近场声全息试验用于医用制氧机噪声控制

为了降低家用制氧机的运行噪声,采用了近场声全息技术进行制氧机噪声场数据采集和声场重建.根据声压频谱图、声压辐射云纹图、声速频谱图、空间声速分布图以及时间/频率/声压图谱等可视化信息,选择了针对声源、传播途径的隔声罩、涂敷阻尼胶、石膏板吸声和加装部件减振胶垫等简单有效的噪声控制措施.试验表明,近场声全息技术是一种有效地进行噪声源控制和声辐射特性研究的重要工具.     

阶次跟踪及发动机排气非稳态噪声分析

汽车加速过程排气噪声是一种强非稳态的噪声,使用传统的频谱分析方法往往会出现"频率模糊"现象。为了了解发动机加速阶段排气噪声特性、研究发动机转速对加速过程排气噪声的影响,采用了阶次跟踪方法对某四缸发动机加速过程排气噪声进行了测试,分析了发动机加速过程排气噪声的主要阶次及主要噪声源,揭示了发动机排气噪声声压级变化与发动机转速的关系,为该发动机排气消声器的设计和优化提供了重要的参考依据。     

基于LabVIEW的车床主轴箱噪声源识别系统的开发

利用LabVIEW8.2和声卡开发了车床主轴箱噪声源识别系统.系统不仅可以测量车床噪声声压级,而且可以对采集到的车床噪声信号进行时域分析和频域分析,能够快速、准确定位车床主轴箱噪声源,具有很大的实用价值.     

汽车车内噪声源识别方法研究进展

随着现代汽车技术的发展,汽车车内噪声已成为汽车重要性能及乘座舒适性的评价指标之一.汽车的噪声问题已引起国内外相关科技工作者的极大关注.文章阐述了汽车车内噪声源和噪声产生的机理、对各种噪声源识别方法的优缺点进行了归纳总结,并对国内外噪声的识别方法的研究现状进行了综述.     

基于传递函数估计的近场声全息的噪声源识别

在近场声全息(NAH)声场测量中,噪声的存在使近场声全息重建精度降低,影响声场重建的实现。本文提出一种基于传递函数估计的双测量面NAH技术,首先采用双测量面对噪声源信号进行测量,然后基于传递函数法引入一种合理的传递函数估计,结合参考传声器信号来求解全息面复声压,最后利用前后测量面数据相位差异来求解格林函数,根据声场重建公式进行近场声全息声场重建。数值仿真及重建误差分析表明,存在测量噪声影响的情况下,本文提出的方法相比传递函数法NAH重建误差更小,能够更准确地识别声源位置并提高声全息重建精度。最后对某型拖拉机前端进行近场阵列扫描试验,验证基于传递函数估计的双测量面NAH的有效性。     

集成运算放大电路噪声谱矩阵计算及噪声性能分析

由于集成运放电路内部具有大量噪声源,特别是运算放大器本身等效输入电压和电流噪声源的相关性,使运放电路噪声分析较困难。常用的噪声功率迭加方法由于无法考虑噪声源相关性会引起较大误差。本文提出用噪声谱矩阵表示具有噪声相关的运算放大器ｅ-ｉ噪声,推导了集成运放电路等效输入噪声谱迭加公式。不仅可以对运放电路的噪声进行准确计算及性能分析,而且可以计算电路内各噪声源的贡献,对低噪声集成运放电路参数设计有重要指导意义。     

一种汽车加速行驶噪声源识别技术

介绍了基于数据采集与信号测试分析技术的噪声源识别的一种方法,即利用噪声传递函数识别加速行驶噪声源,能够快速、精确地识别出主要噪声源。     

机械噪声的产生及其控制方法

对设备产生机械噪声的原因以及噪声的传播与辐射形式作了简要的说明和分析。例举了机械设备中常见的几种噪声源,并对其传播形式作了扼要叙述,同时针对噪声源的控制原则与步骤进行了较详细的介绍。     

微型车车外噪声的声强特征研究

从分析声强测量技术的原理出发,研究了微型车表面声强的测量条件、测量方法,分析了测量过程与结果。利用声强倍频程分析和叠加原理,合成每一测点的总声强,并通过表、图点、等声强线3种方法对车身表面声强进行表示;根据测量结果,分析了引起微型车表面噪声的分布,得出引起车外噪声的主噪声源,为进一步的降噪工作提供指导。     

水中运动声源的声全息参数选取研究

针对水中运动噪声源难以识别问题,采用声全息技术建立运动噪声源的声全息动态识别方法,详细推导全息重构公式,建立测量系统和重构声源的坐标系关系,利用采集到含有多普勒效应的声信号构造出全息数据完成重建,对运动声源的信号采集和多普勒消除等方法进行研究.利用所编制的程序进行仿真验证,分析重构参数的选取原则,给出重构频率、重构距离...     

