A New Technique of High-performance and Fast Tensioning Prestressed Anchorage CableEI北大核心

Research purposes: The large-span transition section tunnel of the Badaling Great Wall station on the Beijing-Zhangjiakou high-speed railway with the maximum excavation width of 32.7 m, and the largest excavation area of 494.4 m 2 , is the world's biggest traffic tunnel in the world with the largest excavation width and excavation area, which has difficult construction and high security risks. The initial support system of tunnel is mainly realized by prestressed bolt, prestressed cable and shotcrete. After test, anchor cable tension using the traditional anchor cable construction technology can't meet the design requirements, at the same time, it takes about 30 days to achieve prestressed tensioning. Therefore, we need to study the high-performance fast tensioning prestressed anchor cable technology, to effectively control surrounding rock deformation, to ensure the safety of construction, improve construction efficiency. Research conclusions:(1) The traditional anchor cable construction technology is adopted. The anchor cable tension value is mainly controlled by the grip force between the anchor rope and grouting body and the cohesive force between grouting body and surrounding rock. (2) The grip force between the anchor rope and the grouting body can be increased by about 2 times by increasing the "barb"; The cohesive force between the grouting body and the surrounding rock can be increased by 1.5 times by 6 ~ 7 MPa high-pressure grouting process. (3) The modified sulphoaluminate cement slurry can reach more than 30 MPa within 1 day of the slurry strength, so as to realize fast anchor cable tension within 1 day after grouting completion. (4)The research results can be used for reference in similar prestressed anchorage cable construction projects. © 2018, Editorial Department of Journal of Railway Engineering Society. All right reserved.     

Role of steering wheel feedback on driver performance: driving simulator and modeling analysis

When driving in curves, how do drivers use the force appearing on the steering wheel? As it carries information related to lateral acceleration, this force could be necessary for drivers to tune their internal model of vehicle dynamics; alternatively, being opposed to the drivers' efforts, it could just help them stabilize the steering wheel position. To assess these two hypotheses, we designed an experiment on a motion-based driving simulator. The steering characteristics of the vehicle were modified in the course of driving, unknown to drivers. Results obtained with standard drivers showed a surprisingly wide range of adaptation, except for exaggerated modifications of the steering force feedback. A two-level driver model, combining a preview of vehicle dynamics and a neuromuscular steering control, reproduces these experimental results qualitatively and indicates that adaptation occurs at the haptic level rather than in the internal model of vehicle dynamics. This effect is related to other theories on the manual control of dynamics systems, wherein force feedback characteristics are abstracted at the position control level. This research also illustrates the use of driving simulation for the study of driver behavior and future intelligent steering assistance systems.     

Development of simplified analytical methods for predicting the response of offshore structures to blast and fire loading

This paper discusses structural response to blast loading and temperature changes in fires. Both extreme events can be modelled using a range of analytical techniques from simple methodologies to the very complicated finite element analysis. The relatively simple techniques are appropriate for this type of problem and degree of accuracy required given the level of uncertainty in the loading. Given specific boundary conditions and physical properties, the methodologies proposed in the paper provide as good estimates of the dynamic response to blast loading and temperature increases in fires as the more sophisticated finite element method. Experimental data compares well with the analytical results.     

Fleet deployment optimization for liner shipping Part 2. Implementation and results

We use linear programming (LP) for solving the problem of the optimal deployment of an existing fleet of multipurpose or fully containerized ships, among a given set of routes, including information for lay-up time, if any, and type and number of extra ships to charter, based on a detailed and realistic model for the calculation of the operating costs of all the ship types in every route and on a suitable LP formulation developed in earlier work of the authors. The optimization model is also applicable to the problem of finding the best fleet compostion and deployment, in a given set of trade routes, which may be the case when a shipping company is considering new or modified services, or a renewal of the existing fleet. In addition, two promising mixed linear-integer programming formulations are suggested.     

Cross-shelf circulation and phytoplankton distribution at the summertime New England shelfbreak front

We investigate aspects of the secondary (cross-shelf) circulation at the Middle Atlantic Bight shelfbreak front using high-resolution data collected on the New England Shelf in August 2002. The alongshore shelfbreak jet coincides with the front at the seaward edge of the cold pool (remnant winter shelf water) and there is a suggestion of a cross-stream convergence centered at the jet core. Despite indications of convergence we found no evidence of a surface subduction on the seaward side of the front. At depth 70 m near the shelfbreak there was a patch of chlorophyll, located within a local temperature–salinity maximum which, though significantly below the euphotic zone, appeared to be photo-acclimated and viable. The chlorophyll feature could be the result of a local subduction by a larger scale eddy circulation seaward of the front.Dye tracer experiments directly observed the convergence at the foot of the shelfbreak front and subsequent upwelling of bottom boundary layer water along the shoreward side of the shelfbreak front. But, we found no evidence that this upwelling influenced productivity at the front. Further, since there was no cross-shelf maximum in subsurface chlorophyll at the front, we conclude that this productivity is in general, sustained by a broadly distributed local vertical nutrient flux from an underlying nutrient reservoir.     

