汽车发动机厂柔性生产方式下的现场检测技术

为满足轿车市场对产品需求的多样性,现代企业必须采取多品种混线生产,即柔性化生产模式,尤其对于动力总成类企业。众所周知,检测技术是制造工艺的一个重要组成。据此,文章提出为适应柔性化生产,在线检测工艺与装备需要具备的一些特点,如:工序间检验夹具的柔性化、坐标测量机配置在生产现场、建立专用的生产测量室以及量规的通用化和柔性化等。文章通过针对性的实例进行了介绍和说明。     

钢悬链式立管涡激振动疲劳损伤参数分析

针对钢悬链式立管的结构特性,采用了简化后的振动模型。先对立管进行了模态分析;再根据立管的模态特性结合环境水流参数,采用模态叠加法对立管进行了涡激振动疲劳损伤分析。分析过程中,通过改变流速大小、立管壁厚、立管外径、内部介质以及抑制立管涡激振动的螺旋列板长度等参数,对立管的涡激振动疲劳损伤进行了相应的参数分析。结果表明:立管疲劳损伤随水流速度的增大、立管外径的增大以及内部介质密度的降低呈现上升趋势,但是壁厚变化对立管疲劳损伤大小影响却不显著。     

LQR control on multimode vortex-induced vibration of flexible riser undergoing shear flow

Under the actions of ocean currents and/or waves, deep-sea flexible risers are often subject to vortex-induced vibration (VIV). The VIV can lead to severe fatigue and structural safety issues caused by oscillatory periodic stress and large-amplitude displacement. As flexible risers have natural modes with lower frequency and higher density, a multimode VIV is likely to occur in risers under the action of ocean currents, which is considered as shear flow. To decrease the response level of the VIV of the riser actively, a multimode control approach that uses a bending moment at the top end of the riser via an LQR optimal controller is developed in this study. The dynamic equations of a flexible riser including the control bending moment in shear flow are established both in the time and state-space domains. The LQR controllers are then designed to optimize the objective function, which indicates the minimum cost of the riser's VIV response and control input energy based on the Riccati equation of the closed-loop system under the assumption that the lift coefficient distribution is constant. Finally, the VIV responses of both the original and closed-loop systems under different flow velocities are examined through numerical simulations. The results demonstrate that the designed active control approaches can effectively reduce the riser displacement/angle by approximately 71%–89% compared with that of the original system. Further, for multimode control, the presented mode-weighted control is more effective than the mode-averaged control; the decrease in displacement is approximately 1.13 times than that of the mode-averaged control. Owing to the increase in flow velocity as more and higher-order modes are excited, the VIV response of the original system decreases slightly while the frequency response gradually increases. For the closed-loop system, the response becomes smaller and more complicated, and the efficiency of the controller becomes lower at a certain flow velocity.     

Flexing service schedules: Assessing the potential for demand-adaptive hybrid transit via a stated preference approach

This paper assesses the demand for a flexible, demand-adaptive transit service, using the Chicago region as an example. We designed and implemented a stated-preference survey in order to (1) identify potential users of flexible transit, and (2) inform the service design of the flexible transit mode. Multinomial logit, mixed-logit, and panel mixed-logit choice models were estimated using the data obtained from the survey. The survey instrument employed a d_p-efficient design and the Google Maps API to capture precise origins and destinations in order to create realistic choice scenarios. The stated-preference experiments offered respondents a choice between traditional transit, car, and a hypothetical flexible transit mode. Wait time, access time, travel time, service frequency, cost, and number of transfers varied across the choice scenarios. The choice model results indicate mode-specific values of in-vehicle travel time ranging between $16.3 per hour (car) and $21.1 per hour (flexible transit). The estimated value of walking time to transit is $25.9 per hour. The estimated value of waiting time at one’s point of origin for a flexible transit vehicle is $11.3 per hour; this value is significantly lower than the disutility typically associated with waiting at a transit stop/station indicating that the ‘at-home’ pick-up option of flexible transit is a highly desirable feature. The choice model results also indicate that respondents who use active-transport modes or public transit for their current commute trip, or are bikeshare members, were significantly more likely to choose flexible and traditional transit than car commuters in the choice experiments. The implications of these and other relevant model results for the design and delivery of flexible, technology-enabled services are discussed.     

基于K&C与轮胎特性的不足转向特性研究

前、后轴车轮平面运动和弹性转向角与轮胎侧偏角的不同导致车辆产生不足转向。提出了适用于低侧向加速度段的不足转向梯度计算方法,并阐述了不足转向梯度在高侧向加速度段存在非线性的原因。在经过校核的某轿车多体模型中建立用户自定义变量,采用仿真值与理论值对比验证了低侧向加速度段的不足转向梯度计算方法精度较高。仿真结果表明,对于高侧向加速度段的不足转向梯度非线性原因解释正确。     

基于直接积分法的弓网耦合系统动态性能仿真分析

针对提速铁路采用的弹性链型悬挂接触网及受电弓结构,建立包含承力索、辅助线、接触线和吊弦4个部件的接触网模型、以及简化为弹簧阻尼机构的受电弓模型。通过接触单元将接触网和受电弓直接耦合起来得到弓网系统的整体模型,进而构建弓网耦合系统的动力学平衡方程。采用直接积分法对建立的平衡方程进行求解,得到反映弓网系统动态性能的抬升位移、接触压力以及应力等数据。与先前研究的参考数据比对结果表明,采用接触单元和直接积分法分析弓网耦合系统的动态性能,切实可行。     

接触网补偿棘轮偏斜原因分析与对策

电气化铁路接触网用补偿棘轮在实验室试验及现场使用时,均发现棘轮轮体有偏斜的现象。通过分析补偿棘轮的受力情况得出结论：由于棘轮本身的特殊结构,棘轮在工作时受到的偏心力矩作用,使其发生偏斜。为防止棘轮偏斜,要尽量提高棘轮框架的整体刚度,加大棘轮框架与棘轮轴的接触面,同时棘轮轴要有定位,以抵抗偏心扭矩。     

大容量预应力混凝土软横跨接触网支柱的研制

文章介绍了代替软横跨接触网钢柱的大容量预应力混凝土软横跨接触网支柱的荷载计算、结构分析和内力计算方法，并通过支柱的卧式和立式对比试验。提出了用卧式试验检验支柱随双向荷载的结构性能方法。     

Dynamic analysis of a bus body frame: determination of the loads and stresses

With the use of the numerical method presented in this article, the dynamic analysis of the bus body frame can be carried out even in the designing phase. According to the results, the weak points of the body from the point of view of extreme loads and fatigue can be found and the correction of the construction can be done. As a new method, FEM models with different complexity are used in the different analysis steps. The applicability of the method as a design procedure and the reliability of the proposed models are verified by calculations and measurements concerning a concrete bus type.