国产吸声材料的吸声系数测定的初步报告

本报告首先列举用驻波分析法所测得的若干国产吸声材料——包括纤维板,木屑板,木丝板,玻璃绵砖,毛毡及棉絮等等——的声波垂直入射的吸声系数,并对于吸声系数的定义以及几种不同吸声系数间的转换问题也作了简单的讨论。测量结果指出:许多产品吸声效率都很低,特别是在低频。(某些产品作为“薄板吸声”来控制室内音质是可以的,但不宜当作多孔性材料来使用。某些厂家在广告中注以“隔声”和“隔热”等名词尤其是不恰当的。)其次,对于(1)材料粉刷,涂漆,和穿孔的影响,(2)有效厚度和流阻的关系,以及(4)薄板,薄的多孔性材料,和穿孔吸声结构的吸声性能等,都作了测量,并附以必要的理论说明。对于穿孔吸声结构阐述较多,主要是由于这种吸声结构应用的范围可以很广泛而目前国内使用得还远不够多。最后作者们根据所测定的结果,对国内吸声材料的使用和制造提出了一些初步的建议。     

三维声传播模型BELLHOP3D的信息传递接口并行优化

近些年,我国对海洋不断深入的探索对复杂环境中声场的快速预报提出了越来越高的需求。BELLHOP3D是一种基于射线法的三维声传播计算模型,在海洋声学中应用十分广泛。BELLHOP3D的计算效率比其他常用模型高,但是仍然有非常大的提升空间。该文使用信息传递接口对BELLHOP3D进行粗粒度的并行优化,并行后的程序计算结果稳定可靠,并行效率高,更适合在实际应用中实现快速的声场预报。并行BELLHOP3D程序可以在https://github.com/nj-zyq/BELLHOP3D＿MPI.git下载。     

Neural networks for prediction of acoustical properties of polyurethane foams

This paper presents a study of neural networks for prediction of acoustical properties of polyurethane foams. The proposed neural network model of the foam uses easily measured parameters such as frequency, airflow resistivity and density to predict multiple acoustical properties including the sound absorption coefficient and the surface impedance. Such a model is quite robust in the sense that it can be used to develop models for many different classes of materials with different sets of input and output parameters. The current neural network model of the foam is empirical and provides a useful complement to the existing analytical and numerical approaches.     

Use of a hybrid adaptive finite element/modal approach to assess the sound absorption of porous materials with meso-heterogeneities

The paper discusses the sound absorptive performance of a porous material with meso-perforations inserted in a rectangular waveguide using a numerical hybrid adaptive finite element-modal method. Two specific applications are investigated: (i) the improvement of porous materials noise reduction coefficient using meso-perforations (ii) the effects of lateral air gaps on the normal incidence sound absorption of mono-layer and two-layer porous materials. For the first application, a numerical design of experiments is used to optimize the sound performance of a porous material with meso-perforations with a reduced number of numerical simulation. An example in which the optimization process is carried out on the thickness and size of the perforation is presented to illustrate the relevance of the approach. For the second application, a set of twenty fibrous materials spanning a large flow resistivity range is used. Practical charts are proposed to evaluate the influence of air gaps on the average sound absorption performance of porous materials. This is helpful to both the experimenter regarding characterization of porous material based on Standing Wave Tube measurements and for the engineer to quantifying the impact of air gaps and for designing efficient absorbers.     

An example of in-plant noise reduction with an acoustical barrier

Existing theories for predicting the distribution of sound intensity in rooms and the performance of acoustical barriers are applied in designing a barrier to reduce noise in an industrial environment. The combination of the theories is found to predict the sound pressure level in the barrier shadow zone reasonably well.     

