Showing papers in "The Journal of Japan Institute of Navigation in 1990"

Analysis of vessels' wind forces through the utilisation of a physical-mathematical model-ii

Abstract: A physical-mathematical model consisting of six elementary fluid dynamic forces and stall effects acting on a ship is proposed by the authors. They then examine specific fluid forces in the model, such as induced drag, cross flow drag and stall effects. This examination generated a new mathematical model. In this paper, data presented in previous papers concerning wind forces on various types of ships was analysed using this new mathematical model. It was found that these formulae could describe measured forces and give reasonable physical representations of the formulae in terms of fluid dynamics. For the estimation of fluid dynamic forces, correlation between the coefficients of wind forces and six nondiemnsional hull parameters (aspect ratio, B/L, B/H, T/L, X/L and Ax/Ay), and the correlation between wind force coefficients were examined. The coefficients of correlations between some parameters or fluid dynamic coefficients had significant levels in these cases. Therefore, each fluid dynamic coefficient of wind forces could be estimated from nondimensional hull parameters and the correlation between fluid dynamic coefficients.

A design and sea trial of fuzzy autopilot for ship - i

Abstract: In 1974 Prof. Mamdani attempted to control a steam engine plant by Fuzzy Control Theory and successful results were obtained. After this the possibility of applying fuzzy control theory to more complicated and extending systems has rapidly increased. In fuzzy control the qualitative experience and knowledge that an operator has acquired are described by fuzzy control rule (a form of if...then). Therefore it is possible to design a sophisticated controller which mimics an operation. In this paper, the authors designed a fuzzy controlled autopilot system and carried out a trial. The result of the test were statistically analysed in comparison with conventional and human steering. The developed system showed a prudent steering as if an able helmsman steered.

Study on the critical range by course changing manoeuver

Abstract: It is very important and necessary to know the critical range at which collision is unavoidable by course changing manoeuvre. To obtain this it has been necessary to develop a mathematical model of collision avoidance and occurrence. The authors have used a new analytical technique,using an area of collision target's position. Different versions of the critical range by course changing are obtained under assumptions such as a) one ship evades while the other stand on b) one ship evades while being pursued by the other. The study shows that the critical range by course changing depends strongly on the two ship's speed difference and on the permissible manoeuvre.

Maritime communication experiment using engineering test satellite v (ets-v)

Abstract: In order to provide small ships with satellite communication, small antennas and digital communication techniques are necessary. The authors carried out an experiment of the propagation characteristics of 2.4 - 4.8Skbit/s data and digital voice communication using a short backfire antenna of 40cm in diameter in Japanese waters and the Indian Ocean.

A reception of images from gms on board by a simple tracking antenna

Abstract: A simple, two-axis controlled satellite tracking antenna for vessels, which has been designed by the present authors originally for satellite broadcasting, is applied to the reception of images from the geostationary meteorological satellite (GMS) onboard. Instead of an expensive vertical gyroscope, small and inexpensive pendulum-type inclinometers are used as sensors for rolling and pitching, which require some adjustment of the obtained values. A rather small parabolic antenna of 0.75m in diameter is used to lighten the load due to wind pressure. The allowable angular error increases, though carrier power at the receiver decreases owing to the reduced aperture area. The nominal value of noise figure of the preamplifier is 1.8 dB. The device was tested for receiving images on a ship in the Pacific Ocean. It was proved that the images received by the device were satisfactory in the vast area with elevation angle down to 30 degrees covering Sakhalin in the north and New Zealand in the south.