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311.
设计了一种带蒙皮和金属底板的双层梯度蜂窝吸波结构,并利用Hashin-Shtrikman(HS)模型获得其等效电磁参数。在此基础上,以反射率低于-10dB带宽最大为优化目标,利用保收敛粒子群优化算法(Guarantee Convergence Particle Swarm Optimization,GCPSO)对四种不同排序方案的双层梯度蜂窝吸波结构进行优化设计。结果表明,入射电磁波的角度和极化方式以及吸波材料的选择、排序和厚度对双层梯度蜂窝结构的吸波性能有很大的影响;不同入射角度下TM极化时的吸波特性明显优于TE极化,在入射角为60^°时最为明显;对比四种方案优化结果显示,case 1方案由于选用损耗角较小的吸波材料充当透波层,分布于蒙皮下面,而选用损耗角较大的吸波材料作吸收层,并置于吸波结构底层,因而具有最大的优化目标函数,吸波效果最佳,且蜂窝高度仅为具有相同吸波效果的case 3方案的49.44%。因此,选择case 1方案作为本文最终优化结果。 相似文献
312.
313.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(5):2467-2480
In this paper, the spinning tether system (STS) is applied to produce the artificial gravity overload with a proposed spin-up scheme in elliptical transfer orbits. To improve the comfort of the astronauts during spinning, the combined control scheme with tension and thrust is designed for spin-up. Then, based on the novel performance function and sliding mode technology, a finite time prescribed performance controller is proposed to track angular velocity for the desired artificial gravity overload. Compared with the existing works, the tracking error is controlled within the preset transient performance and converged to the origin within finite time even in the presence of unknown external disturbance. The stability of closed-loop tracking system is proved by Lyapunov theorem. Finally, the numerical simulations are given to demonstrate the effectiveness and robustness of the proposed controllers in the artificial gravity mission. 相似文献
314.
《中国航空学报》2023,36(3):436-448
Bolt assembly by robots is a vital and difficult task for replacing astronauts in extra-vehicular activities (EVA), but the trajectory efficiency still needs to be improved during the wrench insertion into hex hole of bolt. In this paper, a policy iteration method based on reinforcement learning (RL) is proposed, by which the problem of trajectory efficiency improvement is constructed as an issue of RL-based objective optimization. Firstly, the projection relation between raw data and state-action space is established, and then a policy iteration initialization method is designed based on the projection to provide the initialization policy for iteration. Policy iteration based on the protective policy is applied to continuously evaluating and optimizing the action-value function of all state-action pairs till the convergence is obtained. To verify the feasibility and effectiveness of the proposed method, a noncontact demonstration experiment with human supervision is performed. Experimental results show that the initialization policy and the generated policy can be obtained by the policy iteration method in a limited number of demonstrations. A comparison between the experiments with two different assembly tolerances shows that the convergent generated policy possesses higher trajectory efficiency than the conservative one. In addition, this method can ensure safety during the training process and improve utilization efficiency of demonstration data. 相似文献
315.
利用拟上下解方法,研究了一阶微分方程终值问题u′(t)=f()t,u(t),u(T)=xT拟解的存在性,并通过构造单调迭代序列得到该终值问题的最大最小拟解。 相似文献