Slow flow of a Bingham fluid in a shallow channel of finite width

金沢大学大学院自然科学研究科We present a theory for the three-dimensional flow of a Bingham-plastic fluid in a shallow and wide channel. Focusing attention on slow flows appropriate for gentle slopes, low discharge rates or the final stage of deposition, we ignore inertia and apply the long-wave approximation. For steady flows, the velocity distribution, total discharge, and section-averaged flux are obtained analytically in terms of the fluid property and the geometry of the channel cross-section. Nonlinear stationary waves, which connect a uniform depth upstream to another uniform depth downstream, are then investigated, for both wet and dry beds. A numerical scheme is applied to calculate the transient flow evolution. The final development of the stationary wave due to steady discharge upstream is obtained numerically and the relation between the tongue-like shape of the wave front and the fluid property is discussed. The phase speed of the stationary wave is also derived analytically. Finally, the transient spreading of a finite fluid mass released from a reservoir after a dam break is simulated numerically. The transient development of the front and the final extent of deposition are examined

Slow spreading of fluid mud over a conical surface

金沢大学大学院自然科学研究科We investigate the slow spreading of fluid mud over a gently sloped conical surface which may simulate a shallow basin or a hill. The mud is assumed to behave as a Bingham plastic possessing a finite yield stress and the lubrication approximation is used. Because of the finite yield stress, a variety of non-trivial equilibrium profiles can exist, corresponding to the state of deposit at the end of upward or downward motion. Analytical solutions are derived for axially symmetric deposits. It is shown that the front of the final profile in axisymmetric spreading is of a common form in dimensionless variables, independent of the total mud volume. Transient evolutions are then studied numerically by employing a finite-volume scheme for both axially symmetric and asymmetric spreading from a localized source. The characteristic features of the mud pile at different stages of spreading are examined. The final shape in asymmetric spreading is strongly affected by the total volume released and by the rate of discharge

Numerical study of solitary wave propagation in curved channels

金沢大学理工研究域環境デザイン学系A numerical model is developed for the extended Boussinesq equations expressed in the generalized curvilinear coordinate system. The model is applied to the study of solitary wave propagation through circular channels. The general features of solitary wave propagation are described and the effects of channel width and incident wave height on the transmission and reflection properties are examined. It is shown that the wave transformation becomes significant in wide channels. The maximum crest height at the outer wall of channel is then investigated in detail. The maximum crest height can reach almost twice as large as the incident wave amplitude in wide channels. The numerical results indicate that the maximum crest height can be correlated fairy well with a single dimensionless parameter

3次元数値流体解析および粒子画像流速測定法を用いた直立円柱周辺の洗掘機構の解明

金沢大学工学部研究課題/領域番号:11750452, 研究期間(年度):1999出典：研究課題「3次元数値流体解析および粒子画像流速測定法を用いた直立円柱周辺の洗掘機構の解明」課題番号11750452（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-11750452/）を加工して作