Two-dimensional poroelastic acoustical foam shape design for absorption coefficient maximization by topology optimization method

Optimal shape design of a two-dimensional poroelastic acoustical foam is formulated as a topology optimization problem. For a poroelastic acoustical system consisting of an air region and a poroelastic foam region, two different physical regions are continuously changed in an iterative design process. To automatically account for the moving interfaces between two regions, we propose a new unified model to analyze the whole poroelastic acoustical foam system with one set of governing equations; Biot's equations are modified with a material property interpolation from a topology optimization method. With the unified analysis model, we carry out two-dimensional optimal shape design of a poroelastic acoustical foam by a gradient-based topology optimization setting. The specific objective is the maximization of the absorption coefficient in low and middle ranges of frequencies with different amounts of a poroelastic material. The performances of the obtained shapes are compared with those of well-known wedge shapes, and the improvement of absorption is physically interpreted.     

Inverse acoustical characterization of natural jute sound absorbing material by the particle swarm optimization method

For modeling of jute as acoustic material, knowledge of its non-acoustical parameters like porosity, tortuosity, air flow resistivity, thermal and viscous characteristic lengths is a prime requisite. Measurement of these non-acoustical parameters is not straightforward and involves a dedicated measurement setup. So in order to overcome this issue, the inverse acoustical characterization can be used. In this paper, the particle swarm optimization method (PSO) is used as an optimization method. This method estimates the non-acoustical parameters of jute material in felt form by minimizing the error between experimental and theoretical sound absorption data. In this work, the impedance prediction models for fibrous materials like Johnson–Champoux–Allard model with rigid and limp frame and Garai–Pompoli model is used for sound absorption coefficient calculation by the transfer matrix method along with the PSO. The inverse estimated non-acoustical parameters for jute material are then compared with estimated and experimentally measured parameters for jute felts. Using these inversely predicted parameters, sound absorption of multilayer sound absorbers is also studied.     

Numerical evaluation of tree canopy shape near noise barriers to improve downwind shielding

The screen-induced refraction of sound by wind results in a reduced noise shielding for downwind receivers. Placing a row of trees behind a highway noise barrier modifies the wind field, and this was proven to be an important curing measure in previous studies. In this paper, the wind field modification by the canopy of trees near noise barriers is numerically predicted by using common quantitative tree properties. A realistic range of pressure resistance coefficients are modeled, for two wind speed profiles. As canopy shape influences vertical gradients in the horizontal component of the wind velocity, three typical shapes are simulated. A triangular crown shape, where the pressure resistance coefficient is at maximum at the bottom of the canopy and decreases linearly toward the top, is the most interesting configuration. A canopy with uniform aerodynamic properties with height behaves similarly at low wind speeds. The third crown shape that was modeled is the ellipse form, which has a worse performance than the first two types, but still gives a significant improvement compared to barriers without trees. With increasing wind speed, the optimum pressure resistance coefficient increases. Coniferous trees are more suited than deciduous trees to increase the downwind noise barrier efficiency.     

声学二维平面周期结构的吸声性能建模

声学周期结构兼具优化室内声场环境,节约建筑吸声材料的特性而在现代建筑中广泛使用。针对二维平面周期结构的声场优化特性,建立了一种吸声系数计算模型。首先,根据边界条件理论推导了吸声系数的线性方程组,继而通过数值分析方法进行求解,最后在驻波管和混响室中分别进行实验验证。实验结果表明,测量的吸声系数和理论计算曲线吻合良好,该模型可以准确测算二维平面周期结构的吸声系数。同时分析表明:在平面周期结构中,相同吸声材料面积情况下,吸声材料占比越大,吸声效果越好;在相同吸声材料面积和占比情况下,材料边缘长度越长,高频段吸声效果越好;随着材料边缘长度的减少,边缘效应影响减弱。      

船舶球鼻艏导流罩声障板参数对艉部声场的影响

本文研究了声障板相关参数对球鼻艏导流罩内声纳艉部声场的影响。对某舰缩比模型罩建立了有限元模型，然后运用有限元法声学分析软件，计算了某些频率下声源定向发射的声衰减特性和声场特性。计算结果与已进行的模型罩消声水池的试验结果吻合良好。     

