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Over the past few years in the generation of electricity from wind in new technological approaches, the generation of electricity from wind has been strong and positive interest which is able to be profitable at small scale. Vortex wind turbine could be also defined as to grow in advance, a totally new concept of wind turbine with different or traditional way which means without blades. In the bladeless wind turbine (BWT), there structure is a flexible cylindrical structure over the set up that extracts possible form of energy from moving airstream and utilizing such type of vortex induced vibration (VIV) method to induce the vibration in the structure. It is not only aerodynamic type of forces which could results in structural vibration during operation. The VIV method in which a blades are eliminated in such a way that structure will be having a long cylinder which is arranged on a flexible structure and placed in open environment where there will be moving air at certain velocity ‘air flow field’. The vibration is converted into electrical energy and the electrical energy utilizing a power unit, which is a power generation system i.e., piezoelectric generator arrangement. The result analysis is based on flow induced vibration which is characterized by poor conversion efficiency. The system is consider to be portable for experimentation hence the manufacturing parts is used as light in weight such as sheet, coil, piezoelectric arrangement and etc. It results in low investment and manufacturing cost. Experimental result and analytical data with appropriate conclusion is presented herewith through the present investigation. Results are highlighted based on the phenomenon of induced vibration at even critically low wind speed where traditional and conventional wind turbines may not yield required results.

This paper presents a magnetically coupling bending-torsion piezoelectric energy harvester based on vortex-induced vibration from low-speed wind. The theoretical model of the energy harvester was formulated and validated by wind tunnel experiments. Numerical and experimental results showed that the power output and bandwidth of the proposed harvester are improved about 180% and 230% respectively compared with the nonmagnetic coupling harvester. Furthermore, the effects of cylinder, piezoelectric layer, load resistance, and magnetic nonlinear parameters on the harvester were investigated based on the distributed parameter model. The results showed that the length of cylinder hardly affect output power, but the diameter of cylinder presented complicated influences. The width of piezoelectric beam was negatively correlated with the torsion angle. With increasing the length of piezoelectric layer, an optimal wind velocity and load resistance can be obtained for the maximum output power. With decreasing of the distance between two magnets, the resonant bandwidth, the optimal power output, and torsion angle can be enhanced, respectively. Besides, the magnetic potential energy increased owing to the magnetically coupling, which led to the improvement of onset speed for the energy harvester. This study provides a guideline on improving the performance of bending-torsion vibration piezoelectric energy harvester.

Circular section tubular members with smaller wind load shape coefficient and higher stability are widely used in ultra-high-voltage (UHV) transmission towers. However, the tubular members, especially those with a large slenderness ratio, are prone to vortex-induced vibration (VIV) within a specific wind speed range. The sustained vibration of members can easily cause fatigue failure of joints and threaten the operational safety of transmission lines. Consequently, a novel countermeasure for the VIV of tubular towers using a new type of radial spoiler is proposed, whose mechanism is to change the vortex shedding frequency by destroying the large-scale vortexes into small-scale vortexes. Then, the parametric analysis of different variables is carried out based on the orthogonal experiment and numerical simulation, including the height H and length B of the spoiler and the distance S between adjacent spoilers. The results show that the above three parameters all have significant influences on vortex shedding frequency. Additionally, a practical design method of the new radial spoiler is proposed, and the recommended values of H, B, and S are 1D∼2D, 1.5H∼3H, and 5D∼12.5D, respectively, where D is the diameter of the tubular member. Finally, a numerical verification of the suppression effects is carried out, demonstrating that the proposed quick design method is simple and reliable, which can be widely used in the VIV design of tubular towers.

Previous studies of analysis and prediction of marine risers responses usually focus on vortex-induced vibration (VIV) of cross-flow (CF) direction rather than in-line (IL). Recent studies show that responses of IL direction tend to dominate in some cases. Responses of long riser due to biaxial bending of IL and CF VIV are investigated. Closed-form formulas are derived for estimating maximum normal stress due to the biaxial moment of CF/IL VIV and relations for estimating biaxial stress using CF values are presented. Analytical results are compared with numerical results of the time domain model and a good correlation is observed. It is shown that for tension and bending-controlled modes of vibration if the ratio of displacement amplitude of IL to CF direction is, respectively, higher than 0.22 and 0.35, normal stress due to biaxial bending is noticeably more than one directional (CF) bending stress. For a case study, the maximum biaxial stress along the riser is about 20 and 40% higher than the maximum CF stress along the length of the riser for bending and tension-controlled modes of vibration, respectively. Such results can be important not only directly in design issues, but also they may be noticeable in fatigue analysis.

