Three Dimensional Two-Phase Flow Analysis of Tsunami Pressures

and Forces Acting on a Building with Openings

(HARTANA and Keisuke MURAKAMI)

Hydraulic interactions between tsunami flow and structures located along coastlines include quite

complex phenomena, because the tsunami flow acts on a structure with trapping air. In order to

design structures such as an evacuation building properly, it is important to consider the effect of this

entrapped air in the investigation of tsunami hydrodynamic loads. This study is aimed at

investigating the characteristics of tsunami hydrodynamic loads on multi floor buildings with

openings by using a two-phase flow model in a three dimensional space. Two types of building

models, the building with openings and the building without openings, were examined in this study.

Numerical results were compared with the results obtained from one-phase flow simulations, and

also verified with the experimental ones. The numerical results obtained from the two-phase flow

model show good agreement with the experimental results. Furthermore, the two-phase flow model

simulates the interface between water and air inside the building more accurately than the one-phase

flow model. The openings in the building reduce the sustained pressure acting on the front side. The

effects of the opening ratio and entrapped air to the wave pressures and uplift forces acting on the

floor slab were also discussed.

Snapshots of tsunami inundation on the building with 40% opening at t=7s

Pressure distribution on the building models at t=7s

Two-phase flow One-phase flow Experiment

Bore height=6.64cm

Bore height=11.37cm

Bore height=9.21cm

60% Opening ratio 50% Opening ratio 40% Opening ratio Without openings

Bore height:9.21cm

Bore height:11.37cm

Local Scouring of Gravel Mound due to Tsunami Overflow and Its

Countermeasure

(Akhmad Adi SULIANTO, Keisuke MURAKAMI,Yuki TOKUTOMI and

Kouichi UENO)

Many cases of structural damage have been reported after Tohoku tsunami earthquake. Among those

cases, the failure of breakwater caused by the local scouring on gravel mound due to tsunami

overflow can be selected as one of the typical structural damages. This study is intended to clear the

characteristics of local scouring on gravel mound under several tsunami overflow conditions. Four

cases of discharge and three kinds of gravel diameter were employed to investigate the

characteristics of local scouring under tsunami overflow condition. Furthermore, this study proposed

a horizontal plate which was introduced to reduce the local scouring. Numerical simulation was also

conducted to investigate the flow pattern above the gravel mound and pressure distribution on

proposed horizontal plate. This study revealed that the scales of local scouring, its depth and length,

depend largely on both overflow discharge and gravel size. Based on the experimental data, this

study proposed an equation that can estimate maximum scoured depth under different gravel

diameter as well as several overflow conditions. The horizontal plate showed good performance in

reducing the scale of local scouring. The length of horizontal plate affects the magnitude of vortices

and the maximum scoured depth.

Flow pattern in the case of Q=0.045m3/sec obtained from the numerical simulation

Flow pattern in the case of Q4=0.045m3/sec with horizontal plate located 0.05m and 0.23m

Countermeasures of Reduceing Wave Overtopping at Joint Corner

Between Upright Seawall and Flare Shaped Seawall

(Keisuke MURAKAMI, Daisuke MAKI, Naoto TAKEHANA, Naoya

SUGIMOTO and Ryoya SUYAMA)

This study investigated an application of wave dissipating blocks to reduce the wave overtopping at

a joint corner between upright seawall and flare shaped seawall. A series of hydraulic experiments

were conducted with using a plane basin to clear the effect of wave dissipating blocks on reducing

wave overtopping at the joint corner. Furthermore, this study investigated the possibility of applying

a partition wall, which is installed on the face of the flare shaped seawall, to reduce the wave

overtopping instead of the application of wave dissipating blocks. The partition wall reduced the

wave overtopping at the joint corner in the case of small incident wave angle. In the case of larger

incident wave angle, wave dissipating blocks installed on the both side of the joint corner effectively

reduced the wave overtopping.

Experimental configurations

Snapshot of wave action at the joint corner

Amplifying Characteristic of Wave Activated Pump and Applicability of

Mathematical Model for Its Evaluation

(Keisuke MURAKAMI, Toshiki GOTO and Daisuke MAKI)

This study investigates the amplifying characteristic of a wave activated pump through a series of

hydraulic experiments. The wave activated pump consists of a row of columns that are set in front of

a vertical wall. This study confirms that the wave motion in the pump is effectively amplified under

irregular wave conditions as well as regular wave conditions. The magnitude of a maximum

amplification factor depends on a distance between a seabed and the bottom end of the column. A

mathematical model is also proposed to evaluate the amplifying characteristic of the wave activated

pump. The model estimates the maximum amplification factor and a resonance period in good

accuracy.

Amplification characters of wave activated pump

Agreements of analytical model on the estimation of hydraulic characters of wave activated pump

Study on subjects extracted from grassroots action for Tsunami evacuation

- Case study on Noshima and Uchiumi district in Miyazaki city –

(Keisuke MURAKAMI, Shota MAEBARA and Ayaka MURABE)

Coastal area on eastern Kyushu are vulnerable against huge tsunami disasters caused by Nankai

trough earthquake as well as Hyuganada earthquake. In order to secure lives from those huge

tsunami disasters, it is important to establish an early evacuation system. Noshima and Uchiumi

district, a small fishing village in Miyazaki city, were trying to work out the selection of appropriate

evacuation places by themselves to realize the early evacuation. After the selection of tsunami

evacuation places, the local government decided to maintenance some evacuation routes. This

grassroots action is one of the preferable combinations between mutual help, self-help and public

help. This study summarizes the grassroots action on selecting the appropriate tsunami evacuation

places in Noshia and Uchiumi district. Furthermore, the study reveals some subjects extracted from

this grassroots action.

一次避難場所の配置と想定浸水域 GISによる避難困難エリアの抽出

内海地区

野島地区

N-A

N-B

U-A

U-B

U-CU-EU-D

国道220号

巾着島

野島漁港

内海漁港