错列双钝体断面气动绕流干扰效应的数值模拟

为研究既有桥梁对近桥位复线桥的气动干扰,选取不同梁高典型断面,采用增强壁面处理(EWT)的数值模拟方法,对比研究了主梁断面高度、来流风攻角及风向等因素对错列双钝体断面间的气动特性影响,并对其流场结构进行了分析.研究结果表明:受既有桥梁影响,复线桥主梁断面在位于迎风向和背风向时,三分力系数与单幅断面差异显著.对于不同梁高情况,复线桥监测断面位于背风向时,迎风侧腹板负压区随遮挡面积的增大而增大,扭转效应更为明显,升力方向随梁高变化发生改变;对于不同来流攻角情况,背风向监测断面在负攻角下所受阻力较对应正攻角略大,攻角增大引起了断面间大涡的破裂.断面形状、高度、遮挡面积及来流攻角均在不同程度上引起绕流特性的改变.     

长江阶地粉质黏土相似材料配比试验研究

为确定长江阶地粉质黏土相似材料配比方案,本文研究原材料间配比关系。基于三因素三水平正交试验设计方法,以滑石粉、膨润土、石英砂和水为原料,配置基坑模型试验粉质黏土相似材料,通过剪切试验获取九组配比方案的黏聚力和内摩擦角两个物理力学指标,采用极差法和方差法分析各因素的敏感性与显著性,研究滑石粉、膨润土、石英砂以及水含量对黏聚力和内摩擦角的影响规律。结果表明:极差法与方差法分析结果具有一致性,两种方法能合理判断各因素对考察指标的敏感性与显著性;膨润土掺量虽少,但对粉质黏土的黏聚力有很大程度的影响,其次为滑石粉含量,当滑石粉含量增多时,相似材料黏聚力逐渐增大;滑石粉含量为相似材料内摩擦角的主要控制因素。试验方法和结果可为其他模型试验中土质相似材料的配比提供参考。     

疲劳驾驶转向特征指标的个体差异敏感度分析

个体差异是影响疲劳驾驶识别的重要因素. 为研究基于转向行为的疲劳驾驶识别受个体差异的影响，本文对疲劳驾驶转向特征指标的个体差异敏感度进行分析. 通过实车试验获得自然驾驶数据，对正常和疲劳状态下的指标进行Kruskal-Wallis(KW)检验，以H 统计量表示指标有效性；以H 统计量最大的单被试为基础逐一与其他被试组成双被试组合，采用线性模型拟合双被试组合的H 统计量和指标个体差异度，以斜率绝对值表征指标个体差异敏感度. 研究获得9 个转向特征指标的个体差异敏感度，结果表明，敏感度越低，指标有效性受个体差异影响越小，其中方向盘转角标准差的个体差异敏感度最低为2.056. 本研究可为转向特征指标的性能评估及疲劳驾驶识别模型的特征选择提供参考.     

表面改性剂对橡胶垫板动态性能的影响

通过掺加不同表面改性剂制作了5种配方试样,采用橡胶加工分析仪,材料疲劳试验机和冲击回弹试验仪,研究了有无表面改性剂以及不同种类表面改性剂对橡胶垫板动态性能的影响规律.研究结果表明:加入表面改性剂后,配方1(基准配方)到配方5(表面改性剂为LONSIL 4C)橡胶动静刚度比、损耗功和力学损耗角正切tanδ均依次减小;配方1到配方5储能模量依次减小,Payne效应越来越不明显;配方1到配方5橡胶材料回弹性依次增大;动静刚度比与损耗功、回弹性和tanδ均有很好的相关性.在试验室可以用测试回弹性或损耗功,或tanδ代替测试动静刚度比,以降低低动静刚度比橡胶垫板的研发成本.     