A low-dimensional model of a top-tensioned riser under excitations from vortices and time-varying tension is proposed, where the van der Pol wake oscillator is used to simulate the loading caused by the vortex shedding. The governing partial differential equations describing the fluid–structure interactions are formulated and multi-mode approximations are obtained using the Galerkin projection method. The one mode approximation is applied in this study and two different resonances are investigated by employing the method of multiple scales. They are the 1:1 internal resonance between the structure and wake oscillator (also known as ‘lock-in’ phenomenon) and the combined 1:1 internal and 1:2 parametric resonances. Bifurcations under the varying nondimensional shedding frequency for different mass–damping parameters are investigated and the results of multiple-scale analysis are compared with direct numerical simulations. Analytical responses are calculated using the continuation method and their stability is determined by examining the eigenvalues of the corresponding characteristic equations. Effects of the system parameters including the amplitude of the tension variation, vortex shedding frequency and mass–damping parameter on the system bifurcations have been investigated. The analytical approach has allowed to probe bifurcations occurring in the system and to identify stable and unstable responses. It is shown that the combined resonances can induce large-amplitude vibration of the structure. Counter-intuitively, the amplitude of such responses increases rapidly as the amplitude of the tension variation grows. Comparisons between the analytical and numerical results confirm that the span of the system vibration can be accurately predicted analytically with respect to the obtained response amplitudes of responses. The proposed multi-mode approximation and presented findings of this study can be used to enhance design process of top tension risers.

This article proposes a novel hybrid piezoelectric–electromagnetic vortex-induced vibration energy harvester from flow of water inside of a pipe. The piezoelectric energy harvester was modeled with a macro-fiber composite P2-type while the electromechanical transduction was modeled by an elastic magnet coupled to the bluff body movement. A dual-mass configuration was proposed to increase the energy harvesting efficiency. Theoretical models and the submerged natural frequencies of the hybrid energy harvesters were outlined. Computational fluid dynamics and finite element analysis with ANSYS were used to visualize the response in synchronization and output the voltage extracted from the harvesting mechanisms. The addition of a secondary system improves the amount of harvestable energy and outputs more energy than just a single system. This demonstrates the superiority of a dual-mass hybrid system. A tuned secondary beam was used for L-body configurations to make use of inline oscillations, and the secondary piezoelectric output improved for all configurations. Secondary beam tuning also improved the performance of the harvester by any amount between 21% and 52% when compared against a single-mass hybrid energy harvester. A comparative study showed that the L-vertical and vertical bluff-body-tuned was the best performing hybrid-PE energy harvester based on total voltage output.

Helical strake is a widely-used device for passive flow-induced vibration (FIV) control of cylindrical structures. It is omnidirectional and can effectively reduce FIV response amplitude. Studies on the passive FIV control for cylindrical structures are mainly concerned with a single isolated cylinder, while the influence of wake interference between multiple cylinders on FIV suppression devices is less considered up to now. In engineering applications, multiple flexible cylinders with large aspect ratios can be subjected to complex flow forces, and the effects of wake interference are obvious. The FIV suppression effect of helical strake of a common configuration (17.5D pitch and 0.25D height, where D is the cylinder diameter) in two staggered cylinders system is still unknown. This paper systematically studied the FIV response of multiple cylinders system fitted with the helical strakes by model tests. The relative spatial position of the two cylinders is fixed at S = 3.0D and T = 8.0D, which ensures the cylindrical structures in the flow interference region. The experimental results show that the helical strakes effectively reduce the FIV response on staggered upstream cylinder, and the suppression efficiency is barely affected by the smooth or straked downstream cylinder. The corresponding FIV suppression efficiency on the downstream cylinder is remarkably reduced by the influence of the upstream wake flow. The wake-induced vibration (WIV) phenomenon is not observed on the staggered downstream cylinder, which normally occurs on the downstream straked cylinder in a tandem arrangement.

