研究者詳細 - 中村　友昭

論文 - 中村　友昭

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Two-dimensional numerical analysis of wave-induced instability of artificial shallow composed of dredged soil 査読有り

Nakamura, T., Ishihara, R., and Mizutani, N.

Proc., Coastal Structures 2011, ASCE 頁： 12 2011年9月

A nonlinear three-dimensional coupled fluid-sediment interaction model for large seabed deformation 査読有り

Nakamura, T. and Yim, S. C.

Journal of Offshore Mechanics and Arctic Engineering, ASME 133 巻 ( 3 ) 頁： 14 2011年8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）

A nonlinear three-dimensional two-way coupled fluid-sediment interaction model is developed in this study. The model is composed of a generalized Navier-Stokes solver (GNS) with a volume of fluid module for air-water interface tracking and a sediment transport module (STM) for fluid-sediment interface tracking. The GNS model is based on the finite difference method with a turbulent stress model of large-eddy simulation to compute incompressible viscous multiphase flows. The STM is used to compute nonlinear sediment bed profile change due to bed-load sediment transport. A two-way coupling scheme connecting GNS with STM is implemented at each time step to ensure the fluid-sediment interaction. For validation, the fluid-sediment interaction model is applied to predict cross-shore profile change of a sloping beach due to breaking solitary waves, and the resulting predictions are examined and compared with the measured data from a set of hydraulic tests. It is found that the fluid-sediment interaction model predicts reasonably well the sediment transport and the resulting beach profile change. The sensitivity of model parameters involving the sediment transport to the beach profile change is analyzed. Finally, the fluid-sediment interaction model is applied to predict local scour in front of a quay wall due to a jet flow to demonstrate its applicability to general threedimensional problems.

Three-dimensional coupled fluid-sediment interaction numerical model for suspended sediment analysis 査読有り

Nakamura, T. and Mizutani, N.

Proc., 21th International Offshore and Polar Engineering Conference 頁： 1032-1039 2011年6月

担当区分：筆頭著者記述言語：英語

A three-dimensional two-way coupled fluid-sediment interaction model applicable to suspended sediment analysis is developed in this study. For validation, the developed model is applied to hydraulic experiments on suspended sediment in a steady uniform flow and a swash zone. For both flow conditions, the predictive capability of the developed model is demonstrated against experimental data in terms of time-averaged suspended sediment concentration. Numerical results for the swash zone show that complex suspended sediment transport relates with three-dimensional vortex motion due to plunging breaking waves, and demonstrate the usefulness of the developed model in investigating suspended sediment transport under breaking waves.

Field survey for 2010 Chilean earthquake and tsunami disaster in ports and coasts 査読有り

Takahashi, S., Sugano, T., Tomita, T., Arikawa, T., Tatsumi, D., Kashima, H.,Murata, S., Matsuoka, Y., and Nakamura, T.

Proc., 8th International Conference on Urban Earthquake Engineering 頁： 8 2011年3月

Three-dimensional numerical analysis of jet-induced local scouring in front of quay walls and its countermeasure using filter units 査読有り

Nakamura, T., Shinoda, Y., Mizutani, N., and Koyama, H.

Coastal Engineering Journal, JSCE 53 巻 ( 1 ) 頁： 41-62 2011年3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）

A bow thruster mounted in the bow of a vessel is generally used to improve its maneuverability in ports. When a bow thruster is used near a berth, a jet generated from the bow thruster can cause sediment transport, resulting in local scouring of the seabed in front of quay walls. Countermeasures against such scouring are essential to ensure the stability of the quay walls. In recent years, new protective units called filter units have been used to protect seawalls and river dikes. However, it remains to be determined whether filter units covering the seabed in front of quay walls are effective in preventing jet-induced local scouring. In this study, jet-induced local scouring in front of a quay wall and its countermeasure using filter units are investigated using a three-dimensional two-way coupled fluid-sediment interaction model. The predictive capability of the three-dimensional coupled model is verified against experimental data in terms of average jet flow velocity, pore-water pressure, and the final seabed profile. The results show that the filter units covering the seabed prevent negative effective stress fluctuations on the surface layer of the seabed, and demonstrate the effectiveness of the countermeasure using the filter units.

