The efficiency of congestion charging: Some lessons from cost–benefit analyses

This paper addresses methodological issues in cost–benefit analysis (CBA) regarding congestion charging schemes. Despite suspicion on the reality of travel time savings, it is argued that these savings are a conservative value of surplus gained from a congestion scheme. The methodology of measurement of travel time reliability is not yet stabilised, but the literature review suggests that it may take a growing share of benefits in the future. Sensitivity tests performed on the London and Stockholm case studies with a simulation model underline the need to accurately measure speeds, while the value of travel time appears less critical. Finally, the impact of costs of public funds on public accounts is greatly significant and may increase in the future.     

SCGE modelling in cost-benefit analysis: The Dutch experience

Spatial computable general equilibrium (SCGE) models offer opportunities for computing wider economic effects in cost-benefit analysis (CBA) in a theoretically satisfactory way. This is important for the correct estimation of additional economic benefits and international relocation impacts. In the Netherlands, this potential has only been reached partly. Many different types of models are actually used, none of which yet covers all relevant markets. In CBAs carried out in recent years, ad hoc methods were used more often than models, let alone SCGE models. Moreover, the usual presentation of the model outcomes appears as a ‘black box’ to policy makers. There is much work to be done, in extending SCGE models to strengthen their empirical basis, and in improving the presentation of the outcomes.     

柴油机曲轴断裂原因新析

针对柴油机曲轴断裂的原因,提出了一种新见解--"油楔力"的作用是加速曲轴断裂的一个主要原因.指出"初始裂纹"是曲轴断裂的危险信号;交替变形产生的交变负荷是"油楔力"能量的来源;"油楔力"的作用使裂纹加速扩展,从而导致曲轴载荷截面尺寸不足而发生突然折断,使曲轴断裂发生在材料疲劳破坏之前.消除初始裂纹是曲轴安全运转的保证.     

The implications of piracy on marine insurance: some considerations for the shipowner

A prominent feature of modern day piracy is the ransom that is demanded for the safe release of the ship, cargo and crew. The recent upsurge of this type of piracy, in areas of the world that are of strategic importance to the shipping industry, has created many challenges for shipowners, underwriters and the law relating to marine insurance. The aim of this paper is to examine how the marine insurance market is being affected by the threat of modern day piracy, and seeks to identify the options that are available for the recovery of a ransom payment by the shipowner. Moreover, this study aims to identify the legal issues that might prevent a shipowner from recovering a ransom payment under an insurance policy or from the other interests in a common adventure. The study establishes that a reasonably made ransom payment by the shipowner will amount to an extraordinary expense that is taken to minimise or avert a loss. Such an act can generally be recovered under the insurance policy as a sue and labour expense or from other interests in the common adventure as a general average expense. However, illegality, unseaworthiness and exemption clauses in a marine policy are identified as being legal issues that may prevent a shipowner from recovering the ransom payment. Some of these problems may be overcome if clauses are carefully drafted to specifically cater for modern day piracy in a marine insurance policy. Several inconsistencies may also be resolved by transferring the piracy peril to war risks cover. The shipowner’s duty is to respond to the changing circumstances, by ensuring that his vessel is sufficiently equipped and the crew is properly trained to resist a hijacking.     

Numerical analysis on free surface waves and stern viscous flow of a ship model

This paper deals with numerical techniques for computing the viscous flow past a ship hull with and without a free surface using a Reynolds-averaged Navier-Stokes solver with global conservation. In the first technique, a coarse grid is used to find an approximate solution to the free surface problem. Interpolation of a fine grid is subsequently carried out, and a more exact solution, particularly in the boundary layer and wake, is obtained. In the second technique, a modified Baldwin-Lomax model is introduced to compute the viscous flow with and without a free surface. These numerical techniques are applied to simulations of the flow around a Series 60 and an SR196C ship model. The results are compared with measurement data, and the usefulness of the numerical techniques is demonstrated.     

移动式近海基地的动力定位控制研究

移动式近海基地是一个大型的、浮动的、自行驱动的、由三至五个模块组成的海洋结构.其中的每个模块均能在风、浪、流作用力下实现长期定位.本文首先讨论了针对移动式近海基地的控制架构.然后针对近海基地中的单独模块设计了一个非线性带前馈的比例微分(PD)控制器,并将其应用到多个模块的运动控制中.文中同时给出了所设计的控制系统的仿真结果.     

