Modeling continuous traffic flow with the average velocity effect of multiple vehicles ahead on gyroidal roads

In the future connected vehicle environment,the information of multiple vehicles ahead can be readily collected in real-time,such as the velocity or headway,which provides more opportunities for information exchange and cooperative control.Meanwhile,gyroidal roads are one of the fundamental road patterns prevalent in mountainous areas.To effectively control the system,it is therefore significant to explore the evolution mechanism of traffic flow on gyroidal roads under a connected vehicle environment.In this paper,we present a new continuum model with the average velocity of multiple vehicles ahead on gyroidal roads.The stability criterion and KdV-Burger equation are deduced via linear and nonlinear stability analysis,respectively.Solving the above KdV-Burger equation yields the density wave solution,which explores the formation and propagation property of traffic jams near the neutral stability curve.Simulation examples verify that the model can reproduce complex phenomena,such as shock waves and rarefaction waves.The analysis of the local cluster effect shows that the number of vehicles ahead and the radius information,and the slope information of gyroidal roads can exert a great influence on traffic jams.The effect of the first and second terms are positive,while the last term is negative.

MULTI-SCALE COHERENT STRUCTURES IN TURBULENT BOUNDARY LAYER DETECTED BY LOCALLY AVERAGED VELOCITY STRUCTURE FUNCTIONS

The time sequence of longitudinal velocity component at different vertical locations in turbulent boundary layer was finely measured in a wind tunnel. The concept of coarse_grained velocity structure functions, which describes the relative motions of straining and compressing for multi_scale eddy structures in turbulent flows, was put forward based on the theory of locally multi_scale average. Based on the consistency between coarse_grained velocity structure function and Harr wavelet transformation,detecting method was presented, by which the coherent structures and their intermittency was identified by multi_scale flatness factor calculated by locally average structure function. Phase_averaged evolution course for multi_scale coherent eddy structures in wall turbulence were extracted by this conditional sampling to educe scheme. The dynamics course of multi_scale coherent eddy structures and their effects on statistics of turbulent flows were studied.

Simple analytical model for depth-averaged velocity in meandering compound channels

A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.

Correlation Method of Average Plasma Velocity Measurement in Hall-Effect Thrusters

A new method to measure the average plasma velocity in a Hall-effect thruster is presented. The method is brought forward in virtue of the characteristics of low frequency oscillation induced by the propellant ionization in the channel and the oriented movement feature of the plasma density out of the channel. The method, equivalent to the correlation method generally used in the signal processing field, provides a solution to the problem of specific impulse measurement on a timescale of hundreds of microseconds and makes the time evolution of average plasma velocity clear. The comparison between the measured value and the calibrated value shows that the relative error is about 3%.

A Study on Average Velocity Ratios(V_P/V_S) in the Hohhot-Baotou Area

The geological structure is complex in the Hohhot-Baotou area.Several earthquakes with MS≥6.0 have occurred in the area in history.This article selected the Hohhot-Baotou area as the study region and divided it into 2 sub-regions,each with a spatial scope of 3°×2°,according to the spatial distribution of ML≥1.0 earthquakes occurring between January 2001 and April 2010,and the layout of the seismic network in the study region.Average velocity ratios of respective sub-regions were calculated,and comparative analysis was made on their temporal and spatial variations.Results show that there are slight differences between sub-regions in the variation amplitude of average velocity ratio curves over time,which mostly remains between 2.5% to 2.584%.In the Hohhot area,the average velocity ratio is 1.722,significantly lower than the average velocity ratio of 1.733 in the Baotou area.We preliminarily concluded that this was related to the distribution of fault structures and properties of underground media in the Hohhot area.

Analysis on the velocity relationship and deceleration of long-rod penetration

The relationship between the average penetration velocity,UˉUˉ,and the initial impact velocity, V0V0,in long-rod penetration has been studied recently. Experimental and simulation results all show the linear relationship between UˉUˉ and V0V0 over a wide range of V0V0 for different combinations of rod and target materials. However, the physical essence has not been fully revealed.In this paper, the Uˉ?V0Uˉ?V0relationship is profoundly analyzed using hydrodynamic model and Alekseevskii-Tate model. Especially, the explicitUˉ?V0Uˉ?V0 relationships are derived fromapproximate solutions of Alekseevskii-Tate model. Besides, the decelerationin long-rod penetration is discussed. The decelerationdegree is quantified by adeceleration index,α=2μˉ/(KΦJp)≈Ypρ?1/2p(ρ?1/2p+ρ?1/2t)V?20α=2μˉ/(KΦJp)≈Ypρp?1/2(ρp?1/2+ρt?1/2)V0?2, which is mostly related to the impact velocity, rod strength and rod/target densities. Thus, the state of penetration process can be identified and designed in experiments.