三次元流体・構造・地形変化連成数値計算モデルの開発と没水物体周辺の洗掘現象への適用査読有り

中村友昭，Solomon C. Yim，水谷法美

土木学会論文集B（海岸工学） 57 巻頁： 406-410 2010年11月

波浪による水圧変動を考慮した人工浅場表層土砂の安定性に関する三次元数値解析査読有り

中村友昭，篠田陽介，水谷法美

土木学会論文集B（海岸工学） 57 巻頁： 911-915 2010年11月

Three-dimensional numerical analysis on deformation of run-up tsunami and tsunami force acting on square structures 査読有り

Nakamura, T., Mizutani, N., and Fujima, K.

Proc., International Conference on Coastal Engineering, ASCE 32 巻頁： 10 2010年7月

担当区分：筆頭著者記述言語：英語

A three-dimensional two-way coupled fluid-sediment interaction model (FSM) is applied to investigate run-up tsunami deformation and tsunami force acting on square structures on land. The FSM consists of a generalized Navier-Stokes solver (GNS) for multi-phase flow including porous flow, a volume of fluid module (VFM) for air-water interface tracking, and a sediment transport module (STM) for fluid-sediment interface tracking. In the FSM, a two-way coupling procedure is implemented at each time step to connect the GNS with the VFM and the STM. The predictive capability of the FSM is demonstrated through comparison between numerical results and experimental data in terms of water surface elevation, inundation depth, and tsunami force. The process of tsunami run-up in the presence of square structures is investigated in terms of vortex structures. The result shows that the FSM is a useful tool providing detailed information in discussing run-up tsunami deformation and tsunami force.

Reflection and run-up of tsunami on quay wall and behavior of drifted vessels due to tsunami 査読有り

Mizutani, N., Nakamura, T., and Koike, T.

Proc., International Conference on Coastal Engineering, ASCE 32 巻頁： 10 2010年7月

浚渫土砂により造成される人工浅場の安定性に及ぼす流速変動および水圧変動の影響に関する2次元数値解析査読有り

中村友昭，石原　遼，水谷法美

海洋開発論文集 26 巻頁： 699-704 2010年7月

浮遊砂の移流拡散現象を解析できる三次元連成数値計算モデルの開発とその適用に関する研究査読有り

中村友昭，水谷法美

海洋開発論文集 26 巻頁： 1197-1202 2010年7月

遡上津波の変形と陸上構造物に作用する津波力に関する3次元数値シミュレーション査読有り

中村友昭，水谷法美，藤間功司

ながれ，日本流体力学会 29 巻 ( 2 ) 頁： 107-117 2010年4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）

構造物を複数個設置した陸域への津波の遡上現象と構造物に作用する津波力に関する水理実験を対象に，波動場と地形変化の相互作用を解析できる3次元数値計算モデルを用いて再現計算を行った．その結果，海域での水位変動，陸域での浸水深，構造物への津波力に関する数値計算と水理実験の比較を通じて本モデルの再現性を明らかにした．また，渦芯の抽出により津波の遡上に伴う渦構造の変化を詳細に検討できることを確認した．

Collision analysis of container drifted by runup tsunami using drift collision coupled model 査読有り

Yeom, G.-S., Nakamura, T., and Mizutani, N.

Journal of Disaster Research 4 巻 ( 6 ) 頁： 441-449 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

This study proposes analyzing tsunami generation and propagation of tsunamis, wave runup onto land, object drift, collision with other structures, deformation prediction of colliding and collided-with, and collision force estimation. To reduce calculation load in using the LS-DYNA collision model, we use a drift model using the immersed boundary (IB) method from wave generation to just before collision, and the collision model is used during the collision phase, in which numerical data calculated using the drift model are used as an initial condition of the collision model. Validity of the drift model for wave level, wave force, and drift behavior of a container were verified through comparison with experimental data measured in laboratory experiments. Collision model predictability was also confirmed in terms of drift collision force. Fluid-structure interaction (FSI) between the container and the runup wave is reproduced in numerical drift collision analysis. Through this analysis of a full-scale container based on the international standard with a concrete column, we confirmed the applicability of the collision analysis using the drift simulation as an initial condition for an actual field.

岸壁に作用する局所流による三次元洗掘予測手法の開発と対策工に関する研究査読有り

中村友昭，水谷法美，篠田陽介，小山裕文

土木学会論文集B（海岸工学） 56 巻頁： 486-490 2009年11月

岸壁に入射する津波の反射・遡上特性と小型船舶の打上げ・漂流挙動に関する研究査読有り

水谷法美，小池　竜，中村友昭，子安友加里

土木学会論文集B（海岸工学） 56 巻頁： 841-845 2009年11月

A three-dimensional coupled fluid-sediment interaction model with bed-load/suspended-load transport for scour analysis around a fixed structure 査読有り

Nakamura, T., Mizutani, N., and Yim, S. C.

