考虑螺旋桨体积力的水下机器人水动力特性仿真

为在初步设计时预测ROV的水动力性能,使用CFD技术进行分析,以ROV模型为例,最大程度地保留ROV内部的构件,使模型更加接近真实状况。分别计算ROV在不同工况下的阻力、不同漂角下的横向力和转艏力矩以及添加体积力模型之后的螺旋桨流场状况,很好地模拟出ROV周围的流场,并与已有的试验数据进行对比。结果验证了CFD水动力仿真的可行性和准确性,并还可预测ROV在螺旋桨作用下的进速等,对ROV设计具有实际的参考价值和指导意义。     

一种水下非均质拖曳线列阵动力学仿真方法及试验验证

基于Ablow和Schechter经典差分方法,分析水下非均质拖曳线列阵的受力特性,建立其空间运动控制方程.采用中心差分法和牛顿迭代法对运动控制方程进行离散及时间和空间上的迭代求解,获得水下非均质拖曳线列阵的动力学特性.在此基础上,结合非均质线列阵实尺度模型,设计并开展湖中的实航拖曳试验,分析比较了试验数据与仿真结果.研究表明,本文提出的数学仿真方法有效可靠,可为水下非均质拖曳线列阵动力学特性分析提供一种有效的技术手段.     

一种新的碰撞耗散能快速估算方法及其在船—平台碰撞事故中的应用研究

海洋平台在作业过程中存在遭受船舶碰撞的潜在危险,一旦事故发生将可能导致结构严重损伤从而影响平台的作业安全,因此在平台结构设计阶段需要考虑其抗撞性能.文章以海洋供应船撞击半潜式钻井平台为研究对象,基于碰撞外部动力学理论和DNV规范计算方法,计及平台艏摇运动响应的影响,提出了一种新的耗散能估算方法-DNV`R解析法.以非线性有限元船-平台碰撞数值仿真结果为参考,将该解析法与规范法、Zhang解析法及Liu解析法计算结果进行对比,研究得出:文中所提出的DNV`R解析法弥补了规范法较为保守且仅适用于对心碰撞场景的不足,计算过程简单、便捷,且计算精度与Zhang解析法和Liu解析法基本接近,能够满足船-平台碰撞耗散能快速估算的精度要求.     

Dynamic stride length adaptation according to utility and personal space

Pedestrians adjust both speed and stride length when they navigate difficult situations such as tight corners or dense crowds. They try to avoid collisions and to preserve their personal space. State-of-the-art pedestrian motion models automatically reduce speed in dense crowds simply because there is no space where the pedestrians could go. The stride length and its correct adaptation, however, are rarely considered. This leads to artefacts that impact macroscopic observation parameters such as densities in front of bottlenecks and, through this, flow. Hence modelling stride adaptation is important to increase the predictive power of pedestrian models. To achieve this we reformulate the problem as an optimisation problem on a disk around the pedestrian. Each pedestrian seeks the position that is most attractive in a sense of balanced goals between the search for targets, the need for individual space and the need to keep a distance from obstacles. The need for space is modelled according to findings from psychology defining zones around a person that, when invaded, cause unease. The result is a fully automatic adjustment that allows calibration through meaningful social parameters and that gives visually natural results with an excellent fit to measured experimental data.     

Learning marginal-cost pricing via a trial-and-error procedure with day-to-day flow dynamics

This paper investigates the convergence of the trial-and-error procedure to achieve the system optimum by incorporating the day-to-day evolution of traffic flows. The path flows are assumed to follow an ‘excess travel cost dynamics’ and evolve from disequilibrium states to the equilibrium day by day. This implies that the observed link flow pattern during the trial-and-error procedure is in disequilibrium. By making certain assumptions on the flow evolution dynamics, we prove that the trial-and-error procedure is capable of learning the system optimum link tolls without requiring explicit knowledge of the demand functions and flow evolution mechanism. A methodology is developed for updating the toll charges and choosing the inter-trial periods to ensure convergence of the iterative approach towards the system optimum. Numerical examples are given in support of the theoretical findings.     

