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对交通事故持续时间分析的发展现状进行了综述．首先简要介绍了交通事故的定义,事故种类和交通事故管理系统,并分析了交通事故持续时间的统计分布．然后,对最近应用的几种主要的交通事故持续时间的分析方法及结论进行了概述．主要包括：方差分析,线性回归,非参数回归,决策树法,hazard duration method,模糊逻辑．主要的结论包括;大量的研究发现交通事故持续时间的分布形状是向左偏斜的钟型分布．交通事故数据采集标准化是事故分析中非常重要的环节．传统的统计分析方法处理不完整的数据有局限性．最后,本文提出了将来的发展方向,包括应用人工智能方法建立事故持续时间模型,及建立交通事故数据库标准．     

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概括地回顾了一些关于离线(或脱机)交通信号灯优化设计的方法.其中包括用于在孤立交叉口的单点和区域性的联动控制系统.离线方法在设计时一般利用已有调查出来的交通数据作为固定的输入资料,这个跟实时设计方法所要求的从感应器即时检浏出来的情况作为设计依据是有本质上的区别.但一般沿用的信号配时设计方法都需要依靠已刻在行车线道上(允许通行)的方向指示标志为设计基础,但这个方向指示在确定后在整个优化过程中是维持不变的,这就限制了交通流量在线道上的分布,从而大大减低配时的灵活性,在这样情况下优化出来的结果肯定不会是最好的.直至近期,以行车线道为基本单位的配时设计方法(英文名称为Lane-based method;中文可称为线道法)发展起来.这个方法是由传统的Phase-based method(相位法)所演变出来的.线道法不但包含所有相位法的特点,而且更能为原本受约束的线道和配时设计进行全面优化.线道法可在单点交叉口和区域性的联动控制系统上应用.文末提出一些未来研究发展的新方向.     

A New Explicit Algorithm for Bi-Phasic Mixture Flow in MIM

Metal injection moulding (MIM) is a new technology to manufacture small intricate parts in large quantity. Numerical simulation plays an important role in its development. To predict the specific segregation effect in MIM injection, mixture theory is adopted to model the injection flow by a bi-phasic model. This model conducts to the solution of two-coupled Stokes equations. It is an extremely computational consuming solution in the scope of the traditional algorithms, which induce a serious challenge to cost-effectivity of the MIM simulation. Referred to some methods proposed by Lewis in mono-phasic simulation and the implicit algorithms in MIM simulation, a new explicit algorithm is proposed and realized to perform efficiently this type of bi-phasic flow. Numerically this algorithm is devised to perform the simulation in a fully uncoupled manner except for a global solution of the pressure field in each time step. The physical coupling is taken into account in a sequential pattern by fractional steps. This special algorithm does not need any iteration, so it is straightforward and robust, suitable for MIM simulation and other sorts of simulations for multi-phasic flow.     

One-dimensional model on fuel penetration in diesel sprays with gas flow

In diesel engine, spray penetration is usually changed by in-cylinder gas flow. Accurate prediction on diesel spray with gas flow is important to the optimal design of diesel fuel injection system. This paper presents a theory investigation focusing on the penetration of diesel spray with gas flow. In order to understand the effect of gas flow on the penetration of diesel spray, a one-dimensional spray model is developed from an idealized diesel spray, which is able to predict the spray behavior under different gas flow conditions. The ambient gas flow is simplified as ideal flow that has only constant flow velocity along x-axial and y-axial directions of spray. The x-axial and y-axial directions are respectively defined as along and vertical spray directions. The main assumption is that the y-axial direction gas flow has no effect on the penetration of spray along x-axial direction. The principles of conservation of mass and momentum are used in the derivation. Momentum of in-cylinder air flow is also taken into consideration. Validation of the model at stable condition is achieved by comparing model predictions with experimental measurements of diesel spray without gas flow from Naber's experiments. Furthermore, CFD simulations on penetration of diesel spray with gas flow were performed with the commercial code AVL-fire. The onedimensional model is validated by the penetration results with gas flow from CFD calculation. Results show that a reasonable estimation of the spray evolution can be obtained for both with and without ambient gas flow conditions.     

