Pseudo random interpretation of double hinged ALP under aerodynamic loading

Abstract

Summary Wind produces three different types of effects on structure: static, dynamic and aerodynamic. When the structure deflects in response to wind load then the dynamic and aerodynamic effects should be analysed. The basic mode of an articulated tower is the motion characterized by rigid body sway compliant with a relatively high natural period. The higher modes of oscillation have smaller periods, and their influence is rather insignificant in the overall platform motion. Since the wind velocity spectrum of the fluctuating component has lower frequency energy content, the wind induced vibration of an articulated tower may be significant. The wind induced overturning moment increases linearly with the height of the structure, and thus, as these structures are built in deep and deeper water, the effects of wind drag then become increasingly significant in design. To approach towards the realistic environment, the dynamic analysis of double-hinged articulated tower under the action of wind, waves and current has been carried out. The wave forces with the interaction of current have been computed by the application of Stokes’ fifth order nonlinear wave theory. The sea state with respect to wind speed of 25 m/s (Hs = 18.03 m, Tz = 13.59 s) has been considered and standard wind velocity spectrum Ahsan Kareem has been used for the dynamic analysis. The Pierson Moskowitz sea surface elevation spectrum has been used to model the random wave loads. The responses have been obtained under multi-point wind field. The study shows that energy content under combined action of wave and wind forces is more than energy derived under wave alone forces. Results also show that upper hinge is more dynamically active than lower hinge due to wind forces. PSDF shows that wind forces do not practically affect the bending moment, which is predominantly governed by the second mode of frequency; however, the other response parameters like deck displacement, hinge rotation and hinge shear were affected in significant manner under the action of wind forces.