Advanced oceanic harvesting systems for autonomous undersea sensors

Abstract

The technologies behind autonomous underwater sensory systems are continuously developing resulting in increasing capabilities and operating times. Power supply to these autonomous sensors is commonly facilitated via the use of primary alkaline cells, which causes limitations to operating periods. This study aimed to conduct a feasibility study into the application of small scale power generation to supplement power requirements for underwater autonomous sensory equipment. An assessment of the availability and potential of various forms of energy which may be harvested within the oceanic environment resulted in wave energy being the most suitable form of harvestable energy. With waves as the chosen energy source, two wave energy harvesting devices, a surface buoy energy converter and a heaving point absorber were modelled and developed. The surface buoy energy converter design aims to harvest energy from all six degrees of freedom induced from multidimensional dynamic conditions that exist on the surface of the ocean through the use of linear generators. The heaving point absorber is a sub-surface operating device which incorporates a ball screw mechanism to translate vertical displacement of the waves to rotary motion for utilisation of a rotary generator. Both devices require conversion of the generated power to a useable form for an underwater sensor. For each device an electrical system has been designed to ensure continuous power to the sensors. The status and performance of the devices can be monitored through the use of a data logger with remote communications. Manufacture of prototype devices was undertaken to allow laboratory testing. The devices were tested for watertightness, proof of concept and power generation. These tests successfully proved both concepts and allowed for recommendations into further design improvements. The power production during the testing revealed modest power production of the surface buoy energy converter and a peak power production of approximately 25 Watts from the heaving point absorber.