基于时间效益的城市公交专用道设置流量条件

为了精确分析公交专用道设置临界条件,在基本路段车速模型适用性分析的基础上,引入公交车流量、社会机动车流量、公交车比例等参数,分别建立了改进的混行机动车运行速度模型和设置公交专用道后机动车运行速度模型,并选取单向三车道路段进行实验调查,用采集的数据对改进模型进行标定.运用改进的模型,对公交专用道设置前后车辆运行速度差异性的分析可以发现,随着路段车流量(饱和度)的变化,车辆速度差异的变化呈现无差异、差异变大两个显著的阶段.进而从总出行时间的最小的角度,建立时间效率模型,用于计算设置公交专用道的临界条件.试算结果表明在公交比例较小时公交专用道设置的临界条件低于传统标准,公交比例较大时公交专用道设置的临界条件高于传统标准,公交比例变量的引入有助于细化公交专用道设置的临界条件.

设置间歇式公交专用进口道的流量条件研究

针对交叉口处公交车辆对道路资源需求的动态特征,提出了一种间歇式公交专用进口道的控制系统及控制方法。为了得到间歇式公交专用进口道适用的交通流量条件,首先研究了设置间歇式公交专用进口道后社会车辆和公交车辆的延误;然后通过算例定量分析了设置间歇式公交专用进口道前后交叉口人总延误差的变化规律。研究结果表明:在同一交通流向有两条进口车道的情况下,周期时长为60s、100s、120s的交叉口设置间歇式公交专用进口道的临界交通饱和度分别为0.75、0.65、0.60。当进口道交通饱和度小于临界交通饱和度时,可以考虑在该流向设置间歇式公交专用进口道。

雁石坪水文站流量巡测条件的分析与探讨

水文巡测是21世纪水文资料采集的主要手段和方法,是水文面向社会的根本出路,它将打破以站为家的工作模式,改变传统水文测验方式,建立"站队结合"新型管理模式,同时为整合人力资源,提高工作效率,发展站网,寻求条件艰苦的偏远地区开展水文活动提供了有效的途径。能否开展巡测,就是要对测站水文资料进行技术分析,分析论证各项技术条件能否满足水文巡测的要求。以雁石坪站为实例,对流量巡测条件进行了分析论证。

采用T型喷口的喷水推进船模阻力数值模拟

T型喷口是一种附加在喷水推进装置后方,改变水流纵向喷射方向为横向的模型试验装置。该装置只在船体内部流道上产生力的作用,既可反映常规喷口推进船模自航状态下,推进装置的抽吸作用对船尾边界层的影响,又对船身浮态影响很小,仅通过船模阻力试验和获流区PIV测试试验,结合动量通量法换算,可将常规推进船模自航试验中,推进系统对船体阻力的影响分离出来。通过CFD手段,采用流量边界条件法,对某带有T型喷口推进装置的船模阻力性能进行数值模拟,并与模型试验结果进行比较分析。最后,对T型喷口装置的工作原理进行说明。

水利工程中水闸加固施工技术的应用分析

水闸,作为水利工程的重要组成部分,对保障水资源合理分配和防止洪灾具有重要意义。对其加固施工技术进行研究,以保障其在各种环境和流量条件下的安全运行,是目前研究热点。本研究针对水利工程中水闸加固施工技术应用进行了理论分析与实践应用研究。首先,介绍了水闸加固施工的相关原理和技术要点,包括水闸的功能及结构、水闸的老化和病害分析、水闸的加固原理、以及水闸加固施工中常用技术等内容。其次,通过对国内外水利工程中水闸加固实例的分析,总结了不同环境条件下、不同工况下水闸加固施工技术的优选应用。结果表明,在流速较大、水位变化频繁等复杂工况下,运用新型高强度、抗腐蚀、水下凝固的混凝土材料进行水闸加固,能够有效提高水闸的稳定性和持久性,降低后期维修成本。这些研究成果,为推动水利工程施工技术的发展和提高水闸运行的安全性和稳定性提供了理论支持和应用指导。

交通运输网络中两个结点间有流量约束的最小费用最大流算法

对交通运输网络最小费用最大流的分配是在满足容量限制条件和流量守恒条件下,基于总费用最低的原则进行的,但在实际应用中,通常对交通运输网络中两个结点之间的流量有具体的要求和约束限制条件.针对交通运输网络中两个结点之间有流量约束的最小费用最大流问题进行了分析,总结了两个结点之间的流量不能超过限制值、不能低于限制值以及在一定范围内的3种约束条件.基于连续最短路算法中构造伴随增流网络的思路,设计了这3种约束限制条件下的最小费用最大流分配算法.利用这个算法,可以解决交通运输网络中两个结点之间有流量约束的最小费用最大流分配问题.在交通运输领域,两个结点之间有流量约束的最小费用最大流问题普遍存在,这些算法也为解决实际的运输问题提供了应用基础.

