| With the increasing consumption of fossil energy on land,the development of deep-seaoil and gas resources has drawn extensive attention.The exploitation of offshore oil and gas requires the help of platforms.In general,platforms work in deep sea with severe conditions.When a platform is operating in a mooring,various vessels that frequently pass by result in severe accidental collisions of the platform,such as huge economic losses,environment pollution casualties.Thus,the kinematic response of the mooring platform should be investigated at the beginning of the platform design.The mooring platform has been selected and the external dynamic analysis of a platform under collision has been performed.Main researches are as follows:This paper summarizes the research status of ship collision analysis methods and introduces the fluid methods in collision analysis.As the mooring platform in this paper can be regarded as a multi-body system,the status of multi-body dynamics involved is described.The theory of nonlinear finite element analysis and its key technologies are elaborated in detail.Center difference method which is the basic algorithms of explicit finite element analysis and large deformation dynamics theory,are introduced.According to the practical experience in numerical simulation,contact algorithm,material model and hourglass control are described.In the end,the important part of this paper is focused on the modeling method of the connection in multi-body system.The basic theory of multi-body dynamics is summarized.According to the steps of solving the problem,the coordinate transformation and the calculation of degrees of freedom are introduced in turn.The concept of constraint equations is described.The constraint Jacobian matrix in 2D and 3D space is deduced,and the kinematics and dynamics analysis steps are finally summarized.Using the finite element method,the external dynamics analysis was performed on an actual collision scenario of a mooring platform.A single point mooring platform model is established.When the mooring platform is subjected to the lateral collision of a ship,the time history of the impact strength,the maximum collision depth and the dissipated energy are analyzed.Taking the collision scene of non-mooring platform as a reference,the motion of the struck platform in six degrees of freedom is examined.The conclusion is drawn that the constraint of the mooring system increases the sway speed and displacement of the platformsignificantly.However,the angular velocity and angular amplitude are reduced along an approximately sinusoidal curve.The two arms of YOKE perform circular motion in different vertical planes,and the left and right connecting arms alternately shift in the surge to control the yawing angle of the platform and do complex motion in three-dimensional space.The mooring platform-ship collision model is simplified,and a new finite element-analytical calculation method is proposed to analyze the motion response of the platform under collision loads.Collision analysis is divided into load analysis and kinematic response analysis.In the load analysis,the time-history curve of the collision force was obtained using the finite element method as an input condition for subsequent calculations.In the kinematic response analysis,the dynamical control equations are deduced based on the multi-body dynamics theory.The unknown parameters are solved by the least squares method,and the Newmark method is used to iterate.In addition,an additional mass method was used to improve the analytical formula considering the fluid effect.Verified by the finite element method,the method is consistent with the results.Thus,the proposed method can predict the motion of the platform accurately and efficiently and can also be extended to any collision parameters.By eliminating unknown parameters,the matrix equations are reducing and the program is optimizing.Thus,the calculation time is greatly shortened.Besides,the reason for the error is analyzed in detail. |
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