基于近场聚焦逆波束形成的UUV平台噪声自适应抵消

UUV平台自噪声会对舷侧阵产生干扰,从而影响其探测性能,本文针对平台尾部自噪声源的直达噪声和海面反射噪声,提出了基于近场聚焦逆波束形成的平台噪声自适应抵消方法。文中利用UUV平台设计参数、深度以及运动姿态信息对尾部自噪声传播到舷侧阵的路径建立几何模型,并分析了影响该路径的因素;通过该模型,平台尾部自噪声能够实时自适应地通过聚焦波束形成被估计出来,从而在舷侧阵的接收信号中实现干扰抵消。仿真结果与海试实验数据处理结果表明,该方法能够有效抑制尾部自噪声干扰,显著提高UUV探测弱目标的能力。     

某型艇近场噪声和自噪声数值计算

采用结构有限元软件NASTRAN和声学边界元软件SYSNOISE,对某型艇振动与声学特性数值计算问题进行了研究。通过基于全船三维有限元分析模型的频响分析计算,获得该船结构振动响应特性参数。以振动频响分析计算结果作为声学边界条件,考虑球面点噪声源的影响,建立了全船三维边界元声学分析模型;并采用间接边界元法,对某型艇近场和自噪声声学特性进行了计算。所得计算结果与该船实测数据进行了对比,证明本文计算方法是可行的。     

噪声和振动的有源控制

用和实际噪声源(振源)反相的二次声源产生声,进行干涉,来减小甚至抵消噪声,这不是一个新鲜事,原理也不复杂。但具体实现却取决于声源(振源)的尺寸,辐射分布和抵消场的产生与控制。近期的进展是以控制论和自适应滤波的最新发展和用于自适应信号处理的高速微电子线路的出现为基础的。     

浅海运动噪声源的声场统计特性及其对噪声测距声呐信号处理的影响

本文研究了运动噪声源在分层统计不均匀的媒质中(并考虑随机起伏边界的影响)噪声场时空相关函数的性质。 理论与大量海上实验都证明了,传播的多径效应使相关函数拖散,媒质的折射率起伏与边界起伏引起相关函数的起伏。而噪声源的运动对实时相关器的输出的影响等效于低通滤波器并附加时空相关函数的漂移。相关函数的这些性质大大降低了噪声测距声呐系统的信号处理增益。 相关函数的起伏和畸变,使噪声测距难于实现。为此,本文提出了小间距大跨度的四点阵空间相关测距与二次相关信号处理技术,大大地克服了上述诸因素的影响。本文还对内波引起的长周期大时延起伏的二次相关函数的输出,提出了有限记忆类卡尔曼滤波处理方法,使噪声测距声呐最终实现有效的准确测距与跟踪。     

主被动拖线阵声呐中拖曳平台噪声和拖鱼噪声在浅海使用时的干扰特性

分析了主被动拖线阵声呐中拖曳平台的螺旋桨噪声和主动发射基阵(拖鱼)流噪声对被动接收基阵的干扰作用,指出在浅海声学环境下,直达波和海底、海面反射波会成为声呐系统的严重干扰。给出了拖曳平台和拖鱼在各种不同深度和缆长的情况下干扰源的入射角。从理论上计算了不同参数下干扰噪声对系统响应的影响,系统仿真结果可为声呐设计者抑制这种干扰提供途径。     

襟翼侧缘噪声的理论模拟与分析

襟翼侧缘噪声是飞机机体重要的噪声源,作者应用平面传声器阵列测量技术对民用客机进场着陆过程中的襟翼侧缘噪声进行了测量。基于实验测量结果,本文应用气动声学的基本理论,对飞机襟翼侧缘噪声进行理论的分析和研究,目的是深入的理解襟翼侧缘噪声源声辐射的机理、建立可靠的噪声预测模型,并期望获得可行的飞机机体噪声抑制方法。研究结果表明,同简单的旋涡振荡模型相比,Howe的襟翼侧缘噪声模型更接近于实际襟翼侧缘宽频噪声物理过程。     

大型声呐基阵的全方位强干扰抵消系统

强干扰是制约中远程声呐性能的主要因素。对于大型声呐来说,由于过长的延时量以及过高的运算速率,抗强干扰问题始终未能解决,本文提出一种适用于大型基阵的全方位抗强干扰系统。它是自适应噪声抵消系统与一个可编程迪卡诺(DICANNE)系统的结合,在干扰与信号入射角之间的夹角比较小时,采用低采样速率的自适应噪声抵消系统;在此角度较大时,采用高采样率的DICANNE系统,从而使整个系统具有全方位抗干扰的性能。本方案在采用高性能的DSP器件时,易于实现。文中给出设计框图与硬件实施方法。     

