Ray Yeng Yang

An experimental observation of a solitary wave impingement, run-up and overtopping on a seawall

A sequence of laboratory experiments using solitary waves was performed to model the effect of leading form of three types of tsunamis (a bore, an impinging wave and an overtopping wave) on a seawall on a sloping beach. The wave evolution process, impinging pressure along the seawall surface, total overtopping discharge behind the seawall and the maximum run-up height on the rear slope were measured and compared. Laboratory data were employed to re-examine relevant empirical formulae in the literature. The effect of the presence of the seawall in reducing maximum run-up height using the present setup was briefly discussed. The present data can be used for calibrating numerical and mathematical models.

Rudder Controlling of Underwater Vehicle Using in Kuroshio

In this paper, we investigate an underwater vehicle with two rudders suitable for working in Kuroshio near the eastern Taiwan, where the flow field of ocean current is less than 1.0m/sec. Lift and drag forces of the underwater vehicle submerged in the sea were calculated at different attack of angles and rudders by using finite element method. An on-site experiment with a prototype vehicle was also conducted located on Hsinta Fishing Harbor. Results show that lift force for the rudder of prototype vehicle near the sea surface is only 60% of theoretical calculations. To reduce the turbulence effect, the position of rudders in the front and the rear for the underwater vehicle should not be at the same level. Drag forces increase tremendously with increasing attack of angles compared with the effect of rudder’s quantity. The power-free underwater vehicle has been built and controlled steadily at 0.6~0.7m/sec flow velocity, suitable for carrying generators in Kuroshio.

Intermittent slipping of landslide regulated by dilatancy evolution and velocity-weakening friction law: an efficient numerical scheme

When a block of dense sandy soil moves downhill, the shear-induced soil dilatancy along the basal shear boundary produces a negative value of excess pore pressure that increases the basal frictional resistance. Dilatancy angle, Ψ, the degree to which the basal soil dilates due to the shear, normally evolves during slope failure. A study by other researchers shows that if Ψ is constant, the block of dense soil will remain stable (or unstable) sliding when the velocity-weakening rate of the basal friction coefficient of the block is small (or large) enough. Moreover, during unstable sliding processes, the block of dense soil exhibits “periodic” patterns of intermittent slipping. Here, we used a more efficient and accurate numerical scheme to revisit that study. We expanded their model by assuming Ψ evolves during slope failure. Consequently, we acquired completely different results. For instance, even though the velocity-weakening rate of the friction coefficient is fixed at the same smaller (or larger) value that those researchers use, the stable (or unstable) steady states of landslide they predict will inversely change to unstable (or stable) when Ψ decreases (or increases) with the increase of slide displacement to a value small (or large) enough. Particularly, in unstable processes, the soil block exhibits “aperiodic” styles of intermittent slipping, instead of “periodic”. We found out that the stick states appearing later last longer (or shorter) in the case of decreasing (or increasing) Ψ. Moreover, because the basic states of landslides with impacts of dilatancy evolution are not steady nor periodic, traditional stability-analysis methods cannot be “directly” used to analyze the stability of such landslides. Here, we broke through this technical problem to a degree. We showed that combining a concept called “quasi-steady-state approximation” with a traditional stability-analysis technique can qualitatively predict the instability onset of the landslides. Through this study, we demonstrated that the combination of Chebyshev collocation (CC) and 4th-order Runge-Kutta methods is more accurate and efficient than the numerical scheme those researchers use.

Ship wake structure on the finite sea depth in the presence of wind waves

A kinematics model of the ship wake in the presence of surface waves, generated by wind is presented. It is found that the stationary wave structure behind the ship covered a wedge region with the 16.9° half an angle at the top of the wake and only divergent waves are present in a ship wake for co propagating wind waves. Wind waves field directed at some nonzero angle to the ship motion can cause essential asymmetry of the wake and compressing of its windward half. The extension of Whitham-Lighthill kinematics theory of ship wake for the intermediate sea depth is also presented. The ship wake structure essentially depends from the Froude (Fr) number based on the value of the sea depth and ship velocity. For Froude number less than unit both longitudinal and cross waves are presented in the wake region and Kelvin wake angle increased with Fr. For Fr>1 wake angle decreased with Froude number and finally only divergent waves directed almost normally to the ship track are presented in the very narrow ship wake.Copyright