交通网络两个相邻结点之间有流量约束的最大流分配算法

交通网络最大流的分配是基于容量限制条件和流量守恒条件进行的,但在实际应用中,往往对交通网络中两个相邻结点之间的流量有具体的要求和约束限制。本文对交通网络中两个相邻结点之间的流量约束问题进行了分析,基于寻找增流链的算法,构造了带有上限或下限三种流量约束限制条件下的最大流分配算法,这些算法可以为解决实际的交通问题提供一定的应用基础。

Application of empirical mode decomposition based energy ratio to vortex flowmeter state diagnosis

To improve the measurement performance, a method for diagnosing the state of vortex flowmeter under various flow conditions was presented. The raw sensor signal of the vortex flowmeter was adaptively decomposed into intrinsic mode functions using the empirical mode decomposition approach. Based on the empirical mode decomposition results, the energy of each intrinsic mode function was extracted, and the vortex energy ratio was proposed to analyze how the perturbation in the flow affected the measurement performance of the vortex flowmeter. The relationship between the vortex energy ratio of the signal and the flow condition was established. The results show that the vortex energy ratio is sensitive to the flow condition and ideal for the characterization of the vortex flowmeter signal. Moreover, the vortex energy ratio under normal flow condition is greater than 80%, which can be adopted as an indicator to diagnose the state of a vortex flowmeter.

Mixing time in stirred vessels: A review of experimental techniques

Mixing time is de fined as the time required for achieving a certain degree of homogeneity of injected tracer in a unit operation vessel. It has been used as a key parameter for assessing the performance of a mixing system. From an experimental standpoint, several techniques have been developed for measuring the mixing time. Based on the disturbances to fl ow, they can be classi fied into two groups: non-intrusive and intrusive. However, depending on the type of data generated, they can be also classi fied into direct measurements and indirect measurements(Eulerian and Lagrangian). Since the techniques available for measuring mixing times in an agitated tank do not provide the same information, its choice depends on several factors, namely: accuracy, reproducibility,suitability, cost, sampling speed, type of data, and processing time. A review of the experimental techniques reported in the literature in the last 50 years for the measurement of mixing time in stirred vessels under single and gas–liquid fl ow conditions with Newtonian and non-Newtonian fl uids in the laminar and turbulent regime is made, and a comparison between these techniques is also presented.

Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.

Mixed convective heat and mass transfer analysis for peristaltic transport in an asymmetric channel with Soret and Dufour effects

The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.

Crossing point temperature of coal

A further understanding of the self-heating of coal was obtained by investigating the crossing point temperature（CPT） of different ranks of coal.The tests were carried out using a self-designed experimental system for coal self-heating.50 g（±0.01 g） of coal particles ranging from 0.18 mm to 0.38 mm in size were put into a pure copper reaction vessel attached to the center of a temperature programmed enclosure.The temperature program increased the temperature at a rate of 0.8℃/min.Dry air was permitted to flow into the coal reaction vessel at different rates.The surrounding temperature and the coal temperature were monitored by a temperature logger.The results indicate that CPT is affected by coal rank,moisture,sulfur, and the experimental conditions.Higher ranked coals show higher CPT values.A high moisture content causes a delay phenomenon during the self-heating of the coal.Drying at 40℃decreases the effects of moisture.The reactivity of sulfur components in the coal is low under dry and low-temperature conditions. These components form a film that covers the coal surface and slightly inhibits the self-heating of the coal. The flow rate of dry air,and the heating rate of the surroundings,also affect the self-heating of the coal.The most appropriate experimental conditions for coal samples of a given weight and particle size were determined through contrastive analysis.Based on this analysis we propose that CPTs be determined under the same,or nearly the same conditions,for evaluation of the spontaneous combustion of coal.

Effect of flow rate on environmental variables and phytoplankton dynamics:results from field enclosures

To investigate the effects of flow rate on phytoplankton dynamics and related environment variables,a set of enclosure experiments with different fl ow rates were conducted in an artificial lake. We monitored nutrients,temperature,dissolved oxygen,p H,conductivity,turbidity,chlorophyll-a and phytoplankton levels. The lower biomass in all flowing enclosures showed that flow rate significantly inhibited the growth of phytoplankton. A critical flow rate occurred near 0.06 m/s,which was the lowest relative inhibitory rate. Changes in flow conditions affected algal competition for light,resulting in a dramatic shift in phytoplankton composition,from blue-green algae in still waters to green algae in flowing conditions. These findings indicate that critical flow rate can be useful in developing methods to reduce algal bloom occurrence. However,flow rate significantly enhanced the inter-relationships among environmental variables,in particular by inducing higher water turbidity and vegetative reproduction of periphyton( Spirogyra). These changes were accompanied by a decrease in underwater light intensity,which consequently inhibited the photosynthetic intensity of phytoplankton. These results warn that a universal critical flow rate might not exist,because the effect of flow rate on phytoplankton is interlinked with many other environmental variables.

