Takayuki Nakamura

Characteristics of Lift Forces on a Circular Pile in Waves

Hydraulic characteristics of lift forces on a circular pile due to regular waves are investigated experimentally. The generation of lift forces is discussed. It is found that this is based on the unsymmetry of vortices, and that the characteristics of lift forces, namely, the frequency and the magnitude, are influenced by the vortex patterns. Furthermore, the lift coefficients are calculated from the experimental resuts, and an empirical formula for estimation of the lift coefficients is proposed under some theoretical considerations. Finally, it is concluded that the total wave force for the design of ocean structures has to be considered in terms of the vectorial sum of the in-line forces and the lift forces.

DYNAMIC BEHAVIOR OF VERTICAL CYLINDER DUE TO WAVE FORCE

The equations describing conservation of mass, momentum and energy in a turbulent free surface flow are derived for a controle volume extending over the whole depth. The effect of the turbulent surface oscillations are discussed but neglected in the following analysis, where the equations are applied to the energy balance in a surf zone wave motion. This leads to results for the wave height variation and the velocity of propagation. The results cannot be reconciled completely with measurements and the concluding discussion is aimed at revealing how the model can be improved.A three-dimensional morphodynamic model of sequential beach changes Is presented. The model Is based on variations in breaker wave power generating a predictable sequence of beach conditions. The spectrum of beach conditions from fully eroded-dissipatlve to fully accreted reflective is characterised by ten beach-stages. Using the breaker wave power to beach-stage relationship the model Is applied to explain temporal, spatial and global variations In beach morphodynamlcs.The agents of initial damage to the dunes are water, which undermines them, and animals (including man) which damage the protective vegetation by grazing or trampling. Of these, man has recently assumed predominant local importance because of the popularity of sea-side holidays and of the land-falls of certain marine engineering works such as oil and gas pipelines and sewage outfalls. The need is therefore increasing for active dune management programmes to ensure that under these accentuated pressures, the coast retain an equilibrium comparable with that delicately balanced equilibrium which obtains naturally at a particular location.

Aeration Activations of a Water Chamber Type Breakwater with an Inclined Plate Array as a Front Wall

In order to improve the seawater quality in a harbor, a new type of pile supported breakwater with a water chamber was examined experimentally. The new breakwater is comprised of an inclined plate array as a front wall and a curtain wall as a rear wall. A horizontal plate is also attached to the rear wall at the lower end. Especially, for activating the aeration of basin water, the wave interaction process with the breakwater near the water surface was enhanced. The piston mode wave resonance in the water chamber of the dissipater is a main driving force to activate the entrapment and diffusion of air bubbles to the water. Both the functions of wave energy dissipation and activation of the aeration have been examined. It is seen that the front wall of down fin type is most effective to increase dissolved oxygen rate in the water.

INFLUENCE OF CLEARANCE HEIGHT BELOW A WATER CHAMBER OF INCLINED PLATE ARRAY AS A FRONT WALL ON THE BREAKWATER FUNCTIONS

In the previous study, we have developed a water chamber type breakwater with a dissipative front wall comprised of inclined plate array and a horizontal plate at the bottom. It was intended as an improved water chamber type breakwater comprised of impermeable walls. Especially for the use in the sea area where the tidal difference is comparatively large, say larger than 3m difference. In this study, supposing that the clearance height between the bottom plate of a water chamber and a sea floor is comparatively large because of supporting piles in deep sea, influence of the clearance height on the performance of the breakwater has been examined extensively. For instance , wave transmissions and reflections, and also mean currents about the breakwater. It has become known that the clearance height is not so critical for the breakwater performance.

Effectiveness of a Pile-Supported Breakwater with an Inclined-Plate-Array and a Submerged Plate in a Harbor

We have proposed a new type breakwater supported by piles, which consists of three major parts, i. e., an inclined plate array as a front wall, a vertical rear wall and a submerged plate at the base. It has been confirmed by the two-dimensional experiment that it enables to reduce both reflected and transmitted waves and also induce the mean current about the breakwater. In this study, we have carried out experiments on the performance of this type of breakwater in the three dimensional fields. For the comparisons, conventional breakwaters, such as a curtain-walled breakwater and also a vertical breakwater, were also used as a breakwater model. For the theoretical prediction of nearshore circulation around the harbor, applicability of the numerical analysis based on the Multi-Layered model was extensively examined.