干式离合器摩擦片温度分布

针对干式离合器在汽车传动过程中产生的热失效问题, 研究了摩擦片的温度分布。基于干式离合器的工作原理, 建立了包括主从动部分、摩擦片压力和摩擦因数在内的离合器接合模型。结合轴向弹性作用元件特性和分离轴承与膜片弹簧接触面旋转而与分离拨叉接触面不旋转的结构特点, 将环状压力传感器布置在与分离拨叉的接触面, 估计了实时离合器摩擦片压力。通过干式离合器试验台和摩擦因数模型, 求解了在连续工作400s的摩擦传递转矩和滑摩功, 计算了环境吸热、摩擦生热与对流散热3种边界的摩擦片热负荷, 分析了瞬时冲击接合与频繁接合2种工况下的摩擦片热变形。分析结果表明: 在离合器瞬时冲击2s的接合工况下, 摩擦片热变形最大, 可达0.188mm, 变形后摩擦片的温度显著升高; 在频繁接合工况下, 边界2滑摩热负荷对离合器接合前200s的摩擦片温度分布起主要作用, 边界2、3对流热同时对200s后的温度分布起重要作用。     

基于底盘多子系统协调控制的车辆稳定性控制

针对底盘关键子系统对车辆行驶稳定性影响能力与有效作用区域的差异, 综合考虑轮胎的非线性特性与各子系统间动力学耦合关系, 建立整车14自由度非线性动力学模型, 分别运用非线性H∞控制和模糊控制对转向、悬架和制动子系统进行控制性能研究, 采用多级递阶控制理论设计了组织级、协调级和执行级的车辆稳定性多级协调控制系统。运用滑模控制理论与轮胎逆模型将组织级得到的保持车辆行驶稳定性所需的广义目标控制力和力矩转化为轮胎侧偏角和滑移率, 再基于功能分配原理对各子系统控制功能进行协调, 实现了底盘复杂系统的功能解耦, 并对整车稳定性协调控制系统进行了仿真分析。仿真结果表明: 防抱死制动系统与半主动悬架系统联合控制对车辆稳定性的控制效果相对较差, 主动前轮转向的加入可以明显改善车辆的操纵稳定性。相对于汽车底盘子系统联合控制, 多级递阶协调控制能更好地改善整车行驶稳定性, 使制动距离减小, 保持滑移率基本在目标值0.2附近。     

船用 LNG 燃料储罐蒸发量与维持时间计算方法

在液化天然气(LNG)动力船舶设计中,船用 LNG 燃料储罐中的蒸发量和维持时间的计算,对于 LNG 动力船蒸发气体处理系统的设计有着重要意义。提出了一种基于 LNG 平均蒸发率的LNG 燃料储罐蒸发量和维持时间计算方法。利用传热学公式,对储罐分别装液氮和 LNG 时的蒸发率进行分析,得到储罐的液氮静态蒸发率和 LNG 静态蒸发率之间的关系。根据不同压力下的 LNG密度和汽化潜热的关系,得出储罐内部压力在小范围变化时的平均蒸发率计算公式。运用计算所得的 LNG 平均蒸发率推导出 LNG 蒸发量的计算公式,根据蒸发后储罐中气体质量的变化得出维持时间的计算公式。最后,以某20 m3 LNG 储罐为例,分别使用基于 LNG 平均蒸发率的方法和基于液氮蒸发率的方法计算了该 LNG 储罐的蒸发量和维持时间,其在维持时间内的蒸发量分别为20.72 kg 和34.1 kg,维持时间分别为21.64 d 和13.15 d,基于 LNG 平均蒸发率方法比基于液氮蒸发率方法得出的蒸发量少13.38 kg,维持时间多8.49 d。使用这2种方法进一步计算了蒸发量随时间的变化并进行了比较,结果表明,2种方法计算的储罐蒸发量随时间的变化总体趋势相同,但蒸发量和维持时间差别较大;与基于液氮蒸发率的方法相比,基于 LNG 平均蒸发率的方法所计算的结果更接近实际值,能更好地指导 LNG 动力船蒸发气体处理系统的设计。     

