PIV study of the effect of piston position on the in-cylinder swirling flow during the scavenging process in large two-stroke marine diesel engines

A simplified model of a low speed large two-stroke marine diesel engine cylinder is developed. The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied using the stereoscopic particle image velocimetry technique. The measurements are conducted at different cross-sectional planes along the cylinder length and at piston positions covering the air intake port by 0, 25, 50 and 75 %. When the intake port is fully open, the tangential velocity profile is similar to a Burgers vortex, whereas the axial velocity has a wake-like profile. Due to internal wall friction, the swirl decays downstream, and the size of the vortex core increases. For increasing port closures, the tangential velocity profile changes from a Burgers vortex to a forced vortex, and the axial velocity changes correspondingly from a wake-like profile to a jet-like profile. For piston position with 75 % intake port closure, the jet-like axial velocity profile at a cross-sectional plane close to the intake port changes back to a wake-like profile at the adjacent downstream cross-sectional plane. This is characteristic of a vortex breakdown. The non-dimensional velocity profiles show no significant variation with the variation in Reynolds number.     

Institutional arrangements for coastal conservation in New Zealand

Abstract

The focus of this paper is institutional arrangements for initiative coastal conservation in New Zealand. “Initiative”; conservation refers to positive measures for the protection of the natural environment for reasons related to its inherent worth. Case studies were undertaken in five areas with different biophysical and societal characteristics, where various approaches to coastal conservation are being attempted. In each area, an issue was analyzed to identify conservation policies and their relationship to ecological and human needs, and to administrative and legal frameworks. Analysis demonstrated that initiative conservation policy can encompass user and community needs while maintaining ecological priorities. Institutional arrangements do not appear to restrict the development of this type of policy in New Zealand, but they do limit its formal expression and implementation. Arrangements for cohesive conservation areas spanning the land‐sea interface are particularly lacking.     

Investigation of engine restart stability after idle stop for a mild type HEV powertrain

Stringent regulations on exhaust emissions and fuel economy for vehicles have become major issues in the automotive industry. Hybrid electric vehicles (HEV) are one of the crucial alternative plans to current conventional vehicles, but they have drawbacks, which include increases in total hydrocarbon (THC) emission from the engine and deterioration of the combustion stability with frequent stopping and restarting of the engine. Intake port fuel film is evaporated up during the deceleration state due to the fuel-cut. The λ (relative A/F ratio) at engine restart is lean because part of injected fuel is used to form the fuel film in the intake port. This study revealed the behavior of a fuel film in engine stop with fuel-cut and in engine restart with a simulation model. To investigate the fuel film characteristics, a simulation model was applied and validated with a single-cylinder engine. The simulation result shows that λ of at least 1.2 is required for a stable engine restart. The minimum injection quantity of the first cycle for stable combustion is suggested to be at least 240% of the steady-state idle condition.     

佛开高速公路软基路堤拓宽处理及拼接现场试验

佛开高速公路拓宽工程的关键技术问题之一是软基路堤的地基处理和拼接。通过试验段工程进行了路基拼接和拓宽时,不同复合地基处理方法的原型试验,研究表明,搅拌桩地基下卧层的单位压缩量小于素混凝土桩地基,拓宽路基断面的最大沉降和最大沉降速率出现在素混凝土桩加固区;老路对拓宽路堤的荷载反应敏感,老路最大沉降速率出现在拓宽路堤荷载施加完成之后;拓宽路基具有比较小的工后沉降,所采用的地基处理方法和路基拼接方法满足设计要求。     

Dynamic analysis of spiral bevel geared rotor systems applying finite elements and enhanced lumped parameters

The dynamics of spiral bevel gears like most high-speed precision gears employed in motor vehicles and off highway equipments are substantially affected by the structural characteristics of the shafts and bearings. The lumped parameter model is one of the common tools applied to perform gear dynamic analysis. Even though the lumped parameter approach is computationally fast and conveniently efficient, it typically uses limited number of coordinates and may not fully account for the shaft-bearing structural characteristics accurately. In this analysis, the finite element formulation, that can generally represent more complete characteristics of the shaft-bearing assembly, is employed to enhance the current lumped parameter synthesis theory using the concept of effective mass and inertia elements. Computational output shows that the enhanced lumped parameter synthesis model is capable of predicting sufficiently accurate dynamic response when compared to the direct dynamic finite element calculations, and much more precise response than previous lumped parameter results, especially when the gear dynamics are associated with the pinion or gear bending modes. Even though this analysis focuses primarily on the spiral bevel geared rotor systems, the proposed methodology and analysis results can be easily extended to other types of gears.     

Technology analysis and low-cost design of automotive radar for adaptive cruise control system

Recently, the advanced driver assistance system (ADAS), which helps mitigate car accidents, has been developed using environmental detection sensors, such as long and short range radar, lidar, wide dynamic range cameras, ultrasonic sensors and laser scanners. Among these detection sensors, radars can quickly provide drivers with reliable information about the velocity, distance and direction of a target obstacle, as well as information about the vehicle in changing weather conditions. In the adaptive cruise control system (ACCS), three radar sensors are usually needed because two short range radars are used to detect objects in the adjacent lane and one long range radar is used to detect objects in-path. In this paper, low-cost radar based on a single sensor, which can detect objects in both the adjacent lane and in-path, is proposed for use in the ACCS. Before designing the proposed radar, we analyzed the world-wide radar technology and market trends for ACCS. Based on this analysis, we designed a novel radar sensor for the ACCS using radar components, such as an antenna, transceiver module, transceiver control module and signal processing algorithm. Finally, target detection experiments were conducted. In the experimental results, the proposed single radar can successfully complete the detection required for the ACCS. In the conclusion, the perspective and issues in the future development of the ACCS radar are described.     

Patterns of United States-Canadian maritime container flows

The focus of this paper is to identify the origins and the destinations of containerized movements between the United States and Canada during 1977. Additionally, the paper examines the nationality or flag of the carrier with regard to such flows.     

21世纪的美国交通

就美国交通的基本情况、发展模式、交通工具的选择和新技术的应用、智能交通系统及私有化和外包等诸多方面进行了深入的探讨，对美国交通的发展趋势做出了详尽而有理有据的预测，这样的综合介绍无疑会使我国的交通规划与发展颇受裨益。     

应用Superpave体积设计法设计冷再生沥青混合料

旧沥青路面的再生利用是我国公路建设即将面临的重要课题,其中冷法再生是一种重要方法。本文针对乳化沥青冷再生沥青混合料的设计提出了修正Superpave设计法,经室内试验验证,证明该法取得了较好的效果。