基于云模型和蒙特卡洛方法的通航环境系统风险评价

在通航环境系统风险评价的实践过程中,往往面临很多不确定性因素,这使得风险评价工 作的开展面临一定的困难。为充分利用不确定性信息并克服其不利影响,将云模型和蒙特卡洛方 法引入船舶通航环境系统风险评价,构建了基于正态云模型和蒙特卡洛思想的通航环境系统风险 综合评价模型,并给出了实现方案。模型中,以正态云模型为工具实现风险评价过程中定性描述 和定量表示之间的相互转换,实现了基于云模型的通航环境系统各因素的风险评价;采用蒙特卡 洛方法得到通航环境系统风险云模型的三个关键参数。以杭州湾跨海大桥通航环境风险综合评价 为例,对所建模型的可行性和有效性进行了验证。研究表明,该模型能够作为在不确定性环境下 实现通航环境系统风险综合评价的一种有效方法。     

重要抽样模拟及其在结构可靠度计算中的应用

本文基于蒙待卡罗法的基本原理,阐述了重要抽样模拟技术的理论要点。通过算例,对重要抽 祥模拟和直接抽样模拟的有效性进行了比较,对重要抽样密度函数及其参数取值给予评估。对 重要抽样模拟次数以及密度函数均值的选用,也提出了建议。      

斜坡式防波堤的可靠性分析

对港口工程中常用的可靠度计算方法进行阐述,给出了斜坡堤护面块体稳定性可靠性分析的功能函数,介绍了港口工程中常用的单变量极值分布。以秦皇岛水文观测数据为基础,统计换算斜坡堤护面块体的质量,采用极值分布理论对护面块体的计算质量进行分布拟合,对比得出对数正态分布可以对护面块体质量分布进行较好的适线。从算例计算结果对比中可以发现,Monte Carlo模拟的可靠度指标计算结果比验算点法的计算结果低。两种方法计算的可靠度指标均比规范要求的低。利用Monte Carlo模拟计算结构可靠度,选择合理的模拟次数即可。     

Seasonality patterns in the container shipping freight rate market

Shipping indexes have attracted many researchers because they reflect the overall trend of corresponding seaborne markets and can provide implications for the future. Apart from the Baltic Dry Bulk Index (BDI) and correlated indices, the China Containerized Freight Index (CCFI) has been gaining more attention. As a country with large-scale manufacturing, China is an important exporting country and the CCFI was chosen to reflect the container shipping market because the data are more convincing and representative. There have been no systematic attempts to understand the seasonality patterns of container freights. Seasonality patterns reveal the regular fluctuation patterns within a 1-year period. They exist in time series, which are observed more than once a year, like the CCFI. To investigate the nature of seasonality (stochastic and/or deterministic) in container freight rates across different line services, we analyze the CCFI. This paper uses the HEGY method and Monte Carlo method comprehensively to figure out the small sample problem. In addition, seasonal dummy variables are used to test deterministic seasonality. Except for the Japan service series, which contains a half-year unit root, the other container freight rates seem to only involve a non-seasonal unit root at the zero frequency. Deterministic seasonality exists in all the line service series. Furthermore, the seasonality depends on the balance between supply and demand. Under this premise, the seasonal law of freight rates is much obvious.     

电动二轮车驾驶人头部损伤再现不确定性方法

为了减少交通事故中不确定性信息在受伤害者损伤再现中造成的不利影响,采用拉丁超立方(LHS)试验设计和响应面蒙特卡洛相结合的方法对电动二轮车驾驶人头部损伤再现进行损伤不确定性分析。首先采用多体系统动力学方法对具有详细事故信息(含视频信息)和损伤记录的2起电动二轮车事故中的汽车碰撞速度进行再现和不确定性分析,并对比事故信息(视频信息、最终位置、电动二轮车驾驶人的运动学),进而验证事故再现结果的有效性。在此基础上,应用有限元方法将获得的电动二轮车驾驶人头部碰撞的边界条件加载至THUMS人体头部有限元模型,分析电动二轮车驾驶人头部损伤参数的不确定性与简明损伤准则AIS累计频率的分布关系,并对比电动二轮车事故案例中电动二轮车驾驶人的头部损伤法医鉴定记录。研究结果表明:蒙特卡洛不确定性分析方法能够较准确地预测电动二轮车事故中的汽车碰撞车速,采用该分析方法获得的电动二轮车驾驶人头部损伤等级与法医鉴定的脑部损伤记录高度吻合;蒙特卡洛不确定性分析方法可以适用于评估电动二轮车事故中电动二轮车驾驶人的头部损伤等级,研究结果可为电动二轮车驾驶人头部损伤研究提供理论依据和实证方法。     