考虑风险爱好驾驶人的相依Weibull随机交通分配模型

建立了考虑风险爱好驾驶人的相依Weibull随机交通分配(Weibull-DSA) 模型, 分析了感知等价路径负效用的Weibull边缘生存函数, 假设驾驶人总是选择感知等价路径负效用最小的路径到达目的地, 采用Copula方法构建了感知等价路径负效用的联合生存函数, 预测了路径选择概率; 设计了模型的迭代求解算法, 对模型进行了理论分析和数值验证; 研究了广州市交通调查获得的风险系数, 基于风险爱好和风险中立驾驶人, 比较了采用Weibull-DSA模型与经典的Logit-SUE和Weibit-SUE模型计算的路径选择概率、路段交通量、饱和度与系统总出行时间。计算结果表明: 随着风险系数的降低, 3种分配模型的交通系统总出行时间变大; 在风险中立情况下, 应用Weibull-DSA模型、Logit-SUE模型和Weibit-SUE模型计算得到每OD对的所有连接路径选择概率的最大差值, 分别为0.17、0.33、0.34, 在风险爱好情况下, 由3种模型得到的最大差值分别为0.20、0.36、0.41, 因此, 采用Weibull-DSA模型计算得到的不同路径选择概率的最大差值明显小于经典模型计算得到的最大差值; 相对于风险中立情况, 风险系数使得每OD对的所有连接路径选择概率的最大差值变大; 无论是风险爱好还是风险中立驾驶人, 采用Logit-SUE和Weibit-SUE模型计算得到的路段饱和度均小于0.9, 采用Weibull-DSA模型计算得到路段饱和度大于0.9;与经典模型计算结果不同, 采用Weibull-DSA模型得到的不同路径选择概率的最大差值相差较小, 一些路径获得更多交通量, 使得路径中通行能力最小的路段的饱和度大于0.9, 这一特征给出了城市路网中部分瓶颈路段拥堵现象一个新的解释。     

车辆转向架全域应力推演与实时监控

为了提高疲劳强度评定和疲劳寿命预测的可靠性与精度, 基于结构可测位置应力提出了全域应力推演方法进行任意位置的应力预测。引入了基于无网格计算的径向基函数插值理论, 建立了新的插值域选择规则, 改进了传统Multi-Quadric(M-Q)径向基函数。为了验证改进的M-Q径向基函数的插值性能, 在对转向架构架施加横向载荷为58 kN, 牵引载荷为55 kN, 垂向载荷为85 kN, 选取了应力不可直接测量的8个位置, 分别采用改进的M-Q径向基函数与薄板样条(TPS)径向基函数进行插值精度比较。分析结果表明: 采用改进的M-Q径向基函数预测的应力最大相对误差为0.090 6%, 平均相对误差为0.028 4%, 采用TPS径向基函数预测的应力最大相对误差为1.611 3%, 平均相对误差为0.604 2%, 因此, 采用改进的M-Q径向基函数推演转向架构架应变片不可测位置应力的计算精度远优于采用TPS径向基函数的精度; 结合改进的M-Q径向基函数插值算法, 开发了一套车辆转向架全域应力推演和实时监控系统(TPL Monitoring), 具有良好的交互性、实时性和可扩展性。     

高速三体船片体构型数学表达和兴波阻力计算

高速三体船以其优良的减阻性能、耐波性和稳性而具有广阔的军事和商业应用价值。尽管已有大型实船付诸应用,但高速三体船型的兴波阻力预报和减阻设计问题并未解决,而这又是高速三体船实际应用的重要环节。采用帐篷函数法进行高速三体船的片体构型设计,并据此计算各船型参数。将改进的线性兴波阻力数值算法应用于高速三体船的兴波阻力计算,根据模型试验结果,验证了计算方法的有效性。     

Time control point strategy coupled with transfer coordination in bus schedule design

A schedule consisting of an appropriate arrival time at each time control point can ensure reliable transport services. This paper develops a novel time control point strategy coupled with transfer coordination for solving a multi‐objective schedule design problem to improve schedule adherence and reduce intermodal transfer disutility. The problem is formulated using a robust mixed‐integer nonlinear programming model. The mixed‐integer nonlinear programming model is equivalently transformed into a robust mixed‐integer linear programming model, which is then approximated by a deterministic mixed‐integer linear programming model through Monte Carlo simulation. Thus, the optimal scheduled arrival time at each time control point can be precisely obtained using cplex . Numerical experiments based on three bus lines and the mass rapid transit system in Singapore are presented, and the results show that the schedule determined using the developed model is able to provide not only reliable bus service but also a smooth transfer experience for passengers. Copyright © 2016 John Wiley & Sons, Ltd.     

