Toshiro Suhara

Observation of the Power Spectrum of Ocean Waves Using a Cloverleaf Buoy

Abstract The power spectra of typical sets of ocean wave data obtained in the open ocean using a cloverleaf buoy are analyzed to determine an idealized form for the spectrum of ocean surface waves. It is shown that most of the single-peaked spectra observed in a generation area can be described well by the spectral form of the JONSWAP type. Two parameters α and γ characterizing the spectral form are calculated for each spectrum measured. Their relations to the dimensionless peak frequency fm (=fmU/g) are then determined. These relations are further converted into fetch relations for α and γ through a relation between f and a dimensionless fetch F (=gF/U2). Another spectral form proposed by Toba (1978) is examined and shown to fit as well to the observed spectra at high frequencies This fact shows quasi-equivalence of the JONSWAP spectrum and Tobas spectrum in the high-frequency range. On the basis of the agreements of both spectral forms at high frequencies, properties of the dimensionless constant α&...

Moored instrument observations in the Kuroshio south of Kyushu

In each of the (fiscal) years 1979–1982, multilayer current measurements by means of moored instruments were carried out in the Kuroshio off Tanegashima Island, south of Kyushu, with particular interest in the baroclinic layer (0–1,000 m) of the intense current. Most of the moored instruments were in position for more than 30 days, the maximum duration being 145 days. This paper describes some noticeable features of the mean and fluctuation fields in the surface Kuroshio as inferred from the the new data sets.Vertical profiles of horizontal velocities show that the eastward current of the Kuroshio in the region is confined to the upper 600 m on average and below this level the mean current is directed to the southwest along the local isobaths. This is believed to be the first observation of the “level of no motion” in this region. It is argued that the indicated level of no motion would lead to much smaller values for the Kuroshio transport than previous values referred to the 1,000 m level — for example, earlier estimates by Nitani (1972).The fluctuation field in the upper intense current appears to be dominated by an organized motion with a time scale of about 30 days. This can be seen clearly in the time variations of water temperature and local volume transport, but less clearly in the velocity records. The horizontal transfer components of momentum and heat are calculated and it is suggested that the transverse momentum transfer, U′V′ tends to be negative (offshore) in the region of anticyclonic shear of the upper Kuroshio; no evidence for a “negative eddy viscosity effect” is found.

The structure and adhesion of coatings deposited by wire explosion spraying

The coating method and the characteristics of wire explosion spraying, as developed in our laboratory, are described. A study of the mechanism of adhesion between the coating and substrate in two metal systems, W-mild steel and W–Cu which differ in mutual solubility, is discussed. Metallographic observations using electron probe and soft x ray confirmed the presence of a solid solution boundary layer in the case of the mild steel substrate, with a critical shearing stress of adhesion measured by our method ranging from 20 to 26 kg/mm2, which is nearly equal to the shearing strength of the tungsten coating itself of 24 kg/mm2; fracture propagated within the coating itself. In the case of the copper substrate the critical shearing stress of adhesion was from 9 to 13 kg/mm2 which is much weaker than the shearing strength of copper, 28 kg/mm2; the fracture propagated along the boundary between the coating and substrate. Theoretical considerations attempt to explain the mechanisms of formation of the structure...

STRUCTURE AND WEAR CHARACTERISTICS OF COMPOSITE COATING DEPOSITED BY WIRE EXPLOSION SPRAYING

New composite coatings composed of two different metallic constituents were fabricated by means of the wire explosion spraying method. The fabrication method of composite coatings was outlined and their structures and properties were studied to show the excellent wear resistance of these coatings. Three types of composite coatings tested are (1) high carbon steel and molybdenum, (2) high carbon steel and tungsten, and (3) high carbon steel and tantalum. Regardless the coating types, the abrasive wear of the coatings was minimum when the volume of high carbon steel was twice as much as that of the other metal.

An analysis of the T-shaped crack along the fiber-matrix interface in unidirectional composite materials.

In this paper a fracture problem in unidirectionally fiber-reinforced composites containing a T-shaped crack at the interface is considered. The T-shaped crack consists of an interface crack and a crack perpendicular to the interface. A system of integral equations is formulated based on the two-dimensional elasticity and Fourier transforms. The integral equations are evaluated by a numerical method using only the Gauss-Chebyshev integral formula, which was developed by the present authors in the last paper. First, the numerical results are compared with the previous results for a T-shaped crack in an homogeneous material, verifying the present method to be highly satisfactory. Next, three kinds of stress intensity factors (SIF), such as Mode I SIF of a perpendicular crack and Mode I and II SIF of an interface crack, are presented for Glass/Epoxy, Carbon/ Epoxy and Tungsten/Copper composite systems with various geometrical parameters.

Experimental Determination Of Optimum Condition For Wire Explosion In Water And PMMA

Through wire explosion in water and polymethyl-methacrylate (PMMA), electric energy stored in a condenser is converted into mechanical energy. The condition of explosion maximizing the conversion efficiency, namely the appropriate dimension (the diameter and/or the length) of wire as well as the pertinent setup of a discharge circuit, has been determined experimentally.

Bow flare damages of large full ships due to wave impact

In this report, wave impact on the bow of a ship is analyzed by classifying the phenomenon into two types: one concerned with the impact of the bow with the surface of water (impact of Wagner type), and the other originated from the impact of the bow with a breaker (impact of Bagnold type). Computation formulas both for the pressure and for the design of shell plate at the bow were established upon the basis of the data of actual damages. The design standard presented here is, as stated before, a tentative criterion set up according to the experiences of damages. It might be appropriate to add in conclusion that for certain kinds of ships, however, there may be room for modifications to be introduced in some of numerical values in the standard.

A Study of Motion and Strength of Floating Marine Structure in Waves

Many floating marine structures of various kinds have been constructed for varied purposes ; however, researches and technical experiences for such structures, some of which are quite different from conventional ships, are not so exhaustive and comprehensive, as those for the ships, and many problems still remain unsolved.Taking an opportunity of construction of newly developed iron ore loading station with submersible, column stabilized, catamaran hulls, a systematic study was made on the motion and strength of the structure in waves. Theoretical analysis of the motion and strength of the structure was carried out first. Secondly, the theoretical results of its motion in waves were compared with that of model tank test. Thirdly, in order to check the theoretical calculation the stress measurements were made at the time of launching. Finally, during the ocean towage of the structure from Japan to India, comprehensive measurements of motion of and stress in the structure in waves were conducted simultaneously with the accurate measurements of waves by means of a clover-leaf buoy.Conclusions of the present study are summerized as follows : 1) Motions of floating marine structure with catamaran hulls in irregular waves can be estimated with sufficient accuracy for engineering purpose by the spectral computations of responses utilizing the linear superposition principle using the response functions which are obtained by the strip method usually used for ship motions in oblique waves and are corrected by the results of model tank test.2) Longitudinal stress of the structure can be estimated with fairly good accuracy, by the finite element method using the response function of longitudinal bending moment in waves which is also calculated by the strip method.