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ラングミュアー循環流は運動量の鉛直および横断輸送を促進するため，水面には主流速の低速および高速縞が形成されるとともに強い3次元性を有する流れ構造が現れる．また，ガスおよび溶存物質などのスカラー輸送にも大きな影響を与えるため，水域場の環境特性を理解あるいはモデリングするためにはラングミュアー循環流の発生・形成メカニズムを明らかにする必要がある．本研究ではステレオPIVを導入して流速の全3成分の横断面分布を同時計測した．水面形状計測もPIVに同期させて画像計測した．このようなマルチカメラシステムによって流速と水面の位相関係を明らかにした．さらに横断面のアスペクト比を系統的に変化させて循環セルの生成特性への影響を調べるとともに，これらの形成機構をCL2モデルと渦度方程式の構成項比較により考察した．

実河川の高水敷には多様な樹木群が形成される．特に低水路と高水敷の境界部では一般に群生密度が大きい．高水時には境界部の樹木群によって大きな抵抗が発生し，主流速分布は低水路と高水敷のそれぞれに変曲点をもち，従来の単一変曲点をもつ混合層的な流れとはその様相は大きく異なる．そこで本研究では境界部に単列樹木を有する複断面開水路流れにおける乱流構造を明らかにするために，超音波流速計(ADV)を用いた流速3成分計測を行い，植生の配置間隔が2次流や乱流統計量の分布に与える影響やと2次流，レイノルズ応力およびせん断抵抗の関係を定量的に評価・考察する．さらにLESによって低水路／高水敷間の濃度交換特性を計算するとともに，効率的な交換を促進する樹木間隔の存在を明らかにした．

ラングミュアー循環流を対象とした室内実験や海洋観測のほとんどが，水表面のストリーク構造からその存在を推測しており，直接的にラングミュアー循環流の横断面構造を捉えたものは一部の研究を除きほとんどない．本研究では，高速度カメラを風洞水槽の水中部に設置してPIVによって循環流の多点同時計測に成功した．実験結果より系統的にアスペクト比および風速を変えることにより，流れの3次元構造の変化や2次渦の発生個数の増減特性を明らかにした．特にアスペクト比が4の場合には風速の増加によって2次渦の個数が減少し，また一定風速の下ではアスペクト比の減少に伴い個数が増加する興味深い結果が得られた．さらに位相解析を行い，波の谷では循環流が鉛直方向に縮められ，波の峰では引き伸ばされる特性が解明された．

自然河川や人工水路などの開水路流れの自由水面上に風が吹くと，底面境界層と同様に空気・水界面に流速シアーが生じる．さらに風速が増加すると波が発達し，水中には波動が伝達する．底面境界層で発生するヘアピン渦などの組織乱流渦はこのような自由水面シアーや波動の影響を受けることが予想されるが，現状ではこれらの効果についてはほとんど不明である．そこで本研究では高速度カメラを用いたPIV計測によって，空気・水界面の流速シアーや波が開水路の組織乱流構造や渦生成に与える影響を明らかにした．さらに2次元重力波が卓越するケースについては得られたデータを波成分と乱れ成分に分離して，平均流，波および乱れの三者間のエネルギー輸送動態を定量評価した．

Transport mechanism of suspended sediment is one of great interests in river engineering, because there are complicated interactions among flow structure, particle motion and bed forms. A lot of previous studies have been conducted on velocity measurements and numerical simulations in these suspended sediment flows. However, there are still many uncertainty about turbulence modulation, that is to say, the particle effects on flow structure. In order to reveal this significant topic, we conducted simultaneous measurements of fluid velocity, particle velocity and sediment concentration by using a discriminator particle tracking velocimetory (D-PTV) and a discriminator particle image velocimetory (D-PIV). It was found from the present study that the larger sediment particles enhance the turbulence intensities and Reynolds stress, while the smaller size particles depress them. Furthermore, we also revealed that this tendency becomes more remarkable as the sediment concentration is larger.

It is important to evaluate the falling and accumulating processes of the complicated-shaped blocks dumped to river and sea bottoms to create artificial fishery area. This paper presents a computational method for multiphase fields with a T-type solid model, which allows us to deal with the movements and collisions of the complicated-shaped objects in free-surface flows. In the T-type model, an object is represented by multiple tetrahedron elements and contact-spheres are placed near the surfaces. Thus, the volume, mass and inertial tensors are accurately represented, while the computational load to treat collisions of the objects is quite small. It was shown that the accumulation of the multiple blocks dumped into a water tank was reasonably predicted by the present method.

