Identification of dynamic parameters in low-mobility mechanical systems: application to short long arm vehicle suspension

The identification of dynamic parameters in low-mobility mechanical systems is addressed and applied to short long arm (SLA) front car suspension. The main goal of the identification technique is to obtain, from experimental measurements, the values of those dynamic parameters (masses, location of the centre of masses, terms of the inertial matrix of the links, constant friction terms and elastic and viscous damping constant terms) that affect the dynamic behaviour of the system. Moreover, additional but important information that could be obtained from the procedure is related to the weight of those terms inside the dynamics of the system, so that simplified dynamic models based on relevant and well-identified parameters can be established. First, a systematic procedure will be presented for obtaining the equations of motion in a linear form with regard to the dynamic parameters to be identified. The main drawbacks related to the identification of parameters in low-mobility mechanisms will be pointed out, mainly the difficulty of determining a natural cutoff point into the singular values of the observation matrix which allows us to determine the true dimension of the set of base parameters and of obtaining an observation matrix well conditioned from the numerical point of view that allows an identification in the presence of measurement error. The procedure proposed for overcoming these problems will be based on the development of symbolic relationships among the physical parameters in order to determine the true rank of the observation matrix and on the consideration of a reduced subset of the base parameters set. These relevant parameters will be selected according to their influence on the dynamic behaviour of the mechanical system. A virtual benchmark will be used for testing purposes. The dynamic models based on relevant parameters show a better adjustment than the complete ones, mainly when the level of noise in the measurements used in the identification process increases.     

基于数值模拟的木拱廊桥洪水响应分析

近年来,木拱廊桥抗洪防灾方面的研究多基于水毁案例的经验总结来提出宏观维护策略,缺乏对于洪水荷载与廊桥结构受力的量化分析。因此,提出了基于计算流体动力学(CFD)与有限元方法的木拱廊桥抗洪安全性能分析方法,研究不同洪水频率下的荷载分布规律,并对桥体拱架的洪水响应及结构安全进行量化评估,为木拱廊桥预防洪水和安全监控提供参考依据。结果表明:受洪水荷载的作用,杆件上的水平力沿水深方向呈线性分布,竖向力呈均匀分布;主拱结构产生形变,迎水面向河内挤压,背水面向两岸拉伸,上部结构朝水流方向倾斜;主拱上背水面的端平苗受拉力作用,易脱开节点导致桥面塌落,基础的摩擦系数和土体抗剪性能决定了支座的稳定,是影响廊桥整体结构抗洪安全性能的关键因素。     

A railway vehicle multibody model for real-time applications

Hardware in the loop (HIL) techniques are widely used for fast prototyping of control systems, electronic and mechatronic devices. In the railway field, several mechatronic on board subsystems are often tested and calibrated following the HIL approach. The accuracy of HIL tests depends on how the simulated virtual environment approximates the physical conditions. As the computational power available on real-time hardware grows, the demand for more complex and realistic models of railway vehicles for real-time application increases. In past research activities, the authors worked on the implementation of simplified real-time models for several applications and in particular for an HIL test rig devoted to the type approval of wheel slide protection systems. The activity has then been focused on the development of a three-dimensional model of the dynamics of a railway vehicle for more complex applications. The paper summarises the features and the results of the study.     

Modelling cyclic container freight index using system dynamics

ABSTRACT

This paper investigates the cyclical nature of container shipping market represented by a containerized freight index and proposes a predictive cyclical model of the market. In contrast to the traditional spectral analysis (univariate), system dynamics reflect the drivers of the market in both supply and demand side, and therefore, it is a multi-variate system equilibrium approach consisting of various causal spillovers from sub-components of the market. This study is the first to analyze the cycle of container market using system dynamics. By utilizing system dynamics cyclicality approach, one-step ahead predictions are generated for monthly containerized freight index and compared to conventional benchmarks for post-sample validation. Our study can also help policymakers and shipping liners for better management and invest timing of container ship.     

交通管控措施对市域新冠疫情传播的阻断效果分析

面对局部暴发的新冠肺炎（COVID-19）疫情，进行城市交通管控是阻断疫情传播、控制疫情发展的重要途径。为了揭示不同交通管控措施对COVID-19传播的阻断效果，以不同阶段暴发疫情的荆州、孝感、荆门和石家庄4个行政市为研究区域，统计分析了市内道路封闭、客运交通停运和小区人口流动控制等3种典型交通管控措施实施前后的市域疫情传播趋势。基于经典的传染病动力学理论，考虑潜伏者传染性、人口迁徙、市内小区人口流动建立了市域COVID-19疫情传播SEIR优化模型，对比分析了4个行政市有/无交通管控措施以及不同交通管控措施对于疫情发展的阻断效果。研究结果表明：4个行政市的日发病率均与14 d前的迁入指数紧密相关；3种交通管控措施对阻断疫情传播效果明显，使荆州、孝感、荆门、石家庄无交通管控措施时的感染者峰值人数分别下降61.29%、53.71%、66.16%、66.33%；3种管控措施的阻断效果表现出一定的差异性，市内道路封闭措施的阻断效果最为明显，其不同实施节点可使市域潜伏者人数和感染者人数分别下降40.54%~70.88%和49.11%~64.34%。通过及时、全面地实施3种交通管控措施可以有效阻断疫情传播、控制市域疫情发展。考虑潜伏期特性的改进SEIR模型能够准确预测疫情发展趋势，可为疫情流行期间城市交通管控方案的制定提供技术参考。     