Water masses and cyclonic circulation in Bay of La Paz, Gulf of California, during June 1998

The Bay of La Paz, a coastal and shallow basin of the Gulf of California (depth<420 m), exchanges mixed-layer waters with the Gulf of California predominantly through Boca Grande (Big Mouth), in the northeastern part of the bay. Equatorial Surface Water (ESW) flows from the gulf to the bay; once there, due to evaporation processes, this water increases its salinity above 35.00, therefore becoming Gulf of California Water (GCW) Mass. During June 1998, the baroclinic circulation in the bay was dominated by a cyclonic gyre. The hydrographic dome, related to this gyre, is depicted until approximately 150-m depth. However, the vertical mixing of water between the mixed-layer and the ones below practically does not occur because of the development of a sharp pycnocline. This fact and the isolation of the bottom of the bay by a bathymetric sill (approximately 250-m depth) at Boca Grande induce low oxygen content, particularly in the bottom-waters (O₂<0.1 ml/l). Chlorophyll values are higher and with larger vertical fluctuations within the Bay of La Paz than outside.     

Dynamic Response of a Six-axle Locomotive to Random Track Inputs

Spectral analysis techniques are employed to analyze the dynamic response of a six-axle locomotive on tangent track to vertical and lateral random track irregularities. The locomotive is represented by a thirty-nine (39) degrees of freedom model. A linear model is employed by considering small displacements, linear suspension elements and a linear theory for the wheel-rail interaction. Power spectral densities of displacements, velocities and accelerations and the statistical average frequencies of the system are obtained for each degree of freedom. Comparison of the calculated dominating frequencies with existing experimental values shows good agreement. The technique of spectral analysis is an effective tool for model validation, and for the determination of rail vehicle response to track irregularities. The probability functions for the response can be used as a measure for the ride quality of rail vehicles and for the study of fatigue damage of components.     

Maritime commercial malpractices and piracy under international law

The term 'Piracy' tends to be used in a loose, popular sense to refer to various acts of violence or lawlessness at sea which are not, strictly speaking, acts of piracy in law. In this article, the author examines the concept of piracy under international law and related notions such as hijacking and mutiny. In this context, he shows that the 'malpractices' of robber bands in such places as the inshore waters of Nigeria and The Philippines are not acts of piracy jure gentium.     

Specification of a tour-based neighborhood shopping model

This paper presents a state-of-the practice neighborhood shopping travel demand model. The model structure is designed to incorporate decisions across five dimensions of shopping travel, including decisions of: (1) household tour frequency; (2) participating party; (3) shopping tour type; (4) mode, and (5) destination choices using a tour-based nested-logit model. As a neighborhood model, we have also captured the interrelated effects of three main factors associated with shopping travel decisions both within and outside of the neighborhood, including the residential location within the neighborhood, the neighborhood regional setting and the household structure. The model was validated using the travel data collected in three neighborhoods located in the Puget Sound region, WA. Results show that household socio-demographics have significant effects on the decisions for household tour frequency, mode and destination choices, while the characteristics of the traveling party have considerable impacts on the decisions for tour type. The level of service and the zone attractions influence decisions about mode and destination choices. The day of week variable (weekday versus weekend) is statistically significant in all models, indicating that weekday shopping travel decisions differ from weekend, across all five dimensions of interest. The paper concludes with a discussion about how the model can be used to examine policy-related neighborhood issues (e.g. accessibility).     

Research on the CTCS-4 Train Control System Based on Track Circuit Information FusionEI北大核心

Research purposes: CTCS-3 train control system is adopted in Chinese high-speed railway with speed of 300 km/h or higher. It is based on track circuit to check train occupancy and adopt quasi-moving block. In recent years, rapid development of national economy has put forward higher requirements for the capacity of high-speed railway. As a higher level train control system, CTCS-4 train control system can realize virtual block or moving block, and further shorten headway, but it is still in the stage of theoretical research. So this paper aims to analyze the characteristics of high-speed railway, and to propose a scheme for the implementation of CTCS-4 train control system based on track circuit fusion. Research conclusions:(1)When the wireless communication between vehicle and ground is interrupted, transport efficiency of CTCS-4 train control system can not meet the transport demand of high-speed railway.(2)CTCS-4 train control system should have the CTCS-2 backup function, which can make non-communication trains run normally and ensure the transport efficiency.(3)CTCS-4 train control system should integrate track circuit information, which can make RBC obtain position information of non-communication trains, improve the availability of the system and avoid complicated operational rules.(4)Due to complexity of high-speed railway and change of existing equipment, virtual block can be used in early stage of CTCS-4 train control system.(5)The research results can provide some references for CTCS-4 train control system in high-speed railway. © 2018, Editorial Department of Journal of Railway Engineering Society. All right reserved.