主变室外部声场分布主要影响因素对比研究——以220kV户内变电站为例*

为了解决城市户内变电站噪声对环境的影响问题,研究户内变电站主变室外噪声分布状况,该文采用RAYNOISE软件对220 k V户内变电站不同类型的门窗和进风口进行模拟分析,主变室内放置1台主变压器。模拟结果显示,是否设置隔声门对室外声场的影响不大,而消声百叶对室外声场的影响较大,比普通百叶的降噪效果高3～4 d B;同时设置隔声门和消声百叶的降噪效果比普通百叶和金属门高5～6 d B。该文通过一系列的模拟计算,推导出了户内变电站主变室外部三维空间的噪声预测模型,以期为变电站的噪声控制和改造工程提供科学指导和技术支持。     

嵌入式质量块对隔声门低频段隔声性能的影响

针对隔声门低频隔声性能差的问题,将嵌入式质量应用于隔声门中以提高隔声门在低频段的隔声性能,通过建立两个相邻混响室的有限元模型计算隔声门的隔声量。基于该模型,并结合隔声门低频隔声性能的评价方法,对在低频段影响隔声门有效隔声量的相关参数进行了参数关联性研究和优化,优化结果表明：对于92 mm厚,容重24 kg/m3的玻璃棉,使用灰铸铁作为质量块,并合理布置各个质量块的大小及其在玻璃棉中的相对位置可以有效提高隔声门在低频段的隔声性能;与普通隔声门相比,在低频段嵌入式质量隔声门的有效隔声量增加了5.0 dB。     

A new laboratory facility for the determination of airborne sound insulation of party walls

The laboratory test chamber described in this paper was designed to provide a test facility for the measurement of airborne sound insulation of party walls and their associated flanking construction. Initially developed as a research tool to overcome the need to carry out field measurements on new dwelling types, the results obtained in the chamber were found to be in close agreement with the results of field measurements in dwellings with similar constructional detailing. It is concluded that a chamber of this type provides a simple and economic means of assessing in the laboratory the airborne sound insulation of dwellings.     

Cellular automaton model for evacuation process with obstacles

A bidimensional cellular automaton model is used to simulate the process of evacuation of pedestrians in a room with fixed obstacles. A floor field is defined so that moving to a cell with lower floor field means approaching an exit door. The model becomes non-deterministic by introducing a “panic” parameter, given by a probability of not moving, and by a random choice to resolve conflicts in the update of pedestrian positions. Two types of exit doors are considered: single (where only one person can pass) and double (two persons can pass simultaneously). For a double door, the longest evacuation time turns out to occur for a very traditional location of the door. The optimum door position is determined. Replacing the double door by two single doors does not improve evacuation times noticeably. On the other hand, for a room without obstacles, a simple scaling law is proposed to model the dependence of evacuation time with the number of persons and exit width. This model fails when obstacles are present, as their presence introduces local bottlenecks whose effect outweighs the benefits of increasing door width beyond a certain threshold.     

Differences between acoustical insulation properties measured in the laboratory and results of measurements in situ

The writer examines all the causes of variations in insulation properties measured in the laboratory and in the field, i.e. connections, locations, flanking walls, doors, windows, equipment and workmanship.     

The effect of construction material, contents and room geometry on the sound field in dwellings at low frequencies

An experimentally validated finite element method is used to model the sound level in rooms at low frequencies. It is demonstrated that the dimensions of rectangular rooms strongly influence the sound pressure level difference. Additional factors were investigated which are not normally considered in the frequency range where diffuse sound field conditions can be assumed. Three effects were investigated: room damping due to wall vibrations, furniture, the effect of small deviations from simple rectangular shapes. It is confirmed by field measurements that the vibrations of masonry walls and floors introduce less damping than surfaces of lightweight construction. Assigning to the FE model a damping equivalent to a surface absorption of 0.02 reproduces the effect of walls of heavyweight construction. Damping equivalent to a surface absorption of 0.15 reproduces the effects of plastered timber-frame walls, floors and ceilings. The work was briefly extended to a room pair built with heavyweight and lightweight material of construction. The modification of the shape of the room frequency response highlights well the effect of material of construction. In-situ and laboratory measurements show that furniture has little effect on steady-state room response below 100 Hz. Modelling a wall recess smaller than 0.5 m improved the agreement between prediction and measurements but the assumption of a simple rectangular room remains appropriate.     

Awakening effects of simulated sonic booms and aircraft noise on men and women

In the course of several studies, 22 male and female subjects, ranging in age from 5–75 years, have been stimulated while asleep by simulated sonic booms (ranging in intensity from 0·6 to 5·0 lb/ft² (239·5 N/m²), as if measured out of doors at ground level) and by indoor recordings of subsonic jet flyover noise (ranging in intensity from 101 to 119 PNdB, as if measured out of doors). The summarized results of these studies suggest that (i) children (5–8 years of age) are uniformly unaffected by noise during sleep; (ii) older subjects are more sensitive to noise than younger subjects; (iii) women are more sensitive to noise during sleep than are men; (iv) within an age group, individuals may vary widely with respect to their relative sensitivities to noise during sleep; and (v) the frequency of behavioral awakening is a function of the intensity of both the simulated sonic booms and the subsonic jet flyover noise.     