Time-domain structural analysis during block turnover and lifting using 2D flexible multibody dynamics

Ship construction involves the assembly of several blocks on a dock. When a block is lifted using a crane, it undergoes deformation. Until now, structural analysis has been applied in a few cases to evaluate the stress on such blocks. Therefore, this study proposes an evaluation method for time-domain stress using 2D flexible multibody dynamics. We adopt the discrete Euler-Lagrange equation to achieve robustness during the numerical integration of problems that involve high stiffness. We formulate the equations of motion of 2D shell elements based on the absolute nodal coordinate formulation, which is an efficient analysis technique for nonlinear and large deformation cases. We also derive the two types of kinematic constraints (ball and fixed joints) between the rigid and shell element, which can be attached to an arbitrary point. Based on the theories, we develop the program to build models, including 2D flexible multibody dynamics and several joints, and to solve the equations of motion efficiently. As a result, it is successfully applied to the dynamic analysis of the block turnover by a gantry crane and the block lifting by a floating crane. The von-Mises stresses that change over time are compared to the maximum yield stress and analyzed according to the wave direction.     

Dynamic congestion pricing with day-to-day flow evolution and user heterogeneity

This paper investigates evolutionary implementation of congestion pricing schemes to minimize the system cost and time, measured in monetary and time units, respectively, with the travelers’ day-to-day route adjustment behavior and their heterogeneity. The travelers’ heterogeneity is captured by their value-of-times. First, the multi-class flow dynamical system is proposed to model the travelers’ route adjustment behavior in a tolled transportation network with multiple user classes. Then, the stability condition and properties of equilibrium is examined. We further investigate the trajectory control problem via dynamic congestion pricing scheme to derive the system cost, time optimum, and generally, Pareto optimum in the sense of simultaneous minimization of system cost and time. The trajectory control problem is modeled by a differential–algebraic system with the differential sub-system capturing the flow dynamics and the algebraic one capturing the pricing constraint. The explicit Runge–Kutta method is proposed to calculate the dynamic flow trajectories and anonymous link tolls. The method allows the link tolls to be updated with any predetermined periods and forces the system cost and/or time to approach the optimum levels. Both analytical and numerical examples are adopted to examine the efficiency of the method.     

公路工程项目组合施工进度风险防范策略

为了降低公路工程施工进度风险，考虑风险事件的交互关系提出了公路工程项目组合施工进度风险防范策略。首先，通过公路工程建设文献资料梳理和专家筛选补充，构建了公路工程项目组合施工进度风险三级指标体系。然后，利用网络层次分析法解析了公路工程项目组合施工进度风险指标间的交互关系，运用Super Decisions软件确定了各级风险指标的权重。最后，通过系统动力学建立了公路工程项目组合施工进度风险水平评估模型，在验证模型的有效性后运用Vensim软件对施工进度风险水平进行模拟。在此基础上，为降低公路工程施工进度风险，综合考虑风险破坏和交互程度改进传统“概率-损失”风险矩阵，对不同风险防范策略实施后的管控效果进行仿真模拟，进而提出了相应的风险防范策略集。研究结果表明：风险间交互关系致使公路工程项目组合施工进度风险在整个施工阶段呈上升趋势，且施工阶段中后期风险上升趋势明显升高，有必要对风险进行控制；采取单一风险防范策略后总体施工进度风险降低[0.13%，10.12%]，下降程度并不显著；采取组合风险防范策略后总体施工进度风险下降[10.45%，17.42%]，显著度明显提高。该结果厘清了公路工程项目组合施工进度风险的交互关系，验证了风险防范策略的科学有效性，为解决公路工程项目组合施工进度的风险防范问题提供了依据。     

兰新铁路第二双线穿越大风区综合选线研究

大风区段对铁路的建设及运营安全存在着各种危害,高速铁路由于具有速度高、车体轻的特点,其安全受到强风威胁会更大,高速铁路穿越大风区防风设置是世界性难题,目前尚无已成功运营的先例,高速铁路大风区综合选线需综合考虑防风设置、防排水、防沙、接触网防风等因素,科学合理进行方案比选研究。通过分析新疆境内四大风区分布及特点,利用既有兰新铁路设施及防风科研成果,对兰新铁路第二双线在穿越大风区段落综合进行选线设计研究,充分分析路基地段的防风设施设置以及线路平纵断面的防风布置选择,确保高速铁路在大风区安全、快速通过,以确定科学、合理的线路设计方案。