Vortex-induced vibrations of inclined and curved flexible cylinders with a strip-theory-based discrete vortex method

Non-vertical flexible structures, such as inclined and curved cylinders, are encountered in deep-sea applications and exhibit more complex vortex-induced vibration (VIV) responses than vertical cylinders due to geometric non-uniformity and flow-curvature interaction. These complexities challenge both full-scale computational fluid dynamics (CFD) and reduced-order models, emphasizing the need for an accurate and efficient CFD-based approach. This study presents a meshless numerical methodology employing strip-theory-based discrete vortex method (SDVM) to simulate the VIV in non-vertical flexible cylinders. The full-scale flow is approximated by a sequence of flow strips, each resolved using SDVM without empirical hydrodynamic coefficients. Structural dynamics are modeled using a tensioned Bernoulli–Euler beam and solved in time domain. The methodology is validated against two benchmark experiments: an inclined flexible cylinder and a steel catenary riser (SCR) in uniform flow. Simulations verify the independence principle up to 60° inclination. For the SCR, a mixed standing-traveling wave pattern is observed, with downward energy transfer from the top. Additionally, a novel modal group switching behavior, characterized by abrupt shifts in the dominant frequency and amplitude, is also identified over a broad range of incoming flow velocities. The proposed methodology offers an efficient and accurate tool for simulating VIV in complex offshore structures, bridging the gap between simplified reduced-order models and full-scale CFD simulations.