Search Results (329)

Vortex-induced vibration (VIV) is one of the main causes of fatigue failure in subsea pipelines and has recently attracted significant attention from researchers. Previous studies have mainly focused on idealized straight pipes, with limited consideration of gravity-induced slight curvature in free-spanning fluid-conveying pipes. In reality, the deformation configuration of a free-spanning fluid-conveying pipe is not fixed but varies with parameters such as internal flow velocity and tension, which in turn affect its dynamic behavior. A theoretical model, taking into account the axial stretching effect and the gravity-induced initial slight curvature, is developed to predict the VIV responses of free-spanning fluid-conveying pipes. The governing equations are derived based on Hamilton’s principle. The interaction between the external flow and the pipe structure is simulated using the van der Pol equation. By combining the Galerkin method and the Runge–Kutta method, the vibration responses of the pipe are obtained. The accuracy of the proposed model is validated by comparing the predicted VIV response curves and bifurcation diagrams with those reported in previous studies. The initial static deformation of the structure under different tensions and internal velocities is obtained through numerical calculations. It is found that the gravity-induced slight curvature leads to a reduction in the VIV response mode. The static deformation of the pipe decreases with increasing axial tension, while it increases with increasing internal flow velocity. Under the same external flow velocity, the gravity-induced initial deformation reduces the dominant vibration frequency and causes the vibration response to transition from quasi-periodic to periodic motion. Full article

A flywheel energy storage system (FESS) is a device that employs a high-speed rotating flywheel for energy storage, where the motor is a core component enabling the energy conversion. Since the motor rotor is integrated onto the flywheel rotor (FR), when the FESS operates, the vortex motion of the FR causes misalignment between the motor rotor and stator, and the resulting unbalanced magnetic pull (UMP) will induce changes in the vibration characteristics of the FR. This paper presents a permanent magnet synchronous motor (PMSM) designed for a FESS and analyzes the variation pattern of the UMP induced by rotor eccentricity in this motor utilizing the finite element method. Furthermore, the UMP is equivalently modeled using the motor stiffness, and a dynamic model of an active magnetically suspended rigid flywheel rotor that considers the UMP in the motor is established. In this study, the motor position offset ratio β is defined to quantify the axial distance between the motor position and the FR mass center. This paper analyzes the variation law of the vibration characteristics of the FR with the magnitudes of the UMP and the motor position offset ratio β using numerical calculations. Finally, the correctness of the calculated results is verified using experimental testing. This investigation demonstrates that the value of UMP fluctuates as the rotor’s rotation angle increases, while its average value exhibits a linear increasing trend with the growth in rotor eccentricity. As UMP and β increase, the first- and second-order critical speeds of FR exhibit a clear decreasing trend. Meanwhile, variations in these two factors also exert different influences on the vibration amplitude induced by the mass imbalance response of the FR. Therefore, when designing an active magnetically levitated flywheel energy storage system, the influence of motor parameters on the vibration characteristics of FR should be taken into consideration. Full article

Vortex-induced vibration (VIV) poses a significant serviceability concern for wide streamlined box girders of long-span suspension bridges. This study investigates the VIV performance and aerodynamic mitigation of a wide streamlined box girder with a width-to-depth ratio (B/D) of approximately 10 through sectional model wind tunnel testing. The original cross-section was found to exhibit pronounced heaving and torsional VIV at positive wind angles of attack, with amplitudes considerably exceeding the prescribed serviceability limits. A systematic experimental investigation was conducted to evaluate the influence of three geometric parameters, i.e., wind fairing inclination angle, inspection rail position, and pedestrian railing porosity and panel arrangement, on VIV performance. Experimental results demonstrate that reducing the wind fairing inclination angle from 65° to 45° is the most effective mitigation measure. An appropriate porosity of the pedestrian railing is shown to substantially improve VIV performance. Furthermore, under equivalent overall porosity, a uniformly distributed alternation of solid and ventilated panels yields markedly superior VIV suppression compared with continuously sealed arrangements. Subsequent flutter and aerostatic wind tunnel tests confirm that the recommended cross-section preserves the favorable flutter stability and aerostatic performance of the original design. Strouhal number analysis reveals that the VIV lock-in is governed by St ≈ 0.12. Notably, the St number obtained from the pitching moment coefficient is nearly twice that obtained from the lift coefficient. Full article