存在饱和输入的欠驱动船舶航迹跟踪控制

针对控制输入存在饱和限制的欠驱动船舶的航迹跟踪问题,提出鲁棒饱和控制方法。以船舶纵向速度和艏向角速度为虚拟输入,设计饱和运动学控制器,并引入二阶滤波器形式对控制器进行简化;利用反步法并引入Nussbaum型函数,设计饱和动力学控制器,以实现对任意光滑航迹的跟踪控制,并保证跟踪误差收敛至零点附近的一个有界区域内。仿真算例验证了设计方法的有效性和鲁棒性。     

Understanding ship-grounding events

The paper presents a simple procedure to estimate the damage to a ship bottom and the associated seabed topology that results from a dynamic grounding event. The seabed is modeled as a rigid body and parameterized by a quadratic surface, i.e., a paraboloid, which can in principle model a wide range of seabed topologies. A nonlinear finite element program (LS-DYNA) is used to simulate the contact force versus the lateral penetration, from which the horizontal force component of powered grounding is estimated. The simplified procedure for analyzing dynamic and static grounding events is outlined. Simulations are performed for different ship speeds and for different initial levels of obstruction over the keel. It is shown that a static approach may replace the dynamic grounding simulation, thereby considerably reducing the computational work. The static approach allows for the quick estimation of the energy absorption during powered grounding, which is imperative for decision making during critical situations. The ultimate goal of the study is to provide a near real-time prediction of the risk of rupture of the cargo tanks and hull girder failure. Moreover, the residual strength of damaged ships is an important issue that is related to operations involved in the salvage of wrecked vessels, such as re-floatation and towing.     

Comparison of the crashworthiness of various bottom and side structures

The purpose of this work is to compare the resistance with damage of various types of double bottom structures in a stranding event. The comparative analyses are made by use of a commercial, explicit finite element program. The ship bottom is loaded with a conical indenter with a rounded tip, which is forced laterally into the structures in different positions. The aim is to compare resistance forces, energy absorption and penetration with fracture for four different structures. Those four structures are: a conventional double bottom, a structure (presently protected through a patent) with hat-profiles stiffened bottom plating, a structure where all-steel sandwich panel is used as outer shell and a bottom structure stiffened exclusively with hat-profiles. The paper shows that it is indeed possible to elevate the crashworthiness of side and bottom structures with regards to the loading considered here without increasing the structural weight.     

海洋地震拖缆阻力试验研究

海洋地震拖缆是海洋油气资源勘探中的重要设备,为研究海洋地震拖缆在拖曳状态以及有横向干扰时的阻力特性,进行了缩比模型实验。基于应变测试技术,设计研发了一套高灵敏度测力机构,用于间接测量拖缆及其附件的首端张力值,以求得拖缆的实际阻力。通过对实测数据比较,分析了拖缆速度及横向干扰对拖缆阻力的影响。实验结果表明,在低速拖曳下拖缆阻力与速度的三次方成正比关系;在有横向干扰时,拖缆阻力可看作无干扰时的平衡力和与干扰频率有关的正弦脉动力的叠加,当干扰频率一定时,脉动阻力幅值与平衡阻力的比值基本为常数。基于以上实验结果,结合量纲分析法,能够对实际拖缆阻力进行较好的估算。     

气体-固体粒子两相流理论及其应用

本文运用气体─固体粒子两相流理论，将流动视为气体和固体粒子伪流体的混合物的流动，对内破裂现象进行了理论研究，并给出了基于实验结果和考虑相容百分数的影响的固体粒子阻力系数公式。运用有限控制体积法进行了数值模拟计算，结果可信。这项研究还为多相流的传输、泥沙沉积现象等研究提供了理论和计算基础。     

Crew resource management training in the maritime industry: a literature review

The study is based on a literature review of recent empirical research on crew resource management (CRM) training in the maritime industry, organised around what non-technical skills to learn and how. The review indicates that existing work is dominated by individualistic theories of learning with less focus on learning as a social process. Five main categories of skills that need to be trained are identified: assertiveness, decision-making, communication, situation awareness and team coordination. We argue that it is necessary to operationalise these broad concepts further, emphasising the work context and crew-specific needs. The review also shows that a combination of classroom lectures and simulator-based exercises is commonly used in maritime education and training in these skills. The learning effect seems to be suffering from training programmes that are exported ‘as is’ from aviation and not adjusted to the maritime domain or to operation-specific needs. This paper examines maritime crew resource management training from a social learning perspective, involving the view that learning is a context bound, social process that might take place in communities of practice (CoP). A CoP is a group (e.g. a crew) wherein members share an activity and learn from each other. It is argued that CRM training programmes will benefit from including a social learning perspective. Factors that enable the assessment of teams are discussed, and it is argued that the training should be tailored to existing crews, emphasising a learning environment as close to reality as possible.     

声呐罩结构强度的分析

安装于艇体的声呐罩综合性能要求高,结构复杂.本文介绍采用有限元法和模型试验法,分别得出其结构强度计算和测量结果,并对其结果进行对比分析.使我们能够全面、准确地了解声呐罩结构强度,确保其强度满足规范要求.     

Nonstationary response of floating structures to random waves

Even if ocean waves are treated as a stationary random process, dynamic responses of floating structures to random waves at the transient state are always nonstationary. When nonstationary response statistics is desired, a common technique is to apply Monte Carlo simulations; however, its implementation is costly in computational time. Analytically, this article develops an efficient method for computing nonstationary response statistics, including evolutionary power spectrum and time-varying mean-square values. Assuming a hydrodynamic software has been employed to get various frequency response functions, a prerequisite of the proposed method is to get the elevation-to-motion transfer function formulated in its pole-residue form. The proposed method is applicable to arbitrary wave spectrum and has been based on pole-residue operations implemented in the Laplace domain to obtain closed-form solutions for the response evolutionary power spectrum. Numerical examples choose a single-degree-of-freedom Spar model and a six-degree-of-freedom Floating Production Storage and Offloading model to a Pierson–Moskowitz wave spectrum, and the correctness of the computed mean-square values is verified by Monte Carlo simulations.     

