Experimental Study of Sand Bed Configurations in Front of a Vertical Wall Under Wave Action

When a 2-D progressive wave train normally or obliquely approaches a vertical wall and then is normally or obliquely reflected from it, the combination of the approaching and reflected waves may result in a standing wave or a short-crested wave in front of the wall. This paper presents the experimental observations of sand bed configurations under the action of these water waves in front of the wall. The geometry of sand ripples under these water waves in front of the vertical wall is presented as a function of flow parameters, such as the water particle semi-excursion and the mobility number.

Morphology and internal architecture of a banner bank off Chengshan Headland, Shandong Peninsula

A banner bank off the north coast of the Chengshan Headland, Shandong Peninsula, has been described on the basis of echo sounder bathymetry, side-scan sonar and high-resolution seismic data sets. The bank is in NWW direction, approximately parallel to the coastline. The bank consists of sandy silt or clayed silt. Sand waves and megaripples are observed on the north side, which result from strong tidal currents around the headland and storm waves in winter. These bed forms indicate that the bank is influenced by the modern hydrodynamics. The bank is separated from the coast and Holocene subaqueous clinoform around the Shandong Peninsula in its east part. High-resolution seismic profiles reveal that the bank was formed during two periods： the earlier seismic unit Ua, and later seismic units Ub and Uc which overlays Ua with erosional surfaces on its south side and north side, respectively. As comparing with the clinoform, the bank has a different internal architecture. In the west of the bank, however, topography and surface sediment characteristics suggest that the bank links to the clinoform. The authors propose that seismic Ua is a residual part of early clinoform deposit. After the sediments in the north and south of Ua were eroded by strong currents, the Ub and Uc started to deposit probably by a complex hydrodynamic process. These results provide new insights into the evolution of the bank and its relation with the Holocene subqueous clinoform.

EXPERIMENTAL STUDY ON BED FORMS AND FLOW RESISTANCE OF LIGHT－WEIGHT MATERIALS WITH DIFFERENT DENSITIES

Experiments were conducted to investigate bed forms and flow resistance of light-weight sediment in an open channel flow. Three different synthetic materials of specific gravity 1. 055, 1. 46, each with uniform sizes D50 for 1. 25mm, 1. 05mm, 1. 40mm were used. Some conclusions were obtained from the resultS of these experiments and the data of other reliable sources[1, 2, 3, 4]. They indicate that the grain resistence is greatly affected by D50, and bed form resistances is the function of the downstream slope and the height of the dune. As well as natural sand, Y is not only the function of Y', but also affected by the relative roughness Rb/D50 and the size of the sediment.

Theoretical and Experimental Analysis of Vortex Origin

Several investigations refer to the issue of creation and identification of vortices in flows with different regime and presence of obstacles. Reasons have to do with the crucial role that vortices play in nature and industrial processes （sediment transport, mixing, radiation, noise, etc.）. Despite the contributions, further work is needed in order to perform more analysis of the mathematical arguments used to explain this phenomenon. In this idea order, the paper presents some advances in mathematical analysis and experimental results. In the first section, we do a description of the fluid motion from a fractional view through a sequence of three steps： Darcy＇s law, Navier-Stokes equations and Reynolds equations. Next, a representation of the temporal change of kinetic energy is found, which allows the possibility of the two signs. We obtain a description of the process of vortex creation. A length that represents the transition between flow and vortex intensity is found; then a succession of lengths is established that allows scaling from micro to macro. In the second section, experimental results are present; we consider vortex creation and its detection upstream of a bed form similar to that found in rivers, installed in an open channel, equipped with a water circulation system. For vortex detection, a methodology based on the particle image velocimetry PIV technique is proposed. So, we fulfill two objectives： vortex identification and its passage frequencies behind the bed form installed in the channel. Such procedure allows a computer process time reduction in vortices identification task.

The velocity patterns in rigid and mobile channels with vegetation patches

The hydraulic characteristics in an open channel with vegetation are very important in controlling the environment pollution and restoring the river ecology. This paper studies the influence of the bed form and the vegetation patch density on the spatial velocity pattern. Rigid fiberglass circular cylinders are used to simulate the vegetation and a 3-D acoustic Doppler velocimeter (ADV) is used to measure the local flow velocities. Two types of bed forms and a series of vegetation patch densities are considered. The experimental results show that the bed form significantly influences the vertical distribution of the streamwise velocity. Besides, the velocity is affected by the bed form while the lateral distribution shape of the streamwise velocity as well as the lateral and longitudinal distribution shapes of the depth-averaged velocity is less affected. When all test conditions but the bed condition remain the same, as a result of the water energy consumption by the sediment movement, the velocity in the mobile bed case is smaller than that in the rigid bed case. The vegetation patch density has a significant effect on the flow velocity. The distributions of the flow velocity at different locations show different trends with the increase of the vegetation patch density. The upstream adjustment length is not affected by the vegetation patch density, but the steady wake length is very much affected.