干旱区间歇性河流河道两侧地下水运动模型及其求解方法

本文根据间歇性河流河道充水和停水过程周期性重复出现的水文特征,建立了河道两侧区域地下水运动的一维非稳定流模型,提出了把流量边界条件与水位界条件相互转换来求解模型的一种方法。最后应用上述模型分析西北某内陆河下游间歇性输水条件下河道两侧地区地下水位恢复状况,为输水生态效应的定量评价提供了理论基础。

The characteristics of rill development and their effects on runoff and sediment yield under different slope gradients

Rill formation is the predominant erosion process in slope land in the Loess Plateau, China. This study was conducted to investigate rill erosion characteristics and their effects on runoff and sediment yielding processes under different slope gradients at a rate of 10°, 15°, 20° and 25° with rainfall intensity of 1.5 mm min-1 in a laboratory setting. Results revealed that mean rill depth and rill density has a positive interrelation to the slope gradient. To the contrary, width-depth ratio and distance of the longest rill to the top of the slope negatively related to slope gradient. All these suggested that increasing slope steepness could enhance rill headward erosion, vertical erosion and the fragmentation of the slope surface. Furthermore,total erosion tended to approach a stable maximum value with increasing slope, which implied that there is probably a threshold slope gradient where soil erosion begins to weaken. At the same time, the correlation analysis showed that there was a close connection between slope gradient and the variousindices of soil erosion: the correlation coefficients of slope gradient with maximal rill depth, number of rills and the distance of the longest rill from the top of the slope were 0.98, 0.97 and-0.98, respectively,indicating that slope gradient is the major factor of affecting the development of rills. Furthermore,runoff was not sensitive to slope gradient and rill formation in this study. Sediment concentration,however, is positively related to slope gradient and rill formation, the sediment concentrations increased rapidly after rill initiation, especially. These results may be essential for soil loss prediction.

干旱区间歇性河流河道两侧地下水运动模型及其求解方法

本文根据间歇性河流河道充水和停水过程周期性重复出现的水文特征,建立了河道两侧区域地下水运动的一维非稳定流模型,提出了把流量边界条件与水位边界条件相互转换来求解模型的一种方法。最后应用上述模型分析西北某内陆河下游间歇性输水条件下河道两侧地下水位恢复状况,为输水生态效应的定量评价提供了理论基础。

Experimental study on convection heat transfer and air drag in sinter layer

Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimental method. The experimental results show that heat conduction of sinter impacts the measurement of convection heat transfer coefficient. Convection heat transfer increases with the increase of air volumetric flow rate. Sinter layer without small particles(sample I) gives higher convection heat transfer coefficient than that with small particles(sample II). Under the considered conditions, volumetric convection heat transfer coefficient is in the range of 400-1800 W/(m3·°C). Air pressure drop in sinter layer increases with the increase of normal superficial velocity, as well as with the rise of air temperature. Additionally, air pressure drop also depends on sinter particle size distribution. In considered experimental conditions, pressure drop in sinter sample II is 2-3 times that in sinter sample I, which resulted from 17% small scale particles in sinter sample II.

Feasibility of monitoring a mine fan by using interaction of vibrator system

The impeller of turbo machinery is a typical nonlinear multi-oscillator system.The vibration of each module is coupling, including fluid-solid coupling of the blade.The subject of our investigation was a KDF-5 mine fan for which we analyzed air vibration signals and axial vibration signals by using correlation dimension analysis under five variable working conditions.The results indicate that their correlation dimension curves show a uniform trend.That is to say, the characteristics of the variation signals of the integral structure are correlated and mutually embodied.It proves that it is possible to monitor the working state of a mine fan by coupling the vibration signals and air vibration signals for these are more sensitive in representing the status of the impeller system.

Detailed string stability analysis for bi-directional optimal velocity model

The class of bi-directional optimal velocity models can describe the bi-directional looking effect that usually exists in the reality and is even enhanced with the development of the connected vehicle technologies. Its combined string stability condition can be obtained through the method of the ring-road based string stability analysis. However, the partial string stability about traffic fluctuation propagated backward or forward was neglected, which will be analyzed in detail in this work by the method of transfer function and its H∞ norm from the viewpoint of control theory. Then, through comparing the conditions of combined and partial string stabilities, their relationships can make traffic flow be divided into three distinguishable regions, displaying various combined and partial string stability performance. Finally, the numerical experiments verify the theoretical results and find that the final displaying string stability or instability performance results from the accumulated and offset effects of traffic fluctuations propagated from different directions.

Enhancement of Critical Heat Flux in Tight Rod Bundle with Wire Spacer

The experiment of CHF （critical heat flux） was conducted for water boiling two-phase flow in three-pin tight rod bundle. The effects of with and without wire spacers and the pitch to diameter ratio p/d on CHF were investigated under the conditions of mass flux range 250-430 kg/（m2·s）, inlet temperature from 70 ℃ to 92 ℃ and the pressure of 0.1 MPa. The CHF was enhanced by wire spacers in comparison with the results of CHF without wire spacers. The CHF was enhanced by reducing thep/dfrom 1.18 to 1.10 under the same flow rate condition, although it did not change appreciably with the change ofp/d under the same mass flux condition.