To investigate the dynamic response of marine risers under multi-parameter coupling effects, physical model tests of marine risers are designed and performed in this study. The tested parameters consist of structural parameters (materials, boundary condition and top tension) and environmental flow parameters (flow velocity, wave height and wave period). Three riser specimens including aluminum tube (Al), polymethyl methacrylate tube (PMMA) and unplasticized polyvinyl chloride tube (UPVC) are adopted to qualitatively simulate metallic risers and composite risers with distinct stiffness differences. A total of 216 sets of vibration test data are acquired from the indoor flume experiments. Based on experimental data, the individual effects of various parameters on the vibration amplitude and dominant frequency of risers are first analyzed via single-factor comparative tests. Subsequently, an XGBoost machine learning model is established to predict the cross-flow vibration amplitude of risers; stratified sampling and 5 × 5-fold cross-validation are utilized to optimize model hyperparameters. The model achieved a high goodness-of-fit of R² = 0.9296 during the development phase (training and internal validation), demonstrating favorable prediction accuracy. Finally, the SHAP interpretability method is introduced to quantify the contribution weights of individual parameters as well as the interaction mechanisms under multi-parameter coupling. Both single-parameter and multi-parameter analyses are performed, with representative results such as material = −3.965 and flow velocity = 2.085. The results indicate that the riser vibration amplitude exhibits a prominent negative correlation with material properties, boundary conditions, and top tension, while showing a positive correlation with flow velocity, wave height, and wave period. Full article

To investigate the dynamic transmission of unsteady hydraulic excitation within pumped-storage units, this study presents a numerical investigation on the three-dimensional shafting vibrations of a pump-turbine based on a one-way transient fluid-structure interaction approach. To resolve the flow field, we adopt the shear stress transport (SST) k-ω turbulence model in conjunction with the Zwart-Gerber-Belamri (ZGB) cavitation model, and the combined numerical approach is first calibrated against experimental measurements. The results indicate that under the 70% partial load, an eccentric helical vortex rope develops inside the draft tube, generating intense low-frequency pressure pulsations that induce chaotic shaft orbits and distinct orbital drift at the turbine guide bearing. Conversely, near the optimal efficiency point (90% load), the vortex rope transitions into a slender, straight conical core, yielding minimum vibration magnitude and exceptional operational stability. At the 100% rated load, the vortex rope expands into a robust straight conical structure extending continuously into the elbow section. Stress analysis reveals that while equivalent stress concentrations consistently occur at the blade root regions, a reduction in the cavitation number at both 90% and 100% loads leads to a counterintuitive decline in blade surface peak stress values. Additionally, stiffness sensitivity analysis demonstrates that the relative change rates of the shaft runout are highly sensitive to the stiffness variations of the turbine guide bearing, where a stiffness reduction triggers a substantial runout growth of approximately 100% along the X- and Y-directions, whereas the variations in the upper and lower guide bearings exert extremely weak impacts. Full article

Sediment transport beneath subsea pipelines is essentially a highly complex multiphase flow problem, involving strong coupling between hydrodynamics, structural response, and sediment transfer. Accurately capturing this process is of significant scientific and engineering importance for predicting seabed evolution and ensuring the structural safety and stability of subsea pipelines. In this study, the coupled vortex-induced vibration (VIV) and scour behaviour of subsea pipelines under steady current conditions is investigated using a computational fluid dynamics (CFD)-based numerical approach. The solver is developed within SedFoam by incorporating dynamic mesh motion to account for pipeline vibration. The pipeline is modelled as a single-degree-of-freedom system with a vertically mounted spring and a concentrated mass. The numerical results reveal a strong interaction between pipeline VIV and the evolving seabed morphology. Repeated pipeline motion toward the seabed significantly modifies the local scour profile and promotes the formation of a sand dune beneath the pipeline. The presence of the sand dune alters the near-bed flow field and suppresses vortex shedding beneath the pipeline. As the scour process develops and the fluid–structure–seabed interaction intensifies, the VIV response of the pipeline is progressively reduced. The present study highlights the important coupling mechanisms between pipeline vibration and seabed scour and provides insights into the dynamic evolution of pipeline–seabed interaction. Full article

