Tsunami Breakwater Research Articles

EFFECT OF OVERFLOW NAPPE NON-AERATION ON TSUNAMI BREAKWATER FAILURE

Sliding force and punching pressure were contributing factors to widespread breakwater damage caused during the 2011 Great East Japan Tsunami (Takagi and Bricker, 2015), and were dominant factors causing displacement of caissons from the world’s deepest breakwater: the Kamaishi bay-mouth composite tsunami breakwater (Arikawa et al., 2012; Bricker et al., 2013). The current study focuses on understanding the physics necessary to correctly model the problem of breakwater over-topping by tsunami. To effectively model the physical behavior of the system, scaled model studies were carried out by Mudiyanselage (2017). The earlier numerical investigations carried out by Bricker et al. (2013) and Mudiyanselage (2017), did not prove conclusive to numerically model tsunami breakwater overflow using OpenFOAM employing a 2-D modeling approach. This was shown to be a major hurdle in prediction of the sliding force on the caisson due to the inability of modeling the non-aerated overflow jet over the caisson. Validation of the numerical model would allow parametric study of the flow physics for varying overflow conditions. As a result, a threefold approach of experimental model, analytical model, and numerical model studies was proposed. To achieve sufficient reliability and have complete flexibility, OpenFOAM was chosen for the numerical setup. This numerical model was used to validate the experiments carried out by Mudiyanselage (2017). The numerical model validates and reproduces the flow physics very well. Overall, the numerical results indicate that non-aeration could provide about 8-19% additional force. It was observed that the force on the caisson has a periodic fluctuating behavior. Additionally, the aeration mechanism and overflow jet breakup during the flow was also investigated. It was observed that the highly 3-dimensional behavior of the overflow jet results in the aeration of the cavity underneath the jet. This also explains why the previous studies Bricker et al. (2013) and Mudiyanselage (2017) failed to correctly model the overflow jet using a 2-D modeling approach.

DEVELOPMENT OF MULTISCALE MULTIPHYSICS INTEGRATED SIMULATOR FOR TSUNAMI RUNUP CALCULATION COUPLED WITH STRUCTURE ANALYSIS

The 2011 Great East Japan Earthquake (GEJE) has shown that Tsunami disasters not only cause flooding damage but also can be a phenomenon accompanied by many damage of structures. In order to evaluate the damage of the building due to the tsunami, a three dimensional numerical tank with structure analysis is required, but the calculation cost is very high to calculate from the tsunami source of the tsunami to the inundation zone. Therefore, the purpose of this research is to develop a system that can calculate the destruction of buildings from a wave source of the tsunami in a series and confirm its validity. Specifically, the stability of Tsunami breakwaters in Kamaishi Bay and the seawalls in Otsuchi Bay was investigated.

Multiscale coupled three-dimensional model analysis of the tsunami flow characteristics around the Kamaishi Bay offshore breakwater and comparisons to a shallow water model

ABSTRACTA two-way coupled two-dimensional (2DH) shallow water to three-dimensional (3D) Navier–Stokes equation model, named 2-way Coupled Long Wave to Navier–Stokes 3D (2CLOWNS-3D), is applied to the 2011 Tohoku-oki Earthquake Tsunami in Kamaishi Bay, Japan. 2CLOWNS-3D simulates the entire evolution of the tsunami from its source to inundation at the coast, in which the 3D model component is used to model the flow through the submerged opening of a large-scale offshore tsunami breakwater. 2CLOWNS-3D is compared with a 2DH model simulation in order to identify where it becomes beneficial. It is found that flow rates through the submerged breakwater opening, and thus the resulting inundation heights, are similar between 2DH and 2CLOWNS-3D model simulations when an appropriate momentum dispersion coefficient is applied to the former. However, significant differences between the model simulations are identified in relation to; hydrodynamic forces acting on the submerged caissons, velocities in the large-scale jet structure emanating from the breakwater, and bed shear stresses in the vicinity of the breakwater. Furthermore, the characteristics of the large-scale jet structure simulated by the 3D model are reasonable when employing the realizable k-ε turbulence closure. Our results demonstrate the practical merit of 2CLOWNS-3D for simulating complex geophysical scale flows.

The Value of Local Wisdom Smong in Tsunami Disaster Mitigation in Simeulue Regency, Aceh Province

When tsunami occurred in 26th December 2004, the number of people who died in Aceh Province land were 300.000 people whereas in Simeulue only 7 people who died. It is supposed that there is local wisdom in Simeulue community. The study is aimed to reveal the form of local wisdom smong in Simeulue community. The verification qualitative approach is used to test the ability descriptively. Data collection technique used in-depth interview, participatory observation, documentary study and literature study. Data analysis technique used Delphi method. The result of study showed that the local wisdom smong is tsunami early warning system which is implemented by Simeulue community through manafi-nafi (folkfore), mananga-nanga (cradlesong to lull a baby to sleep), and nandong (humming). Besides, morphology and the land use very support the mitigation toward tsunami. The people who live behind the hill are protected by lush vegetation as tsunami breakwater. The local wisdom smong is socialized through appeal information boards and songs included in UKM products which much consumed by community. All these ways become effective in increasing the community’s knowledge of tsunami disaster mitigation. The government consistency to socialize smong need to be intensified to young generation in order that the local wisdom smong is not disappeared in Simeulue community.

