双速搅拌工艺

根据传统二次搅拌理论,提出了混凝土双速搅拌工艺,介绍了双速搅拌工艺的原理及优点,并指出了该工艺的实现方案.该工艺的应用可降低生产成本,提高混凝土的强度和生产率.     

高速铁路路基边坡纤维团粒喷播生态防护技术

针对高速铁路路基绿化工程高要求、少维护等特点,提出纤维团粒喷播技术,并详细阐述了其机理及特点.通过在京雄城际铁路路基边坡工程中的应用,归纳总结了该技术施工工艺流程:平整坡面→坡面覆土→铺设铁丝网→喷播基质→养护管理.喷播基质是利用喷播机械将性能优越的基质材料喷附至铁路路基坡面上的.工程应用表明该技术施工快,质量好,养护维修量小,经济性高.     

鱼雷发动机三组元比例控制器数值模拟

利用计算流体力学软件Pumplinx模拟鱼雷发动机中三组元比例控制器的内部流场,分析计算中不同压差情况下对比例控制器性能的影响,以及叶片与定子间间隙大小对于比例控制器性能的影响,同时对不同叶片数目下性能进行对比。计算结果表明:由于比例控制器为被动旋转马达结构,其转速和流量均随时间呈周期性脉动变化,随着工作压差增大,转速脉动幅度基本保持不变,而流量和扭矩脉动幅值增加;随着间隙增大,泄漏量增大,但流量、扭矩、转速脉动幅值大幅降低,出口流量较为平稳;叶片数目增多后比例控制器转速降低、排量降低。由计算结果推断出目前比例控制器的最优叶片数目为4。本文可为进一步研究比例控制器精度问题提供参考。     

大学计算机基础课程教学方式的改革与实践

随着信息技术和计算机技术迅速发展和普及，传统的计算机基础教学方式面临新的挑战。本文探讨了当前形势下大学计算机基础课程教学模式的改革方向，根据多年的教学实践，探讨了高校计算机基础教学改革模式。     

Theory of safety surrogates using vehicle trajectories in macroscopic and microscopic settings: Application to dynamic message signs controlled traffic at work zones

This paper presents a new mathematical framework for obtaining quantitative safety measure using macroscopic as well as microscopic traffic data. The safety surrogate obtained from the macroscopic data is in terms of analysis performed on vehicle trajectories obtained from the macroscopic data. This method of obtaining safety measure can be used for many different types of applications. The safety surrogate for the traffic dynamics are developed in terms of a new concept of Negative Speed Differentials (NSD) that involve a convolution of vehicle speed function obtained from vehicle trajectories and then performing the integration of the square of the output for its negative values. The framework is applicable to microscopic traffic dynamics as well where we can use car following models for microscopic dynamics or the LWR model for macroscopic dynamics. This paper then presents the use of this new safety surrogate on the development of a feedback control law for controlling traffic in work zones using Dynamic Message Signs. A hybrid dynamics model is used to represent the switching dynamics due to changing DMS messages. A feedback control design for choosing those messages is presented as well as a simple simulation example to show its application.     

Mental models of driving and speed: biases,choices and reality

This paper provides a review of research performed by Svenson with colleagues and others work on mental models and their practical implications. Mental models describe how people perceive and think about the world including covariances and relationships between different variables, such as driving speed and time. Research on mental models has detected the time-saving bias [Svenson, O. (1970). A functional measurement approach to intuitive estimation as exemplified by estimated time savings. Journal of Experimental Psychology, 86, 204–210]. It means that drivers relatively overestimate the time that can be saved by increasing speed from an already high speed, for example, 90–130?km/h, and underestimate the time that can be saved by increasing speed from a low speed, for example, 30–45?km/h. In congruence with this finding, mean speed judgments and perceptions of mean speeds are also biased and higher speeds given too much weight and low speeds too little weight in comparison with objective reality. Replacing or adding a new speedometer in the car showing min per km eliminated or weakened the time-saving bias. Information about braking distances at different speeds did not improve overoptimistic judgments of braking capacity, but information about collision speed with an object suddenly appearing on the road did improve judgments of braking capacity. This is relevant to drivers, politicians and traffic regulators.     

