转子压缩机摩擦噪声机理探究

为了研究转子压缩机摩擦噪声的形成机理,基于摩擦耦合引起摩擦系统自激振动的理论,建立了全尺寸的转子式空调压缩机摩擦噪声的有限元模型,模型中的接触对有:曲轴与上下法兰接触形成主副轴承,曲轴偏心部与滚子接触形成轴颈轴承,曲轴下偏心部端面与下法兰接触形成止推轴承.定义各个接触对的接触属性为库伦摩擦.利用复特征值分析法研究了该系...     

汽车刹车装置摩擦噪声的试验研究

本文对刹车时发出的尖叫摩擦噪声的机理进行了研究。通过对不同工况下摩擦噪声及振动的测量和频谱分析,以及对刹车装置动力学模型的分析与研究表明：尖叫摩擦噪声是由摩擦引发的高频自激振动所致。同时还探讨了这种噪声产生的原因及不同工作条件对其影响的规律。     

某车车内噪声信号的测试与分析

依据国标规定,对某车车内噪声进行测试。利用傅立叶变换对在不同转速工况下测得的噪声信号进行频谱分析,得到其关键频率。在对急加速工况分析的过程中发现虽然傅立叶变换可以分析出整体的变化规律,但不能得到其细节信息。由此采用小波分析对其进行补充,利用小波变换的“自适应变化”的时频窗结构得到信号的细节,并加以处理得到更多的频率信息。     

干扰噪声中获取有益信号的研究

把传模拟的干扰噪声与理想信号进行迭加后，使信号带有明显的噪声。通过带波滤波器后，滤掉了噪声，从而得到了有用信号。     

分形噪声中谐波信号的提取

本文提出一种分形噪声中谐波信号的提取算法。它利用小波变换对1／f噪声的白化作用,结合自适应自调谐滤波器组,在小波域实现了分形噪声与谐波信号的分离。仿真结果表明,该算法能够有效地抑制分形噪声,显著地提高信噪比。     

时滞摩擦尖叫噪声模型的稳定性研究

应用Olgac直接法对单自由度时滞摩擦噪声模型的稳定性进行了分析,建立了无摩擦尖叫噪声的稳定区域.对模型的自然频率、阻尼和接触摩擦综合系数对摩擦尖叫噪声的影响进行了数值分析.结果显示,摩擦力时滞的数值对摩擦噪声的发生有重要的影响.随着摩擦力时滞数值的增大,模型无摩擦噪声的稳定区和有摩擦噪声的不稳定区交替出现.模型的自然频率越高,就越容易发生摩擦噪声.模型的阻尼越小,也越容易发生摩擦噪声.模型的接触摩擦综合系数越大,也越容易发生摩擦噪声.对模型进行了非线性仿真分析,仿真结果显示,法向振动引起的接触分离是摩擦振动受限的一个非线性因素.     

高速工况下乘员耳侧噪声信号重构方法

高速工况下,车内噪声信号具有随机性和波动性的特征。将一种基于经验模态分解(EmpiricalModeDecomposition, EMD)和反向传输(Back Propagation, BP)神经网络的算法,用于重构车内乘员耳侧噪声信号。首先通过对车内乘员耳侧噪声贡献量分析,确定关键噪声源信号;其次对选择的噪声源信号进行EMD分解,得到有限个相对平稳的固有模态函数(Intrinsic Mode Function, IMF)分量;然后采用极值点划分法,按各个分量的波动情况进行重新划分,将信号分量重构为高频、中频和低频3个分量;最后对不同频段的部分建立相应BP神经网络模型,并将不同频段分量的重构结果叠加作为原信号的重构结果。以在某轿车采集到的5个噪声信号源为基础,利用该方法进行乘员耳侧噪声信号重构,并对其进行分析。结果表明:提出的噪声重构方法可以实现高速工况乘员耳侧噪声信号的重构,并具有良好的性能。     

音响系统中的噪声信号

噪声（通俗地叫噪音）是最常遇到的音响系统问题之一,无论是在录音制作还是扩音演出等活动中,噪声无处不在,如何尽量减小和避免噪声的干扰,认识噪声的来源和解决方法又有哪些呢？     

脑在噪声中感觉信号的能力

脑在噪声中感觉信号的能力朱兵王嘉赋胡大炜王均义王炜（南京大学物理系,生物物理研究所,南京·２１００９３）１引言人们在喧闹的茶馆里轻声谈话能互相听见,这是脑从背景噪声中感觉信号的一种能力,如何用实验来模拟和检测这种听觉功能,并从理论上解释噪声在脑识别信...     

