日本財団 図書館


Specifications of the air turbine and generator show Table 2. One 10kW/50kW switchover generator (switched over according to wave height) and two 30kW generators, which are capable of generating up to a total of 110kW, are carried on board.

 

Table 2 Specifications of the air turbine and generator

330-1.gif

 

The turbine generators are always running or ready to run except during special situations like rough weather or maintenance. They generate power automatically under favorable oceanic conditions and remain idle when oceanic conditions are not suitable for power generation, such as low waves. On the other hand, in stormy weather with very high waves, if turbine generators are about to reach a dangerous rotational speed, airflow to the turbines is shut off automatically by a safety valve.

During open sea tests, the supply and demand of electric power on Mighty Whale is self-complete and no shore power is supplied. That is, the electric power generated by waves is used as the main power, and to supplement it, batteries and an auxiliary diesel generator are carried on board; these power sources as a whole constitute the power supply system of the Mighty Whale. When power generation takes place, power is supplied from the turbine generators to various loads like measuring equipment and any remaining power is used to charge the batteries. If the power from the turbine generators is deficient or no power can be generated, power is supplied to the loads from the batteries. When the battery runs low, the auxiliary generator is started to supply power to the loads and charge the batteries. All of these system operations can be controlled automatically.

As a way of using wave energy for multiple purposes, one future prediction is that electric power generated by wave energy will be used to operate an air compressor to pump up or circulate seawater. An air compressor has been installed for this purpose in the machine room and the volume of compressed air produced by the air compressor is measured.

 

2.4 Mooring system

Since the Mighty Whale is a floating structure, the mooring system to keeping it safely positioned in a given area at sea is extremely important.

As shown by Table 1, the environmental conditions were severe. In addition, there were few cases in which an offshore structure with as large displacement as the Mighty Whale had ever been moored with chains by catenary mooring in seas as shallow as 40m. Therefore, the design of the mooring system was one of the most important considerations for the research and development of the Mighty Whale.

Under these environmental conditions, a six-point catenary mooring was used as shown in Figure 4. Four lines consisting of a Class 2 studless link chain 160mm in diameter connected with a Class 2 stud link chain 130mm in diameter were used on the weather side. Two lines of a Class 3 stud link chain 81mm in diameter were used on the lee side.

 

330-2.gif

Figure 4 Schematic of mooring system

 

Large-diameter chains were used to increase the unit weight of chains to reduce the effect of the vertical motion on mooring tension and to suppress the steady-state displacement caused by the drifting force of winds, tidal currents, and waves. Furthermore, intermediate weights were installed on the chains between the floating structure and seabed to increase the weight of the suspended portions of the chains. As a result, the characteristic curve of the mooring line could retain some flexibility even when the horizontal displacement with the slow drift oscillations of the floating structure was at its maximum as shown in Figure 5. Thus, it was possible to suppress the effect of the floating structure's vertical motion.

The mooring chains used were NK-certified. The inter mediate weights were made of cast steel. To protect the mooring lines at their mounting portions from abrasion and to prevent them from falling off the chains, an in-line method was used in which the half-divided intermediate weights were mounted around the chains. As for the anchor, a gravity-type concrete anchor was used due to the case of installation and because the seabed was sandy and its slope as gentle as 1/100.

 

 

 

前ページ   目次へ   次ページ

 






日本財団図書館は、日本財団が運営しています。

  • 日本財団 THE NIPPON FOUNDATION