1314 美観を備えた新型津波防波堤の波高軽減効果(GS1-3 熱工学・流体工学)

1314 美観を備えた新型津波防波堤の波高軽減効果(GS1-3 熱工学・流体工学)

湾口防波堤の多重配置による津波高さの低減効果について

湾口防波堤の多重配置による津波高さの低減効果について

Overview of the 2011 Tohoku Earthquake Tsunami Damage and Its Relation to Coastal Protection along the Sanriku Coast

At 14:46 local time on 11 March 2011, a magnitude 9.0 earthquake occurred off the coast of northeast Japan. The very large local tsunami heights and damage to coastal structures and other civil infrastructure were strongly dependent on the location. To verify the effectiveness of several types of tsunami protection strategies, we analyzed three typical areas from the Sanriku ria coast. Detailed survey data are shown with photographs and are discussed with regard to severity of damage and tsunami event. The roles of offshore tsunami breakwaters and coastal forests are discussed for severe tsunami, which exceeds 10 m near the coast. The survey observations and results from numerical calculations clearly indicate the reduction of tsunami damage due to an offshore barrier in Kamaishi Bay.

大船渡湾口津波防波堤の効果に及ぼす開口部3次元形状の影響について

The well-known destructive tsunami triggered by 2011 great Tohoku earthquake in East Japan has shown that the existing tsunami breakwaters are not enough to prevent big tsunamis. Some breakwaters were completely collapsed by earthquakes or tsunamis. It was found out that, even though in the intact condition from the tsunami attack, the existing tsunami breakwaters were insufficient for sheltering corresponding harbor and coastal areas, typically in Ofunato Bay. In order to solve the tsunami disaster problem, the control function of tsunami breakwaters was revised and improved as compared to the previous one. Especially, the 3-D structure of the opening mouth of tsunami breakwater is a major point of this study.

RESEARCH ON STABILITY OF OPENING SECTION AT BAYMOUTH BREAKWATER

The baymouth breakwater is to protect the port area from tsunami. It narrows the bay mouth and prevents tsunami from flowing in the port area. A submerged breakwater is built at the central opening section of the baymouth breakwater (Tsunami breakwater) to close the bay mouth as much as possible. Because of narrowness, it is expected strong current is generated at the opening section of the breakwater when tsunami occurs. The purpose of this study is to examine the stability of the opening of the breakwater on the basis of the result of numerical wave tank. Thus, conducting the experiments of the stability of the opening of the breakwater in large flume confirms the validity of results of calculations.

CASE STUDIES OF TSUNAMI CONSIDERING WITH TIME LAG OF FAULTS RUPTURE IN EASTERN JAPAN SEA

The 2011 tohoku earthquake tsunami inflicted catastrophe on Tohoku region in Japan. Magnitude of the tsunami exceeded design conditions of tsunami breakwater, seawalls and so on. A difficulty of fixing a design tsunami was re-recognized from the view point of disaster prevention. Of course, since total faults rupture scale was huge, the tsunami became so large that we were not able to anticipate in advance. Seismic researchers, that analyzed the 2011 tohoku earthquake, are pointing out that several faults slid with time lag. The faults rupture time lag should be also considered as one of the reason why the tsunami became large. However, even if the parameters of faults rupture could be set in terms of a disaster prevention design, it is so hard to determine faults rupture time lag. Therefore, this paper investigated influence of faults rupture time lag on tsunami height by numerical simulation. Case studies were carried out to evaluate tsunami that was generated two faults with time lag. Two simulation methods were applied. One of them is that tsunami generated by two faults with time lag calculated simultaneously (simultaneous simulation). Another one is a method based on the superposition. Simulation of tsunami caused by each fault is conducted independently. The tsunami profiles from two simulations are added considering with the time lag of faults rupture. This is positioned as a convenient method in order to reduce computational cost. Case studies were performed in Japan Sea and both simulation results were compared at 33 locations. As the results, faults rupture time lag affected tsunami height. And the time lag, makes to occur maximum tsunami height, was different at each location. Finally, it was confirmed that the convenient method based on the superposition could give almost same result as simultaneous simulation.

