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Sarah M. Cook Dale A. Lawrence 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):2696-2705
The heliogyro solar sail employs high aspect ratio blades that are rigidized by spinning about the central spacecraft, eliminating the need for structural booms typically used to tension traditional square sails. The easily scalable heliogyro gains its maneuverability by actuating the blades at their root with sinusoidal pitch profiles. The blade vibration caused by maneuvering must be attenuated using active control since there is little inherent damping in the blade material. Due to the small root pitch control torques required, on the order of 2 µNm, compared to the large friction torques associated with a root pitch actuator, it has only recently been shown that a single blade heliogyro impedance controller can add damping to the lowest frequency torsional modes of the blade in the presence of modeled actuator friction torques. However, the need to measure blade twist away from the actuator at the root creates a non-collocated control system. Some inherent damping at the blade’s higher frequency modes is therefore needed to stably add damping to the larger-magnitude low-frequency modes, hence control design is sensitive to the accuracy of the blade damping model. Recently, damping characterization tests performed on a small-scale heliogyro blade in a high-vacuum chamber invalidated the assumption of a linear viscous torsional blade damping model that was previously used in blade control designs. This paper describes the formulation of three modal damping models based on the new experimental data and their integration into the single blade heliogyro model. A comparison of the robustness and performance envelopes for the baseline proximal blade twist feedback controller using these damping models shows the ability to meet the required settling time of less than 720 s necessary for a heliogyro technology demonstration mission. This comparison of physically realizable root pitch control systems for a heliogyro blade is critical to increasing the sailcraft to Technology Readiness Level three. 相似文献
203.
《中国航空学报》2020,33(6):1812-1823
The temperature-induced variation in operating force of flow control valves may result in performance degradation or even jam faults of fuel metering unit (FMU), which significantly affects the safety of aircrafts. In this work, an analytical modeling approach of temperature-sensitive operating-force of servo valve is proposed to investigate the temperature characteristics in varying temperature conditions. Considering the temperature effects, a new extended model of flow force is built and an analytical model of valve friction is also derived theoretically based on the dynamic clearance induced by thermal effects. The extremum condition of friction is obtained to analyze the characteristic-temperature points where jam faults occur easily. The numerical results show that flow force increases firstly and then decreases as temperature increases under a constant valve opening. The maximum friction of flow servo valve can be uniquely determined when the structural parameters and ambient temperature are given. The worst situation just happens at the characteristic-temperature points, which are linearly related to the axial temperature gradients of valve spool. Such evaluations may give an explanation for the temperature-induced jam faults of vulnerable valves and provide a reference for designers to determine a suitable working-temperature range of valves in practice. 相似文献
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A.A. Leonov A.M. Galper N.P. Topchiev A.V. Bakaldin O.D. Dalkarov E.A. Dzhivelikyan A.E. Egorov M.D. Kheymits V.V. Mikhailov P. Picozza R. Sparvoli S.I. Suchkov Yu.T. Yurkin V.G. Zverev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(10):3420-3427
The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ~20?MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ~0.01° and ~1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°. 相似文献
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针对含滚阻和摩擦的平面多体系统,给出了通用的力学模型,利用第一类Lagrange方程建立了系统的动力学方程,为便于约束力的计算,利用局部方法列写约束方程,并以矩阵形式给出了该系统滚阻力偶和摩擦力的广义力.该系统动力学方程是非光滑的,通过建立滚阻定律的互补条件以及光滑铰链约束力的互补条件,给出了具有约束稳定化的基于事件驱动法的数值算法,将非光滑约束力、铰链约束力的求解以及滚轮滑动与粘滞的判断问题统一转化为一个线性互补问题进行求解.对两个算例进行了数值仿真,算例数值结果表明了该方法的可行性和有效性. 相似文献
210.
采用集中质量法,建立了齿轮-转子-轴承系统的六自由度的多间隙弯扭耦合的非线性振动模型,模型中考虑了齿面摩擦、时变啮合刚度、齿侧间隙和支承间隙等因素.根据系统在转速、齿侧间隙、齿面摩擦以及啮合阻尼等参数下的全局分岔图和Poincare截面图,研究了各参数对系统分岔特性的影响.分析可知:在一定的齿侧间隙、啮合阻尼和低齿面摩擦因数下,随着转速的逐渐增加,系统通过拟周期分岔进入混沌.当齿面摩擦因数逐渐增加时,系统由良好润滑状态进入干摩擦,系统的混沌运动区域也因此在一临界点产生裂变,且通过激变的途径二次进入混沌;在一定的转速、啮合阻尼和齿面摩擦因数下,随着齿侧间隙的增加,系统通过激变进入混沌,同时可以发现,系统产生混沌和分岔主要发生在量纲一齿侧间隙小于3和大于7的区域,且最终通过倒分岔锁相为周期1运动;在一定的转速、啮合阻尼和齿侧间隙的条件下,随着齿面摩擦因数的增加,系统通过激变进入混沌.同时发现,随着啮合阻尼的增加,混沌区域逐渐裂变成2个、3个和4个混沌窗口,但最终都经由拟周期锁相为周期1运动. 相似文献