随机风浪中舰船横摇倾覆概率分析

以路径积分法为基础,采用Gauss-Legendre公式探讨了随机风浪作用下舰船的运动及其倾覆概率计算。考虑阻尼力矩、复原力矩的非线性及风浪的随机性,建立了随机风浪中舰船运动的非线性微分方程,应用路径积分法给出白噪声随机扰动和定常风倾力矩作用时横摇角概率密度函数随时间的演变,按照现有的倾覆准则给出舰船倾覆概率的表达式。通过算例,验证了路径积分法的准确性,分析了各个参数对横摇角概率密度的影响,计算得出了不同风速、不同航速下的倾覆概率,以及倾覆概率随时间的变化。研究表明,此方法简便可行,并能在数量上预报舰船在随机风浪下的倾覆概率。     

旋转惯导捷联算法

针对旋转惯导计算原理,分析了转台测角、测速误差对系统精度的影响。为确定其影响程度,将转台测角、测速误差等效为相应量值的陀螺仪漂移。理论计算和仿真结果表明,转台测量误差特别是测速误差对惯导系统造成较大的影响。提出改进的旋转惯导捷联算法,该算法在姿态更新和导航计算后引入转台转角信息而不涉及转速信息,从算法原理上消除了测速误差对系统精度的影响。     

两种目标定位方法的误差分析

单站球坐标定位法和梯度法是目标定位中经常使用的2种方法.针对2种目标定位方法的定位精度问题,分别介绍了2种方法的原理及误差处理过程.通过理论分析和仿真计算对上述方法的目标定位精度进行比较,结果表明,梯度法比单站球坐标定位法具有更高的目标定位精度.     

非理想条件下三轴磁通门传感器误差修正方法

三轴磁通门传感器应用较为广泛,但非正交误差和非水平误差影响了三轴磁通门传感器的磁场测量精度.根据三轴磁通门传感器测量原理,分析了非理想条件下与理想条件下磁场转化矩阵关系.为消除三轴磁通门传感器中非正交误差和非水平误差的影响,建立了以磁场转化矩阵参数为自变量的优化模型.采用全局优化能力强、寻优效率高的微分进化算法求解该优化模型,求得磁场转化矩阵参数即可实现非正交误差和非水平误差的同时修正.三轴磁通门传感器误差修正实验表明,该方法在一定程度上可有效消除三轴磁通门传感器中非正交误差和非水平误差的影响,对提高三轴磁通门传感器磁场测量精度具有重要意义.     

舰炮装定坐标法射击原理及误差研究

舰炮对岸火力支援过程中,由于地形遮蔽等因素的影响,有时无法对岸上目标进行射击观测和射击诸元计算。为解决对岸上不可观测目标射击难题,提出了舰炮装定坐标法射击原理,建立了目标相对坐标计算模型,分析了射击误差及变化规律,显著提高了舰炮对岸火力打击能力和火力使用的灵活性。     

航海英语教材中若干误译探析

航海英语翻译能力是衡量国际船员英语水平高低的一项重要指标,但部分教材中的翻译还存在不足之处。本文以一本培训教材为例,详细分析了教材中出现的误译,希望引起航海英语教师和专家重视,共同提高航海英语翻译质量。     

Vertical random vibration analysis of vehicle–track coupled system using Green's function method

A vertical vehicle–track coupled dynamic model, consisting of a high-speed train on a continuously supported rail, is established in the frequency-domain. The solution is obtained efficiently by use of the Green's function method, which can determine the vibration response over a wide range of frequency without any limitations due to modal truncation. Moreover, real track irregularity spectra can be used conveniently as input. The effect of the flexibility of both track and car body on the entire vehicle–track coupled dynamic response is investigated. A multi-body model of a vehicle with either rigid or flexible car body is defined running on three kinds of track: a rigid rail, a track stiffness model and a Timoshenko beam model. The results show that neglecting the track flexibility leads to an overestimation of both the contact force and the whole vehicle vibration response. The car body flexibility affects the ride quality of the vehicle and the coupling through the track and can be significant in certain frequency ranges. Finally, the effect of railpad and ballast stiffness on the vehicle–track coupled vibration is analysed, indicating that the stiffness of the railpad has an influence on the system in a higher frequency range than the ballast.     

