超低空反导中的多径效应仿真

为得到超低空背景下目标特性参数对脉冲雷达导引头目标检测的影响,根据导引头和目标的空间几何关系,推导了波程差、多普勒频移、相位差的表达式,并结合比例导引法建立多径效应仿真模型。针对目标飞行参数进行仿真,并结合仿真结果对参数的影响效果进行了分析,为导引头末制导段的弹道规划与有效地规避多径效应提供参考依据。     

A new approach for pulse amplitude measurement using Lagrange’s interpolation for radiation or particle detectors

In radiation detector signal processing, usually, the charge-sensitive preamplifier converts the small charge signal coming from the semiconductor-based detector into voltage form and then the signal is further amplified to measure the energy of the incoming radiation. The voltage pulse from a charge-sensitive preamplifier (CSPA) is amplified using a shaping amplifier which reduces the signal bandwidth. To achieve better energy resolution, precise measurement of the peak amplitude of shaping amplifier output is required. The signal processing methods are available in which the signal from the charge-sensitive preamplifier can be directly digitized using high-speed Analog to Digital Converters (ADC), and then further signal processing such as gain and shaping is carried out inside the Field Programmable Gate Arrays (FPGA). For multiple detector systems, digital signal processing methods are quite difficult to implement in Field Programmable Gate Arrays (FPGA). In this context, The development of an alternative technique is initiated that uses a charge-sensitive preamplifier, shaping amplifier, low sampling analog-to-digital converter, and FPGA, where LaGrange’s interpolation technique is implemented in FPGA to precisely measure the peak of the analog pulse. In this paper, the comparison of the proposed method with other pulse amplitude measurement techniques is discussed. Results show that the implemented technique gives similar energy resolution compared to digital pulse processing and standard peak detector-based techniques.     

Optimization for aerodynamic performance of double serpentine nozzles with spanwise offsets using Taguchi-based CFD analysis

Serpentine nozzles are widely used in combat aircraft to realize strong stealth characteristics. Based on the layout characteristics within a confined space, a series of double serpentine nozzles with spanwise offsets are established. Using computational fluid dynamics and Taguchi method, the influence mechanisms of the Distribution of Area (DA), Distributions of Centerline for the first and second ‘S’ sections in the Vertical direction (DCV1 and DCV2), and Distribution of Centerline in the Spanwise direction (DCS) are analyzed. The impact of these factors on the total pressure recovery coefficient can be ranked as DA > DCV2 > DCS > DCV1, whereas their impacts on the discharge coefficient and axial thrust coefficient can be ranked as DCV2 > DCS > DA > DCV1. Considering the statistical significance of these factors, a nozzle in which DA changes rapidly at the exit and DCV1, DCV2, and DCS change rapidly at the entrance gives the best aerodynamic performance. Compared to the worst configuration, the total pressure recovery coefficient, discharge coefficient, and axial thrust coefficient are improved by 1.6%,3.5% and 3.6%, respectively. DA influences the gas flow acceleration in the entire serpentine channel, resulting in different wall shear stress and friction losses. The various centerline distributions influence the gas flow acceleration effects and form complex wave structures in the constant-area extension section, resulting in different local and friction losses.     

Oblique detonation wave triggered by a double wedge in hypersonic flow

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...     

铝锂合金曲面件超低温成形工艺

针对铝锂合金室温成形性差和热成形性能弱化的难题,利用发现的超低温下伸长率与硬化指数同时提高的双增效应,提出铝锂合金曲面件超低温成形新工艺.通过2195铝锂合金板材在不同温度和热处理状态下的超低温变形行为研究,确定发生双增效应的临界温度为低于-140℃,伸长率可提高至40％以上、硬化指数达到0.44;利用建立的超低温成形...