Purpose This paper aims to analyze the effect of fin geometry on mechanisms of flow induced vibration. Finned tube arrays are used in a heat exchanger to increase its efficiency. Therefore, it is necessary to investigate the effect of geometric parameters of the fin fluid elastic instability and vortex shedding. In this paper, the effect of fin height, fin density and tube pitch ratio for parallel triangular tube array on fluid elastic instability and vortex shedding is analyzed. Design/methodology/approach Experimental analysis was carried out on a parallel triangular finned tube array with a pitch ratio of 1.79 subjected to water crossflow. The experimentation aims to study fluid elastic instability and vortex-induced vibration mechanism responsible for flow induced vibration for finned tube array. A fully flexible finned tube array of the copper tube was used with its base diameter of 19.05 mm and thickness of 2 mm. Over the tube surface, crimped fins of height 6 mm and the same material are welded spirally with fin density 8.47 mm and 2.82 mm. Experimental analysis was carried out on a test setup developed for the same. The results obtained for the finned tube array were compared with those for the plain tube array with the same base tube diameter. Findings For parallel triangular tube array of copper material, test results show that critical velocity increases with an increase in fin pitch density for low pitch tube array. Before the occurrence of instability, the rate of growth in tube vibrations is high for plain tubes compared to that with fin tubes. The results based on Owen’s hypothesis show vortex shedding before the occurrence of fluid elastic instability. The effect of fin geometry on vortex-induced forces is analyzed. For the tube array pattern understudy, the values of Conner’s constant K for coarse fin-tube and fine fin tube array are obtained, respectively, 6.14 and 7.25. Originality/value This paper fulfills the need for research on the effect of fin geometry on fluid elastic instability and Vortex shedding on a tube array subjected to water cross flow when the pitch ratio is less than two, i.e. with a low pitch ratio.

The vortex-induced vibration may cause fatigue of a bridge structure, affecting the safety of vehicles and the comfort of pedestrians. Inerter is a two-terminal device, which has been applied in many areas. This paper studies the problem of suppressing the vortex-induced vibration of a bridge by using an inerter-based dynamic vibration absorber (IDVA). The performances in terms of the suspension travel and the vertical displacement of the bridge with different IDVAs in suppressing vortex-induced vibration are compared, and the effect of the installation position of IDVA on the performance of suppressing vortex-induced vibration is shown. The performance indexes for the vertical displacement of six IDVA arrangements are obtained by using an iterative method, where the performance indexes for the vertical displacement are minimized by using the optimization toolbox in a commercial software. The result shows that the optimal installation positions and the number of suitable installation positions are affected by the resonant mode. Among the six arrangements, one arrangement is identified to have the best performance of suppressing vortex-induced vibration. All the six arrangements have reduced the suspension travel performance.

The fluid-induced vibration heat transfer enhancement technology has great potential, because it can effectively improve the heat transfer efficiency without consuming additional energy. A reasonab...

Ship rudders, as well as other common underwater appendages, take the form of hydrofoils with a finite trailing-edge thickness to produce wake vortex shedding, which causes vibrations, due to the fluid-structure interactions. Notably, underdetermined phenomena, such as the lock-in phenomenon, raise significant concerns about the structural stability of rudders of large container ships. However, methods to accurately evaluate the stability at the lock-in region are unavailable, because of its high instability, which requires high computational costs, especially for underwater applications. In this study, to address these deficiencies, methods to estimate ship rudders’ structural response and stability at lock-in regions were developed by incorporating hybrid-coupling techniques. The effect of the lock-in phenomenon was investigated using an S-N curve and the fatigue structural-failure probability to quantify the risks. The structural response to the stability analysis was obtained using hybrid-coupling fluid-structure interaction analysis methods by preconditioning the solutions to reduce the numerical instability for first bending and twisting modes with the modified Theodorsen function and to share a single interface between the structure and flow solvers on the OpenFOAM computational fluid dynamics (CFD) toolbox. The accuracy of the structural responses was validated with experiments for the lock-in frequencies, velocity range, and, most importantly, amplitudes of the structural responses of a cantilever hydrofoil. Structural-stability analysis results using the proposed methods demonstrated a significant increase in the probability of premature structural failure, thereby demonstrating the usability of the methods by structural designers in the early design stages.

As extreme events increase in frequency, flow-disrupting large-scale structures become ever more susceptible to collapse due to local scour effects. The objective of this study was to validate the functionality of passive, flow-excited scour sensors that can continue to operate during an extreme event. The scour sensors, or piezo-rods, feature continuous piezoelectric polymer strips embedded within and along the length of slender cylindrical rods, which could then be driven into the soil where scour is expected. When scour erodes away foundation material to reveal a portion of the piezo-rod, ambient fluid flow excitations would cause the piezoelectric element to output a voltage response corresponding to the dynamic bending strains of the sensor. The voltage response is dependent on both the structural dynamic properties of the sensor and the excitation fluid’s velocity. By monitoring both shedding frequency and flow velocity, the exposed length of the piezo-rod (or scour depth) can be calculated. Two series of experimental tests were conducted in this work: (1) the piezo-rod was driven into sediment around a mock pier to collect scour data, and (2) the piezo-rod was used to monitor its own structural response by collecting vortex-shedding frequency data in response to varied flow velocities to establish a velocity–frequency relationship. The results showed that the piezo-rod successfully captured structural vortex-shedding frequency comparable to state-of-practice testing. A one-dimensional numerical model was developed using the velocity–frequency relationship to increase the accuracy of voltage-based length prediction of the piezo-rod. Two-dimensional flow modeling was also performed for predicting localized velocities within a complex flow field. These velocities, in conjunction with the velocity–frequency relationship, were used to greatly improve length-predictive capabilities.