固体-流体連成系の理論および数値解析に関する研究

取得学位：博士(工学)，学位授与番号：博乙第149号，学位授与年月日：平成9年9月30日,学位授与年：199

湾曲・分岐・合流部を有する大規模河川・水路網を遡上する津波の基本伝播特性の解明

金沢大学理工研究域本年度は,湾曲・分岐・合流部を有する河川・水路網を遡上する津波の基本伝播特性に関して,以下の検討を実施した.(1)波流れ共存場解析のための高精度数値解析モデルの開発河川を遡上する波浪は,河川流によりブロックされ,波高が増幅するとともに,波長が減少する(Wave-Blocking).本年度は,こうした波長変動を精度良く解析でき,高波数領域にも適用可能な新しい波浪変形モデル(理論および数値モデル)の構築を行った.また,砕波減衰や任意反射境界を取り扱うための手法を新たに開発した.現在,空間的に非一様な流速分布を有する河川に孤立波が入射した場合の波浪伝播特性を解析中である.(2)湾内に入射した孤立波の透過・反射特性の解析湾内に入射した津波は,河川・水路網を遡上する前に,湾形状の影響を受けて局所的に波高を増幅させる.ここでは,台形型の湾を対象に,平面波動水槽と湾模型を用いた室内実験を実施し,壁面近傍の局所的な波高増幅特性を検討するとともに,実験結果と解析結果を比較し,解析手法およびその結果が定性的並びに定量的検討に十分な精度を有することを示した.また,入射波高および湾形状(収縮角)を変化させて,体系的な数値解析を実施し,孤立波の透過・反射特性を解明した.(3)水路・河川網における孤立波伝播特性の解析多数の分岐合流部を有する複雑形状領域の波浪伝播特性を簡易に解析できるように従来の解析モデルを拡張し,モデル地形を対象に孤立波の伝播特性を解析した.また,本数値モデルが,複数の水理構造物を含む領域や複雑形状を有するダム貯水池等の波浪解析にも適用可能であることを示した.研究課題/領域番号:13750486, 研究期間(年度):2001-2002出典：「湾曲・分岐・合流部を有する大規模河川・水路網を遡上する津波の基本伝播特性の解明」研究成果報告書　課題番号13750486（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（ https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-13750486/）を加工して作

石川県加越海岸における波浪特性および関連する地形変化指標の季節変動

This study investigates the seasonal variability of wave characteristics and related morphological indices on the Kaetsu Coast in Ishikawa, Japan based on long-term wave data observed at Kanazawa Port from I 971 to 2012. First, the seasonal variations of wave energy flux are investigated in combination with the directional distribution. Most of the incoming wave energy is concentrated in the winter season, in which high waves from the WNW, NW, and NNW direction frequently impact the coastline. Second, the characteristics of wave breaking in the near shore area, and breaker height and depth, are examined. Re­lated morphological indices such as the closure depth and the Sunamura index are also estimated. The seasonal variations of these properties indicate common patterns, in which the values are highest in winter, medium in spring and autumn, and lowest in summer. The cumulative probability of breaker depths varies significantly from season to season. The estimated closure depth also indicates distinct seasonal changes. These results indicate that the cross-shore width of significant morphological change is substantially var­iable according to the time. The estimations of the Sunamura indices suggest that the shoreline is advanced during the summer, while shoreline recessions generally occur in other seasons. The transitions from shoreline recessions to shoreline advances are deduced to occur in March. and from advances to reces­sions in September. Third, an analysis ofinfragravity waves is conducted. The patterns of the daily as well as monthly variations of infragravity wave heights are similar to that of wind waves. A strong linear cor­relation exists between the heights of infragravity waves and wind waves

日本海沿岸における地域波浪特性の相互比較

This study examines the long-term wave data observed along the coastline of the Sea of Japan. The focus was mainly placed on the wave climate at Wajima Port, which is located on the outer coast of the Noto Peninsula in Ishikawa Prefecture. The wave characteristics at Wajima were first compared with those at Kanazawa, which is located relatively close (90 km) to Wajima. The wave climate at Wajima and Kanazawa indicated similar features in terms of wave height and period. The influence of Noto Peninsula was substantial only in terms of the incoming wave direction. While neither a statistically significant trend nor jump was found for the long-term variation of annual wave height at these sites, an increasing trend and an abrupt jump around 1990 have been detected in the long-term variation of wave periods at Kanazawa. The wave periods in July have significantly increased at both Wajima and Kanazawa. The wave properties were then compared with those at Rumoi and Hamada Port, which are respectively located 830 km and 510 km away from Wajima. Over a long stretch of the Sea of Japan coast covering Rumoi, Wajima, Kanazawa, and Hamada, wave climate indicated similar and significant seasonal changes. The difference in the properties of significant waves around these four sites was about 10 %. Significant wave height and period correlated very well with second order polynomials at each site. In contrast, wave directions along the coastline indicated significant differences. At Rumoi and Hamada, neither significant trends nor jumps in long-term annual wave periods were detected. The statistical test revealed that the long-term increasing trends and abrupt jumps of wave period in summer were intrinsic to the waves at Wajima and Kanazawa, located in the central coastal areas adjacent to the Sea of Japan