Investigation on the sensitive and insensitive zones of the rail support stiffness for the dynamic response of a vehicle system under low excitation frequencies

The variation of the rail support stiffness is an inherent issue of railway tracks. There is still no consensus on the influence of the rail support stiffness variation on the dynamic response of the vehicle–track system. One view indicates that changes of the support stiffness do not have considerable influence on the vehicle dynamic response. The main influence factor is the rail deflection. However, the opposite view presents that the influence of the support stiffness on the system dynamic response is obvious. Reasons that lead to the dispute of previous studies are the neglect of the influence of the excitation frequencies and a lack of understanding of stiffness sensitive zones. In this study a vehicle–track coupling model with equivalent overall support stiffness is employed to investigate the response of the vehicle to changes of the track stiffness and excitation frequencies. Results show that for each of frequencies (1–40?Hz) the dynamic response of the vehicle is only sensitive to a certain range of the support stiffness. A stiffness sensitive zone for each excitation frequency can be observed. In order to further study the influence of the subgrade on the vehicle system dynamic response a vehicle–track-subgrade model is utilised. The subgrade stiffness belonging to the stiffness sensitive zone has a significant influence on vehicle vibrations. For overall support stiffness of the rail higher than 20?kN/mm, the stiffness sensitive zones of low excitation frequencies can be avoided.     

基于施工全过程的矩形盾构隧道结构受力分析方法及应用

为探索如何在衬砌结构设计中充分考虑施工过程对结构受力的影响,在现场监测结果的基础上,采用理论分析和数值模拟的方法,建立基于施工全过程的衬砌结构受力分析方法,即考虑衬砌结构在施工过程中各主要受力阶段之间的非线性时变效应,采用增量法进行结构内力和变形的计算,分析结构在施工过程中各受力阶段的荷载模型以及结构刚度随内力变化的折线模型。将该方法应用到实际隧道工程中,并与传统设计方法进行对比分析。实践表明,建立的基于施工全过程的衬砌结构受力分析方法是合理可行的,其可以较全面地反映出衬砌结构在施工阶段的真实受力状态; 脱出盾尾阶段和同步注浆阶段为结构在施工期的不利受力阶段。     

破碎泥质岩隧道滞后形变与衬砌刚度关系规律试验研究

为了解破碎泥质岩隧道滞后变形与衬砌刚度的关系,以云桂铁路小寨隧道工程为依托,通过室内模型试验对小寨隧道实际开挖、支护及支护完成后围岩的劣化过程进行模拟,对围岩劣化过程中二次衬砌的围岩压力、位移及内力的变化规律进行研究。研究结果表明： 衬砌刚度对于控制泥质岩隧道滞后变形有着重要的影响; 二次衬砌的刚度越大,其承受的围岩压力及内力越大,则最大弯矩越大,容易出现开裂;针对小寨隧道的实际情况,30 cm的初期支护+I25b型钢钢架+40 cm的C35钢架混凝土二次衬砌是较优的支护结构设置。     

芜宁桥静载试验研究

为了检验芜宁桥的实际承载能力,对该桥进行了静载试验研究。试验结果表明该桥实际结构整体刚度未完全满足要求,实测残余变形不能完全满足小于20％的要求,这与该桥的湿接缝混凝土强度实测值不能满足设计规定强度的测试结果相符合。     

Analysis of handling performance based on simplified lateral vehicle dynamics

In this article, the analysis methods for vehicle handling performance are studied. Using simple models, dynamic characteristic parameters such as yaw, natural frequency, and the damping coefficient of a vehicle can be theoretically formulated. Here, the vehicle is simplified by a bicycle (single-track) model, and the tire is modeled by an equivalent cornering stiffness and first order lag. From the experimental road data, the tire model parameters (equivalent cornering stiffness and time lag constant) are extracted. These parameters are then inserted into the theoretically formulated equations of dynamic characteristic parameters. For the purpose of validating the efficiency of the suggested methods, experimental road tests (where the cars have different handling performances) are performed. The results show that vehicle handling performance can be sufficiently represented by the suggested dynamic characteristic parameters. So, it is concluded that the proposed method has practical use for the development of new cars or for the comparison of similar cars since the evaluations of the vehicle handling performance can be efficiently determined by the suggested dynamic characteristic parameters.     

