Study On The Law Of Sound Propagation Near The Wall

With the widespread application of sonic measurement technology in industrial power plants,how to accurately measure the propagation time of sound in the area has become the key to this technology.However,the existence of complex and variable wall environments in industrial power plants will affect the propagation time and propagation path of the sound,thereby reducing the accuracy of the acoustic wave measurement technology.Based on the characteristics of acoustic propagation,this paper conducts research on two types of power wall environments common in power plants,namely infinite wall surfaces(hereinafter referred to as wall surfaces)and particulate accumulation media.Firstly,the wave equations of sound in gas and solid are deduced according to the equations of motion,continuity,state and Hook's law of solid media.The acoustic scattering fields and scattering attenuation coefficients in granular media are introduced.The signal cross-correlation algorithm is used to calculate the corresponding acoustic propagation time.Based on the COMSOL Multiphysics finite element simulation software,the acoustic propagation model of the wall and particle stacking medium is established for simulation calculation.The upper and lower computer hardware systems are connected through Lab VIEW virtual development software.At last,an experimental platform for cold wall and particle-packed filling bodies was established.The simulation results were thus verified and the conclusions were obtained as follows:(1)Different sound source conditions such as the diverse types of sound source,the relative position of the sound source and the wall surface,the duration of the pulsed sound source,and the distance between the sound source and the wall surface do not affect the sound propagation speed near the wall surface.(2)The sound velocity distribution near the wall surface is of "spoon-bottom" type,and there is a dispersion effect on the sound.Sounds of different frequencies have different sound velocity distributions near the wall surface.The higher thefrequency is,the smaller the maximum value of the sound velocity becomes,while the larger the minimum value is,the shallower the "bottom of the spoon" becomes.Since the maximum speed value of sound is always at the wall,and the size of the affected area and the corresponding point of the minimum speed of sound are related to the wavelength of the sound,the corresponding empirical relationship is obtained and the area length of influence is about one-third of the wavelength,and length of the corresponding point of the minimum speed of sound from the wall is about one-fifth of the whole wavelength.The experiment firstly verified the existence of this phenomenon by measuring the speed of sound with a single pickup,and then measured the area of influence on the wall with double pickups.The results are comparatively in line with the simulation conclusions,but the sound speed numerical value is smaller than the simulation results,and there maybe a certain viscosity loss.(3)The sound field in the particle accumulation medium is mainly appeared as a superposition of the background sound field and the scattering field.The simulation results show that the attenuation coefficient of sound propagation in the filling body has nothing to do with the height of the filling body,and it is only related to the sound frequency and the nature of the particles.There is also a correlation coefficient between them.When the coefficient is less than 1,sound can pass through the filling body.At this time,the corresponding frequency is the critical frequency and the diameter of the particle size can be calculated by measuring the critical frequency.In the experiment,by analyzing the progress in which pickups placed on the upper and lower surfaces received the acoustic signals passing through the filling body,the sound propagation characteristics are found,and the results were consistent with the simulation.However,the speed of sound in the simulation remained basically unchanged and it's decreasing with the increasing frequency.