Kenichiro Shimosako

NEW STABILITY FORMULA FOR WAVE-DISSIPATING CONCRETE BLOCKS COVERING HORIZONTALLY COMPOSITE BREAKWATERS

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.

ESTIMATING THE SLIDING DISTANCE OF COMPOSITE BREAKWATERS DUE TO WAVE FORCES INCLUSIVE OF IMPULSIVE FORCES

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Numerical Simulation of Hydraulic Overflow Pressure Acting on Structures behind the Seawall

The 2D numerical wave flume based on VOF method, called CADMAS-SURF, was applied to hydraulic pressures acting on the structures because of the flooded water. The validity of this model is verified due to the comparison with experimental data. Then the numerical simulation of the hydraulic pressure was carried out. The numerical results suggested the importance of detached breakwaters to decrease the amount of flooded water and hydraulic pressures.

Performance Design of Maritime Structures and Its Application to Armor Stones and Blocks of Breakwaters

Reliability design considering probabilistic nature is quite suitable for coastal structures because waves are of irregular nature and wave actions fluctuate. However, solely considering the probability of failure is considered insufficient, as deformation (damage level) should also be taken into account. This paper discusses performance design as an advanced design methodology for maritime structures, focusing on deformation-based reliability design of armor stones and blocks of breakwaters. The stability performance of breakwater armors is specifically considered by describing the design criteria (allowable limits) of damage level with respect to different design levels including probabilistic aspects. The accumulated damage during a lifetime is also discussed.

DEVELOPMENT OF HIGH PRECISION TSUNAMI RUNUP CALCULATION METHOD COUPLED WITH STRUCTURE ANALYSIS

The 2011 Great East Japan Earthquake (GEJE) has shown that tsunami disasters are not limited to inundation damage in a specified region, but may destroy a wide area, causing a major disaster. Evaluating standing land structures and damage to them requires highly precise evaluation of three-dimensional fluid motion – an expensive process. Our research goals were thus to develop a coupling STOC-CADMAS (Arikawa and Tomita, 2016) coupling with the structure analysis (Arikawa et. al., 2009) to efficiently calculate all stages from tsunami source to runup including the deformation of structures and to verify their applicability. We also investigated the stability of breakwaters at Kamaishi Bay. Fig. 1 shows the whole of this calculation system. The STOC-ML simulator approximates pressure by hydrostatic pressure and calculates the wave profiles based on an equation of continuity, thereby lowering calculation cost, primarily calculating from a e epi center to the shallow region. As a simulator, STOC-IC solves pressure based on a Poisson equation to account for a shallower, more complex topography, but reduces computation cost slightly to calculate the area near a port by setting the water surface based on an equation of continuity. CS3D also solves a Navier-Stokes equation and sets the water surface by VOF to deal with the runup area, with its complex surfaces of overflows and bores. STR solves the structure analysis including the geo analysis based on the Biot’s formula. By coupling these, it efficiently calculates the tsunami profile from the propagation to the inundation. The numerical results compared with the physical experiments done by Arikawa et. al.,2012. It was good agreement with the experimental ones. Finally, the system applied to the local situation at Kamaishi bay. The almost breakwaters were washed away, whose situation was similar to the damage at Kamaishi bay.

FIELD EXPERIMENTAL PROJECT OF FLAP-GATE BREAKWATER FOR TSUNAMI AND STORM SURGE PROTECTION

A flap-gate breakwater for tsunami and storm surge protection was previously developed through hydraulic model experiments and numerical simulations. In this study, applicability of the flap-gate breakwater through a field experiment is shown. Although the field experiment is carrying out at Yaizu fishing port in Shizuoka prefecture, Japan, some technical investigations have been obtained. Feasibility of maintenance and characteristics of age deterioration and corrosion will be verified through continuous experiments to be conducted in the future.

A study on Wave Energy Absorption of Breakwater with OWC type Wave Energy Convertors

東日本大震災において原子力発電所が被災したことに より,自然エネルギーの利用が見直されている.振動水 柱型空気タービン方式(OWC型)波力発電装置は30数 年にわたる研究開発と実証試験が行われた実績があるも のの,発電コストが高いことから,開発が停滞していた. OWC型波力発電装置は,小島ら(1983)の波力発電ケ ーソンと同様,ケーソン前面に没水部が開口した空気室 を設けており,入射波によって空気室内に水塊が上下動 し,同時に空気室に設けられたノズルを通して空気流が 生じ,この空気流によって空気タービン発電機を駆動す る.この課題は,エネルギーの1次変換効率(入射した 波エネルギーと空気室内の圧力と水位変動から計算され るエネルギーの比)が,波の周期が共振周期を外れると 急減する点であった.そのため共振する周期帯を広げ, 発電出力向上を目的として,図-1に示すような法線直角 方向に突出したプロジェクティングウォール(以下, PW)と呼ぶ壁構造を空気室の前面に設置した.本研究 では,PW-OWC型の波力発電装置を取り付けたケーソン の発電効率について,中規模と大規模の水理模型実験に より検討した.

Uplift Forces on Pier Deck of Coastal Bridges and the Role of Air

Recent failures of coastal bridges during extreme storm events have focused attention on the need for research on wave loading of coastal structures suspended slightly above the still water level. This paper presents findings from large-scale experimental work carried out in the wave basin. Measurements from physical model tests are used to gain insights on the dynamics of wave-loading of coastal bridges and to derive prediction methods for both quasi-static and impulsive wave loads. The effect of openings in the bridge deck is also discussed, and guidance derived for design purpose.

On the Hydraulically Rational Shape of Armor Block and Foot-Protection Block for Rubble Mound of Composite Breakwaters

A rubble mound of composite breakwater is usually covered with armor blocks and foot-protection blocks to prevent its deformation. Although the design method for armor blocks and foot-protection blocks seems to have been almost established, nowadays, the site conditions are becoming severer. Therefore more rational design methods are required. The purpose of this study is to obtain the new knowledge correlating to the stability and cost reduction for the foundation of composite breakwater. Wave forces acting on the armor blocks were measured and the rational shape of block which reduces the uplift force was proposed. Hydraulic stability tests for foot-protection blocks with various scales were conducted and the rational designs were investigated.

Effect of Armor Layer and Crown Wall on Wave Overtopping of Rubble Mound

Recently, randomly placed special armor blocks with single unit versus double unit width are being gradually used for protecting rubble mound breakwaters. With this in mind, we conducted a series of experiments to examine wave overtopping of various types of rubble mound breakwaters. Results indicate that (i) differences in width and void ratio of the armor layer affect both wave energy dissipation on the armor layer and in turn the wave overtopping and wave forces on the crown wall, and (ii) wave overtopping is affected by differences in the height of the armor layer relative to the crown wall height. Also discussed is an alternative design of the crown wall using a perforated wall concept to reduce wave overtopping.