Efficient prediction of ground noise from helicopters and parametric studies based on acoustic mapping

Based on the acoustic mapping, a prediction model for the ground noise radiated from an in-flight helicopter is established. For the enhancement of calculation efficiency, a high-efficiency second-level acoustic radiation model capable of taking the influence of atmosphere absorption on noise into account is first developed by the combination of the point-source idea and the rotor noise radiation characteristics. The comparison between the present model and the direct computation method of noise is done and the high efficiency of the model is validated. Rotor free-wake analysis method and Ffowcs Williams-Hawkings (FW-H) equation are applied to the aerodynamics and noise prediction in the present model. Secondly, a database of noise spheres with the characteristic parameters of advance ratio and tip-path-plane angle is established by the helicopter trim model together with a parametric modeling approach. Furthermore, based on acoustic mapping, a method of rapid simulation for the ground noise radiated from an in-flight helicopter is developed. The noise footprint for AH-1 rotor is then calculated and the influence of some parameters including advance ratio and flight path angle on ground noise is deeply analyzed using the developed model. The results suggest that with the increase of advance ratio and flight path angle, the peak noise levels on the ground first increase and then decrease, in the meantime, the maximum Sound Exposure Level (SEL) noise on the ground shifts toward the advancing side of rotor. Besides, through the analysis of the effects of longitudinal forces on miss-distance and rotor Blade-Vortex Interaction (BVI) noise in descent flight, some meaningful results for reducing the BVI noise on the ground are obtained.     

静电悬浮加速度计的地面测试与评定方法综述

本综述将静电悬浮加速度计性能指标项目归为五类,阐述了它们与需求的关系,强调了采样率为10SPS、相应的闭环传递函数带宽为3Hz的必要性。指出实验室标定会受到环境振动噪声的干扰,通常的标定方法均不适用,静态标定的首要困难在于准确测定失准角;用专用摆台作动态标定可以大致判断标度因数并观察两台加速度计模型方程各参数的一致性;为了在专用摆台上进行各项性能测试,加速度计检验质量需要在地面重力下悬浮;落塔试验的功用有限,并非加速度计性能指标的量化评定试验;射前检验加速度计噪声采用分析证实的方法,为了降低噪声,必须依靠详尽的理论分析和实验验证,一一找出各种影响因素及其影响程度,采取有力措施,切实加以改进。
     

一种数据采集卡自动校准系统及关键技术研究

数据采集卡已成为航空航天设备、现代武器装备生产验证、维修保障系统的重要部分。介绍了一种专用数据采集卡自动校准系统,分析了设计背景及实现的功能,同时提出了校准过程中噪声抑制、通道低电势和控制高可靠性三项关键技术的解决途径。     

New correlated MIMO radar covariance matrix design with low side lobe levels and much lower complexity

In this paper, a new correlated covariance matrix for Multi-Input Multi-Output (MIMO) radar is proposed, which has lower SideLobe Levels (SLLs) compared to the new covariance matrix designs and the well-known multi-antenna radar designs including phased-array, MIMO radar and phased-MIMO radar schemes. It is shown that Binary Phased-Shift Keying (BPSK) waveforms that have constant envelope can be used in a closed-form to realize the proposed covariance matrix. Therefore, there is no need to deploy different types of radio amplifiers in the transmitter which will reduce the cost, considerably. The proposed design allows the same transmit power from each antenna in contrast to the phased-MIMO radar. Moreover, the proposed covariance matrix is full-rank and has the same capability as MIMO radar to identify more targets, simultaneously. Performance of the proposed transmit covariance matrix including receive beampattern and output Signal-to-Interference plus Noise Ratio (SINR) is simulated, which validates analytical results.     

低噪声封装器件噪声参数不确定度评定

本文开展了基于Maury公司的Tuner和Agilent公司PNA-X矢量网络分析仪组建的超快噪声参数测量系统的不确定度评定研究工作,通过分析测量系统的输入、输出数据,独立开发了不确定度评定的测量模型,设计了满足国际标准ISO/IEC98-3要求的不确定度评定方法,编制了不确定度仿真软件,首次报道了四个噪声参数的不确定度数据,最佳估计值和95%概率下得包含区间。     

卫星通信频谱监测中的一种形态学滤波预处理方法

针对卫星信号监测中监视频带宽、背景噪声非平坦造成的信号漏检和误检的问题,结合卫星通信信号的特点提出了一种频谱校正的新方法。该方法将接收的频谱信号视为一维灰度图像,通过改进的形态学滤波检测法,估算出信号中非平坦的背景噪声基底,利用估计的噪声基底完成对原频谱信号的修正,可提高信号检测的准确性。仿真结果表明,该方法降低了信号带宽对传统形态学滤波中结构元素长度选择的影响,计算量小,能高效地实现非平坦频谱信号的底噪校正。     

原子磁强计原子气室无磁加热温控系统设计

介绍一种用于原子磁强计原子气室的无磁加热温控系统设计。针对温控系统加热电流产生的磁场干扰,设计了双层加热丝加热膜结构的加热器件,该加热器件利用同层平行反向电流和层间平行反向电流产生的磁场相互抵消以减小加热电流磁场噪声;设计了滑动平均滤波器对采集的温度信号实施滤波以减小随机噪声的干扰;结合设计的高频加热信号的产生电路、幅度控制电路和功率放大电路开展了实验测试。测试结果表明,研制的双层加热丝加热膜结构加热器件相比单层加热丝加热膜结构加热器件的电流磁场噪声抑制能力提高了约16倍,实现的无磁加热温控系统的温控能力达到1. 2‰。     

跟踪微分器在GLONASS定位数据处理中的应用研究

本文介绍了GLONASS定位系统,给出了跟踪微分器的滤波特性。将跟踪微分器用于GLONASS定位数据处理。进行了误差分析及仿真研究。结果表明,这种方法可显著提高GLONASS定位精度,减小定位误差,具有一定的优越性。     

船舶桨轴舵及船体艉部耦合振动噪声数值研究

为研究船舶桨轴舵及船体艉部耦合振动噪声特性,将CFD整体计算得到的非定常力作为激励源,以分布载荷的形式加载于有限元模型上,并结合模态叠加法和声学边界元法建立了桨轴舵及船体艉部耦合振动噪声的数值计算方法。通过分析振动响应计算结果,发现频率较低时耦合系统振动响应受工况影响比频率较高时更加明显;振动响应最大幅值所在频率受结构特性和激励源的共同影响;在桨-轴系统中,桨叶的振动传递损失最大。通过对比不同模型的桨叶振动计算结果,发现桨-轴系统模型的计算值与桨-轴-船系统模型更为接近且不复杂,比单桨模型更为实用。通过分析振动噪声计算结果,发现振动响应频谱和声场分布均可反映结构的固有特性;船体振动贡献的总声压在耦合系统中占90%以上,而桨叶振动仅为1%左右,在预报螺旋桨引起的振动噪声时,需要将船体振动噪声考虑在内。     

合成孔径雷达图像解译技术探讨

首先对合成孔径雷达图像解译的研究背景及发展历程作了简单介绍，然后分别从斑点噪声抑制、边缘检测、区域分割、目标检测与识别等方面进行了分类探讨。指出新的解译技术应综合利用新特征、新信息和新的研究理论，开展多信息合作与融合机制的研究以及人工智能的应用。