Marine Energy Development Research Division

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Marine Energy Development Research Division

There are several kinds in ocean energy such as tidal current, ocean current, wave, water temperature difference and so on. Among them, we are mostly interested in the tidal current power which is abundant in Nagasaki. We are supporting the “Tidal demonstration field” through the measurement of tidal current velocity by the ADCPs (Fig.1) and are cooperating and supporting the “Practical realization project of tidal current power technologies” by the Ministry of Environment. In these projects, the power generators are assumed to be Megawatt grade and the early practical utilization is awaited. However, the applicable sea area with strong tidal current for the megawatt class generator is limited, so that we are developing a new type of low cost and high efficiency tidal power generator which can be applied in sea areas not strong as in Goto Islands. (Fig.2) We are preparing a model experiment in the circulating water channel as the feasibility study of this system and are also seeking collaborative R&D with other universities and companies.

  • Fig. 1 Two ADCPs for observation of tidal current and turbulence deployed in Naru-Strait, Goto
  • Fig. 2 Low cost and high efficiency tidal current power generator, CG and the experimental model

Energy Science Unit

Current members of this unit are specialized in marine environmental engineering, high-speed fluid engineering, thermal engineering, electrical engineering and control engineering, etc. and the ocean energies involved so far are tidal current, wave and water temperature difference. Some of the present research results are follows: Fig. 3 shows the results of the average flow velocity distribution of the tidal currents in Tanoura and Naru Straits in Goto. From this figure, it may be possible to choose the installation point of the tidal current power generator. Fig. 4 shows a new experimental system for offshore wind power generation, which can automatically control the field magnetic flux and maintain constant voltage and output even if the wind speed changes. In addition, we are conducting research on high performance evaporators for ammonia using inner spiral grooved steel pipes, assuming use in ocean thermal energy conversion (OTEC), and have developed a prediction model of heat transfer coefficient and flow mode.

  • Fig. 3 Distribution of average tidal current speed in Naru and Tanoura Straits in Goto
  • Fig.4 New experimental system for offshore wind power generation

Structural Engineering Unit

The current members of this unit are specialized in structural engineering and material strength studies. When using structures and equipment in the ocean, major problems in engineering are corrosion and fatigue. We considered duplex stainless steel as a corrosion resistant material that can be used in the ocean and investigated the fatigue strength of the interface of clad steel in which mild steel was combined with thin duplex stainless steel from the viewpoint of cost. Fig. 5 shows the fatigue crack propagating at the interface between duplex stainless steel and mild steel. Fig. 6 shows the propagation test results.

  • Fig. 5 Fatigue crack propagating at the interface between duplex stainless steel and mild steel (Duplex stainless steel upper part than cutout)
  • Fig. 6 Fatigue crack propagation test results at the interface between duplex stainless steel and mild steel