Abstracto

BEHAVIOUR OF DOUBLE PENDULUM LOADING PLATFORM UNDER OCEAN CURRENT

Moazzam Aslam, Nazrul Islam, Mohd Moonis Zaheer, Mehtab Alam

Articulated loading platform (ALP) is one of the promising compliant offshore structure and economically attractive for deep water conditions because of their lessened structural weight in comparison to conventional platform. The structure does not resist any force in bending due to wind, waves and currents rather forces are resisted by a large buoyancy force. In this paper, dynamic analysis of the tower under regular waves has been carried out with current forces. The Lagrangian approach has been applied for the derivation of nonlinear equations. The effects related to nonlinearity due to variable submergence, buoyancy, added mass, instantaneous position of the tower and relative-velocity squared drag force are considered in the analysis. NewMark’s-β integration scheme has been used for the solution of equation of motion in time domain. Modified Morison equation is used to model the fluid forces as these equations account for non-linearities associated with vortex shedding effects accurately in comparison to standard Morison equation. The Study has been carried out to compare the response of double hinged articulated tower under regular waves using Airy’s wave theory evaluated with Chakrabarti’s modification and that obtained by using Stokes’ fifth order nonlinear wave theory in the presence of ocean current. Stokes fifth order non-linear theory agrees closely in deep and intermediate water and it is found that for higher waves the difference in the values of responses obtained by Airy’s and Stokes’ are lesser while the difference is significantly higher for smaller waves. It is found that the deck displacement response as well as hinge rotation and hinge shear obtained using Stokes’ theory are lesser than that obtained using the Airy’s theory.