11.Research on Ocean Utilization and Environment-Friendly Infrastructure Technology

Background and Objectives

Effectively using ocean space is crucial for Japan as a maritime country. Technological development to effectively utilize the huge ocean space is indispensable for the economy of the future. Since more severe waves and wind due to frequent typhoons must be considered, however,
technological development is needed to overcome such severe natural conditions.

Research topics

Potential waste disposal sites are available only in shallow sea areas that are inevitably close to mega-cities due to land space being significantly limited by the geographical features of Japan. Therefore, developing evaluation technology of long-term stability of waste disposal sites is required to secure the ocean environment from the risk of large-scale spills. Developing recycling technology is also essential for safe and secure human life.
To reduce human-oriented adverse environmental impact on the ocean, recycling technology must be developed, especially for the dredged and disposed material in the coastal area.

The following three topics are focused in this research theme.

1. Research on effectively using ocean space.
2. Research on evaluating the long-term stability of waste disposal sites in the sea.
3. Research on mitigation of adverse environmental impact.

Activities in FY 2010

In researching the properties of extreme waves, we performed cross-sectional experiments on swells that were propagated from offshore to the shoreline, considering that swells with a period of over 14 seconds that act on an offshore platform constructed on a continental shelf, shallower than 200m, are shallow water waves. Especially, previous research has shown that the spectrum of swells with a long period has large kurtosis and directional spreading and that freak waves are generated easily in a deep water region. We therefore studied the behavior and observed specifications of waves in a shallow water region and a very shallow water region and found that second-order nonlinear interactions due to wave shoaling dominated in a shallow water region, shallower than kh=1.36, and that skewness μ3 and kurtosis μ4 increased with a specific relationship.
(Figures a and b).