Predicted and measured plate velocities induced by turbulent boundary layers

A method for the prediction of velocity levels of a fuselage plate excited by turbulent boundary layers is described. The aim is to identify a method for the prediction of the relative changes of the velocity levels caused by variations of plate geometry and flight conditions. The Corcos, Efimtsov and Chase models are used to characterize the dynamic surface pressure cross-spectra. Predicted results using these models are compared with the result of in-flight measurements of plate velocities. It is found that the Corcos model gives the best agreement with the measured results for three different flight conditions. The Efimtsov extension and Chase models tend to underestimate the plate response in the lower frequency range. It is evident that the velocity level of the plate elements of the fuselage very much depends on the speed of the aircraft. An increase of the speed of the aircraft by 10% is likely to increase the plate velocity level by 3 dB and a reduction of the speed by 10% would give a reduction of 3 dB.     

高功率超声脉冲激励下金属板的非线性振动现象研究

对高功率超声脉冲作用下金属板中的超谐波、次谐波、准次谐波以及混沌等非线性振动现象进行了实验和理论研究.在实验中,高功率超声换能器产生脉冲调制的高频振动激励金属板产生非线性振动,利用激光测振技术测量不同尺寸和不同固定方式下金属板复杂的非线性振动情况,并对其进行了时序分析、频谱分析以及相空间分析.根据实验条件,提出包含非线性接触阻尼的振动-碰撞动力学模型,用以研究强超声振动-碰撞作用下的板非线性振动机制,并进行了相应的理论计算.计算结果表明,超声换能器的变幅杆与金属板之间的间歇性高频碰撞作用是金属板强非线性振 关键词： 非线性板振动 强超声脉冲激发 振动-碰撞动力学     

湍流边界层压力起伏激励下弹性板的噪声辐射

本文提出一个统一的理论计算湍流边界层压力起伏激励下无限大弹性板的噪声辐射。用波数-频率谱传递函数表征包括弹性板和流体负荷在内的整个系统的特性,导出了噪声场互谱函数的一般表示式。这是复波数平面上的一个积分,它可以归结为两类极点的留数和。由于压力起伏的迁移峰引入的极点产生直接传递的噪声场,它在流体中呈现为渐消的非均匀波,因为这个极点处在高波数区。另一些由于结构传递函数引起的极点产生带有流体负荷的板的共振辐射场。这些极点的位置和留数可以用共振散射理论进行近似计算。对于水动力噪声情况,感兴趣的频率厚度乘积相当低,这时零阶对称模式对噪声辐射起主要作用。     

Definition of road roughness parameters for tire vibration noise control

Road roughness plays an important role in the generation of tire vibration noise. However, it is unclear which kinds of road roughness parameters should be controlled to reduce the noise. In this paper, we define the essential road roughness parameters that govern tire tread vibration and provide information on tire/road noise abatement. The detailed effects of road roughness parameters on tire tread vibration are estimated using a tire/road contact model. The results reveal that pavement asperity height itself is not an essential parameter, but asperity height unevenness, asperity radius, and asperity spacing are important for the abatement of tire vibration noise.     

Interactive simulation of aircraft noise in aural and visual virtual environments

This paper describes a novel aircraft noise simulation technique developed at RWTH Aachen University, which makes use of aircraft noise auralization and 3D visualization to make aircraft noise both heard and seen in immersive Virtual Reality (VR) environments. This technique is intended to be used to increase the residents’ acceptance of aircraft noise by presenting noise changes in a more directly relatable form, and also aid in understanding what contributes to the residents’ subjective annoyance via psychoacoustic surveys. This paper describes the technique as well as some of its initial applications. The reasoning behind the development of such a technique is that the issue of aircraft noise experienced by residents in airport vicinities is one of subjective annoyance. Any efforts at noise abatement have been conventionally presented to residents in terms of noise level reductions in conventional metrics such as A-weighted level or equivalent sound level L_eq. This conventional approach however proves insufficient in increasing aircraft noise acceptance due to two main reasons – firstly, the residents have only a rudimentary understanding of changes in decibel and secondly, the conventional metrics do not fully capture what the residents actually find annoying i.e. characteristics of aircraft noise they find least acceptable. In order to allow least resistance to air-traffic expansion, the acceptance of aircraft noise has to be increased, for which such a new approach to noise assessment is required.     