Enhancing nearfield acoustic holography using wavelet transform

When there are low signal to noise relationships or low coherences between measured pressure and a reference sensor, a pressure field measured and estimated by NAH (Nearfield Acoustic Holography) becomes noisy on the hologram and source planes. This paper proposes a method to obtain the high coherent de-noised pressure signals from low coherent noisy ones by combining a wavelet algorithm with NAH. The proposed method obtains the de-noised field from acoustic fields on a noise source plane reconstructed through backward propagation of NAH. Thus this method does not need high coherent pressure signals on the hologram surface while the conventional nearfield acoustic holography requires high-coherent signals. The proposed method was verified by numerical simulation using noisy signals, composed of original signals and imposed noises distributed on the hologram surface.     

基于板件贡献分析的装载机驾驶室低噪声设计

分别建立某装载机驾驶室及室内声腔有限元模型,通过单点输入多点输出(single input and multiple output,简称SIMO)法模态试验验证了声振耦合模型的准确性,测取悬置点激励进行频率响应分析及室内噪声预测。对驾驶室进行声学灵敏度分析,采用声传递向量法对驾驶室进行声学板件贡献度分析并对关键板件进行形貌优化,同时添加橡胶阻尼材料抑制壁板振动,进行二次声压虚拟预测。结果表明,声学灵敏度分析可得到多阶关键声振耦合频率,声传递向量法板件贡献度分析能准确定位产生噪声峰值的关键板件,形貌优化及添加阻尼材料的方案降噪效果显著,室内总声压级降低了4.43dB。此方案系统地为低噪声车身设计提供了技术路线,减少了传统方案的主观性和重复性,缩短了研发周期,降低了研发成本。     

振速法在轴承噪声测量中的应用

分析了轴承振动和噪声关系,提出了轴承振速法测量轴承噪声的原理,以此为依据制作了噪声仪并进行了验证。试验结果表明：新型轴承噪声测试仪对轴承噪声测试行之有效,不受背景噪声影响,可以在现场环境下应用。     

同频带耦合噪声源的量化识别

提出一种将盲信号处理用于同频带耦合噪声源的量化识别新方法。盲信号处理是一种在源信号相互独立的假设下,仅利用观测信号恢复出源信号的方法。盲信号处理存在固有的幅值和顺序的不确定性,使得其只能用来进行源识别的定性分析。在不考虑顺序不确定性的前提下,利用自适应噪声抵消自适应估计传递函数的特性,消除幅值不确定性在源量化识别中的影响。理论和水池试验均验证了该方法的可行性。提出的量化识别算法,同样可以解决自适应噪声抵消中参考输入相互耦合的问题,提高其分析精度。     

基于小波域维纳滤波的光纤面板暗影检测

通过分析光纤面板透光图像的噪声性质,提出在小波去噪的始末对图像取对数、指数变换,成功转换噪声模型,有效去除高斯及斑点噪声.并提出在小波域采用维纳滤波算法以增强去噪功能,实现更为有效地去除光纤面板透光图像中的噪声.最后对去噪图像进行暗影检测,实验结果表明,采用此算法进行去噪,检测出的暗影定位更加精准,冗余信息大量减少,有...     

Gear fault diagnosis using active noise cancellation and adaptive wavelet transform

Acoustic signal from a gear mesh with faulty gears is in general non-stationary and noisy in nature. Present work demonstrates improvement of Signal to Noise Ratio (SNR) by using an active noise cancellation (ANC) method for removing the noise. The active noise cancellation technique is designed with the help of a Finite Impulse Response (FIR) based Least Mean Square (LMS) adaptive filter. The acoustic signal from the healthy gear mesh has been used as the reference signal in the adaptive filter. Inadequacy of the continuous wavelet transform to provide good time–frequency information to identify and localize the defect has been removed by processing the denoised signal using an adaptive wavelet technique. The adaptive wavelet is designed from the signal pattern and used as mother wavelet in the continuous wavelet transform (CWT). The CWT coefficients so generated are compared with the standard wavelet based scalograms and are shown to be apposite in analyzing the acoustic signal. A synthetic signal is simulated to conceptualize and evaluate the effectiveness of the proposed method. Synthetic signal analysis also offers vital clues about the suitability of the ANC as a denoising tool, where the error signal is the denoised signal. The experimental validation of the proposed method is presented using a customized gear drive test setup by introducing gears with seeded defects in one or more of their teeth. Measurement of the angles between two or more damaged teeth with a high level of accuracy is shown to be possible using the proposed algorithm. Experiments reveal that acoustic signal analysis can be used as a suitable contactless alternative for precise gear defect identification and gear health monitoring.     

