Volume Transport through the Tsushima Straits Estimated from Sea Level Difference

The relations between the volume transport and the sea level difference across the Tsushima Straits have been investigated using current data provided by ADCP mounted on the ferry Camellia, plying between Hakata and Pusan. Empirical formulas to deduce the volume transports using the sea level differences across the eastern and western channels are proposed, considering the seasonal variation of the vertical current structure. The interannual variation of volume transport through the Tsushima Straits for 37 years from 1965 to 2001 is estimated using the empirical formulas. The total volume transport through the Tsushima Straits, averaged for 37 years, is 2.60 Sv and those of the eastern and western channels are 1.13 Sv and 1.47 Sv, respectively. The total volume transport through the Tsushima Straits tends to decrease with a roughly 15 year variation until 1992, then begins to increase.     

Volume Transport Variability Southeast of Okinawa Island Estimated from Satellite Altimeter Data

A nine-year-long record of the northeastward volume transport (NVT) in the region southeast of Okinawa Island from 1992 to 2001 was estimated by an empirical relation between the volume transport obtained from the ocean mooring data and the sea surface height anomaly difference across the observation line during 270 days from November 2000. The NVT had large variations ranging from −10.5 Sv (1 Sv ≡ 10⁶ m³s⁻¹) to 30.0 Sv around its mean of 4.5 Sv with a standard deviation of 5.5 Sv. This large variation was accompanied by mesoscale eddies from the east, having a pronounced period from 106 to 160 days. After removal of the eddy, NVT was found to fluctuate from 2 Sv to 12 Sv with a quasi-biennial period.     

Semi-Lagrangian methods for a finite element coastal ocean model

Coastal ocean hydrodynamic models are subject to a number of stability constraints. The most important of these are the Courant–Friedrichs–Levy (CFL) constraint on gravity waves, a Courant (Cr) number constraint on advection, and a time step constraint on the vertical component of viscous stresses. The model described here removes these constraints using a semi-implicit approximation in time and a semi-Lagrangian approximation for advection. The accuracy and efficiency of semi-Lagrangian methods depends crucially on the methods used to calculate trajectories and interpolate at the foot of the trajectory. The focus of this paper is on evaluation of several new and old semi-Langrangian methods. In particular, we compare 3 methods to calculate trajectories (Runge–Kutta (RK2), analytical integration (AN), power-series expansion (PS)) and 3 methods to interpolate (local linear (LL), global linear (GL), global quadratic (GQ)) on unstructured grids. The AN and PS methods are both efficient and accurate, and the latter can be expanded in a straightforward manner to treat time-dependent velocity. The GQ interpolation method provides a major step in introducing efficient and accurate semi-Lagrangian methods to unstructured grids.     

Dynamic analysis of vehicle–deck interactions

This paper presents the review and studies at various levels of problems concerning the authors’ previous research on the dynamics of vehicle–deck interactions. The various levels of study include the dynamic structural behavior of vehicle–deck systems, vehicle vibrations, damping effects of vehicles on structural systems, dynamic interactions between tire and deck surface, and vehicle securing on decks during ship motions, etc. The study includes analytical, numerical and experimental analysis. Practical problems encountered by Ro–Ro ship designers are addressed by discussing those analysis. It is shown that influences from the dynamics of vehicle–deck interactions are relevant to a number of aspects of issues, such as the excitation frequency range, how detailed information of the structural system response is required, the structure characteristics, and positions and orientations of vehicles on decks, etc. The study contributes to the knowledge for the naval architect and vehicle engineer on how significant the dynamics of vehicle–deck interactions are when dealing with relevant problems.     

Ocean Model Simulation of Southern Indian Ocean Surface Currents

The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N-60°S and 30°E-120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good.     

Three-dimensional hydrodynamic model, study cases for quarter annular and idealized ship channel problems

An extended version of the three-dimensional hydrodynamic model, ADCIRC 3D-DSS, was utilized to simulate both horizontal and vertical flows in a (quarter) annular harbor (QATP and ATP) and rectangular basin with an idealized ship channel (RBSC). Comparison of horizontal and vertical solutions to the analytical solution and results of other researchers are in good agreement. The vertical velocity solution is highly sensitive to the horizontal velocity solutions. The presence of the sidewall boundary may also affect the vertical solutions. Around the sloping bank of RBSC channel with one-third gradient, the vertical velocity becomes important. The maximum vertical velocity approaches ±50% of the sediment fall velocity of fine sand.     

Analysis of stiffened shell for ships and ocean structures by finite element method

Static analysis of stiffened shells has been carried out using an eight-noded isoparametric element for the shell and a three-noded curved beam element for the stiffener. A same displacement function is used for the shell and the stiffener elements. A modified technique has been followed to analyse the shell, which is an improvement over the degenerated shell concept. The stiffness matrix of the curved beam element is generated irrespective of its position and orientation within the shell element. The stiffness matrix of the stiffener is then transferred to all the nodes of the shell element. Numerical examples of stiffened shells with concentric and eccentric stiffeners have been analysed and the results presented together with those available in published literature.