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本文仔细讨论了相位算子在单模压缩态光场中的行为,计算了压缩态下相位算子的平均值和涨落。在得到了严格的、普遍性的结果后我们详细地讨论了压缩真空态这一特殊情形下的结果。此外,本文还讨论了严格的结果在经典极限下的渐近行为。 相似文献
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非线性对称平板光波导TE模色散特性的近似计算 总被引:1,自引:0,他引:1
本文利用微扰法,导出了克尔型非线性对称平板光波导TE模传播常数的近似计算公式。结果表明,本文公式得到的结果与精确结果吻合得很好。 相似文献
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本文提出一个激光振荡的模型,并根据Dekker的耗散系统的量子化程序分别用密度算子方法和Langevin方法导出激光运动方程式。与Lamb的库理论结果进行了比较,可以看到Lamb的结果是本文结果的零级近似。 相似文献
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本文针对McWhirter提出的最小二乘Systolic结构进行了有限字长误差分析,对引起误差积累的各种因素分别做了理论推导,证明了误差积累是有界的,并且误差积累的上界是不大的。本文还给出了计算机模拟的结果,它与理论结果是一致的。 相似文献
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本文在X_α方法的基础上导出了原子的电子亲合势(EA)的表达式,并用原子的X_α程序计算了74个常用原子的EA值。作者计算得到的大多数EA值接近实验结果,并总结了EA大小的一般规律。为了便于比较,还列举了其它几种方法的结果:此外,还讨论了本文结果和实验差别的一些原因. 相似文献
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利用气流调制以产生声音是一个比较有效的方法。人的发声器官、旋笛、电动气流扬声器以及一般哨子等都是根据这个原理。气流声源的特点是效率高,功率可以很大,有实用价值。关于气流声源的发声原理,过去已有一些讨论,但有的是过分简化,有的比较细致,但又过于繁复,不便计算。本文从气体动力学的基本原理出发,求得气流声源的气流-压力特性,并用图解法求得在给定气室压力和气流喷口面积比的条件下声辐射特性的方法,考虑到气流声源的气流特性和辐射关系都是非线性的,但是辐射声功率主要由基频决定,从而用近似理论求得了声功率、气流产额和气流效率的简单表达式,和严格理论的结果相比,误差不到1分贝。文中把结果画成图表以便计算,并讨论了最佳设计的问题。 相似文献
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《Journal of sound and vibration》1998,210(3):391-401
The differential equations governing the transmission of one-dimensional sound waves in a non-uniform duct carrying a subsonic compressible mean flow have been the subject of a recent debate [1, 2]. Of the two formulations presented, one is considered to be non-acoustical and the other as neglecting the spatial variation of the speed of sound. The present paper shows that both formulations are acoustical and represent valid approximations to correct conditions for isentropic sound propagation in a subsonic low Mach number duct. Each formulation is associated with an “error wave”, which is essentially a hydrodynamic wave when the mean flow Mach number is small. Three-port modelling is required, however, to capture this wave when the Mach number of the mean flow is relatively large and a numerical matrizant approach is described which can be used for this purpose. 相似文献
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S.J. KIMJ.Y. SONG 《Journal of sound and vibration》2002,258(2):309-325
The advancement of virtual reality (VR) technology in cyberspace is amazing, but its development is mainly concentrated on the visual part. In this paper, the development of VR technology to produce sound based on the exact physics is studied. Our main concern is on the sound generated from vibrating structures. This may be useful, for example, in apprehending sound field characteristics of an aircraft cabin in design stage.To calculate sound pressure from curved surface of a structure, a new integration scheme is developed in boundary element method. Several example problems are solved to confirm our integration scheme. The pressure distributions on a uniformly driven sphere and cylinders are computed and compared with analytic solutions, and radiation efficiency of a vibrating plate under one-dimensional flow is also calculated. Also, to realize sound through computer simulation, two concepts, “structure-oriented analysis” and “human-oriented analysis”, are proposed. Using these concepts, virtual sound field of an aircraft cabin is created. 相似文献
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本文评述了各向同性和横向各向同性柱状分层固体声散射理论和实验研究进展介绍了描述圆柱状界面薄层特性的弹簧模型,也讨论了该领域中有待进一步研究的一些问题。 相似文献
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本文讨论某种介质(其中包括许多球形粒子,例如浓悬浮体)对平面波的散射问题,计算了粒子之间的声相互作用场,从而得到了粒子的等效散射截面。当粒子大小比声波波长小很多时,可有如下的结论:(1)由于声相互作用,一个粒子的散射截面只有原来的Q倍,从几何上看,这是由于粒子的互相遮蔽的结果,其遮蔽因子为Q= |1-(γ0A0(1)+γ1A1(1)|2;(2)考虑到相互作用之后,散射系数与浓度不再是线性关系;(3)当粒子的尺度比声波波长小很多但比粘滞波波长大很多时,相互作用之后粒子的散射系数与频率的关系仍服从瑞利散射。但当粒子半径接近或小于粘滞波波长时,散射系数与频率的关系比四次方要高。
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单个气泡的声衰减的实验结果可以用热传导粘滞和辐射损失来解释,但对于气泡层中(这里有许多气泡)的实验来说,上述机理却不能解释。因为根据这些机理算得的理论值比实验值小很多,这一问题三十多年来尚未解决。本文考虑气泡之间的声相互作用,算得的相互作用场和原始入射场有90°的相位差,这等效于在每个气泡上附加了一项阻力,从而使其阻尼增大很多。应用本文理论与上述实验结果比较,两者符合得很好。本文理论也指出,声相互作用并不改变气泡的共振频率,只是使其共振曲线展宽。当声波频率低于共振频率时,气泡的伴振质量增大,劲度减小。当频率高于共振频率时,情况则相反。
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P. THAMBURAJJ.Q. SUN 《Journal of sound and vibration》2002,254(1):23-36
This paper presents a study on the optimization of sound transmission loss across anisotropic sandwich beams. It has been found in earlier studies that there is a significant increase in the sound transmission loss for sandwich beams with anisotropic materials compared to those with isotropic ones. The optimization studies presented in this work further validate this concept. The material and geometric properties of the structure are treated as the design variables with the objective to maximize the sound transmission loss across the beam. Appropriate constraints are imposed to maintain material and structural integrity. 相似文献
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H. DONGC. MADSHUS A.M. KAYNIAJ.M. HOVEM L.R. HOLE 《Journal of sound and vibration》2002,256(5):821-833
This paper extends an earlier study on sound propagation over poro-elastic layered ground to range-dependent and topographic ground. The model is based on a pressure-velocity finite-difference formulation and is coded in the computer program PORAC. To highlight the influence of range-dependent parameters and topographic features on sound propagation, four cases are considered: (i) a homogeneous poro-elastic half-space (the base case); (ii) the base case with a zone in the ground with a higher permeability; (iii) the base case with a zone of higher stiffness; (iv) the base case with a rectangular hill. The paper presents typical results of sound propagation in these cases comprising synthetic time histories of overpressure in the atmosphere and ground vibration as well as snapshots of the response of the atmosphere-ground system at selected times. Comparative results in these cases serve to highlight the effect of the various non-homogeneities considered in this study. 相似文献