轴对称射流气动声场的数值模拟

构造了Kirchhoff积分和CFD计算相结合的算法,采用高精度差分格式对不同喷口马赫数的轴对称射流进行数值模拟,并以此作为近场声源,运用Kirchhoff积分方法研究远场气动噪声.数值结果表明,远场噪声具有方向性,噪声声压在离开对称轴20°处达到最大值.随着传播距离增大,噪声方向性逐渐减弱.     

用HQ管抑制管道风扇噪声的数值模拟

针对HQ管抑制风扇噪声这一主动控制噪声的方法开展研究,包括理论分析和数值模拟,在圆管情况下使用HQ管的消声效果预测和HQ管各几何参数对消声效果影响的讨论.结果表明:HQ管在抑制风扇低频噪声方面有十分显著的效果.     

喷流噪声预测中小尺度湍流声源模型

本文在Tam & Auriault提出的喷流噪声预测方法的基础上,导得计算轴对称喷管伴随格林函数的方程以及声源谱、伴随格林函数与噪声谱密度函数之间的关系,比较了几种典型的声源模型,并且采用了一种随频率变化的长度尺度.验证结果表明,TA预测模型中随频率变化长度尺度与Harper-Bourne提出的声源模型的结合能给出更好的预测结果.     

喷流噪声控制方法实验研究

概述了当前国内外喷流噪声控制方法发展概况.通过实验比较了V形槽喷嘴、圆瓣形喷嘴、斜口喷嘴和凸台组合喷嘴等几种不同几何形状喷嘴在Ma=0.8～1.4范围内的喷流噪声特性及推力性能.实验结果表明,斜口喷嘴、凸台组合喷嘴降噪效果最为明显,不过两种喷嘴的推力损失较大.V形槽喷嘴和圆瓣形喷嘴有着相同的降噪机理,即能将噪声从低频段向高频段迁移,而且推力损失相对较小,有着广泛的应用前景.     

圆环电流场的普遍分布

对圆环电流在全空间的磁场分布,先用椭圆积分计算矢势,再经旋度运算求得磁场的普遍表达式,绘制磁场量值的空间分布图,而将圆环电流平面内、中心轴线上和远区的场作为特例方便地进行讨论。     

圆环电流磁场的普遍分布

对圆环电流在全空间的磁场分布,先用椭圆积分计算矢势,再经旋度运算求得磁场的普遍表达式,绘制磁场量值的空间分布图,而将圆环电流平面内、中心轴线上和远区的场作为特例方便地进行讨论.     

运动边界产生的孤立波解

本文给出了求解劝边界Boussinesq方程的差分格式,计算了动边界以不同形式运动时所产生的波。数值结果表明了孤立波解的存在。     

数值积分求解均匀带电圆环平面上的电场分布

本文用数值积分的方法计算椭圆积分，求出在均匀带电圆环平面上的场强与电势．     

q-NONLINEAR CAVITY FIELD STATES GENERATED BY THE EXCITATIONS ON A q-COHERENT STATE

It is shown that photon-excitation state defined by |α,k〉_q=a^{{\dagger k}}_q|α〉_q (k=1,2,3...) up to a normalization constant can be produced in nonlinear processes in q-nonlinear cavities. The mathematical and quantum statistical properties of this state are studied in detail. We show that this state, along with the number states absented in it, forms a complete set. We also show by numerical method that this state exhibits quantum-squeezing for some values of |α| and always reveals quantum-antibunching effect.     

Z-80微处理机组成的自动匀场装置

利用Z-80微处理机组成非闭环的负反馈自动匀场单元,实现了对F×90Q谱仪分辨率的自动调整和控制,分辨率稳定度达0.10Hz。适合各类PFT谱仪进行长时期累加实验。     

光栅计量装置中离焦误差的控制

探讨光栅成像式莫尔条纹计量装置中离焦误差的影响，提出用莫尔条纹方向的稳定性来提高光栅定位精度的方法。     

用量糖计改装的法拉第磁光效应实验装置

本文介绍一种用量糖计改装的法拉第磁光效应实验装置。磁光介质采用石榴石磁光薄膜。该实验装置结构紧凑、精度高、功耗低。     

ACTIVE CONTROL OF A MOVING NOISE SOURCE—EFFECT OF OFF-AXIS SOURCE POSITION

An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary noise source. When the primary noise source moves, the active control of the noise becomes much more difficult, as the primary noise field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving source also causes difficulties from an acoustical perspective. A moving source not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active noise control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving source, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary source moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary source moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary source.     

PROTECTING AGAINST NOISE TRAUMA BY SOUND CONDITIONING

The World Health Organization estimates that more than 12% of the world population is at risk for developing noise-induced hearing loss. At present, sound conditioning presents one means of reducing the deleterious effects of noise trauma. This phenomenon is now known to occur in a variety of mammals, including gerbils, chinchillas, guinea pigs, rabbits, rats, mice, and, of most importance, human subjects. A variety of sound conditioning paradigms have been proven successful in preventing morphological and physiological damage. Proposed mechanisms include the upregulation of endogenous antioxidants, the number of NMDA receptors, heat shock proteins, calcium buffering systems, and neurotrophic factors. Further studies are needed to understand the protective mechanisms afforded by sound conditioning. It is convincible that sound conditioning will benefit human subjects and provide a treatment for noise-induced hearing loss. The data presented in this review describe the current status and understanding of the phenomenon of sound conditioning.     

ROAD TRAFFIC NOISE INFLUENCED BY ROAD BUMPS

Noise levels from different kinds of vehicles were measured on streets close to road bumps. In comparison with free flowing traffic, the acceleration after road bumps increased peak noise levels from 1 to 13 dB (A) max. Although the results are of a pilot nature, it is suggested that noise consequences should be included in the planning of road bumps.     

一维势阱中被噪声驱动的粒子的逃逸问题

通过计算机数值模拟直接解朗之万方程，得到一维势阱中被高斯白噪声驱动的粒子的逃逸率，并与理论结果进行了对照。