Flow interference among bluff bodies can strongly amplify or suppress unsteady aerodynamic forces and induced vibrations thereof. However, the behaviour of tandem square-cylinder interference and its passive control in the laminar regime remains insufficiently quantified, particularly near the known critical tandem spacing ratio (L/D ≈ 4.5). This study systematically analysed and determined how a splitter plate placed downstream of the second cylinder modulates the aerodynamic forces, symmetry of vortex shedding, wake topology, and associated wake metrics in two-dimensional incompressible laminar flows. Unsteady finite-volume numerical simulations were conducted using ANSYS Fluent (2022 R1) at Re = 150. The tandem cylinder spacing (L) was varied over L/D = 2–6 (D, the cylinder side length), and the splitter gap (G) was varied over G/D = 1–6. The splitter plate acted as a strong wake stabiliser at small gaps (G/D = 1), where vortex shedding was largely suppressed and lift fluctuations were minimal (for example, C_l,rms ≈ 0.055), and the DC experienced negative drag (C_d ≈ −0.13), consistent with elongated and weakly rolled-up shear layers and extended recirculation. The splitter plate acted as a sharp control “switch” at a critical splitter gap G/D ≈ 2, where the wake transitioned to unsteady shedding, the Strouhal number (St) jumped to values that remained nearly constant for G/D = 2–6, and the wake metrics indicated earlier roll-up (reduced vortex formation length and recirculation length) and greater lateral spreading (increased wake width). The outcome was influenced by the tandem regimes: for 1.5 < L/D < 4, persistent shielding and negative downstream drag predominated. However, near the critical gap (L/D ≈ 4.5), the restoration of shear-layer impingement at G/D ≥ 2 resulted in a downstream drag surpassing the isolated-cylinder baseline (C_d,SC ≈ 1.49) by approximately 3–8%. In the co-shedding regime, when L/D = 5, there was a notable increase in drag, approximately 12.3% more than that on an isolated cylinder. Conversely, when L/D = 6, the system approached aerodynamic independence without any amplification (approaching the single-cylinder value). The interference metrics showed a maximum combined drag reduction of ~68.6% at L/D = 4.5 and G/D = 1, whereas the upstream cylinder drag was only weakly affected. The results of the present study establish splitter placement as an effective passive control method for suppressing or recovering interference-driven unsteadiness, thereby supporting designs in bluff-body aerodynamics, heat-transfer equipment, and vibration-mitigation systems. Full article

The distributed electric propulsion (DEP) system offers significant potential for enhancing aerodynamic efficiency, reducing emissions, and enabling innovative aerodynamic configurations. However, the strong coupling between propeller slipstream effects and wing structural dynamics presents new challenges for aeroelastic analysis. To address this issue, this paper proposes an aeroelastic modeling approach tailored for DEP systems that systematically accounts for the effects induced by propeller slipstreams. Specifically, the induced velocity generated by the propeller slipstreams is computed using a slipstream tube model and incorporated into the unsteady aerodynamic modeling via the unsteady vortex lattice method. Under appropriate assumptions, a state-space formulation of the unsteady aerodynamic forces is derived, while the wing structural dynamics are represented using the finite element method. After establishing the subsystem models, a complete aeroelastic model of the DEP system is assembled based on the input–output relationships among the subsystems. Nonlinear simulations are conducted using this integrated model. The results demonstrate the potential of distributed propellers for suppressing wing vibrations and alleviating structural loads. Full article

A novel circular-T-attachment (CTA) oscillator is proposed to improve the oscillation response and energy-harvesting performance. This combined section is designed to change the boundary layer separation and avoid vortex reattachment, effectively enhancing energy conversion in the galloping branch. Results indicate that in the vortex-induced vibration (VIV) branch, the harvested fluid energy increases with reduced velocity. As system damping increases, the oscillatory response transitions from soft galloping (SG) to hard galloping (HG), indicating a progressive weakening of the self-excited transition to galloping. Within the tested parameter range, the galloping branch provided the most favorable energy-conversion performance. The maximum amplitude ratio reached 2.43, while the maximum active power and energy conversion efficiency (ECE) reached 19.3 W and 26.2%, respectively. Compared with a conventional triangular prism oscillator at the same reduced velocity, the proposed CTA oscillator achieved increases of 9.29 W in active power and 12.59 percentage points in energy conversion efficiency. These results clarify the flow-induced response mechanism of the circular-T-attachment oscillator and provide new insights for improving the performance and expanding the application range of flow-induced motion energy conversion systems (FIMECSs). Full article

