非饱和重塑黄土抗剪强度影响因素的试验研究

通过直剪试验研究了非饱和重塑黄土在不同含水量、干密度与加荷等级情况下的粘聚力与内摩擦角变化,以确定含水量、干密度与加荷等级分别对非饱和重塑黄土抗剪强度的影响。从黄土矿物成分的微观角度分析了含水量与干密度对黄土抗剪强度造成影响的原因。受颗粒之间的相互作用与粒间水的张力作用,非饱和重塑黄土的粘聚力随干密度的增大而增大,呈指数变化;非饱和重塑黄土的内摩擦角随干密度的增大而少量增大,近似呈线性变化。     

跨京山铁路钢—混凝土组合箱梁体外预应力施工技术

北京市五环路京山铁路立交桥采用了钢-混凝土连续梁桥体外预应力技术,该桥在设计施工中存在很多难点问题。详细介绍了工程施工采用的转向器的安装、体外索套管的安装、钢绞线下料与穿束、体外预应力索的张拉、防松装置和减振器的安装技术,对今后的类似工程有借鉴参考意义。     

车轮偏心对转向盘摆振的影响分析

为了提升整车操纵稳定性和舒适性,采用理论分析和实车试验相结合的方法探讨了车轮偏心对转向盘摆振的影响。从理论上分析了车轮偏心引起的激振力和车轮动不平衡对转向盘摆振的贡献;以某B级车为研究对象,进行了多个因素的对比试验。结果表明:调整车轮动平衡对转向盘摆振稍有影响,调整下摆臂后衬套也有一定影响,但都不能明显减小振动加速度幅值;调整车轮偏心对转向盘摆振有显著影响,调整车轮偏心后,振动加速度幅值减小了近2倍;车轮偏心比动不平衡对转向盘摆振的影响更大,通过调整车轮安装定位方式消除安装偏心,对转向盘摆振现象的改进效果明显。     

道路曲线偏角及夹角的计算方法与精度分析

曲线型道路线形复杂,若能用简明且精度可靠的数学模型算出曲线偏角与夹角,必将在纵横断面测绘、边桩和中桩测设中提高其工作效率。对此,根据圆曲线、缓和曲线的特点,推导出弦线与切线夹角、切线与切线夹角、弦线与弦线夹角的一般计算方法和精确计算方法,结合实际数据进行了验证,并在长深高速公路唐山段勘测设计和施工中应用,提高了效率,保证了精度,收到了良好的效果。     

基于增量谐波平衡法的汽车转向轮非线性摆振的研究

采用振幅作为控制参数,应用增量谐波平衡法,求得方程解的表达式,分析了系统的分岔和极限环振动现象,并用龙格库塔法进行数值计算验证,结果表明:增量谐波平衡法在汽车转向轮摆振分析中有效可靠,有足够的精度,并运用Floquet理论对周期解的稳定性进行分析,进而确定了极限环的稳定性,最后分析了各结构参数对摆振的影响。     

缸内直喷CNG发动机点火提前特性分析

将4气门4缸车用汽油机改装为缸内直喷CNG发动机,在发动机台架试验及燃烧过程试验基础上,对发动机的充气效率、点火提前角进行了基础标定,并分析了发动机的点火提前特性.研究表明:发动机采用缸内直喷,输出扭矩对点火提前角变化敏感;随着点火提前角增大,发动机最高燃烧压力升高,出现最大燃烧压力所对应的曲轴转角逐渐靠近上止点,发动...     

多塔悬索桥的两个主要控制指标及其计算工况

以千米级3塔连跨悬索桥——泰州大桥为工程背景,比较了国内规范对加劲梁竖向挠跨比的相关规定,指出了该规定的实质目的是使行车平稳、安全.通过ANSYS有限元程序对比分析了泰州大桥4种汽车荷载典型工况下的整体位移,结果表明:加劲梁梁端竖向转角与加劲梁竖向挠跨比无本质联系(对于大跨度悬索桥);加劲梁梁端竖向转角与中塔纵向抗弯刚...     

力平衡半球谐振陀螺的信号检测

根据半球谐振陀螺的动力学方程和闭环反馈理论,推导出离散激励器和信号检测器在壳体环向的角度配置;研究了在力平衡模式下半球谐振陀螺的信号闭环检测方法.当陀螺壳体绕中心轴旋转时,由于哥氏效应,谐振子振型相对壳体产生进动,通过控制双点激励力的幅值比,实现振型对壳体转动角度的跟踪,从而完成半球谐振陀螺在力平衡模式下的信号检测.     

A path-following driver–vehicle model with neuromuscular dynamics,including measured and simulated responses to a step in steering angle overlay

An existing driver–vehicle model with neuromuscular dynamics is improved in the areas of cognitive delay, intrinsic muscle dynamics and alpha–gamma co-activation. The model is used to investigate the influence of steering torque feedback and neuromuscular dynamics on the vehicle response to lateral force disturbances. When steering torque feedback is present, it is found that the longitudinal position of the lateral disturbance has a significant influence on whether the driver’s reflex response reinforces or attenuates the effect of the disturbance. The response to angle and torque overlay inputs to the steering system is also investigated. The presence of the steering torque feedback reduced the disturbing effect of torque overlay and angle overlay inputs. Reflex action reduced the disturbing effect of a torque overlay input, but increased the disturbing effect of an angle overlay input. Experiments on a driving simulator showed that measured handwheel angle response to an angle overlay input was consistent with the response predicted by the model with reflex action. However, there was significant intra- and inter-subject variability. The results highlight the significance of a driver’s neuromuscular dynamics in determining the vehicle response to disturbances.     

Nonlinear PI front and rear steering control in four wheel steering vehicles

Vehicle steering dynamics show resonances, which depend on the longitudinal speed, unstable equilibrium points and limited stability regions depending on the constant steering wheel angle, longitudinal speed and car parameters.

The main contribution of this paper is to show that a combined decentralized proportional active front steering control and proportional-integral active rear steering control from the yaw rate tracking error can assign the eigenvalues of the linearised single track steering dynamics, without lateral speed measurements, using a standard single track car model with nonlinear tire characteristics and a non-linear first-order reference model for the yaw rate dynamics driven by the driver steering wheel input. By choosing a suitable nonlinear reference model it is shown that the responses to driver step inputs tend to zero (or reduced) lateral speed for any value of longitudinal speed: in this case the resulting controlled vehicle static gain from driver input to yaw rate differs from the uncontrolled one at higher speed. The closed loop system shows the advantages of both active front and rear steering control: higher controllability, enlarged bandwidth for the yaw rate dynamics, suppressed resonances, new stable cornering manoeuvres, enlarged stability regions, reduced lateral speed and improved manoeuvrability; in addition comfort is improved since the phase lag between lateral acceleration and yaw rate is reduced.

For the designed control law a robustness analysis is presented with respect to system failures, driver step inputs and critical car parameters such as mass, moment of inertia and front and rear cornering stiffness coefficients. Several simulations are carried out on a higher order experimentally validated nonlinear dynamical model to confirm the analysis and to explore the robustness with respect to unmodelled dynamics.