研究者詳細 - 中村　友昭

論文 - 中村　友昭

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地盤内部の応力変動の影響を考慮した漂砂量式を用いた遡上津波による地形変化シミュレーション査読有り

中村友昭，水谷法美

海洋開発論文集 24 巻頁： 57-62 2008年7月

Tsunami scour around a square structure 査読有り

Nakamura, T., Kuramitsu, Y., and Mizutani, N.

Coastal Engineering Journal, JSCE 50 巻 ( 2 ) 頁： 209-246 2008年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Tsunami-induced local scour around a land-based square structure on a sand foundation was investigated with laboratory experiments and numerical simulations. The laboratory experiments revealed that a scour hole at the seaward corner of the structure could be reproduced and the maximum scour depth was affected by the relative tsunami wave height and embedded depth of the structure. It was also found with the numerical simulations that a scour hole around the seaward corner of the structure could be evaluated with not only flow velocities but also effective stresses because restricting force between sand particles decreased with the effective stresses.

Tsunami-induced local scour around a square structure 査読有り

Nakamura, T., Kuramitsu, Y., and Mizutani, N.

Proc., Solutions to Coastal Disasters 2008, ASCE 頁： 106-117 2008年4月

担当区分：筆頭著者記述言語：英語

Tsunami-induced local scour around a land-based structure with a square cross-section on a sand foundation was investigated with both laboratory experiments and numerical simulations. An isolated long wave was adopted as an incident tsunami wave. In the hydraulic model experiments, it was found that the maximum scour depth at the seaward corner of the structure was sensitive to the relative overtopping height of the tsunami wave. In the numerical simulations, it was revealed that the local scour around the seaward corner of the structure could be evaluated with not only flow velocities on the foundation but also effective stresses near the surface of the foundation because restricting force between sand particles declined due to a decrease in the effective stresses.

Effects of pore water pressure on scour - in case of local scour due to runup tsunami -

Nakamura, T., Mizutani, N., and Kuramitsu, Y.

Proc., Geomorphological Comparative Research on Natural Disaster Mitigation in the Coastal Regions of Tropical Asia 頁： 165-172 2007年11月

担当区分：筆頭著者記述言語：英語

Large-scale sediment transport due to the 2004 Indian Ocean Tsunami resulted in substantial erosion and scour around many structures. In this paper, we investigated tsunami-induced local scour around a land-based structure with a square cross-section on a sand foundation with both hydraulic model experiments and numerical simulations capable of computing interactions between tsunami waves and sand beds composed of nonlinear materials. In the hydraulic model experiments, we found that local scour holes around the seaward corner of the structure could be reproduced, and the maximum final scour depth at the seaward corner of the structure was sensitive to the relative incident tsunami wave height and the relative embedded depth of the structure. In the numerical simulations, we revealed that the tsunami-induced local scour around the seaward corner of the structure could be evaluated with not only flow velocity on the sand foundation but also effective stress inside the surface layer of the foundation because the effective stress acting on the foundation significantly affected restricting force between sand particles.

遡上津波による陸上構造物周辺の局所洗掘に関する研究査読有り

中村友昭，倉光泰樹，水谷法美

海岸工学論文集 54 巻頁： 856-860 2007年11月

Three-dimensional numerical analysis on runup tsunami deformation around containers on an apron and tsunami-induced wave pressure acting on the containers 査読有り

Nakamura, T., Shiraishi, K., Usami, A., Mizutani, N., Miyajima, S., and Tomita, T.

Proc., Asian and Pacific Coasts 2007 頁： 865-879 2007年9月

担当区分：筆頭著者記述言語：英語

Many drifting debris resulted from a series of devastating tsunamis triggered by the Sumatra-Andaman earthquake. In recent years, a huge demand for container ships leads to the increase in containers piled up on an apron. Once such a huge tsunami strikes a port area, it is possible that drifting containers cause severe destructions of port facilities. In this study, runup tsunami deformation around containers fixed on an apron is investigated with a three-dimensional numerical simulation. It is consequently revealed that an upper limit of maximum wave pressure acting on the containers due to a runup tsunami wave is evaluated with maximum runup height in front of the containers, assuming a hydrostatic condition.

Local scour around a square structure due to runup tsunami 査読有り

Nakamura, T., Mizutani, N., and Kuramitsu, Y.