基于神经网络的磁性目标磁矩反演方法

针对磁性目标定位中的磁矩反演问题,提出一种基于神经网络的磁矩反演技术。首先,基于最小二乘原理,建立了磁性目标磁矩反演模型;其次采用Hopfield网络进行了优化求解,并针对模型求解过程中鲁棒性差的弊端,对网络进化策略进行了自适应修正;最后设计了仿真实验对其有效性进行了检验,仿真结果表明利用修正后的网络求解磁矩反演问题结果令人满意,具有一定的实用性。     

自适应神经网络用于船舶动力定位系统

船舶动力定位（DP）采用一种控制系统驱动装在船上的侧推器和尾部推进器或者几个全回转的推进器，使船定位在海平面的要求位置上。船受到风、浪及流等海洋环境力的作用时会漂移离开原位置，传统的控制方法是采用PID（比例、积分、微分）反馈控制。顾和李（1994）提出了一种新的基于人工神经网络的控制方法，它具有许多优越性：①一个可随意调节的目标函数以适合不同的需求──定位精度高或节约定位能量后前馈控制并能自适应于不同的环境力变化包括非线性的波浪漂力；本文在目标函数中引入了与速度相关的项，从而提高控制质量。这一方法也可用于自动驾驶船舶沿设定的轨迹航行。计算机模拟结果表明本方法能达到很好的控制效果。     

波斯湾中受随机波作用的某新建离岸导管架平台时域动力分析研究（英文）

API RP2 A WSD is a design code in practice for design of jacket platforms in the Persian Gulf but is based on the Gulf of Mexico environmental condition. So for the sake of using this code for the Persian Gulf, it is better to perform a calibration based on this specific region. Analysis and design of jacket platforms based on API code are performed in a static manner and dynamic analysis is not recommended for such structures. Regarding the fact that the real behavior of the offshore jacket platforms is a dynamic behavior, so in this research, dynamic analysis for an offshore jacket platform in the Persian Gulf under extreme environmental condition is performed using random time domain method. Therefore, a new constructed offshore jacket platform in the Persian Gulf is selected and analyzed. Fifteen, 1-h storm, simulations for the water surface elevation is produced to capture the statistical properties of extreme sea condition. Time series of base shear and overturning moment are derived from both dynamic and static responses. By calculating the maximum dynamic amplification factor(DAF) from each simulation and fitting the collected data to Weibull distribution, the most probable maximum extreme(MPME) value for the DAF is achieved. Results show that a realistic value for DAF for this specific platform is 1.06, which is a notable value and is recommended to take into practice in design of fixed jacket platform in the Persian Gulf.     

基于iSIGHT的UUV优化设计平台

水下航行体(UUV)外形设计的优劣对UUV的最终性能有着举足轻重的影响。传统的设计方法是通过反复的选型-计算-修改来实现的,这种方法不但效率低下,而且由于选型范围有限,常导致得不到最优解。为解决这一问题,本文研究了UUV的参数化设计方法,并通过自编程序实现了在SolidWorks中的参数化建模。利用iSIGHT优化设计平台强大的过程集成能力和各种寻求最优参数的技术,实现了iSIGHT集成并驱动SolidWorks,Gridgen,CFX等软件并寻求最优参数的设计流程。并针对某UUV,以最小阻力为目标,利用NLPQL优化算法进行了优化设计。结果表明,本设计平台达到了实现UUV参数化设计并优化的目的,提高了设计效率。     

一种评估受冲击舰艇生命力的新方法

舰艇在冲击环境中的生命力是其技术性能的要素之一,正确分析舰艇生命力是舰艇生命力设计、管理、优化的前提.本文针对以往舰艇生命力评估中的一些不足之处提出了一种新的分析方法,该方法将舰艇生命力评估作为一个分类问题进行处理.它采用支持向量机技术,根据有限的学习样本建立了预测舰艇在冲击荷载作用下生命力的计算模型.对舰艇某子系统生命力的计算实例表明,该方法准确率较高,具有广泛的应用前景.     

CABOSFV算法中集合稀疏差异度阈值确定方法

在实际应用中,CABOSFV算法初始参数———集合稀疏差异度阈值b的确定是否合理,对聚类结果是否有效起决定作用。本文针对如何科学方便地确定集合稀疏差异度阈值b进行了深入研究,给出了集合稀疏差异度阈值确定方法,并通过该方法进行了实例计算。计算结果表明,由于该方法能够确定聚类结果中类的对象组成最小数量,聚类结果的粗糙与精细程度可以人为控制,对聚类结果的准确及高效提供了很好的保证,能够为CABOSFV算法进行聚类提供合理的阈值。