无减摆器旋翼桨叶气弹稳定性分析

无减摆器旋翼具有桨毂结构简单、桨毂气动阻力小、桨毂维护简便等优点,但取消了桨毂减摆器后必须确保桨叶在摆振方向有足够的阻尼以保证桨叶的摆振稳定性。基于气弹耦合的方法是实现无减摆器旋翼桨叶摆振稳定性的一个有效方法。建立了无减摆器无铰式旋翼桨叶带有预锥角、下垂角、后掠角和预扭角等结构参数的非线性气弹动力学模型,利用伽辽金方法把桨叶偏微分运动方程简化为非线性常微分平衡方程和关于平衡位置的小扰动运动方程,分析了桨叶的气弹稳定性并进行了参数影响分析。数值结果表明,合理的桨叶结构参数和气弹耦合可确保无减摆器旋翼桨叶在摆振方向的气弹稳定性。     

Nonlinear attitude tracking control for spacecraft formation with multiple delays

This paper addresses the attitude tracking control for spacecraft formation with delay free and communication delays. With help of the idea of sliding control, an adaptive attitude synchronization control architecture is established. Furthermore, by introducing a nonsmooth feedback function, a new class of nonlinear controllers for the attitude tracking of spacecraft is developed. Both parameter uncertainties and unknown external disturbances are dealt with via the kind of controllers. Finally, some simulation results are given to demonstrate the effectiveness and advantages of the proposed results.     

Experimental investigation of transient thermal behavior of an airship under different solar radiation and airflow conditions

Knowledge of the thermal behavior of airships is crucial to the development of airship technology. An experiment apparatus is constructed to investigate the thermal response characteristics of airships, and the transient temperature distributions of both hull and inner gas are obtained under the irradiation of a solar simulator and various airflow conditions. In the course of the research, the transient temperature change of the experimental airship is measured for four airflow speeds of 0 m/s (natural convection), 3.26 m/s, 5.5 m/s and 7.0 m/s, and two incident solar radiation values of 842.4 W/m² and 972.0 W/m². The results show that solar irradiation has significant influence on the airship hull and inner gas temperatures even if the airship stays in a ground airflow environment where the heat transfer is dominated by radiation and convection. The airflow around the airship is conducive to reduce the hull temperature and temperature nonuniformity. Transient thermal response of airships rapidly varies with time under solar radiation conditions and the hull temperature remains approximately constant in ∼5–10 min. Finally, a transient thermal model of airship is developed and the model is validated through comparison with the experimental data.     

大学生英语议论文体情态动词的使用特征探索——以“can”为例

分析了32篇英语专业学生议论文作文中情态动词"can"的使用情况,描述并解释了情态动词"can"使用量差异,并从新的角度归类了语料中情态动词"can"的评价功能,探索了学习者使用这些功能特征的原因,并对英语专业写作教学提出了建议。     

Response and adaptation of bone cells to simulated microgravity

Bone loss induced by microgravity during space flight is one of the most deleterious factors on astronaut’s health and is mainly attributed to an unbalance in the process of bone remodeling. Studies from the space microgravity have demonstrated that the disruption of bone remodeling is associated with the changes of four main functional bone cells, including osteoblast, osteoclast, osteocyte, and mesenchymal stem cells. For the limited availability, expensive costs and confined experiment conditions for conducting space microgravity studies, the mechanism of bone cells response and adaptation to microgravity is still unclear. Therefore, some ground-based simulated microgravity methods have been developed to investigate the bioeffects of microgravity and the mechanisms. Here, based on our studies and others, we review how bone cells (osteoblasts, osteoclasts, osteocytes and mesenchymal stem cells) respond and adapt to simulated microgravity.     

基于SCA的网电对抗平台架构设计及其应用

为了满足战场环境下网电对抗平台对不同信息层次的探测、攻击与防御能力以及通用化、模块化、协同的需求,设计了基于SCA的网电对抗平台的功能体系架构,并以组网雷达对抗为例,给出了基于此体系架构的多平台协同组网雷达对抗波形开发方案,仿真测试表明此网电对抗平台的功能体系架构具有可行性和通用性。     

本生灯预混火焰淬熄距离实验分析

淬熄距离是表征壁面淬熄效应的一项重要参数.通过直接拍摄火焰位置图片,得到甲烷本生灯预混火焰淬熄距离随来流预混气速度与当量比的变化关系.实验结果表明,本生灯火焰淬熄距离随来流速度的变化规律在不同当量比范围内是不同的.而在同一速度下,随来流当量比增大,淬熄距离贫油时减小,富油时先增大再减小,最后在某一当量比时淬熄距离保持一个定值.这一变化关系是由来流预混气对壁面的冷却作用和火焰面对壁面的加热作用共同影响所造成的,尤其是富油预混火焰的双层结构会极大地影响淬熄效应.      

线性系统的最小解耦设计—一般情形

利用线性系统“根”的概念，研究了输出分块情形下的最小阶动态解耦设计问题，一方面利用根刻画了解耦补偿器的最小阶数，并且给出了设计最小阶补偿器的算法，另一方面获得了新的解耦判据。     

空间发动机真空起动点火时差及其实现方法

液体火箭发动机在真空中起动时，燃烧室内易产生三相共存的状态，其中凝聚相能引起不正常的起动压力峰而损坏发动机。本文研究了甲基肼和四氧化二氮组合为推进剂时真空起动的点火时差，以便尽量减少着火前上述状态的存在程度。给出了利用控制阀通电时差、充填时差和控制阀响应时差这三种起动方式来实现该点火时差的方法。前两种方法已在某远地点发动机上使用并获得成功。     

直升机模型桨叶颤振试验研究

提出了直升机模型桨叶颤振试验技术及试验方法。通过激桨叶的扭转频率、测桨叶的挥舞响应,试验得到了桨叶颤振裕度与旋翼转速、桨叶弦向有效重心位置及桨叶扭转刚度之间的关系,即桨叶颤振裕度随旋翼转速的提高而降低;在相同转速下,桨叶扭转刚度越低或桨叶弦向有效重心位置越后。