重力辅助环路热管稳态运行特性的实验研究

 随着环路热管应用领域不断扩展,其可能在各种姿态下运行,包括重力辅助姿态。对环路热管在重力辅助姿态下的稳态运行规律和特性进行了实验研究,并同平放及反重力条件下的运行特性进行了比较。通过实验可得出,在重力辅助姿态下,环路热管存在两种驱动模式,即重力单独驱动模式和毛细力与重力共同驱动模式。当热载荷较小时,环路热管工作在重力单独驱动模式,蒸汽管线内为气液两相工质,回流液体对储液器的冷却作用加强,运行温度明显低于平放及反重力条件下之值,热导显著增大;当热载荷大于某一临界值,环路热管工作在毛细力与重力共同驱动模式,蒸汽管线内为单相蒸汽,运行温度同平放及反重力条件下之值基本一致。最后,从环路热管系统压力平衡和储液器能量平衡的角度对上述实验现象进行了解释和分析。     

一种无人直升机的双发动机控制策略

针对某无人直升机双发动机控制问题,提出两台发动机采用并联控制方式使其输出功率保持一致,利用两个发动机转速较高者替代旋翼转速作为转速反馈信号,提高旋翼转速的平稳性,并给出了影响旋翼转速平稳性的两个主要扰动因素总距和前飞速度的前馈补偿控制量的试验测量和计算方法;进一步利用两个发动机缸头温度差对其控制量进行差动补偿,从而使得两个发动机的输出功率趋于一致,提高传动系统的平稳性,抑制机身扭振.最后,通过地面系留试验和试飞试验验证了该控制策略的可行性和有效性.      

FL-26风洞条带悬挂支撑內式天平研制

FL-26风洞条带悬挂支撑內式六分量天平采用管状结构的试验方案,有效地解决了天平的静校问题;天平内腔采用扁圆结构,有效地解决了天平轴向力元件处的强度和刚度问题,较好地降低了前后测量梁上下应变不对称的程度,同时增大了侧向力及偏航力矩的输出;用关于天平轴向对称布置的双铰链梁测量滚转力矩,提高了滚转力矩分量的测量精准度。本文主要介绍条带悬挂支撑內式六分量天平研制难点、解决方案及天平动校结果。     

盒式六分量应变天平热态试验气动结构特性

为了探索盒式六分量应变天平热态试验时三维力传感器输出信号异常的现象,从四分量机械单台式天平与盒式六分量应变天平的气动布局、主体结构及热态试验方面展开了对比分析,受结构及安装制约,盒式六分量应变天平无法消除或补偿高温热流在稳定段上产生的热应力.为保留喷管模型试验器最具特色的高温试验功能,利用对称布置方案,调换燃油加温器至稳定段出口.热态试验证明:在增强天平的平衡性、减少天平机械连接、简化燃油加温器安装和调试的情况下,天平的推力测量值从异常的负值恢复正常,解决天平输出信号异常问题,满足天平热态试验性能要求.      

基于单目视觉的机器人避障方法研究

避障问题一直是机器人领域研究的热点和重点。设计一种基于单目视觉的避障系统,能够同时检测机器人正前方和两侧的障碍物,且对低纹理障碍物同样具有效果。该系统采用特征尺度检测器完成机器人视野正前方障碍物的检测,对于视野两侧的障碍物运用光流平衡策略进行规避,而对于低纹理的障碍物则利用图像熵的方法进行检测。整个系统在地面移动机器人上进行了测试,实验结果表明,该方法能在复杂的环境下可靠地完成机器人的避障任务。     

产生伪随机序列的一种方法

由于混沌是一种动态的、类随机的非线性系统,且具有对初始条件敏感、连续的功率谱、各态遍历等特性,因此可产生伪随机序列.本文就是将混沌连续的功率谱进行反褶、平移、相加、缩放等变换构造出了一种新的伪随机序列,通过理论分析和仿真试验,初步验证了该序列的各项特性是满足了Golomb的3个公设.此序列产生方法简单,基本可以广泛应用于保密通信等领域.     

