Study The Electromagnetic Properties Of Ship Wakes Bubble Film

When ship moves in the sea, a bubble film, ship wake is generated in backward direction. Factors of the ship wake existing are the friction of the hull with water body, and disturbance of propeller in the sea. Wakes are of bubble films with variety physical properties. Affected by the weather, air temperature, water temperature, sea area, moving speed and other factors, the ship wake has different physical properties and appearance characteristics. Studying and mastering these characteristics and features, the ship types and tonnage can be mapped out as well as moving speed and other information. The research in this present paper has great significance for the military, marine observation and other related fields.The electromagnetic properties of the ship wake bubble film are studied and investigated, as well as the graphic characteristics are calculated and analyzed, in this dissertation, in which the following aspects are described in detail.Firstly, the generation of wake bubble film is simulated using self-made simple experimental device. Image acquisition is performed on stationary water surface, single propeller wake and double propeller wake using MATLAB to process and extend the image of the gray. Through transforming the gray histogram and analysis the experimental results of three different images, the frequency distribution of the three different gray levels is obtained. Canny algorithm is used to detect weak edges and reach the conclusion of the experiment. The conclusion provides the basis for further research on the ship wake image information.Secondly, the thesis analyses the basic theory of the airborne magnetic sensor detection wake magnetic field and the basic theory of the magnetic anomaly detecting caused by ship motion in water systematically. The mathematical model is established based on above.Thirdly, from the Maxwell equations and the basic of magnetic fluid dynamics equations, the calculation method and the solving method of the magnetic anomaly are analyzed and derived by the electromagnetic wake in the geomagnetic field. Under certain conditions, the magnetic anomalies on different distance of ship wakes are estimated and analyzed. The results show that the strength of the magnetic field gets weaker and weaker with increasing of wake downstream distance. The magnetic field strength decreases sharply in initial 4km, and the magnetic field strength decreases slowly in 5km～12km. When it is more than 20km, the magnetic field anomaly is getting smaller. They have an apparent inverse relationship between the distance and the magnetic field. The results also show that when wake downstream distance is in less than 20km, the magnetic field strength calculation results is between 0.17 X 10-4A/m～2.2×10-4A/m, and the results can be effective detected by the magnetometer.