微波BJT器件噪声参数的抽取

将内部含有噪声的二端口电路网络等效为一个无噪声网络和在其输入端接入等效噪声源的组合，如微波BJT器件的级联噪声模型，即En-In模型。根据噪声网络理论，     

矢量拖线阵不同形状水听器流噪声响应特性

拖线阵声呐流噪声大小与水听器形状密切相关,为了揭示矢量拖线阵流噪声响应特性,研究了不同形状矢量水听器滤波特性及其噪声抑制特点。基于波数-频率谱分析方法,导出了圆柱形、球形、胶囊形矢量水听器的波数响应函数以及噪声功率谱解析表达式;并根据湍流边界层压力起伏Carpenter模型数值计算了矢量水听器波数响应函数、流噪声响应特性与水听器形状和几何尺寸之间的变化规律,得到了不同形状矢量水听器抑制流噪声特点。研究结果表明,细长胶囊形矢量水听器具有较好的流噪声抑制性能。      

谐波线谱簇干扰自适应抵消器

对于舷侧阵声呐本地干扰抵消技术,优良参考信号的抬取以及数据融合是关键．木文首先分析舷侧阵声呐使用频段内自噪声的频率分布特性,然后提出谐波线谱簇干扰抵消器的概念．文献１中给出单频线带干扰抵消器的理论分析,本文给出多频线谱于扰抵消器的理论分析．基于陷波滤波器品质因素的表达式,给出恒Ｑ值线谱干扰抵消器的设计方法．同时提出一种性能优良的实现谐波线谱簇合成的方法．计算机仿真结果以及海试数据分析结果令人满意．     

基于空时级联滤波的拖船自噪声抵消方法

拖船自噪声属于近场多途强干扰信号,具有显著角度扩展现象,是影响拖曳阵探测性能的重要因素之一。在逆波束形成自噪声抵消方法基础上,结合空域和时域滤波,提出了空时级联滤波的拖船自噪声抵消方法。首先,由方位估计器估计拖船自噪声方位,经过波束形成空域滤波估计得到自噪声信号;然后,利用自噪声空域滤波输出设计最优维纳滤波器,将自噪声抵消在阵元级。基于简正波声场模型的仿真和实际海试数据的处理表明,该方法能够有效抵消拖船自噪声,性能优于逆波束形成方法。     

Acoustic multipath structure in direct zone of deep water and bearing estimation of tow ship noise of towed line array

In the towed line array sonar system, the tow ship noise is the main factor that affects the sonar performance. Conventional noise cancelling methods assume that the noise is towards the endfire direction of the array. An acoustic experiment employing a towed line array is conducted in the western Pacific Ocean, and a strange bearing-splitting phenomenon of the tow ship noise is observed in the array. The tow ship noise is split into multiple noise signals whose bearings are distributed between 10° and 90° deviating from the endfire direction. The multiple interferences increase the difficulty in recognizing the target for the sonar operator and noise cancellation. Therefore, making the mechanism clear and putting forward the tow ship noise splitting bearing estimation method are imperative. In this paper, the acoustic multi-path structure of the tow ship in deep water is analyzed. Then it is pointed out that the bearing-splitting phenomenon is caused by the main lobe of direct rays and bottom-reflected rays, as well as several side lobes of direct rays. Meanwhile, the indistinguishability between the elevation angle and the bearing angle due to the axial symmetry of a strict horizontal line array causes the bearing to deviate from the endfire direction. Based on the theory above, a method of estimating bearing of the tow ship noise in deep water is proposed. The theoretical analysis results accord with the experimental results, which helps to identify the target and provide correct initial bearing guidance for noise cancelation methods.     

ACTIVE CONTROL OF ENVIRONMENTAL NOISE, VII: PERFORMANCE OF MULTI-FREQUENCY, MULTI-CHANNEL, FREEFIELD SOUND CANCELLING SYSTEMS

The paper considers the performance of multi-frequency, multi-channel, free field sound cancelling systems for the reduction of discrete frequency and periodic noise. The approach uses a method of directional active noise control. Large sound reductions from these systems have been made possible through: (a) synthetically generating the cancelling sound and synchronizing with the primary source; (b) automatic alignment of all stability regions of the control system and; (c) avoiding instability produced by these multi-channel systems.     

Active noise control in finite length ducts

A simple technique for the active control of sound in ducts, initially suggested by Olson and May [1], is investigated in detail. A simple, “virtual earth” principle, feedback loop is used to drive the sound pressure to a minimum at a microphone placed close to a loudspeaker in the duct wall. This produces a reflection of downstream travelling plane waves. A detailed investigation of the loudspeaker near field has enabled the optimum position of the microphone to be identified. The system is shown to be especially effective at the frequencies of the longitudinal duct resonances, where the acoustic response of the duct produces a high loop gain. Results are presented which show a reduction of up to 20 dB in the amplitude of low frequency broadband noise at a position downstream of the cancelling source.     

