Nodal Point Relation for the Distribution of Sediments at Channel Bifurcation

This technical note explores the applicability of the general nodal point relation to describe the distribution of sediments at channel bifurcation. Experiments were conducted in a physical model of channel bifurcation to estimate the coefficient and exponent of the nodal point relation for different nose angles and upstream discharges. It was found that the nose angle is the major variable for the distribution of sediments to the downstream branches. The value of the exponent k found from experimental results was compared with that of a theoretical analysis. For a stable equilibrium, the value of k is greater than 5/3 from theoretical consideration when the Engelund–Hansen sediment transport formula is used. This was confirmed from the experimental results. This suggests that the distribution of sediments at channel bifurcation can be expressed by the general nodal point relation.     

用于MIMO广播信道的带多波束选择的正交随机波束成形算法

本文提出一种基于有限反馈的波束和用户选择方案,在这种方案中,用户端利用一个随机正交码本对其信道方向信息(CDI)进行量化,计算其最大信号与干扰加噪声功率比(SINR),并把这些信息反馈给基站;基站根据接收到的这些反馈信息,按照和容量最大的准则选择出多个正交波束以及相应的多个用户.和sharif等人最近提出的方案相比,我们提出的方案能根据系统参数,如用户数和信噪比(SNR),对选择的波束成形矢量及其对应的用户的数量和集合进行调整,当用户数量较小时,和容量性能得到了很大的提升,同时避免了选择波束成形矢量时的用户冲突,另外,基站也不需要广播波束成形矢量给各个用户.     

Improved Channel Cross Section with Two-Segment Parabolic Sides and Horizontal Bottom

A channel cross section with parabolic sides and horizontal bottom has been recently published and proved to be more economical (provide lesser construction cost per unit length) than the trapezoidal cross section. This paper presents a new and improved cross section with two-segment parabolic sides and horizontal bottom. Each side of the cross section consists of two parabolic segments smoothly connected. Closed-form relationships for the cross-sectional area and perimeter are developed. For specific parameter conditions, the new cross section produces most of the common cross sections, including the parabolic sides—horizontal bottom and trapezoidal cross sections, as well as new cross-sectional shapes. It provides an additional degree of freedom in determining the optimal cross-sectional design. A spreadsheet-based optimization model for the new cross section that minimizes the total construction cost (excavation and composite linings) is developed. The constraints of the model include channel discharge and physical requirements, such as flow depth, top width, and side slope with fixed or depth-dependent freeboard. The model was validated and the cross-sectional performance was evaluated using different design scenarios. The optimization results show that the new cross section is more economical and more flexible than a cross section with (one-segment) parabolic sides. As such, it should be of interest to the irrigation and drainage engineers.     

武汉市杨泗港快速通道四新段工程总体设计

杨泗港快速通道四新段是武汉市"三环、十三射"中的"一射",路线全长5.67 km。通过分析工程功能定位、道路等级及总体设计,着重介绍了车道数、快速路形式、标准横断面布置、总体布置方案、结构形式和绿化景观方案,为高架快速路的设计提供参考。     

Analytical investigation of heat transfer enhancement in a channel partially filled with a porous material under local thermal non-equilibrium condition

Forced convection through a channel partially filled with a porous medium is investigated analytically in the present work. Thermally developed condition is considered and the local thermal non-equilibrium model is utilized to obtain the exact solutions of both fluid and solid temperature fields for flow inside the porous material as well as for flow in the clear region. Nusselt number is obtained in terms of the porous insert thickness (S), porosity (?) as well as pertinent parameters such as thermal conductivity ratio (k), Biot number (Bi), and Darcy number (Da). The values of S by which the temperature difference between the two phases approach to zero, for different values of Bi, k, and Da number are obtained. It is found that three mechanisms affect the Nu number i: clear fluid conduction ii: internal heat exchange in the porous medium iii: channeling effect in the clear flow. The value of S, which yields the highest Nu number is found to vary linearly from 0.8 to 0.97 as the value of Da decreases from 10⁻³ to 10⁻⁷. At the expense of reasonable pressure drop the optimum thickness of porous material in order to enhance the heat transfer rate is found S = 0.8.     

