SOUND RADIATION FROM A VIBRATING RAILWAY WHEEL

The sound radiation characteristics of a railway wheel are investigated by using boundary element calculations. The axisymmetry of the wheel allows an axi-harmonic formulation to be used, in which the wheel is defined by a two-dimensional mesh of its cross-section and the motion is decomposed into harmonics of different numbers of nodal diameters. The radiation ratios of the wheel, vibrating in its various normal modes, are calculated for a range of frequencies. The effects of variation in the wheel radius, web thickness and tyre depth are also investigated. From these results, simple formulae are proposed that allow the radiation ratios to be approximated closely. These are more convenient than the boundary element calculations for calculating the rolling noise from a wheel since they are a function of a few simple geometrical parameters. The directivity of wheel radiation is also considered, with comparisons with measured data indicating that simple monopole and dipole characteristics can be applied.     

虚拟现实、虚拟仪器及其对大学物理实验建设的影响

本论述了虚拟现实技术和虚拟仪器技术的内容和特点,分析了它们对大学物理实验教学的影响以及大学物理实验室建设的方向。     

一款基于声卡的虚拟信号发生器的设计

本文设计了一款成本低廉的基于计算机声卡的多功能虚拟信号发生器。将其应用于电子技术实验教学中,减少了实验所需的硬件设备,降低了实验室建设费用,使学生对实验课的兴趣更加浓厚。     

IDENTIFICATION OF CRACK LOCATION IN VIBRATING BEAMS FROM CHANGES IN NODE POSITIONS

It is known that the effect of a single crack in an axially vibrating thin rod is to cause the nodes of the mode shapes move toward the crack. This paper is an analytical/experimental investigation of the analogous problem for a thin beam in bending vibration. The monotonicity property linking changes in node position and crack location does not hold in the bending case. The analysis of the direct problem, however, shows that the direction by which nodal points move may be useful for predicting damage location. Analytical results agree well with experimental tests performed on cracked steel beams.     

虚阴极振荡微波辐射

本文概述在EPA-74脉冲线加速器上进行的虚阴极振荡微波辐射实验。1kA,400keV的电子束流经短磁线圈聚焦形成虚阴极,产生波长在6.2～11.5mm的微波辐射,峰值功率约1MW。从提高效率考虑,拟采用特殊设计的实验结构,以形成多级虚阴极振荡。     

由宽波段多光子作用产生的锂原子高位态辐射

本文报道了以６２０．０－６６０．０ｎｍ范围内任意波长激光下产生的锂原子高位态辐射的实验结果，并对有关的激光发机制进行了讨论。     

声速测定中声强的综合衰减系数的测定

本对声速测定实验中声强的衰减进行分析,介绍测量声强综合衰减系数的实验方法并给出实验结果。     

利用声反馈测声速的原理

本文提出了利用声反馈测声速的新方法，详细地给出了其理论依据     

激光产生等离子体的研究

强激光（≈１０＾８－１０＾９Ｗ．ｃｍ＾－＾２）轰击固体靶产生等离子体，用４ｋＶ电势引出，得到最高总束流峰值为４．５ｍＡ，观察到离子最高电荷态为Ｃ＾３＾＋，Ａｌ＾３＾＋，Ｃｕ＾４＾＋，Ｔａ＾５＾＋，Ｐｂ＾４＾＋。另外，还详细研究了激光能数对等离子体的影响及激光等离子体的损失。     

计算机操作中人体静电放电辐射瞬态电场与磁场的研究

分析了静电放电（ESD）辐射场的偶极子模型。用高采样速率数字示波器和定做的宽带电磁与磁场探头测量了计算机操作中人体静电放电产生的瞬态电场与磁场。用FFT分析了静电放电辐射场的频谱。研究了静民放电辐射场对某电路高频信号的影响。研究结果表明,即使是很低电压（2kV）的静电放电,其辐射近场的电场达几百V/m,磁场可达几十A/m静电放电辐射场的频谱极宽,从数兆赫到数千兆赫。静电放电对高频电路的试验结果表明,若不采取有效的防护措施,人体静电放电辐射电磁场会对电路造成一定的影响,如对集成电路与元器件造成“潜在效应”的损害,对电路造成电磁干扰,甚至损坏电子器件。     

FORMULAE OF SOUND FIELD IN ENCLOSURES

It is considered necessary that an additional term representing the direct sound be introduced into theclassical normal mode solution of sound field in enclosures,to accord with practice and to make the formu-la more useful.     

超声调制光法测量弱散射液体的声速

本文介绍一种利用超声调制光波现象测量超声波在弱散射液中传输速度的方法。     

气固两相介质音速研究

本文分析计算了不同气固两相介质的音速,与实验结果比较得到了较好的吻合,验证了普朗特的理论分析.结合汽液两相音速分析表明,求解两相介质音速时可以不考虑相变的影响.以两相音速为基础的激波结果与理想气体激波结果的趋势吻合,较基于单相音速的激波更合理,说明了两相介质音速结果的正确性.     

声波衰减的数值模拟

为了采用计算流体力学方法对热声制冷机进行数值模拟,以突破热声热机现有计算方法的限制,基于压力修正算法的基本思想开发了用于模拟非稳态小马赫数可压缩流动的数值程序,并将其应用于声波衰减的数值模拟.对一维及二维声波衰减过程的模拟显示,数值计算的结果与声学理论的预测符合良好,说明了方法的正确性.     

声速测量实验中压电接收端的声压随位置变化的规律

本文介绍了我们所研究的共振干涉接收端声压振幅方程以及用微机解此方程的数学计算方法。     

MODELLING OF VIBRATING SYSTEMS USING TIME-DOMAIN FINITE ELEMENT METHOD

In this paper, several dynamic systems are modelled using the time-domain finite element method. Galerkin's weak principle is used to model the general second order mechanical system, and is applied to the dynamics of the simple pendulum. Problems that arise during the approximation of the final momentum are also investigated. Furthermore, additional dynamic analysis methods are suggested for hybrid co-ordinate systems that have both slew and flexible modes. The proposed methods are based on both extended Hamilton's principle and Galerkin's weak principle. The matrix wave equation is propagated in a space domain, satisfying the geometric/natural boundary conditions. As a result, the flexible motion can be obtained, and this was compatible with the applied control input. A numerical example is used to demonstrate the effectiveness of the proposed modelling methods for the hybrid co-ordinate systems.     

无纤维吸声材料研究进展

简要地介绍了吸声材料的基本特点，阐述无纤维性吸声材料（特别是微穿孔板吸声结构）取代传统的纤维性吸声材料的可能性及其重要意义，较详细地介绍了近年来德国以及我国科研人员在纤维吸声材料研究上取所得的进展。     

圆柱圆锥状空腔声共振频率的测量

提出一种测量圆柱和圆锥状空腔声共振频率的方法,由微机和信号处理板配合构成的系统完成频响曲线的测量和运算,实验得到的数据和理论计算值相吻合。     

声场中的驻波模拟

本文以惠威中国消音室为案例,研究了三维长方体空间内驻波方程及对应空间的频率条件,用Matlab模拟驻波图样并计算出人的听觉范围内所有能产生驻波的频率值,为室内声学和虚拟声学研究提供了参考指标.