A computational method has been proposed to predict the interactions between free-surface flows and elastic bodies included in the flows. A solid model, whose deformations due to fluid forces are solved with a finite element method, is introduced into the MICS, a computational method for incompressible multiphase fields. A solid object included in the flows is divided into multiple tetrahedron elements, through which fluid-solid interactions are taken into account using a tetrahedron sub-cell method. The developed computational method was applied to the experimental results, which were obtained in an accelerated tank with elastic plates. As a result, the validity of the prediction method was confirmed.

A computational method has been developed to predict the movements of driftwoods transported by three-dimensional free-surface flows. A T-type solid model is introduced into the prediction method, MICS, which deals with a free-surface flow including floating objects as a multiphase flow field. In the T-type model, a driftwood is represented by multiple tetrahedron elements and its volume, mass and inertial tensors are accurately represented. The contact forces are evaluated with the contact-spheres distributed near the surfaces. The MICS with the T-type model was applied to experimental results and it was shown that the movements and accumulation of driftwoods are reasonably predicted by the present method.

A computational method has been proposed to predict the movements of arbitrarily-shaped solid bodies in a viscous incompressible fluid. This method is based on the 3D MICS, a computational method for incompressible multiphase fields. In this paper, the numerical procedures of solid-body movements are improved by introducing the quaternion that enables us to evaluate the rotating motions of solid bodies more accurately than the time-integration method. The proposed method has been applied to the assembly of tetrahedrons and it was shown that the fluid-body interactions are suitably treated. In addition, as a result of the computation of a falling rectangular body in water, it was confirmed that the position of the body and the falling speed are adequately predicted with the present method.

It is very important to reveal the coherent structure in meandering compound open-channel flows for predicting the transport properties of suspended sediments in rivers in flood. However, flow-visualization techniques such as PIV and PTV, have not sufficiently been applied to such flows in previous studies, and thus, there is almost no detailed information on coherent turbulence in meandering compound open-channel flows. Therefore, in this study, we conducted some PIV measurements with high-speed CMOS camera. As the results, the time-averaged velocity properties and coherent turbulence structure were investigated and discussed.

A computational method has been proposed for shallow water equations, which is based on the prediction method for incompressible fluids on collocated grid system. In the proposed method, called MACS (MAC method on Collocated grid for Shallow water equations), the momentum equations are discretized with a C-ISMAC method and the water depth h is treated implicitly. The continuity equation is also discretized implicitly and its numerical solutions for φ = hn+1-hn are obtained by solving simultaneous equations. The unit flow rates are corrected with the iterative computations based on the C-HSMAC method. The new treatment for the continuity equation is proposed and it enables us to predict dam-break problems, hydraulic jumps and sub-and super-critical flows stably and accurately without artificial diffusions.

In actual rivers, many aquatic plants are often observed and they have significant effects on hydrodynamic properties. In such vegetated open-channel flows, velocity profiles are largely changed in the vertical and spanwise directions. The vegetated canopies generate coherent turbulent motions that promote momentum and mass transports between over and within canopy. It is thus needed to investigate these turbulence characteristics and coherent motions in hydraulic engineering and river environment. In the present study, we conducted a large eddy simulation in vegetated open-channel flows, and revealed numerically the turbulence structure and correlation properties in the whole depth region including within-canopy and over-canopy layers.

A computational method has been proposed to predict the flooded flows entering residential areas due to levee breaks and tsunamis. The focus is placed on the local free-surface flow whose momentum is so large that some buildings may be destroyed. The computational method is based on 3D MICS, a computational method for incompressible multiphase fields. In order to deal with complicated-shaped buildings in the areas, a tetrahedron sub-cell method has been newly introduced in 3D MICS. The arbitrarily-shaped bodies are represented as the assembly of multiple tetrahedron elements and their volumetric fraction in 3D computational cell is evaluated by the sub-cell method. A numerical model for the actual urban area near a river was set up and the artificial flooded flows were demonstrated with the present method.

The collapse of a permeable dam mainly due to overflows has been investigated with experiments and numerical studies. In order to numerically predict this process, the treatment of fluid forces acting on permeable materials is essentially important. In contrast to the previous numerical methods, 3D MICS, a computational method for incompressible multiphase fields, allows us to deal with the movement of solid bodies included in free-surface flows without any empirical formulations, such as a resistance coefficient, Cd. The validity of 3D MICS is discussed through the comparison with the experimental results.

