Study On Method Of Target Strength Prediction Of Acoustically Transparent Sail

The development of underwater acoustic countermeasures has gradually put forward higher requirements for the submarine’s acoustic invisibleness performance.The sail is the largest protrusion on the submarine and has a significant contribution to the submarine’s overall acoustic scattering field.Therefore,method of reducing target strength of sail has gradually attracted people’s attention,but there are still few studies on prediction methods for target strength of such water-filled acoustically transparent structures.The engineering prediction methods for target strength of sail under different frequency bands are studied,and the influence of the sound absorbing material laying on the surface and the geometric parameters on the target strength of sail are explored,and then the experiment is carried out.Firstly,the engineering prediction methods for the target strength of sail under different frequency bands are established.In the low frequency band,the modeling of the sail and the prediction of target strength are performed using finite element software.The prediction results of the finite element method are verified by the examples of rigid sphere and steel waterfilled spherical shell,and the calculation efficiency is discussed.In the midto-high frequency band,the planar element method is used as the basis,considering the influence of the backscattering and occlusion effect on the inner surface of the outer shell,a modified planar element method suitable for the acoustically transparent sail is established.On the basis of the method above,the target strength prediction of outer shell,inner structure and overall sail are carried out separately,and reasons for the difference between the prediction results and that of the planar element method are analyzed.Afterwards,using target strength engineering prediction method above,the influence of sound absorption material thickness and geometric parameters like relative thickness,aspect ratio and tilt angle on target strength of sail are investigated,it was found that the sound absorbing material can effectively reduce target strength under high-frequency conditions at various angles,especially the stern direction.Meanwhile,reducing the relative thickness,increasing the aspect ratio and tilt angle also help to reduce the target strength of the sail at different angles.Finally,an experiment of the sound scattering characteristics of the sail shrinking model was conducted to verify the accuracy of the prediction results of the modified planar element method under medium-to-high frequency conditions,and the test results were analyzed from the perspective of the time-domain echo structure and acoustic imaging.The target strength engineering prediction method proposed takes both high efficiency and accuracy into account,which has certain practical value in engineering.The impact on the absorbing materials and geometric parameters also provides a reference for reducing the target strength of sail in reality.In addition,the pool shrinking model experimental results have reference significance for the detection and identification of sails and even submarines.