电力变压器绕组振动声纹特性分析*

为更加准确分析变压器绕组的状态特征,本文提出一种基于多物理场耦合仿真的变压器绕组振动声纹特性分析方法。根据实验条件,建立变压器绕组振动噪声模型,考虑变压器绝缘油在噪声传播过程中的作用,对S13-M-200/10型号的油浸式变压器进行短路实验,测量油箱表面的振动加速度以及周围空间的声音信号。仿真结果与实测数据对比分析,油箱表面的振动加速度集中频率为100Hz,空间声音信号集中频率为100Hz和200Hz,验证仿真模型的有效性。最后,建立变压器机械故障的仿真模型,分析得到变压器发生机械故障时,声音信号中100Hz频率分量减少,200Hz频率分量增加,为变压器绕组故障诊断提供依据。     

燃料电池有轨电车声学优化*

基于线路噪声实验,系统测试分析了燃料电池有轨电车的噪声特性,研究了噪声分布以及空气传声、结构传声路径对噪声的贡献。结果表明改善车辆地板、空调、顶板和风挡的隔声性能,尤其是在500～1250 Hz的1/3倍频带范围内的隔声性能将有助于改善车辆内部声学环境。优化燃料电池系统控制,降低冷却单元转速将有助于改善车辆外部声学环境。在此基础上提出减震降噪建议措施,再次进行线路噪声实验,结果表明该措施有效。     

散热片对变压器声辐射的影响及优化分析

油浸式配电变压器表面布有大量散热片结构,使得油箱振动声辐射变得复杂.该文研究了散热片结构对油浸式变压器辐射声场的影响,在此基础上提出了散热片结构尺寸的优化措施.建立了考虑流固耦合的变压器振动和声学分析模型,提出了散热片声场效应评判准则,基于模态分析和频响分析探讨了散热片对变压器振动声辐射影响的振动效应、声源效应和声障效...     

STRUCTURE-BORNE NOISE AND VIBRATION OF CONCRETE BOX STRUCTURE AND RAIL VIADUCT

In this study, the vibration and acoustic resonance, and dominant frequency range of simple concrete box and viaduct are examined from the measurement results. A narrow band analysis—fast Fourier transform (FFT) method is used to analyze the measurement results and finite element method (FEM) is used to validate resonance frequencies for noise and vibration. The experiment of the concrete box structure is a preliminary study of analyzing resonance frequency radiated from the vibrating concrete structure since railway viaduct is a concrete box structure too. According to their noise and vibration spectra, it shows that the vibration resonance is more significant than the acoustics resonance.Based on the measurement results of the rail viaduct structure-borne noise and vibration, the relationship in terms of transfer function and coherence between noise and vibration are evaluated. They show that the dominant frequency range for noise and vibration of concrete viaduct is between 20 and 157 Hz, the resonance frequencies are 43 and 54 Hz and have significant tonal noise characteristics. The experimental results are in good agreement with the theoretical relationship between sound and vibration.     

薄膜型声学超材料对低频振动的隔声特性分析

高效共振混合机工作频率为60 Hz,且系统处于共振,产生较大低频噪声。针对振动机械产生的有害噪声,分析了高效共振混合机低频高加速度共振混合过程的特点,得到了60 Hz低频声波穿透力强的特点,相比传统的以吸声材料构建的50～100 mm厚度、隔声效果小于10 dB的隔声罩,分析了薄膜型声学超材料在低频减振降噪中的隔声特性。通过多物理场仿真分析,60 Hz时隔声量为31.4 dB,确定了硅橡胶弹性薄膜的预应力和质量块的面密度;采用3D打印机快速成型技术,构建了隔声实验装置,分析了独立隔声单元、面密度、薄膜尺寸等隔声特性规律。基于人耳在实际环境中感受到的噪声强度,提出了噪声衰减量和插入损失的分析方法,在距离声源380 mm和1000 mm的位置,60 Hz时隔声量分别为27 dB和38 dB。研究成果丰富了低频隔声特性理论,为薄膜型声学超材料的工程设计和优化提供了技术支撑。     

