Analysis of Riser Mechanical Behavior Using Beam-Column Theory

Abstract

Abstract Conventional calculation method for analyzing riser mechanical behavior is based on the fourth-order differential equation. In this paper, a simple analysis model and calculation method has been provided. The whole riser is modeled as a continuous beam-column with N span under actions of both axial and lateral loads. One span of the beam-column is cut out as an equilibrium unit to establish the equilibrium differential equation which is different from previous governing equation. Results shows that the equilibrium differential equation established can deal with any kind of lateral force of riser. However the difficulty of solving riser behavior governing equation is reduced through transforming the four-order differential equation into a second-order one. The correctness of the analysis model and the calculation method has been verified through case study at last. Introduction Marine riser is the key equipment connecting subsea wellhead and floating drilling platform (ship) in deep-water drilling and exploration. Scholars have done quite a number of researches on riser mechanical behavior. Cliton G. Gosse(Cliton G. Gosse and G. L. Barksdale,1969) developed a mathematical model to analyze the marine riser behavior, and the nonlinear differential equation describing the static mechanics is solved by using the finite-difference approximation. Burke B G (Burke B G, 1973) deduced the riser mechanical deformation control differential equation with elastic mechanics method. Robert M. Sexton et al (Robert M. Sexton and L. K. Agbezuge, 1976; T.N.Gardner and M.A.Kotch,1976) developed a computer model making a dynamic analysis of the riser by calculating the riser stress, deflections and lower ball joint angle. Bruce E. Bennett (Bruce E. Bennett and Michael F. Metcalf, 1977) made some nonlinear dynamic analysis of coupled axial and lateral motions of marine riser, and the analysis method allowed engineers to investigate riser pipe bucking stability. W. R. Azpiazu (W. R.Azpiazu and V.N.Nguyen, 1984) analyzed the vertical dynamics of marine riser to determine the amplitude of dynamic forces and displacement caused by heave action. A. D. Trim (A. D. Trim, 1991) derived an equation of axial motion of a tensioned marine riser and a number of partical problems were considered, including the dynamic response following an emergency disconnection. V. J. Modi et al (V.J Modi et al, 1994) derived an equation of motion for a marine riser undergoing large deflections and rotations. Geir Moe (Geir Moe and Bjern Larsen, 1997) developed a differential equation describing the motions of marine riser with asymptotic solution. Chainarong Athisakul, et al (Chainarong Athisakul, et al, 2002) presented a variational approach to two-dimensional large strain static analysis of marine risers. A. Ertas (A. Ertas, 2006) proposed the riser dynamic differential equation, which is solved by the finite difference method. Khan R. A. (Khan R. A., 2006) made some dynamic analysis of risers subjected to regular or irregular wave with ABAQUS software, and the variation of riser bending stress with low frequency drilling ship movement and wave motion and current velocity were also analyzed. Chang (Chang, et al, 2008; Sun, et al, 2009; Ju, et al, 2011) did some research on riser stochastic nonlinear dynamic response, hanging axial dynamic analysis and wave-induced long-term fatigue analysis with theoretical and numerical simulation method. Zhou (Zhou et al, 2013) studied the mechanical properties of riser subjected to shear flow with experimental method and found the riser "one third effect" which can be explained through an analysis of the mechanical model and material mechanics theory. The purpose of this paper is to analyze the mechanical behavior of riser using Beam-Column Theory.