Study On The Fine Acoustic Scattering Characteristics Of Underwater Small-Size Composite Structure Cylinder

The study of acoustic scattering of underwater target can provide target information for active sonar,including target geometry and surface acoustic characteristics,which can be used as basic information for target classification and recognition.However,the theoretical and experimental researches on the acoustic scattering characteristics of underwater targets are mainly focused on the large and simple target structures,such as submarines and underwater vehicles.For the internal complex structure or the small size structure,the acoustic wave wavelength is comparable to the target scale,and the diffraction effect is enhanced,so the acoustic scattering mechanism becomes complex and the theoretical solution of the model is difficult.This paper introduces the basic theory of acoustic scattering of underwater target,including the shape function,wave equation and potential function of acoustic scattering field of target.Combined with the finite element numerical calculation method and taking the underwater acoustic array structure as the model,the acoustic-structure interaction law and frequency response characteristics of such composite structures are analyzed.The main contents and conclusions are as follows:1.A numerical model of target acoustic scattering field based on finite element method is constructed,and the peak frequency of resonance scattering of core-axis fiber hydrophone is predicted based on elastic resonance scattering theory.The peak frequency of the sensitivity frequency response curve of the fiber hydrophone corresponds to the elastic scattering resonance frequency.At this frequency point,the acoustic scattering intensity of the hydrophone target is the largest,and its scattering echo is most easily detected.2.The frequency-angle spectrum of target echo data can reflect the fine internal features of the structure.Based on COMSOL Multiphysics,the acoustic scattering model of composite cylinder with periodic internal structure is established.Bragg scattering fringes and bowl-shaped additional wave fringes can be observed in the water-filled ribbed cylinder,and the number of fringes is consistent with the theoretical calculation.3.The time-domain structure of the target echo signal can be used to analyze the echoes of different parts of the structure and various elastic echoes.The time-domain numerical simulation model of acoustic scattering of underwater targets is established,and the time-domain echo signal structures of different materials,different geometric shapes,fillers and composite structures are analyzed.4.Based on the actual fiber hydrophone skeleton structure,a three-dimensional acoustic scattering analysis model of small size composite cylinder is established.The effects of different geometrical dimensions,including the length and thickness of the mandrel,on the elastic resonance scattering frequency of the structure are analyzed.The results show that the longer and thicker the mandrel structure is,the higher the elastic resonance scattering frequency will be.5.Based on the framework of fiber hydrophone and the actual structure of acoustic array,a two-dimensional model of small size composite cylinder was established,and the acoustic scattering characteristics of targets in the frequency range of 70～100khz and the Angle range of 0～180 degrees were calculated.The frequency-angle spectra of these two typical targets were obtained,so as to analyze the unique characteristic wave patterns of these structures.However,there are not symmetrical structure model,which are hardly calculate by the two-dimensional model,only through a three-dimensional model for simulation,the performance requirements for computer are extremely strict,it is also an important factor of the three-dimensional model can only be used for low frequency,the study of high frequency acoustic scattering usually needs to use two-dimensional model.6.The acoustic scattering characteristics of the target are tested in the outfield experimental pool,get the frequency-angle spectra of the actual test,and comparing with simulation results,found that the frequency of the cylinder matched well with simulation results,and the oval ring due to the resolution and the vibration of the experimental platform error,there is a large difference between the result and simulation result.Finally,on the basis of these studies,the related content of underwater target acoustic image is preliminarily studied,and the simple target image is obtained.