In order to explore the influence of noise from the accelerated trains on the sound environment along the railway the health of residents living along the railway,an investigation was carried out in four operation divisions of the railway based on the national standards for sound source and environmental noise.

The method for evaluating the effective elasric moduli of void-containing solid is also introduced. The numerical calculation given in this paper shows the influence of the void volume concentration and layer thickness on the sound reflection coefficients and interface wave velocity, providing a theoretical basis for inverse deduction of the mechanical properties of void-containing layer based on ultrasonic measurements.

The sound power of every source can be calculated separately by the system; therefore, the effects of design parameters for engine and aircraft on the sound power can be inspected through change in these parameters.

The detaited situation of the electromagnetic radiation interference effecting on the sound level meter with RF electromagnetic field is presented in this paper. The research and design of the anti power frequency magnetic field interference effecting on the sound level meter by using power frequency magnetic field test equipment is described also.

In the process of studying the acoustic field produced by vibration of the submerged cylindrical shell, the structure dynamic equation, Helmholtz equation in the fluid field and the continuity conditions of the fluid-structure interface compose the coupling vibration equation of the sound-fluid-structure. By use of the solution of the equation, the influence of the low order mode on the sound radiation is discussed.

2. We assume that the laser beam radiates evenly the whole surface of the half-infinite liquid. The influences which the optical penetration effect、thermal diffusioneffect and electrostriction effect act on the sound resource are considered. And we buildthe one-dimension model.

The influence of the parameters on the sound velocity is discussed qualitatively for the general case and shown quantitatively by numerical results for an example.

We investigate the frequency and temperature dependence of energy losses and also the dependence of the absorption coefficient on the sound wave vector.

A temperature dependence of the free phonon path is calculated for the examined temperature interval based on the thermal diffusion obtained and the literature data on the sound propagation velocity.

We study the problem of determination of the sound field of a point harmonic source in the coastal zone and the influence of a cylindrical body floating above the source on the sound field formed in the marine medium.

Effect of geometric structure parameters on the sound absorbing properties of a metal fiber material

The sound velocity in a fibre shows a pronounced anisotropy, that is, the sound velocity along the axis of an oriented fibre is much greater than that perpendicular to it, and therefore it may be used as a measure of the molecular orientation α in the fibre,α= 1 - Cα2/C2where C and Cu are velocities of sound along an oriented fibre and a completely un-oriented fibre respectively.The apparatus used consisted of a pulse generator which sends a pulse of 70 μsec duration with a repetition frequency of 100 times...

The sound velocity in a fibre shows a pronounced anisotropy, that is, the sound velocity along the axis of an oriented fibre is much greater than that perpendicular to it, and therefore it may be used as a measure of the molecular orientation α in the fibre,α= 1 - Cα2/C2where C and Cu are velocities of sound along an oriented fibre and a completely un-oriented fibre respectively.The apparatus used consisted of a pulse generator which sends a pulse of 70 μsec duration with a repetition frequency of 100 times per second to the moving coil of a loud speaker. The fibre was coupled to the vibrating membrane through a spring clamp. When exited by the pulse, the system underwent damped oscillation with a natural frequency of about 4000 Hz. At the other end of the fibre, about 200 cm from the clamp, a crystal pick-up was located, the output of which was sent to an oscilloscope with the sweep circuit triggered by the pulse voltage. The time of propagation of the longitudinal vibration along the fibre from the clamp to the pick-up was observed from the oscilloscope record, and the sound velocity in the fibre calculated.Since the mechanical properties of fibre depend considerably on the moisture regain and tension, the effect of relative humidity and tension in the fibre on the sound velocity were studied.The best choice of the experimental conditions for the determination of molecular orientation by the sound velocity method appears to be the following: room temperature, 28 - 30℃; relative humidity, 60%; and under a tension somewhat below the critical Young's modulus of the fibre.The sound velocities in the fibres of different draw ratios (r) were determined and extrapolated to r = 1 to give the value for Cu. Experimental results indicate that the degree of molecular orientation of monofils of Nylon 6 increases to approximately 80% after drawing and after-treatment.The degree of orientation for several products of Nylon 6 fibre such as yarns, monofils, and cords was determined. Fibres that possess greater breaking length show higher degree of orientation.

In this paper, the effect of a random fluctuation surface on the sound field of a harmonic point source in positive sound velocity gradient shallow water is consideved. Approximate expressions for the pole equations and amplitude functions are obtained. It is found that the results of reference [1] are the limiting case of the results of this paper.

The field of a harmonic point source in layered media has certain angular distribution. Although by ray theory the angular distribution of sound field can be calculated for given receiving point, but the effect of the frequency on the angular distribution function and the sound field in shadow zone can not be calculated. In this paper, by the normal-mode theory the angular distribution of the sound field in layered media is discussed, the general expression of angular distribution function and attenuation law...

The field of a harmonic point source in layered media has certain angular distribution. Although by ray theory the angular distribution of sound field can be calculated for given receiving point, but the effect of the frequency on the angular distribution function and the sound field in shadow zone can not be calculated. In this paper, by the normal-mode theory the angular distribution of the sound field in layered media is discussed, the general expression of angular distribution function and attenuation law for directional reception are obtained. The results given above can be used for calculation of the sound field in shadow zone and they represent the influence of the frequency on the sound field. Investigating the channel of the underwater sound and the effect of the signal detection in it, by utilizing the obtained results, the optimum receiving direction can be chosen. For given medium model the numerical calculations are produced, and analysis and discussion are conducted.