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931.
932.
933.
《中国航空学报》2021,34(5):331-340
The morphing trailing edge based compliant mechanism is a developing technology which can increase lift-drag ratio for variable flight modes by bending down the trailing edge. Composite material design is integrated into topology optimization for the morphing trailing edge based compliant mechanism in the paper. A two-step optimization strategy is established to solve the integrated design problem. Initially, lamination parameters are introduced and viewed as a bridge between structure stiffness and fiber angles for composite material. Design variables include the lamination parameters and element density. The least-squares between actual and desired displacements at output points along trailing edge is adopted to evaluate the deformed capability of the trailing edge. An integrated optimization model for the composite morphing trailing edge is established with the volume constraints. The optimal topologic shape and lamination parameters are initially obtained. Subsequently, a least-squares optimization between fiber angles and the optimal lamination parameters is implemented to obtain optimal fiber angles. Finally, morphing capability of composites trailing edge based compliant mechanism is investigated by simulation and experiments. The results indicate the composites trailing edge based compliant mechanism can approximately bend down 8 degrees and satisfies the design requirement. 相似文献
934.
《中国航空学报》2020,33(12):3149-3157
The coherent structure and instability of the interaction of incident shock wave with boundary layer developing on a compression corner are experimentally studied. The experiments are carried out in a supersonic wind tunnel of Mach number 2. Particular attention is paid to shock patterns and unsteady shock motions induced by the separation bubble. The high-speed schlieren is used to visualize the flowfield evolution and to characterize the instability. The snapshot proper orthogonal decomposition of schlieren sequences is applied to investigate the primary coherent structure in the flowfield. Fast Fourier transform and continuous wavelet transformation are applied to characterize the instability. The results show that there are large-scale low-frequency oscillations of the shock waves and small-scale high-frequency pulsations in the separation region. The peak frequency of shock oscillation is mainly concentrated in the range of 100–1000 Hz. The pulsation of the small flow structure in the separation bubble is mainly concentrated above 12.5 kHz. Based on the results of experimental analysis, the preliminary mechanism of the large-scale instability of such interaction is obtained. 相似文献
935.
《中国航空学报》2020,33(9):2472-2489
Compared with serial mechanisms, the parallel mechanism (PM) theoretically exhibited higher positioning accuracy, dynamic performance, strength-to-weight ratio, and lower manufacturing cost, but they had not been widely used in the practical application. One key issue, positioning accuracy, which directly affected their performance and was greatly influenced by the errors of kinematic structure parameters was analyzed. To effectively enhance the positioning precision of PMs, a novel modeless kinematic calibration method, namely the split calibration, was presented and its compensation effect of the positioning error was comprehensively compared with that of an integrated method on two different types of PMs. A strange phenomenon-correct and incorrect identified results were derived from two different PMs by the same integrated method, respectively-which had not been reported yet was discovered, and the origin of it was revealed utilizing numerical simulations. Finally, respective merits and drawbacks of these two methods obtained in this paper provided underlying insights to guide the practical application of the kinematic calibration for PMs. 相似文献
936.
为校正中机身壁板由于重力和调姿内力产生的变形,提高中机身壁板装配调姿精度,提出了一种基于力位协同控制的装配调姿方法。通过将调姿机构等效为并联机构,推导了调姿机构的解析正反解模型;根据螺旋理论,建立了力传感器测量值与重力、调姿内力之间的映射关系,实现重力补偿值的动态计算,基于局部刚体-弹性连接假设,通过多元线性回归方法构建了调姿内力转化为位置补偿量的模型;根据Clamped-Free变形协调原理,简化了定位器调姿内力之间的协调关系,在此基础上提出了重力前馈补偿和调姿内力转化为位置补偿的力位协同控制策略,并对其进行了理论分析与设计。最后,对所提出的控制策略进行了仿真分析,结果表明采用力位协同控制方法,调姿定位精度提高35.3%,调姿内力降低77.8%,通过应用实验,说明了该方法的可行性和有效性。 相似文献
937.
