A prediction model for in-line and cross-flow coupled vortex-induced vibration of a near-wall circular cylinder
Meng-Meng Tao, Xu Sun, Peiyi Han
Abstract
Proximity of seabed complicates vortex-induced vibrations of submarine pipelines. Empirical models are better in engineering problem than high fidelity simulations and experiments to some extent. Present paper aims to propose a model consisting of structure and wake oscillators to predict in-line and cross-flow coupling vibration of a near-wall cylinder. Based on phenomena, mechanisms, and data analysis, some hydrodynamics, namely vortex shedding frequency and time-varying/time-averaged lift/drag coefficients, are modeled by Reynolds number, thickness of boundary layer, and gap (G) between cylinder and wall. Model responses reflect effects of the wall on the cylinder's vibration successfully. When G/D drops from 2 to 1 (D is diameter of the cylinder), amplitudes decrease monotonously, and the maximum amplitude shifts to a smaller reduced velocity (Ur). Vibrations and resonant tend to start/end at a larger/smaller Ur, leading to narrowing lock-in regions. Time-averaged transverse displacements increase monotonously in whole, while streamwise displacements drop in the resonance regime. Trajectories are shapes of symmetric “8,” being similar to that of an isolated cylinder in free stream. There are some unique features when G/D decreases from 1 to 0.35. First peak of in-line vibration tends to disappear. Trajectories become asymmetric shape of “8” or oval because the cylinder tends to vibrate in approximating frequencies in 2 directions. With further researches on effects of wall proximity, improvements of hydrodynamics can be better to enhance model's rationality and accuracy. An accurate model is essential to analyze the safety and reliability of submarine pipelines suffering vibration.