In this paper, cross-flow vortex-induced vibration (VIV) responses of a circular cylinder surrounded with different control rods have been investigated in a wind tunnel. The number of rods n is set equal to 3 and 6, and the ratios of diameters d / D (where d is the diameter of small rods, D is the cylinder diameter) are assumed to 0.10, 0.16 and 0.20. The spacing ratios of s (s = G / D, where G is the gap distance between the main cylinder surface and the control rod surface) are selected as 0.2, 0.4 and 0.6 respectively. The Reynolds number based on the main cylinder is in the region of Re = 4 000–42 000. Results show that the VIV can be significant suppressed if placing the control rods in appropriate arrangement. And the gap between the rod and the main cylinder plays a more important role in the VIV amplitude response. When the spacing ratio between the rod and main cylinder is 0.2, VIV can be best suppressed by 96.7%. However, rods do not always suppress VIV and the responses can be more severe in other spacing ratios (s = 0.4, 0.6). And typical vortex shedding frequency lock-in phenomenon can be observed. When the spacing ratio is 0.2, other than the natural frequency component, St frequency is also presented in the frequency spectrum of wake velocity.

This paper aims to analyze mode shapes and corresponding strain distribution in a two-dimensional plane structure exhibiting flow-induced vibration in the wake field of four different upstream bluff bodies such as cylinder, square, triangle, and D-shape. This research is important from the point of view of flow-induced piezoelectric energy harvesting; wherein, induced strain in the structure is directly related to the amount of energy generated. Mainly, all investigations are carried out at low Reynolds number ( Re = 200); however, to widen the scope of the work, other Reynolds numbers are also considered ( Re = 300, 500, and 750 ). The results obtained indicated that the plane structure vibrates in different mode shapes under different wake fields. The square section dominantly gives rise to the fundamental mode vibration, whereas, cylinder, D-shape, and triangular bluff body induce vibration in a mix of fundamental and higher bending modes. Analysis of the corresponding flow regime shows that the position of reattachment point of the downstream shear layer plays an important role in the realization of different vibration modes. The strain distribution under different cases revealed that the wake of a cylindrical bluff body produces highest peak strain, and D-shape bluff body results in highest cumulative strain. From the aspect of energy harvesting, a quantitative comparison of strain-induced and per second charge generation have indicated that for an equivalent flow condition, the D-shape will produce higher energy per unit time than the cases of a square, cylinder, and triangular cross-sections.

Vortex-induced vibration (VIV) is a fluid structure interaction phenomena that can lead to the fatigue failure of high-rise structures. To study the basic principles and method of VIV suppression for a cylinder structure, a two-dimensional simulation model using a cylinder with two degrees of freedom in-line and cross-flow directions is presented herewith. A nonlinear energy sink is added to cylinder structures to assess its impact on vibration suppression. As a result, this study aims to investigate the VIV of cylinder under the action of the NES at low Reynolds numbers. The accuracy of the simulation model is verified by the comparison with the experimental results. Particularly, the VIV response is investigated with different mass ratio $$\beta$$ between the NES and cylinder (namely $$\beta$$ of 0.15, 0.2 and 0.3) at Re = 100 in air environment by analyzing the vibration response, phase diagram, time–frequency and vorticity contours of cylinder and NES oscillator. Three distinct function modes of NES for selected mass ratio $$\beta$$ are also observed. The results indicate that the NES can change between resonance capture states, from weak to strong, when the mass ratio $$\beta$$ increases to a defined value. In this case, the main vibration frequency of the cylinder varies over time, and the motion is in the chaotic state. The NES can also effectively reduce the vibration amplitude in both the in-flow and cross-flow directions.

The vortex-induced vibration test of the deep-sea riser was carried out with different excitation water depths in the wave-current combined water flume. By dimensionally changing the multi-stage water depth and hydrodynamic parameters such as outflow velocity at various water depths, the dynamic response parameters such as dominant frequency, dimensionless displacement and vibration trajectory evolution process of the riser under different excitation water depths were explored to reveal the sensitive characteristics of the dynamic response of vortex-induced vibration of the risers under different excitation water depths. The results show that different excitation water depths will change the additional mass of the riser and the fluid damping and other parameters, which will affect the spatial correlation and stability of the vortex shedding behind the riser. In the lock-in region, the distribution range of the characteristic frequency becomes narrow and centered on the lock-in frequency. The increase of the excitation water depth gradually advances the starting point of the lock-in region of the riser, and at the same time promotes the excitation of the higher-order vibration frequency of the riser structure. Within the dimensionless excitation water depth, the dominant frequency and dimensionless displacement are highly insensitive to the excitation water depth at high flow velocity. The change of the excitation water depth will interfere with the correlation of the non-linear coupling of the riser. The “8-shaped” gradually becomes irregular, and the vibration trajectories of the riser show “O-shape”, “X-shape” and “Crescent-shape”.