消除图像脉冲噪声的模糊结合滤波器

提出模糊结合滤波用于消除脉冲噪声方法。它由噪声率检测、噪声污染程度W评价和模糊结合滤波器组成。根据选择中值滤波或最大最小排除均值滤波。由W确定模糊隶属函数及模糊判决规则。建立了模糊结合滤波的数学模型。模拟实验表明,椒盐噪声概率为80%时,滤波输出的峰值信噪比为25.8dB,均方误差为171,而且能很好地保护图像细节。     

Signal Processing for Remote Condition Monitoring of Railway Points

Abstract:  The dependability of railway points (turnouts or switches) is a key part of any railway system; the Potters Bar crash (10 May 2002) in the UK, which led to seven fatalities is a key example of a failure of this subsystem. Present maintenance of points involves overly frequent inspection by maintenance staff. A remote condition monitoring approach would lead to more efficient inspection routines and directed anticipatory maintenance trips. To assist the creation of a suitable fault-detection algorithm, the authors analysed existing force and current data for the 'as commissioned' case of a turnout and for situations with different fault conditions. Signal processing of this data revealed several different methods that can be used to distinguish between fully functioning points, and different fault conditions of the points. Specifically, clustering of statistical parameters and their application to wavelet levels and coefficients, provided clear discrimination of most critical faults. This demonstrates a good first step towards a condition monitoring-based maintenance regime for points that is both safer for passengers and maintenance personnel and that has the potential to be more effective and economical.     

CIS信号检测与处理技术

ＣＩＳ（接触式图象传感器）是一种新型图象传感器。由于ＣＩＳ头比ＣＣＤ部件更紧凑,因此可使的产品体积更小。阐述了ＣＩＳ的特点,基本结构和信号处理技术,另外,还介绍了自选研制的ＣＩＳ信号处理系统及ＣＩＳ的信号实侧波形。     

光纤准白光干涉信号数字化处理方法

提出一种光纤准白光干涉信号数字化处理方法。该方法采用干涉条纹脉冲实现干涉包络信 号同步采集,克服了导轨移动速度不均匀造成的影响;通过高斯函数曲线拟合方法高精度确定干涉信号零光程差点;大大提高了准白光干涉信号定位精度。为消除包络信号采样边界点不确定性带来的误差,采用外插法进行补偿。实验表明,采用该方法对光纤准白光干涉信号零光程差位置的定位精度优于0.5个干涉条纹。     

纳米测量中的光栅信号细分技术

文章介绍了一种高精度位移测量方法,以LabVIEW作为工具,对高精度线性衍射光栅干涉仪(LDGI)的正交弦波信号进行采集、处理和分析,进行准确、快速的计数和细分,计算出精确的位移,并进行方向判断.以软件进行信号处理、位移计算,并对可能存在的信号异常进行纠错,简化了硬件,减少了电气环节引入的干扰.实验数据表明:该方法有效地进行高精度位移测量,标准差在20nm以下.     

基于数字希尔伯特变换的OCT信号处理与系统实现

信号处理方法的选择是光学相干层析(OpticalCoherenceTomography,OCT)系统研制的重要环节,直接决定着OCT系统的硬件构建和实现。应用硬件实现OCT信号处理的方法虽然速度快,但存在硬件开销大,系统配置可调节性差等缺点。进而采用了基于数字希尔伯特变换的软件方法来处理OCT信号。该数字处理方法对探测得到的离散干涉实信号进行解析拓展,得到同时具有振幅信息和相位信息的复信号,其中的振幅信息被用于OCT的图像重建。介绍了研制的光纤OCT系统和各驱动单元的同步时序控制,最后给出了人体皮肤和洋葱的OCT高清晰层析图。     

振动信号短时功率谱时-频二维特征提取方法及应用

提出了一种基于图像处理技术的信号短时功率谱时一频二维特征提取方法，构造了一组对早期故障比较敏感的无量纲特征指标βm，δx和δ∑。理论分析和应用实例表明：这些特征参数比较全面地反映了信号中早期异常冲击成分的酝酿和发展，可有效地应用于旋转机械状态监测。     

空调设备噪声测试室的声学设计

空调设备的噪声指标已成为人们选择产品的一个重要衡量因素，其噪声测试室的建立正呈上升趋势，在满足声学指标的同时，兼顾空调设备噪声测试的特殊性，是设计此类噪声测试室成败的关键。文章以实际设计为例，介绍这类噪声测试室在声学设计中应采取的技术措施。     

Computational fluid dynamics simulation of friction stir welding: A comparative study on different frictional boundary conditions

Numerical simulation based on computational fluid dynamics (CFD) is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity (BV) models and the boundary shear stress (BSS) models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.     

Information processing by simple molecular motifs and susceptibility to noise

Biological organisms rely on their ability to sense and respond appropriately to their environment. The molecular mechanisms that facilitate these essential processes are however subject to a range of random effects and stochastic processes, which jointly affect the reliability of information transmission between receptors and, for example, the physiological downstream response. Information is mathematically defined in terms of the entropy; and the extent of information flowing across an information channel or signalling system is typically measured by the ‘mutual information’, or the reduction in the uncertainty about the output once the input signal is known. Here, we quantify how extrinsic and intrinsic noise affects the transmission of simple signals along simple motifs of molecular interaction networks. Even for very simple systems, the effects of the different sources of variability alone and in combination can give rise to bewildering complexity. In particular, extrinsic variability is apt to generate ‘apparent’ information that can, in extreme cases, mask the actual information that for a single system would flow between the different molecular components making up cellular signalling pathways. We show how this artificial inflation in apparent information arises and how the effects of different types of noise alone and in combination can be understood.