卵砾石层管推进工程超挖及卡钻对管材与土壤互制行为的影响研究

非明挖工法在都市施作时,常因困难地质(如卵砾石层)或障碍物而造成施工困难、工期延误或发生灾损。本文主要针对非明挖施工法里的管推进施工法(Pipe-jacking Method),探讨管推进工法施工时可能遭遇的困难,以及施工困难状况下之管材土体互制行为。探讨的施工困难包括超挖、挤压、卡钻等问题。本研究针对超挖范围、卡钻位置、阻力大小以及推进力施加位置等,以ABAQUS有限元素软件进行三维数值仿真,探讨直线推进施工中的问题。     

软土地基水下真空预压固结离心模型试验

采用新发明的真空吸水系统应用于离心机中,可以使土体产生向上渗流并模拟软土地基真空预压。为获得理想的水下真空预压固结对比效果,竖井采用2种不同井间距的砂井,密封膜采用完全覆盖的形式。用发明的装置产生水下真空得以模拟软土水下固结行为。介绍了模型制作、试验程序及真空发生系统,并分析了孔隙水压力、变形、不排水剪切强度的改变和不同井间距对固结速率的影响。     

Approximations to the magic formula

Pacejka’s tire model is widely used and well-known by the automotive engineering community. The magic formula describes the brake force, side force and self-aligning torque in terms of the longitudinal slip and slip angle, plus several corrections. This paper uses approximation theory to obtain different types of approximations to the magic formula: rational functions (RA) resulting from the Remez algorithm, expansions in a series of Chebyshev polynomials (ACh), a series of Chebyshev rational polynomials (ARChPs), a series of rational orthogonal functions (ORF) and a series of ARChPs that result from grade-1 ORFs. The last expansion shows the fastest convergence and most effective computation. Jacobi rational polynomials can also be obtained to complement this expansion and facilitate fine-tuning in specific areas of the error curve. This work is complemented by obtaining the original rational approximations to the inverse tangent function, which take advantage of the curve symmetry to reduce the computation load and provide models that include the influence of the vertical load. The convergence properties of the development in series and the error values resulting from numeric examples for the three types of stress are shown. The proposed final ARChP expressions show very low error (1%) compared to the original magic formula. They can be computed 20 times faster; they can be evaluated, derived and integrated analytically easily; and their coefficients can be obtained from tests using common least-squares algorithms.     

CO2 air–sea disequilibrium and preformed alkalinity in the Pacific and Indian oceans calculated from subsurface layer data

This work estimates new regionalized empirical parameterizations for preformed alkalinity (A_T^o) and the CO₂ air–sea disequilibrium (?C_dis). Both are key terms for the computation of anthropogenic CO₂ in the back-calculation methods. Data from the subsurface layer (75–180 m depth range) covering an area from North to South and from 19°E to 67.5°W (Pacific and Indian oceans) were taken from GLODAP (The Global Ocean Data Analysis Project) database. The subsurface layer is proved as a reliable reference for representing the main characteristics of the different water masses of the oceans. Besides, handing data from the two ocean basins altogether makes the new parameterizations of A_T^o and ?C_dis to be more globally consistent. Nevertheless, each ocean basin, at least in some regions, has different oceanographic characteristics based on its proper dynamical processes and water masses formation. In order to maintain each ocean basin ‘identity’ the whole domain was divided in six different regions (two of them sharing waters from Pacific and Indian oceans) and parameterizations in each region for both terms were obtained. Previously, data were transformed into a grid of 4°lat. × 5°lon. and the results obtained from the parameterizations were visualized and compare with pCO₂ climatologies. From the comparisons with previous ?C_dis estimations good results are obtained showing the reliability and robustness of the new regionalized empiric parameterizations.     

Satellite remote sensing of the Polar Oceans

The advent of satellite remote sensing has opened doors for detailed monitoring of the polar regions at a relatively high temporal resolution. Several sensors have been developed over the years, the most noteworthy of which are the visible, the infrared and the microwave systems. The visible and infrared systems are most intelligible to the human eye and provide images that have good spatial resolution. However, because of persistent cloudiness and several months of darkness in the polar regions the most promising sensors appear to be the microwave systems, both passive and active. The passive microwave sensors have been the source of consistently derived ice cover and ice extent data and have provided about fifteen years of global data sets. The Synthetic Aperture Radar (SAR), on the other hand, is noted for very high resolution and a wide range of applications including ice dynamics and ice/wave interaction studies. Nevertheless, there are applications which require the use of the visible and infrared channels, such as the mapping of chlorophyll pigment concentrations in the marginal ice zones which require an ocean color scanner. Also, the infrared sensors are most effective for detecting physical temperatures over cloud-free ice and open water surfaces. Furthermore, altimeters could play an important role in mapping ice surface topography and in evaluating ridge and lead statistics. A review of past, present and future satellite systems, methods and techniques of interpretation and potential applications to the study of the polar oceans is presented.     

FRP正弦波形夹心桥面板的等效有限元模型

以FRP正弦波形夹心桥面板作为研究对象,得到等效正交各项异性实心板,通过理论分析和数值对比,证明了方法的可行性;采用该法对一实际的FRP正弦波形夹心板桥进行了模态分析。