Situation and prospects of shipboard integrated power system reconfiguration technology北大核心CSCD

当前,船舶综合电力系统(IPS)正朝着复杂化、模块化、自动化方向发展,研究快速、稳定、能够应对各种突发状况的船舶综合电力系统重构技术对保障船舶安全和可靠航行具有重要意义。首先,综述当前国内外在船舶综合电力系统重构技术方面的研究进展,讨论集中式重构和分布式重构的特点,并对数学优化算法、启发式算法、人工智能算法等进行归纳总结;然后,分析面对多重并发故障时重构技术所面临的困难与挑战,提出需重点关注混杂系统建模和分层分布式重构框架的建立;最后,从重构模型建立、算法优化、分布式架构等方面对未来船舶综合电力系统重构的发展提出设想和建议。     

Monocular visual servo-based stabilization control of underactuated unmanned surface vehicle北大核心CSCD

［Objectives ］ Aiming at the accurate posture stabilization problem of an under-actuated unmanned surface vehicle (USV) in GPS-denied environments, a monocular visual servo stabilization control scheme is proposed based on homography.［Methods］By virtue of the homography decomposition technique, posture errors with an unknown scale factor are directly reconstructed from current and desired images, which thoroughly removes the calibration of extrinsic camera parameters and priori information on visual targets; with respect to the under-actuation constraint, a periodic function to persistently excite the yaw angle is incorporated into the continuous time-variant output feedback controller, allowing the USV to be stabilized in the absence of image depth, movement velocities and model parameters.［Results］Under the framework of the Lyapunov theory, the closed-loop visual servo system of the USV is rigorously proven to be asymptotically stable by Barbalat lemma.［Conclusions］By installing an onboard monocular camera, USV posture errors can be precisely stabilized with the aid of the proposed visual servo strategy, providing significant technique support for practical applications including docking, berthing, dynamic positioning, etc. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Enhanced selective forwarding scheme for alert message propagation in vehicular <Emphasis Type="Italic">ad hoc</Emphasis> networks

Vehicle-based applications were recently introduced to improve traffic safety and efficiency. These applications are classified into either safety-oriented or non-safety-oriented applications. Safety-oriented applications are typically provided by means of vehicle-to-vehicle (V2V) communications to support reliable and fast alert message propagation to all surrounding vehicles when an emergency occurs on the road. In vehicular ad-hoc network (VANET) broadcast-based packet forwarding is typically preferred for the propagation of urgent traffic-related information to all reachable nodes within a specified dangerous region. However, this approach may cause broadcast storm problems, which can lead to serious contention between transmissions from adjacent nodes. In this paper, we propose an alert message propagation scheme that is based on selective forwarding and aims to i) minimize the number of rebroadcasting nodes and ii) guarantee reliable and fast alert message delivery to all reachable nodes. Our scheme was evaluated using two different highway scenarios. The simulation results demonstrated that the performance of the proposed scheme was better than that of existing broadcast schemes in terms of the message delivery latency, the message delivery ratio, and the message rebroadcasting ratio.     

HCCI combustion characteristics during operation on DME and methane fuels

The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest because it can simultaneously achieve high efficiency and low emissions. However, the ignition timing is difficult to control because this engine has no physical ignition mechanism. In addition, combustion proceeds very rapidly because the premixed mixture ignites simultaneously at multiple locations in the cylinder, making it difficult to increase the operating load. In this study, an HCCI engine was operated using blended test fuels comprised of dimethyl ether (DME) and methane, each of which have different ignition characteristics. The effects of mixing ratios and absolute quantities of the two types of fuel on the ignition timing and rapidity of combustion were investigated. Cool flame reaction behavior, which significantly influences the ignition, was also analyzed in detail on the basis of in-cylinder spectroscopic measurements. The experimental results revealed that within the range of the experimental conditions used in this study, the quantity of DME supplied substantially influenced the ignition timing, whereas there was little observed effect from the quantity of methane supplied. Spectroscopic measurements of the behavior of a substance corresponding to HCHO also indicated that the quantity of DME supplied significantly influenced the cool flame behavior. However, the rapidity of combustion could not be controlled even by varying the mixing ratios of DME and methane. It was made clear that changes in the ignition timing substantially influence the rapidity of combustion.     

