Kenkichi Tamura

Experimental Study on a Self Standing Hybrid Riser System Throughout Tests on a Deep-Sea Model Basin

The present paper introduces a concept of a hybrid riser, Self Standing Hybrid Riser (SSHR), particularly in development for ultra deepwater around 3000 meters. Main problems faced in the initial definitions for design of such risers in the described scenario are discussed. Unique laboratory test with reduced model carried out in waves, current and riser top oscillation experiments in a very deepwater wave tank is shown. And, experimental results are shown and discussed, especially considering difficulties faced to carry out this experiment. Discussions are addressed in terms of vortex induced vibration (VIV) around buoyancy can, riser line pipe and flexible jumper.Copyright

Development and sea trial of an Autonomous Underwater Vehicle equipped with a sub-bottom profiler for surveying mineral resources

In recent years, Autonomous Underwater Vehicle (AUV) has received much attention as a tool of ocean survey. One of the method for the efficient of hydrothermal deposits investigation is multiple vehicle operation of AUVs. The aim of our work is to development the small and inexpensive AUV and operate together with other AUVs. This paper introduce the first AUV in our project, and show the result for the sea trial of the AUV.

Model experiment of a launcher of a Deep-Sea Monitoring Robot System

National Maritime Research Institute (NMRI), in cooperation with Underwater Technology Research Center, Institute of Industrial Science, University of Tokyo, is developing a Compact Deep-Sea Monitoring Robot System for investigation of sunken ships in deep sea. This system is consisted of a launcher and a small vehicle, and it has characteristics of both AUV and ROV. A launcher corresponds with its mother ship by using optical fiber cable. There is no umbilical cable between a launcher and a vehicle, and the communication is performed by acoustic communication. A launcher submerges holding a vehicle by gravity. It controls its rudders for approaching to a target point. Just before reach the sea bottom, a launcher releases an anchor, launches a vehicle to start mission. In order to pursue the best configuration for effective horizontal movement during descending motion, preliminary calculation and experiments were carried out for two types of configurations, a fuselage with fins and rudders and a fuselage with rudders but no fins. This paper describes the results of calculation and experiments at a deep-sea model basin. The basic mechanism of descend were confirmed.

Behavior Characteristics of Hang Off Riser That Considers Oscillation of Floating Structure

A riser system has been used widely as the progress of ocean developments. The vibration is one of the most important problems from the safety aspect of a riser system. In this paper, we conducted the model experiment of a hang-off riser at the Deep-Sea Basin in the National Maritime Research Institute of Japan. Translational and rotational motions of the upper floating structure are simulated by the forced-oscillation device. The motion of the riser was measured using 3D video tracking system. Numerical analysis program for simulating the behavior of riser was also developed. This program used the improved Morison’s equation as a method of evaluating hydrodynamic force. The validity of this calculation method was verified through the comparison with the experiment results.Copyright

Tracking experiment of multiple AUVs by a semi-submersible ASV

We have developed a semi-submersible ASV (Autonomous Surface Vehicle) that tracks and controls AUVs (Autonomous Underwater Vehicles) on behalf of the mothership. In September 2016, we conducted tracking, positioning and communication tests of multiple AUVs by using the ASV. The results of the trials proved the performance as designed. And the ASV succeeded the test of each AUV tracking and multiple AUVs tracking.

Development and sea trial of the compact cruising type AUV system

In this paper, we present an overview of two cruising AUVs recently developed by National Maritime Research Institute of Japan. Sharing the same hardware and software architectures, two AUVs divide their responsibilities by employing acoustic bottom survey devices of different purposes. Pursuing the easiness in generating a behavior plan corresponding to a specific mission, pattern-based behavior planner is developed and commonly used by two AUVs. Right after their completion, two AUVs were deployed in Suruga Bay and successfully achieved lots of missions imposed on their trial dives. Results of trial dives of our AUVs are also presented in this paper.

Development and sea trial of the parametric sub-bottom profiler system for autonomous underwater vehicles-off Hatsushima Island-

The exploration of buried deposits under the sea sediment requires high directivity and low attenuation beams. The parametric sub-bottom profiler meets these requirements; moreover, it is comparatively small and can be easily mounted on autonomous underwater vehicles (AUVs). For this reason, we are developing a new PSBP system for AUVs. This paper presents the recent results of the PSBP system for AUV during the sea trial conducted under the “Zipangu of the Sea” Project as a sub-program of SIP (Strategic Innovation Promotion), managed by the Cabinet Office of the Japanese government.

Development of a regional underwater positioning and communication system for control of multiple autonomous underwater vehicles

A new complex system of underwater positioning and communication has been developed for control of multiple autonomous underwater vehicles (AUVs). It consists of a semi-submersible autonomous surface vehicle (ASV), a hovering type AUV, and three surface buoys. The operational concepts for control of multiple AUVs are discussed.

Coral monitoring with fluorescence imaging lidar

It has been pointed out that globally hermatypic corals in coral reefs have been seriously damaged in recent years, and it is predicted that such damages will expand in area in the future. It is important to monitor corals globally, in detail, and over long-term periods, for preservation of the marine environment and biodiversity. The spot-check method, one of the major coral monitoring methods, is operated by snorkelers or divers, and therefore, its operation is limited by the seastate, and its monitoring areas are often for specific observation points. On the other hand, the satellite remote sensing, another major coral monitoring methods, can cover composite coral reef areas, but the image resolution is a few meters, and it is not possible to monitor small size coral colonies and deep sea areas. The boat-based fluorescence imaging lidar system has been developed to complement these coral monitoring methods. This system obtains linear coral observation data along the boat track, and makes it possible to build a cooperative coral monitoring network. Since most hermatypic corals have fluorescent proteins, living tissues can be monitored using the blue-to-green fluorescence from UV excitation. It is possible to observe the UV-excited fluorescence images from live coral even in the daytime, by the UV excited fluorescence imaging lidar. Additionally, laser bathymetry is also possible by time-of-flight measurement. We have succeeded in observing the pseudo-coral fluorescent images and depths down to 30 m depth at the testing basin. Secondly, we have succeeded in observing the live coral fluorescent images and their depths by the lidar system using a glass-bottom-boat at Taketomi island, Okinawa, Japan. The system summary and observed data are reported in this paper.

Development of CO 2 Slurry Release Nozzle for CO 2 Ocean Storage

Ocean storage of CO2 is one of greenhouse gas control technologies. The authors developed a release nozzle based on the concept of a CO2 sending method for the ocean storage, COSMOS, where liquid CO2 is released as a mixture with dry ice, CO2 slurry, at the depth as shallow as 500 m to sink to deep water. The authors have carried out the development of CO2 slurry release nozzle. At first preliminary experiments with a single-tube nozzle were conducted. The results of the preliminary experiments implied that the plugging of nozzle outlet should be prevented to allow the slurry to be released continuously. Then, the authors proposed the concept of coaxial double-tube release nozzle and demonstrated the effectiveness of the concept by injection experiments with a double-tube slurry injection unit. Slurry injection experiments were carried out with two types of inner tube with different inner diameter to investigate the effect of the nozzle dimensions and the slurry flow on the slurry drops released from the nozzle. The length of the mixing zone in the nozzle (Delta), which is the length from the outlet of the inner tube to the outlet of the outer tube, and the slurry injection rate were varied in the experiments. The surface of slurry drops from the nozzle with smaller Delta was more stable than that from the nozzle with larger Delta. Moreover, as the injection rate was increased, the instability of the slurry drop surface was increased. These results suggest that the nozzle dimensions and the slurry flow would affect the size and shape of slurry drops from the nozzle.