Abstract
In this paper, a dynamic model of an offshore drilling riser is developed based on the Hamilton principle. The developed dynamic model is transformed into a finite element model by introducing an approximate solution which chooses the Hermite cubic interpolation function of bending beam element as the shape function. Thereafter, the standard Newmark integration is applied to numerically simulate the dynamic responses of offshore drilling risers with varied system parameters, including the length of riser, top tension ratio, and buoyant factor. Based on the results of numerical simulation, under the influences of sea wind, sea current, and the periodic excitation of sea wave, the offshore drilling riser experiences a fast lateral deflection phase in the beginning, a reciprocating deflection phase in the following long duration, and then, a periodic oscillation when it reaches the dynamic stable condition, respectively. The riser system working in deeper water with a higher top tension ratio and a lower buoyant factor shows more controllable vibration and less lateral deflection.
Highlights
According to the aforementioned works, the dynamic characteristics of offshore drilling risers have been continuously investigated during the past half century; in the published papers, several important steps both in the process of the dynamic modelling and in the solution procedure via finite element analysis were always omitted
In this paper, a completed procedure about both the model development and the corresponding solution flow path for offshore drilling riser is intended to be introduced in detail, which is a foundation work for the authors’ further research plan to analyse both the geometric nonlinearity and the contact nonlinearity on the dynamic responses of a riser-well-drilling string coupling system when it is applied in deep water drilling
(1) In this paper, the mathematical model of an offshore drilling riser system developed by using the Hamilton principle was introduced in detail, and the corresponding finite element model was, derived, so that the dynamic responses of offshore drilling risers with varied system parameters were numerically simulated by using the standard Newmark integration
Summary
P where P is the functional equation of the skew curve π(x, t), whose variation can be expanded as δ (δT(x, t) − δV(x, t) + δW(x, t))dxdt, Tw δ⎛⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎜⎝. As can be observed in equation (24), it is a challenge to solve the dynamic model of the riser analytically Under such circumstances, the finite element method is always considered due to its extensive adaptability. In order to discretize the developed riser model, an approximate solution of the deflection of the ith riser segment is set as πi(x, t) [N(x)]Si(t),. When introducing the approximate solution shown in riser shown in equation (24), the variation of functional equation (27) into the dynamic model of the offshore drilling equation can be expressed as δ. E Newmark integration algorithm is applied to solve the developed finite element model, and the dynamic responses of the riser system in time domain can be obtained via numerical simulation. A7 δ ∗ dt, as where dt is the size of time step
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