Prediction of velocity distribution in straight open-channel flow with partial vegetation by singular perturbation method

A numerical analysis model based on two-dimensional shallow water differential equations is presented for straight open-channel flow with partial vegetation across the channel. Both the drag force acting on vegetation and the momentum exchange between the vegetation and non-vegetation zones are considered. The depth-averaged streamwise velocity is solved by the singular perturbation method, while the Reynolds stress is calculated based on the results of the streamwise velocity. Comparisons with the experimental data indicate that the accuracy of prediction is significantly improved by introducing a term for the secondary current in the model. A sensitivity analysis shows that a sound choice of the secondary current intensity coefficient is important for an accurate prediction of the depth-averaged streamwise velocity near the vegetation and non-vegetation interfaces, and the drag force coefficient is crucial for predictions in the vegetation zone.

Analytical solutions for transverse distributions of stream-wise velocity in turbulent flow in rectangular channel with partial vegetation

The theory of poroelasticity is introduced to study the hydraulic properties of the steady uniform turbulent flow in a partially vegetated rectangular channel. Plants are assumed as immovable media. The resistance caused by vegetation is expressed by the theory of poroelasticity. Considering the influence of a secondary flow, the momentum equation can be simplified. The momentum equation is nondimensionalized to obtain a smooth solution for the lateral distribution of the longitudinal velocity. To verify the model, an acoustic Doppler velocimeter （ADV） is used to measure the velocity field in a rectangular open channel partially with emergent artificial rigid vegetation. Comparisons between the measured data and the computed results show that the method can predict the transverse distributions of stream-wise velocities in turbulent flows in a rectangular channel with partial vegetation.

基于平均速度分析的近地表纵波速度反演

面波频散曲线对于横波速度、纵波速度、层厚等近地表地球物理参数的敏感度相差较大,现阶段通过频散曲线可以获得较为精确的近地表横波速度与厚度信息,但无法直接对纵波速度进行反演.研究表明,泊松比对于波长(W)-探测深度(D)关系较为敏感.基于这一发现,本文根据频散曲线与反演获取的横波速度结构计算平均速度,获取W-D关系曲线.但合成数据测试证明,因近地表浅层对应的W-D曲线变化较小,且浅层纵波速度反演不准确会使误差累积,直接反演W-D曲线无法获取可靠的纵波速度剖面.本文改进了基于平均速度分析的近地表纵波速度反演方法,在目标函数中加入了对浅层信息较为敏感的W/D-D信息,同时对W-D曲线与W/D-D曲线进行联合反演.合成数据测试证明可以获取较为准确地浅层与深层纵波速度.将该方法应用于实际地震数据中,联合反演得到的纵波速度剖面与微测井数据较为吻合,证明本文提出的方法可以不借助其他信息,仅通过面波频散信息,获取更为准确地近地表纵波信息.

热风加热沥青路面冲击射流共轭传热特性

为提高热风加热沥青路面的就地再生加热效果,基于热风冲击射流对流换热和沥青路面内部导热的共轭传热过程,建立了热风加热沥青路面的冲击射流共轭传热理论模型,选取有限容积法得到了共轭传热模型的通用离散方程,采用压力-速度耦合半隐式算法(semi-implicit method for pressure linked equations,SIMPLE)获得了整个求解域内温度场分布,选取平均热流密度和平均换热系数反映沥青路面加热效果,通过正交试验研究了热风出口速度和热风出口温度对路面加热效果的影响程度。仿真和试验结果表明:理论计算与实验温度场分布趋势吻合度高,两者平均误差为8.4%;平均热流密度和平均换热系数在加热初期均从最大值急剧下降,而后下降幅度逐渐减小趋于平衡,两者的仿真计算与实验结果趋势相同,平均误差分别为6.4%和7.8%;热风出口速度和热风出口温度对平均热流密度均有显著影响,热风出口速度对平均换热系数有显著影响,热风出口温度对平均换热系数的影响相较于平均热流密度指标表现为不显著。研究结果为后续沥青路面就地热再生热风加热温度控制和加热器设计提供了理论依据。

黑龙江结雅河口段流量对河道水动力特征的影响

黑龙江结雅河口段属于弯曲分汊型河段,水流条件复杂,且属于中俄界河,河势变化关乎国界线的稳定。为探明不同流量对河道水动力特征的影响,采用原位观测法对结雅河汇流比、汊道分流比、水动力轴线、深泓线水位、最大垂向平均流速随流量的变化特征开展研究。结果表明,结雅河的汇流比一般不低于0.3,汇流量对黑龙江干流径流量影响很大;分汊河段,河道流量越小,主槽分流比越大,且不低于0.5;流量越大,主流越偏向于凹岸;卡伦山站流量越大,结雅河口以上河道的水位和流速受到的顶托作用越明显。

