Research On Acoustic Scattering Characteristics And Coupling Mechanism Of Complex Targets On Fluctuant Sea Surface

In order to improve the tracking and recognition ability of acoustic homing torpedo to surface warship targets in shallow sea environment.This thesis proposes two multipath acoustic scattering prediction models for warship targets.One is a simplified multipath acoustic scattering model of warship targets based on simple harmonic motion synthesis method(SM),and another one is a precise multipath acoustic scattering model of warship targets based on strip theory for warship motions prediction(PM).Based on the multipath acoustic scattering prediction model of warship targets,the frequency domain indirect method and the acoustic scattering plate element method(PEM)are used to establish the“Highlight” jump prediction model of warship navigation in arbitrary paths under the action of fluctuant sea surface(HM).In the SM model,the influence of sea surface on the amplitude and period of six degrees of freedom(DOF)motion such as roll,pitch and yaw is described by empirical statistics.The coordinate transformation of vertices of the target in the continuous motion state is realized by rotation matrix and translation matrix.On this basis,the contribution of six DOFs to acoustic scattering at different detection angles is analyzed by using SM.The results show that roll and yaw have a greater impact on the azimuth echo from the abeam detection,while pitch has a greater impact on the echo of fore and aft detection.For the PM model,the six DOFs dynamic model of warship on randomly fluctuant sea surface is established based on the strip theory,which can predict the warship motions by the sea surface of various wave spectra.Using the statistical model of the reflection coefficient of the fluctuant sea surface,a PM model with the effect of the fluctuant sea surface is established using Monte Carlo method.It is proposed that target strength(TS)of the complex targets on fluctuant sea surface will satisfy the statistical regularity of ChiSquare distribution.The results show that the overall trend is basically the same from the measured and predicted results of warship model acoustic scattering,the values are close,and the average error is less than 2d B.And it is found that the echo strength(ES)amplitude of warship under the action of wave conforms to the statistical regularity of Chi-Square distribution over time,which shows that PM is accurate and credible.For the HM model,based on the frequency domain indirect method and acoustic scattering PEM,the “Highlight” distribution characteristics of single semi-submerged rigid sphere,double semi-submerged rigid sphere and the main part of the underwater part of the surface warship under the action of fluctuant sea surface are researched respectively,and the“Highlight” jump prediction model of warship navigation in arbitrary paths under the action of fluctuant sea surface is established.The results show that heave and roll have great influence on the pitch observation angle of the target.Yaw has a great influence on the horizontal observation angle of the target.The prediction and the measured results are in good agreement,which can accurately predict the time-domain echo characteristics of the surface warship model based on the bow,midship and stern rudder under any motion trajectory,as well as the detection distance,ship speed and ship components interval.For mastering the acoustic scattering characteristics of complex targets with fluctuate sea surface and its coupling mechanism,this thesis carried out an experimental study on the acoustic scattering characteristics of moving targets on the randomly fluctuate sea surface,and obtained the measured data of the scattering echo of the surface warship at the level and directly above under different wave spectrum parameters.The fine characteristics of sound scattering in the time domain and frequency domain of the surface warship under the action of calm sea and fluctuate sea surface,as well as the statistical regularity of fluctuation of ES measured over time are obtained.Research have shown that the ES of warship under the action of waves conforms to the statistical regularity of Chi-Square distribution over time.The echo characteristics of the linear motion of surface warship are composed of several Ushaped curves,which are caused by the “Highlight” of the bow,amidships and two stern rudders,etc.And at the same time,the echo structure of the surface ship in a circular motion presents a ribbon-like characteristic similar to a DNA double helix.In addition,the average error between the theoretical prediction amplitude of the ES and the measured results is less than 2d B when the warship model passes through the horizontal emission array 120 k Hz ～180k Hz and the bottom emission array 20 k Hz ～ 40 k Hz,and the overall trend is basically the same.It verifies the accuracy and effectiveness of the acoustic scattering prediction model established in this thesis.The research works presented here may provide a certain guidance significance and reference value for the improvement of the accuracy of acoustic guidance torpedoes.