It is necessary to investigate coherent turbulence structure in meandering compound open-channel flows for predicting the transport and distribution of suspended sediment in actual rivers. However, in previous studies, flow-visualization techniques such as PIV and PTV, have not been applied sufficiently, and thus, there is almost no detailed information of coherent turbulence in meandering compound open-channel flows.Therefore, in this study, we conducted innovative flow-visualization measurements by using a multi-layer scanning PIV system, and could analyze instantaneous velocity vectors on horizontal planes at several different elevations simultaneously.As the results, the correlation properties between the different elevations were revealed in the meandering compound open-channel flow.

It has been reported that tsunamis, which have arrived at river mouths, sometimes run up in rivers and that the wave flows cause serious damage in structures. In order to evaluate the related local phenomena, such as the transportation of floating materials, fluid forces caused by wave flows and flows over river banks, a 3D computational method, MICS (Multiphase Incompressible flow solver with Collocated grid System) is thought to be effective, since it enables us to deal with the front of free surface flows and evaluate fluid forces without empirical formulations. Some basic hydraulic experiments were carried out and the measured wave flows and their flooded flows were compared with the predictions.

This paper presents a computational method for shallow water equations on the basis of the prediction method proposed for incompressible Navier-Stokes equations on a collocated grid system. In the proposed method, the momentum equations are discretized with a semi-implicit method with respect to the water depth, h. The continuity equation is discretized implicitly and its numerical solutions are obtained by solving simultaneous equations. The unit flow rates, M and N, are corrected with the converged results for h. It has been shown that the proposed method is numerically stable and that higher-order schemes for convection terms, C-HSMAC and C-ISMAC methods, which have been proposed for the computations of incompressible flows, are available for shallow water equations as well.

It is important to evaluate the detailed inundation process of flood flows in the area where multiple buildings closely exist. In this study, a small-scale experimental model is used to measure the initial stage of the unsteady free-surface flows which extend among impermeable boxes that simulate the arrangement of buildings. The experimental results are numerically predicted with a 3D computational method for multiphase flows, 3D MICS, which enables us to deal with the front area of free-surface flows without additional manipulation. As a result of computations, it has been shown that the unsteady process of flood flows are reasonably predicted with 3D MICS.

It is very important in river management and hydraulic engineering to investigate the hydrodynamic properties in vegetated open-channel flows. There are a lot of experimental and numerical studies on open-channel flows over vegetated canopies, in which velocity distributions are largely varied with not only vertical but also streamwise and spanwise diretions. In particular, it is needed to reveal such dispersive properties of velocity components, because it is considered that the velocity dispersion has significant relations with turbulence transport and generation due to vegetations. Therefore, in this study, turbulence measurements were conducted in vegetated canopy open-channel flows by using two-component laser Doppler anemometer, and turbulence structure and dispersive effects were revealed experimentally.

Coherent horizontal vortices are often observed in compound open-channel flows. The hydrodynamic properties of horizontal eddies were intensively studied by a lot of researchers, because these eddies have significant relations with momentum exchanges between a main-channel and floodplains. However, there is almost no detailed information about the meandering properties of the horizontal eddies developed in a straight open-channel.Therefore, in the present study, a large eddy simulation was conducted in the transition region between the straight and meandering floodplain flows. As the results, coherent eddy structure and correlation properties were investigated numerically in such a complex open-channel flow.

The applicability of the computational method for multiphase flows, MICS (Multiphase Incompressible flow solver with Collocated grid System), is investigated for the incipient motion of a cylinder under the shielding effects in a duct flow. In order to understand the actual phenomena, hydraulic experiments are conducted with two cylinders, one fixed and another movable. In the experiments, the distance of the two cylinders are widely changed and critical flow rates that rotate the movable cylinder are measured. As a result, resistance force and sheltering coefficients are derived and the defects of the usual evaluation method to derive these values are pointed out. The incipient motion of the cylinder is numerically investigated with MICS. As a result of the computations, it is shown that the behaviors of the movable cylinder are reasonably predicted with MICS, while MICS needs no empirical coefficients regarding the resistance force and sheltering effects.

Suspended sediment in open-channel flows has been paid great attention in river engineering. It has been pointed out that flow resistance is changed by the existence of sand particles. Moreover, knowledge of interaction between sand-particles (solid-phase) and water (fluid-phase) is necessary to improve sediment transport rate formula. However, the mechanism of particle-fluid interactions is not fully understood. In this study, simultaneous measurements were conducted with discriminator PTV in rough open-channel flows with suspended sediment. The roughness elements were set up on the channel-bed. Consequently, the relative velocity between particles and fluid and the turbulence modulation were investigated by changing the particle concentration systematically.