A Review Of Road-Gully Spacing Methods

ABSTRACT Methods of spacing gullies on surface-water drainage schemes have changed significantly during the last thirty years as the understanding of the hydrology and hydraulics of the subject has advanced. Rules of thumb which take no account of road geometry or inlet efficiency have been replaced by more rigorous methods, the most advanced of which considers time-varying intensity storms. The methods currently used are not consistent and vary in their approaches. This paper reviews the methods used in the past, and discusses the methods which are currently employed at present.     

Efficient Algorithm for Gradually Varied Flows in Channel Networks

This paper presents an efficient solution technique for one-dimensional unsteady flow routing through a general channel network system—dendritic, looped, divergent, or any combination of such networks. The finite difference method is used to solve the de St. Venant equations in all the branches of the network simultaneously. The number of equations to be solved at a time during any iteration is reduced to only four times the number of branches of the network. This results in a significant reduction in storage requirements and solution time. Importantly, the algorithm does not require any special node numbering schemes and the nodes can be numbered independently for each branch. The algorithm is also suitable for programming on a parallel-processing computer.     

Performance Analysis of an ATM Buffered Switch Transmitting Two-Class Traffic over Unreliable Channels

In this article we analyze the performance of a space division output buffered switch operating in an ATM multimedia environment as follows. Fixed size packets arrive onto the switch inputs in each time slot. These packets are of two classes. Class-1 packets, representing real time communications, are sensitive to delay but insensitive to loss. Class-2 packets, representing nonreal time communications, are insensitive to delay but sensitive to loss. The switch transmits these two-class packets over communications channels which are unreliable. That is, the packets could be lost before reaching the other end.To respond to the class-1 delay sensitivity, the switch gives class-1 packets higher service priority over class-2 packets. And to respond to the class-2 loss sensitivity, the switch requires an acknowledgment for each class-2 packet it transmits. It is this latter response that is the major contribution of the article. In particular, it gives rise to two service times, rather than one as has usually been considered in the published literature.For the purpose of the analysis, the switch is modelled as a priority, discrete time, batch arrival, single server queueing system, with infinite buffer and two service times: one deterministic for class-1 and one geometric for class-2. Three performance measures are analyzed: occupancy, unfinished work, and waiting time.     

Modeling the Exogenous Coordination of Mobile Channel-based Systems with Petri Nets

In this paper, we discuss how to model systems that communicate through and are coordinated by mobile channels. Mainly, we focus on modeling the exogenous coordination behavior imposed by these channels. We use Petri Nets as our modeling language, for they provide a graphically and mathematically founded modeling formalism. We give Petri Nets for a set of mobile channel types. This allows us to construct models of applications, by taking the Petri Net of each component and each mobile channel, and composing them together. For this purpose, we define a special Petri Net composition function. We also discuss analysis and simulation of these models and their exogenous coordination behavior.     

Case Study: Two-Dimensional Model Simulation of Channel Migration Processes in West Jordan River, Utah

The paper presents the application of a two-dimensional depth-averaged numerical model to simulate the lateral migration processes of a meandering reach in the West Jordan River in the state of Utah. A new bank erosion model was developed and then integrated with a depth-averaged two-dimensional hydrodynamic model. The rate of bank erosion is determined by bed degradation, lateral erosion, and bank failure. Because bank material in the West Jordan River is stratified with layers of cohesive and noncohesive materials, a specific bank erosion model was developed to consider stratified layers in the bank surface. This bank erosion model distinguishes itself from other models by relating bank erosion rate with not only flow but also sediment transport near the bank. Additionally, bank height, slope, and thickness of two layers in the bank surface were considered when calculating the rate of bank erosion. The developed model was then applied to simulate the processes of meandering migration in the study reach from 1981 to 1992. Historical real-time hydrographic data, as well as field survey data of channel geometry and bed and bank materials, were used as the input data. Simulated cross-sectional geometries after this 12-year period agreed with field measurements, and the R2 value for predicting thalweg elevation and bank shift are 0.881 and 0.706, respectively.