Flow-Induced Vibration Screening of a Thermoplastic Composite Pipe Water Injection Jumper

An active subsea field in the Gulf of Mexico has adopted a thermoplastic composite pipe (TCP) water injection jumper for its waterflood upgrade. The TCP spool is lightweight and flexible — relative to the traditional steel-only spool segments used in subsea jumpers. As such, the flow-induced vibration (FIV) threat from internal fluid flow must be assessed for the intended service. A three-tiered approach is used to assess the level of FIV threat expected in this TCP subsea jumper application. A high-level screening based on widely used industry guidelines indicates a high susceptibility to FIV fatigue failure for the steel product in the jumper, with no applicability to the TCP material. A comprehensive screening based on structural finite element analysis and computational fluid dynamics shows that the vibration levels and stress cycling due to FIV will be acceptable for the intended water injection application and a 30-year design life, when adopting a factor of safety of 10 for subsea service.

Extremely large-amplitude oscillation of soft pipes conveying fluid under gravity

In this work, the nonlinear behaviors of soft cantilevered pipes containing internal fluid flow are studied based on a geometrically exact model, with particular focus on the mechanism of large-amplitude oscillations of the pipe under gravity. Four key parameters, including the flow velocity, the mass ratio, the gravity parameter, and the inclination angle between the pipe length and the gravity direction, are considered to affect the static and dynamic behaviors of the soft pipe. The stability analyses show that, provided that the inclination angle is not equal to π, the soft pipe is stable at a low flow velocity and becomes unstable via flutter once the flow velocity is beyond a critical value. As the inclination angle is equal to π, the pipe experiences, in turn, buckling instability, regaining stability, and flutter instability with the increase in the flow velocity. Interestingly, the stability of the pipe can be either enhanced or weakened by varying the gravity parameter, mainly dependent on the value of the inclination angle. In the nonlinear dynamic analysis, it is demonstrated that the post-flutter amplitude of the soft pipe can be extremely large in the form of limit-cycle oscillations. Besides, the oscillating shapes for various inclination angles are provided to display interesting dynamical behaviors of the inclined soft pipe conveying fluid.

INVESTIGATION OF ROTATIONAL AND LONGITUDINAL MOTIONS OF A SUPER LONG ROD IN INCLINED BORE-HOLES

The article deals with a super long elastic tubular rod with an internal fluid flow. The rotational and longitudinal motions of straight and curved rods in inclined bore-holes are studied. The bifurcation states of the rod at these motions are investigated. The purpose of the study is to detect at the beginning of bifurcation states of straight and curved rods taking into account their friction interaction with the inner surface of a bore-holes. The reasons of appearance of bifurcation protrusion of the rod are stated. Among these reasons, an internal longitudinal force and torque are identified and described as main ones. Research methods are based on the construction of boundary-value problems determining the stress­strain state and stability of super long straight and curved rods in an inclined bore-hole. Solving the problems allows detecting the beginning of bifurcation states of rods. KEY WORDS: SUPER LONG ROD, STRIGHT AND INCLINED BORE-HOLE, ROTATIONAL AND LONGITUDINAL MOTIONS, BIFURCATION STATES, LONGITUDINAL FORCE, TORQUE.

Effectiveness of the segment method in absolute and joint coordinates when modelling risers

This paper presents two formulations of the segment method: one with absolute coordinates and the second with joint coordinates. The nonlinear equations of motion of slender links are derived from the Lagrange equations by means of the methods used in multibody systems. Values of forces and moments acting in the connections between the segments are defined using a new and unique procedure which enables the mutual interaction of bending and torsion to be considered. The models take into account the influence of the velocity of the internal fluid flow on the riser’s dynamics. The dynamic analysis of a riser with fluid flow requires calculation of the curvature by approximation of the Euler angles with polynomials of the second order. The influence of the sea environment, such as added mass of water, drag and buoyancy forces as well as sea current, is considered. In addition, the influence of torsion is discussed. Validation is carried out for both models by comparing the authors’ own results with those obtained from experimental measurements presented in the literature and from COMSOL, Riflex and Abaqus software. The validation is concerned with vibrations of cables and the riser with internal fluid flow as well as with frequencies of free and forced vibrations of a riser fully or partially submerged in water. The numerical effectiveness of both formulations is examined for dynamic analysis of the riser, whose top end is moving in a horizontal plane. Conclusions concerned with the effectiveness of both formulations of the segment method and the influence of torsional vibrations on numerical results are formulated.