Development and optimization of a Shape Memory Alloy wave energy dissipation system for offshore applications.

摘要

The beaches along the coastlines are invaluable national assets that are continually being assaulted by ocean waves. In order to reduce the destructive forces of ocean waves, coastal engineers have looked into various ways of damping the waves incident on the shorelines. Until now, the focus has been on increasing damping and absorption by using both hard stabilization methods, such as breakwaters, and hydrodynamic methods, such as bubble screens. A relatively new concept is the "point-absorber" technique, where wave energy is both focused on a resonant heaving body via diffraction, and dissipated by some internal mechanism. This research project focuses on increasing the structural damping of wave energy point absorbers by using the Shape Memory Alloy (SMA), Nickel Titanium (Nitinol). Nitinol is naturally suited to the task of damping ocean waves because it is corrosion resistant, can absorb energy at low frequencies, and has temperature sensitive material properties that can be engineered to account for seasonal variations in wave height. The research project consists of three phases. Those are (a) an analysis of the hydrodynamics of wave absorbers, (b) an analysis of the structural mechanics of SMA dampers, and (c) a coupled experiment and validation of the effectiveness of the method. The hydrodynamic analysis is designed to provide the forcing function required in designing the damper. The analysis of the SMA damper focuses on understanding the benefits and limitations of the material in order to define a design space, and ultimately develop a damper for evaluation. This careful analysis of the material properties leads to the development of tapered-damper design. Tapered-dampers leverage the difference between super-elastic and failure stresses, enabling the SMA to attenuate waves having wide ranges of amplitudes and periods. Finally, an experiment is conducted to demonstrate the performance of the system in a coupled environment. Executing the experiment requires the development of both scaling laws and a low-loss heave system. The results of the experiment demonstrate that SMA wires can be used to attenuate the aptitudes of incident waves.