Incorporating uncertainty and risk in transportation investment decision-making

This paper presents a framework for addressing uncertainty and risk for large-scale transportation investments involving public–private participation. Demand, fare/toll and demand responsive costs are considered in the uncertainty analysis. Uncertainty analysis provides information on economic feasibility of the project. A set of relaxation policies is proposed to form various Ownership, Tenure and Governance (OTG) strategies reflecting the nature and level of participation by the public and private entity. A Monte Carlo Simulation-based Value at Risk is used to quantify risk. Finally, a methodology is proposed to integrate uncertainty and risk. The framework is tested on the proposed multibillion dollar Detroit River International Crossing connecting the cities of Detroit in the USA with Windsor in Canada. The analysis provides insights to probable outcomes for this transportation infrastructure investment under different OTG scenarios.     

Can high speed rail offset its embedded emissions?

This paper analyzes the climate implications of investments in high speed railway lines given uncertainty in future transport demand, technology and power production. To capture the uncertainty of estimated parameters, distributions for the annual traffic emissions reduction required to compensate for the embedded emissions from the construction of infrastructure are calculated using Monte Carlo simulation. In order to balance the annualized emissions from the railway construction, traffic volumes of more than 10 million annual one-way trips are usually required. Most of the traffic diverted from other modes must come from aviation and the project cannot involve the extensive use of tunnels.     

双重不确定下应急物资多式联运可靠路径优化

为按时、可靠地将应急物资运达目的地，综合考虑需求和运输环境的双重不确定性、节点疫情感染风险、成本约束、班期限制和转运能力限制等，构建以可靠度最大为目标的应急物资多式联运可靠路径优化模型。同时针对所求问题的NP-难特点，设计蒙特卡洛自适应遗传算法和模拟退火遗传算法进行求解，并引入优劣解距离法对算例的运行结果进行分析。研究结果表明：蒙特卡洛自适应遗传算法较模拟退火遗传算法在求解质量和求解时间方面更优，在交叉概率为0.80，变异概率为0.08，种群大小为50的最佳参数组合下，得到的优化路径最大可靠度为85%，且求解出来的最优路线均未经过存在疫情感染风险的节点，求解结果较好。参数分析表明：在交叉概率相同的条件下，两种算法的平均运行时间均随着变异概率的降低而减少，随着变异概率的增加而增加；多式联运路径优化的决策会受水铁班期的影响。     

Ultimate strength assessment of simply supported pitted platings: A new stochastic approach based on Monte Carlo simulation

The ultimate strength assessment of platings affected by random corrosion wastage is a key factor for the reliable design of new ships and the structural health monitoring of aged structures, as pitting corrosion wastage significantly affects the ultimate capacity of platings under compression. In this respect, significant efforts have been undertaken in the last decade to assess the ultimate strength drop-off of pitted platings under compression and several interpolating design formulas, based on a large number of FE simulations, have been developed. Nevertheless, current Rules and guidelines don't provide any explicit strength check criterion for pitted platings. Hence, the main aim of current research is the development of a new framework for the ultimate strength assessment of pitted platings, based on a stochastic approach and the endorsement of Monte Carlo simulation. A new formula, which allows evaluating the statistical properties of the plating ultimate strength in presence of random corrosion wastage, is developed. Subsequently, a benchmark study is carried out, to compare the new formula with the existing ones available in literature and a wide set of FE simulations, carried out by Ansys APDL. Current results are discussed, and the effectiveness of the new formula is verified.     

基于蒙特卡洛方法的邮船建造质量评价体系不确定性分析

为避免因建造质量问题导致的后续返工，需要在邮船建造过程中对建造质量进行控制，一套合适的建造质量评价体系可客观地反映建造质量，为质量控制提供标准。建立邮船建造质量评价体系的结构和数学模型，各部分的权重可使用层次分析法（Analytic Hierarchy Process，AHP）或德尔菲法确定，并使用蒙特卡洛方法对该体系的不确定性进行研究。结果说明该体系具有较好的稳健性。船厂在使用该体系时需要结合实际情况，尤其应注意内装质量部分的权重。