动脉僵硬指数对冠心病的预测

目的探讨动脉僵硬指数(arterial stiffness index,ASI)对冠心病的预测价值。方法采用四川宇峰科技发展有限公司生产的血管硬度测量仪测量40例冠心病患者(冠心病组)与40例健康人的ASI。冠心病组根据冠状动脉造影的结果分为三个亚组:1支血管病变组(n=14)、2支血管病变组(n=16)及3支血管病变组(n=10),分析血管病变支数与ASI的关系。结果冠心病组与对照组的ASI值分别为124.4±22.9、88.2±15.9,冠心病组的ASI值较对照组明显增大,差异具有显著的统计学意义(P<0.01)。1支血管病变组、2支血管病变组及3支血管病变组的ASI值分别为107.2±9.1、121.4±12.6、153.3±22.0,随着冠状动脉病变支数增加,ASI值也相应增加,三亚组之间ASI值比较有统计学意义(P<0.05)。结论ASI可以作为冠心病的一个新的预测指标。     

采用变频调速技术的船用海水泵能耗分析

介绍了变频调速技术的工作原理,给出了普通海水泵和恒压变频海水泵的功耗计算公式;基于现有欧亚航线上的20000TEU级集装箱船对海水冷却系统进行方案设定,给出了中央出冷却水系统和逻辑控制系统的设计方案;通过计算分析了普通海水泵变频和恒压变频海水泵能耗上的差异,验证了能耗计算的准确性。对船上应用变频调速控制系统的能耗和成本降低提供了计算方案。     

京沪高速铁路高架车站道岔区桥梁设计

在京沪高速铁路高架车站道岔区桥梁设计中,考虑了道岔与桥梁的相互作用,道岔梁采用连续梁,较好地控制了道岔距梁缝的距离,在渡线两联连续梁之间插入两孔及简支梁,适当地提高了道岔梁及桥墩的刚度。通过以上措施,道岔区桥梁、轨道,道岔的强度、稳定、位移均能满足规范要求;车速350km/h的高速列车通过道岔区时,＂车-岔-桥＂动力性能满足规范要求。     

隧道钢管钢架与传统格栅钢架受力特性对比试验研究

针对传统格栅钢架和自主设计的4肢钢管钢架支护结构，利用Abaqus通用有限元软件，综合考虑钢管厚度、构件质量、材料成本等因素，系统开展2种隧道支护结构在单独受荷和共同受荷条件下的极限承载力、抗弯刚度、弯曲挠度、破坏形态等力学特性及演化规律的对比试验研究。研究结果表明： 1)钢管钢架和格栅钢架在刚度、承载力、变形破坏形态等方面存在一定差异，在用钢量相同的情况下，钢管钢架具有更高的强度和抗弯刚度，结构变形和受力亦更加合理； 2)钢管钢架自身承载力受钢管壁厚参数影响较为显著，壁厚取值过小会明显降低其承载力，但当壁厚达到一定数值时，继续增加壁厚对提高构件整体强度和抗弯刚度有限，同时会相应增加构件质量和材料成本； 3)在单独受荷条件下，格栅钢架的承载力为445 kN·m，较钢管钢架构件PG-2低393%，此时钢管钢架质量较格栅钢架略低，但每延米单价要高； 4)格栅钢架混凝土构件的极限荷载为174.6 kN·m，较钢管钢架混凝土构件C+PG-2、C+PG-6的极限荷载分别低2.7 %、30.6 %； 5)钢管钢架对于早期变形速度较大的围岩具有较好的适用性。     

A new active variable stiffness suspension system using a nonlinear energy sink-based controller

This paper presents the active case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by actively controlling the location of the point of attachment of the vertical strut to the car body. The control algorithm, effected by a hydraulic actuator, uses the concept of nonlinear energy sink (NES) to effectively transfer the vibrational energy in the sprung mass to a control mass, thereby reducing the transfer of energy from road disturbance to the car body at a relatively lower cost compared to the traditional active suspension using the skyhook concept. The analyses and simulation results show that a better performance can be achieved by subjecting the point of attachment of a suspension system, to the chassis, to the influence of a horizontal NES system.