Absorbing energy using coupled resonances

• Main Author: Crowley, Sarah
• Published: University of Bristol 2013
• Subjects: 532
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629003

This thesis is concerned with the small amplitude response of coupled resonant systems which are subject to forcing. In particular, we consider systems consisting of a primary body with a fixed secondary, internal or external, component that each exhibit resonance. Motivated by the potential to exploit the coupled resonances we consider the effect of tuning the secondary component on the displacement or energy absorption characteristics of the system. Problems are studied in which the entire system is submerged in fluid of finite depth or in which the secondary system consists of a fluid-filled tank, fitted with some mechanism to provide damping, or both, all under the assumptions of linear water wave theory. In Chapter 1 a condition is derived which applies to submerged vertical slatted barriers and its adequacy tested in five model problems. This condition is then implemented in Chapter 2, in which sloshing in a horizontally-forced fluid-filled rectangular tank fitted with multiple screens is analysed. We proceed by fixing the tank to an externally-forced sprung mass and tuning the tank to minimise response amplitudes across all frequencies. The remainder of this thesis is concerned with the extraction of energy from ocean waves by coupled resonant absorbers. Chapter 3 gives a brief introduction and describes the existing power absorption theory for devices constrained to a single mode of motion. A submerged horizontal cylindrical wave energy converter (WEC) is used to illustrate the application of this theory. This analysis is extended to devices of the same geometry containing an internal power take-off system; in Chapter 4 the device contains a system of pendulums and in Chapters 5 and 6 a water tank. Chapter 7 continues this theme, now for a vertical cylindrical WEC containing an internal water tank. In each example, the focus is on determining the best device configuration to obtain a broad-banded response.