Study On Stability And Dynamic Response In Towing Of Air-floating Bucket Foundation

Bucket foundation has been widely used as a new style foundation in theexploitation of ocean resources. Based on the background of the key technologies ofair-cushion towing of the rapid construc tion of large-scale bucket foundation inoffshore wind farms and the foundation type in exploitation of marginal oil fields，it isnecessary to study the m otion responses of bucket foundation and analyze theinteraction between air and water in the bucket、the towing speed、the draft and otherfactors that have influence on the towing security. Due to the less study on the motionresponses of air-floating structures in wa ve, the responses are investigated by themethod of theoretical calcu lations, model tests and numerical simulation. T hereference and evidence can be provided for the rapid construction in offshoreengineering and the application and promotion of bucket foundation as the foundationof offshore structure。Based on the stability theory of tradition al floating body，the initial stability ismodified by the air buoyancy decreasing coefficient and the stability at large angles ofinclination is calculated by th e modification on the level of form stability by aircushion compression coefficient.T he subdivision optimization technology of largescale bucket foundation is put forward.The nonlinear boundary conditions on the ga s-water interface in the bucket arecoped with by the introduction of the dim ensionless parameterαconsidering theinfluence of air cushion. Based on the thre e-dimensional potential flow theory usingthe semi analytical m ethod of eigenfunc tion expansion and progressive m atchingmethod，the basic laws of heave、sway and pitch are studied.Through the mechanism analysis of bucket foundation in wave, the equation ofmotion of bucket foundation in wave is established by cons idering air effect as theform of da mping and the self-oscillator y characteristics of bucket foundation isstudied. The frequency response f unction of dynamic response to wave action isobtained by the response analysis in regular wave；with the irregular wave regarded asstationary ergodic Gaussian random processes，the prediction about m otion andresponse in random wave is made by the combination of time domain and frequencydomain. Model tests about m ulti-bucket foundation composed of som e air-floatingstructure with small diameter are taken. The data about air pressure in bucket、waterpressure at the bottom of bucket、acceleration in the direction of X, Y, Z and th etension in the towing point are measured under the conditions of different freeboard、towing speed and water depth..The numerical simulation for the model is carried outby the marine software MOSES. Analysis of towing system in wave is perform ed bythe combination of test and simulation to the basic law of response and movement.