Rigid flow deflectors are usually used on water flow beds to protect engineering structures such as breakwater in coasts and to regulate flow routes in open channels. To reduce its side-effects, i.e., local scour at the toe of deflectors, a flexible flow deflector is proposed, and the corresponding local scour was investigated in this study. A flume experiment was conducted to investigate local scour. To show the advantage of flexible deflectors, a control experimental test was also conducted using a traditional rigid deflector under the same blockage area configuration and the same flow conditions. The flow field near the flexible deflector was also measured to reveal the local flow field. The results show that the bed-scour develops near the toe edges of both flexible and rigid deflectors, but the maximum and averaged scour depths for the flexible deflector are smaller. This advantage of flexible deflector in scour depth is mainly caused by its prone posture, which induces the upward stretching and enlarging horizontally rotating vortex and the upward shifted vertically rotating vortex. The former dissipates more turbulent energy and the latter results in smaller bed shear stress, which lead to smaller scour depth directly. In addition, the up- and down-swaying movement of the flexible deflector can also assistant to dissipate more turbulent energy, thereby damping the intense of the horseshoe vortices and thus weakening scour depth as well. The results of this study provide an elementary understanding on the mechanisms of a flexible flow structure and an alternative deflector-device to reduce scour depth.

In nearshore regions, bidirectional tidal flow is the main hydrodynamic factor, which induces local scour around submarine pipelines. So far, most studies on scour around submarine pipelines only consider the action of unidirectional, steady currents and little attention has been paid to the situation of bidirectional tidal currents. To deeply understand scour characteristics and produce a more accurate prediction method in bidirectional tidal currents for engineering application, a series of laboratory scale experiments were conducted in a bidirectional current flume. The experiments were carried out at a length scale of 1:20 and the tidal currents were scaled with field measurements from Cezhen pipeline in Hangzhou Bay, China. The experimental results showed that under bidirectional tidal currents, the scour depth increased significantly during the first half of the tidal cycle and it only increased slightly when the flow of the tidal velocity was near maximum flood or ebb in the following tidal cycle. Compared with scour under a unidirectional steady current, the scour profile under a bidirectional tidal current was more symmetrical, and the scour depth in a bidirectional tidal current was on average 80% of that under a unidirectional, steady current based on maximum peak velocity. Based on previous research and the present experimental data, a more accurate fitted equation to predict the tidally induced live-bed scour depth around submarine pipelines was proposed and has been verified using field data from the Cezhen pipeline.

In order to explore the potential application of flexible flow deflector in engineering, experiments were conducted to study the countermeasures against bridge pier protection. A three-deflector structure was proposed to improve the efficiency of reducing scouring depth at bridge piers, including one body and two wings. The performance of the proposed three-deflector structure was subjected to some preliminary laboratory tests, and satisfactory results were obtained.

In this paper, we used typical riverbed topography and hydrodynamic conditions, combined with the arrangement of the Babao ship lock exit guiding wall and three tidal gate construction schemes, to calculate the planar flow regime for the exit channel area. In addition, the variation of the planar flow field at typical moments in local outside the entrance area, the size of the recirculation region, the lateral flow velocity, and the longitudinal flow velocity in the outlet channel are used to analyze and compare the navigational flow conditions of different schemes. The calculation shows that the magnitude and direction of the mainstream flow outside the guiding wall are basically unchanged after the construction of tidal gates. Out-of-port flow patterns are not related to whether or not tide gates are built, and the impact of building gates is primarily in the waters inside the head of the guiding wall. Compared with and without a tidal gate, the time required for transverse velocity to meet navigational requirements is less for each scheme.