The flow induced vibration (FIV) responses of two rigidly connected cylinders at different staggered configurations have been studied numerically. The two cylinders, with an equal diameter of D, ca...

This study proposes a theoretical analysis model to analyse the marine riser's coupled cross-flow/in-line vortex induced vibration (VIV) under heave-induced time varying parametric vibration. Combi...

In the present study, one of the cross-disciplinary problems known as vortex-induced vibration is numerically investigated. Effects of four different low mass-damping ratios; ζ = 0.013, 0.028, 0.074, and 0.124 of a smooth cylinder are taken into account for transition of shear layer 2 (TrSL2) type flow that falls between the Reynolds numbers from 2500 to 10,830 utilizing a two-dimensional cylinder that is free to move in normal-direction. Unsteady Reynolds-Averaged Navier–Stokes solutions indicate that the general trend is well captured with the adopted shear stress transport k-ω turbulence model, however, due to two-dimensional limitations some results are not consistent with experimental data. An inverse relation between the mass-damping ratio and the transition from the upper to the lower branch is detected. Change of drag and lift coefficients with the reduced velocities revealed that the maximum drag coefficient increases with reduced velocity until it reaches Ur = 5 and then decreases dramatically while the lift coefficients decrease consistently from the beginning.

Vortex induced vibration (VIV) is a challenge in ocean engineering. Several devices including fairings have been designed to suppress VIV. However, how to optimize the design of suppression devices is still a problem to be solved. In this paper, an optimization design methodology is presented based on data-driven models and genetic algorithm (GA). Data-driven models are introduced to substitute complex physics-based equations. GA is used to rapidly search for the optimal suppression device from all possible solutions. Taking fairings as example, VIV response database for different fairings is established based on parameterized models in which model sections of fairings are controlled by several control points and Bezier curves. Then a data-driven model, which can predict the VIV response of fairings with different sections accurately and efficiently, is trained through BP neural network. Finally, a comprehensive optimization method and process is proposed based on GA and the data-driven model. The proposed method is demonstrated by its application to a case. It turns out that the proposed method can perform the optimization design of fairings effectively. VIV can be reduced obviously through the optimization design.

A micro-power-generator is developed with piezoelectric ceramics, which can convert the structural vibration energy generated by wind power into electricity to provide energy for micro-devices such as wireless sensor nodes. The vibration modes of the device are analyzed. The standard interface circuit for piezoelectric energy recovery and LTC3588-1 voltage stabilization circuit are selected, and the hardware circuit of the device is designed. The output voltage and power characteristics of micro-power-generator were analyzed under different loads, frequencies and amplitudes. The experimental results show that under the same wind speed, When the blunt body is a cuboid, the power generation effect of this device is the best under the optimal load, with the maximum output power of 350.7 μW. Under the same load with the same shape and structure, the load voltage and output power increase with the increase of wind speed.

The dynamics and stability of flow induced vibration of flow conveying in pipes particularly in case of high velocity flow may lead to severe damage. Predicting the circular natural frequencies and critical fluid velocities is an important tool in design and prevent system failures. In this study transverse dynamic response of simply supported pipe with variable tubular cross sectional area carrying fluid with a constant flow rate is investigated. Euler Bernoulli's beam theory is used to model the pipe. Hamilton's principle will be used to produce the governing equation of motion for the system. The resulting partial differential equation is solved using Galerkin's technique. The impact of the flow velocity and non-uniform variable cross section on the natural frequencies of the system, critical flow velocity and system stability is presented.

In this paper, we propose a model for the transverse oscillation of a square-section cylinder under flow. The fluctuating transverse force due to vortex shedding is represented using a coupled nonlinear wake oscillator, while the unsteady force for galloping caused by the varying incidence angle effects is modelled using the quasi-steady approach. First, we analytically investigate the lift behavior and phase angle variation of the square cylinder under forced vibrations. Comparison with experimental data is used to determine the form of the coupling terms and its values. The present model shows advantages in predicting the phase angle, and it successfully captures the change in sign of the phase. Second, the proposed model is directly applied in predicting free oscillation cases without any tuning. The dynamical behaviors predicted by this model are compared with published experiments under different Scruton numbers, and reasonable agreement can be found. The results indicate that the model can not only be applied in simulating the “pure galloping” and “pure VIV,” but also is able to capture the interactions of VIV and galloping, including combined and separate VIV-galloping motions.

