Time domain analysis procedures for fatigue assessment of a semi-submersible wind turbine

Long term time domain analysis of the nominal stress for fatigue assessment of the tower and platform members of a three-column semi-submersible was performed by fully coupled time domain analyses in Simo-Riflex-AeroDyn. By combining the nominal stress ranges with stress concentration factors, hot spot stresses for fatigue damage calculation can be obtained. The aim of the study was to investigate the necessary simulation duration, number of random realisations and bin sizes for the discretisation of the joint wind and wave distribution. A total of 2316 3-h time domain simulations, were performed.In mild sea states with wind speeds between 7 and 9 m/s, the tower and pontoon experienced high fatigue damage due to resonance in the first bending frequency of the tower from the tower wake blade passing frequency (3P).Important fatigue effects seemed to be captured by 1 h simulations, and the sensitivity to number of random realisations was low when running simulations of more than 1 h. Fatigue damage for the tower base converged faster with simulation duration and number of random realisations than it did for the platform members.Bin sizes of 2 m/s for wind, 1 s for wave periods and 1 m for wave heights seemed to give acceptable estimates of total fatigue damage. It is, however, important that wind speeds that give coinciding 3P and tower resonance are included and that wave periods that give the largest pitch motion are included in the analysis.     

The role of volume-delay functions in forecasting and evaluating congestion charging schemes: the Stockholm case

This paper uses observations from before and during the Stockkholm congestion charging trial in order to validate and improve a transportation model for Stockholm. The model overestimates the impact of the charges on traffic volumes while at the same time it substantially underestimates the impact on travel times. These forecast errors lead to considerable underestimation of economic benefits which are dominated by travel time savings. The source of error lies in the static assignment that is used in the model. Making the volume-delay functions (VDFs) steeper only marginally improves the quality of forecast but strongly impacts the result of benefit calculations. We therefore conclude that the dynamic assignment is crucial for an informed decision on introducing measures aimed at relieving congestion. However, in the absence of such a calibrated dynamic model for a city, we recommend that at least a sensitivity analysis with respect to the slope of VDFs is performed.     

Traffic modelling in system boundary expansion of road pavement life cycle assessment

This paper uses a case study of a UK inter-urban road, to explore the impact of extending the system boundary of road pavement life cycle assessment (LCA) to include increased traffic emissions due to delays during maintenance. Some previous studies have attempted this but have been limited to hypothetical scenarios or simplified traffic modelling, with no validation or sensitivity analysis. In this study, micro-simulation modelling of traffic was used to estimate emissions caused by delays at road works, for several traffic management options. The emissions were compared to those created by the maintenance operation, estimated using an LCA model. In this case study, the extra traffic emissions caused by delays at road works are relatively small, compared to those from the maintenance process, except for hydrocarbon emissions. However, they are generally close to, or above, the materiality threshold recommended in PAS2050 for estimating carbon footprints, and reach 5–10% when traffic flow levels are increased (hypothetically) or when traffic management is imposed outside times of lowest traffic flow. It is recommended, therefore, that emissions due to traffic disruption at road works should be included within the system boundary of road pavement LCA and carbon footprint studies and should be considered in developing guidelines for environmental product declarations of road pavement maintenance products and services.     

The use of gait parameters to evaluate pedestrian behavior at scramble phase signalized intersections

Pedestrian scramble phasing is usually implemented to reduce pedestrian‐vehicle conflicts and therefore increase the safety of the intersection. However, to adequately determine the benefits of scramble phasing, it is necessary to understand how pedestrians react to such an unconventional design. This study investigates changes in pedestrian crossing behavior following the implementation of a scramble phase by examining the spatiotemporal gait parameters (step length and step frequency). This detailed microscopic‐level analysis provides insight into changes in pedestrian walking mechanisms as well as the effect of various pedestrian and intersection characteristics. The study uses video data collected at a scramble phase signalized intersection in Oakland, California. Gait parameters were found to be influenced by pedestrian gender, age, group size, crosswalk length, and pedestrian signal indications. Both average step length and walking speed were significantly higher for diagonally crossing pedestrians compared with pedestrians crossing on the conventional crosswalks. Pedestrians were found to have the tendency to increase their step length more than their step frequency to increase walking speed. It was also found that, compared with men, women generally increase their walking speed by increasing their step frequency more than step length. However, when in non‐compliance with signal indications, women increase their walking speed by increasing their step length more than step frequency. It was also found that older pedestrians do not significantly change their walking behavior when in non‐compliance with signal indications. Copyright © 2014 John Wiley & Sons, Ltd.     

The identification and empirical characterization of vehicular (Lagrangian) fundamental diagrams in multilane traffic flow

Traditional macroscopic traffic flow modeling framework adopts the spatial–temporal coordinate system to analyze traffic flow dynamics. With such modeling and analysis paradigm, complications arise for traffic flow data collected from mobile sensors such as probe vehicles equipped with mobile phones, Bluetooth, and Global Positioning System devices. The vehicle‐based measurement technologies call for new modeling thoughts that address the unique features of moving measurements and explore their full potential. In this paper, we look into the concept of vehicular fundamental diagram (VFD) and discuss its engineering implications. VFD corresponds to a conventional fundamental diagram (FD) in the kinematic wave (KW) theory that adopts space–time coordinates. Similar to the regular FD in the KW theory, VFD encapsulates all traffic flow dynamics. In this paper, to demonstrate the full potential of VFD in interpreting multilane traffic flow dynamics, we generalize the classical Edie's formula and propose a direct approach of reconstructing VFD from traffic measurements in the vehicular coordinates. A smoothing algorithm is proposed to effectively reduce the nonphysical fluctuation of traffic states calculated from multilane vehicle trajectories. As an example, we apply the proposed methodology to explore the next‐generation simulation datasets and identify the existence and forms of shock waves in different coordinate systems. Our findings provide empirical justifications and further insight for the Lagrangian traffic flow theory and models when applied in practice. Copyright © 2015 John Wiley & Sons, Ltd.     

