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Journal of Ocean and Ship Technology
Volume 2 Number 1

ISSN: 0975-301X
Publication Year: June 2011

Hydrodynamic Characteristics of Submerged Semicircular Breakwater
- G. Dhinakaran, V. Sundar, R. Sundaravadivelu and K.U. Graw

Abstract :The concept of semicircular breakwater (SBW) is one of the recently emerging new types of breakwaters. The world’s first semicircular breakwater of rear dissipating type has been constructed at Miyazaki port in Japan during 1992-1993. The submerged SBW is mainly adopted to prevent beach erosion and is built to reduce the incident wave energy on its leeward direction, if submerged SBW used in front of a vertical breakwater. In addition, it facilitates the premature wave breaking which in turn causes the reduction of wave energy. The dynamic pressures exerted on impermeable SBW due to regular waves were measured. The variations of dimensionless pressures, the horizontal and vertical forces on the caisson for three different water depths are presented and discussed in this paper. In addition, the reflection and transmission characteristics as a function of scattering parameter are reported. The experimental results on the dynamic pressures for an impermeable SBW are validated with two dimensional finite element model.

Marine Vessel Classification using Fractional Fourier Transform
- K.K. Sharma, Rajesh Kumar

Abstract: The problem of classifying marine vessels based on their acoustic radiated noise is of major importance in sonar systems used in naval applications. Several methods have been proposed in the literature for this purpose including the method based on the feature vector derived using frequency domain parameters obtained by analyzing the acoustic signature received using underwater sensors. The acoustic signature contains class discriminating information of the marine vessels. In this paper the problem of feature analysis with the aim of feature selection and design of a suitable feature vector for the classification of the marine vessels using fractional Fourier transform (FRFT) is considered. After computing the FRFT of the acoustic signature several parameters such as fractional spectral centroid, fractional spectral roll-off, fractional spectral flux, energy entropy, zero-crossing rate etc. are extracted, and using these features, the targets are classified into different categories. It is observed through the simulation results that use of the FRFT in place of the conventional Fourier transform for computing the feature vector improves inter-class separation in terms of the Euclidean distance. Also, the inter-class separation between marine vessels maximizes at some value of angle parameter of the FRFT.

Strength of Stiffened Composite Plates With Opening
- S. Rahima Shabeen and P. Alagusundaramoorthy

Abstract: The main objective of this paper is to find the ultimate strength of stiffened composite plates with opening under out-of-plane load. Stiffened composite plates with and without opening were fabricated using glass fiber fabric woven roving mat and epoxy resin by hand lay-up process. A special lay-up structure was adopted in the fabrication process and the stiffeners were cast as an integral part of the flange plate. All specimens were tested upto failure. The presence of square opening reduces the strength of the plate by 8 % under out-of-plane load. A finite element model was developed using ANSYS10, and validated with the experimental data and used to find the size of stiffener required to reinforce the opening to regain the loss in strength. The loss in strength due to presence of opening can be regained by slightly increasing the size of longitudinal stiffeners around the opening.

Numerical Study of the Effect of Passing Ship on a Moored Ship
M. Rafiqul Islam, Adi Maimun Abdul Malik, Hassan Abyn

Abstract: Sailing ship generates wave and this generated wave reach to the moored ship nearby and also presence of sailing ship changes the flow around moored ship and cause to the pressure gradient along moored ship. The generated wave from sailing ship plus pressure distribution along the hull of moored ship significantly causes forces on moored ship. These forces results to motion of moored ship and influences loading /discharging operation and also causes to damage the mooring system. These hydrodynamic forces are low frequency and sometimes known as suction forces. These forces and moments depend on hull sizes, ship speed, lateral distances, water depth, and incident wave direction, period and wave height.
This study presents a computational analysis for a moored ship while the other ship passing nearby. The hydrodynamic behaviour between two ships in waves is an interesting and important topic. Nowadays there are many applications in the field of marine hydrodynamics where two vessels are floating in sufficiently close proximity to experience significant interactions. A computational investigation has been carried out to get the motion effect on the moored ship while the ship is passing nearby. The numerical solution was based on linear wave theory and 3-D distribution technique approach to determine the exciting forces and ship’s motion. For the case of simplicity the interaction between the berth and the moored is not taken into account. It is here by noted that the ship is moored in open and deep water. The speed effects have been considered in the Green function for more realistic results. The motion responses of the moored ship for a passing are computed on different wave length, water depth, vessel speed and different separation distances between these vessels. It is found that the sway and yaw have significant effects due to passing vessel which is dangerous for cargo loading and unloading operations and mooring line may be departed and hull can be damaged.

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