Keisuke Murakami

Three dimensional numerical simulation of bore type tsunami propagation and run up on to a dike

Tsunami increases its height on the shallow water area and may transfers into bore when it breaks. Bore type tsunami sometimes produces huge forces and causes large damages on coastal infrastructures. In order to mitigate tsunami damages, bore type tsunami propagation, run-up and its characteristics need to be understood. And aside of experimental study, numerical simulation provides principal physical quantities with higher resolution in time and space. This study discus the validity of a numerical simulation based on VOF method, CADMAS-SURF, and characteristics of bore propagation on to a dike.

Numerical and Experimental Simulation of Two-Phase Tsunami Flow Through Buildings with Openings

During tsunami action on a structure, the structure is subjected to heavy loads with complex phenomena which include the interactions among tsunami, structure and air. In order to mitigate tsunami damages on structures, it is important to understand the characteristics of tsunami hydraulic loads acting on the structures with taking into account the above interactions. In the present study, the characteristics of tsunami forces on a building structure are investigated using a two-phase flow model. Two types of building models, a building without openings and with openings, were dealt with; and the effects of openings on the building under the tsunami hydraulic loads are examined. The simulation results were compared with the results obtained from one-phase flow simulation, and also verified with experimental data. The numerical results show good agreement with the measured ones. Furthermore, the effects of air taken into the flow and opening configuration on the characteristics of pressures and uplift forces were also discussed.

AN EVALUATION METHOD FOR LARGE DRIFTING OBJECT-BRIDGE COLLISION DURING TSUNAMI

During the 2011 Great East Japan earthquake occurring at the North–East pacific region, serious secondary disasters caused by collision of drifting containers or ships occurred in various structures when tsunami came. Drifting objects including large ships and tankers come in and out of ports in Japan. Disaster deterioration caused by drifting objects during earthquake and tsunami has become another problem. In this study, it is assumed that a large drifting ship collides with a large-span bridge in the gulf line during a tsunami. To investigate the impact behavior of the bridge during collision, tsunami simulations and nonlinear dynamic finite element analyses of the whole bridge during collision are performed. Based on the collision force calculations, an approximate analytical method is proposed, and the maximum size of drifting object which can result in the collapse of the whole bridge structure is calculated using this method.

CHANGES OF HYDRAULIC CHARACTERS ON FLARING SHAPED SEAWALL AGAINST SEA LEVEL RISE

Changes of hydraulic characters on the Flaring Shaped Seawall were investigated on a supposition of sea level rise that might be brought near future. Two-dimensional hydraulic experiments were conducted to evaluate some hydraulic characters such as a checking effect of wave overtopping, wave reflection, wave overtopping rate, and wave pressure distributions against sea level rise. A critical maximum wave height, that is a maximum wave height on which no wave overtopping occurs at all, tends to decrease with sea level rise. The model equation that estimates the critical wave height was obtained, and its accuracy was verified. The wave overtopping rate increases with sea level rise. This increasing tendency on longer waves was more significant than that on shorter waves. A clear difference between Flaring Shaped Seawall and vertical one on their checking effect of wave overtopping was observed up to a certain decreased ratio of seawall crown height.

CASE STUDY ON DISASTER MANAGEMENT SYSTEM OF SELF-GOVERNING COMMUNITIES AND THEIR REINFORCEMENT IN MIYAZAKI PREFECTURE THROUGH T0514

This paper deals with an investigation of a disaster management system of self-governing communities against a natural disaster through a questionnaire survey after T0514 that brought the most serious damages in Miyazaki prefecture widely. Many self-governing communities delay their official announcement of evacuation instruction and directive. One of the reasons is that the most of those selfgoverning communities have no objective criteria for their official announcement. The disaster information that covers a narrow area is desired to announce the evacuation instruction and directive at the best opportunity. The risk communications for natural disaster such as landslide and flood are not sufficient between self-governing community and residents, and improvement of this communication is desired to derive an appropriate evacuation against the natural disaster that exceed a maximum credible level.

AN EXPERIMENTAL STUDY ON EFFECTS OF MOUND ON HYDRAULIC CHARACTERISTICS OF THE FLARING SHAPED SEAWALL

A Flaring Shaped Seawall (FSS), a new type of one, can drastically reduce a crest height and wave overtopping quantity in comparison with a conventional upright one. The FSS will usually be set on a mound from the point of a cost of manufacturing and construction. Thus, in this paper, effects of the mound on hydraulic characteristics of the FSS (a wave overtopping rate, a wave run-up height and a reflection coefficient) are clarified from experiments using a two-dimensional flume. Furthermore a method for the FSS on the mound is proposed, and it is shown that the method is adequate under the condition of experiments in this paper.

STUDY ON CHARACTERISTICS OF TRANSPORT OF SPRAY AND SOUND ENVIRONMENT BY NON-WAVE-OVERTOPPING TYPE SEA WALL

Authors have proposed a non-wave overtopping type seawall (Flaring Shaped Seawall) with deep circular cross section in order to facilitate a safe and excellent use of coastal space for various purposes. The seawall satisfies a non-wave overtopping condition with extremely lower crown height in comparison with conventional upright seawall. In this study, wind field near the seawall, water spray transported behind the seawall and sounds when waves running up were measured in the experiments, and compared with an upright seawall.

Reduction of Impulsive Breaking Wave Pressures by Wave Dissipating Works with Low Crest Elevation

Low crested wave dissipating works with low void content were considered in this study to reduce the impulsive breaking wave pressures acting on a non-wave overtopping type seawall. The wave transmission coefficient and wave pressure distribution were measured through two dimensional wave tank experiments. The numerical computation based on Greens Identity Formula was also applied to estimate the transmission coefficient. The wave transmission coefficient decreases linearly with decreasing of the void content. The maximum wave pressures also decrease linearly with decreasing of the void content, and the variations of the maximum wave pressures depending on the relative water depth become small.