Nonlinear Dynamics of Grains in a Liquid-Saturated Soil

A new kind of nonlinearity of inertial type caused by accelerated motionof interacting particles is described. The model deals with an ensembleof grains immersed into a vibrating fluid. First, the nonlinearvibration of two connected grains is studied. The temporal behaviours ofdisplacement and velocity, as well as spectrum of vibration, areanalysed. Numerical simulations are performed. Then an infinite chain ofgrains is considered and the corresponding differential-differenceequation is derived. For the continuum limit the inhomogeneous nonlinearwave equation is solved and temporal profiles are calculated. A newresonant phenomenon is described and the resonant curves areconstructed.     

声纳技术的应用及其最新进展

声纳技术是声学检测新技术在水下介质中的具体应用,文章简要阐述了声纳技术的原理,方法及其发展历史,介绍了声纳技术在军事和非军事方面的主要应用及其最新进展。     

量子声学及其应用

量子声学是声学的一个前沿和刚刚活跃起来的分支,是继电子学、光子学之后发展迅速的一门新学科,本文就量子声学的诞生,定义和所涉及的内容进行了讨论,较为系统地介绍了与量子声学有关的理论、材料、器件和应用进展。     

Surface shear horizontal waves associated with a periodic array of wires deposited on a substrate

The vibrational and electronic spectra of a semi-infinite crystal with a planar surface are modified by the presence of surface inhomogeneities or roughness such as ridges or grooves, quantum wires or tips. We develop a Green's function formalism to investigate the localized and resonant acoustic modes of shear horizontal polarization associated with the surface of a substrate supporting a single and a periodic array of wires. Each material is assumed to be an isotropic elastic medium. The calculation can be applied to an arbitrary choice of the shape and elastic parameters of the wires. The surface modes are obtained as well-defined peaks of the densities of states (DOS). In this paper, we calculate the variation of the density of states associated with the adsorption of a single wire, and the dispersion curves of the surface modes for a periodic array of wires on the flat surface of a substrate. We discuss their behaviors as a function of the elastic parameters and the relationship between resonant modes of the single wire and dispersion curves of the surface modes for a periodic structure. Received 6 December 2000     

The influence of absorption factors on the sensitivity of a virtual room’s sound field to scattering coefficients

Currently there is limited information on what scattering coefficients (SCs) to assign materials in geometrical room acoustic computer models. As a result, room modelers rely on general guidelines and intuition when assigning SCs. How sensitive is the predicted sound field to the user’s choice of scattering coefficients? The sound field’s sensitivity depends on its diffusivity (without SCs); the more diffuse the room’s sound field is, the less sensitive the virtual room is to the selection of SCs. In rooms with no fittings to diffuse sound energy, the sound field diffusivity is influenced by (1) room shape, (2) volume, (3) amount and (4) location of absorption, and (5) the choice of SCs. This investigation focuses only on the latter three factors. A rectangular room is modeled in ODEON v6.5 with 10 absorption schemes. These schemes vary in terms of the area of mirrored reflective surfaces, average absorption coefficient, and standard deviation of absorption. The amount of diffuse reflections at each room boundary as dictated by the SC is increased uniformly in each room. Changes in the room sound field, in particular in the reverberation time (T30), are examined at each step. Sound field diffusivity, and consequently a virtual room model’s sensitivity to SCs, is found to depend most on the area of mirrored reflective surfaces. Also, a proposed quantity called the Scattering Sensitivity Index appears to predict sound field diffusivity.     

The prediction of airborne sound transmission between two rooms using first-order flanking paths

Airborne sound transmission between adjacent rooms can be predicted using the Standard EN 12354-1 (ISO 15712-1), which is equivalent to a first-order approximation of statistical energy analysis (SEA). This paper analyses airborne sound transmission between adjacent rooms in a masonry building, by comparing results obtained from EN 12354-1 to SEA predictions and measurements. It is shown that the restriction of the Standard to first-order flanking paths can lead to large errors in predictions when compared to measurements and SEA results taking into account all transmission paths. This is observed both for individual flanking paths and overall transmission between rooms, for which the Standard provides results similar to those obtained by the first-order approximation of SEA. The paper also looks at possible reasons why previous studies using the approach in EN 12354 have generally shown good agreement with measurements.     