经阴道彩色多普勒超声在子宫内膜病变患者中的应用价值

目的分析经阴道彩色多普勒超声在子宫内膜病变患者中的应用价值。方法选取2021年2月至2022年4月南昌大学第四附属医院收治的88例子宫内膜病变患者作为研究对象,所有患者均接受经阴道彩色多普勒超声及病理学检查,按照病理学检查结果将患者分为息肉组与癌变组,每组44例。比较两组二维超声子宫内膜情况、病灶血流动力学情况、经阴道彩色多普勒超声血流相关参数;以病理学检查结果为金标准,分析经阴道彩色多普勒超声对子宫内膜癌变的诊断效能。结果癌变组子宫内膜厚度厚于息肉组,内膜-肌层分界清晰、病灶回声均匀占比均低于息肉组,差异有统计学意义(P<0.05);癌变组血流丰富占比高于息肉组,差异有统计学意义(P<0.05);癌变组血流阻力指数(RI)、搏动指数(PI)均低于息肉组,时间平均峰值流速(TAP)慢于息肉组,差异有统计学意义(P<0.05);经阴道彩色多普勒超声对子宫内膜癌变的诊断灵敏度为86.36%,特异度为84.09%,准确度为85.23%;诊断息肉的灵敏度为84.09%,特异度为86.36%,准确度为85.23%。结论经阴道彩色多普勒超声对子宫内膜病变的诊断准确率较高,能通过血流动力学、RI、PI、TAP及影像学表现鉴别息肉或癌变。

深度小于30 m正常停钻V_(S30)预测公式精度分析

我国钻孔测速中在正常停孔条件下产生大量深度小于30 m的钻孔数据。由于正常停钻,我国几乎没有此类场地下深度超30 m的钻孔实测数据,故无法以同类场地大于30 m数据直接回归V_(S30)公式。国外区域数据建立的V_(S30)预测公式有区域性,其在场地特征类似才适用;针对我国深度小于30 m正常停孔下V_(S30)预测线性外插公式LEE为具有潜在可行性公式。因此,为了从已有公式中得到可靠的V_(S30)预测公式,基于地质宏观类比,在停钻深度没有到30 m数据条件下发展了对已有公式的精度分析方法。通过对平均剪切波速竖向分布特点的分析,提出“精度分析区间”;并在缺乏停钻深度到30 m直接验证数据的前提下,提出两种分析公式预测精度的方法:方法一中校核对象是实测数据,具有一定直接检验的特点,但仅适用于具有反算能力的公式;方法二是基于所有公式都具有的——换算深度越靠近30 m则V_(S30)预测越准确的特点提出的,适用范围广。以滇中引水工程为案例,应用两种方法于该工程中深度小于30 m的正常停钻数据,为该工程选出精度最高公式LEE。

漂浮植被作用下水流纵向流速的垂向分布及离散特性研究

为探究漂浮植被影响下明渠水流流速及纵向离散系数的沿程变化特性,采用Fluent软件中的k-ε模型进行三维数值模拟并与水槽试验结果进行对比分析,在模型验证合理的基础上,对漂浮植被不同根系下探深度及覆盖率下水流纵向时均流速的垂向分布特性进行研究,并基于改进的分区模型分析了含漂浮植被明渠的纵向离散系数。结果表明:漂浮植被水流垂向上可分为含植被水流层、无植被水流层与近河床层。纵向流速最大值出现在无植被水流层,其大小与植被下探深度及覆盖率呈正相关。含植被水流层的纵向流速随植被根系下探深度和覆盖率的增加而减小,无植被水流层及近河床层的纵向流速随着下探深度和覆盖率的增大而增大,且植被覆盖率及下探深度越大含植被水流层与无植被水流层的流速差异越大。纵向离散系数沿程表现出先增大后减小的趋势,在植被区中下游离散最为剧烈,且与植被下探深度和覆盖率呈正相关。

山东地区场地剪切波速经验外推模型及其适用性

场地剪切波速是进行场地分类和定量估计场地对地震动影响的重要参数,在工程抗震设防和震后震害快速评估等方面具有广泛应用。文中利用山东地区1336个工程场地的剪切波速剖面数据,分别基于常速度外推方法、速度梯度外推方法和条件独立方法建立了山东地区场地剪切波速V_(S20)和V_(S30)的经验外推模型。研究结果表明,常速度外推方法对较浅的钻孔进行波速外推时会产生明显的低估,且预测误差较大。速度梯度外推方法的拟合结果表现出明显的区域性特征,山东地区的V_(S30)预测结果与美国加州和北京平原地区的结果相比,总体上较为接近,但明显低于日本地区。综合考虑建立的3种区域外推模型的精度和预测误差,文中建议优先采用基于条件独立方法建立的山东地区的V_(S20)和V_(S30)经验外推模型,获得的波速外推结果可以较好地为山东地区场地分类提供依据。

