Wave attenuation properties of double trapezoidal submerged breakwaters on flat-bed

This paper investigates the wave attenuation properties of the double trapezoidal submerged breakwaters on the flat-bed by conducting physical experiments subjected to linear and cnoidal incident waves.The method of Goda’s two points is used to separate the heights of incident,reflected and transmitted waves based on the experimental data.The possible factors affecting the wave attenuation properties of the double trapezoidal submerged breakwaters(i.e.,the relative submerged water depth,relative breakwater spacing,wave steepness and relative wave height) are investigated with respect to the reflection and transmission coefficients.The results show that there is a range,within which the breakwater spacing has little impact on the reflection coefficient,and the transmission coefficient tends to be a constant.The influence of the wave steepness is reduced while the breakwater spacing is too large or too small.Within the range of the relative wave height tested in this study,the reflection and transmission coefficients increase and decrease with the relative wave height,respectively.The double trapezoidal submerged breakwaters model indicates a good attenuation effect for larger wave steepness,big relative wave height and within the range of the relative breakwater spacing between 12.5 and 14 according to linear and cnoidal waves.The changes of wave energy spectra between the double submerged breakwaters on the flat-bed are investigated by the fast Fourier transform(FFT) method,showing that wave energy dissipation can be reached more effectively when the relative breakwater spacing is 12.5.     

Three-dimensional bursting phenomena in meander channel

Experiments were conducted in a U-shaped open-channel flume with the intention of investigating the bursting phenomena in the meander channel. The experimental results of the secondary flow fields and the Reynolds shear stress distributions show that the velocity and velocity fluctuation in the transverse direction are not negligible. Moreover, the bursting process is investigated using the three-dimensional quadrant analysis, which is more accurate than using the traditional two-dimensional quadrant analysis for the meandering channel. It is obtained from the experimental results that the internal group of events occurs more frequently than the external group, particularly the internal ejection and internal sweep events. In addition, the transition probabilities of the movements, which are defined as the changes of events from the current situation to the next situation in a time series, show that the stable organizations of events are the most possible movements, whereas the cross organizations of events have the least possible movements.     

二维潮流数学模型可视化平台建设

采用VB与FORTRAN混合编程技术为天津大学泥沙实验室自主开发的ISTU数学模型制作可视化操作平台,并对AUTOCAD制图软件进行二次开发实现二维潮流流场图的绘制。本平台集成度高、界面友好、操作简便、计算快速可广泛适用于二维潮流的数值模拟。     

Nonlinear mechanism of bed load transport

From the group movement of the bed load within the bottom layer, details of the nonlinear dynamic characteristics of bed load movement are discussed in this paper. Whether the sediment is initiated into motion cor-responds to whether the constant term in the equation is equal to zero. If constant term is zero and no dispersive force is considered, the equation represents the traditional Shields initiation curve, and if constant term is zero with-out the dispersive force being considered, then a new Shields curve which is much lower than the traditional one is got, The fixed point of the equation corresponds to the equilibrium sediment transport of bed load. In the mutation analysis, we have found that the inflection point is the demarcation point of breaking. In theory, the breaking point corresponds to the dividing boundary line, across which the bed form changes from flat bed to sand ripple or sand dune. Compared with the experimental data of Chatou Hydraulic Lab in France, the conclusions are verified.     

利用植被消浪护岸的模型实验研究

对于在堤岸上栽种植被消浪这一新的护岸工程。根据实际波浪要素和现有实验设备条件确定出几何比尺和实验形式,选取桧柏树枝作为防浪树的模型,择选出对消浪护岸具有主要影响的因素,确定实验组次,对实验现象和数据作出分析,得出在堤岸上栽种防浪林的宽窄会影响防浪护岸的效果,以及植被在消浪过程的"共振"现象,并且通过实验总结出斜坡的消浪效果好于平坡。     

Incipient Velocity of non-uniform sediment in sloping river bends

A model for incipient movement of sediment in rolling pattern was established. In this model, the starting of sediment particles under low transport rate, the exposure degree of sediment, the lateral slope of water surface and the effect of transverse circulating current induced by the hydraulic structure of bend flow were fully considered. A theoretical formula for the incipient velocity of non-cohesive and non-uniform sediment in sloping river bends was developed. The results from the theoretical formula compared well with the experimental data.     

Time-dependent sediment transport subjected to downward seepage

Experiments were conducted using cohesionless sand particles with median diameter of 0.48 mm to investigate the time variation of sediment transport rate under the influence of local downward seepage.The experimental results show that the bedload transport rate in terms of volumetric sediment transport rate per unit width increased rapidly with time in the presence of suction,eventually reaching a peak beyond which it started to decrease.The trend of reduction was significantly reduced beyond 8 400 s after the test started.The analytical expression was derived in terms of dimensionless sediment transport rate and dimensionless time.The hypothesized relationships were compared with the experimental data,indicating a good agreement with each other.     

狂儒辜鸿铭

辜鸿铭(1857—1928),著名学者,学贯中西,精通多门语言,通晓文学、儒学、法学、土木工程等。毕其一生,致力于向西方传播中国传统文化。辜鸿铭是清末民初驰名中外的文化怪杰。他以西学起家,民国建立后,他在北大讲授英国文学,用偏激的行为方式——留辫子、穿旧服以对抗