Sound field characteristics of underground railway stations – Effect of interior materials and noise source positions

In the case of most underground railway stations, no acoustical solutions are used to reduce train noise. Because the reflecting features of train noise in an underground station are not known, appropriate methods for controlling these features have yet to be established. The aim of this study was to clarify the sound field characteristics of underground stations by putting a sound source and receiver on the railway track and platform, respectively. The impulse responses for two vacant underground stations were measured to clarify the effects of the interior materials of the station (Comparison I), and the sound source was put in each station and tunnel to clarify the effect of the noise source positions (Comparison II). Results showed that the sound fields were similar between the stations whose lateral walls were covered with either metallic or fire-resistant wooden panels (Comparison I), and that the sound field for the sound sources near or in the tunnel presented a higher strength (G) by 5.1 dB and longer reverberation time (EDT) by 0.7 s compared to the sound source in the station (Comparison II). The sound sources in the tunnel presented strong and long reverberations at around 500 Hz due to the convergence effect of the tunnel. Therefore, this study proposes a platform screen with doors to limit noise transmission into the platform.     

Annoyance and self-reported sleep disturbances due to structurally radiated noise from railway tunnels

In Norway, the requirement for structure borne noise from tunnels is L_pAFmax = 32 dB inside dwellings. According to the Norwegian Standard 8175 it is expected that up to 20% of the exposed population are disturbed by the noise at this level. However, the scientific basis for this noise limit is poor. The aim of this study was to determine the degree of annoyance and self-reported sleep disturbances as a function of L_pAFmax. In the present study, 521 dwellings exposed to structural sound from railway rock-tunnels were identified. A questionnaire was sent to one randomly selected person above 18 years of age from each dwelling. The results showed that both noise induced annoyance and reported sleep disturbances were significantly related to L_pAFmax. Other factors that increased the annoyance were high pass-by frequency of freight trains per day, and degree of sound insulation of the windows. At L_pAFmax = 32 dB, 20% were slightly or more than slightly annoyed, and 4% were moderately or more than moderately annoyed. According to the pre-existing assumption that up to 20% of the exposed population are disturbed by the noise at this level, the present results give support to the Norwegian noise limit L_pAFmax = 32 dB inside dwellings of structure borne noise from railway tunnels.     

Power requirements for active noise control in ducts

Active attenuation of noise in a duct generally requires either one or two rings of cancelling loudspeakers located around the duct perimeter. Consideration is given to the acoustic loading on the loudspeakers and it is shown that the use of a horn is likely to create more problems that it solves. Direct radiator operation, with the drive units attached directly to the duct walls, is preferable. The single ring (monopole) system reflects the noise giving rise to upstream standing waves, meaning that the loudspeakers and amplifiers must be able to handle correspondingly larger signals. The double ring (dipole) system absorbs the noise and is more efficient than the monopole system. The dipole system can be made still more efficient over a narrow band of frequencies by tuning both the loudspeakers and the spacing between them.     

Influence of dephasing on shot noise in an electronic Mach-Zehnder interferometer

We analyze shot noise under the influence of dephasing in an electronic Mach-Zehnder interferometer, of the type that was realized recently [Nature (London) 422, 415 (2003)]]. Using a model of dephasing by a fluctuating classical field, we show how the usual partition noise expression T(1-T) is modified. We study the dependence on the power spectrum of the field, which is impossible in simpler approaches such as the dephasing terminal, against which we compare. We remark on shot noise as a tool to distinguish thermal smearing from genuine dephasing.     

某MPV前门区域风噪啸叫与密封优化分析

为解决某MPV前门区域发生“呜呜”风噪啸叫问题,路试验证密封条、车门、A柱区域密封系统以及采用格子波尔兹曼（LBM）方法模拟风洞仿真分析A柱、侧窗区域流场。结果表明车门侧密封条和A柱钣金空腔的气流从密封条唇边泄露,与A柱区域的涡流形成耦合振动,产生啸叫。啸叫问题与车门侧密封条、车门以及A柱造型有关。更改车门侧密封条外唇边根部材料提高压缩负荷,并在与A柱接角处增加两个凸筋,进一步试验验证,啸叫消失,问题得到解决。     

