Zhichuan Wu

An experimental investigation was conducted to examine the wake dynamics and mode transitions of an elastically mounted triangular prism undergoing vortex-induced vibration (VIV) and galloping. Particle image velocimetry measurements were performed in a circulating water channel over the Reynolds number of 4.44 × 104 ≤ Re ≤ 1.14 × 105 in TrSL3 (transition in shear layer, 20 000 ≤ Re ≤ 200 000). The wake structures were analyzed together with the measured displacement histories, allowing the wake evolution to be related to the response branches of the prism. For the stationary prism, alternating vortices shed symmetrically, with increased coherence and a reduced formation length as the reduced velocity increases. For the freely oscillating prism, distinct wake modes emerge within different response branches. The wake evolved from a 2S mode in the VIV initial branch to a 2P mode in the VIV upper branch, and further developed into a 2P + S mode in both the VIV–galloping transition branch and the galloping branch. The wake-mode transitions indicate that the wake of the triangular prism undergoes a progressive reorganization with increasing reduced velocity, involving changes in vortex formation, pairing, and shedding. Compared with the wake behavior commonly studied for circular cylinders, the persistence of the 2P + S mode at high reduced velocities reveals a fundamental influence of cross section on the nonlinear fluid–structure interaction. The present results provide experimental evidence for the wake-mediated mechanisms underlying VIV and galloping of non-circular bluff bodies.

This study presents a series of hydrodynamic experiments on a novel pontoon-type offshore floating photovoltaic (OFPV) structure, designed to improve wave attenuation performance and platform stability in marine environments. Using a 1:14 Froude-scaled physical model capable of representing different connector stiffness levels, nine structural configurations were tested, covering four array scales, three stiffness levels, and two floater sizes. Experiments were conducted under regular wave conditions, with structural responses measured at three representative positions: wave-facing front (T1), mid-array (T2), and leeward side (T3). Recorded parameters included surge acceleration, heave acceleration, pitch angle, and heave displacement. Results show that increasing array scale consistently reduced motion amplitudes at all positions, with heave acceleration at T3 substantially decreased compared with the smallest array. Enhancing connector stiffness significantly suppressed dynamic motions, particularly downstream, while larger floaters notably reduced heave responses under short-period waves. Despite variations in magnitude, response trends with respect to wave period remained broadly consistent across configurations. These findings provide quantitative evidence and engineering guidance for optimizing array configuration, connector stiffness, and floater dimensions to enhance the hydrodynamic performance and operational reliability of large-scale offshore FPV platforms.

A series of experimental tests on flow-induced motion (FIM) and energy conversion of two rigidly coupled triangular prisms (TRCTP) in tandem arrangement were conducted in a recirculating water channel with the constant oscillation mass m_osc. The incoming flow velocity covered the range of 0.395 m/s ≤ U ≤ 1.438 m/s, corresponding to the Reynolds number range of 3.45 × 10⁴ ≤ Re ≤ 1.25 × 10⁵. The upstream and downstream triangular prisms with a width of 0.1 m and length of 0.9 m were connected by two rectangular endplates. Seven stiffness (1000 N/m ≤ K ≤ 2400 N/m), five load resistances (8 Ω ≤ R_L ≤ 23 Ω), and five gap ratios (1 ≤ L/D ≤ 4) were selected as the parameters, and the FIM responses and energy conversion of TRCTP in tandem were analyzed and discussed to illustrate the effects. The experimental results indicate that the “sharp jump” phenomenon may appear at L/D = 2 and L/D = 3 significantly, with substantially increasing amplitude and decreasing oscillation frequency. The maximum amplitude ratio in the experiments is A*_Max = 2.24, which appears after the “sharp jump” phenomenon at L/D = 3. In the present tests, the optimal active power P_harn = 21.04 W appears at L/D = 4 (U_r = 12.25, K = 2000 N/m, R_L = 8 Ω), corresponding to the energy conversion efficiency η_harn = 4.67%.