Abstract
The top tension riser (TTR) is one of the most frequently used equipment in deep-sea petroleum engineering. At present, the research methods of its vortex-induced vibration (VIV) are mainly focused on finite element analysis and experiment. The understanding of its various nonlinear mechanical mechanisms would be inadequate via limited numerical or experimental studies rather than nonlinear analysis of its rich dynamics. Based on the Van der Pol wake oscillator model, the nonlinear dynamic model of the TTR subject to shear flow VIV is established. The proposed model includes the fluid-structure interaction of the TTR under shear flow. Dynamic behavior of the TTR in association with the variation of flow velocity is investigated. The dynamic behavior is simulated by computing the local maximum displacement response via the fifth-order Galerkin discretization. The Poincare map is then utilized to quantify the dynamic property of TTR under each individual flow velocity, which helps identifying the bifurcation path of the nonlinear system. The time history, phase diagram, FFT spectrum, and envelope diagram about the riser VIV at typical flow velocity in different regions of the bifurcation diagram are then given. It is found that the VIV response of the TTR depicts the Hopf bifurcation phenomena with bistable characteristics. Together with the structural eigen-analysis and the three-dimensional spectrum contour, the main dynamic features of the TTR in shear flow are more comprehensively understood. Such understandings may provide new ideas and references for the design and optimization of the riser structural parameters.
Highlights
With the increasing demand for oil and gas resources globally, the exploitation of marine oil and gas resources gradually extend from shallow to deep water
When the vortex shedding frequency is close to the natural frequency of the riser, vortex-induced resonance will occur and may cause serious damage to the riser. e natural frequency of the riser directly affects the excitation of vortex-induced vibration and parametric vibration. erefore, study of the riser eigenvalues that vary with respect to structural parameters is helpful to determine the dynamic characters and VIV responses of the riser
Tang studied the dynamic response for coupled parametric vibration and VIV of top tension riser (TTR) combined with the Van der Pol wake oscillator model [25]
Summary
With the increasing demand for oil and gas resources globally, the exploitation of marine oil and gas resources gradually extend from shallow to deep water. As the deepsea risers are slender with large aspect ratio, the natural frequency and structure stability of the riser are reduced, and the vortex-induced vibration (VIV) of the deep-sea riser depicts more complicated dynamics with increasing water depth. Under this trend, a lot of new problems and new phenomena are emerged [1]. Tang studied the dynamic response for coupled parametric vibration and VIV of TTR combined with the Van der Pol wake oscillator model [25]. Based on the bending vibration theory of the Euler–Bernoulli beam and the high-order Galerkin discretization scheme, the influence of the sea flow velocity on the nonlinear dynamic behavior of the riser system is analyzed by Poincaremap method
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