An Approximate Simple Computational Method to Determine Hydrodynamic Forces on Drag Dominated Offshore Structures

Offshore structures are subjected to highly dynamic, irregular external loads from the air, water and soil. One of the most important forces affecting design, construction, installation, and maintenance of such structures considerably is wave force. Accordingly, accurate calculation of the wave force acting on offshore structures is one of the first steps of design process to ensure structural safety of all components under different environmental conditions. Nevertheless, such calculations are not only difficult but also computationally expensive. The main reasons for such complexities are the probabilistic and randomness of sea waves as well as the dynamics of Fluid Structure Interaction (FSI) which make the assessment of wave loading on offshore structures a challenging procedure in offshore engineering practice. It is therefore the main objective of this research to present effective alternative approximation methods based on the Morison’s equation for determining wave loads acting on the structural components of the offshore supporting structures that are slender compared to the wave length (e.g. legs, braces, spokes and mooring lines). The comparison results show that the proposed method can be more efficient with time and also a reliable method in initial design of offshore platforms with acceptable results compared to the conventional approach.

Keywords:

Offshore structures , Initial design , Wave-induced drag loads , Wave penetration depth , Linearization of Morison’ s equation