Optimisation with genetic algorithm of the acoustic performance of T-shaped noise barriers with a reactive top surface

In this study, the aim is to optimise the acoustical efficiency of T-shaped noise barriers whose top is covered with a series of wells. This research work uses an optimisation method in order to find the best noise barrier profile considering several variable parameters. Numerical simulations of the acoustical propagation are achieved by use of a 2D boundary element method code. The optimisation part is carried out with a global and direct evolutionary optimisation method: a genetic algorithm. The parameters to optimise are the shape of the protection (the depths of the wells on the crowning) and the flow resistivity of absorbing materials considered. The cost function to maximize is defined through a mean value of the acoustical efficiency of the protection compared to a reference configuration, averaged on several receiver points. Final results show significant optimised values of parameters for efficient protections in order to improve classical noise barriers.     

Passive acoustic tomography of the ocean using arrays of unknown shape

It was recently established that ocean acoustic tomography based on an inversion of ray travel times can be implemented without use of any dedicated sound sources by cross-correlating the ambient noise recorded on two line arrays, the shapes of which are known. In contrast to active tomography, the amount of useful information from noise interferometry is proportional to the product of the numbers of receivers in the two arrays. In our study based on the 2D and 3D numerical experiments, we examine a hypothesis concerning the feasibility of simultaneous performance of a passive ray tomography and passive positioning of arrays through cross-correlation of ambient or shipping noise. The numerical experiments are conducted under conditions close to those of a field experiment on passive ocean tomography. It is demonstrated that, when using arrays of 20–40 hydrophones, the sound velocity profile and the array shape can be found from noise correlation to an accuracy adequate for oceanological and acoustic applications.     

Studies of parallel barrier performance by acoustical modeling

An investigation is presented into the performance of parallel barrier configurations, using acoustical scale modeling. A realistic geometry is investigated, with the source being positioned over a paved roadway and the receiver over grass-covered ground. The grass-covered ground surface was properly modeled in terms of its impedance. Results were obtained for a range of barrier types, and demonstrate that frequency dependent effects are evident in barrier insertion loss data. In most cases, the barrier on the far side of the source did not significantly affect sound levels at the receiver. The most effective barrier design was found to be that of a gradual grass-covered slope up to an upright, thin barrier.     

Sound transmission of an active acoustic structure with porous materials based on the(u,p) formulation

<正>A method based on the combination of the(u.p) formulation and finite element method was applied to calculating the acoustical performance of a double-wall active acoustic structure with porous materials.The(u,p) formulation based on the displacement in solid phase and the pressure in fluid phase was developed to investigate the sound propagation in porous materials.The acoustic performance of the double-wall active acoustic structure having porous materials was calculated and the measurement was taken.The numerical results matched well with the measured data.More than 10 dB transmission loss of the double-wall active acoustic structure can be improved in the resonance frequency with active control,and its absorption coefficient is up to 0.6 over 500 Hz.The relative error between the prediction and measurement is less than 5%at the resonance frequency of the porous materials.     

Minimum acoustical requirements for school buildings

Present-day schools need to be considered from the acoustical point of view to a much greater extent than the formalised schools of a few generations ago, because of the current increase in noise levels in such buildings.The acoustical design of school buildings requires that the selection of the site, as well as the control of exterior and interior noise throughout the whole building, must be taken into consideration.A method for determining the minimum distance between school buildings and various noise sources is presented.The minimum thickness of various building materials for facades and inner partitions which meets sound insulation specifications is calculated.     

