Numerical Study Of Air Guns And Performance Otimization Of Air-gun Array

The air gun is the mainly artificial seismic energy source used for marine seismic exploration because of its good seismic properties and reliable,eco-friendly features.In addition,pressure load produced by air gun bubble may also cause damage to marine structures like exploration vessel,marine work ship and mining equipment.In order to achieving the goals of interpretation of marine seismic data and shock environment analysis for ocean structures,the wavelet generated by air guns and the characters of it are essential,as from the wavelet,important information such as pulse energy,signal-noise ratio and spectrum characteristic can be obtained.The air gun works in terms of array mode and different air-gun arrays have different wavelet and their seismic properties are also distinct.So for purpose of achieving multifarious marine seismic exploration in different environment needs to optimize the air-gun arrays and improve their seismic properties.Therefore,how to ascertain the far-field wavelet of air-gun arrays and how to improve their performance are the two major issues in air-gun area.At present,actual measurement,analysis-reduction and numerical simulation are the three major methods to obtain the wavelet of air-gun source.In addition to good external environment conditions,the actual measurement requires immense human,material and financial resources.The analysis-reduction has strong dependence on marine seismic data and the mathematical algorithm,and the facticity of the obtained wavelet is doubted.Numerical stimulation is the most widely used method and the wavelet was gained from the wavelet model on platform of computer.Based on the classical wavelet model,a new model which draws open thermodynamic system in and takes thermodynamic factors such as gas release and heat transfer into consideration was established in this thesis.And in order to calculate the interaction between the cluster guns and air guns within one array,the coherent factor was added in the wavelet model of cluster guns and air-gun array.The numerical results meet the data of Nucleus software well.Besides,an intelligent optimization model which combined the above air-gun array model and particle swarm optimization was established in this thesis.Then,this optimization model was applied to few simple arrays and one actual array,and the performance of these arrays was improved substantially.In addition,a new and practical optimization technique,” gun exchange”,was used in the array optimization,and it can improve the P/B ratio effectively without alter the types of the air guns.Finally,an air-gun bubble experiment was conducted in this thesis.The experiment compared the effects of two different types of port(“ring port” and “four-port”)and various gun diameters on the motion of bubbles,which can fill the gap and provide reference for study and design of air-gun.