微肋薄膜减阻的实验研究

作者根据湍流附面层结构新的解释及非光滑特殊造型表面可以减小流体阻力的事实,作者研制了微肋条减阻薄膜,贴在赛船上参加比赛,获得好成绩[1、2] 。作者在风洞中做了贴及不贴微肋薄膜平板试验对比。结果贴微肋薄膜可减阻约 7%。      

风对建筑绕流流动的数值方法

本文利用k-ε湍流模型及SIMPLE方法,在二维条件下,就风对建筑绕流流动进行了数值模拟,建筑及地面的边界条件采用以低Re数k-ε湍流模型中导出的壁函数处理近壁湍流。自由边界采用外推格式。对于计算域中的建筑物则利用控制粘性系数的方法处理。并对计算结果和风洞实验进行了比较。 为了研究建筑物之间的气流及压力分布,本文还对并列两栋建筑的不同情况进行了数值计算和分析。     

Optimal speckle reduction in polarimetric SAR imagery

Speckle is a major cause of degradation in synthetic aperture radar (SAR) imagery. With the availability of fully polarimetric SAR data, it is possible to use the three complex elements (HH, HV, VV) of the polarimetric scattering matrix to reduce speckle. The optimal method for combining the elements of the scattering matrix to minimize image speckle is derived, and the solution is shown to be a polarimetric whitening filter (PWF). A simulation of spatially correlated, K-distributed, fully polarimetric clutter is then used to compare the PWF with other, suboptimal speckle-reduction methods. Target detection performance of the PWF, span, and single-channel |HH|² detectors is compared with that of the optimal polarimetric detector (OPD). A novel, constant-false-alarm-rate (CFAR) detector (the adaptive PWF) is as a simple alternative to the OPD for detecting targets in clutter. This algorithm estimates the polarization covariance of the clutter, uses the covariance to construct the minimum-speckle image, and then tests for the presence of a target. An exact theoretical analysis of the adaptive PWF is presented; the algorithm is shown to have detection performance comparable with that of the OPD     

Cascaded detector for multiple high-PRF pulse Doppler radars

A postdetection design methodology for a multiple high-pulse-repetition frequency (PRF) pulse Doppler radar has been developed. The postdetection processor consists of an M out of N detector where range and target ambiguities are resolved, followed by a square-law detector which enhances the minimum signal-to-noise (S/N) power-ratio per pulse burst performance. For given probabilities of false alarm and detection, formulas are derived from which the three thresholds associated with the cascaded detector can be found. Fundamental tradeoffs between the minimum S/N required, number of ghosts, and the number of operations (NOPs) that the cascaded detector must perform are identified. It is shown that the NOPs and the number of ghosts increase and the minimum S/N required decreases as the binary M out of N detector passes more detections to the square-law detector     

应用局部应力应变法预测机匣疲劳寿命

本文在用有限元对带孔圆筒机匣进行了弹塑性分析的基础上,设计了带孔薄板等效模拟试件,试图作为取代圆筒机匣低循环疲劳寿命预测和试验的等效模拟构件,为此对带孔圆筒机匣与带孔薄板等效模拟试件同时进行了低循环疲劳寿命预测和试验,取得了满意的结果。通过对上述结果分析对比,找出了设计真实构件的等效模拟试件准则,为今后复杂构件的低循环疲劳寿命预测,设计等效模拟试件提供了依据。      

平板边界层转捩的数值模拟

对于自由湍流引起的压力梯度为零的平板边界层转捩过程的数值模拟,本文提出了一个单方程湍流模型 (VL M模型),对湍流粘性系数和湍流长度尺度都进行了修正以正确引入低雷诺数效应。数值计算表明,该模型在自由来流湍流度为 0.03～8%的大范围内能正确模拟边界层转捩全过程,包括转捩区起点位置和转捩区长度、边界层内的平均及脉动参数分布等。本文还提出了上述转捩过程的时均化五阶段模型。      

氢燃料超音速燃烧室实验研究

本文介绍超音速燃烧冲压发动机燃烧室实验研究,模型燃烧室呈突扩台阶和扩张形,用电弧加热空气。燃烧室入口Ma =2 1,总温 12 0 0K,总压 7× 105Pa。      

大多普勒容限巴克码脉压

 本文介绍用补偿式非相干型旁瓣抑制滤波器(SSF)实现13位巴克码脉冲压缩旁瓣抑制的理论计算及实验结果。补偿式非相干型SSF采用最小二乘近似逆滤波方法设计,若子脉冲宽度为0.7μs,峰值旁瓣电平不超过-30dB,这种SSF的多普勒容限能达到-40kHz～+40kHz。理论计算及实验结果都表明,所设计的补偿式非相干型SSF的多普勒容限比具有同样长度冲激响应序列的R-G-ISSF有显著改善。