A multi-layer scanning 3-D PIV system was developed, in which the different elevated laser light sheets (LLS) were projected into the tilting flume almost simultaneously. This specially designed PIV system is able to measure time-dependent velocity components in the 3-D region at the same time. In this study, turbulence measurements were conducted in a compound open-channel flow, in which large-scale horizontal eddies were observed near the junction region between the main-channel and floodplain, and as the results, it was found that there were large correlation properties between the different elevated layers and the tube-like horizontal eddies were transported in the downstream.

This study describes an experimental investigation on turbulence characteristics and the water-surface fluctuations in adverse wind-driven open-channel flows by using both a laser Doppler Anemometer (LDA) and a wave gauge simultaneously. In this study, it was shown that the velocity fluctuations of water flow near the interface in not only cocurrent flow but also adverse flow are significantly affected by the water surface in every range of frequency. However turbulence characteristics in water layer in adverse wind-driven open-channel flows are different from those in cocurrent flow, and there exists a high correlation between turbulence and the surface fluctuations in predominant frequency due to high-sheared wind flow.

The transportation of sedimentation in 2D branched and non-uniform duct flows is numerically predicted with a computational method, which has a conservative scheme for convection terms in 5th-order accuracy with a flux control technique (FVM-QSI scheme). The governing equations including a turbulence model are discretized with strong conservative forms in curvilinear coordinates on the collocated grid system. The predicted results are compared with the measured values and its applicability is discussed.

流下方向にワンド模型を2つ配置した開水路流れにおいて, 上流ワンドのアスペクト比および上流ワンドと下流ワンドとの設置間隔を系統的に変化させた12ケースと単体ワンドの全13ケースを対象に実験を行った. 計測機器はPIVを使用し, 計測対象は下流ワンドとした. その結果, 上流ワンドのアスペクト比が大きくワンド設置間隔が小さいほど主流部での時間平均流速分布は主流側へ流向が変化し, 境界部付近で発生する内部せん断層の位置が変化することが明らかとなった. また, 乱れ特性量の絶対値は増加し, 乱流混合が活発に行われていることもわかった. さらに, ワンド周辺での組織構造についてウェーブレット変換を用いて, 流れ構造を3つの周波数帯に分割解析した. これより上流ワンドのアスペクト比と設置間隔を変化させると, 組織渦の軌跡はかなり変化することが明らかとなった.

The present study describes an experimental relationship between turbulence structures in water layer and the water-surface fluctuations in wind-driven open-channel flows by using both a laser Doppler Anemometer (LDA) and a wave gauge simultaneously. The purpose of this study is to make clear the characteristics of surface fluctuations on water dynamics in air-sheared open-channel flows, and to evaluate the effects of surface fluctuations on vertical momentum transport in the water layer. As the results of experiments, it is shown by spectral analysis that the velocity fluctuations near the interface in both only open-channel flow and wind-driven open-channel flow are significantly affected by the water surface in every range of frequency, and that there exists a high correlation between turbulence near the air-water interface and the surface fluctuations in a predominant frequency due to high-sheared wind flow. Moreover, it is recognized by wavelet analysis that the turbulence structures in weak wind-driven open-channel flows are governed by both wall shear and wind-induced flows.

Measurements of instantaneous flow fields and the dye concentration in and around side cavity that was set around the permeable wall, were conducted. Measurements of flow properties were conducted by PIV. On the other hand, DV-camera was used for measurements of dye concentration. Permeable flow from the side wall of the side cavity was divided into 4 kinds of patterns. From the upstream wall, side wall, downstream or upstream and side wall. The permeable flow rate was set to 3 patterns. The 3%, 5% and 8% of the main-channel flow rate were changed. The aspect ratio (the streamwise length of the side cavity/the lateral length of the side cavity) was set to 2.Flow patterns were changed. In the case of the permeable flow from upstream wall, side wall and upstrea and side wall, the center point of circulation flow moved to the downstream. On the other hand, in the caseof permeable flow from the downstream wall, the center point changed to the upstream. Dye concentration distribution in all cases was that high concentration area was observed at the upstream in the side cavity.In and around the circulation flow, there was low concentration. In the case of permeable flow from the upstream and side wall, the influences on flow fields or concentration fields were the greatest.