Proc., Coastal Structures 2007, ASCE 頁： 1891-1902 2007年7月

担当区分：筆頭著者記述言語：英語

On December 26, 2004, a series of lethal tsunamis caused by the Sumatra-Andaman earthquake struck the coastal areas of many countries along the Indian Ocean, resulting in substantial erosion and scour around coastal structures due to large-scale sediment transport. In this study, local scour due to a runup tsunami wave around a land-based square structure was investigated with both hydraulic model experiments and numerical simulations. As a result, the hydraulic model experiments revealed that the deepest scour hole was located near the seaward corner of the structure, and the maximum scour depth was affected by the relative incident tsunami wave height and the relative embedded depth of the structure. From the numerical simulations, it was also found that the local scour around the seaward corner of the structure resulted from flow velocities on a reclaimed beach during restricting force between sand particles fell down due to a decrease in effective stresses inside the sand at the seaward corner of the structure.

Tsunami wave force and its estimation method - forces on a rectangular body -

Mizutani, N., Nakamura, T., and Usami, A.

Proc., INDO-JAPAN Workshop on Coastal Problems and Mitigation Measures - Including the Effect of Tsunami 頁： 135-145 2007年7月

Sand suction mechanism in artificial beach composed of rubble mound breakwater and reclaimed sand area 査読有り

Hur, D.-S., Nakamura, T., and Mizutani, N.

Ocean Engineering 34 巻 ( 8-9 ) 頁： 1104-1119 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

An artificial beach has been constructed compensating for losing of the natural one caused by the development of coastal area. In this paper, the hydraulic model tests are carried out to investigate the suction phenomenon on the artificial beach constituted of rubble mound breakwater with gravel and the reclaimed sand area. In addition, the numerical model for waves, structures and seabed interaction as well as the numerical method based on the u-p approximation of the Biot equations is developed for investigation of suction mechanism. After verification of the numerical models by comparing numerical results with experimental data, the numerical models are further used to clarify the detailed suction mechanism of the reclaimed sand. The factors that affect the suction phenomenon are examined experimentally and their critical values are presented. Also, it can be pointed out that the vertical discharge velocity as well as the volumetric strain around the still water level of the boundary between the breakwater and the beach gets up to the critical value, the reclaimed sand starts to flow out to the offshore, and it finally leads to caves and cave-ins in the reclaimed zone.

陸上遡上津波による矩形構造物周辺の洗掘と地盤の応力変動に関する研究査読有り

中村友昭，倉光泰樹，水谷法美

海岸工学論文集 53 巻頁： 521-525 2006年11月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（学術雑誌）

スマトラ島沖地震に伴う大津波によりインド洋沿岸の国々で陸上構造物の周囲に大規模な洗掘が生じた事例が報告されている．このような津波による洗掘は定常流や周期波による洗掘とその発生機構が異なると推測されることから，現在までに護岸や円柱を対象に局所洗掘に対する検討がなされてきたが，陸上遡上津波による陸上構造物周辺の洗掘を検討した研究は極めて少ない．本論では，港湾構造物を模した矩形の陸上構造物を取り扱い，水理模型実験と数値計算により陸上遡上津波による構造物周辺の洗掘を検討した．その結果，地盤表面の流速だけでなく地盤内部の応力状態も構造物沖側隅角部の洗掘に影響を与えている可能性があることが明らかになった．

護岸背後の地盤の陥没現象と裏込土砂の流出発生限界に関する研究査読有り

中村友昭，許　東秀，水谷法美

海岸工学論文集 53 巻頁： 836-840 2006年11月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（学術雑誌）

裏込土砂の流出により海岸護岸背後の舗装路面の下に空洞が形成され，床版の落下に到った事例が過去に報告されている．この原因として考えられている堤体背後の裏込土砂の流出に関して，現在までに海岸堤防や矢板式護岸を対象に検討が行われているが，重力式護岸を取り扱った研究は極めて少ない．本研究では，実際に土砂流出に伴う護岸背後の陥没が確認された重力式直立型護岸を取り扱い，護岸下部の目地からの土砂流出機構を水理模型実験と数値計算により考究した．その結果，護岸下部の土砂内部に生じる体積ひずみとそのすぐ沖側に生じる沖向き流速の増加に伴い裏込土砂の流出が生じやすくなる傾向が明らかになった．

Tsunami wave force and its estimation method - forces on a rectangular body -

Mizutani, N. and Nakamura, T.

Proc., Geomorphological Comparative Research on Natural Disaster Mitigation in the Coastal Regions of Tropical Asia 頁： 25-31 2006年8月

記述言語：英語

Wave force due to run-up tsunami is investigated in this paper. Laboratory experiments have been conducted to measure wave pressure and forces on a rectangular body. Numerical simulation has also performed to compute deformation of tsunami on apron and resultant wave pressure and wave forces on the body. Present numerical simulation method has been shown to have excellent performance in simulating wave deformation and wave forces. Moreover, a simple estimation method of the wave force has been proposed in this study.