To illustrate the influence of the in-line coupling on the prediction of vortex-induced vibration (VIV), the simulation results of the coupled cross-flow and in-line VIVs of flexible cylinders- obtained with three different wake oscillator models with and without the in-line coupling- are compared and studied in this paper. Both the cases of uniform and linearly sheared flow are analysed and the simulation results of the three models are compared with each other from the viewpoints of response pattern, fluid force, energy transfer and fatigue damage. The differences between the simulation results from the three models highlight the importance of the in-line coupling on the prediction of coupled cross-flow and in-line VIVs of flexible cylindrical structures.

In this paper, the cavitating flow over a flexible NACA66 hydrofoil is studied numerically by a modified fluid-structure interaction strategy with particular emphasis on understanding the flow-induced vibration and the cavitating vortical flow structures. The modified coupling approaches include (1) the hydrodynamic solution obtained by the large eddy simulation (LES) together with a homogenous cavitation model, (2) the structural deformation solved with a cantilever beam equation, (3) fluid-structural interpolation and volume mesh motion based on the radial basis functions and greedy algorithm. For the flexible hydrofoil, the dominant flow-induced vibration frequency is twice of the cavity shedding frequency. The cavity shedding frequency is same for the rigid and flexible hydrofoils, demonstrating that the structure vibration is not large enough to affect the cavitation evolution. The predicted cavitating behaviors are strongly three-dimensional, that is, the cavity is (a) of a triangular shape near the hydrofoil tip, (b) of a rectangular shape near the hydrofoil root, and (c) with a strong unsteadiness in the middle of the span, including the attached cavity growth, oscillation and shrinkage, break-off and collapse downstream. The unsteady hydroelastic response would strongly affect the cavitation shedding process with small-scale fragments at the cavity rear part. Furthermore, three vortex identification methods (i.e., the vorticity, the Q- criteria and the Ω method) are adopted to investigate the cavitating vortex structures around the flexible hydrofoil. It is indicated that the cavity variation trend is consistent with the vortex evolution. The vortex structures are distributed near the foil trailing edge and in the cavitation region, especially at the cavity-liquid interface. With the transporting downstream the shedding cavities, the vortices gradually increase in the wake flows.

The vortex induced vibration (VIV) of marine risers has been investigated by many researchers in experimental studies of a straight flexible riser model as well as a rigid cylinder to reveal the dynamic response characteristic and the mechanics behind it. However, due to the limitation of experimental apparatus, very few studies are about the VIV of a steel catenary riser (SCR) which is with a complex geometry. To investigate the VIV features and to further develop the corresponding numerical predictions of a SCR under steady current, a large-scale model test of a SCR was towed in an ocean basin at various speeds. Fiber Bragg grating strain sensors are instrumented on the riser model to measure both in-plane and out-of-plane responses. The characteristics of oscillating amplitude and dominating frequency response, the phenomenon of mode competition and travelling wave and the fatigue damage of the steel catenary riser in inline and cross-flow direction under steady current are analyzed.

In recent years, vortex-induced vibration (VIV) has been widely employed to collect small-scale wind energy as a renewable energy source for microelectronics and wireless sensors. In this paper, a two-degree-of-freedom (2DOF) VIV-based piezoelectric energy harvester (VIVPEH) was designed, and its aerodynamic characteristics were thoroughly investigated. First, based on the traditional model theory and combined with the knowledge of vibration dynamics, the governing equations of the 2DOF VIVPEH were established. The dynamic responses, including the displacement and voltage output, were numerically simulated. Compared with the traditional 1DOF VIVPEH, the 2DOF VIVPEH proposed in this paper produced two lock-in regions for broadband wind energy harvesting. Furthermore, it was unveiled that the first- and second-order resonances were induced in the first and lock-in regions, respectively. Subsequently, a parametric study was conducted to investigate the influences of the circuit and mechanical parameters on the energy harvesting performance of the 2DOF VIVPEH. It was found that when the 2DOF VIVPEH was induced to vibrate in different lock-in regions, its optimal resistance became different. Moreover, by varying the masses and stiffnesses of the primary and secondary DOFs, we could adjust the lock-in regions in terms of their bandwidths, locations, and amplitudes, which provides a possibility for further customization and optimization. Published version This work was financially supported by the State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, China (GZ21114); National Natural Science Foundation of China (Grant No. 52071059, 52192692, 52061135107); and The Fundamental Research Funds for the Central Universities (No: DUT20TD108).