Journal of Offshore Mechanics and Arctic Engineering, ASME 131 巻 ( 3 ) 頁： 9 2009年8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）

The predictive capability of a three-dimensional (3D) numerical model for sediment transport and resulting scour around a structure is investigated in this study. Starting with the bed-load and suspended-load sediment transport (reference) model developed by Takahashi et al. (2000, "Modeling Sediment Transport Due to Tsunamis With Exchange Rate Between Bed Load Layer and Suspended Load Layer," Proceedings of the 27th International Conference on Coastal Engineering, ASCE, Sydney, Australia, pp. 1508-1519), we first introduce an extension to incorporate Nielsen's modified Shields parameter to account for the effects of infiltration/exfiltration flow velocity across the fluid-sand interface on the sediment transport (the modified Shields-parameter model). We then propose a new model to include the influence of the effective stress to account for the stress fluctuations inside the surface layer of the sand bed (the effective-stress model). The three analytical models are incorporated into a 3D numerical solver developed by Nakamura et al. (2008, "Tsunami Scour Around a Square Structure," Coast. Eng. Japan, 50(2), pp. 209-246) to analyze the dynamics of fluid-sediment interaction and scour. Their solver is composed of two modules, namely, a finite-difference numerical wave tank and a finite-element coupled sand-skeleton pore-water module. The predictive capability of the three alternative coupled models is calibrated against hydraulic experiments on sediment transport and resulting scour around a fixed rigid structure due to the run-up of a single large wave in terms of the sediment transport process and the final scour profile after the wave run-up. It is found that, among the three models considered, the proposed effective-stress model most accurately predicts the scouring process around the seaward corner of the structure. The results also reveal that the deposition and erosion patterns predicted using the effective-stress model are in good agreement with measu

波浪場と地形変化の相互作用を考慮した3次元数値モデルの開発と侵食・洗掘現象への適用査読有り

中村友昭，Solomon C. Yim

海洋開発論文集 25 巻頁： 1227-1232 2009年7月

Local scour in front of quay wall caused by bow thruster and its countermeasure using filter units 査読有り

Mizutani, N., Nakamura, T., Shinoda, Y., and Koyama, H.

Proc., 19th International Offshore and Polar Engineering Conference, ISOPE 頁： 1280-1287 2009年6月

記述言語：英語

This study is intended to investigate local scour in front of a quay wall and its generation mechanism. Hydraulic model experiments have been conducted to investigate the local scour in front of quay wall. Also, countermeasures against local scour using armor stones and filter units are investigated based on the experiment. To consider the mechanism of local scour, numerical simulation has been conducted. The numerical computation method employed in this study includes a flow simulation inside seabed and dynamic response of seabed like sediment transport. Time variation of pore pressure obtained in the experiments indicates the generation of local liquefaction due to strong flow and its response of seabed, and this may encourage the local scour. Experimental results clearly show that armoring by filter units is effective to reduce the local scour.

Mechanism of backfilling sand discharge from a gap under a vertical revetment 査読有り

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

Journal of Waterway, Port, Coastal, and Ocean Engineering, ASCE 134 巻 ( 3 ) 頁： 178-186 2008年11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）

Coastal disasters such as sliding, settlement, and overturning of coastal structures as well as subsidence of reclaimed areas occur due to toe scouring and backfilling sand discharge. In this study, the sand discharge mechanism from a gap under a vertical revetment without wave absorption and foot protection is investigated using hydraulic model experiments and newly developed numerical simulations. In the hydraulic model experiments, sand discharge and sinkholes similar to those observed in the field surveys are reproduced, and it is found that sand discharge is very sensitive to wave steepness and relative gap height. In numerical simulations, a comparison with the experimental data demonstrates the validity of the numerical methods. It is revealed that sand discharge tends to occur with an increase of the maximum seaward velocity just outside the gap under the revetment as well as the maximum volumetric strain inside the most offshore side of the sand inside the gap.

流体・構造連成解析による漂流コンテナの衝突力の算定に関する研究査読有り

廉　慶善，中村友昭，宇佐美敦浩，水谷法美

海岸工学論文集 55 巻頁： 281-285 2008年11月

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