公路交通噪声频率特征及等效频率研究

为了确定不同车型在不同行车速度下的噪声频率分布特性及等效频率值,更加准确的对交通噪声的影响进行评估,本文对单车稳态辐射噪声的频率特性进行了现场测定,并对不同类型车辆的频率特性数据进行了分析。结果表明,不同类型车辆车速与频带声压级之间的相关性随频带中心频率的变化而变化。FHWA模型对公路交通噪声中介于500 Hz～2000 Hz频段的噪声有较好的预测效果,而对低于500 Hz和高于2000 Hz的交通噪声的预测精度较差。车辆类型不同,车辆产生噪声的中心频率、声能量集中分布的频率范围以及等效频率均不相同。     

AN ACOUSTIC TRANSFORMER COMPOSED OF HORNS AND ITS APPLICATION

A new acoustic transformer was developed by connecting three horns to improve radiation performance in the frequency region below 500 Hz. The proposed acoustic transformer was evaluated by numerical analysis using the commercial computer program SYSNOISE and by experiment. The acoustic transformer is composed of three horns, one of which was used in an inverted form. A design model was developed by use of Webster's horn equation and showed that the transformer can improve radiation efficiency. This was confirmed by numerical calculation using SYSNOISE. An acoustic projector was designed by use of the developed transformer and a piezoelectric unimorph-type actuator. The sound pressure measured at the mouth of the constructed acoustic projector was compared with the sound pressures evaluated at the same location by numerical calculation to investigate the differences between the numerical simulation model and the actual acoustic projector. Sound pressures generated by several acoustic radiators were calculated numerically and compared with the measured and calculated sound pressures of the developed acoustic projector to evaluate the effects of use of the proposed acoustic transformer. The comparative evaluation shows that the proposed acoustic transformer can provide up to a 10 dB gain over use of a horn in the narrow band low-frequency region from 100 to 200 Hz.     

船用三通调节阀流-固耦合噪声数值模拟

针对船用PN10DN32三通调节阀噪声声压频谱、声指向性等声学特性规律不明确,噪声声压级是否满足使用要求的问题,基于流-固耦合理论,同时考虑流-固耦合面及流体域内的脉动声学激励源,开展阀门噪声数值模拟研究。分别对三通调节阀在80%及60%开度阀外1 m处的噪声进行数值模拟,分析研究噪声声压频谱特性及声指向性规律。结果表明：80%及60%开度下的噪声声压级分别为49.14 dB(A)、50.79 dB(A),均小于60 d B(A)的噪声限制,满足使用要求。该文为船用三通调节阀噪声数值模拟提供了理论及方法参考。     

主变压器噪声特性分析及复合隔声结构设计*

超高压变电站的主变压器的噪声影响已引起广泛关注。以某典型化设计的500kV变电站A的主变压器为例,进行了现场测试,得到其主变压器噪声能量主要集中在中低频范围内,且具备明显的线谱噪声特征。针对该噪声特点,提出了一种内插微穿孔板的双层带孔板型声学超材料的复合隔声结构。使用传递矩阵理论对该复合结构进行了分析,并在阻抗管中进行了实验验证。实验结果表明：该复合隔声结构具备针对性隔声要求,理论与实验传递损失曲线基本吻合。     

Concrete bridge-borne low-frequency noise simulation based on train–track–bridge dynamic interaction

Both the vibration of a railway bridge under a moving train and the associated bridge-borne noise are time-varying in nature. The former is commonly predicted in the time domain to take its time-varying and nonlinear properties into account, whereas acoustic computation is generally conducted in the frequency domain to obtain steady responses. This paper presents a general procedure for obtaining various characteristics of concrete bridge-borne low-frequency noise by bridging the gap between time-domain bridge vibration computation and frequency-domain bridge-borne noise simulation. The finite element method (FEM) is first used to solve the transient train–track–bridge dynamic interaction problem, with an emphasis on the local vibration of the bridge. The boundary element method (BEM) is then applied to find the frequency-dependent modal acoustic transfer vectors (MATVs). The time-domain sound pressure is finally obtained with the help of time–frequency transforms. The proposed procedure is applied to a real urban rail transit U-shaped concrete bridge to compute the bridge acceleration and bridge-borne noise, and these results are compared with the field measurement results. Both sets of results show the proposed procedure to be feasible and accurate and the dominant frequencies of concrete bridge-borne noise to range from 32 Hz to 100 Hz.     