Three-dimensional numerical analysis on tsunami deformation due to container on apron and tsunami-induced wave pressure acting on container

Nakamura, T., Shiraishi, K., Usami, A., and Mizutani, N.

Proc., 8th International Summer Symposium, JSCE 頁： 107-110 2006年7月

エプロン上のコンテナに作用する津波の流動場と波圧及び津波力に関する3次元数値解析査読有り

中村友昭，白石和睦，宇佐美敦浩，水谷法美，宮島正悟，富田孝史

海洋開発論文集 22 巻頁： 517-522 2006年7月

捨石護岸背後の埋立土砂の吸い出し機構査読有り

中村友昭，許　東秀，水谷法美

土木学会論文集B 62 巻 ( 1 ) 頁： 150-162 2006年3月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（学術雑誌）

捨石護岸の背後に設置した埋立土砂が海域へ流出する吸い出し現象を取り扱い，水理模型実験と新たに開発した波動場および地盤の数値計算手法を用いて捨石護岸背後からの埋立土砂の吸い出し機構を考究した．その結果，土砂吸い出しは静水深での捨石護岸の幅と入射波の波長の比とアーセル数の影響を強く受けること，埋立海浜の前面に生じる直立型捨石護岸内部の鉛直方向流速が限界値に達し，さらに捨石護岸近傍の静水面付近にある埋立海浜内部に生じる体積ひずみが増加することで土砂吸い出しが生じることを明らかにした．加えて，吸い出し防止工法の一つであるフィルター工法の設置は捨石護岸内部の流速場や埋立海浜内部のひずみ場の観点からも有効な手法であることが明らかとなった．

波動場・地盤連成数値計算手法に基づく埋立土砂の吸い出し機構に関する研究査読有り

中村友昭，許　東秀，水谷法美

海岸工学論文集 52 巻頁： 836-840 2005年11月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（学術雑誌）

本研究では，捨石護岸の背後に設置した埋立土砂が海域へ流出する吸い出し現象を取り扱い，新たに開発した波動場と地盤に対する数値計算手法により直立型捨石護岸背後からの埋立土砂の吸い出し機構を考究した．その結果，埋立海浜の前面に生じる捨石護岸内部の流速の鉛直方向成分が限界値に達し，さらに捨石護岸近傍の静水面付近にある埋立土砂内部に生じる体積ひずみが増加することにより埋立土砂の吸い出しが生じることを明らかにした．加えて，波動場と地盤に対する新たな数値計算手法の妥当性や吸い出し防止工法としてのフィルター工法の有効性を確認した．

Experimental study on suction mechanism of reclaimed area behind a rubble mound breakwater 査読有り

Hur, D.-S., Nakamura, T., Mizutani, N., and Iwata, K.

Proc., Asian and Pacific Coasts 2005 頁： 847-856 2005年9月

記述言語：英語

Suction mechanism of reclaimed sand behind a rubble mound breakwater, which has never been studied so far, is investigated with two-dimensional hydraulic model experiments. Two types of breakwater are adopted: an inclined rubble mound breakwater and an upright rubble mound breakwater. It is consequently revealed in the laboratory experiment that cave-ins and caves, which are quite similar to ones observed in the field, can be reproduced, and the Ursell parameter and the relative breakwater width have significant effects on sand suction. In addition, it is necessary that filters and/or geotextile sheets are installed for the prevention of sand suction accidents.

捨石護岸背後の埋立土砂吸い出し機構に関する研究査読有り

許　東秀，中村友昭，岩田好一朗

海岸工学論文集 51 巻頁： 791-795 2004年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）

近年，人工海浜土砂の吸い出し現象が注目を集めている．本研究では，従来あまり検討されていない捨石護岸を取り扱い，水理模型実験と数値計算により，埋立土砂吸い出し現象や吸い出し機構を捨石護岸および埋立土砂内部の流速場と関連づけて考察した．その結果，土砂吸い出しは背後土砂内に生じる沖向き流速の影響を強く受け，ある限界流速に達すると土砂吸い出しが生じやすくなり，最終的に埋立土砂のくぼみや陥没の発生に到ることを明らかにした．加えて，現地と類似した埋立海浜のくぼみや陥没を水理実験で再現できたこと，アーセル数は土砂吸い出しに大きな影響を及ぼすこと，線形・非線形抵抗を考慮した数値計算手法の妥当性などが判明した．

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