Liner shipping network design with emission control areas: A genetic algorithm-based approach

To curb emissions, containerized shipping lines face the traditional trade-off between cost and emissions (CO₂ and SO_x) reduction. This paper considers this element in the context of liner service design and proposes a mixed integer linear programming (MILP) model based on a multi-commodity pickup and delivery arc-flow formulation. The objective is to maximize the profit by selecting the ports to be visited, the sequence of port visit, the cargo flows between ports, as well as the number/operating speeds of vessels on each arc of the selected route. The problem also considers that Emission Control Areas (ECAs) exist in the liner network and accounts for the vessel carrying capacity. In addition to using the MILP solver of CPLEX, we develop in the paper a specific genetic algorithm (GA) based heuristic and show that it gives the possibility to reach an optimal solution when solving large size instances.     

Modeling free-flow speed according to different water depths—From the viewpoint of dynamic hydraulic pressure

In this paper, we propose a method of modeling free flow speed from the viewpoint of hydroplaning. First, the lift forces for different water depths were estimated using Bernoulli’s equation. Compared with the result of the experimental test performed by the Japan Automobile Research Institute, the hydrodynamic pressure coefficient was determined to be 0.03 (tf s²/m⁴). The validation of the predicted lift force is found in another published paper. A very good match is found between the computed values by the proposed numerical model and the data in other published papers. Then, the loss of contact force is considered to evaluate the hydroplaning performance of a tire. To simulate the hydroplaning speed, a tire-sliding model was utilized to obtain the traction and friction forces between the road surface and the tire. The observation data obtained in Japan in 2009 is compared with the physically computed hydroplaning speed, yielding the conclusion that the traction force at the measured desired speed is, on average, 23.4% of the traction force at hydroplaning speed. The analytical model offers a useful tool to quantitatively show that the free flow speed changes as the water depth increase.     

双块式轨枕外形质量快速检测系统研制及应用

SK?2型双块式混凝土轨枕是高速铁路无砟轨道结构中的重要预制件,单一生产厂日均产量达到800~1400根,但目前的人工检测方式无法满足双块式轨枕的出厂检验要求。本文提出的双块式轨枕外形质量快速检测系统可满足TB/T 3397—2015《CRTS双块式无砟轨道混凝土轨枕》的出厂检验要求,与双块式轨枕生产线相匹配,大大提高了检测效率,实现了双块式轨枕全参数、自动化、智能化检测。检测数据自动上传至生产管理平台,可对双块式轨枕生产质量进行跟踪管理。     

The identification and empirical characterization of vehicular (Lagrangian) fundamental diagrams in multilane traffic flow

Traditional macroscopic traffic flow modeling framework adopts the spatial–temporal coordinate system to analyze traffic flow dynamics. With such modeling and analysis paradigm, complications arise for traffic flow data collected from mobile sensors such as probe vehicles equipped with mobile phones, Bluetooth, and Global Positioning System devices. The vehicle‐based measurement technologies call for new modeling thoughts that address the unique features of moving measurements and explore their full potential. In this paper, we look into the concept of vehicular fundamental diagram (VFD) and discuss its engineering implications. VFD corresponds to a conventional fundamental diagram (FD) in the kinematic wave (KW) theory that adopts space–time coordinates. Similar to the regular FD in the KW theory, VFD encapsulates all traffic flow dynamics. In this paper, to demonstrate the full potential of VFD in interpreting multilane traffic flow dynamics, we generalize the classical Edie's formula and propose a direct approach of reconstructing VFD from traffic measurements in the vehicular coordinates. A smoothing algorithm is proposed to effectively reduce the nonphysical fluctuation of traffic states calculated from multilane vehicle trajectories. As an example, we apply the proposed methodology to explore the next‐generation simulation datasets and identify the existence and forms of shock waves in different coordinate systems. Our findings provide empirical justifications and further insight for the Lagrangian traffic flow theory and models when applied in practice. Copyright © 2015 John Wiley & Sons, Ltd.