Chan-Vese模型两相自适应窄带的阴影区检测方法

为得到快速高精度的声呐图像阴影区检测效果,提出Chan-Vese模型两相自适应窄带检测方法。利用各向异性二阶邻域马尔可夫模型估计声呐图像的纹理特征参数,实现原始图像平滑去噪;由块方式的k-均值聚类算法确定图像的初始两类分割,初步确定阴影区大致位置,并根据此大致位置,自适应初始化零水平集函数,来减少人为干预,提高检测速度;在此基础上,提出建立Chan-Vese模型两相窄带水平集进行声呐图像检测,完成局部寻优,排除全局图像中孤立区对检测的影响,使阴影区检测结果更加精确。通过对真实声呐图像的检测实验结果分析,验证提出的检测方法能够去除原始图像的部分噪声,提高检测精度和速度,有一定的自动性和适应性。      

Recommendations for enhancing the role of the auditory modality for processing sonar data

Submarine warfare continues to pose a threat in present-day military operations. Visual displays play a dominant role for operator detection and classification of underwater and surface targets. However, the visual modality is ineffective for the detection of transient signals. In spite of quieter submarines, transient sounds such as hull popping are difficult to disguise, which makes them more likely to be detected via an auditory display. Operators tend to use auditory displays less often because several factors can impede effective aural processing. In this paper, the sonar problem is reviewed followed by some proposed techniques for making more effective use of the auditory modality for the presentation of sonar signals as a means of further improving operator detection and classification of targets. Some recommendations for augmenting the aural presentation of sonar signals over headphones are then discussed. Key research areas include: (1) a reduction of the sound level of the ambient noise in noisy environments should improve the likelihood that the operator will detect weak signals; (2) the provision to replay sound bites of interest and to compare these against a library of known archetypes should lead to increased accuracy in target classification; (3) the ability to present sonar beams in a three-dimensional auditory display where the spatial position of each sonar beam corresponds to the actual position of the source in the ocean should enable the operator to monitor multiple beams and increase his/her situational awareness. Ultimately, the viability of an auditory display is dependent on operator hearing acuity.     

声纳导流罩吸声障板声学特性的研究

本文研究内容属于舰艇声兼容性技术研究的一部分。应用声学软件SYSNOISE计算了,声纳定向发射时某试验用声纳导流罩及尾部吸声障板的声场特性,同时进行相同工况的水下模型试验。计算结果与试验结果吻合良好,说明应用声学软件对声纳声场进行计算是一种可行的方法,有可能推广至其他的水下模型的声场计算。结果数据反映了吸声障板对声纳定向发射时声场的影响,为舰艇总体声纳导流罩内吸声障板的结构设计、声兼容设计提供依据。     

Adaptive noise cancelling and condition monitoring

When mechanical signature analysis methods are applied to the detection of faults within a complex machine, one is often confronted with a situation in which the diagnostic signal is embedded in a background noise. Coherent filtering techniques are of help in improving the signal to noise ratio (SNR) only when a synchronizing signal is available; on the other hand, the adaptive noise cancelling (ANC) technique can be successfully applied to increase the signal to noise ratio even in those situations where a synchronization signal is not available. Adaptive noise cancelling is a form of optimal filtering in which use is made of an auxiliary or a reference signal. In the work reported here it has been shown that the statistical and spectral analyses techniques which fail to detect and diagnose faults because of a poor signal to noise ratio can be made effective by using an adaptive noise cancelling technique. The expression for the signal to noise density ratio at the output of the noise canceller is derived for a simplified model of a machine.     

微弱信号源的和波束定向方法与分裂波束定向方法的性能比较

本文讨论水下辐射噪声源的精确定向问题，给出被动声纳和波束定向与分裂波束定向方法的性能比较。指出在一定信噪比下，分裂波束精确测向技术比和波束定向技术具有较高的定向精度。但是，随着信噪比的下降，两者趋于一致。推导了估计定向精度的分析表达式，给出在直线阵和圆弧阵情况下，延时估计和声源入射角偏差之间的换算公式和数值模拟结果。同时给出数字式声纳用以计算入射信号左波束和右波束数据的互谱来实现分裂波束定向的方法。     

水听器阵共模干扰抵消研究

硬件电路设计不当等原因将会导致水听器前放电路中存在共模干扰,水听器阵共模干扰将会"污染"A/D采样信号,从而对声纳目标探测与跟踪及其他后续处理造成困扰。在实际的声纳系统中,最好是采用硬件预处理的方式避免共模干扰,但对于已经被污染了的采集数据而言,则只能通过干扰抵消等信号处理的方式对被"污染"了的原始数据加以修复或还原。本文对水听器阵共模干扰特性进行了详细分析,并根据其干扰特性,提出了基于错位相减技术和基于独立分量分析的两种干扰抵消方法。湖试数据处理结果验证了本文方法的可行性。