小卫星动量轮非线性特性建模与仿真方法

动量轮是三轴稳定卫星姿态控制的关键执行部件。由于小卫星本身的转动惯量较小，微弱的干扰力矩有可能导致整个卫星控制系统性能下降。因此，建立一个基于动量轮实际物理特性的理论仿真模型对小卫星姿态控制系统设计至关重要。本文提出了一种多输入多输出非线性建模方法，并给出了基于SIMULINK的动量轮物理特性仿真模型。该模型可以同时输出动量轮所有特征参数的实时值。最后，通过开环和闭环控制数值仿真，对模型进行了验证。数值实验结果与实际物理部件的测试结果一致。本方法可以为小卫星姿控系统的仿真提供一个有效的、精确的、可以直接应用的部件级模型。     

波音737自驾脱开后驾驶盘偏转现象浅析

通过两起航线实例．结合波音公司技术支援部门的意见，分析了在近进着陆阶段自驾脱开后驾驶盘偏转的原因，供飞行人员和维护人员参考，以避免此类不安全事件的发生。     

共轴刚性旋翼直升机着舰流场计算分析

以CFD软件为基础,建立了适用于共轴刚性(双)旋翼直升机着舰飞行时的气动计算模型.应用这一模型,首先计算了Robin旋翼的悬停状态算例,计算结果与试验数据进行了对比.然后着重分析了共轴刚性旋翼直升机在着舰与着陆时的流场异同,并进一步分析了着舰飞行时不同风向角对直升机俯仰、滚转和偏航力矩的影响,获得了一些对直升机着舰飞行有指导意义的结果.     

基于ANSYS的襟缝翼滚轮接触应力场分析

结合滚轮的实际使用环境和载荷,建立了滚轮与圆盘的有限元模型,对滚轮接触应力场进行了分析,从而弥补了赫兹接触理论的局限性,有效地确定了试验载荷,以指导开展模拟试验。     

函道螺旋桨设计方法研究

由于函道和螺旋桨互相干扰的复杂性,函道螺旋桨的设计需要较长时间。本文提出了一种在函道螺旋桨初步设计阶段确定桨叶外形的简便方法。首先,根据动量理论计算通过桨盘的流量,再由工程经验估算桨盘前后的压差增量,然后运用叶素理论设计桨叶的几何形状。为了验证该方法的可行性,加工了桨叶和函道,并进行风洞实验。结果表明,设计值与实验测量值吻合较好,说明该方法实用、有效,采用该方法可以加快函道螺旋桨设计过程。     

Jitter reduction of a reaction wheel by management of angular momentum using magnetic torquers in nano- and micro-satellites

Nowadays, nano- and micro-satellites, which are smaller than conventional large satellites, provide access to space to many satellite developers, and they are attracting interest as an application of space development because development is possible over shorter time period at a lower cost. In most of these nano- and micro-satellite missions, the satellites generally must meet strict attitude requirements for obtaining scientific data under strict constraints of power consumption, space, and weight. In many satellite missions, the jitter of a reaction wheel degrades the performance of the mission detectors and attitude sensors; therefore, jitter should be controlled or isolated to reduce its effect on sensor devices. In conventional standard-sized satellites, tip-tilt mirrors (TTMs) and isolators are used for controlling or isolating the vibrations from reaction wheels; however, it is difficult to use these devices for nano- and micro-satellite missions under the strict power, space, and mass constraints. In this research, the jitter of reaction wheels is reduced by using accurate sensors, small reaction wheels, and slow rotation frequency reaction wheel instead of TTMs and isolators. The objective of a reaction wheel in many satellite missions is the management of the satellite’s angular momentum, which increases because of attitude disturbances. If the magnitude of the disturbance is reduced in orbit or on the ground, the magnitude of the angular momentum that the reaction wheels gain from attitude disturbances in orbit becomes smaller; therefore, satellites can stabilize their attitude using only smaller reaction wheels or slow rotation speed, which cause relatively smaller vibration. In nano- and micro-satellite missions, the dominant attitude disturbance is a magnetic torque, which can be cancelled by using magnetic actuators. With the magnetic compensation, the satellite reduces the angular momentum that the reaction wheels gain, and therefore, satellites do not require large reaction wheels and higher rotation speed, which cause jitter. As a result, the satellite can reduce the effect of jitter without using conventional isolators and TTMs. Hence, the satellites can achieve precise attitude control under low power, space, and mass constraints using this proposed method. Through the example of an astronomical observation mission using nano- and micro-satellites, it is demonstrated that the jitter reduction using small reaction wheels is feasible in nano- and micro-satellites.     

Stability-based SDRE controller for spacecraft momentum management

Momentum management of spacecraft aims to avoid the angular momentum accumulation of control momentum gyros through real-time attitude adjustment. An attitude control/momentum management controller based on state-dependent Riccati equation is developed for attitude-stabilized spacecraft. The governing equations of the system are formulated as three-axis coupled with full moment of inertia, which fully capture the nonlinearity of the system and are valid for systems with significant products of inertia or strong pitch to roll/yaw coupling. The state-dependent Riccati equation algorithm brings the nonlinear system to a linear structure having state dependent coefficients matrices and minimizing a quadratic-like performance index. The system equations are nondimensionalized, which avoid numerical problems at the same time make the weighting matrix more predictable. To guarantee closed-loop system stability, the state-dependent Riccati equation algorithm is also modified based on pole placement technique. The state-dependent Riccati equation is online calculated through the computational-efficient θ-D technique which reaches a tradeoff between control optimality and computation load. The dynamic characteristics of the system at torque equilibrium attitude are analyzed. Constraints on moment of inertia for successful momentum management are provided. Simulations demonstrate the excellent performance of the controller.     

非均匀速度来流条件下液体射流喷雾特性

实验研究了非均匀速度来流条件下液体横向射流喷雾特性.实验利用多孔板实现速度的不均匀,应用片光照相得到喷雾中心截面照片,使用相位多普勒粒子分析仪(PDPA)测量液滴的直径和速度.实验结果表明:在非均匀速度来流中,射流的弯曲和破碎机理有所不同,导致穿透深度和雾化特性发生改变.与均匀速度来流相比,正速度梯度来流时射流穿透深度...     

飞轮隔振平台组合系统的动力学建模

为分析隔振平台对星上飞轮扰动的衰减效果,研究了飞轮隔振平台组合系统的动力学建模问题.首先推导出含有静动不平衡量的飞轮加隔振平台组合系统的动力学模型.从模型中得出,飞轮和平台之间存在耦合;转子的静动不平衡会体现为飞轮的多项扰动力和扰动力矩.其次,对这些扰动项进行量级分析,并据此简化系统方程.最后利用数值仿真将简化模型与之前的完整模型作对比,验证了此简化模型的合理性;并通过初步的整星系统仿真,说明了隔振系统对航天器姿态稳定度的改善效果.     

航空发动机高压旋转涡轮盘腔流动与换热

在同模型实验参数范围内，且数值解和实验解基本吻合的前提下，对发动机原型参数进行数值模拟，求解了旋转系下流体流动与换热微分方程组，通过对气体域和固体域进行共扼计算，并将动量方程与能量方程福合求解。结果表明利用低参数下实验数据支持的数值计算程序对真实参数的模拟是合理的，对于复杂的非线性现象，数值外推法比传统实验外推更加准确。