As core structural components for deep-sea oil and gas exploitation, deep-sea risers are continuously subjected to wind, wave, and current loads, which readily induce vortex-induced vibration (VIV) and further trigger structural fatigue damage. Furthermore, the progressive exploitation of deepwater and ultra-deepwater oil and gas resources has exacerbated the complexity and risk of riser VIV, rendering it a critical engineering problem that urgently requires effective solutions. This paper presents a comprehensive review of numerical studies on deep-sea riser VIV, systematically elaborating the fundamental principles, research advances, and application scenarios of three mainstream numerical approaches: semi-empirical models, computational fluid dynamics (CFD) models, and computational structural dynamics (CSD) models. The respective accuracy advantages and inherent limitations of each numerical method are thoroughly analyzed. Additionally, this review focuses on key research hotspots and challenging issues, including VIV responses of flexible risers, dynamic fluid–structure boundary coupling, internal–external flow coupling effects, wake interference of multi-riser systems, efficient VIV prediction, and vibration suppression optimization. The current technical bottlenecks in existing research are clarified. This study aims to provide a systematic theoretical framework and methodological reference for subsequent numerical investigations and engineering applications of riser VIV, and offer technical support for the optimal structural design and safety risk prevention of deep-sea riser systems. Full article

Water channel experiments were conducted to investigate the influence of aspect ratio (H/D = 0.9–1.9) on the flow-induced motion (FIM) and hydrokinetic energy conversion performance of an elastically mounted circular cylinder with T-shaped attachments (Cir-T-Att). The results indicate that the aspect ratio critically governs the vortex-induced vibration (VIV) to galloping transition by modulating the effective angle of attack. While larger H/D promotes galloping and higher amplitudes under low damping, this benefit is negated under elevated system damping, where amplitudes are uniformly suppressed. Consequently, the maximum power output exhibits a non-monotonic dependence with H/D. Within the investigated parametric range, peak performance occurs at H/D = 1.1, with a total damping ratio ζ_total = 0.122 and reduced velocity U_r = 11.25. For practical harvester design, the optimal H/D should be selected by aligning the intended oscillation regime with local flow characteristics. Full article

The tower with an attached vent stack is a special arrangement in chemical tower structures. Flow-induced vibration of this configuration directly affects the safe operation and structural fatigue life of the equipment. This paper investigates the vortex-induced vibration (VIV) characteristics of a two-cylinder system consisting of a tower and its attached vent stack. Through fluid–structure interaction (FSI) simulations of two unequally sized cylinders in a bundled arrangement, the vibration responses under first and second-mode critical wind speeds with a flow direction of 0° are analyzed. The analysis examines lift and drag coefficients, vibration displacements, and wake flow evolution to reveal the vibration response pattern under multi-parameter coupling. When the lift forces obtained from FSI are applied in a static calculation, the static results for both the first and second-mode critical wind speeds are approximately 250% larger than the FSI results, indicating a significant discrepancy. Further analysis shows that in the FSI simulations, a notable phase difference exists between the fluid excitation and the structural response, causing the lift force to do negative work during part of the vibration cycle, thereby limiting the net energy input. Under the second-mode critical wind speed, the lift distribution along the tower height is significantly non-uniform. The conventional static calculation method neglects both the phase difference and the non-uniform lift distribution along the height, leading to overly conservative predictions. Full article