Speed variation during peak and off-peak hours on urban arterials in Shanghai

Increased speed variation on urban arterials is associated with reductions in both operational performance and safety. Traffic flow, mean speed, traffic control parameters and geometric design features are known to affect speed variation. An exploratory study of the relationships among these variables could provide a foundation for improving the operational and safety performance of urban arterials, however, such a study has been hampered by problems in measuring speeds. The measurement of speed has traditionally been accomplished using spot speed collection methods such as radar, laser and loop detectors. These methods can cover only limited locations, and consequently are not able to capture speed distributions along an entire network, or even throughout any single road segment. In Shanghai, it is possible to acquire the speed distribution of any roadway segment, over any period of interest, by capturing data from Shanghai’s 50,000+ taxis equipped with Global Positional Systems (GPS). These data, hereafter called Floating Car Data, were used to calculate mean speed and speed variation on 234 road segments from eight urban arterials in downtown Shanghai. Hierarchical models with random variables were developed to account for spatial correlations among segments within each arterial and heterogeneities among arterials. Considering that traffic demand changes throughout the day, AM peak, Noon off-peak, and PM peak hours were studied separately. Results showed that increases in number of lanes and number of access points, the presence of bus stops and increases in mean speed were all associated with increased speed variation, and that increases in traffic volume and traffic signal green times were associated with reduced speed variation. These findings can be used by engineers to minimize speed differences during the road network planning stage and continuing through the traffic management phase.     

Incorporating Driver Behaviors in Network Design Problems: Challenges and Opportunities

The goal of a network design problem (NDP) is to make optimal decisions to achieve a certain objective such as minimizing total travel time or maximizing tolls collected in the network. A critical component to NDP is how travelers make their route choices. Researchers in transportation have adopted human decision theories to describe more accurate route choice behaviors. In this paper, we review the NDP with various route choice models: the random utility model (RUM), random regret-minimization (RRM) model, bounded rationality (BR), cumulative prospect theory (CPT), the fuzzy logic model (FLM) and dynamic learning models. Moreover, we identify challenges in applying behavioral route choice models to NDP and opportunities for future research.     

Is equilibrium in transport pure Nash,mixed or Stochastic?

The classical theory of transport equilibrium is based on the Wardrop’s first principle that describes a Nash User Equilibrium (UE), where in no driver can unilaterally change routes to improve his/her travel times. A growing number of economic laboratory experiments aiming at testing Nash-Wardrop equilibrium have shown that the Pure Strategy Nash Equilibrium (PSNE) is not able to explain the observed strategic choices well. In addition even though Mixed Strategy Nash Equilibrium (MSNE) has been found to fit better the observed aggregate choices, it does not explain the variance in choices well. This study analyses choices made by users in three different experiments involving strategic interactions in endogenous congestion to evaluate equilibrium prediction. We compare the predictions of the PSNE, MSNE and Stochastic User Equilibrium (SUE). In SUE, the observed variations in choices are assumed to be due to perception errors. The study proposes a method to iteratively estimate SUE models on choice data with strategic interactions. Among the three sets of experimental data the SUE approach was found to accurately predict the average choices, as well as the variances in choices. The fact that the SUE model was found to accurately predict variances in choices, suggests its applicability for transport equilibrium models that attempt to evaluate reliability in transportation systems. This finding is fundamental in the effort to determining a behaviourally consistent paradigm to model equilibrium in transport networks. The study also finds that Fechner error which is the inverse of the scale parameter in the SUE model is affected by the group sizes and the complexity of the cost function. In fact, the larger group sizes and complexity of cost functions increased the variability in choices. Finally, from an experimental design standpoint we show that it is not possible to estimate a noise parameter associate to Fechner error in the case when the choices are equally probable.