Transmission of solitary waves through slotted barriers: A laboratory study with analysis by a long wave approximation

Economic and long-term social impacts of tsunami waves, as shown in the 2004 Indian Ocean tsunami, have been devastating. In addition to the passive measures such as the tsunami early warning systems, active protective measures such as tsunami breakwaters and tsunami-resistant buildings are also necessary. Slotted barriers are low cost structures that can be very effective in reducing the transmitted energy of long waves. In this study, the transmission of tsunami waves, with the leading wave being modeled by a solitary wave, through slotted barriers in the form of a row of circular cylinders is studied experimentally. The results are also analyzed by a method based on long wave approximations. It is found that the spacing between two adjacent cylinders is one of the main factors that control the transmission of solitary waves through slotted barriers. Reflection coefficients and the reduction of drag force on coastal structures protected by slotted barriers are also discussed in the paper.

A short history of tsunami research and countermeasures in Japan

The tsunami science and engineering began in Japan, the country the most frequently hit by local and distant tsunamis. The gate to the tsunami science was opened in 1896 by a giant local tsunami of the highest run-up height of 38 m that claimed 22,000 lives. The crucial key was a tide record to conclude that this tsunami was generated by a “tsunami earthquake”. In 1933, the same area was hit again by another giant tsunami. A total system of tsunami disaster mitigation including 10 “hard” and “soft” countermeasures was proposed. Relocation of dwelling houses to high ground was the major countermeasures. The tsunami forecasting began in 1941. In 1960, the Chilean Tsunami damaged the whole Japanese Pacific coast. The height of this tsunami was 5–6 m at most. The countermeasures were the construction of structures including the tsunami breakwater which was the first one in the world. Since the late 1970s, tsunami numerical simulation was developed in Japan and refined to become the UNESCO standard scheme that was transformed to 22 different countries. In 1983, photos and videos of a tsunami in the Japan Sea revealed many faces of tsunami such as soliton fission and edge bores. The 1993 tsunami devastated a town protected by seawalls 4.5 m high. This experience introduced again the idea of comprehensive countermeasures, consisted of defense structure, tsunami-resistant town development and evacuation based on warning.

Application of Three-dimensional Non-hydrostatic Numerical Model to Tsunamis in Coastal Areas

The numerical simulator (STOC) has been developed to estimate tsunami damage on coastal areas in which there are lotsof structures. STOC consists of two sub-models: three-dimensional and non-hydrostatic model (STOC-IC) and multilayerhydrostatic model (STOC-ML). The present model, especially STOC-IC is validated by experiments on flowaround a rectangular weir and tsunamis passing a tsunami breakwater. In addition, applying the combination model of STOC-IC and STOC-ML to tsunami simulation in actual topography of harbor, it confirms that non-hydrostatic phenomenaappear around seawalls and bending section of channels.

大船渡湾における栄養塩の季節変動特性と負荷量の推定

Ofunato bay is highly enclosed because of a tsunami breakwater. Therefore, water quality problems, such as eutrophication and ocean anoxic, have been caused in the inside of the bay. Field observation was carried out to clarify the characteristics of water quality in Ofunato bay in 2003 and 2004. The purpose of this paper is to study the seasonal variation characteristics and the load of nutrients. The amount of inflow of nutrients was calculated using the material balance model using field observation data. It shows that a lot of nutrient is released from sediment when anoxic water has occurred. Unusual increase of phytoplankton was observed when river inflow was increased. They have great effect on water quality.

Experimental Study on Multi-directional Wave Force to Breakwater

A tsunami breakwater is constructed at the mouth of Kamaishi bay, the Iwate prefecture in the northem part of Japan.The caissons have slit members at their fronts.For the design of this type of caissons, it is important to estimate the wave pressure on the members as well as the caisson stability, The present paper experimentally studies on wave pressures of the slit members in a multi-directional wave basin.Compared wave pressures in uni directional wave with that in multi-directional one, the maximum wave pressure on a member becomes much Iager in the uni-directional wave condition.Therefore, the model test in multi-directional sea is important to get a reliable results.

津波防波堤開口部潜堤の耐津波安定性

津波防波堤開口部潜堤の耐津波安定性

On the Function of Tsunami Breakwaters: (Report No. 2)

(1971). On the Function of Tsunami Breakwaters: (Report No. 2) Coastal Engineering in Japan: Vol. 14, No. 1, pp. 63-72.

FODBL STUDY OF TRANSFORMATION OP TSUNAMIS IN URADO BAT

For the city and harbour of Kochi, including Urado Bay, facing the Pacific Ocean, an experimental study has teen carried out on the problem of protection from tsunami disasters, and future harbour planning; that is, dredging, reclamation and construction of breakwaters against tsunamis. A hydraulic model of horizontal scale 1/250 and vertical l/lOO was used according to Froud's similitude. The transformation of the design tsunami m the hay was studied to find the effect of the tsunami breakwaters, dredging and reclamations by use of the model which was able to reproduce the Chilean Tsunami.