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Braiding is a mesmerizing phenomenon since flow and sediment transport interact and are able to change the morphology of a channel in a rapid and complex fashion. Conventional two-dimensional morphodynamic models estimate bedload distribution using shear stress distribution. However, it is unclear if the use of such shear stress distributions is relevant or applicable for all situations when using two-dimensional morphodynamic modelling. This thesis strives to investigate whether shear stress distributions are useful to predict bedload transport pathways. This study focuses upon prediction of bedload transport pathways using a morphodynamic model (Delft3D) of an anabranch of the Rees River (New Zealand). Observed bedload transport pathways were compared to modelled bedload transport pathways in an attempt to validate the predictive ability of the model. Results show that there is a significant correlation between predicted bedload transport pathways and the apparent bedload transport pathways derived from the field measurements. Furthermore, bedload transport predictions were in good agreement with observed data in areas where the model’s predictions of high shear stress were comparable to field observations. However, substantial bedload transport predictions in low shear stress areas were not adequately captured by the model, suggesting that the observed pathways were not due to high shear stress, but rather to other sediment supply sources.

WOS: 000229849000009, Calculation of shear stresses in open channel flow is very important in civil engineering applications such as structural design, determination of velocity distribution and sediment transport. It is argued in literature that the velocity distribution equations for pipe flow may be used in open-channel flow analysis. However, due to irregular boundary sheer stress, this claim seems to be unreasonable and the irregularities should be taken into consideration. In this study, wall shear stresses for turbulent flow in rectangular open channel are investigated. Using mean velocity measurements and assuming validity of the logarithmic velocity distribution perpendicular to wetted perimeter, dimensionless shear stresses in the unified velocity distribution are determined. A semi-theoretical method is applied for the solutions of non-linear equations. A shear stress distribution equation is proposed to calculate irregular boundary shear stresses on the wall and bed in smooth rectangular channels.

26-27 Sep. 1996 (19th), 水素気泡法を用いた渦構造を理解する定量的情報技法を提案した。本技法を用いて、円柱後流の近傍から遠方までの対流循環渦領域における速度のみならず速度勾配テンソルも計測することが出来た。本技法で得た値に基づき、渦の全体構造を見るため、流れ場の渦度、渦度数、主変形速度、せん断応力およびラプラシアンP(Pは動圧)のような、渦構造を特性化する物理量の等高線を可視化した。その結果は、渦が円柱後流近傍を移動するときは、不安定シート状から安定棒状へ構造を変化し、また、円柱後流遠方では、安定棒状から3次元構造および渦列への再配列を誘導する不安定シート状へ、再び構造を変化することを示唆している。, A technique for quantitative information was proposed to understand the vortex structure by means of hydrogen bubble techniques. Using the technique, not only the velocity but the velocity gradient tensor were obtained in the vortex region convecting from the near wake to the far wake of a circular cylinder. Based on the values obtained in the technique, the contours of the physical quantities which characterize the vortex structures, i.e. vorticity, vorticity number, principal value of the rate of deformation, shear stress and Laplacian P (P: kinematic pressure) in the flow field, were illustrated to see the overall structure of the vortices. These results suggest that the vortices change in structure from unstable sheet-like vortices to stable rod-like vortices as the vortices traveling in the near wake of the cylinder. And in the far wake of the cylinder the vortices once again change in structure from stable rod-like vortices to unstable sheet-like vortices which induce three dimensional structure and the rearrangement of the vortices in the vortex streets., 資料番号: AA0001127012, レポート番号: NAL SP-35

International audience; This work deals with the detachment of biofilm subjected to a shear stress. Biofilms are developed on plates, under very low shear stress for one month and then subjected to an erosion test for 2 h in a Couette-Taylor reactor (CTR). During the erosion test, the plate was fixed on the external cylinder of the CTR. The presence of the plate modifies the velocity field in the CTR. A first zone close to the facing step region is characterized by the detachment of the stream lines. A second zone, downstream, is characterized by a pure shear flow: the distribution of the shear stress is uniform; the residual biofilm mass was measured and the detachment can be classically related to the magnitude of shear stress. In the first zone, the recirculating flow induces a strong non-uniform distribution of shear stress. The residual biofilm mass was also measured and found to be much lower than in the uniform shear stress zone, whereas the magnitude of shear stress is of the same order or even smaller. The assumption of elastic rheology for the biofilm enables the strong detachment observed in the region subjected to non-uniform shear stress to be explained.

The shear distributions of fibre–bonded ceramic composite were investigated using finite element analysis. The effect of notch distances on the shear stress distributions in a double notch shear (DNS) specimen was investigated under static and impact loading conditions. The stress concentration near the notch roots became larger as the notch distance increased. The effects of variations in the notch distances upon the shear strength of fibre bonded ceramics (FBC) and carbon–fibre reinforced silicon nitride (CFRSN) were experimentally investigated with static and impact tests. The shear strength decreased with an increase of the notch distance for both the static and impact tests, except that the notch distance was too small. The impact shear strength was larger than the static one regardless of notch distance. The shear strength evaluated by a DNS test was smaller than that obtained from a short beam bending (SBB) test.