浙江古城墙传统灰浆材料的分析研究

灰浆材料一直是古代建筑类文化遗产研究的重要对象,文保工程中使用传统灰浆的诸多优点已广为人知,在认识传统灰浆的基础上开发新的石灰基粘结保护材料已然成为国际研究热点。随着中国的经济发展,很多古建筑的保护也开始提上日程,然而关于中国传统灰浆材料的研究颇为薄弱。实地调查浙江地区多座古代城墙遗址,采集灰浆样品,利用多功能密度仪、粉末X射线衍射仪(XRD)、傅里叶红外光谱仪(FTIR)、热重-差热分析仪(TG-DSC)和湿化学分析技术,对浙江地区7处古城墙灰浆样品进行了分析检测和研究。结果表明：这些古城墙使用的胶结材料是纯“白灰灰浆”,主要成分是碳酸钙,含量在75%～90%之间,其原料主要是钙质生石灰,个别来自镁质生石灰;其中有4座城墙灰浆添加有糯米成分,说明该地区在明代向灰浆里添加糯米等有机材料是建筑城墙十分普遍的工艺技术;检测发现这些建筑灰浆的密度较低,且数值相差较大,在1.2～1.9 g·cm-3之间,应是环境长期侵蚀的结果。同时,也分析了这些砌筑灰浆的其他物化特征,为下一步古城墙本体保护和保护材料的研发,以及传统灰浆全国范围内的比较研究提供了科学依据。     

Interferometric and noise signatures of Majorana fermion edge states in transport experiments

Domain walls between superconducting and magnetic regions placed on top of a topological insulator support transport channels for Majorana fermions. We propose to study noise correlations in a Hanbury Brown-Twiss type interferometer and find three signatures of the Majorana nature of the channels. First, the average charge current in the outgoing leads vanishes. Furthermore, we predict an anomalously large shot noise in the output ports for a vanishing average current signal. Adding a quantum point contact to the setup, we find a surprising absence of partition noise which can be traced back to the Majorana nature of the carriers.     

Analytical prediction of break-out noise from a reactive rectangular plenum with four flexible walls

This paper describes an analytical calculation of break-out noise from a rectangular plenum with four flexible walls by incorporating three-dimensional effects along with the acoustical and structural wave coupling phenomena. The breakout noise from rectangular plenums is important and the coupling between acoustic waves within the plenum and structural waves in the flexible plenum walls plays a critical role in prediction of the transverse transmission loss. The first step in breakout noise prediction is to calculate the inside plenum pressure field and the normal flexible plenum wall vibration by using an impedance-mobility approach, which results in a compact matrix formulation. In the impedance-mobility compact matrix (IMCM) approach, it is presumed that the coupled response can be described in terms of finite sets of the uncoupled acoustic subsystem and the structural subsystem. The flexible walls of the plenum are modeled as an unfolded plate to calculate natural frequencies and mode shapes of the uncoupled structural subsystem. The second step is to calculate the radiated sound power from the flexible walls using Kirchhoff-Helmholtz (KH) integral formulation. Analytical results are validated with finite element and boundary element (FEM-BEM) numerical models.     

Experimental investigation on environmental noise inside dwellings

This research deals with the problem of evaluating the community noise inside dwellings, when traffic noise is to be considered as a reference term for determining the nuisance due to a superimposed disturbing noise of a different nature. A number of 24-h sampling recordings of environmental noise inside various dwellings in Rome are analysed, both with and without a superimposed industrial noise. The commonly accepted ISO criterion, based on the difference between the disturbing noise level and the background noise level in db(A), is compared with the method of the L_DI index which directly measures the noise nuisance.     

A hybrid finite element – statistical energy analysis approach to robust sound transmission modeling

When considering the sound transmission through a wall in between two rooms, in an important part of the audio frequency range, the local response of the rooms is highly sensitive to uncertainty in spatial variations in geometry, material properties and boundary conditions, which have a wave scattering effect, while the local response of the wall is rather insensitive to such uncertainty. For this mid-frequency range, a computationally efficient modeling strategy is adopted that accounts for this uncertainty. The partitioning wall is modeled deterministically, e.g. with finite elements. The rooms are modeled in a very efficient, nonparametric stochastic way, as in statistical energy analysis. All components are coupled by means of a rigorous power balance. This hybrid strategy is extended so that the mean and variance of the sound transmission loss can be computed as well as the transition frequency that loosely marks the boundary between low- and high-frequency behavior of a vibro-acoustic component. The method is first validated in a simulation study, and then applied for predicting the airborne sound insulation of a series of partition walls of increasing complexity: a thin plastic plate, a wall consisting of gypsum blocks, a thicker masonry wall and a double glazing. It is found that the uncertainty caused by random scattering is important except at very high frequencies, where the modal overlap of the rooms is very high. The results are compared with laboratory measurements, and both are found to agree within the prediction uncertainty in the considered frequency range.     

Structural acoustic silencers--design and experiment

The effectiveness of introducing flexible structural layers into air conveying ducts for controlling noise is investigated through theoretical and experimental means, focusing at low frequencies where conventional passive silencing technology is least effective. Previous theoretical work has shown that using flexible rather than rigid walls has the potential to achieve high transmission losses. The physical mechanisms responsible for structural acoustic silencing, including the relation between transmission loss peaks and structural resonance corresponding to different transverse structural modes, are presented. Sensitivity of the performance to acoustic and structural boundary conditions is discussed. To eliminate radiated noise from these walls (breakout noise), a rigid walled cavity is introduced under the flexible plate. The challenge is to find means to reject plane waves in the two-duct system. Designs that overcome these issues and achieve appreciable transmission loss are investigated. Results based on three-dimensional finite element simulations are compared with experimental results.