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The problem of generating optimal paths for curvature-constrained unmanned aerial vehicles (UAVs) performing surveillance of multiple ground targets is addressed in this paper. UAVs are modeled as Dubins vehicles so that the constraints of UAVs' minimal turning radius can be taken into account. In view of the effective surveillance range of the sensors equipped on UAVs, the problem is formulated as a Dubins traveling salesman problem with neighborhood (DTSPN). Considering its prohibitively high computational complexity, the Dubins paths in the sense of terminal heading relaxation are introduced to simplify the calculation of the Dubins distance, and a boundary-based encoding scheme is proposed to determine the visiting point of every target neighborhood. Then, an evolutionary algorithm is used to derive the optimal Dubins tour. To further enhance the quality of the solutions, a local search strategy based on approximate gradient is employed to improve the visiting points of target neighborhoods. Finally, by a minor modification to the individual encoding, the algorithm is easily extended to deal with other two more sophisticated DTSPN variants (multi-UAV scenario and multiple groups of targets scenario). The performance of the algorithm is demonstrated through comparative experiments with other two state-of-the-art DTSPN algorithms identified in literature. Numerical simulations exhibit that the algorithm proposed in this paper can find high-quality solutions to the DTSPN with lower computational cost and produce significantly improved performance over the other algorithms. 相似文献
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高超声速强激波的稳定捕捉仍极具挑战性。目前工程计算中普遍应用的数值格式在模拟多维强激波时通常会遭遇明显的激波不稳定现象,且数值格式的激波稳定性对计算网格表现出严重的依赖性。基于矩阵稳定性分析法,对比了具有不同耗散性质的数值格式稳定捕捉激波的能力,分析了空间二阶精度格式的激波稳定性及限制器对激波稳定性的影响。在此基础上,重点探究了计算网格对激波稳定性的影响规律,研究了网格长宽比和畸变角度对激波稳定性的影响。结果显示,在激波附近通过增大网格长宽比或改变网格畸变角度可有效改善激波捕捉的稳定性;相比于增大网格长宽比,改变网格畸变角度提升激波捕捉稳定性的效果更加明显。在此基础上,结合数值耗散分析对高马赫数下数值激波失稳现象的网格依赖性机制进行了探讨。 相似文献
375.
针对在轨运行航天器在空间等离子体环境和空间带电粒子活动下诱发航天器表面梯度电势存在的客观现实,航天器在空间碎片的撞击下会诱发表面带电或深层电介质带电的航天器放电。为了在实验室模拟航天器表面存在电势差的真实情况,采用对航天器外表面分割的方法,在分割的表面间预留不同间距且在2靶板间加装电阻的方法创造具有梯度电势的高电势2A12铝板作为靶板。利用自行构建的梯度电势靶板的充放电测试系统、超高速相机采集系统和二级轻气炮加载系统,开展高速撞击梯度电势2A12铝靶的实验室实验。实验中,弹丸以入射角度为60°(弹道与靶板平面的夹角)、撞击速度约为3 km/s的条件撞击间距分别为2、3、4和5 mm的2A12铝高电势靶板,利用电流探针和电压探针采集放电电流和放电电压。实验结果表明:放电产生的等离子体形成了高电势与低电势靶板间的放电通道,且在梯度电势靶板间距分别为2、3 mm时诱发了一次放电,放电电流随高低电势靶板间间距的增加而减小;在梯度电势靶板间距分别为4、5 mm时诱发了二次放电,放电电流随高低电势靶板间间距的增加变化不明显。 相似文献
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377.
《中国航空学报》2022,35(8):132-142
Solar power satellite receives great attention because it can release the energy crisis and environmental problems in the future. However, the launch and maintenance costs are tremendous due to the large system mass and large fuel consumption to counteract space perturbations. To reduce mass and fuel, a novel quasi-Sun-pointing attitude in Sun-frozen orbit is proposed. The Sun-frozen orbit has a nonzero eccentricity vector that always points towards the Sun. The quasi-Sun-pointing attitude is a periodic solution of the Sun-pointing attitude angle. Although about 3 % electricity must be given up because of the variation of Sun-pointing attitude angle, little control action is required to deal with the solar radiation pressure and gravity-gradient torque. The algorithm to obtain initial conditions is proposed. The influences of system parameters and structural flexibilities are studied. Simulation results reveal that the quasi-Sun-pointing attitude in Sun-frozen orbit dramatically reduce fuel consumption, the dry mass, and complexity of the control system. In addition, structural vibration is hardly induced by the gravity-gradient torque. Thus, the bending stiffness as well as the mass of the supporting structure can be reduced. 相似文献
378.
《中国航空学报》2023,36(5):306-327
Evidential Reasoning (ER) rule, which can combine multiple pieces of independent evidence conjunctively, is widely applied in multiple attribute decision analysis. However, the assumption of independence among evidence is often not satisfied, resulting in ER rule inapplicable. In this paper, an Evidential Reasoning rule for Dependent Evidence combination (ERr-DE) is developed. Firstly, the aggregation sequence of multiple pieces of evidence is determined according to evidence reliability. On this basis, a calculation method of evidence Relative Total Dependence Coefficient (RTDC) is proposed using the distance correlation method. Secondly, as a discounting factor, RTDC is introduced into the ER rule framework, and the ERr-DE model is formulated. The aggregation process of two pieces of dependent evidence by ERr-DE is investigated, which is then generalized to aggregate multiple pieces of non-independent evidence. Thirdly, sensitivity analysis is carried out to investigate the relationship between the model output and the RTDC. The properties of sensitivity coefficient are explored and mathematically proofed. The conjunctive probabilistic reasoning process of ERr-DE and the properties of sensitivity coefficient are verified by two numerical examples respectively. Finally, the practical application of the ERr-DE is validated by a case study on the performance assessment of satellite turntable system. 相似文献
379.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1769-1783
Lunar final approach navigation is critical for pin-point lunar landing in future missions. This study investigates the use of lunar gravity gradient measurements for autonomous navigation of a lunar probe during the final approach phase. As the spacecraft approaches the Moon, the strength of gravity gradient signals improves. A spaceborne gravity gradiometer can precisely measure local gravity gradients, and the latest lunar gravity model GL1500E is used to provide reference values. The employed truncation degree and order of the gravity model are increased stepwise considering the decreasing altitude of the spacecraft in order to reach a compromise between computational costs and model accuracy. An iterative Kalman filter is developed for coupled orbit and attitude estimation using gravity gradient measurements and attitude quaternions obtained from star sensors. A simulated spacecraft with a gradiometer noise level of 0.01 E is considered. Simulation results show that the spacecraft’s position converges rapidly and achieves an accuracy of less than 100 m at the last epoch. 相似文献