The Study Of Non-linear Coupling Model In Vortex-Induced Vibration

With the development of marine engineering and exploration of deepwater resource, vortex-induced vibration (VIV) of deepwater riser and pipeline is a common concern bath nationally and internationally. There are three research directions, including experiment, numerical simulation and semi-empirical mathematical model. Main reasons for the semi-empirical model can attract extensive attention worldwide are that the cost is high in experiment and computer resources demand is big in numerical simulation.In the presented VIV response analysis of solid cylinder using semi-empirical model, two prediction models were adopted respectively, including power equation based on the basic equations of particle dynamics (D'alembert-Lagrange principle) and wake oscillator model based on the Hamilton principle.Dynamic mesh technology was adopted to achieve the simulation of moving wall boundary. And computational fluid dynamics (CFD) techniques, which analytically solve the viscous Navier-Stokes equations in order to obtain the hydrodynamic forces directly, were developed based on loose coupling algorithms in time domain. The codes can simulate successfully the VIV response of rigid and flexible rigid in 2-dimension flow fluid domain. In the study, a research was implemented to analysis the reliability, validity and uncertainty of 2D VIV coupling code. The turbulence was presented by SST model, and fourth order Runge-Kutta algorithm used for cylinder movement resolution and the time rate of change of fluid kinetic energy with a control volume and net fluid kinetic energy flux across the boundaries were output at the same time.Hamilton principle was used to establish wake oscillator model in VIV, which was of great applicability and expansibility. The hydrodynamic force and nonlinear fluid damping were quantified in the construction of wake oscillator model. There are two methods introduced to construct hydrodynamic force, including empirical hydrodynamic coefficient and point vortex model. The mathematical form of nonlinear fluid damping was given to satisfy the self excited vibration feature and nonlinear fluid-structure interaction relationship. Finally, the new wake oscillator model was solved based on the experimental data, and the results were compared with the Facchinetti's wake oscillator model. Finally, the fluid oscillator was analyzed in stability based on modern nonlinear mechanics.