Considerable numbers of earthquake disasters have been experienced in Japan. Thus the study and research of earthquake disaster prevention are highly aware in Japan. In a railway industry, for instance, infrastructures have been reinforced, and a new alert system has been employed to regulate the operating system to stop trains immediately if a great earthquake occurs. A railway is organized by a variety of individual technologies and functions safely and properly as a system; therefore it is beneficial for the system safety to study and examine the individual potential cases of disasters caused by earthquakes from various different viewpoints. Recent reports imply that rail vehicles could derail solely by the ground motions of earthquakes without fatal damages of vehicles and tracks. Therefore, in this paper, the vehicle safety in terms of the dynamic stability and the possibility of derailment directly caused by the track excitations of great earthquakes is specifically studied. The rail vehicles are supposed to involve severe vehicle body motions, wheel lifts, and derailing behaviors. In this study, such extreme responses of the vehicles are focused on; thus at the start, a new vehicle dynamics simulation is developed with unique modeling specifically taking account of internal slide forces between the vehicle body and the bogie resulting from large motions of vehicles. Then, the simulation is employed to assess the safety of vehicles on excited tracks with sinusoidal displacements, and the numerical results are analyzed. Through the assessment and the analyses, four major outcomes are obtained. First, the limit excitation amplitudes for the wheel lift of flange height, defined as safety limits in this paper, are presented in the frequency range of 0.5–2.5Hz. Second, two types of critical vehicle motions are captured; one is a rocking motion involving large wheel lift observed in lower frequency excitations and the other is a severe horizontal impact of a wheel to a rail observed in higher frequency excitations. In the latter cases, the vehicles derail with slightly larger excitations than those of the wheel lift of flange height. Third, the roll characteristic of a vehicle body is demonstrated as a dominant factor for the vehicle dynamic motions in terms of large wheel lift and derailment. Finally, the unique modeling in the developed simulation is evaluated, and its advantages for precise prediction of the extreme vehicle responses are confirmed.
Moving slender elastic elements such as ropes, cables and belts are pivotal components of vertical transportation systems such as traction elevators. Their lengths vary within the host building structure during the elevator operation which results in the change of the mass and stiffness characteristics of the system. The structure of modern high-rise buildings is flexible and when subjected to loads due to strong winds and earthquakes it vibrates at low frequencies. The inertial load induced by the building motion excites the flexible components of the elevator system. The compensating ropes due to their lower tension are particularly affected and undergo large dynamic deformations. The paper focuses on the presentation of the non-stationary model of a building-compensating rope system and on the analysis to predict its dynamic response. The excitation mechanism is represented by a harmonic process and the results of computer simulations to predict transient resonance response are presented. The analysis of the simulation results leads to recommendations concerning the selection of the weight of the compensation assembly to minimize the effects of an adverse dynamic response of the system. The scenario when the excitation is represented as a narrow-band stochastic process with the state vector governed by stochastic equations is then discussed and the stochastic differential equations governing the second-order statistical moments of the state vector are developed.
In this study, the modeling and formulation for tether motion with time-varying length, large rotation, large displacement and large deformation are proposed. A tether or cable is an important element in lift systems, construction machines for transportation and often is used with a time-varying length. In some cases, these systems are large and the tether has a long length, large deformation and large displacement. The dynamic behavior of a tether in extension and retraction using the proposed method is discussed in this paper. In the passage through resonance, significant tether motions with large rotation and large deformation result. In the analysis of this phenomenon, the transient fluctuations of the motion amplitudes are examined and compared with the corresponding steady state motions. The accuracy and the cost of the calculations are also verified by comparison with the experimental results.
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