冲压机械振动对高铁桥梁及行车动力影响分析

高速铁路桥梁的平顺性和稳定性对运营列车的平稳性和安全性有很大影响。为研究冲压机械产生的外部振动激励对高铁桥梁的影响,首先通过对此机械引起的地面振动进行实测,并结合有限元分析软件,确定最大冲击荷载作用下产生的地面振动及传播至桥墩处的振动;然后通过建立列车-轨道-桥梁耦合动力学模型,将桥墩处的地面振动作为激励输入,分析列车以不同速度通过时车辆、桥梁动力学响应。结果表明:地面冲击振动有限元模型计算结果与实测结果基本相符,验证了模型的可靠性;地面振动对桥梁响应会产生一定的影响,距振源50 m处地面振动对桥梁所产生的影响较距振源80 m处(桥墩处)的大,但对运行车辆的影响很小;随着车速由250 km/h至350 km/h,车辆及桥梁各结构的动态响应均有所增大,但都未超出安全限值。因此,冲压机械冲击作用导致的地面振动对列车-轨道-桥梁系统动态服役性能影响非常有限。     

多类型信息下的网络交通流演化模型

交通信息发布机构提供描述信息和规范信息给不同的出行者，描述信息接收者依据信息和经验更新路径行程时间认知，根据认知选择路径；规范信息接收者仅根据经验更新认知.规范信息遵从者选择推荐路径，非遵从者依据认知选择路径.两类信息遵从率都取决于信息准确度.依据非线性动力学理论分析了模型性质，研究表明，模型不动点存在但是不一定唯一，不动点状态与信息混合使用情况有关.数值试验结果表明，模型不动点与随机用户均衡点不同，以恰当比例混合使用两类信息可提高交通流稳定性.     

导管螺旋桨水动力学性能的影响因素

为了获取导管螺旋桨水动力性能的主要影响因素，指导导管螺旋桨的优化设计，采用计算流体力学CFD对Ka4-7010+19A导管螺旋桨进行水动力性能研究，分析不同导管长度、导管攻角、螺旋桨纵倾角及多导管组对其水动力特性的影响。结果表明：减少导管长度将使推力系数及扭矩系数同时增大，而敞水效率下降；适当增加导管长度可以略微提高其敞水性能；减小导管攻角在一定进速范围内使推力系数和扭矩系数同时大幅度增加，增加导管攻角将导致推力系数和扭矩系数同时下降；当螺旋桨纵倾角保持在10°以内时，不会对敞水性能产生太大影响。对于多导管螺旋桨而言，前置、后置及不同附属导管直径大小都对敞水性能有很大影响，其中后置大导管组螺旋桨能明显降低螺旋桨扭矩系数，并且能在低进速范围内提升敞水效率。研究成果可支撑导管螺旋桨的优化设计。     

燃机动力学建模中复杂结构处理方法研究

提出了三种以动力学相似为基础的转子动力学建模关键技术,并以某型燃气轮机建模为例,对该关键技术进行了验证。利用三种方法,对该燃气轮机的动力学特性进行研究,并与整机试验结果进行了对比。结果表明,动力学分析的准确程度主要由模型决定,本文所提出的三种建模关键技术能够反映结构的真实特性,可用于具有类似结构的双转子系统。     

Interactive travel choices and traffic forecast in a doubly dynamical system with user inertia and information provision

This study models the joint evolution (over calendar time) of travelers’ departure time and mode choices, and the resulting traffic dynamics in a bi-modal transportation system. Specifically, we consider that, when adjusting their departure time and mode choices, travelers can learn from their past travel experiences as well as the traffic forecasts offered by the smart transport information provider/agency. At the same time, the transport agency can learn from historical data in updating traffic forecast from day to day. In other words, this study explicitly models and analyzes the dynamic interactions between transport users and traffic information provider. Besides, the impact of user inertia is taken into account in modeling the traffic dynamics. When exploring the convergence of the proposed model to the dynamic bi-modal commuting equilibrium, we find that appropriate traffic forecast can help the system converge to the user equilibrium. It is also found that user inertia might slow down the convergence speed of the day-to-day evolution model. Extensive sensitivity analysis is conducted to account for the impacts of inaccurate parameters adopted by the transport agency.