四轴水平振动输送机的物料速度仿真分析与实验

针对当前四轴水平振动输送机的物料速度随输送机偏心轴相位角变化规律不明确的问题,以某钢厂水平振动输送机的参数为基础,对机体与物料速度进行了理论推导和仿真分析。首先,推导了机体激振力与机体速度的通用公式,并对3种初始相位角对应的机体速度进行了仿真,分析了初始相位角对机体速度的影响规律;然后,对机体速度和物料速度进行了对比仿真,并研究了物料起始运动时间、初始相位角以及角频率对物料速度的影响规律;最后,采用仿真软件分析了固定高速轴(或低速轴)的初始相位角时,物料稳态平均速度随低速轴(或高速轴)相位角变化的规律,并对相关内容进行了实验验证。研究结果表明:输送机4个偏心轴以及齿轮等相关部件组装完成后,物料的稳态平均速度不随任一个偏心轴质心相位角的变化而变化;在输送机稳定运行时,物料的稳态平均速度与其加入料槽内的先后顺序无关;此外,针对某一机型的最佳物料速度,在高速轴(或低速轴)的初始相位角不同时,两种轴的相位角差也可能不同,单纯指定相位角差3π/4、π/2或3π/2等特定角度以利于物料输送的方案是不合理的,应该同时规定高低速偏心轴的相位角。

淹没刚性植被明渠紊流沿程流动特性差异

淹没刚性植被通过改变水流结构,造成时均流速、紊动强度、雷诺应力等水力参数垂线分布不均匀和沿程差异化。采用声学多普勒测速仪(ADV)测量3种淹没度(3.0、4.0、5.0)下的流速,结合统计学方法,系统分析植被段内及其上、下游过渡段流速和紊动特性差异。结果表明:植被显著增强了水流紊动,且紊动特性取值与淹没度正相关;植被段内流速差异在低淹没度下的植被层内和高淹没度下的自由流动层内更加显著,而紊动特性沿程增强,且垂线分布具有相似性,最大值点位于冠层顶部附近;当淹没度满足KH涡的形成和发展条件时,随淹没度的增大,植被段内紊动特性垂线分布出现转折点(临近此点梯度急剧减小并趋于0)的断面数量增多,经验证,在充分发展的紊流区此点可作为KH涡的上边界点。

非均匀散粒粗糙床面明渠水流流速结构PIV试验研究

鉴于床面非均匀散粒粗糙直接影响明渠水流的流速结构问题,基于PIV水槽试验,研究了非均匀散粒粗糙床面明渠水流的流速结构,探讨了水流时均流速沿流向和沿垂线的分布规律,分析了脉动流速的象限分布特征。结果表明,梅花形排列的大尺度非均匀散粒粗糙显著影响了颗粒顶部以下的水流结构,大、小颗粒周围时均流速结构相似,颗粒大小明显影响了流动分离区形状尺度和内外层流体分界点位置;象限分析显示外层流体中,大颗粒使其上方区域Q2、Q4事件的概率减小;内层流体中Q1、Q3事件占主导,颗粒上游及大颗粒附近相比下游及小颗粒附近更易产生强紊流事件。

长江上游分汊河段不同深度水流的紊动特性研究

分汊河段水流的紊动特性对河床冲淤变化和鱼类生境有重要影响,而关于分汊河段水流紊动特性的水平分布的研究较少。为了厘清分汊河段水流的紊动特性,以长江上游部分河段为原型,开展概化模型试验,并对不同深度水流的3个方向(纵向、横向和垂向)的时均流速、紊动强度及紊动能的水平分布特征进行研究。结果表明:分汊水流在分流和汇流区域有低流速区,该区域的水流紊动较强。不同深度水流的紊动强弱与滩体水平剖面面积呈正相关关系,与河床的距离呈负相关关系;近底水流的强紊动区域较为分散;上层水流的强紊动区域较为集中。

巷道平均风速单点测试方法误差研究

为验证巷道平均风速单点测试方法可行性,提高巷道平均风速单点测试方法精度,采用Fluent数值模拟方法,计算各种断面形状、断面尺寸及支护方式巷道断面上平均风速单点测试误差分布。研究结果表明:在任意断面形状、断面尺寸及支护方式巷道断面上任意测点,巷道平均风速单点测试误差均小于6%,因此,巷道平均风速单点测试方法可行。根据巷道断面上平均风速单点测试误差分布情况,尽可能将风速传感器布置在误差小的位置,可进一步提高巷道平均风速单点测试方法精度。研究结果可为解决巷道平均风速快速精准测试问题,进而推进矿井通风智能化发展提供参考。