Huliang Dai

In this study, a novel offset support design for enhancing the stability of fluid-conveying pipes is proposed. Specifically, by offsetting the simple support, the nonlinear stiffness in both tension and bending of the pipes is effectively increased. On the basis of the absolute nodal coordinate formulation (ANCF), a theoretical model for a pipe with an offset support under various boundary conditions is established and validated through experiments. A systematic investigation is subsequently conducted to explore the effects of the offset position and amplitude on the static deformation, stability, and nonlinear dynamic behaviors. The results indicate that the proposed offset support can significantly increase the stability of the fluid-conveying pipe and reduce its deformation amplitude. In most cases, a larger offset amplitude generally corresponds to a higher critical fluid velocity and a smaller deformation amplitude. With respect to the support position, placing an offset support at one-quarter of the span from the supported end can substantially improve the stability of simply supported pipes. With respect to cantilevered pipes, adding an offset support at the free end can considerably increase the critical flow velocity of the pipe. When the flow velocity is in the subcritical region, a pipe with an offset support maintains in-plane static deformation with a small amplitude. In the supercritical flow velocity region, compared with a pipe without an offset support, a pipe with an offset support has a smaller nonplanar configuration. This study provides new insight into enhancing the stability of fluid-conveying pipes via an offset support design, which features simple implementation and considerable application potential in engineering practice.

A slope-discontinuous pipe with both ends fixed has recently been shown to exhibit flutter once the internal flow velocity exceeds a critical value. This behavior is distinctly different from that observed in slope-continuous pipes. To investigate the dynamic characteristics of a slope-discontinuous pipe conveying fluid, a nonlinear dynamical model for a V-shaped pipe is developed in this study using the absolute node coordinate formulation (ANCF). The obtained results are compared with those from the finite element method (FEM) and validated against experimental data, confirming the reliability of the proposed augmented dimensional ANCF approach. The influence of the break angle θ between the two segments on the nonlinear vibrations of the V-shaped pipe is examined in detail. The results show that as θ increases, the natural frequency of the pipe first rises and then falls, reaching a peak at θ = 90°. Additionally, the displacement amplitude progressively decreases with increasing θ. As the flow velocity increases, the pipe first undergoes buckling, followed by flutter. The flutter mode may transition between periodic and non-periodic behaviors. The critical flow velocity for buckling remains nearly consistent across different break angles and is considerably higher than that of a straight pipe. In contrast, the critical flow velocity for flutter varies significantly with the break angle.

A slope-discontinuous pipe with both ends fixed has recently been shown to exhibit flutter once the internal flow velocity exceeds a critical value. This behavior is distinctly different from that observed in slope-continuous pipes. To investigate the dynamic characteristics of a slope-discontinuous pipe conveying fluid, a nonlinear dynamical model for a V-shaped pipe is developed in this study using the absolute node coordinate formulation (ANCF). The obtained results are compared with those from the finite element method (FEM) and validated against experimental data, confirming the reliability of the proposed augmented dimensional ANCF approach. The influence of the break angle θ between the two segments on the nonlinear vibrations of the V-shaped pipe is examined in detail. The results show that as θ increases, the natural frequency of the pipe first rises and then falls, reaching a peak at θ = 90°. Additionally, the displacement amplitude progressively decreases with increasing θ. As the flow velocity increases, the pipe first undergoes buckling, followed by flutter. The flutter mode may transition between periodic and non-periodic behaviors. The critical flow velocity for buckling remains nearly consistent across different break angles and is considerably higher than that of a straight pipe. In contrast, the critical flow velocity for flutter varies significantly with the break angle.

Vortex-induced vibration (VIV) energy harvesting has emerged as a promising method for powering sensor nodes. Multi-frequency coupling effects in fluid–structure interaction systems can enhance the output performance of VIV-based energy harvesters. Base excitation is one effective way to stimulate these effects. The multi-frequency coupling mechanism involves complex nonlinear interactions. These include the vortex shedding frequency ( f _s ), the structural natural frequency ( f _n ), the natural frequency of the bluff body ( f _sp ), the natural frequency of the piezoelectric beam ( f _p ), and the base excitation frequency ( f _b ). Maximizing the performance of the harvester requires a clear understanding of the frequency matching relationships among its components. It also depends on the development of effective optimization strategies that can enhance energy conversion and improve overall efficiency. This study examines the enhancement of VIV energy harvesting using multi-frequency coupling effects induced by base excitations. It aims to clarify the underlying mechanisms of multi-frequency coupling dynamics. The work also seeks to establish optimization criteria for key frequency matching. A theoretical model was established to examine the influence of base excitation on spherical VIV-based energy harvesting, and corresponding experimental studies were conducted. Compared with the pure VIV model, introducing base excitation amplifies the vibration response of the spherical bluff body within its lock-in region through frequency matching. Furthermore, it supplies a continuous energy input even outside the lock-in region. Consequently, the effective wind speed range is significantly expanded and the output performance is improved. The study elucidates the influence of the excitation frequency on the output performance of spherical VIV. In particular, the effects of key frequency ratios, namely, f _b / f _n , f _s / f _n , and f _sp / f _p , on energy harvesting performance were systematically investigated, revealing their crucial roles in achieving maximum output efficiency. The results show that base excitation significantly broadens the effective operating flow velocity range—from 2.2 ∼ 5.4 m s ⁻¹ to 2.2 ∼ 7.2 m s ⁻¹ . Under optimal frequency matching conditions (wind speed of 4.47 m s ⁻¹ , f _b = 14.3 Hz, and f _sp / f _p = 1.03), the maximum output voltage reached 69.36 V, representing an increase of 41.45 V compared to VIV alone, and 61.75 V compared to base excitation alone. A distinct soft response behavior was observed when varying the frequency ratio f _s / f _n , whereas a linear response was observed when varying f _b / f _n . Furthermore, the system demonstrated adaptability to varying inflow angles, with base excitation significantly enhancing voltage output within the range of 150° to 210°.