Guided plate wave scattering at vertical stiffeners and its effect on source location

This paper examines guided wave transmission characteristics of plate stiffeners and their influence on the performance of acoustic noise source location. The motivation for this work is the detection of air leaks in manned spacecraft. The leaking air is turbulent and generates noise that can be detected by a contact-coupled acoustic array to perform source location and find the air leak. Transmission characteristics of individual integral stiffeners are measured across a frequency range of 50-400 kHz for both high and low aspect-ratio rectangular stiffeners, and comparisons are made to model predictions which display generally good agreement. It is demonstrated that operating in frequency ranges of high plate wave stiffener transmission significantly improves the reliability of noise source location in the plate. A protocol is presented to enable the selection of an optimal frequency range for leak location.     

船舶辐射噪声信号仿真及评价

船舶辐射噪声信号仿真应尽可能多地仿真特定船舶辐射噪声的信号特征,达到具体应用对信号仿真度的要求。对船舶辐射噪声仿真信号进行评价,是调整仿真参数和判定仿真信号是否达到要求的必要步骤。该文给出了一套对实测船舶辐射噪声信号进行重构仿真及评价的方法,仿真过程考虑了信号的听觉、连续谱、调制谱和线谱特征,评价方法对各特征进行指标提取和量化,并通过实测与仿真信号之间的相似度计算评价仿真信号的仿真度。对实测船舶辐射噪声信号进行重构仿真的试验结果显示,仿真信号具有较高的特征仿真度,与计算的仿真度评价数值一致。     

Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces

Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate's boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation.     

瓦状阻尼橡胶块对高铁车轮减振降噪的影响分析

依据声学测试标准,为了评价某型高铁车轮在安装不同形式橡胶块装置后的减振降噪效果,在半消声室内基于B&K振动噪声测试分析系统,对裸轮和橡胶块车轮开展振动声辐射室内测试实验,并基于有限元方法对车轮模态进行了仿真分析。测试结果可知:相比裸轮,WA、WB车轮模态阻尼比显著增加,车轮的减振效果明显,其中WA车轮的减振效果略优于WB车轮。径向激励下,WA车轮声功率级降低了8 dB(A),WB车轮声功率级降低了5.5 d B(A);轴向激励下,WA车轮声功率级降低了8.2 dB(A),WB车轮声功率级降低了6.2 dB(A)。分析可知橡胶块装置能有效抑制车轮的滚动噪声和曲线啸叫,对车轮的减振降噪有积极作用。     

Continuous judgment by category-ratio scaling of aircraft noise

A continuous judgment by category-ratio (CJCR) scaling method was used to evaluate the instantaneous annoyance of original and modified aircraft sounds. The result from the proposed method resulted in a temporal stream of annoyance levels for the whole flyover sequence that could be further analyzed. The test subjects were continuously rating their instantaneous annoyance on a Borg CR 100 scale® during the playback of 10 flyover sequences. Using a category-ratio (CR) scale instead of a category (C) scale, mathematical operations such as calculations of average were enabled but gave also advantages in terms of higher resolution in the responses. The results showed differences in perception in the time segment where the sound had been modified. The temporal stream of annoyance was also converted into overall judgments of the sounds, these estimations showed consistency with previous results obtained using the semantic differential and paired comparison method.     

Influence of mesoscale urban morphology on the spatial noise attenuation of flyover aircrafts

The influence of urban morphology of low-density built-up areas on spatial noise level attenuation of flyover aircrafts is investigated at a mesoscale. Six urban morphological parameters, including Building Plan Area Fraction, Complete Aspect Ratio, Building Surface Area to Plan Area Ratio, Building Frontal Area Index, Height-to-Width Ratio, and Horizontal Distance of First-row Building to Flight Path, have been selected and developed. Effects of flight altitude and horizontal flight path distance to site, on spatial aircraft noise attenuation, are examined, considering open areas and façades. Twenty sampled sites, each of 250 m * 250 m, are considered. The results show that within 1000 m horizontal distance of flight path to a site, urban morphology plays an important role in open areas, especially for the buildings with high sound absorption façades, where the variance of average noise level attenuation among different sites is about 4.6 dB at 3150 Hz. The effect of flight altitude of 200–400 ft on average noise level attenuation is not significant, within about 2 dB at both 630 Hz and1600 Hz in open areas. Urban morphological parameters influence the noise attenuation more in open areas than that on façades. Spatial noise attenuation of flyover aircrafts is mainly correlated to Building Frontal Area Index and Horizontal Distance of First-row Building to Flight Path.     