Piezoelectric vibration energy harvesting has attracted considerable attention because of its prospects in self-powered electronic applications. There are a many low-velocity waters in nature, such as rivers, seas and oceans, which contain abundant hydrokinetic energy. In this paper, an optimal geometric piezoelectric beam combining magnetic excitation is identified and applied to a vortex-induced vibration energy harvester (ViVEH) for low velocity water flow, which is composed of a continuous variable-width piezoelectric beam carrying a cylindrical bluff body. The finite element simulation and experiment are first carried out to study the harvesting characteristics of the designed variable-width beam ViVEH without considering the magnetic excitation. The influence of the width-ratio and flow velocity on the harvesting voltage is studied in detail. The optimal structure, a ViVEH equipped with triangular piezoelectric beam, is then obtained by the superior energy harvesting performance for low velocity water flow. From the experimental results, at a flow velocity of 0.6 m/s, the highest root mean square (RMS) voltage and RMS voltage per unit area are 19.9 V and 0.07 V/mm2, respectively. Furthermore, magnetic excitation is introduced to improve the scavenging performance of the optimal triangular beam ViVEH, different polarity arrangements are compared, and the optimal case, the arrangement of horizontal repulsion and vertical attraction (HR-VA), is obtained. This case can scavenge the highest power of 173 μW at a flow velocity of 0.5 m/s, which is increased by 127% compared to a conventional constant-width beam ViVEH with no magnetic excitation.

In the study of the cross-flow vortex-induced vibration of the cylinder, it is found that with the increase in the Reynolds number, the upper branch of the vibration amplitude and the lock-in region show an increasing trend. Currently, there are relatively few studies on two-degree-of-freedom VIV at high Reynolds number. In this paper, the Launder and Sharma low Reynolds number k–ɛ turbulence model is modified by limiting the kinetic energy generation term and dissipation term, which is similar with the limiter used in SST k–ω model. Based on the modified turbulence model, the two-degree-of-freedom vortex-induced vibration of the cylinder with different Reynolds numbers is simulated with the two-dimensional RANS method. The accuracy of the improved turbulence model and its applicable Reynolds number range are verified by comparing with experiments and relevant numerical simulations. The effects of Reynolds number on the vibration characteristics of cylinder with low mass damping ratio are discussed, which provide a theoretical reference for the study of vortex-induced vibration under high Reynolds number.

Vortex-induced vibration (VIV) for flexible cylinders under combined uniform and oscillatory flow is a challenging and practical issue in ocean engineering. In this paper, a time domain numerical model is adopted to investigate the characteristics of cross-flow VIV response and fatigue damage under different combined flow cases. Firstly, the adopted VIV model and fatigue analysis procedure are validated well against the published experimental results of a 4-m cylinder model under pure oscillatory flows. Then, forty-five combined flow cases of the same cylinder model are designed to reveal the VIV response characteristics with different non-dimensional oscillation period T* and combined ratio r. The combined flow cases are classified into three categories to investigate the effect of r on cylinder’s dynamic response, and the effect of T* is described under long and short period cases. Finally, fatigue analysis is carried out to investigate how the structural fatigue damage varies with the variations of r and T*. The captured characteristics of structural response and fatigue damage are explained through the VIV mechanism analysis.

As a fundamental fluid-structure interaction (FSI) phenomenon, vortex-induced vibrations (VIVs) of circular cylinders have been the center of the FSI research in the past several decades. Apart from its scientific significance in rich physics, VIVs are paid great attentions by offshore engineers, as they are encountered in many ocean engineering applications. Recently, with the development of research and application, wake-induced vibration (WIV) for multiple cylinders and galloping for VIV suppression attachments are attracting a growing research interest. All these phenomena are connected with the flow-induced vibration (FIV). In this paper, we review and give some discussions on the FIV of offshore circular cylinders, including the research progress on the basic VIV mechanism of an isolated rigid or flexible cylinder, interference of multiple cylinders concerning WIV of multiple cylinders, practical VIV suppression and unwanted galloping for cylinder of attachments. Finally, we draw concluding remarks, give some comments and propose future research prospects, especially on the major challenges as well as potentials in the offline/online modelling and prediction of real-scale offshore structures with high-fidelity CFD methods, new experimental facilities and applications of artificial intelligence tools.