中心斜裂纹矩形薄板的极限断裂强度分析

对具有中心穿透斜裂纹在弹性断裂和完全塑性断裂两种破坏模式下的断裂强度进行了分析.在弹性破坏模式下,利用应变能密度因子准则对不同的裂纹倾斜角和不同的矩形板长宽比对斜裂纹的初始扩展角度的影响进行了数值计算和讨论.对于延性材料的完全塑性断裂模式,利用弹塑性有限元对不同裂纹倾斜角下的矩形板的极限拉伸强度进行了分析,并对中心穿透裂纹拉伸强度简化计算公式进行了考虑裂纹倾斜角度的修正.     

水下滑翔机滑翔运动的能量分析及水动力性能研究

水下滑翔机是一种新型水下无人潜航器,它通过改变自身的浮力在海中前进,续航时间可长达数月或一年.文中对水下滑翔机滑翔运动过程中的能量变化进行了分析,建立了上浮和下潜运动数学模型,通过数值计算方法对水下滑翔机不同速度和攻角下的水动力进行了计算和分析,可为水下滑翔机总体设计与运动控制提供参考.     

Factors with the greatest influence on drivers' judgment of roundabouts safety. An analysis based on web survey in Italy

The aim of this paper is to identify the roundabout geometric characteristics affecting the safety perception while the typical maneuvers (entry, circulation, exit) are being carried out. The tool used was an on-line questionnaire, filled out by about 1.650 respondents. Four different dimensionality reduction methods (Cluster Analysis, Correspondence Analysis, Exploratory Factor Analysis and Confirmatory Factor Analysis) were used to analyze the data collected from the survey, in order to examine the key factors affecting the safety perception during the typical roundabout maneuvers. The considerations arising from the final model are the following: 1) the respondents' opinions regarding the safety perception of maneuvers are not preconceived ideas, but they originate from specific safety perceptions due to roundabout geometric configurations; 2) the users prefer definitely single lane roundabouts; this is an important confirmation of most results in the literature; 3) it was quantified the extent of the relationship between the safety perception of the typical roundabout maneuvers and the following aspects: a) maneuver type, b) geometric characteristics of the roundabouts design elements. This is the innovative aspect of the present research whose results have implications regarding theory, infrastructure and the application of new safety technologies.     

A list of accident scenarios for three legs skewed intersections

The term ‘scenario’ is used in the safety field to designate a prototype or a model of an accident process characterised by chains of facts, actions, causal relations and consequences in terms of damage to people and property. The prototypical scenarios, properly realized, provide a basis on which to consider the action to be taken, but also a concrete backup for accident information for use in information campaigns or training. The objective of this study is to define the prototypical accident scenarios for a particular configuration of road intersection: the skewed intersection. Limited sight distance at skewed intersections leads to safety issues. A non-skewed intersection provides the best operating conditions as drivers can easily sense the direction in which they are travelling, estimate the speeds of the opposing traffic and smoothly complete a maneuver in shorter time. In skewed intersections, instead, the ability of drivers to recognize any conflicting vehicles diminishes in comparison to right-angle intersections. The logical-deductive approach used in this paper for the determination of accident scenarios is based on an analysis of a large database of incidents, which occurred on several roads in eastern Sicily on 35 skewed intersections at three-legs. The skew angle of the minor leg of all the intersections studied is between 15° and 20°. This research allowed to develop accident scenarios related to particular configurations of intersections, compatible with the Italian rules. Prototypical scenarios are constructed using samples of accidents occurring on a particular type of study area, especially when they are based on files from in-depth investigations. The method used is an inductive approach, based on an examination of each case, grouping together similar cases and building a prototypical scenario using this case grouping. From the in-depth analysis of database accidents 9 prototypical accident scenarios have been identified for the skewed intersections.     

地铁明挖车站-市政桥梁合建结构的关键技术研究

地铁明挖车站和市政桥梁合建时,为同时满足2种不同类型构筑物的安全和使用功能要求,需对其中的关键技术难题进行分析研究,以采取合理可行的结构形式。依托成都地铁白佛桥明挖车站与其上部市政桥梁的建设,总结国内类似工程经验,根据工程特点确定桥梁承台与地铁车站顶板进行固结连接,桥梁跨度与地铁车站框架柱跨进行匹配,同时桥墩避开地铁车站端头井、换乘节点等复杂结构受力区域进行布设; 建立三维荷载-结构模型,计算分析上部桥梁荷载对地铁车站结构构件内力及变形的影响,并根据计算结果,对桥墩影响范围内的车站顶底板和侧墙的厚度及配筋进行增强,桥墩轴线下方的地铁车站框架柱采用型钢-混凝土组合结构,以满足合建结构的承载能力、变形、裂缝控制等要求。另外,选取LS-DYNA软件,采用非线性时程分析法对合建结构进行抗震计算分析,计算结果显示： 车站板、墙、梁等构件在支座处出现应力集中现象,各结构构件的承载力强度及变形均满足规范要求。