Flexible Bodies in Multibody System Codes

Multibody codes are'efficient tools to simulate nonlinear dynamic behaviour of rigid and flexible multibody systems undergoing large overall motions overlaid by small elastic deformation. This paper gives an overview of common approaches for the equations of motion of flexible body models and presents a general way to prepare the required data including geometric stiffening terms. In particularly, for the nodal approach the data are derived using standard results of a finite element analysis of the body. The computation of coefficient matrices describing the equations of motion is done outside the finite element code by matrix manipulations only. The data are stored in a standardised object-oriented structure. Consequently, the data set is independent of the formulation of the multibody system code.     

与速度有关的高负荷轮轨接触的粘着力(一)

为确定与速度有关的轮轨间的粘着力,设计了一种包含了与温度、弹性模数以及屈服点有关的动力学模型.     

Application of NETSIM in modeling B‐signals

NETSIM is a powerful microscopic simulation model and has been applied to numerous traffic studies. However, it appears that there are few attempts to use it to study bus operations. One of the possible reasons may be the difficulty in modeling some of the unique characteristics in bus operations. A similar challenge was faced when a recent evaluation on bus operations involving priority signals (B‐signals) was undertaken in Singapore. This paper describes the difficulties faced when NETSIM was applied in modeling bus priority signals and the techniques adopted to overcome them. This study shows that, by incorporating innovative techniques, NETSIM can be effectively used to model bus operations along with other traffic in a network.     

暗挖双连拱隧道穿越浅基础高层楼群区施工技术

北京城市铁路东直门区间采用双连拱隧道结构形式 ,在富水松散地层中从两栋浅基础高层居民楼中间采用浅埋暗挖法通过 ,施工难度极大。本文主要阐述针对该段复杂的施工边界及约束条件 ,在处理地层与结构、隧道施工与既有建筑物相互作用 ,所采用的技术方法和特殊条件下的高层建筑防护技术 ,以及监测在施工中的应用 ,以期为今后类似工程的施工提供参考和借鉴。     

新型船舶运动控制平台及海上试验

研制出一艘以水动力学相似准则缩尺的无人驾驶遥控模型船，模型船装有PC／104为主控计算机的船舶控制器，模型船由岸上主PC机遥控，用Honeywell公司的HMR3000碰罗经测量航导，用差分GPS系统定位，自主控制和推进，该遥控篡自治船舶运动控制已经进行了两次海上试验并取得成功，本文介绍该平台的系统设计，控制系统硬件和软件和海上试验经。     

Planktonic community structure and carbon cycling in the Arabian Sea as a result of monsoonal forcing: the application of a generic model

The Arabian Sea exhibits a complex pattern of biogeochemical and ecological dynamics, which vary both seasonally and spatially. These dynamics have been studied using a one-dimensional vertical hydrodynamic model coupled to a complex ecosystem model, simulating the annual cycle at three contrasting stations. These stations are characterised by seasonally upwelling, mixed-layer-deepening and a-seasonal oligotrophic conditions, respectively, and coincide with extensively measured stations on the two JGOFS ARABESQUE cruises in 1994. The model reproduces many spatial and temporal trends in production, biomass, physical and chemical properties, both qualitatively and quantitatively and so gives insight into the main mechanisms responsible for the biogeochemical and ecological complexity. Monsoonal systems are typified by classical food web dynamics, whilst intermonsoonal and oligotrophic systems are dominated by the microbial loop. The ecosystem model (ERSEM), developed for temperate regions, is found to be applicable to the Arabian Sea system with little reparameterisation. Differences in in-situ physical forcing are sufficient to recreate contrasting eutrophic and oligotrophic systems, although the lack of lateral terms are probably the greatest source of error in the model. Physics, nutrients, light and grazing are all shown to play a role in controlling production and community structure. Small-celled phytoplanktons are predicted to be dominant and sub-surface chlorophyll maxima are robust centers of production during intermonsoon periods. Analysis of carbon fluxes indicate that physically driven outgassing of CO₂ predominates in monsoonal upwelling systems but ecological activity may significantly moderate CO₂ outgassing in the Arabian Sea interior.     

Optimal Active Suspension Design Using a Frequency-shaping PID Filter

By the incorporation of frequency-shaping into the linear quadratic methods used in active suspension design it is possible to achieve improvements in both body frequency response and road-holding. The use of a PID filter for this purpose also leads to robustness of the system to disturbance forces. Zero steady-state deflections are achieved for applied body loads by the integral action with excellent attenuation of the transient response. The resulting system consists of a hydraulic actuator in parallel with a body spring of arbitrary stiffness and is optimal with equivalent full state feedback.     

Privatization trends at the world's top-100 container ports

Over recent years, the role of the private sector in seaports has been greatly expanded. Yet, in practice, the extent of privatization in ports can vary significantly, in part due to the different methods employed to bring about private sector participation. This paper identifies and analyses, through a survey of ports, recent trends in regard to privatization at the world's top-100 container ports. The survey has benefitted from, and seeks to extend, a previous survey undertaken by the International Association of Ports and Harbours (IAPH). Findings suggest that, although the influence of private sector actors in ports is growing, the role of public sector agencies also remains significant.     

Development and Evaluation of a High Voltage Supply Unit for Electrorheological Fluid Dampers

Controllable dampers using electrorheological (ER) fluids have attracted considerable interest in recent years. They are proposed for use in semi-active suspensions for ground vehicles. The main advantages of ER fluid dampers are their fast response, ease of control, simple construction and low power requirements. This paper describes the development and testing of a high-voltage supply unit for modulating the damping force of an ER fluid damper. Experimental results on the vibration isolation characteristics of an ER fluid damper with different control strategies, obtained using a quarter-car model test rig, are also presented.