环筋对水下平底圆柱壳的声振特性影响

本文建立了计算两端带平底板的有限长圆柱壳水中声辐射的FEM／BEM三维模型，探索了加筋的高度、宽度、数目对平底圆柱壳的辐射功率、辐射效率、法向声强、声场指向性的影响规律。计算方法是在有限元软件ANSYS中做加筋平底圆柱壳建模、模态分析基础上，将有关数据（网格、模态）导入边界元软件SYSNOISE中计算流体结构耦合状态下的辐射声场特性。结果表明：（1）随着环筋高度、宽度增大，激励点声压峰和法向声强峰在0-400Hz频率范围内数目减少且峰向高频方向移动，同时辐射声功率在减小（除个别模态峰值外），而辐射效率随筋高增大而增大。（2）环筋数目的增加使激励点辐射声压和法向声强峰数目明显减少，使辐射声功率明显低于无筋圆柱壳的辐射声功率，辐射效率随环筋数目增大而增大。（3）环筋宽度变化对声场指向性影响不大；圆柱壳声场指向性随环筋高度和数目增加出现较大变化，尤其是在研究的频段内的f=51Hz和f=301Hz上。这对于水下结构辐射噪声预报以及噪声抑制具有重要意义。     

Aircraft noise annoyance modeling: Consideration of noise sensitivity and of different annoying acoustical characteristics

Noise annoyance due to aircraft flyover noise was assessed under laboratory conditions. The main objectives of the study were: (i) to identify influential acoustical features of noise annoyance, (ii) to propose noise indices to characterize these acoustical features and (iii) to enhance annoyance models including influential acoustical and non-acoustical variables. Therefore, a verbalization task was performed by the participants of the experiment to collect their whole impression concerning the aircraft flyover noises for which they rated annoyance. This verbalization task highlights that noise annoyance was influenced by three main acoustical features: (i) the spectral content, (ii) the temporal variation and (iii) the perceived sound intensity. Four combinations of noise indices were used to propose multilevel annoyance models, in combination with the individual noise sensitivity. Noise sensitivity was found to highly contribute to annoyance models and should therefore be considered in future studies dealing with noise annoyance due to aircraft noise. Different combinations of noise indices coupled with noise sensitivity were found to be promising for future studies that aim to enhance current annoyance models.     

基于听觉特性的舰船辐射噪声信号仿真

针对工程应用中对舰船辐射噪声信号仿真结果在听觉感受上模拟度欠佳的问题,建立了一种基于音色参量谱质心的辐射噪声仿真方法。采用基于实测谱的连续谱仿真模拟,并且通过整体对比实测信号的听觉特性来搜索符合特征样本音色的线谱族幅值参量,在一定程度上改善了仿真信号的听觉特征。通过仿真最优匹配度趋势来寻求最优搜索次数,用以缩短仿真时间,得到了符合工程应用的结果。     

平行场激励下压电板厚度振动的再探讨

本文进一步详细分析了平行场激励下压电板厚度振动,给出其诸振频率方程的新形式及耦合模的机电耦合系数,研究了耦合模及纯模的调频特性,并将结果用于两个实例中。     

The effect of proximity of the landing gear lights on its turbulent wake

A simplified model of a landing gear is tested in a wind tunnel to investigate the effect of the landing light location on the resulting noise generation. Examination of the near-field pressure fluctuations, combined with phase-locked stereoscopic particle imaging velocimetry of the unsteady wake identified two distinct sources of pressure fluctuations. The higher frequency source has a wide frequency band and is situated in the outer regions of the wake near the lights. On the other hand, the lower frequency source is found to be stronger, has a narrower frequency band and is developed further downstream in the wake, closer to the wake centreline. The lower frequency source is observed to be rather robust as it is hardly affected by the location of the landing lights, whereas the higher frequency source becomes weaker as the spacing between the lights is reduced. The effect of a splitter plate positioned downstream of the landing gear strut is also investigated as a means of reducing the lower frequency pressure fluctuations. Although the lower frequency source is considerably weakened by the splitter plate, substantial enhancement of the higher frequency source is observed.     

