Kenichi Asakawa

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.

Development of autonomous underwater vehicle 'AQUA EXPLORER 2' for inspection of underwater cables

A new autonomous underwater vehicle (AUV) named AQUA EXPLORER 2 (AE-2) has been developed. AE-2 can trace buried underwater cables and can measure their burial depth at a low operating cost. It can be controlled through a low-bit-rate acoustic link, and can send a video signal through another high-bit-rate acoustic link. Compared with its prototype AQUA EXPLORER 1000 (AE-1000), performance has been considerably improved due to an overall revamping of the mechanical and electrical design. The continuous operating period is now six times longer for a total of 24 hours at a velocity of one knot, while its dry weight has been reduced by half to 260 kilograms. The first long pool test and the first sea trial were successfully carried out.

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.

Experimental results of Autonomous Underwater Vehicle 'AQUA EXPLORER 2' for inspection of underwater cables

This paper describes the results of sea tests of an Autonomous Underwater Vehicle named AQUA EXPLORER 2 (AE-2). The experimental results of the acoustic video-signal transmission system are also be presented. AE-2 can find and trace buried underwater cables by using a cable tracking sensor and can measure the burial depth of cables. Two sea tests were successfully performed. The purposes of these sea tests were to evaluate the performance of the vertical and horizontal motion, cable tracking, and video image transmission system. In the first sea test, AE-2 succeeded in tracking the electric cable which was laid in a calm bay. In the second sea test, AE-2 succeeded in tracking a real telecommunication cable which was laid in the Pacific Ocean. The image of the seabed can be sent in real time to a mother vessel via an acoustic data transmission system, and digitally recorded on a hard-disk on the vehicle simultaneously. Its transmission speed is 16-32 Kbits/sec and it can transmit two pictures of 160 by 120 pixels per second.

DC cable sensors for locating underwater telecommunication cables

In this paper, three novel cable-locating methods for underwater vehicles are presented. In those methods, tri-axial flux gate magnetometers are used to detect the static magnetic field induced by direct current flowing in underwater cables. The position and laying direction of the cable are calculated and displayed on an onboard display. The sea trial was carried out successfully in February 1996. In the experiment, the underwater cable, in which direct current of one ampere was flowing, was accurately located from distance of five meters. The results of the experiment and the theory are described.

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.