Coupled analytical-numerical approach for determining hydrodynamic responses of breakwater with multiple OWCs

A coupled analytical-numerical approach has been developed that allows one to study the hydrodynamic responses of breakwaters of arbitrary geometry that have multiple OWCs with horizontal openings. The approach incorporates the eigenfunction of the OWC fluid domain into the boundary element method, which automatically satisfy the boundary condition at the OWC opening. As a result, the exact geometry of the OWCs no longer needs to be modelled and the number of elements will be largely reduced especially when dealing with 3D breakwaters. With the present approach, a class of 2D OWC-integrated breakwater concepts in existing literature was simulated for validation and parametric study. The approach was then applied to the 3D breakwater with multiple OWCs under slender OWC assumptions, and the numerical results obtained are compared to data from a reduced scale model test. The 2D case studies show that the present approach is able to generate accurate results on reflection and transmission, wave loads, and energy extraction efficiencies with a higher efficiency than conventional boundary element method. Comparison of 3D results with the model test results shows that the prediction of the natural frequency and the wave reflection and transmission coefficients are in good agreement.     

非埋式桩板结构路基水平承载试验研究

非埋式桩板结构广泛应用于我国高速铁路的建设工程中,尤其是山区陡坡段,但对该结构的水平承载特性缺乏相应的研究。以杭黄高铁陡坡段非埋式桩板结构路基为原型,通过水平承载模型试验,研究结构内力弯矩、土压力分布形式,分析结构变形规律以及路基破坏形式。研究表明:当非埋式桩板结构路基承受水平荷载时,结构内力变化以桩基为主,并且随着水平荷载的增加,桩基弯矩呈基本不变至稳步增长最后剧烈增大的趋势;结构变形以水平位移为主,最大水平位移达7.25 mm,承载板发生内高外低的翘曲变形;当水平荷载达到一定时,路基边坡发生浅层破坏与局部压溃破坏,桩板结构的桩基于桩顶处与滑动面附近产生裂缝。试验过程中,桩板结构整体稳定性良好,但在水平荷载超过一定范围时结构变形过大,因此在水平推力较大的地段应谨慎选用非埋式桩板结构路基。     

Monitoring blade loads for a floating wind turbine in wave basin model tests using Fiber Bragg Grating sensors: A feasibility study

The blade loading contains sufficient information about the unsteady aerodynamics of Floating Wind Turbines (FWTs), and it serves as the basis for advanced controller developments. Wave basin model test is among the most reliable and economical methods for FWT investigations. However, few FWTs were reported being able to monitor the blade loads during wave basin tests. The main obstacles include strict space/mass limitations in model manufacturing and problems associated with signal transmission between rotating blades and stationary signal processing unit. In this paper, the feasibility of detecting blade loads for model FWT in wave basin tests is investigated. An on-line monitoring system is developed based on Fiber Bragg Grating (FBG) sensors and a Fiber Optical Rotary Joint (FORJ). Extensive validation tests are conducted under different environmental and operational conditions. Results show that the proposed FBG-FORJ sensing system presents impressive feasibility and reliability. As the authors know, it is among the first attempts to monitor the blade loads in real-time for model FWTs in wave basin tests. The present study will serve to enrich the knowledge about unsteady aerodynamics of FWTs and lay the foundation for experimental studies on advanced FWT controllers.     

自适应期望跟车间距和行为习惯的驾驶人跟驰模型

为满足智能车辆的个性化需求，提高智能车辆人-机交互协同的满意度和接受度，构筑双层驾驶人跟驰模型框架，提出自适应驾驶人期望跟车间距和行为习惯的个性化驾驶人跟驰模型。首先，提取个体驾驶人跟驰均衡状态的数据，采用高斯混合和概率密度函数(Gaussian Mixture Model and Probability Density Function, GMM-PDF)建立第 1 层模型，即驾驶人期望跟车距离模型。然后，将期望跟车距离参数引入模型，基于高斯混合-隐马尔可夫方法(Gaussian Mixture Model and Hidden Markov Model, GMM-HMM)学习驾驶习性，建立第2层模型预测加速度，即个性化驾驶人跟驰模型。其次，研究不同高斯分量个数对模型效果的影响，对比双层模型与 Gipps 模型、最优间距模型(Optimal Distance Model, ODM)、单层模型及通用模型的性能。最后，8位被试驾驶人的自然驾驶行为数据验证结果表明：高斯分量数量与模型性能存在一定的正相关性；在最优高斯分量数量下，8位被试驾驶人在训练集上预测误差均值为0.101 m·s-2，在测试 集上为0.123 m·s-2；随机选取其中1位驾驶人的2个跟车片段数据进行模型计算，结果显示，加速度的平均误差绝对值分别为0.087 m·s-2和0.096 m·s-2，预测效果优于Gipps模型、ODM模型、单层 模型及通用模型30%以上，与驾驶人实际跟驰行为的吻合度更高。     

