Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.2208/jscejoe.78.2_I_865

Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> The estimated height of the tsunami wave in the southern coastal area of Kyushu due to the Nankai trough has been examined by the Kagoshima prefectural government and Miyazaki prefectural government and certain knowledge. However, the time fluctuations of the tsunami water level along the coasts of Miyazaki prefecture, which has shallow topography, and the coasts of Osumi peninsula and Tanegashima in Kagoshima prefecture, have not been sufficiently investigated.</p><p> This study focuses on water level fluctuations when a wide range of active faults move. (1) The relationship between the maximum water level arrival time of the tsunami and the coastal topography in the coastal area was examined. (2) The relationship between the tsunami water level along the Tanegashima coast due to the reflected waves from the Osumi peninsula was clarified. In this study, we found the following. (1) In coastal areas with shallow terrain, the maximum water level is reached in the first incident wave, but in the case of bay terrain, it was found that the maximum arrival time of the tsunami occurs later than the first wave of tsunami. (2) As a result of arranging the main appearance spectra of water level fluctuations along the coast of Shibushi bay, it was confirmed that the water level rises in different major period in the inner part of the bay and the mouth of the bay that depended resonance period of the bay. (3) It was found that there are most of the eastern coast area of Tanegashima occure the maximum water level from the first wave from tsunami, but the western coast area occure the maximum water level that was affected that some reflected waves from the Osumi peninsula.</p>

DOI： 10.2208/kaigan.77.2_I_301

Language：Japanese   Publisher：International Journal of Disaster Risk Reduction  

DOI： 10.1016/j.ijdrr.2021.102511

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> It has been pointed out that the generation of tsunami edge waves propagating in the shore line on the continental shelf is one of the causes of the spread of the disaster areas of the Hokkaido Tokachi-oki Earthquake Tsunami (2003) and the Tohoku-Pacific Ocean Earthquake Tsunami (2011). In 2017, there was a M5.3 earthquake with an epicenter of the central western of Kagoshima bay where no active faults identified.In this paper, we investigated the relationship between fault parameters and tsunami height for the entire Kagoshima Bay using a two dimensional model assuming a direct earthquake occurring in the bay.Next, we investigated the generation of tsunami height and edge waves in the coastal area by reproducing the detailed 3D topography of the coastal area in the central western part of the bay and using a 3D computational fluid model. As the results, When the source location and the fault parameters were changed, the maximum wave was the first wave at the offshore measurement point in most cases.At the coastal measurement points, there were several points that satisfied the edge wave dispersion relational expression, and there is a possibility that standing edge waves and progressive edge waves were generated in the central coastal area of the bay.</p>

DOI： 10.2208/kaigan.76.2_I_277

Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> Most main ports in Japan have established their Port Business Continuity Plan (Port-BCP) in case a supposing natural disaster might draw functional disorder in the port. The objectives of Port-BCP are to maintain the minimum vital activities such as transporting emergency supply, and to resume its functions within the allowable period. The existing plans, however, only focus on earthquake or tsunami disasters as the natural exerting force, but fail to consider volcanic disasters. For Kagoshima Port, which locates only 10km apart from the crater of Sakurajima volcano, developing the Port-BCP preparing for a future large-scale explosive eruption is indispensable. This study proposes a numerical model of advection-diffusion-sedimentation of tephra flows to estimate the amounts of deposited volumes fallen in water basin of Kagoshima Bay, and as well as proposes hydrodynamic models to simulate drifting and landing of the fallen tephra under the tidal motions in the basin. As the results, the following tephra deposit characteristics are found; the deposited area of the pumice becomes narrower than that of ash due to the large fall velocity, the width of deposit areas decreases as the wind velocity increases due to the predominance of advection over diffusion, the maximum volume of tephra deposition in the basin occurs under north wind condition because of the relative location of Sakurajima to the basin.</p>

DOI： 10.2208/kaigan.76.2_I_1321

Language：Japanese   Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

Scopus

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.2208/kaigan.75.I_31

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.2208/kaigan.75.I_37

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> In Ibusuki port coast, a coastal improvement project is in progress applying the idea of integrated shore protection system combining several coastal works and beach nourishment. For the construction of these works, the local groundwater environment system named as "natural sand-steaming hot spring" should be carefully conserved, because that is an important tourism resource in the region. This study intends to evaluate the impact on the hot-spring groundwater system by the beach nourishment work. In this purpose, we conducted in-situ field measurements to monitor the variations of the groundwater levels and sand temperature in the sandy beach by placing test nourishment sands.</p><p> The results show that any significant effects have not been obtained in the areas behind the seawall and neighboring region of the nourishment, whereas, the marked risings in groundwater level and sand temperature have been observed in the beach nourishment area.</p>

DOI： 10.2208/kaigan.75.I_37

Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> Sand steam hot spring using underground hot spring water has been used for a long time on the sandy beach of Ibusuki coast of Ibusuki city, Kagoshima prefecture. In recent years, a coastal maintenance project has been implemented in this coastal area. Therefore, detailed on-site observation has carried out about the effusion of underground hot spring water. In this paper, we developed a multiphase flow solver that adds a calculation term to reproduce flow and temperature fields in porous media. Then, we examined the influence of the tide level on the temperature in the sandy beach and the effusion of the hot spring water. As a result, it was possible to reproduce the phenomenon that the temperature field in the sandy beach fluctuate greatly with the tide level fluctuation. And we clarified the phenomenon that the vertical upward flow was always generated at the shoreline position at the time of the low tide.</p>

