| Deep sea is very rich in oil and gas resources.It is said that about 44%world's oil geological reserves will come from deep sea in future.The strategic objectives of the China's oil and gas exploration and development will shift to the deep sea.Development of deep water resources need drilling platform,however,drilling riser system is also one of the key equipments.Drilling riser system is the key to connect the wellheads and drilling platform.If failure accident occurs in drilling riser,it may result in serious drilling accidents,and cause huge economic losses and casualties.The drilling riser has effects of gravity and top tension.Due to the working condition,drilling riser also has effects from external marine environmental loads and internal drilling condition,such as drill string and drilling fluid.Under the effect of the complicated working condition,the drilling riser is labile to failure.Rupture and collapse accident for drilling riser has happened in South China Sea in recent years,which caused significant economic losses.At present,the relevant domestic and foreign scholars did a lot of theoretical and experimental research on the mechanical behavior and vortex-induced vibration characteristics for drilling riser.However,the research on mechanical behavior of the drilling riser considering marine environment and drilling condition,mechanical behavior under the effect of the non-uniform flow,and three-dimensional vortex induced vibration theory is scared.Therefore,based on working environment of the deepwater drilling riser system,conducting experiment study of the deepwater drilling riser mechanical behavior,analyzing the mechanical behavior rule under the different drilling condition and current,establishing the dynamic and three-dimensional vortex induced vibration theory analysis method.It is significant to enhance the safety and reliability of deep water drilling riser.The main endeavor and contributions of the dissertation are as follows:(1)Literature review at home and abroad.Analyzed the basic characteristics of the drilling riser configuration,widely collected and analyzed the theory and experimental mechanical behavior study status of the drilling riser,summarized achievements and existing problems in the research field both at home and abroad.On this basis,proposed the research direction and train of thought.(2)Carried out research on theory calculation method of the ocean environment load.Analyzed the vortex-induced vibration principle,deduced the the wake oscillator model by Van der Pol equation,determined the key parameters of the model;created the calculation method for both of the shallow and deep sea marine environment load considering the wind,wave and current based on the causes of the formation of wind,wave and flow as well as the characteristic parameter related to marine environment;found the influence of marine environment parameters on the marine environment load.(3)Created the drilling riser mechanical behavior experiment system which considering both of the ocean environment and drilling condition.Designed the riser experimental model and experimental parameters,created deepwater drilling simulation experiment device,which include drilling fluid circulation system,the drill string rotation system,the tension system,drilling rig system,control and acquisition system,realized the collection of the riser experimental parameters based on fiber Bragg grating testing technology.(4)Carried out the experimental study of the vortex-induced vibration for drilling riser.Carried out the study of the vortex-induced vibration response mechanism under the different uniform and shear flow velocity;processed the experimental data by modal analysis and fast Fourier transform,got the vortex-induced vibration characteristic parameters such as displacement time history,the corresponding standard deviation of the spatial distribution and strain response spectrum,and the trajectory;found the vortex-induced vibration response mechanism under the uniform flow and shear flow,and the drill string mechanism of action on drilling riser' vortex-induced vibration response;results showed that vortex-induced vibration can be inhibited by drilling pipe string and drilling string had no affect on vortex induced vibration frequency;when the vortex shedding frequency is close to maximum order of the natural frequency,the lock-in phenomenon occurs,and the dominant frequency equals to this natural frequency.The experimental results also provide a basis for the theoretical model for the subsequent validation.(5)Carried out the dynamics behavior theory research on deepwater drilling riser.Duduced the movement differential equation of drilling riser,established dynamic analysis model for drilling riser,soloved the dynamic model by the finite element method combined with Newmark-? method,compiled the riser dynamic analysis program by Fortran,analyzed the influence of the top tension,current,wind speed,platform migration on the riser's deformation.Analysis results showed that the current type and velocity distribution and velocity is an important reason which influence the dynamic characteristics of the riser;wind speed is low,the impact on the deformation of the riser is limited,but when the wind speed increases to a certain degree,the displacement of the riser increase significantly;angle and the upper deformation of the riser is obvious affected by misregistration of the platform.(6)Carried out the three-dimensional vortex induced vibration theory research for deepwater drilling riser.Established the natural frequency calculation method by the basic equation of curved beam transverse vibration,analyzed the influence of the length,tension,thickness of the drilling riser on riser's natural frequency;established the three-dimensional vortex-induced vibration model for deepwater drilling riser based on the dynamics votex theory and dynamics analysis model,soloved the model by the finite element method,compiled the riser vortex induce vibration program by Fortran,verified the program by the experimental results which was with good accuracy;simulated the riser morphological characteristics,trajectory and the three dimensional space form under different current velocity.The simulation results showed that the displacement of the cross flow direction is larger than the one in the in line direction;the vibration of modal order time increased with the current velocity;the cross flow deformation and in line deformation made the riser become more distortion in space which may have impact on the safety of the riser.In conclution,created the deepwater drilling riser experimental mechanics behavior simulation technology,and dynamics behavior andthree dimensional vortex induced vibration theory analysis method through this study.The research work of this paper is of great both theoretical significance. |
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