Study On Acoustic Scattering And Radiation Force By Submerged Targets Based On PWS Method

Due to the excellent underwater propagation performance of acoustic waves,they play an important role in underwater objects’ exploration,information communication and even military application.Mostly,the plane acoustical waves are applied in the underwater acoustic exploration.However,when the plane waves encounter an obstacle,the strength and propagation distance of plane acoustical waves would attenuate in some degree owing to the phenomena of diffraction.Therefore,increased attention has been focused on other incident acoustical beams in order to get rid of the inconvenience of the plane waves.In recent years,investigation dealing with Bessel beams have attracted more and more attentions from scholars all over the world,so that Bessel beams are applied from electromagnetic field into underwater acoustical fields.In fact,A Bessel beam is a nondiffraction beam,which means that its amplitude could remain unchanged over a finite distance.In addition,self-healing ability is an exclusive ability for Bessel beams,meaning that the incident Bessel beams can re-form and has the initial intensity even after encountering an obstacle.Therefore,the acoustical scattering and acoustical radiation force of Bessel beams should be attached by more attentions.The main research work is as follows:Firstly,in this paper,based on the investigations dealing with Bessel beams from foreign and domestic researchers,the on-axis scattering characteristics of rigid,liquid and elastic spheres are introduced for ordinary Bessel beams.According to the two-dimensional figures of back-scattering for rigid spheres illuminated by various kinds of cone angles,peak-to-peak intervals are shown in back-scattering TS of rigid spheres.Besides,threedimensional far-field scattering directivity patterns are seemingly all symmetrical for Rayleigh region and Mie resonance region.And,with the increasement of incident dimensionless frequency,directive property becomes more and more obvious.In addition,according to the resonance scattering theory,resonance of elastic spheres and elastic shells could be suppressed by Bessel beams.Secondly,research of Bessel beams has been concentrated on the on-axis illumination,but off-axis incident illumination is an universal condition,which should be gained more attentions.As a result,not only on-axis scattering is shown in the paper,but also multipole expansion of acoustical Bessel beams with arbitrary order and location is introduced in this paper.Besides,formulas of arbitrary acoustical field are expressed in this paper.As a result,the scattering characteristics of submerged objects could be calculated through formulas of acoustical field and incident acoustical beam expressions.Through the comparison of threedimensional directive patterns for on-axis and off-axis scattering,symmetry disappears obviously.Even for elastic spheres,the symmetric characteristics for resonance frequency could also beak up and directive property is not transparent.Thirdly,when acoustical waves encounter the submerged objects,the transfer of energy and momenta between incident acoustical waves and objects can be induced,which could cause the radiation force for the objects.Based on the acoustical radiation tensor expressions,the derivation of acoustic radiation force could be transferred from the near field to the far field through the divergence theorem.As a result,the computation and derivation of the acoustical force could be simplified in a high degree regardless of the outer surface shape of the submerged objects.Therefore,the three-dimensional acoustical force of not only spheres but also prolate and oblate spheroids are both indicated via partial-wave series methods in this paper.And,the negative axial acoustic radiation force has an intimate relationship with the suppression of the backscattering.Additionally,the maximum of amplitude of the negative acoustic radiation is also related with acoustic impedance between host medium and objects illuminated by incident Bessel beams.The characteristics of threedimensional acoustical radiation force are influenced by the order of Bessel beams and incident location greatly.Based on the PWS method,expression formula of acoustical scattering and radiation force from various kinds of spherical particles illuminated by Bessel beams are given in this paper,which is also beneficial for investigations about physical property of Bessel beams.Meanwhile,the discussion of acoustical radiation force can benefit application of acoustic radiation force on engineering fields in future.