Study on Reinforcing Technology System for the Overlapped Running Shield Tunnels underneath the Track Group of High Speed Railways北大核心CSCD

The large settlements of tracks will emerge due to multiple disturbances in the construction of over- lapped shield tunnels, which affects the running safety of trains. Based on the overlapped Sungang station-Honghu station shield running tunnels of Shenzhen Metro line 7 passing underneath 26 tracks of high speed railways, a rein- forcement technology system consisting of”track support + subgrade reinforcement + interlayer soil consolidation + internal support of the lower tunnel”was developed. The settlements of tracks were mainly monitored automatically with manual monitoring as an auxiliary one. The results show that the maximum settlement of main track caused by constructing overlapped shield tunnels is -5.9 mm which is less than the control value of 10 mm, ensuring the opera- tion safety and verifying the reliability and practicability of the reinforcement technology system. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Study on the Stress and Deformation Behaviors of a Deep and Irregular Foundation Pit as the Shield Launching Shaft in a Sea Reclaimed Cofferdam北大核心CSCD

With the development of the tunnel technology in China, the shield tunnel will become an important way to build the Sea-crossing channel. Taking the current largest diameter Shantou Bay shield tunnel in China as the engineering background, this paper introduces the challenges faced by the construction of the shield launching shaft in the reclamation cofferdam: e.g. deep, irregular excavation, deep silt layer and great influence of the seawater. Based on the practical conditions, a top-down construction technique of large ring beam considering two working conditions of foundation pit excavation and shield launching is proposed. Based on three-dimensional finite element analysis and field measurement, the stress characteristics and soil deformation of foundation pit are studied. The results show that the top-down construction technique of large ring beam can effectively control the deformation of the foundation pit and save construction time. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Constrained nested logit model: formulation and estimation

A model of traveller behaviour should recognise the exogenous and endogenous factors that limit the choice set of users. These factors impose constraints on the decision maker, which constraints may be considered implicitly, as soft constraints imposing thresholds on the perception of changes in attribute values, or explicitly as hard constraints. The purpose of this paper is twofold: (1) To present a constrained nested logit-type choice model to cope with hard constraints. This model is derived from the entropy-maximizing framework. (2) To describe a general framework to deal with (dynamic) non-linear utilities. This approach is based on Reproducing Kernel Hilbert Spaces. The resulting model allows the dynamic aspect and the constraints on the choice process to be represented simultaneously. A novel estimation procedure is introduced in which the utilities are viewed as the parameters of the proposed model instead of attribute weights as in the classical linear models. A discussion on over-specification of the proposed model is presented. This model is applied to a synthetic test problem and to a railway service choice problem in which users choose a service depending on the timetable, ticket price, travel time and seat availability (which imposes capacity constraints). Results show (1) the relevance of incorporating constraints into the choice models, (2) that the constrained models appear to be a better fit than the counterpart unconstrained choice models; and (3) the viability of the approach, in a real case study of railway services on the Madrid–Seville corridor (Spain).     

Torsional stiffness and weight optimization of a real bus structure

In this paper, the structural optimization of a real bus structure is proposed. The proposed optimization has been accomplished by means of genetic algorithms. The structural behavior of the bus structure when subjected to weight and torsion was also analyzed using the finite element method (FEM). The results demonstrate that improved weight and torsional stiffness are achieved with the optimized structure.     

Improvement of drivability and fuel economy with a hybrid antiskid braking system in hybrid electric vehicles

When braking on wet roads, Antilock Braking System (ABS) control can be triggered because the available brake torque is not sufficient. When the ABS system is active, for a hybrid electric vehicle, the regenerative brake is switched off to safeguard the normal ABS function. When the ABS control is terminated, it would be favorable to reactivate the regenerative brake. However, recurring cycles from ABS to motor regenerative braking could occur. This condition is felt to be unpleasant by the driver and has adverse effects on driving stability. In this paper, a novel hybrid antiskid braking system using fuzzy logic is proposed for a hybrid electric vehicle that has a regenerative braking system operatively connected to an electric traction motor and a separate hydraulic braking system. This control strategy and the method for coordination between regenerative and hydraulic braking are developed. The motor regenerative braking controller is designed. Control of regenerative and hydraulic braking force distribution is investigated. The simulation and experimental results show that vehicle braking performance and fuel economy can be improved and the proposed control strategy and method are effective and robust.     

Analytical study on the performance of a high power pretensioner

In this paper, a numerical procedure to estimate the performance of the high power pretensioner used in the seatbelt of a passenger vehicle is presented. The data on the gas explosion pressure in a 10-cc volume and the data on the displacement of the rack according to time were applied to the numerical procedure. The procedure was implemented using MATLAB. The testing device, which met the automobile industry standards, was created. Experiments were carried out seven times under the same conditions, and the mean values of the web retraction and belt load were used as the representative data. By comparing the simulation results to the test results, the numerical procedure presented in this paper was verified.     

Urban traffic studies from aerial photographs

Two problems concerning the use of aerial photographs for conducting traffic studies in urban areas are considered in this paper: (1) Suitable procedures requiring simple equipment and methods and the appropriate formulae for determining the traffic characteristics of density, volume, traffic count, speed, composition; (2) Problems relating to flight planning for traffic surveys from the points of view of duration of photography and the scale of the photography from considerations of the reliability of the determined traffic characteristics, vehicle identification, and also economy. The conclusions concerning the flight planning were applied in a test flight from which traffic data were determined as illustrated in a sample calculation.     

Experimental investigations on the damping effect due to passengers on flexural vibrations of railway vehicle carbody and basic studies on the mimicry of the effect with simple substitutions

The effect of passengers on a railway vehicle is usually considered as additional mass in designing a carbody. However, previous studies by means of stationary excitation tests or running tests using actual vehicles indicate that passengers behave not as mass but as damping. In this paper, the authors examined the passengers' damping effect under controlled excitation conditions on a roller rig through a series of excitation tests using a commuter-type vehicle. Large and multi-modal reductions of flexural vibrations of the carbody were observed when passengers existed. Influences of the number of passengers, distributions and postures of passengers were investigated. The authors also tried to mimic the damping effect by passengers using flexible tanks filled with fluids. Three kinds of fluids which have different viscosities have been tested. As a result of the excitation tests, good vibration reduction effects were observed by applying those tanks, and it has been found that the flexible tanks filled with fluids bring about vibration reduction effect (including multi-modal reduction) which is equal to or rather better than the case of similar mass of passengers in the carbody; the difference of viscosity gave little affect on the damping abilities. From these measurement results, a possibility of realising effective damping devices against flexural vibrations of railway vehicle carbodies representing passengers damping effect, in a simple, economical and environmental friendly way, has been demonstrated.     

Calibration efficiency improvement of rule-based energy management system for a plug-in hybrid electric vehicle

This paper presents a calibration method of a rule-based energy management strategy designed for a plug-in hybrid electric vehicle, which aims to find the optimal set of control parameters to compromise within the conflicting calibration requirements (e.g. emissions and economy). A comprehensive evaluating indicator covering emissions and economy performance is constructed by the method of radar chart. Moreover, a radial basis functions (RBFs) neural network model is proposed to establish a precise model within the control parameters and the comprehensive evaluation indicator. The best set of control parameters under offline calibration is gained by the multi-island genetic algorithm. Finally, the offline calibration results are compared with the experimental results using a chassis dynamometer. The comparison results validate the effectiveness of the proposed offline calibrating approach, which is based on the radar chart method and the RBF neural network model on vehicle performance improvement and calibrating efficiency.