对蹲距式起跑技术的再研究

短跑的起跑对各国短跑运动员都至关重要。科学、合理的起跑技术是提高运动员短跑成绩的关键,本文即针对蹲距式起跑技术的细节改进做一些分析研究。     

On the high-frequency response of unsteady lift and circulation: A dynamical systems perspective

In this paper, we consider the unsteady aerodynamics of a two-dimensional airfoil as a dynamical system whose input is the angle of attack (or airfoil motion) and output is the lift force. Based on this view, we discuss the evolution of lift and circulation from a purely dynamical perspective through step response, frequency response, transfer function, etc. In particular, we point to the relation between the high-frequency gain of the transfer function and the physics of the development of lift and circulation. Based on this view, we show that the circulatory lift dynamics is different from the circulation dynamics. That is, we show that the circulatory lift is not lift due to circulation. In fact, we show that the circulatory–non-circulatory classification is arbitrary. By comparing the steady and unsteady thin airfoil theory, we show that the circulatory lift possesses some acceleration (added-mass) effects. Finally, we perform simulations of Navier–Stokes equations to show that a non-circulatory maneuver in the absence of a free stream induces viscous circulation over the airfoil.     

面向创业型经济社会的创业型大学建设——以浙江万里学院为例

浙江万里学院提出的"建设创业型大学"发展目标,顺应了全球经济向创业型转变的历史趋势,体现了应用型本科教育在服务中求生存的发展规律,是对地方应用本科院校可持续发展的准确定位。实现这一发展目标,学院需要在创业教育研究引领下,以改革与创新为动力,塑造教育家型领导团队,打造创业型师资队伍,全面创新创业型大学办学体制和创业型培养体制。     

具有辅助性服务的多级适应性M^X/G/1休假排队

利用嵌入Markov链的方法研究了具有辅助性服务的多级适应性M X/G/1休假排队,并首先给出了系统稳态队长和等待时间的母函数及其它们的随机分解结果,然后分析系统的忙期、全假期和忙循环,最后讨论特例,并推导出一些结论.     

喷油定时和涡流比对低温燃烧影响的模拟研究

基于计算流体动力学(CFD)软件和耦合自行编写的程序,对一台柴油机进行低温燃烧模拟研究,对比分析不同废气再循环(EGR)率、喷油定时和涡流比对燃烧和排放的影响.结果表明,随着EGR率增大,燃烧放热过程滞后,缸内压力、温度和放热率峰值和累计放热量降低,壁面油膜生成增加,氮氧化物(NO_x)排放大幅降低的同时,碳烟(soot)、未燃碳氢化物(UHC)和CO排放增加;固定EGR率为40%的同时将喷油定时曲轴转角从353°提前至345°,可使燃烧放热过程适当提前,并有利于提高热效率和改善燃油经济性;保持EGR率为40%,喷油定时曲轴转角为345°时,随着涡流比的增大,soot和UHC排放减少,而CO排放出现先减少后增大的趋势,涡流比为3.0时,综合效果较好.     

基于催化燃烧辅助供热的燃料电池低温启动过程研究

提出了一种解决燃料电池系统低温启动的策略,将氢气和空气预混合气体在燃料电池外部进行催化燃烧,然后将燃烧后的尾气通入燃料电池阴极流场和水流场以加热燃料电池系统.基于此低温启动策略,搭建了低温启动试验平台,研究了反应物混合气流量、氢气体积分数等参数对燃料电池低温启动过程的影响.试验结果表明:增大反应物混合气流量或增加氢气体积分数均能缩短低温启动时间;当流量为3L.min-1,氢气体积分数为5%时,电池内部温度在540s内上升到冰点以上温度,可以初步满足低温启动的要求.     

变革环境中的大学生就业问题研究

通过对大学生就业难的现状描述,指出就业观念转变滞后、职业认知能力较差、职业准备不够,职业能力较弱、就业服务不完善是导致大学生就业困难的重要原因,认为强化就业指导、转变就业观念、完善就业导向的激励措施、改革高等教育体制和模式、鼓励大学生自主创业是化解大学生就业困境的重要举措。     

高校体育社团促进阳光体育运动开展的研究

运用文献资料法、逻辑分析法对高校体育社团和阳光体育运动产生的时代背景进行分析,同时对其概念进行界定,并对高校体育社团开展活动时间的业余性、形式的灵活性、参与的志愿性、活动的文化性和健身娱乐性、内容的丰富性等特点进行分析,论述体育社团促进阳光体育运动在高校开展的作用.     

Euler flow in a supersonic mixed‐compression inlet

Numerical simulation of a two‐dimensional mixed compression supersonic inlet is carried out by solving unsteady compressible Euler equations via a stabilized finite element method. The geometry of the inlet is similar to the one used by Anderson and Wong for experimental investigation for Mach 3 flow. The computations are capable of simulating the start‐up problems associated with the inlet. The critical back pressure for the successful operation of the inlet is computed. The effect of inlet back pressure on the total pressure recovery and the flow distortion level is analysed. Contrary to the popular belief, it is found that in addition to the throat to inlet capture area ratio, the ramp geometry close to the throat plays an important role in the start‐up dynamics. It is demonstrated via simulations that, everything else being same, the geometries of ramp upstream of the throat that are associated with a curvature higher than a certain threshold, result in unstarting the intake. Copyright © 2005 John Wiley & Sons, Ltd.     

Safety Assessment and Optimization of Semi-batch Reactions by Calorimetry

Semi-batch reactors are widely spread in the fine chemicals and specialties industry. The reason is that, compared to the pure batch operation, the feed of at least one of the reactants provides an additional way of controlling the reaction course, which represents a safety factor and increases the constancy of the product quality. Process temperature and feed rate can be optimized to satisfy safety constraints, i.e. cooling capacity and allowable accumulation. An economically better way of operating a semi-batch reactor is to adapt the feed rate to the allowed accumulation of reactants. An experimental method based on calorimetry will be presented and illustrated by an example. This revised version was published online in July 2006 with corrections to the Cover Date.