小阻尼封闭空间声压级灵敏度分析与优化设计

本文研究了小阻尼界面封闭空间低频声学有限元分析、灵敏度分析和优化设计问题。分别用模态法和直接法计算了封闭空间内声压级响应，并推导了声压级响应对声空间边界形状控制参数的灵敏度分析公式，在此基础上建立了小阻尼空间声学问题的优化模型，同时给出了优化求解算法，并在JIFEX软件中进行了程序实现。本文提出的灵敏度分析和优化设计方法可以使声场的边界布局更为合理，从而达到改进小阻尼界面封闭空间声学性能的目的。数值算例验证了本文提出的灵敏度分析和优化算法的有效性。     

耦合声阻抗在扩散吸声体设计中的应用研究

为解决小房间的音质设计问题,需要设计不同的扩散吸声体。利用共振吸声的边缘效应,通过不同共振频率的共振器耦合共振时的非线性声阻抗变化组合,形成既能高效吸声,又能均匀散射的声学界面。数值分析及实验结果表明,新型的扩散吸声体内部没有任何传统吸声材料的情况下,单位面积吸声量在中低频段可达1.3 m2,在高频段由于非线性声阻抗与共振器的辐射阻抗不匹配影响,相应吸声量降低到0.7 m2左右。耦合声阻抗的运用使得新型扩散吸声体吸声的效率高,频带宽,免去传统吸声材料的使用,在小房间的声学应用中具有突出的优势。     

Computational studies of steady-state sound field and reverberant sound decay in a system of two coupled rooms

The acoustical properties of an irregularly shaped room consisting of two connected rectangular subrooms were studied. An eigenmode method supported by a numerical implementation has been used to predict acoustic characteristics of the coupled system, such as the distribution of the sound pressure in steady-state and the reverberation time. In the theoretical model a low-frequency limit was considered. In this case the eigenmodes are lightly damped, thusthey were approximated by normal acoustic modes of a hard-walled room. The eigenfunctions and eigenfrequencies were computed numerically via application of a forced oscillator method with a finite difference algorithm. The influence of coupling between subrooms on acoustic parameters of the enclosure was demonstrated in numerical simulations where different distributions of absorbing materials on the walls of the subrooms and various positions of the sound source were assumed. Calculation results have shown that for large differences in the absorption coefficient in the subrooms the effect of modal localization contributes to peaks of RMS pressure in steady-state and a large increase in the reverberation time.      

Sustainable acoustic absorbers from the biomass

There is currently considerable interest in developing sustainable absorbers, either from biomass materials or recycled materials, and it is the former that is the subject of this paper. A number of potential candidate materials are available from the biomass in the form of organic fibres. Non-fibrous materials, such as configurations of whole straw or reed, can also act as sound absorbers. A combination of impedance tube and reverberation chamber measurements have been carried out for a number of biomass materials and the effectiveness of current models for the prediction of the absorptive properties of natural fibres has been investigated. Examination of the acoustical characteristics of a range of natural fibres has confirmed their effectiveness as porous sound absorbers and also the limitations of current models for predicting their performance. Examination of the acoustical performance of materials consisting of different configurations of whole reeds and straws has revealed that these also possess considerable potential for application as broadband sound absorbers with particularly good low frequency absorption characteristics. The combination of natural fibres and whole reeds offer the possibility of developing a range of sustainable absorbers which act very effectively across the complete audio frequency range.     

Acoustical characteristics of porous materials

The diversity of porous materials is noted. However, this study is particularly relevant to the use of sound absorbent materials in architectural acoustics. The theory of sound propagation within an idealised porous material consisting of a rigid matrix through which run parallel cylindrical pores normal to the surface is reviewed. Extensions to pores of arbitrary orientation and cross-section are achieved by introducing physically-measura ble microstructural constants rather than phenomenological bulk parameters that might be frequency dependent. By comparison of several theories that account for sound propagation within an elastically-framed porous material a basis is laid for an improved formulation, that takes into account both viscosity and heat conduction.The application of various propagation theories to model the reflection and transmission of sound at porous boundaries is considered. Particular attention is paid to the common assumption of local reaction and to the adequacy of modelling the porous interface as that of a quasi-homogeneous fluid. Finally the most widely used methods of measuring acoustical characteristics of porous materials at normal and oblique incidence and of obtaining their values by empirical means are surveyed.