考虑交通运行条件影响的驾驶员特征聚类

为提升驾驶员特征聚类方法的适用性与可靠性，本文基于机动车运行轨迹分析提出考虑交通运行条件影响的驾驶员特征聚类改进方法。首先，经过对车辆运行轨迹数据的分析发现，不同道路类型和平均速度条件会显著影响驾驶行为的集计特征；其次，提出改进的驾驶员特征聚类方法，第1步设计考虑道路类型与平均速度因素的车辆轨迹的切片和分类方法，从而稳定提取典型交通条件下的驾驶行为特征参数，第2步选用高斯混合模型聚类驾驶员特征。聚类案例表明， 在相同的道路类型和平均速度条件下，驾驶员类型越激进，其速度变异系数、加速度标准差和平均减速度等参数均值越高。不同聚类方法的对比表明，改进方法在驾驶员聚类的类内聚集度和类间分离度方面均表现更好，能有效提升驾驶员聚类的适用性与可靠性。     

船舶消防系统失效模型的建立与分析

消防系统是保障船舶生命力的重要复杂系统。针对消防系统存在着失效不确定和失效路径模糊的问题,结合船舶的特点应用故障树建立了船舶消防系统失效模型。为了有效地避免故障树的计算量组合爆炸问题,采用二元决策图对该模型进行定性和定量分析。分析结果明确了系统失效路径,简便地得到了各失效因素的关键重要度,计算结果精确,并提出了相应措施来降低船舶消防系统失效的发生。     

Validation of vessel seakeeping model tuning algorithm based on measurements at model scale

Wave-induced vessel motion prediction plays a critical role in ensuring safe marine operations. The operational limiting criteria can usually be calculated by applying presumed linearized vessel motion transfer functions based on the specified vessel loading condition, which may deviate from the real vessel condition when the operation is executed. Reducing the uncertainties of the onboard vessel loading condition can therefore improve the accuracy of vessel motion prediction and hence improve the safety and cost-efficiency for marine operations. However, parameters related to the onboard vessel loading condition can be difficult to measure directly, such as the center of gravity and moments of inertia. In addition, the hydrodynamic viscous damping terms are always subject to significant uncertainties and sometimes become critical for accurate vessel motion predictions. A very promising algorithm for the tuning of these important uncertain vessel parameters based on the unscented Kalman filter (UKF) that uses onboard vessel motion measurements and synchronous wave information was proposed and demonstrated previously by application to synthetic data. The present paper validates the UKF-based vessel seakeeping model tuning algorithm by considering measurements from model-scale seakeeping tests. Validation analyses demonstrate rational tuning results. The observed random errors and bias in relation to the measurement functions due to the applied simplification and linearization in the seakeeping simulations can lead to biased tuning. The importance of designing the state space and the measurement space is demonstrated by case studies. Due to the nonlinear relationship between the uncertain vessel parameters and the vessel motions, the tuning is shown to be sensitive to the mean state vector and selection of the surrounding sigma points.     

沙漏模式在无线电陆空通话英语教学中的应用

本文主要介绍在国外流行的沙漏教学模式的由来及其框架结构。并阐述了这一教学模式中涉及到的语言呈现阶段、语言强调阶段和语言练习阶段引入到飞行专业《无线电陆空通话》英语教学实践中的运用,从而证明沙漏教学模式在《无线电陆空通话》英语教学中的实用性和有效性。     

Using the Bayesian updating approach to improve the spatial and temporal transferability of real-time crash risk prediction models

This study aimed to improve the spatial and temporal transferability of the real-time crash risk prediction models by using the Bayesian updating approach. Data from California’s I-880N freeway in 2002 and 2009 and the I-5N freeway in 2009 were used. The crash risk models for these three datasets are quite different from each other. The model parameters do not remain stable over time or space. The transferability evaluation results show that the crash risk models cannot be directly transferred across time and space. The updating results indicate that the Bayesian updating approach is effective in improving both spatial and temporal transferability even when new data are limited. The predictive performance of the updated model increases with an increase in the sample size of the new data. In addition, when limited new data are available, updating an existing model is better than developing a model using the limited new data.     

Case studies of shipping along Arctic routes. Analysis and profitability perspectives for the container sector

Arctic sea routes have for long attracted interest from observers and shipping companies because of their shorter distances between the Atlantic and the Pacific. The prevalence of sea ice prevented the real development of a significant traffic, but did not prevent research from trying to assess the economic viability of these routes. With the actual present melting of sea ice in the Arctic, this effort at modeling the profitability of Arctic shipping routes received a new impetus. However, the conclusions of these studies vary widely, depending on the chosen parameters and their value. What can be said of these models, from 1991 until 2013, and to what extent can a model be drawn, capitalizing on twenty years of simulations?