应用新法规的某款卡车车外通过噪声测试方法

随着汽车行业及汽车使用环境的发展,根据我国汽车产品的实际情况,重新制订了汽车车外噪声限值及测试方法。应用车外通过噪声新的测试方法,针对某款N1类微型卡车进行车外噪声新方法的测试,确认哪些因素、参数、工况等能影响测试结果;并对比车外噪声老测试方法的测试结果,分析两者的差异性,并指导后续车型的开发设计。     

抗交串自适应噪声对消系统在管道相关检漏技术的应用

管道相关检漏技术通过对泄漏引发的振动信号的处理来完成检漏工作 ,系统原理和结构都非常简单。但在实际应用中 ,它有应用的局限性。在强噪声环境下 ,传感器接收到的包含独立噪声和公共噪声的信号 ,会导致相关曲线中出现虚假的峰值。为提高该类仪器的抗干扰性能 ,本文引入了一种新型的自适应滤波器结构——抗交串自适应噪声对消系统 (CTRANC)。在 Windows95平台上 ,我们编制了一个相关检漏软件 ,其中加入了 CTRANC模块。仿真的结果是令人满意的。     

Psychoacoustic study on contribution of fan noise to engine noise

There are more researches on engine fan noise control focusing on reducing fan noise level through optimizing fan structure,and a lot of research achievements have been obtained.However,researches on the effect of fan noise to engine noise quality are lacking.The influences of the effects of fan structure optimization on the engine noise quality are unclear.Thus,there will be a decline in fan noise level,but the deterioration of engine noise quality.Aiming at the above problems,in consideration of fan structure design and engine noise quality,an innovative method to analyze the contribution of fan noise to engine noise quality using psychoacoustic theory is proposed.The noises of diesel engine installing different cooling fans are measured by using the acoustic pressure method.The experiment results are regarded as analysis samples.The model of sensory pleasantness is used to analyze the sound quality of a diesel engine with different cooling fans.Results show that after installing 10-blade fan in medium diameter the sensory pleasantness at each test point is increased,and the increase is 13.53% on average,which indicate the improvement of the engine noise quality.In order to verify the psychoacoustical analysis,the subjective assessment is carried out.The test result shows the noise quality of engine installed10-blade fan in medium diameter is most superior.1/3 octave frequency spectrum analysis is used to study the reason of the improvement of engine noise quality.It is found that after installing proper cooling fan the sound pressure level below 400 Hz are obviously increased,the frequency assignment and spectral envelope are more reasonable and a proper cooling fan can optimize the spectrum structure of the engine noise.The psychoacoustic study is applied in the contribution of fan noise to engine noise,and the idea of engine sound quality improvement through the structure optimization is proposed.     

采样噪声对北斗全球信号测距误差的影响分析

随着北斗卫星导航系统的全球化,基于软件定义无线电的北斗接收机在北斗导航定位中的应用越来越广泛。但是北斗接收机在实时动态差分等高精度测量应用场景下,其基带采样ADC受到采样时钟抖动影响,再叠加固有的量化噪声和热噪声,对北斗信号的扩频测距精度产生不可忽略的影响。本文首先针对北斗公开的B1I、B1C、B2I、B2a和B3I 5种全球信号,描述了ADC采样中时钟抖动、量化噪声和热噪声等采样噪声的数学模型,提出了影响测距的信噪比综合公式,再通过载噪比进而得出测距误差的一般表达式,并给出了高精度测量要求下不同参数选择的工程化定量分析方法,然后针对不同参数对北斗信号测距误差的影响进行了仿真分析,仿真结果表明,在0. 6 cm的测距误差目标下,要求时钟抖动不大于45 ps,接收机中心频率不大于80 MHz,带宽不小于25 MHz,量化位数不少于7位,载噪比不小于30 d B。最后,针对北斗B2I信号进行了实测实验,在时钟抖动为35 ps,接收机中心频率61. 38 MHz,带宽32 MHz,量化位数12位,载噪比67 d B时,解算的测距误差为0. 41 cm,验证了本文方法的有效性。