Junya Ishiwata

Autonomous Underwater Vehicle for surveying deep ocean

There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. AUVs (Autonomous Underwater Vehicle) were considered and chosen, as the most suitable tool for conduction survey concerning these global environmental problems. JAMSTEC has started to build a long range cruising AUV. The plan for its development is in several steps. As the first step an AUV, named URASHIMA was built in 1999, and sea trials have been held since 2000. URASHIMA dived to 3,518m depth in 2001. At the end of February 2005, the vehicle was able to cruise autonomously and continuously for 317km. This paper describes outline of the vehicle, presents some experimental results.

Operation of the Under Water TV on Chikyu

The Under-Water TV (UWTV) is used as a reentry support system for the scientific drilling by the drilling vessel “Chikyu”. The “Chikyu” UWTV performs scientific operations cost-effectively where the normal Remotely Operated Vehicles (ROVs) in the market can’t be available. The UWTV in the 2nd generation has been tested in a sea trial and operated in the subsequent scientific drilling project. The shape of the UWTV frame has been modified after the trial and the behavior of the UWTV during its dives has been improved. The tension data in the operations has been measured and the effect of the dynamic behavior is extracted from the data. Then the extracted dynamic effect is used as the indicator to see the UWTV situation under the sea surface and to prevent the UWTV from the operational failure.Copyright

Utilization of Surface Drilling Data for Estimation of Sediment Properties in Scientific Drilling of Tohoku Earthquake Zone

Japan Agency for Marine-Earth Science and Technology (JAMSTEC) operates the scientific deep-sea drilling vessel Chikyu, which undertook the drilling project under Japan Trench Fast Drilling Program (JFAST) to determine the mechanism of the catastrophic Tohoku Earthquake and the resulting huge tsunami. As targeted drilling sites were located about 1,000 m below the seafloor, at water depths of 7,000 m, JFAST was a challenging deep riserless drilling.Drilling operation can also provide information on the properties of the drilling layer. This is important as a main aim of the scientific drilling is to obtain core samples from sediment layers under the seabed for evaluating sediment properties. Even a rough estimate of sediment properties could potentially provide an important notice for conducting coring operations.Thus, we attempted to estimate properties of sediment layers using surface drilling data, such as drilling torque acquired from JFAST, and compare with properties of the core samples. As shear stress of sediment is a key parameter, it was estimated from surface drilling data. It was then compared with shear stress data determined from laboratory tests using core samples, and data from temperature sensors set in borehole.Copyright