基于隧道污染机制的内壁亮化耐污涂层技术试验研究与应用

为提高隧道行车视觉环境，实现内壁涂层亮化耐污对提升隧道运营安全与节能的促进作用，解决现有我国隧道品质提升缺乏内壁涂层技术选型依据的问题，开展基于隧道内壁污染机制和分布特点的涂层亮化耐污机制研究，并以接触角和反射率为主要指标，进行4种不同涂层材料的亮化耐污试验。试验结果表明： 在相同平整度条件下，材料接触角越接近超疏水接触角，耐污效果越好，并可使反射率保持在较高水平，在后期运营中具备较明显的易清洗优势，且清洗后的反射率与刚实施完成后的反射率接近，说明这类材料对提升公路隧道运营品质、降低运营成本具有积极的促进作用。     

On the sway stability improvement of car–caravan systems by articulated connections

The present analysis is addressed to some promising connection arrangements between the towing vehicles and the towed trailers, where the two units are linked by four-bar isosceles trapeziums in place of the conventional pintle hitch. Two types of instability, of the divergent type or the oscillating type, may be analysed by the Routh–Hurwitz criterion or by the direct analysis of the characteristic equation. The constant term of this equation vanishes at the divergent instability threshold (zero of a real root), whereas the equation splits into two lower degree algebraic ‘sub-equations’ when the oscillating instability arises (pair of pure imaginary roots). A large field of geometrical configurations of the four-bar linkage may be quickly tested by numerical search procedures, including those where the sidebars of the linkage converge towards the inside of the drawing car and shift the relative centre of rotation forward, and those converging backward towards the trailer. Maps of the critical velocity as a function of the geometrical or physical parameters may be easily traced. They clearly show the favourable influence of the forward four-bar connection in general and the benefits achievable comparing with the conventional coupling. Actually, it is conceivable to increase the critical speed by optimising the four-bar design depending on the weight distribution on the axles and on the other geometrical and physical properties. Moreover, this type of connection may produce significant corrections to the under-steering or over-steering conduct of the articulated vehicle. The off-tracking and the manoeuvrability along curved paths are also studied, showing the benefits or the drawbacks of the four-bar linkage for the various configurations.     

Measurement and mathematical model of a driver's intermittent compensatory steering control

The compensatory (feedback) component of a human driver's steering control is examined. In particular, the effect of the cognitive process is studied. Model predictive control theory is used to implement models of intermittency in cognitive processing. Experiments using a fixed-base driving simulator with periodic occlusion of the visual display are used to reveal the nature of the driver's steering behaviour. An intermittent serial-ballistic control strategy is found to match the measured behaviour better than intermittent zero-order hold or continuous control. The findings may enable some insight to driver-vehicle interaction and vehicle handling qualities.     

Design and validation of a robust active trailer steering system for multi-trailer articulated heavy vehicles

ABSTRACT

Multi-trailer articulated heavy vehicles (MTAHVs) are increasingly used around the world due to their economic and environmental benefits. However, MTAHVs exhibit poor maneuverability and low lateral stability, which may lead to fatal traffic accidents. Given the safety risks, it is necessary to solve the steering and stability problems of MTAHVs before they are safely mass deployed on our roads. To this end, active trailer steering (ATS) based on the linear quadratic regulator (LQR) technique has been explored. The LQR-based ATS demonstrates improved maneuverability and enhanced lateral stability. In the ATS design, the vehicle and operating parameters are assumed constant. Thus, it is natural to question the robustness of the ATS in presence of vehicle and operating parameter uncertainties. To address the problem, this paper proposes a robust ATS system. The robust ATS controller is designed using a linear matrix inequality (LMI) based LQR method. In the design, both vehicle and steering actuator parameter uncertainties are considered; to enhance the robustness of the ATS, the weighting matrices of the proposed controller are optimized. The robust controller is applied to an A-Train Double, one type of MTAHV. The effectiveness of the robust ATS is demonstrated using numerical and hardware-in-the-loop real-time simulations.     

Stability control of 4WS vehicles using robust IMC techniques

A robust nonparametric approach to vehicle stability control by means of a four-wheel steer by wire system is introduced. Both yaw rate and sideslip angle feedbacks are used in order to effectively take into account safety as well as handling performances. Reference courses for yaw rate and sideslip angle are computed on the basis of the vehicle speed and the handwheel angle imposed by the driver. An output multiplicative model set is used to describe the uncertainty arising from a wide range of vehicle operating situations. The effects of saturation of the control variables (i.e. front and rear steering angles) are taken into account by adopting enhanced internal model control methodologies in the design of the feedback controller. Actuator dynamics are considered in the controller design. Improvements on understeer characteristics, stability in demanding conditions such as turning on low friction surfaces, damping properties in impulsive manoeuvres, and improved handling in closed loop (i.e. with driver feedback) manoeuvres are shown through extensive simulation results performed on an accurate 14 degrees of freedom nonlinear model, which proved to give good modelling results as compared with collected experimental data.