Tongming Zhou

This study investigates the effects of the restitution coefficient on the coupled vortex-induced vibration (VIV) and wall impact dynamics of a near-wall cylinder with a small gap ratio of 0.1. A two-dimensional fluid–structure interaction (FSI) model is established at Re = 150 for an elastically mounted cylinder undergoing pure transverse motion. Employing an overset grid scheme and a velocity reversal impact model, the structural vibration, impact loads, hydrodynamic forces, and wake evolution are systematically analyzed over a reduced velocity range of 2 ≤ Ur ≤ 14 under three restitution coefficients: b = 0, 0.5, and 1.0. The wall confinement substantially suppresses vortex development on the gap side, leading to two distinct wake regimes: a no-shedding (NS) mode for Ur = 2–5 and a single-sided shedding (SS) mode for Ur = 6–14. The NS–SS transition triggers a sharp increase in the root mean square vibration amplitude at Ur = 6 and forms a well-defined lock-in regime for Ur = 6–12. Continuous cylinder-wall collision occurs within the lock-in range, whereas collision is absent at low reduced velocities (Ur = 2–5) due to insufficient vibration amplitude and at high reduced velocities (Ur = 13–14) owing to the elevated time-averaged equilibrium position and attenuated vibration response. The mean collision force reaches its maximum at Ur = 10. The wall impact process is characterized by gap fluid compression, instantaneous velocity reversal, and inertia-dominated pressure and lift pulses, followed by post-collision high-frequency velocity oscillations and hysteresis. An increase in the restitution coefficient strengthens impact intensity, amplifies high-frequency dynamic responses, and prolongs the hysteresis stage, while exerting a negligible influence on the wake topology and low-frequency VIV characteristics. The studied FSI system presents a typical dual-timescale coupled behavior, where the global dynamic response is dominated by single-sided vortex excitation and weakly modulated by collision-induced nonlinearities.

This paper presents the numerical results of three-dimensional flow characteristics around a finite wall-mounted conical cylinder with an aspect ratio fixed at AR = 4 and the end diameter ratio (D1/D2) ranging from 0.5 to 1.0 at a low Reynolds number, Re = 50–500. The flow characteristics are discussed in terms of time-averaged streamlines, distribution of singular points, topological structures, three-dimensional mean streamwise vortices, and instantaneous spanwise vortices. Compared to an infinite height configuration, the downwash flow caused by the free-end suppresses the formation of the Kármán vortex street in the wake. The critical Reynolds number for horseshoe vortex formation exhibits a significant dependence on D1/D2, decreasing to Re = 150 when D1/D2 = 0.5. Two distinct topological patterns are identified in the time-averaged streamline behind the cylinder. Three flow patterns above the free-end of the finite conical cylinder are demonstrated, providing additional insights into flow structures on free-end surfaces. The stable Quadrupole, Sextupole, and Octupole types of time-averaged streamwise vortices are compared across different Re and D1/D2. Furthermore, this work not only reconciles the time-averaged and instantaneous interpretations with the solenoidal condition of the vorticity field but also clarifies the fundamental mechanisms behind the topological transition from hairpin to braid vortices driven by strain rate.

This study investigates the coupling effects between ship roll response and internal sloshing through combined experimental measurements and potential flow simulations. The roll motion response of a ship with internal sloshing is characterized by a two-peak variation with incident wave periods. The periods at the peaks correspond to the first and second ship roll resonant periods. Systematic experiments demonstrate the transition of dominant roll amplitudes from the second to the first resonant period with increasing filling depth, governed by sloshing-induced restoring and overturning moments. A conceptual oscillator model is further introduced to interpret the two-peak variation in roll motion. The findings provide a new physical and theoretical basis for predicting roll resonance of ships with internal sloshing, offering valuable insights for the design of offshore structures.

This paper reports the experimental results of the vortex-induced vibration (VIV) and pipe-wall impact of an inclined near-wall flexible pipe transporting three representative internal flows with oblique angle (θ) ranging from 0° to 45°. The flexible pipe with an aspect ratio of 57 was fixed at both ends. The tests were performed in a recirculation water flume in the reduced velocity range of Ur = 7.92–23.92 using the non-intrusive optical measurement. The experimental results indicate that the existence of internal flow causes the tilt of the peaks of root-mean-squared (RMS) amplitude toward the downstream of internal flow. Nevertheless, with increasing θ, the peaks of RMS amplitude tilt to the upstream of internal flow. The mode competition of the pipe conveying gas flow is the weakest, but it is the most sensitive to θ. In contrast, the most intense mode competitions are observed in the pipe conveying gas–liquid flow and the pipe conveying liquid flow for the in-line and cross-flow directions, respectively. Five pipe-wall impact patterns are identified based on the impact position and frequency, and the partition of wall-impact pattern is provided in the s/L–Urn diagram. The impact position undergoes spatial transfer with the change of θ, especially for the pipe conveying gas flow. By comprehensive consideration of the spatial-temporal evolution of VIV response and impacting segments, the independence principle is invalid in predicting the VIV of near-wall flexible pipe span conveying internal flow.