Robust H∞ controller design for attitude stabilization of flexible spacecraft with input constraints
Chuang Liu Keke Shi Zhaowei Sun 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1498-1522
This paper addresses the attitude stabilization and vibration suppression problem for flexible spacecraft subject to model parameter uncertainty, controller perturbations, external disturbances and input constraints. The attitude model of flexible spacecraft is described and converted into a state space form in terms of passive and active vibration suppression schemes. A novel state feedback controller is proposed based on the exactly available expectation of a new variable, which is introduced to model a randomly occurring controller gain perturbation. Based on Lyapunov stability theory, sufficient conditions for the existence of the nonfragile H∞ controller considering input constraints are given based on linear matrix inequalities (LMIs) in terms of additive perturbation and multiplicative perturbation. Then, the developed controller subject to required constraints can be obtained, where the nonfragile property is fully considered to improve the tolerance to uncertainties in the controller. Numerical simulations are performed to demonstrate the effectiveness and superiority of the proposed control strategy in attitude stabilization and vibration suppression, where it should be noted that the passive vibration suppression scheme is superior for high natural frequencies while the active vibration suppression scheme is superior for low natural frequencies. Moreover, the low natural frequencies have more influence on the performance of attitude stabilization and vibration suppression. 相似文献
938.
Mehdi Akhoondzadeh Angelo De Santis Dedalo Marchetti Alessandro Piscini Gianfranco Cianchini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):248-263
After DEMETER satellite mission (2004–2010), the launch of the Swarm satellites (Alpha (A), Bravo (B) and Charlie (C)) has created a new opportunity in the study of earthquake ionospheric precursors. Nowadays, there is no doubt that multi precursors analysis is a necessary phase to better understand the LAIC (Lithosphere Atmosphere Ionosphere Coupling) mechanism before large earthquakes. In this study, using absolute scalar magnetometer, vector field magnetometer and electric field instrument on board Swarm satellites, GPS (Global Positioning System) measurements, MODIS-Aqua satellite and ECMWF (European Centre for Medium-Range Weather Forecasts) data, the variations of the electron density and temperature, magnetic field, TEC (Total Electron Content), LST (Land Surface Temperature), AOD (Aerosol Optical Depth) and SKT (SKin Temperature) have been surveyed to find the potential seismic anomalies around the strong Ecuador (Mw = 7.8) earthquake of 16 April 2016. The four solar and geomagnetic indices: F10.7, Dst, Kp and ap were investigated to distinguish whether the preliminary detected anomalies might be associated with the solar-geomagnetic activities instead of the seismo-ionospheric anomalies. The Swarm satellites (A, B and C) data analysis indicate the anomalies in time series of electron density variations on 7, 11 and 12 days before the event; the unusual variations in time series of electron temperature on 8 days preceding the earthquake; the analysis of the magnetic field scalar and vectors data show the considerable anomalies 52, 48, 23, 16, 11, 9 and 7 days before the main shock. A striking anomaly is detected in TEC variations on 1 day before earthquake at 9:00 UTC. The analysis of MODIS-Aqua night-time images shows that LST increase unusually on 11 days prior to main shock. In addition, the AOD variations obtained from MODIS measurements reach the maximum value on 10 days before the earthquake. The SKT around epicentral region presents anomalous higher value about 40 days before the earthquake. It should be noted that the different lead times of the observed anomalies could be acknowledged based on a reasonable LAIC earthquake mechanism. Our results emphasize that the Swarm satellites measurements play an undeniable role in progress the studies of the ionospheric precursors. 相似文献
939.
研究了发动机能量输入、工质电离、等离子体加速及能量转换过程及机理,同时分析了磁等离子体推力器在空间推进任务中的应用前景.研究表明磁等离子体推力器主要利用电磁力加速和磁喷管的能量转换作用来实现加速,这种方式在大功率条件下,能够获得大推力、高功率和较长工作时间,在大功率轨道航天器和深空任务中有广阔的应用前景. 相似文献
940.
针对反应机理对湍流预混值班火焰稳燃的影响,使用大涡模拟(LES)耦合输运概率密度(PDF)方法模拟了湍流射流火焰的燃烧流场。化学反应过程采用被广泛应用的SMOOKE (16组分,46步)和DRM22 (22组分,104步)机理,概率密度输运的确定采用欧拉随机场来实现。计算结果表明,LES/PDF模型可以准确地模拟该类火焰的速度分布,火焰褶皱等结构。反应机理的点火延迟时间的准确与否是模拟值班射流火焰的关键,预混射流出口处的小尺度掺混引起的点火和火焰传播过程是值班射流火焰稳燃的关键。 相似文献