulated natural wind

The paper reports on wind tunnel experiments with an elastically suspended circular cylinder vibrating under the excitation of natural wind of high turbulence degree. The natural wind turbulence was simulated bysuperposing the low frequency part of the natural wind turbulence on the background high frequency turbulence of thewind tunnel flow. This was done by controlling the propeller rotation speed according to an artificially generated lowfrequency speed sample function drawn from a suitable random process model.The experiment provided statistical data on the intermittend random occurrence and size of strong lock-in vibrationsin resonanse with the vortex shedding excitation. The purpose of the experiment was to obtain data support forthe formulation of a sufficiently detailed stochastic model to allow computersimulation of reasonably realistic fatigue damage accumulation at "hot spots" of tubular structural elements subject to thenatural wind. The engineering relevance of the investigation is supported by comparing with the unrealistic highlyconservative rules of wind induced fatique commonly given in codes of practice. The stochastic lock-in model aswell as the related fatigue calculation procedure is reported in the paper.