DOI： 10.2208/kaigan.75.I_31

Language：Japanese   Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

Scopus

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.2208/kaigan.74.I_85

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：土木学会西部支部  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：土木学会西部支部  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：土木学会西部支部  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：土木学会西部支部  

Language：Japanese   Publisher：Japan Society of Civil Engineers  

&nbsp;Conventionally, for the estimation of a wave pressure to a structure by a tsunami, a method assuming hydrostatic pressure has been proposed. The method is adopted as a design guideline for the tsunami evacuation building. However, the method was targeted to the wall surface of a single structure. Verification under the condition that a plurality of structures are arranged is not sufficient. From this background, this study covers regularly arranged cylinder groups. The relationship between the installation interval of the cylinder, the generated wave pressure and the specific energy was studied by numerical calculation and model experiment. As a result, it was found that the wave pressure characteristics to the cylinder in the grid-arranged column group are strongly influenced by the lattice spacing.

DOI： 10.2208/kaigan.74.I_259

Language：Japanese   Publisher：Japan Society of Civil Engineers  

&nbsp;In Ibusuki port coast, a coastal improvement project is in progress applying the idea of integrated shore protection system combining jetties, offshore breakwaters, seawalls and beach nourishment. For the construction of these works, the local environment of the hot spring groundwater system named as &ldquo;natural sand-steaming hot spring&rdquo; should be carefully conserved, because that is an important tourism resource in the region. This study intends to estimate the impact of the beach nourishment on the hot spring groundwater. Comprehensive field observations continued for four seasonal periods on the groundwater levels and temperatures have been conducted to understand their fluctuating characteristics under the tidal motions. From the observation results of the groundwater levels and temperatures, their horizontal, vertical and temporal variations have been analyzed. The characteristic behaviors of the groundwater flows, such as a cold seawater mass penetrates into the hot groundwater flows during flood tide, a hot water mass seeps out on the surface of the sandy beach during ebb tide, have been confirmed.

DOI： 10.2208/kaigan.74.I_85

Language：Japanese   Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

Scopus

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：土木学会  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：公益法人土木学会西部支部  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：公益法人土木学会西部支部  

Language：Japanese   Publisher：Japan Society of Civil Engineers  

&nbsp;This study investigates characteristic changes of edge waves by a topographic obstacle like a cape experimentally and numerically. The experiments were conducted in a small wave tank with setting a step-type shelf to measure two dimensional water surface fluctuations. The dispersion relationships and on-offshore wave heights of the edge wave components are found to be consistent with those described by the edge wave theory. In the numerical analysis where a concentric circle topography for the shoreline and shelf edge was set, characteristics of edge wave propagation and on-offshore distributions of edge wave height were analyzed. These results are found to reproduce the characteristics expressed by the edge wave theory. The characteristic changes of edge wave celerity and plane wave height distribution by a topographic obstacle are discussed based on the experimental and numerical results by changing experimental conditions and dimension of a model obstacle systematically.

DOI： 10.2208/kaigan.73.I_169

Language：Japanese   Publisher：Japan Society of Civil Engineers  

&nbsp;In the 2011 Tohoku tsunami, coastal urban areas were widely damaged by its huge hydrodynamic forces. However we have not fully revealed the huge tsunami hydrodynamic force acting on the structures. This is due to insufficient understanding on the relationships tsunami surge heights and shape of structure. When a huge tsunami strikes a uprigth structure, the tip of the tsunami runs vertically up the front face of the structure; herein, this phenomenon is called the tsunami jet flow. In response to the above background, this study aimes to improve the reproducibility of the tsunami water level fluctuation, by introduce dynamic contact angle to VOF model. It is found that the present model has certain accuracy on the reproducibility of the tsunami water level fluctuation.

DOI： 10.2208/kaigan.73.I_889

Language：Japanese   Publisher：Japan Society of Civil Engineers  

&nbsp;In the 2011 Tohoku tsunami, the number of oil tanks in petrochemical complexes along the coast were damaged by its huge hydrodynamic forces. The detailed mechanism how the tsunami force acts on a specific point or specific member of the grouped tanks has not been sufficiently clarified. The aim of this study is to investigate hydrodynamic tsunami forces acting on oil tanks arranged in a grid system. The possibilities that the hydrodynamic pressure inside the grouped tanks become greater than that acting on a single tank are revealed, and the characteristics of the pressures are found to be depending on the position and arrangement of the grouped tanks. It is also noted that the starting time of water level rise is much affected by the spacing conditions of the tank arrangement.

DOI： 10.2208/jscejoe.73.I_90

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：日本自然災害学会  

Language：English   Publishing type：Research paper (scientific journal)  

This study applied an extreme learning machine to produce rapid forecasts of tsunami waveforms in coastal areas using tsunami signals recorded at specified locations. The remarkable training speed of the algorithm means that it can run in real-time, and therefore it is suitable for early warning systems in near-field tsunami events. Additionally, as a universal function approximator, the proposed method can capture nonlinearities exhibited by the tsunami. Therefore, it provides advantages over the standard inversion analysis used in many existing studies, which is typically developed under a linear assumption. We applied the proposed method to the 2011 Tohoku earthquake tsunami. Our results demonstrate that the proposed method is more accurate and does not significantly increase the computing time, when compared with the standard method. Furthermore, our model uncertainty analysis proves that the method is robust and reliable, despite its dependency on the random input weights and biases (the forecasts from several consecutive runs showed insignificant variability).

Other Link： http://www.sciencedirect.com/science/article/pii/S0378383915002070

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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