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341.
有迎角的再入旋转钝锥由于周向烧蚀滞后将产生滚转力矩。在烧蚀滞后滚转力矩的计算方法中。本文主要介绍滞后引射率和粗糙度对壁面磨擦系数联合影响的一种快速计算方法。给出计算结果与实验数据的比较,分析烧蚀滞后滚转力矩的模数随飞行参数的变化。 相似文献
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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
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《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
345.
介绍了一种径向调制永磁齿轮,运用有限元技术,通过变更仿真条件中的传动比和转速,并对仿真结果中的输出转矩和传动效率进行分析,从而获得传动比和转速对输出转矩和传动效率的影响规律。结果表明,随着传动比的增大,输出转矩呈二次曲线规律变化,而传动效率则呈减小趋势;相同传动比下,随着主动转子转速的增大,输出转矩和传动效率均呈减小趋势;提出了以传动效率〖WTBX〗η〖WTBZ〗为目标值的等效率曲线概念,得到了η=90%时的等效率曲线i~n1(i和n1分别代表传动比和主动转子转速),当n1和i的交点位于等效率曲线下方时,即可满足η>90%。 相似文献
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