变压器典型工作环境对声功率测量结果的影响

变压器两侧常建有高大的防火墙,其从声学角度可视为刚性反射壁面,会改变变压器的辐射声场,进而影响变压器声功率测量结果。本文利用有限元、边界元等数值计算方法建立了变压器声辐射的仿真模型用以分析反射壁面对变压器声功率测量结果的影响,并通过实际测量验证了仿真计算所得结论。结果表明,反射壁面对变压器声功率测量结果的影响程度随反射壁面到变压器箱体距离增加而减弱,且当反射壁面距变压器箱体5 m以上时,其对变压器声功率基频及各谐波成份测量结果的影响均在2 dB以内。另外反射壁面对变压器噪声高频成份声功率测量结果的影响较大,而对100 Hz、200 Hz等低频成份测量结果影响较小,基本低于3 dB。     

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.     

The identification of sound generating mechanisms of tyres

Tyre noise is generated by several mechanisms. With a modern tyre, wall vibration, air pumping and air resonant radiation are all considered to be important. But tyre noise generating mechanisms are still not clear due to the complication of tyre vibration behaviour. Vibrations of the tyre shell are the combination of several different wave types which appear at different frequencies. In a low frequency range, where the tyre behaves like an elastically supported beam, the circular ring model is used to analyze the dispersion relations. Above 300 Hz, which is the transition point from one-dimensional to two-dimensional waveguide properties of the passenger car tyre, a cylindrical shell model is used to analyze flexural waves propagation. Two important features on the wave propagation, wave-guide behaviour and the curvature effect of the tyre wall are analyzed. In consideration of noise radiation from tyre waves, most of the tyre waves observed in this study are inefficient sound radiators since their wavenumbers are larger than the acoustic wave number. As a result, It is observed that one of the most important features in sound radiation of a tyre shell is acoustically excited wave motion of the tyre wall.     

Ambient habitat noise and vibration at the Georgia Aquarium

Underwater and in-air noise evaluations were completed in performance pool systems at Georgia Aquarium under normal operating conditions and with performance sound tracks playing. Ambient sound pressure levels at in-pool locations, with corresponding vibration measures from life support system (LSS) pumps, were measured in operating configurations, from shut down to full operation. Results indicate noise levels in the low frequency ranges below 100?Hz were the highest produced by the LSS relative to species hearing thresholds. The LSS had an acoustic impact of about 10?dB at frequencies up to 700?Hz, with a 20?dB re 1?μPa impact above 1000?Hz.     

Measurement of the resistivity of porous materials with an alternating air-flow method

Air-flow resistivity is a main parameter governing the acoustic behavior of porous materials for sound absorption. The international standard ISO 9053 specifies two different methods to measure the air-flow resistivity, namely a steady-state air-flow method and an alternating air-flow method. The latter is realized by the measurement of the sound pressure at 2 Hz in a small rigid volume closed partially by the test sample. This cavity is excited with a known volume-velocity sound source implemented often with a motor-driven piston oscillating with prescribed area and displacement magnitude. Measurements at 2 Hz require special instrumentation and care. The authors suggest an alternating air-flow method based on the ratio of sound pressures measured at frequencies higher than 2 Hz inside two cavities coupled through a conventional loudspeaker. The basic method showed that the imaginary part of the sound pressure ratio is useful for the evaluation of the air-flow resistance. Criteria are discussed about the choice of a frequency range suitable to perform simplified calculations with respect to the basic method. These criteria depend on the sample thickness, its nonacoustic parameters, and the measurement apparatus as well. The proposed measurement method was tested successfully with various types of acoustic materials.     

Development of noise and vibration ride comfort criteria.

A laboratory investigation was directed at the development of criteria for the prediction of ride quality in a noise-vibration environment. The stimuli for the study consisted of octave bands of noise centered at 500 and 2000 Hz and vertical floor vibrations composed of either 5 Hz sinusoidal vibration, or random vibrations centered at 5 Hz and with a 5 Hz bandwidth. The noise stimuli were presented at A-weighted sound pressure levels ranging from ambient to 95 dB and the vibration and acceleration levels ranging from 0.02--0.13 grms. Results indicated that the total subjective discomfort response could be divided into two subjective components. One component consisted of subjective discomfort to vibration and was found to be a linear function of vibration acceleration level. The other component consisted of discomfort due to noise which varied logarithmically with noise level (power relationship). However, the magnitude of the noise discomfort component was dependent upon the level of vibration present in the combined environment. Based on the experimental results, a model of subjective discomfort that accounted for the interdependence of noise and vibration was developed. The model was then used to develop a set of criteria (constant discomfort) curves that illustrate the basic design tradeoffs available between noise and vibration.     

