共查询到20条相似文献,搜索用时 15 毫秒
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K S Viswanathan 《Pramana》1986,27(1-2):307-320
An expression has been derived for the collision operator for phonons in a solid, which is valid at very low temperatures.
The set of coupled equations for the elastic deformation and the phonon density or second sound has been reduced to a simple
tractable form and the dispersion equation for the coupled waves consisting of the acoustic modes and second sound has been
derived. It is shown that only the longitudinal mode interacts with the second sound. It is also shown that as a result of
the interaction with the second sound, the longitudinal velocity along the principal axis acquires a correction term that
is proportional to bothγ
2 andT
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The author felicitates Prof. D S Kothari on his eightieth birthday and dedicates this paper to him on this occasion. 相似文献
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M.M. Späh 《Applied Acoustics》2009,70(2):361-368
A method for characterisation of structure-borne sound sources is proposed and investigated for the special but common case of machines in heavy-weight homogeneous building structures. The method is based on the concept of the reception plate where the total structure-borne sound power from the machine under test is assumed equal to the power dissipated by a plate attached to the machine. The method is relatively simple and allows comparison of sources on a power basis, and of tests results at different laboratories. Additionally the data obtained is in a form suitable for transformation into an installed structure-borne power and thence for the resultant sound pressure generated in buildings. The method is validated by cross-spectral and mobility methods. A study of the uncertainty of the power estimate was performed by numerical modelling and measurement. 相似文献
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An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average. 相似文献
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It has long been recognized that single-number quantities R′w, DnT,w or Dn,w result in different conclusions in objective rating of airborne sound insulation between dwellings. The difference between the values of these single-number quantities (SNQ), however, does not prove which of them describes the sound transmission between rooms most correctly. The main object of this article was to study which SNQ correspond best with transmitted living sound levels in buildings when reverberation time, volume of receiving room and sound insulation are taken into account. Data of 100 field measurements of airborne sound insulation were collected as well as 207 reverberation times of furnished rooms. The transmitted sound levels of living sounds were evaluated on the basis of known living sound spectra and measured level differences D. The results show that the SNQs standardized to reference reverberation time of 0.5 s lead in all cases to best correlation between the SNQs and the sound levels of transmitted living sounds. It was also checked whether the rating by DnT,w would lead to higher transmitted sound levels of living sounds in larger rooms, but this was not detected. The use of DnT,w makes rooms of different volumes equal in regard to required sound insulation between them. It is thus justified to replace R′w with DnT,w as the SNQ for rating the airborne sound insulation. Widening the frequency range down to 50 Hz or up to 5000 Hz did not give noteworthy improvement in the correlation. 相似文献
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Three-dimensional coupled-mode model and characteristics of low-frequency sound propagation in ocean waveguide with seamount topography 下载免费PDF全文
Ya-Xiao Mo 《中国物理 B》2022,31(8):84301-084301
Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional (3D) coupled-mode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the 3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order Padé approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount. 相似文献
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The role of the phase-dependent nonlinear processes that accompany the interaction of a weak signal wave with an intense pump wave is investigated for the case of the pump frequency being a multiple of the signal frequency. Phase relations that provide the maximum absorption of sound by sound are determined. It is shown that, as the frequency ratio of the waves increases, the role of the phase-dependent absorption rapidly decreases and becomes negligible. 相似文献
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近些年,我国对海洋不断深入的探索对复杂环境中声场的快速预报提出了越来越高的需求。BELLHOP3D是一种基于射线法的三维声传播计算模型,在海洋声学中应用十分广泛。BELLHOP3D的计算效率比其他常用模型高,但是仍然有非常大的提升空间。该文使用信息传递接口对BELLHOP3D进行粗粒度的并行优化,并行后的程序计算结果稳定可靠,并行效率高,更适合在实际应用中实现快速的声场预报。并行BELLHOP3D程序可以在https://github.com/nj-zyq/BELLHOP3D_MPI.git下载。 相似文献
