The Offshore Floating Type Wave Power Device "Mighty Whale" and Its Multi-Purpose Utilization
"Mighty Whale" is an offshore floating type wave power device based on the oscillating water column (OWC) principle. It converts wave energy into electric energy, and produces a relatively calm sea area behind the device. These electric energy and calm sea area will be able to utilize for varied applications such as to improve a deteriorated ocean environment and fish farming.
JAMSTEC constructed the prototype of Mighty Whale on May 1998 for open sea tests in order to investigate practical application. The open sea tests have carried out since September 1998 at Gokasho Bay in Mie Prefecture and are still continuing.
This paper presents an outline of the prototype and study of multi-purpose utilization of Mighty Whale.
Key Words: wave energy, wave power generation, oscillating water column, renewable energy
Ocean energy typically taking the forms of wave energy, ocean thermal energy, ocean currents and tidal currents energy is the renewable and inexhaustible energy that exists on the earth in a huge quantity, though its energy density is low. It also draws attention from an environment conservation point of view as an energy source causing less environmental loads with little emission of greenhouse effect gases or hazardous wastes. Particularly, development of technology to utilize wave energy is considered important, as it is the form of energy that can be easily recovered in the coastal zone and would make an economical distributed type energy source readily available at isolated islands, remote areas and developing countries.
In the meantime, water and bottom eutrophication is serious in the coastal zone of Japan due to its heavily populated and industrialized coastlines and utilization of wave energy is also expected to provide a remedy to these problems. Japan's coastal zone provide bases of mariculture and marine sports as well and needs for a calm sea area located near the coastline are expected to intensify increasingly in the future. However, it is difficult to secure calm sea areas newly for these purposes and development of technology to expand calm sea areas offshore is desired.
The Japan Marine Science and Technology Center (JAMSTEC) has been conducting research and development of an offshore floating type wave power device, the "Mighty Whale" that use an ocean energy source, wave energy. The Mighty Whale has a wave power generation function for converting wave energy into electrical energy and a wave height dissipation function for producing a relatively calm sea area behind it.
Construction of The prototype was completed by May 1998. Following construction, the prototype was towed to the test location near the mouth of Gokasho Bay in Mie Prefecture. The open sea tests were begun in September 1998, after final positioning and mooring operations were completed as shown in Figure 1. The tests are still continuing and results are expected to provide a realistic understanding of the performance, safety, and economic features of the device.
This paper presents an outline of the prototype and study of multi-purpose utilization of Mighty Whale considering from the standpoint of technology in ocean utilities.
2. Outline of the prototype of Mighty Whale, 
2.1 Environmental conditions for the system design
The environmental conditions associate with environmental loading depend on the assumed return period for the system design. The assumed return period determines the severity of the wind/wave conditions (caused for instance by an extreme typhoon) to which the structure may be subjected at least once.
* Japan Marine Science and Technology Center
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