Hydrodynamic Performance of Submerged Tandem Breakwaters and Integrated Hybrid Floating Structures

Abstract

In the present study, the gravity wave interaction with submerged tandem breakwater of different structural configurations and integrated hybrid Floating structures are investigated based on the small-amplitude wave theory. The boundary value problem is analysed in two- dimension using Multi-Domain Boundary Element Method (MDBEM) considering the linearized wave theory in finite water depth. The wave transformation characteristics, wave forces and wave energy dissipation are analysed with and without the presence as reef structure in front of the primary submerged breakwater. The comparative study is performed for the submerged tandem breakwaters of various shapes (trapezoidal, triangular, rectangular, and thin-walled) and types (rubble mound, permeable, impermeable) that are designed to function together as a tandem breakwater. The effect of varying angle of incidence, relative submergence depth, and relative gap between the reef structure and primary breakwater on wave induced force, wave reflection, transmission and energy dissipation characteristics are derived for the suggested submerged breakwater and tandem breakwater models. In case of floating structures, the hydrodynamic characteristics of Fixed Floating Structure (FFS) of various configurations such as Rectangular Fixed Floating Structures (RFFS) and Trapezoidal Fixed Floating Structures (TFFS) coupled with submerged breakwaters of two different shapes namely, rectangular breakwater (RBW) and trapezoidal breakwater (TBW) are investigated for the variation in physical parameters such as a change in structural parameters of the submerged breakwater (shape, relative submergence depth, relative crest width, and structural porosity), structural parameters of FFS (shape and structural width), wave parameter (angle of incidence) and relative spacing between the FFS and submerged breakwater. Furthermore, three typical Submerged Floating Tunnel (SFT) cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of submerged rubble mound breakwater (SRMB) under similar operating conditions are investigated as comparative study to investigate the influence of SFT shape on hydrodynamic performance. Further, in the case of Wave Energy Converter (WEC) integrated into a Pile-Restrained rectangular Floating Breakwater (PRFB) in presence of a partially reflecting vertical seawall is analysed for scattering and radiation problems under a framework of small amplitude linear wave theory using the Boundary Element Method (BEM). The linear power take-off (PTO) damping is employed to calculate the absorbed power, while the rectangular floating breakwater is designed to heave with pile restrained in position. In addition, on assuming only iv a small amount of sloshing within the tank of the hybrid floating breakwater (within the application scope of linear potential wave theory), the WEC capabilities and the hydrodynamic coefficients (wave reflection and transmission coefficients) were estimated for a certain range of excitation frequencies with the help of numerical and experimental investigations. The study on the submerged tandem breakwater structure and floating structures illustrates that the presence of the reef like structure decreases aids in lowering the wave stresses inflicted on the primary breakwaters and aids in optimum wave transformations. On the other hand, studies on WEC integrated with structures can assist the designer to determine the appropriate degrees of efficiency of the WEC device without sacrificing the hydrodynamic performance by fine- tuning the system's geometrical parameters.