基于遗传算法的最小阻力船型优化设计

遗传算法是一种全局最优化算法,它能够克服传统优化方法的缺点和不足,从而获得全局最优解。因此,为了获得阻力性能更好的优良船型,将遗传算法进行适当改进并用于船型优化中,进行最小阻力船型优化设计,以非线性兴波阻力理论(Rankine源法)为基础,利用遗传算法并结合CAD技术进行船型优化设计。在优化过程中,把总阻力作为目标函数,设计变量取船型修改函数的参数,确保排水量为基本约束条件下,对船体前半体型线进行优化研究。选取某高速巡逻艇作为初始船型进行优化计算,获得的最优船型总阻力降低了13.1%,兴波阻力降低了21.7%,表明遗传算法用于船体线型优化设计是行之有效的。     

锥管中流动工作介质的声传递特性研究

锥管是船舶管路系统中的典型管件,对其声传递特性的研究是管路系统声学设计和分析的组成内容之一。文章考虑锥管截面积沿长度变化对平均流速的影响,推导了锥管的声传递矩阵;以无反射终端为条件,获得管路元件传递损失的理论公式。通过算例说明了流动马赫数和锥角大小对锥管声传递特性的影响。     

短波串行调制解调器设计

介绍一种用于无线衰落多径信道数据通信的高速串行MODEM系统。首先对信号格式进行了简要介绍,然后对其中的关键技术进行了详细阐述,包括调制解调技术、同步捕获技术、频偏估计及校正技术、自适应均衡技术,给出了各部分的实现方案。     

基于小生境遗传算法的单体船船型参数优化

针对船型参数优化中变量众多的特点,提出了一种基于小生境遗传算法和Holtrop总阻力计算公式的单体船船型参数优化方法.该方法中以总阻力作为目标函数,以主要船型参数为优化变量,在保持排水量不变的情况下优化主要船型参数,得出修长系数、水线面系数和宽吃水比均能收敛到相应的临界值,因此优化时可优先确定这些参数值.采用该方法对DTMB5415船的船型参数进行了优化,结果显示优化后的船型总阻力性能要明显优于原船型.该方法对于单体船船型参数优化具有较强的实用性.     

高速三体船阻力性能研究

对中体和侧体均为Wigley船型的高速三体船模在Fr=0.1～0.8时3个横向偏距、5个纵向偏距共15个状态进行了阻力试验,将高速三体船线性兴波阻力理论计算结果与模型试验结果进行了比较,并据模型试验结果分析了横向偏距和纵向偏距对兴波阻力系数的影响,其中各状态的形状因子(1 K)按普鲁哈斯卡法确定,对形状因子与偏距的关系也进行了探讨.     

Why do paratransit operators resist participation in bus rapid transit? Case evidence from Bogota,Mexico City,Johannesburg and Lagos

ABSTRACT

Public transport in cities of the Global South is mainly provided by paratransit operators who self-regulate their services in the absence of adequate formal transport supply and due to weak or no formal regulatory framework and enforcement. Paratransit operators compete with each other for passengers as every passenger translates into profit. Governments in the Global South have sought to reform public transport services through Bus Rapid Transit (BRT) to regulate and ensure efficiency, address the problems of drivers competition and negative externalities associated with paratransit operations. Paratransit operators have been considered as one of the barriers to public transport reforms such as BRT without much consideration for their style of operations. This neglect has contributed to their resistance and low interest in participating in BRT and has even led to opposition. Consequently, non-consideration of incumbent operators in the implementation of transit reforms has been one important reason for delay or failure in their introduction. In this study, we identify reasons why paratransit operators resist and show low interest in BRT even in situations where public institutions have opted not to replace them but rather invite them to participate in the reforms. The basis is a case study analysis of four cities with different characteristics and different BRT implementation strategies where paratransit operators showed resistance and low interest to participate. We identify (1) loss of autonomy, flexibility and established practices/routines, (2) financial and economic risk avoidance and (3) lack of trust in governments who initiate reforms as a basis for their resistance and low interest. These findings are theoretically substantiated by organisational management and social psychology concepts that explain resistance to change. Understanding and recognising these reasons may help planners in designing more appropriate strategies for paratransit reforms.     

三塔斜拉桥受横桥向风载时的计算方法

应用平面杆系有限元计算程序代替了空间有限元计算程序 ,阐述了对三塔斜拉桥受横向风载时的计算步骤和计算方法 ,具有概念清楚 ,计算简单和易于掌握的优点。     

三体船兴波问题的数值计算

以基于NURBS(non-uniformra tionalB-splines,非均匀有理B样条)的广义高阶面元法讨论了三体船兴波波形与兴波阻力的数值计算问题。对两种不同船型的三体船进行了计算,计算结果与试验结果的比较表明了该方法的有效性。文中还讨论了高速方尾三体船侧体的横向偏距和纵向偏距对兴波阻力的影响。     

一种新型水上减阻仿生技术研究

传统排水型两栖车辆航速在15km/h时出现"阻力墙"现象,致使水阻力急剧增大,限制航速进一步提升。文章从蛇怪蜥蜴高速踏水方式构思,基于固-液体高速作用动力学原理,提出了一种基于改变两栖车体航态的仿生减阻技术。其依靠仿生叶轮与水的高速作用产生向上托举力和向前推进力,将两栖车体托举出水面,进入高速滑行状态,从而避开"阻力墙"现象。仿真分析了刚性叶片夹角θ、入水深度h、转速ω等物理参数对水动力性能的影响,着重讨论了转速ω的影响,并给出了临界范围。结合先期原理试验,初步验证了此仿生技术能够实现两栖车体辆从排水状态进入高速滑行状态,从而避开"阻力墙"现象,达到减少水阻力的目的。     

船舶前缘引流减阻及流场特性数值模拟

为了减少船舶的粘性阻力,针对一条中低速船舶在其前缘开孔引流探索减阻效果。不计自由液面的影响,采用有限体积法和SIMPLEC算法,湍流模型为SSTk-ω两方程模型,压力采用标准格式,动量方程、湍动能方程和湍流耗散比率方程均采用二阶迎风格式,耦合求解Navier-Stokes方程和连续性方程,分析前缘引流对船体周围流场的影响及减阻效果。计算结果与原型船模的对比性分析显示:船艏压力系数明显降低,尾部压力系数有变化,船体壁面切应力略有降低,引流后总减阻率达到2%以上。