Mixing Center of a Channel

For longitudinally uniform stretches of waterways there is a mixing center for the across-channel location of a steady point source in steady flow, such that complete mixing is achieved as soon as possible and there is no concentration overshoot at either of the two shorelines. A mathematical definition of the mixing center is the zero of the first oscillatory cross-channel diffusion mode. With the shorelines plus four interior data points across the channel, the starting estimate for the mixing center suffices to keep peak shoreline concentrations to within 6% of optimal. For comparison, a source at mid flow gives 18% shoreline concentration overshoot in the test case. Should very high precision be required, the Appendix gives an iterative construction that converges to the first oscillatory diffusion mode.     

MC-MLAS: Multi-channel Minimum Latency Aggregation Scheduling in Wireless Sensor Networks

Data aggregation is a key, yet time-consuming functionality in wireless sensor networks (WSNs). Multi-channel design is a promising technique to alleviate interference as a primary reason for long latency of TDMA aggregation scheduling. Indeed, it provides more potential of parallel transmissions over different frequency channels, thus minimizing time latency. In this paper, we focus on designing a multi-channel minimum latency aggregation scheduling protocol, named MC-MLAS, using a new joint approach for tree construction, channel assignment, and transmission scheduling. To our best knowledge, this is the first work in the literature which combines orthogonal channels and partially overlapping channels to consider the total latency involved in data aggregation. Extensive simulations verify the superiority of MC-MLAS in WSNs.     

触变型堵剂GX—I封堵大孔道技术的研究及应用

用一种工业无机胶结材料、固化剂（混合无机盐溶液）及触变性调节剂（复合无机物）配制成了具有明显触变性的堵剂浆液GX－I。详细考察了各个组份的用量对浆液初凝时间、触变性（以浆液静切力G10s和G10min表示）、流变性及固结体抗压强度的影响。得到了分别适用于封堵低温井大孔道、裂缝及封堵水泥环以上套漏（无机材料用量以水灰比表示W／C＝0.44-0.5),封堵较高井温油井出水层（W／C＝0．67－1．0）,水井调剖（W／C＝1．2－1．4）的GX－I堵剂。给出了可用于60－90℃、初凝时间为6－10小时的3个基本配方。用这3个配方堵剂浆液堵岩心,堵塞率＞97％。简要介绍了中原油田11口井使用GX－I堵剂的良好效果,包括层间封窜2口,堵套漏1口,油井堵水3口,注水井分层调剖5口,详细分析了封堵1口注水井管外窜槽情况。     

Hydraulic Jumps in Sloping Channels: Sequent Depth Ratio

A large variety of hydraulic jumps on horizontal and sloping inverts at the end of an ogee standard weir is investigated. An ogee standard weir was used to create supercritical flow and slopes of 0.0, ?0.025, ?0.05, ?0.075, and ?0.10 were built downstream of the weir. Based on the momentum equation in the horizontal direction, a method to predict the sequent depth ratio is presented. The theory agrees well with the results of the writers and previous investigators. A correlation was developed to predict the minimum Froude number needed to establish jumps on negative slopes. Observations showed that in those cases where the gravity force component in the jump was opposite to the flow direction, the water surface of the surface roller became undular and unstable. The hydraulic jump on an entirely adverse slope was almost impossible to control. The analysis of experimental data showed that the negative slope of the basin reduces the sequent depth ratio, while a positive slope increases the sequent depth ratio.     

Creeping Film Models for Rotating Channels

A theoretical analysis is presented for the development of a liquid film at the walls of vertically placed centrifugal separators. The liquid film arises at the walls of these separators due to the action of the centrifugal force on the entrained liquid phases. The analysis applies to situations, for which the liquid load is small, i.e., the film thickness is much smaller than the height of the channel. This implies that the film can be regarded as a laminar boundary‐layer type flow with negligible inertia effects. Solutions are presented for situations in which the liquid droplets flow co‐currently and counter‐currently with the gas flow.     

Gravitational and Shear Instabilities in Compound and Composite Channels

Linear analysis of gravitational instabilities in the presence of a shear layer and shear instabilities in the presence of a free surface is performed. This study is relevant to shallow mixing layers, such as flow in compound and composite channels and inflows at channel junctions. The variations of the channel bed, velocity profile, Froude number, and friction coefficients with the transverse (lateral) coordinate are considered. It is found that there is a threshold Froude number above which the flow is unstable with respect to gravity waves and below which the flow is unstable with respect to shear waves for a certain range of the bed friction number. For values of Froude number larger than the threshold value, the influence of the shear layer and channel walls on the characteristics of the gravitational instability is strong when the channel and the shear layer are of comparable width. This influence reduces as the channel becomes wider and disappears in the limit when the channel width becomes infinite. When the Froude number is below the threshold value, free surface deformation in the form of gravitational waves exerts a strong stabilizing influence on the shear instability. In particular, the value of the critical bed friction number decreases when either the Froude number of the fast stream (main channel) or the slow stream (flood plain) increases. That is, shallow mixing layers become more stable as the Froude number increases. Comparisons of the linear stability calculations with experimental data show reasonable agreement.     

Bed-Shear Stress Characteristics of a Simple, Prismatic, Rectangular Channel

This paper examines the use of data obtained from large eddy simulations in exploring the instantaneous characteristics of boundary shear stress. The probability density functions (PDF) of the shear stress are shown to be non-Gaussian, whereas the PDF of the shear force per unit length is found to be approximately Gaussian. Conditional sampling is used in order to provide an insight into the average behavior of an extreme shear stress event. Finally, proper orthogonal decomposition illustrates that the behavior of the shear stress is complex and cannot necessarily be attributed to a single major flow event.     

Anomalous Contraction Scour? Vertical-Contraction Case

Clear-water scour due to a short vertical (pressure flow) contraction was investigated in a laboratory channel. Two approach velocities were studied for a (nominally) single configuration of depth and degree of contraction, with experiments conducted for various durations up to a maximum of 48 h, and the evolution of the scour hole over time monitored. The location of maximum scour in both cases was observed to occur downstream of the contraction, with maximum scour depths substantially in excess of values predicted by published models, even though equilibrium scour conditions were not reached.     

变频器在焦油离心机中的应用

本文着重论述了变频器在焦油离心机生产运行中的应用,记录了焦油离心机变频器在运行中出现的各种问题,并提出了解决方案以及运行维护建议。有效地提高了生产设备的稳定运行,显著地提高了经济效益。     

High SNR sum capacity analysis of BD MIMO BC systems with imperfect CSI

We investigate the sum capacity of Block Diagonalization precoding Multiple Input Multiple Output Broadcast Channels (BD MIMO BC) with imperfect Channel State Information (CSI) at the base station. Since it is difficult to obtain the exact expression, a lower and an upper bounds of the sum capacity under Gaussian channel estimation errors are drived instead. Analyses show that the gap between two bounds is considerably tight at all Signal to Noise Ratio (SNR) region. From the lower bound of the sum capacity, we can see that the multiplexing gain tends to be zero at high SNR region, which indicates that the BD MIMO BC system with channel estimation errors is interference-limited at high SNR.