Kenichi Ohno

Stability of Armour Units on Breakwater Heads under Multidirectional Waves

This study gain the assessment referring to the stability weight of armour stones for the breakwater head and trunk under multidirectional waves through the series of laboratory experiments in the multidirectional wave basin and the numerical calculations of the stone weight using the velocity measurements and the static stability formula for the armour stone on the heads and trunk. Furthermore, in order to support more comprehensive understanding of the stability weight of armour stones on the head and trunk under multidirectional waves, the dynamic stability formula for the armour stone, which is taken the rolling motion of stones on the slope of breakwaters at every moment into consideration, is developed.

VELOCITY FIELD MEASUREMENTS OVER BREAKWATER HEADS UNDER 3D WAVES

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

WAVE KINEMATICS ON BREAKWATER HEADS AND STABILITY OF ARMOUR LAYERS UNDER MULTIDIRECTIONAL WAVES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

EVALUATION SYSTEM FOR REFLECTION COEFFICIENT OF SEAWALL WITH DAMAGE OF ARMOR ON CROWN AND SLOPE

To introduce the performance design into the decision making problem of the repair or renewal of the damaged armor block on seawall, a performance evaluation system of seawall with the accumulative damage of armor is necessitated. In this study, numerical experiments and model tests are conducted to investigate the reflection coefficient of the seawall under condition of the damage progression of armor blocks on crown and slope of seawall. The regressive prediction properties between the reflection coefficient and the damage parameter could not be recognized from those results. The performance evaluation system is developed using a neural network system, which evaluates the causal relation of the reflection coefficient and the accumulative damage parameter. The neural network with a three-layer calibrated by the numerical experiments can predict the reflection coefficient of seawall under the damage progression of armor layer within about 10% errors.

Short-Term Change of Offshore Crescentic Bar Topography along Tottori Coast

The present study deals with a short-term change of an offshore bar topography along Tottori coast during 4 years (2004-2008). This coast has a multiple offshore bar system. An inner bar lies around 100m offshore and an outer bar lies between 200m and 500m offshore. The outer bars have crescentic feature with an offshore convexity. Wave length of the outer bars are 500m-1000m and shows small yearly change. The shore line has a cusping feature. Their wave length are 300m-450m (Kimura and Ohno, 2007). Inner bars also show crescentic feature in winter. The wave length ratio of cusp, inner bar and outer bar is roughly 1: 1: 2. In early winter, amplitude of the outer bar reduces and in the late winter, it grows again. The difference reaches to 100m. This change seems corresponding to the integrated incident wave energy.