Research On Acoustic Multi-beam Measurement Method For Water Flow Field Characteristics

Multi-beam sonar is a survey instrument widely used in the field of seabed sounding.It has the advantages of wide coverage,high efficiency and multi-function.This paper applies it to the measurement of spatially complex non-uniform flow field and proposes multi-beam flow measurement.Thoughts and focus on the adaption of the problem.Firstly,the scheme of acoustic multi-beam flow measurement system is designed.The acoustic scattering model of array echo is established based on volume reverberation theory,and the array echo signals of complex non-uniform flow field are simulated.Then,the beamforming and time window layering are performed.Lastly,The Doppler frequency offset is estimated using a complex autocorrelation algorithm,and then the spatio-temporal distribution of the high-resolution multi-beam stratified radial velocity of the water flow field is obtained..Secondly,aiming at the adaptability problem of multi-beam flow measurement,a unified resolution high-precision layering method which is less affected by interlayer interference is proposed.A high-precision layering method with uniform resolution is designed.The sliding average method is used to reduce the influence of interlayer interference.The feasibility of the system is verified by simulation,and the measurement of complex non-uniform flow field is realized.Thirdly,on the basis of measuring the stratified and radial Doppler frequency offset,the measurement method of multi-beam three-dimensional flow velocity is further studied.A method for synthesizing three-dimensional flow velocity by using two sets of symmetrical four-beam measurements in a fan plane is proposed.The multi-beam measurement to three-dimensional coordinate transformation method is derived.In addition,time and space correlation is used to remove outliers and smooth the spatial results.Finally,aiming at the beam focusing problem in near-field region,a multi-point near-field focused beamforming method is proposed,which improves the applicability of multi-beam current measurement method.