Theoretical And Experimental Study On Optical Detection Of Ship Radiated Noise

When the ships and other underwater vehicles are sailing in the sea water,the air bubble curtain is formed on both sides of the ship and the stern part,and the larger noise is radiated to the surroundings.They are called bubble wake and noise wake respectively,they interact with each other and influence each other.The existing optical wake detection is mainly based on the existence of the bubble,which leads to the difference between the laser transmission characteristics in the ship's wake and the laser transmission characteristics in the undisturbed sea water,and achieve the goal that indirectly detect the moving target in the water,without considering the interaction and influence between bubble wake and the noise wake.An optical method of considering their interaction and influence at the same time detection noise wake and bubble wake is proposed in this thesis,and a theoretical model of wake bubble scattering under noise is established,and the correctness of the theoretical model and the feasibility of the detection method is validated experimentally.1.On the basis of summarizing the characteristics of noise wake and bubble wake,the key characteristic parameters such as noise frequency and bubble size are selected to establish the ideal noise wake and bubble wake model.The motion characteristics of particles,bubbles in the noise wake area are analyzed,it is concluded that the movement of bubbles and particles under the action of noise wake and the movement of bubbles and particles in the undisturbed water have significant differences.The presence of noise waves causes the particles and bubbles to change from irregular movement under static water to periodic oscillation.The influence of the frequency and intensity of noise wave on the motion of bubbles and particles in the wake is studied,the results show that the oscillation period of particles and bubbles is approximately the same as that of the noise wave period;With the increase of sound intensity,the oscillation amplitude of particles and bubbles is also larger;Under the same frequency and intensity of the noise,the amplitude of the bubble is larger than that of the particle.At the same time,it is also found that the velocity of particles and bubbles can be affected by low velocity turbulence.2.The two-beam heterodyne Doppler detection system is established.The scattering characteristics of simulated noise wake and bubble wake model are studied experimentally. The scattered light intensity and frequency shift of the scatterer in the static environment,noise wake,noise wake and bubble wake environment were measured respectively,and according to the conclusion the scatterer properties and its environment was analyzed.The experimental results show that the Doppler frequency shift and the frequency shift peak of the scatterer are different under different environments.The Doppler shift and peak of the scatterer in the hydrostatic environment are irregular;The Doppler shift of the scatterer in the noise wake is obviously concentrated in a certain frequency range,and the peak value is larger;Under the combined action of the noise wake and the bubble wake,the Doppler frequency shift peak of the scatterer is significantly increased than that of the noise wake alone,and the peak value is higher.Conclusion was consistent with theoretical analysis.3.The variation of the scattering light characteristics with the noise frequency and intensity under the condition of the presence of the noise wake and the bubble wake are studied in theory and experiment.The results show that the Brillouin frequency shift in the scattered light increases with the increase of the noise wave frequency,as the scatterer moves intensively,the range of Doppler shift also increases with the noise wave frequency;With the increase of the intensity of the noise wave,the peak of the Brillouin frequency shift also increases.4.The preliminary conclusions of the experimental studies shows that using optical heterodyne detection method based on the Doppler frequency shift,through detecting the scattering frequency range and peak of the scatterer in waters,to determine the existence of noise wake,wake bubbles in sea water;Furthermore,the frequency,the intensity of the ship noise and the size,the concentration and the movement speed of the scatterer in the wake can be obtained,so as to determine the distance,azimuth,velocity and displacement of the ship target to be measured.