Local scour and vortex-induced vibrations around cylindrical structures in curved channels pose significant risks to the safety and stability of critical hydraulic infrastructure, such as bridge piers. To address these engineering challenges and elucidate the underlying flow mechanisms, this study conducts numerical simulations of flow past two side-by-side circular cylinders of equal diameter in a curved channel under subcritical conditions at Re = 3900, using the Realizable kε turbulence model. Spectral Proper Orthogonal Decomposition (SPOD) is introduced to quantitatively characterize the energy distribution and dominant coherent structures. Taking the spacing ratio L/D and the placement angle α as key design parameters, the flow field characteristics, modal energy distribution, and coherent structure evolution are systematically investigated for two side-by-side cylinders in three-dimensional straight and curved channels. The numerical results show that, in the straight channel, as L/D increases from 2 to 4, the flow field evolves from strong coupled interference to weak interaction. The vortex shedding frequency structure evolves from a single dominant frequency to a multi-frequency distribution with rich harmonic components, indicating a transition in wake dynamics from energy concentration to multimodal dispersion, accompanied by a significant improvement in flow stability. Under curved channel conditions, the results reveal an asymmetric flow field caused by pronounced energy concentration on the inner side of the channel. SPOD analysis further indicates that as the placement angle α increases from 30° to 90°, the modal energy distribution changes from concentrated to dispersed, the frequency spectrum broadens with enhanced harmonic components, and flow instability gradually intensifies. Overall, the spacing ratio L/D mainly governs the wake-interference pattern, whereas the placement angle α regulates the frequency structure and energy distribution. Among all the cases investigated, relatively favorable flow stability is achieved at L/D = 4 and α = 30°. The SPOD-derived modal energy distributions show that the streamwise fluctuation length of the dominant-mode energy is approximately 0.25 m at α = 30°, compared with 0.5 m at α = 90°, with the energy bandwidth nearly doubling. The combined CFD-SPOD approach effectively captures energy evolution and coherent structure characteristics of complex flows across spatial, temporal, and spectral dimensions. This enables a shift from conventional flow-field description to frequency-based mechanism analysis and provides a theoretical basis for structural layout optimization and scour protection in hydraulic engineering. Full article

Vortex-induced vibration (VIV) is the main cause of fatigue failure in steel catenary risers (SCRs). This study developed a fluid–structure interaction (FSI) model, combining Reynolds-Averaged Navier–Stokes (RANS)-based computational fluid dynamics (CFD) with the Newmark-β algorithm, to simulate VIV responses under ocean currents and platform heave motion. First, the FSI model analyzed SCR behaviors under steady currents, then was adapted to oscillatory flow mimicking heave motion. A finite element model (FEM) was built, using the simulated VIV response as displacement boundary conditions to compute the equivalent stress time history along the riser. Finally, Miner’s rule was applied to quantify fatigue damage in three scenarios: current-only, heave-only, and the combined action of both factors. The results indicate that, in the South China Sea’s 10-year return period sea state, the SCR experiences a broad vortex-induced resonance interval under ocean current loads, with a maximum vibration amplitude of 0.7D. At the associated resonant height, platform heave motion triggers near-complete lock-in of the SCR’s VIV. The peak fatigue damage induced by ocean currents alone, platform heave motion alone, and their combined action all concentrates at the riser touchdown point (TDP). Over the 600 s VIV response duration, fatigue damage from platform heave motion alone constitutes 8.48% of that caused by ocean currents alone, while the combined action results in fatigue damage 1.847 times that of ocean currents alone. Thus, the combined action significantly amplifies both the magnitude and spatial non-uniformity of VIV-induced fatigue damage in SCRs. Full article

This paper investigates the effects of two control measures on vortex-induced vibration and wake-induced vibration of suspension bridge cables through wind tunnel experiments. For a single cable, a passive suction/jet ring arrangement is proposed, and its vortex-induced vibration suppression performance under different density configurations (single-segment and two-segment dense arrangements) is analyzed. Experiments show that the total length of the ring is positively correlated with the control effect. The two-segment arrangement is significantly better than the single-segment arrangement when the total length is 1/4 of the cable length, with a maximum reduction in vibration displacement of 88%. For double cables, a spacer with an integrated tuned mass damper (TMD) is used. The results show that the TMD can effectively suppress vortex-induced vibration and wake-induced vibration. Its control effect depends on the installation position and the damper’s natural frequency. Installation at mid-span and 1/4-span positions can significantly reduce the vibration response, especially for suppressing first-order mode vibration. This study provides an optimized aerodynamic and damper combination scheme for cable wind vibration control. Full article