Stop-and-go traffic analysis: Theoretical properties,environmental impacts and oscillation mitigation

This study aims (i) to analyze theoretical properties of a recently proposed describing-function (DF) based approach (Li and Ouyang, 2011; Li et al., 2012) for traffic oscillation quantification, (ii) to adapt it for estimating fuel consumption and emission from traffic oscillation and (iii) to explore vehicle control strategies of smoothing traffic with advanced technologies. The DF approach was developed to predict traffic oscillation propagation across a platoon of vehicles following each other by a nonlinear car-following law with only the leading vehicle’s input. We first simplify the DF approach and prove a set of properties (e.g., existence and uniqueness of its solution) that assure its prediction is always consistent with observed traffic oscillation patterns. Then we integrate the DF approach with existing estimation models of fuel consumption and emission to analytically predict environmental impacts (i.e., unit-distance fuel consumption and emission) from traffic oscillation. The prediction results by the DF approach are validated with both computer simulation and field measurements. Further, we explore how to utilize advantageous features of emerging sensing, communication and control technologies, such as fast response and information sharing, to smooth traffic oscillation and reduce its environmental impacts. We extend the studied car-following law to incorporate these features and apply the DF approach to demonstrate how these features can help dampen the growth of oscillation and environmental impact measurements. For information sharing, we convert the corresponding extended car-following law into a new fixed point problem and propose a simple bisecting based algorithm to efficiently solve it. Numerical experiments show that these new car-following control strategies can effectively suppress development of oscillation amplitude and consequently mitigate fuel consumption and emission.     

Bottleneck model revisited: An activity-based perspective

The timing of commuting trips made during morning and evening peaks has typically been investigated using Vickrey’s bottleneck model. However, in the conventional trip-based approach, the decisions that commuters make during the day about their activity schedules and time use are not explicitly considered. This study extends the bottleneck model to address the scheduling problem of commuters’ morning home-to-work and evening work-to-home journeys by using an activity-based approach. A day-long activity-travel scheduling model is proposed for the simultaneous determination of departure times for morning and evening commutes, together with allocations of time during the day among travel and activities undertaken at home or at the workplace. The proposed model maximizes the total net utility of the home-based tour, which is the difference between the benefits derived from participating in activities and the disutility incurred by travel between activity locations. The properties of the model solution are analytically explored and compared with the conventional bottleneck model for a special case with constant marginal-activity utility. For the case with linear marginal-activity utility, we develop a heuristic procedure to seek the equilibrium scheduling solution. We also explore the effects of marginal-work utility (or the employees’ average wage level) and of flexible work-hour schemes on the scheduling problem in relation to the morning and evening commuting tours.     

整体桥面钢桁梁桥桥面荷载传递途径的研究

在多横梁整体桥面结构中,桥面荷载有两条传递途径:一是通过纵梁、纵肋和钢桥面板纵向传递到节点横梁,再传到下弦节点;二是通过节间内横梁及钢桥面板横向传递到下弦杆,再传到下弦节点.前者引起节点处横梁的竖向弯曲,后者引起下弦杆的竖向弯曲.本文采用有限元法对该类型桥面结构中桥面荷载的传递情况进行分析计算和试验研究.研究结果表明:影响传力比(路径传递的荷载与一个节间总荷载的比)的主要因素有下弦杆与桥面系(纵梁、纵肋和钢桥面板)的竖向刚度比α和节间横梁与节点横梁的竖向刚度比β;路径2的传力比R2随着α的增加而增加,当α小于8.3时,R2的增加速度较快,当α大于25后,R2变化很小;R2随着β的增加而增加,但增加速度略有减慢;不同节间内通过两条路径传递的荷载比例变化不大,理论值与试验值吻合良好.