Hydro-response of grid-like floating structure subjected to a mono-directional flow

Abstract

Harvesting hydrokinetic energy from flowing water in rivers requires construction of special structures. The obstacles that need to be considered in designing such structures include shape, size constraints and challenges imposed by the river such as unsteady velocity and pressure. The aim of the current study is to investigate the hydraulic response of the grid-like floating structure subjected to mono-directional flow at different velocities. The study also includes the hydroinduced stress distribution pattern to determine the critical areas of stress. The floating structure considered in this study is a combination of a wedge on the front, which is rigidly connected to a grid-like platform supporting 12 hulls at the back. The grid-like platform has been designed to accommodate a set of 8 turbines with 2.3m blade radius each to generate electricity from the river. ANSYS was used in this study to simulate the hydro-responses of the floating structure at 6 different flow velocities. An experiment was carried out to validate the analysis. In this test, a scaled down floating structure model was subjected to running water at various flow velocities. The key parameters such as drag force, pressure, pressure gradient, and wall shear stress were plotted to show their variations to the change in velocity. Axial and shear stress distribution patterns and formation of vortex had also been observed. In general, both the drag force and maximum pressure increase quadratically with velocity. Formation of vortices is observed behind the wedge and each hull. These vortices become more apparent with the increase in velocity. Strips of large wall shear stress are observed at the wedge and on the first row hulls, where maximum von-Mises stress occurred at the wedge. These parts of the floating structure may require special attention in design. For practical convenience, a series of equations, in terms of various hydro responses useful for design purposes, has been determined as the main contribution of the study.