水下点火固体火箭发动机两相流流场数值分析

利用FLUENT软件,使用湍流模型和VOF(volume of fluid)模型对水下点火固体火箭发动机的气液两相流场进行数值分析,对点火初期喷管中燃气的流动过程和燃气泡的发展过程进行了仿真,数值模拟了固体火箭发动机尾流场燃气密度、压力和温度的分布规律。研究表明:点火初期,喷管内流场将有一个完整激波建立的过程,除此之后的喷管尾流区域,由于气体受到压力扰动的影响,激波结构被破坏,没有形成连续的膨胀—压缩波;射流过程中燃气泡头部一直保持较大直径,中部燃气通道存在随轴向周期性的膨胀-压缩现象;喷管尾流区,各流动参数出现不同程度的振荡现象:喷管出口燃气密度受外界水的压缩及传质传热的影响,出现峰值后逐渐稳定;喷管出口燃气总压由于受水环境的急剧压缩,在喷管出口附近形成一个高压区;喷管出口燃气温度经三次周期变化后,温度逐渐降至1750K以内。      

扑翼微型飞行器飞行姿态模型研究

扑翼微型飞行器飞行质量主要取决于能否对其飞行姿态进行有效控制, 而建立准确的飞行姿态模型尤为重要.通过对鸟和昆虫的飞行机理尤其是其飞行过程中翅膀的运动规律进行研究, 并考虑机械设计方面的因素, 对扑翼微型飞行器的飞行姿态建立了较为完整的动力学模型和数学模型.由分析可知机身所受外力为空气动力、重力和机翼作用于机身的驱动力, 而采用扑动与扭转两个自由度飞行的机翼所产生的驱动力是由瞬时平移力和扭转循环力合成的瞬时空气动力.数值仿真证实了动力学模型的正确性.      

先进战斗机的飞行控制计算机系统研究

 先进战斗机具有超声速巡航、隐身性、敏捷性和短距/垂直起降(STOVL)等技术特征。这要求先进战斗机不但在气动外形和推进系统与传统战斗机不同,而且还必须改善飞行控制系统的结构和功能。首先详细分析了F-22战斗机和联合攻击机（JSF）的飞行控制计算机系统组成和结构,并对它们的典型特征进行了分析。随后,根据中国目前的微电子工业技术和软件技术水平,探讨了研制适合中国的下一代战斗机飞控计算机系统的多项关键技术和发展思路。     

Model Development and Adaptive Imbalance Vibration Control of Magnetic Suspended System

对星载磁悬浮单框架控制力矩陀螺,建立其转子的平动与转动的动力学方程。所建模型反映了转子的动、静不平衡特性,以及转子运动与框架、星体运动的耦合关系。模型是主动磁悬浮控制与动框架效应分析的基础。对动、静不平衡量未知的转子,设计了自适应对中控制器。在分散PD、比例交叉反馈控制器与高低通滤波器的基础上,通过动、静不平衡量的辨识与补偿控制,使转子绕其惯量主轴旋转,衰减角动量交换执行机构高速转子因不平衡而对基座产生的干扰力,消除星上主要颤振源,达到降低卫星姿态抖动的目的。     

中小企业产业投资基金的逆向选择问题分析

主要研究在信息不对称条件下,从产业投资基金管理人的角度出发,利用模型证明中小企业的逆向选择行为会影响产业投资基金的运作,进而为基金管理人提出解决逆向选择问题的建议和策略。     

Launch cost reduction by the reuse of the core stage of Ariane 5

The high cost of launching payloads into Earth orbit is a main limiting factor on the development of space. In order to reduce the high cost of launch, reuse of (parts of) the launch vehicle is needed. This study analyses the possibilities of recovering and reusing the core stage of Ariane 5. Recovery of the core stage sets demands on re-entry trajectory, attitude, stability, thermal protection, structural strength, terminal deceleration, salt water protection, recovery and refurbishment. All these subject areas require solutions to their individual problems. Added subsystems to the stage are defined and their mass is determined. These masses are used to determine the financial feasibility of the recovery concept, by weighing the payload demise and operational cost against the gains of reduced production cost. It is concluded that the recovery is technologically feasible, using a detachable ablative heat shield on the nose of the stage and a stabilisation device (an inflatable drag cone), a parachute system and an engine enclosure device. Total mass of these systems is 1320 kg, with financial savings amounting to $8.5 million per flight.     

金融租赁:中小企业融资的现实途径

无论从股权资本缺口还是从债务资金缺口看,我国中小企业的发展都面临着融资困难的问题,而金融租赁业在解决这一问题上具有优势.应从创造好的运行环境,加快租赁业对内资企业开放的步伐及促进租赁业务方式多样化方面推进金融租赁业健康快速发展,以破解中小企业融资难的问题.     

基于视觉的无人作战飞机跑道障碍物检测方案

提出了基于视觉的无人作战飞机跑道障碍物检测方案.结合应用特征和流的障碍物检测方式的特点,使用多尺度特征点匹配光流估计方法代替普遍使用的微分光流计算方法,直接对图像序列计算稀疏光流场;利用相关假设,在存在一定导航误差的情况下,对跑道障碍物进行实时检测;同时对跑道障碍物视觉检测方案的误差和适用区间进行了分析;通过自主开发的"无人作战飞机自主着陆实时仿真验证平台"进行仿真,结果显示该方案能够有效检测跑道上存在的障碍物.      

HISTORICAL PROCEDURES AND G-DSG METHOD BASED MANUFACTURING PLANNING

Oriented to CAD/CAM seamless integration, this paper presents an idea for synthetically considering the qualitative history model, which represents the whole course of modeling, and the quantitative geometry model, which contains the extended Brep model, CSG and feature pedigree. History model building captures in background the dynamic interactive definition of engineering requirement and then explicitly conveys the original intention to successive application layers, which isc onductive to the decision support of manufacturing planning in not only automatic geometry re-constructing but also machining set-up. G-DSG theory as an earlier achievement is applied to generate the topology-independent generalized mid-model as an input to manufacturing planning, which istherefore simplified and its accuracy is simultaneously improved. Manufacturing planning lays emphasis on optimizing the mapping in both geometry and function from part itself to detail machining scheme. Comparatively, process planning pays more attention to the mapping to those items like tool, fixture, etc. Theoretically, such an idea is also beneficial to realizing the parametric NC machining trajectory generation and maintaining its dynamic consistency with the update of the design model.     

小型和微型无人机的气动特点和设计

讨论了当前包括固定翼、扑翼和微型旋翼的小型无人驾驶飞行器(SUAV)和微型无人驾驶飞行器(MAV)的进展和未来发展可能涉及的技术问题。讨论了低雷诺数空气动力特性,包括分离气泡和展弦比的影响。介绍了用于拍动翼的非定常空气动力特性和高升力机理。讨论了目前存在的2种设计方法——多学科/多目标优化设计和探索式/进化式的设计方法,以及在设计中柔性翼和主动智能控制的重要性。