Improved method for analyzing automotive transmission parts (shaft/gear) manufactured using the warm shrink fitting process

There are three sub-processes associated with the assembly of an automobile transmission: heat fitting, shrink fitting, and combination fitting. In the heat fitting stage, the gear is heated to a specified temperature and then squeezed towards the outer diameter of the shaft. The stress of the heat-fitted gear depends on the yield strength of the gear. In the shrink fitting process, the gear is typically squeezed towards the shaft at room temperature using a press. An alternate method, known as warm shrink fitting, heats the already warm gear and safely squeezes it toward the shaft. The warm shrink fitting process for automobile transmission parts is becoming more commonplace, but the additional heating can cause the dimensions of the assembled parts (shaft/gear) to change with respect to both the outer diameter and the profile of the gear. As a result, there may be additional noise and vibration between gears. To address these problems, we analyzed the warm shrink fitting process using the contact pressure caused by fitting interference between the outer diameter of the shaft and the inner diameter of the gear, fitting temperature, and the profile tolerance of the gear as design parameters. In this study, a closed form equation for predicting the contact pressure and fitting load is proposed. This equation is used to develop an optimization technique for the warm shrink fitting process. The reliability of the model was verified using experimental results measured in the field, and FEM with thermal-structural coupled field analysis. Actual loads measured in the field showed good agreement with the results obtained by theoretical and finite element analysis, and expansion of the outer diameters of the gears agreed well with the results.     

Development of evolutionary cone type LSD for SUV/RV utilizing the axiomatic approach and the ultrasonic nano crystal surface modification technology

Surface topology, cone angle and the forces acting on the cone of the clutch type limited slip differential (LSD) are major design parameters for the bias ratio and the noise condition. Therefore much research has been dedicated to these developments but the results have been used to submit patents. A new cone type limited slip differential for sport utility vehicles and recreational vehicles, which has a very simple structure and easy compliance with the vehicle performance, has been developed by the axiomatic approach and the ultrasonic nano crystal surface modification (UNSM) technology. The design criteria and optimal value of the design parameters are determined by the axiomatic approach utilizing CAE tools. Test methodologies in a test rig and in a vehicle were also developed. Test results showed good performance of bias ratio and noise level but durability is still under testing. This study is an extension of F2006P266, FISITA 2006.     

Design of Integrated Chassis Control logics for AFS and ESP

The performance of most electronic chassis control systems in the past has been optimized individually. Recently, a great research effort has been dedicated to the integration of chassis control systems in an effort to improve the vehicle performance. This involves orchestration of individual control modules so that they can jointly contribute to the enhancement of their control effect. In this research, two integrated control logics for AFS (Active Front Steering) and ESP (Electronic Stability Program) have been developed. Of the two logics, one uses a supervisor that rules over the individual modules. The other logic uses a CL (Characteristic Locus) method, which is a frequency-domain multivariable control technique. The two logics have been tested under various driving conditions to investigate their control effects. The results indicate that the proposed integrated control logics can yield vehicle performance that is superior to that of the individual control modules without any integration scheme.     

大众汽车公司的机械式G型增压器

本文介绍了德国大众汽车公司设计、生产的采用螺旋推进压气原理的工作的Ｇ型增压器，对其原理、结果及应用作了详细的分析说明。     

Bicycle commuting in an automobile-dominated city: how individuals become and remain bike commuters in Charlotte,North Carolina

Transportation - In Charlotte, North Carolina less than one half of 1% of commuters ride a bicycle to work despite several decades of public investment in bicycle infrastructure and planning. Like...     

The demand for public transport. part II. supply and demand factors of public transport

Abstract

This two‐part article, concerned with the way public transport ridership is affected by the various relevant factors, is based on the Executive Summary of The Demand for Public Transport (Webster and Bly 1980), the report of the TRRL‐sponsored International Collaborative Study on Factors Affecting Public Transport Patronage. Part I of the article, which was concerned with the social and economic conditions in which public transport operates, showed the importance of the background factors such as income, car ownership and land use on public transport usage: it also indicated how the longer‐term impacts of the more direct demand factors (fares, service levels) often show themselves in changes in car ownership levels, activity patterns (i.e. where people live, work, shop, socialize, etc) and land‐use development.

Part II reviews the current state of knowledge on the effects of changes in fare levels and quality of service and of the introduction of various traffic and transport measures (traffic restraint, bus priority, etc): it outlines current methodology on costing public transport services and draws the supply and demand sides together in a consideration of particular strategies which are at the disposal of the operator, the planner and the policy maker.