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The result of a measurement is an approximation of the true value of the measurand and is complete when it is accompanied by its uncertainty. Building acoustics requires an assessment of the uncertainties that is understandable and corresponds closely to reality. The new standard ISO 12999-1 gives general uncertainty values for typical sound insulation measurements. The objective of this work is to determine the most accurate method for evaluating the uncertainty of in situ façade sound insulation measurements for both the Dls,2m,nT values in one-third octave bands and the global magnitude Dls,2m,nT,w. We establish a comparative analysis between the uncertainty values proposed by the standard ISO 12999-1, the uncertainty values deduced from interlaboratory activities and the average uncertainties deduced from individual calculations for each in situ measurement. The comparison is based on uncertainty calculations for around 1000 in situ façade sound insulation measurements made by our laboratory. The uncertainties given by the standard ISO 12999-1 for Dls,2m,nT in one-third octave bands are, at low and high frequencies, higher than the values deduced from individual calculations and smaller than the calculated values at mid frequencies. We believe that for Dls,2m,nT, it is advisable wherever possible to make individual uncertainty calculations for each in situ façade measurement. Nevertheless, the comparison with ISO 12999-1 points to the suitability of including some uncertainty components in the calculation, such as the related to the measurement procedure or source directivity, which are not normally considered in the uncertainty evaluation. Although we have clearly endorsed the use of individual calculations to determine the uncertainty of the sound insulation magnitude in one-third octave bands, we believe the uncertainty proposed by standard ISO 12999-1 could be a more realistic and reasonable approximation for the global magnitude Dls,2m,nT,w. Therefore if an individual calculation of the uncertainty of the global magnitude is required the Monte Carlo simulation has been shown to be a good method. 相似文献
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强激光脉冲在水中的自聚焦传输、成丝、击穿及击穿后产生的声波,近年来成为强激光脉冲传输应用研究领域的一个热点。强激光脉冲电离产生的空泡在溃灭过程中,对周围水体产生压缩,从而在水下产生声波。在现有理论基础上,考虑空泡含气量、水的粘滞系数和水的表面张力系数对空泡运动及其产生声波的影响。给出双空泡运动方程,分析空泡间距对空泡溃灭和其产生声压关系。根据实际情况,计算不同温度情况下单空泡和双空泡运动过程及其产生的声压,并进行相互比较。计算结果表明: 水温越高,空泡运动时达到的最小半径越小,空泡振荡周期和溃灭时间延长,产生声压越高。随双空泡间距减小,空泡溃灭时达到的最小半径线性减小,而其产生的最大声压则单调增大。 相似文献
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针对三维浅海环境下孤立子内波对低频声信号传播特性的影响问题,基于Oxyz坐标系下的三维浅海低频声场有限元计算方法,以声能流为研究对象,仿真分析了内波存在对低频声信号传播特性的影响规律。研究结果表明:受内波影响,在xOz平面,声能流垂直分量的传播偏转角度呈现周期性的起伏规律;随着声源深度的增加,内波对声能流偏转角度的影响深度也随之增加。对xOy平面,当声源位于温跃层以上时,随着接收深度的增加,各深度平面上声能流水平分量的偏转角越大;随着声源深度的增加,内波对各深度平面上声能流的影响逐渐减弱。 相似文献
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F. Schwabl 《Journal of statistical physics》1985,39(5-6):719-737
Structural phase transitions of second order can be divided into two groups: (i) distortive phase transitions, with a soft (ultimately overdamped) optic mode, and (ii) elastic phase transitions, with an acoustic soft mode or no soft phonon for shear or isostructural transitions, respectively. The propagation of sound shows significantly different features in these two cases. We consider the theory of the critical variation of the velocity of ultrasonic modes as well as the damping and dispersion near transitions of second order.Talk given at the Conference on Transport and Propagation in Nonlinear Systems, Los Alamos, May 21–25, 1984. 相似文献
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V. A. Gusev 《Moscow University Physics Bulletin》2009,64(3):277-281
Theexact solutions of intensive sawtooth waves and beams in a medium with a sound speed inhomogeneity have been found. It has been shown that the focusing on the medium inhomogeneity is strongly pronounced for a single pulse, resulting in the formation of narrow high-amplitude areas. It has been determined that the refractive infomogeneity can lead to a shift of the amplitude maximum of the initial focused beam and the transformation of the converging beam into a dispersing one. 相似文献
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A correction of Walsh's method for bulk sound velocity calculation for shocked porous materials is accomplished based on the Wu-Jing thermodynamic equation of state. The corrected bulk velocities for solid and porous samples with low porosities are in good agreement with the corresponding experimental data published previously. On the basis of this corrected equation, the influence of thermoelectrons on the bulk velocity of shocked materials is discussed in detail at pressures of 50, 70 and 200 GPa. Some interesting phenomena are revealed, which seem to be the unique features of a dynamic-pressure-loading process and could not be found in static experiments. 相似文献
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