Detection Technology Of Wake Microbubble Based On Light Scattering

The high-speed rotation of propeller of a moving ship can cause a large amount of air into the water to generate a length of the bubble wake.The bubbles in the wake will destroy the uniformity of the seawater medium,so that the light wave will be scattered when transmitting in the wake.Different from the large bubble,the microbubbles in the wake can survive for a long time,which make it possible to detection the remote ship by using the light scattering characteristics of these microbubbles.This thesis studies on the detection method of the wake bubbles based on light scattering.Firstly,based on Mie scattering theory,the scattered light intensity distribution characteristics of single bubble in water are studied,and the attenuation mechanism of bubble in water to incident light energy is studied through extinction coefficient,scattering coefficient and absorption coefficient.The calculation results of the bubble with the diameter of 0.5～100μm show that the scattered light energy is mainly concentrated in the forward direction.And with the increase of bubble diameter,this phenomenon is more obvious.In addition,the influence of the size of bubble on the extinction coefficient and scattering coefficient is also studied.On the basis of single bubble research,it is further discussed that the scattering light of the bubble group is a linear superposition of the single bubble if the condition of irrelated scattering is satisfied.Secondly,based on the theoretical research of bubble Mie scattering,a method of measuring the bubble size distribution based on small angle forward scattering was studied.The Whale Optimization Algorithm and Chahine algorithm are used to determinate the bubble size distribution from the forward scattering light intensity.What’s more,the Tikhonov regularization is used to construct the regularized objective function and linear equation,which improves the stability and anti-noise capability of the algorithm.And the method of measuring bubble number concentration based on Lambert Beer law is studied.The results show that the attenuation degree of incident light is related to the bubble number concentration and size.Finally,experiments are designed.A forward scattering light detection system is set up to measure the size distribution of simulated wake bubble produced by the bubble machine.On this basis,based on Lambert Beer law,the attenuation characteristics of bubble number concentration with time are studied by measuring the transmitted light power.The experiment results show that the attenuation of bubble number concentration with time is first fast and then slow.