A hybrid SEA/modal technique for modeling structural-acoustic interior noise in rotorcraft

This paper describes a hybrid technique that combines Statistical Energy Analysis (SEA) predictions for structural vibration with acoustic modal summation techniques to predict interior noise levels in rotorcraft. The method was applied for predicting the sound field inside a mock-up of the interior panel system of the Sikorsky S-92 helicopter. The vibration amplitudes of the frame and panel systems were predicted using a detailed SEA model and these were used as inputs to the model of the interior acoustic space. The spatial distribution of the vibration field on individual panels, and their coupling to the acoustic space were modeled using stochastic techniques. Leakage and nonresonant transmission components were accounted for using space-averaged values obtained from a SEA model of the complete structural-acoustic system. Since the cabin geometry was quite simple, the modeling of the interior acoustic space was performed using a standard modal summation technique. Sound pressure levels predicted by this approach at specific microphone locations were compared with measured data. Agreement within 3 dB in one-third octave bands above 40 Hz was observed. A large discrepancy in the one-third octave band in which the first acoustic mode is resonant (31.5 Hz) was observed. Reasons for such a discrepancy are discussed in the paper. The developed technique provides a method for modeling helicopter cabin interior noise in the frequency mid-range where neither FEA nor SEA is individually effective or accurate.     

ARJ21客机降落阶段起落架噪声试验研究

为了测量ARJ21客机的起落架噪声,在飞行现场分别采用改进的频域波束形成和解卷积算法对降落阶段的起落架噪声进行了测量。通过比较两种算法发现,解卷积算法比改进的频域波束形成算法具有更好的声源识别能力。为了提高传声器的利用率,设计了多臂螺旋阵,并且利用线性插值消除了多普勒效应。根据主起落架和前起落架的分布位置不同,将声源识别区域划分为两部分,在140—800Hz范围内对不同频段的1/3倍频程的起落架噪声进行了测量。结果发现:在250 Hz以上频段,主起落架为主要噪声源,且在中心频率500 Hz的1/3倍频程内为唯一强声源;前起落架在中心频率630 Hz的1/3倍频程内为主要噪声源。通过试验得到了主起落架和前起落架噪声在不同频段的分布特点,为起落架降噪设计提供了支持。      

Vibration and sound signatures of human footsteps in buildings

The acoustic signature of a footstep is one of several signatures that can be exploited for human recognition. Early research showed the maximum value for the force of multiple footsteps to be in the frequency band of 1-4 Hz. This paper reports on the broadband frequency-dependent vibrations and sound pressure responses of human footsteps in buildings. Past studies have shown that the low-frequency band (below 500 Hz) is well known in the literature, and generated by the force normal to the ground/floor. The seismic particle velocity response to footsteps was shown to be site specific and the characteristic frequency band was 20-90 Hz. In this paper, the high-frequency band (above 500 Hz) is investigated. The high-frequency band of the vibration and sound of a human footstep is shown to be generated by the tangential force to the floor and the floor reaction, or friction force. The vibration signals, as a function of floor coverings and walking style, were studied in a broadband frequency range. Different walking styles result in different vibration signatures in the low-frequency range. However, for the walking styles tested, the magnitudes in the high-frequency range are comparable and independent of walking style.     

Acoustic absorbers at low frequency based on split-tube metamaterials

The remarkable properties of acoustic metamaterials have attracted massive researches and applications, especially on low-frequency sound absorptions. Currently, most of the acoustic metamaterial absorbers employ resonances in plastic cavities, and their structural strengths are important in many circumstances, especially in harsh environment. However, studies of metamaterials including this point are very scarce. Here, we propose an acoustic metamaterial for low-frequency (<500 Hz) absorptions, composed of three nested square split tubes with inverted opening directions. The efficiency of the absorber is investigated both numerically and experimentally, and absorptions at the peeks are found to exceed 90% and the frequency can be effectively adjusted by tuning its geometric parameters. We further test its yield strength under compression and confirm its buckling behavior happens from the outmost layer. This tunable acoustic metamaterial with a fairly good mechanical strength may lead to broad applications in noise reduction.