Chapter 5 - Environmental Loads, Motions, and Mooring Systems

Abstract

As floating solar generating stations become larger and are located in more open bodies of water subject to extreme weather conditions, designing for survival becomes ever more challenging. This chapter commences with an overview of the physical properties of gravity water waves as found in oceans, seas, lakes, and reservoirs which result from wind blowing over the water surface. The next section on wave generation provides an appreciation of the height of waves which the floating solar array has to withstand as a function of wind speed, fetch distance, and duration. Wave spectra are introduced as a standard method of describing the characteristics of waves along with the fact that waves can travel very large distances in oceans arriving at a given location from different directions. Wave characteristics are modified as they travel from deep to shallow water through the process of shoaling and alter direction due to refraction. The net movement of water due to currents modifies the steepness of the waves either increasing or decreasing it depending on the relative direction of travel. The largest waves can be predicted using extreme value analysis for different return periods. A knowledge of the wave characteristics and the hydrodynamic response of the floating system enables an estimation of the loads on the structure. Wave loads due to both diffraction and drag are characterized. As well as the global loads on the structure localized very short duration high-impact loads can occur particularly on large flat surfaces due to wave slam.