金属材料疲劳损伤检测的非线性声学方法*

金属材料的疲劳损伤有前期、后期两个阶段,前期疲劳损伤主要来源于位错,而随着疲劳程度的不断加深,位错密度也不断的增加,这将导致疲劳后期微裂纹的产生。这两个阶段产生声学非线性效应的机理不同,分别用位错模型、微裂纹模型对其产生非线性效应的机理进行了阐述,并对不同阶段的疲劳试样进行了相关实验研究。实验结果表明:对于材料早期疲劳损伤,随着疲劳程度的增加,其接收声波信号中的非线性谐波成分越来越显著,并且随着激励电压的增加,非线性效应更加明显,因此可用接收信号中的谐波激发情况来评估材料的早期疲劳损伤程度。而对于材料疲劳后期出现微裂纹后,其产生的非线性与早期疲劳损伤相比,谐波成分更加丰富,并且随激励电压的增加谐波幅度增加明显,可据此来判断材料中的疲劳损伤阶段。     

有界大洋对纬向风强迫的响应及共振

为揭示北太平洋主、次要气候模态即太平洋年代际振荡(PDO)和北太平洋流涡振荡(NPGO)的形成机理及其振荡周期与大洋水平尺度之间的联系,采用中纬β通道中的约化重力准平衡线性大洋模型,解析求解了纬向风强迫下的大洋流场响应,讨论了其中的共振问题.1)有界大洋的响应形态分别类似于冬季PDO和NPGO的流场模.2)响应形态分别表现为在大洋西海岸以东,前者有一个椭圆状流涡,后者有南北两个旋转方向相反的流涡并构成流涡偶;在整个大洋,前者有一个洋盆尺度环流,后者在大洋南北分别有两个旋转方向相反的洋盆尺度环流;在中纬度西风急流异常位置偏北和偏南,则能分别强迫出以上的两种情况.3)大洋流场对纬向风场强迫的响应频率(周期)与纬向风强迫频率(周期)相同,但大洋响应要滞后于纬向风的强迫;而响应流场即流函数的强度则与纬向风强迫的大小成正比.当纬向风强迫频率(周期)与该大洋固有频率(周期)相同时,二者会有共振发生,此时大洋响应最为强烈;而二者频率(周期)相差较远时,响应则不大.摩擦越小共振就越强,共振的个数也越多.有界大洋东西向的长度对其固有频率(周期)即共振频率(周期)有明显影响,并起着决定作用;当该长度减小时,相邻两个共振周期的间隔会增大.海洋大气间的两两非线性相互作用,使得随机风场的振荡包含了从极低频到高频的各种成分;通过该共振,可从中挑选出与大洋固有频率相同或相近的共振频率,在该频率上流场对风场的响应最为强烈,从而也就锁定了PDO和NPGO的周期.最终结论为:非线性相互作用、风场对流场的强迫、共振是造成PDO和NPGO的三个关键因子;该解析解的性质为时变的共振Rossby波.     

Structural-borne acoustics analysis and multi-objective optimization by using panel acoustic participation and response surface methodology

This paper is aimed to investigate the structural-borne acoustics analysis and multi-objective optimization of an enclosed box structure by using the panel acoustic participation (PAP) and response surface methodology (RSM). The acoustic frequency response function is applied to achieve the critical frequency of interest under each excitation. The PAP analysis is then carried out at all critical frequencies and the remarkable acoustic panels are identified. The correlation coefficient matrix method is proposed for reselecting and grouping the positions of acoustic panels identified to paste damping layer to control noise. With the help of faced central composite design, an efficient set of sample points are generated and then the second-order polynomial functions of sound pressure response at each critical frequency are computed and verified by the adjusted coefficient of multiple determination. The functional relationships between sound pressure responses and the thicknesses of damping layers are investigated, and multi-objective optimization of the thicknesses of damping layers is developed. The results indicate that, by using the PAP and RSM, the structural-borne acoustics at critical frequencies are calculated conveniently and controlled effectively. The optimization process of the explicit optimization model proposed in this paper is simple and the computational time is saved.     

海洋环境下的材料摩擦学研究进展与展望

海洋是人类赖以生存的载体,与人类未来发展休戚与共.海洋科学领域的发展常常依赖于海洋专用材料的研究和展.海洋极端环境下的摩擦磨损是制约海洋材料应用与推广的关键问题之一,主要表现在材料在海洋苛刻环境下的腐蚀行为、电化学腐蚀以及材料在载荷和腐蚀环境下的耦合摩擦学行为.本文中分析了海洋环境的特点及其关键摩擦学问题,阐述了海洋环境下的材料摩擦学的研究内涵,对金属材料、高分子材料、陶瓷材料在海洋环境下的摩擦学问题进行了探讨,并结合海洋材料摩擦学现有研究进展及发展趋势,对海洋环境下的材料摩擦学相关研究前景进行了展望.