DYNAMIC ANALYSIS OF OFFSHORE STRUCTURES

Abstract

The objective of this thesis is to carry out the dynamic analysis of Steel jacket type offshore structures when subjected to deterministic sea waves, A review of Literature on Offshore Structures with regard to their types, location, load-ings and methods of analysis has been made Formulation of an algorithm employing an economiser technique and its conversion in computer code 'OFFDYN' is carried out. Elastic plane frame idealization of a fixed base steel jacket type structure has been considered. Discretization of the structure into master and slave nodes and subsequent condensation at a few master d.o.f., so as to attain gross reduction in size of the problem is intended. Morison' s equation, utilizing Airy' s Linear wave theory has been used for computation of water particle velocity and acceleration and hence wave forces at condensed master d.o.f. have been achieved. Wave forces are calculated using: (i) Linearised drag forces (ii) Nonlinear drag forces An eigenvalue study, in order to decide the time step length and for evaluation of Rayleigh's damping coefficients has also been carried out. Dynamic analysis is based on Hilber's Step by step integration scheme which is used due to its inherent advantages. Lastly, the conclusions with respect to the dynamic analysis of offshore towers subjected to wabe forces are presented.