Numerical-experimental investigation of resonance characteristics of a sounding board

The paper presents results of numerical and experimental investigations into the vibrations of thin-walled structures, considering such their features as the complexity of geometry, the laminated structure of walls, the anisotropy of materials, the presence of stiffeners, and the initial stresses. The object of the study is the sounding board of an acoustic guitar, the main structural material of which is a three-layer birch veneer. Based on the finite-element method, a corresponding calculation model is created, and the steady-state regimes of forced vibrations of the sounding board are investigated. A good correspondence between calculation results and experimental data is found to exist. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 3, pp. 399–410, May–June, 2007.     

Sonic stop-bands for cubic arrays of rigid inclusions in air

Extensive band structures have been computed for cubic arrays of rigid spheres and cubes in air. Complete stop bands are obtained for the face-centered-cubic (fcc) structure; however, there is no gap for the body-centered-cubic (bcc) and simple-cubic (sc) structures. These gaps start opening up for a filling fraction of (27%) for spherical (cubic) inclusions and tend to increase with the filling fraction, exhibiting a maximum at the close-packing. We also propose a tandem structure that allows the achievement of an ultrawideband filter for environmental or industrial noise in the desired frequency range. This work is motivated by the recent experimental measurement of sound attenuation on the sculpture, by Eusebio Sempere, exhibited at the Juan March Foundation in Madrid (Nature 378, 241 (1995)) and complements the corresponding theoretical work (Appl. Phys. Lett. 70, 3218 (1997)). Received: 24 October 1997 / Revised: 1 December 1997 and 26 January 1998 / Accepted: 6 March 1998     

A new approach to perturbation analysis of vibration modes with close frequencies

This paper presents a new method for perturbation analysis of vibration modes with close frequencies. The main idea of this method is to transform the perturbation analysis problem of vibration modes with close frequencies into a perturbation problem associated with repeated frequencies. A numerical example is given to demonstrate the good agreement of eigensolutions obtained by this method with the exact solutions.This project is supported by National Natural Science Foundation of China     

Unsteady characteristics of the cavity flow around a rough circular cylinder

Effects of surface roughness on the unsteady cavitating flow around a two-dimensional circular cylinder were experimentally investigated at Reynolds numbers from 1.36 × 10⁵ to 1.78 × 10⁵. Two patterns of surface roughness were investigated, a double-cut pattern and a single-cut pattern. The cavity elongates with an increase of the surface roughness, especially in supercavitating flow. However, for some roughness parameters tested, the cavity length exhibits an extreme decrease. In a particular case of the double-cut pattern, there exists the minimum cavity behind the cylinder.     

双参数地基上圆（环）板轴对称稳态振动的解析解

本文应用贝塞尔函数理论，根据不同的ω值获得了双参数地基上圆（环）板轴对称稳态振动的解析解。最后，给出了一些计算结果。     

固体材料拉伸波速的共振法测量

文章系统论述了利用弯曲共振和纵向共振两种方式测量拉伸波速的方法，作者改进了传统的纵向共振测试装置，指出了两种方式各自的适用性．在理论上纵向共振方法更为严谨，且误差来源较少，从而具有较高测量精度，实验上测量操作更为方便．     

四角切圆燃煤锅炉燃烧嗓音和炉墙振动频谱特性的试验研究

本文介绍了对国产300吨／时锅炉燃烧噪音和炉内气压波动的测试情况，在测试中用磁带记录仪记录燃烧噪音和炉内压力波动信号，然后进行了频谱分析。结果表明，燃烧噪音的大小和炉墙振动的大小都随着负荷增加而增加，这表明了燃烧动力学是引起炉墙结构振动的主要原因之一。     

Vertical vibration of a circular stamp on an elastic-porous half-space with saturation fluid

A specific problem concerning the vertical vibrating response of a composite layer (elastic-porous and saturation fluid) under rigid circular stamp is studied. The motion of the medium is governed byBiot’s dynamic potential equations and the problem is solved by the method of Fourier-Bessel transformation. Formulae are obtained for the vertical displacement of the rigid phase. Graphs are presented for the amplitude of vibration.     

多自由度振动系统的简正坐标和简正振动模式

通过改变坐标标度,直接写出了多自由度振动系统的频率特征矩阵,介绍了用频率特征矩阵的伴随矩阵的任一列求简正坐标的方法,讨论了系统的简正振动模式,并举例说明.     

分立位置表象中双原子分子振动能级的计算

用离散的位置基矢作为连续位置基矢的近似,构建分立位置表象.在分立位置表象中,哈密顿算符矩阵具有对角占优、带状稀疏的特点,矩阵元不用做积分运算,具有特别简单的解析表达式.分别对双原子分子在Morse势、Murrell-Sorbie势和双阱势中运动情形,进行了数值计算.结果表明,在分立位置表象中计算双原子分子振动能级,方法简便,稳定性好,计算精度高.