Junichi Kojima

High-speed acoustic data link transmitting moving pictures for autonomous underwater vehicles

This paper describes a new high-speed acoustic data link for an autonomous underwater vehicle that can inspect underwater structures at the depth of up to 3000 metes. The acoustic transmission is performed between the AUV and a repeater suspended from a mother ship using an optical fiber cable at distance of 300 meters from the seabed. This configuration reduces the transmission distance and enables high-speed transmission of compressed moving video signal.

Optimization of configuration of autonomous underwater vehicle for inspection of underwater cables

Deals with the configuration of autonomous underwater vehicle (AUV) for inspection of underwater cables considering low hydrodynamic drag, sensor alignment, collision avoidance manoeuvre, turning manoeuvre and rolling motion. The AUV consists of a fuselage of body of revolution with low hydrodynamic drag, fore and aft horizontal wings, upper and lower vertical tails and a pair of horizontal thrusters at both sides of the aft horizontal wings. The shape of the forward horizontal wing and that of the rear horizontal wing can be determined by use of a nonlinear optimization method under the constraints of magnetic sensor alignment for cable tracking, dynamic stability in the vertical plane and the performance of the collision avoidance manoeuvre. The performance of the turning manoeuvre and rolling motion are attributed to thrust force difference between a pair of thrusters at both sides of the rear horizontal wing, because the shapes of the upper and lower vertical tails can be designed from the viewpoint of the dynamic stability in horizontal plane.

Introduction of an advanced census method using fusion of acoustic and visual census of the Ganges river dolphins (Platanista gangetica) inhabiting a long tract of the Ganges river system

An advanced and accurate census methodology that fuses acoustic and visual census of the freshwater dolphins has been successfully introduced for the Ganges river dolphins that inhabit and migrate in a long tract of the Ganges river system. In order to conduct an accurate census of the dolphins, an acoustic array system with provision to display the dolphins real-time direction data on a GUI (Graphical User Interface), i.e. the RAPID-Array (Real-time Acoustic Passive In-situ Dolphin tracking Array) was developed in 2014. Targeting 10-13 Ganges river dolphins (adults, juveniles and calves) that were estimated to inhabit a 7-km stretch, i.e. a part of the entire 200km riverstretch from Bhitora to Allahabad in India, using the array, the initial census using fusion of acoustic and visual census was conducted for one day on 24 November 2015. Based on the data acquired during the census, an estimate of the number of the dolphins was quickly made at the site. The effectiveness of the proposed method was demonstrated for carrying out the census in a long tract of the entire habitat.

Measurement and Analysis of Hydrodynamics of ROV’s Tether Cable

The performance of ROV in ocean current is mainly limited by the hydrodynamic drag force of the tether cable.