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421.
《中国航空学报》2023,36(5):280-285
This paper proposes a frequency reconfigurable triangular antenna actuated by an inflated triangular structure. The open path antenna is transformed from an open type to a closed structure by inflating. Inflatable structures are easy to manufacture by fusing 2 inextensible membranes together along a defined pattern of lines. However, the prediction of their deployed shape remains a challenge. To solve the pattern changed problem, guided by geometric analyses and local buckle characteristics, the inflated triangular structure has been designed and verified by experiment and simulation. In the process of transformation of the antenna, the resonant frequency of the antenna is changed because this frequency is determined by the conformational change. The resonant frequency changes from GHz to kHz when the design of initial structure sizes is from millimeter to meter. The measured peak gains, the frequency, and the radiation direction are also reconfigurable by the initial size. Finally, the reconfigurable resonator array is presented, which is coupled to electric fields to absorb all incident radiation. In this work, the changed pattern design by inflating is applied to the antenna design, and its frequency reconfigurability is achieved. Through the electricity performance analysis of the reconfigurable antenna, precise manufacturing will be possible and provide guidance for manufacturing frequency reconfigurable antennas. 相似文献
422.
《中国航空学报》2023,36(4):190-200
The coherent structures arising during flat-plate boundary layer transition at Mach number 3.4 are investigated using a custom-built hyper-rate imaging system. The evolution of transitional structures is investigated in the Eulerian and Lagrangian reference frames. The upstream evolution of transition is dominated by the generation of new hairpin structures, while the interaction among multiple structural types dominates the evolution downstream. The breakdown of the existing structure, which may be caused by interactions among multiple types of structures with similar scales, is also visualized. 相似文献
423.
Xinlei PAN Weifeng HE Zhenbing CAI Xuede WANG Ping LIU Sihai LUO Liucheng ZHOU 《中国航空学报》2022,35(4):521-537
Titanium alloys have a wide application in aerospace industries as it has greater strength and low density, but it has poor tribological properties. To improve its friction and wear performance, in present work, a femtosecond laser is used to directly irradiate the Ti6Al4V titanium alloy surface in air conditioning, which results in localized ablation and the formation of periodic microstructures but also a strong pressure wave, propagating the material inside. Through the optimization of proces... 相似文献
424.
螺栓连接结构受载时经常会出现滑移,这种滑移会影响结构的动力学性能,继而对结构的性能和寿命造成影响。本文以双螺栓连接结构为对象,通过实验和数值仿真手段研究滑移对结构模态特性的影响。实验结果表明,预紧力的增大会导致共振频率上升,而随着激励幅值增大,共振频率下降且每个周期能量耗散量对模态力的梯度增大。基于实验结果,结合考虑滑移的Iwan模型理论,建立非线性动力学模型,应用四阶龙格库塔法进行求解。根据计算结果对宏观滑移情况下的结构模态进行分析,发现此时二阶弹性模态中的共振频率下降量增大,能量耗散量对模态力的梯度降低。该数值计算模型可以很好地表征螺栓连接结构的模态特性,且计算效率高。 相似文献
425.
Pressure-gain combustion has gained attention for airbreathing ramjet engine applications owing to its better thermodynamic efficiency and fuel consumption rate. In contrast with traditional detonation induced by a single wedge, the present study considers oblique shock interactions attached to double wedges in a hypersonic combustible flow. The temperature/pressure increases sharply across the interaction zone that initiates an exothermic reaction, finally resulting in an Oblique Detonation Wav... 相似文献
426.