The effect of the number of aircraft noise events on sleep quality

BackgroundBoth the WHO and the EC recommend the use of L_night as the primary indicator for sleep disturbance. Still, a key question for noise policy is whether the prediction of sleep quality could be improved by taking the number of events into account in addition to L_night.ObjectivesThe current paper investigates the association between sleep quality and the number of aircraft noise events. The first aim of this study was to investigate whether, for the purpose of predicting sleep quality measured by motility, the nummer of events is adequately represented in L_night for the purpose of predicting sleep quality measured by motility. The second aim was to investigate whether the number of events at a given L_night has an additional predictive value. In addition, it was explored whether the total number of events should be taken into account for the production of sleep quality, or only the number of events exceeding a certain sound pressure level.MethodsThis study is based on data of a field study among 418 people living within a range of 20 km from Amsterdam Airport Schiphol. The data from this study are well suited for this purpose, since for every subject both the number and the exposure level of events are available. Sleep quality was measured by motility, derived from actimeters worn on the wrist, and by self-reported sleep quality scored on a 11-point scale. Mixed linear regression models were built in a stepwise manner to predict sleep quality during a sleep period time.ResultsThe results show that, given a certain equivalent noise level, additional information on the overall number of events does not improve the prediction of sleep quality. However, the number of events above L_Amax of 60 dB was related to an increase in mean motility, indicating lower sleep quality. No effect of number of events was found on self-reported sleep quality.ConclusionsThis study suggests that the number of events is more or less adequately represented in L_night and only the number of high noise level events may have additional effects on sleep quality as measured by motility. This may be viewed as an indication that, in addition to L_night, the number of events with a relatively high L_Amax could be used as a basis for protection against noise-induced sleep disturbance.     

三态噪声激励下分数阶耦合系统的随机共振现象

为了刻画在黏弹性介质中具有质量涨落的耦合粒子的运动行为,本文提出了相应模型,即三态噪声激励下的分数阶耦合系统.利用Shapiro-Loginov公式和Laplace变换,发现了粒子间的统计同步性,并得到了系统输出幅值增益的解析表达.在此基础上,针对模型涉及的关键要素,即耦合系统、分数阶系统和三态噪声,着重分析了耦合系数、系统阶数和噪声稳态转移概率对系统输出幅值增益的广义随机共振现象的影响,并给出了合理解释.具体地说,1)随着耦合系数的增大,共振现象将先增强后减弱,直至收敛.该现象表明适当的耦合作用能够促进系统共振现象的产生,体现了研究耦合系统的重要性.2)随着系统阶数的增大,共振现象将逐渐减弱.当系统阶数取值为1,即系统退化为整数阶系统时,其输出幅值增益的峰值最小,该现象说明分数阶系统能比传统整数阶系统得到更大的输出幅值增益.3)噪声稳态转移概率对系统输出幅值增益的影响会随着与之相关的其他参数的变化而变化.在一定参数条件下,三态噪声不仅能够使系统输出幅值获得比双态噪声激励时更大的增益,还能改变系统的共振类型.最后,通过数值仿真验证了上述结果的正确性.     

Reduction of radiated exterior noise from the flexible vibrating plate of a rectangular enclosure using multi-channel active control

This study attempted to control the radiated exterior noise from a rectangular enclosure in which an internal plate vibrates by acoustic excitation and noise is thus radiated from that plate. Multi-channel active control was applied to reduce the vibration and external radiation of this enclosed plate. A piezoelectric ceramic was used as a distributed actuator for multiple mode control of the vibration and radiated noise in the acoustically excited plate. To maximize the effective control, an approach was proposed for attachment the piezoelectric actuator in the optimal location. The plate and internal acoustic space in the enclosure are coupled with each other. This will change dominant frequency characteristics of the plate and, thus, those of the externally radiated noise. Active noise control was accomplished using an accelerometer attached to the plate and a microphone placed adjacent to that plate as an error sensor under acoustic excitation of sine wave and white noise. It was found that the control of radiated external radiation noise requires a microphone as an error sensor, a sound pressure sensor due to vibration of the plate, differences in the dominant frequency of externally radiated noise, and complex vibration modes of the plate.