Nonlinear modal electromechanical coupling factor for piezoelectric structures containing nonlinearities

Within the linear framework, the Modal Electromechanical Coupling Factor (MEMCF) is an important indicator to quantify the dynamic conversion of mechanical energy and electrical energy of piezoelectric structures. It is also an important tool to guide the piezoelectric damping design of linear structures. Advanced aircraft often fly in maneuvers, and the variable working conditions induce drastic changes in the load level on structures. Geometric and contact nonlinearities of thin-walled structures and joint structures are often activated. To achieve a good vibration reduction effect covering all working conditions, one cannot directly use linear electromechanical coupling theory to instruct the piezoelectric damping design for nonlinear structures. Therefore, this paper defines the Nonlinear Modal Electromechanical Coupling Factor (NMEMCF) and proposes the corresponding numerical method for the first time to quantitatively evaluate the electromechanical coupling capability of nonlinear piezoelectric structures. Three candidate definitions of the NMEMCF are given, including two frequency definitions and one energy definition. The energy definition is the most promising one. It is not only applicable to both conservative and dissipative nonlinear structures but also compatible with the linear MEMCF. In addition, based on the energy formula, the NMEMCF can be obtained by only performing one nonlinear modal analysis in the open-circuit state. The analytical findings and the numerical tool are validated against two piezoelectric structures with different types of nonlinearities. A strong correlation among the NMEMCF, geometric parameters, and energy dissipation is observed. The results confirm that the proposed NMEMCF captures the physics of the electromechanical coupling phenomenon associated with nonlinear piezoelectric structures and can be used as an essential design indicator of piezoelectric damping, especially for variable working conditions.     

导引头伺服机构消隙齿轮系统动力学特性分析

消隙齿轮广泛应用于导引头伺服机构惯性稳定平台传动系统中，用于消除回程误差，提高传动精度。目前，对消隙齿轮传动系统的动力学分析大多采用数值方法，然而在求解含时变啮合刚度和间隙的强非线性系统时耗时较长。本文利用集中质量法建立考虑时变啮合刚度的消隙齿轮系统动力学模型，通过对模型的无量纲及归一化处理，运用分段的增量谐波平衡法对消隙齿轮传动系统进行分析，并利用四阶Runge-Kutta法进行数值验证，研究了不同参数对消隙齿轮系统动力学特性的影响规律。结果表明:随扭簧刚度的提高，系统谐振频率也提高，且共振幅值降低;随内部激励的增加、阻尼比的减小，系统由周期运动逐渐变为混沌运动，且共振幅值增大。     

基于动力学模型的旋翼动平衡故障仿真及诊断

旋翼桨叶质量不平衡造成旋翼动不平衡,从而引起直升机振动。针对旋翼动不平衡故障,建立直升机动力学模型,对桨叶质量不平衡进行故障仿真及分析,建立质量不平衡故障与调整配重的对应关系；进而提出一种 BP神经网络和遗传算法结合的旋翼调整方法,建立输入参数与桨叶配重之间的模型,将四片桨叶的挥舞角和机体横滚、俯仰 2个方向的加速度值及相位作为网络输入,通过学习训练,根据输入数据预测调整配重,从而减小直升机 振动,解决旋翼动不平衡问题。     

Energy efficient reactionless design of multi-arm space robot for a cooperative handshake maneuver

Space robots play a significant role in on-orbit capture, space structure construction, and assembly tasks. Since the robotic arms are attached to a free-floating satellite, the motion of the manipulator in such tasks and the satellite are coupled. Multiple-arm space robots can perform complex cooperative tasks and are superior to single-arm space robots. Current work proposes a reactionless manipulation algorithm for a multi-robotic arm based on the iterative Newton–Euler method for space robots with many task and balance arms. The present work demonstrates two tasks and one balance arm to perform a reactionless handshake maneuver in space. This maneuver is presented in detail for a planar and spatial case. The planar case uses 3 DoF robotic arms, while the spatial case uses 6 DoF robotic arms. In addition, the balance arm has been designed considering the efficient usage of energy satisfying reactionless manipulation concept. The design procedure focuses on minimizing energy used during the motion of the balance arm for a known motion of task arms using a genetic algorithm. Moreover, computational experiments are conducted to validate the use of the genetic algorithm for optimization. The results of proposed reactionless manipulation algorithm have been validated with the results available in the literature for the spatial case that uses a different method. In the future, an energy-efficient balance arm will be designed to handle tumbling objects.