Abstract

Floating structures with many floating bodies and beam connectors are recently studied. Floating solar power system with grid layout of floating bodies is one of the examples. Since it has many floating bodies; it needs many computations in time domain dynamic analysis of wave-induced responses. This study proposed a less computing scheme to analyze the multi-body system more quickly. Proposed method analyzes wave forces for some parts of floating bodies instead of analyzing total bodies. It calculates wave forces at a line of floating bodies in x-direction and at a line of floating bodies in y-direction; and wave forces at another parts are estimated by combining the results at each line through bi-axial interpolation. An example multi-body system with beam connectors was analyzed to test the proposed numerical scheme. Wave forces at floating bodies were analyzed by HOBEM (Higher Order Boundary Element Method) and the connectors were analyzed using beam model by FEM (Finite Element Method). The floating body motions and connector stresses were calculated in regular and irregular waves at different heading angles. Their results and CPU time were compared with those by full body analysis.

Introduction

Floating solar power system is recently studied. In general; it has many floating bodies with connectors and mooring systems. Fig. 1 shows some example of the muti-body type structure. It is a floating solar power system in development by Korea Hydro & Nuclear Power Co. (KHNP) and Korea Research Institute of Ships & Ocean Engineering (KRISO). Since the muti-body system has many floating bodies; it needs many computation time to calculate wave forces; added masses and hydrodynamic dampings for full bodies. This study applied a faster method to calculate them at only a longitudinal & a transvers axis and interpolate the results. Wave forces; added mass and hydrodynamic damping can be obtained by integrating velocity potentials around floating bodies. This study applied HOBEM (Choi et al 2000; Hong et al 2005) to calculate velocity potentials. Total system equation can be obtained by combining the floating body parameters and equations of connector beams & mooring lines. This study applied FEM (Hong et al 2018; Kim et al 2018;2020; Kim et al 2020) to formulate the beam and mooring line equations. By solving the total system with time marching such as generalized Newmark method (Chung & Hulbert 1993); the beam stresses and mooring tensions were obtained. The structure as in Fig. 1 was analyzed as an example study by applying the interpolation method. The connector beam stresses and mooring tensions in regular & irregular waves with different heading angles were calculated and the results were compared with full body analysis.

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