It is widely accepted that vortex-induced vibration (VIV) is a major concern in the design of deep sea top-tensioned risers, especially when the riser is subjected to axial parametric excitations. An improved time domain prediction model was proposed in this paper. The prediction model was based on classical van der Pol wake oscillator models, and the impacts of the riser in-line vibration and vessel heave motion were considered. The finite element, Newmark-β and Newton‒Raphson methods were adopted to solve the coupled nonlinear partial differential equations. The entire numerical solution process was realised by a self-developed program based on MATLAB. Comparisons between the numerical calculation and the published experimental test were conducted in this paper. The in-line and cross-flow VIV responses of a real size top-tensioned riser in linear sheared flow were analysed. The effects of the vessel heave amplitude and frequency on the riser VIV were also studied. The results show that the vibration displacements of the riser are larger than the case without vessel heave motion. The vibration modes and frequencies of the riser are also changed due to the vessel heave motion

An experimental investigation on the disturbance effect of jet-type active vibration suppression device on vortex-induced vibration of deep-sea riser was carried out in the wave-flow combined flume. The vibration suppression device was designed in which the jet pipe was horizontally fixed to the front end of the riser. By varying three different excitation spacings and multi-stage outflow velocities, the influence law of the dominant frequency, dimensionless displacement and other dynamic response parameters was studied under different excitation spacings, and the mechanism and sensitive characteristics of the disturbance suppression were explored. The results indicate that the variation of excitation spacing makes gas curtain enter the strong disturbed flow region at different velocities and angles, and the coupling relationship between excitation spacing and reduced velocity is the key factor to enter the strong disturbed flow region to achieve the optimal disturbance suppression. In the strong disturbed flow region, the influence of gas curtain on the dominant frequency is obviously affected by the flow velocity, while the vibration displacement is stable at the same amplitude and is weakly affected by the flow velocity. Gas curtain can effectively disturb the formation of vortex shedding, destroy the strong nonlinear coupled vibration of the riser, and achieve better vibration suppression effect. In the weak disturbed flow region, the vortex length of the riser tail is prolonged, the strong nonlinear coupled vibration of the riser is gradually restored, and the vibration suppression effect of the device gradually decreases.

We present a semi-hollow body as an effective strategy to increase the driving force for vortex-induced vibrations (VIVs) of a circular cylinder. The hollow-body concept is evaluated numerically at Reynolds number Re = 200 and in a range of reduced velocity 3 ≤ Ured ≤ 8 with a mass-spring system released to vibrate in the transverse direction. Our numerical solutions reveal that, compared with solid-cylinder counterparts, the net transverse force is increased significantly through the semi-hollow body. The transverse force acting on the inner surface is found to be developed as a consequence of semi-confined flows driven by the cylinder oscillation. Furthermore, it is shown that the inner force has a phase difference with respect to the force acting on the outer surface. Based on a systematic force analysis, the appreciable increase in the transverse force is attributed to the constructive interference between the inner and outer forces.

Vibration energy harvesting has attracted considerable attention because of its application prospects for charging or powering micro-electro-mechanical system. Abundant hydrokinetic energy of water at low velocity is contained in the fluid environment, such as rivers and oceans, which are widely existing in nature. In this paper, a flow-induced piezoelectric vibration energy harvester (PVEH) with magnetic force enhancement, which is integrated by piezoelectric beam, circular cylinder bluff body and magnets, is proposed and experimental investigated. It could transfer the hydrokinetic energy, both the vortex-induced vibration and magnetic force excitation underwater, into electricity. First, the frequency sweep experiment of the piezoelectric cantilever beam is carried out to determine the resonance frequency where the effect of magnetic force on the vibration characteristic is obtained. Furthermore, the flow-induced vibration experiment platform is setup and the energy harvesting performance of the PVEH is investigated in detail. The effects of the magnet property, flow velocity and the magnetic poles distance on the vibration frequency and the acquisition voltage are demonstrated and discussed. The results show that it could improve the harvesting performance by introducing magnetic force. It has advantages in higher output voltage for the flow-induced PVEH, especially in low velocity water flow, when the flow velocity is 0.35 m/s, the PVEH under attractive magnetic force with magnetic distance of 20 mm scavenges the higher acquisition voltage of 5.2 V, which is increased by 225% than the PVEH with non-magnetic. The results can be applied to guide further fabrication process and optimized design of the proposed flow-induced PVEH underwater with low flow velocity.

In this paper, the dynamics of a viscoelastic pipe conveying fluid attached to a nonlinear energy sink (NES) subjected to a sinusoidal flow is studied, aiming at performance improvement of such flu...

In order to investigate the effect of internal friction of umbilical cable on its vortex-induced vibration (VIV) responses, the experimental study on VIV of bond umbilical cable (BUC) and un-bond umbilical cable (UBUC) was carried out in an experimental tank. A current generator in the laboratory simulated the uniform current, and the current velocities were observed in real time by using a Doppler Velocimeter. In addition, different sizes of top tension were applied to the umbilical cable model. The VIV responses of the umbilical cable model were measured by using Fiber Bragg grating (FBG) strain sensors. The displacement responses of umbilical cable model were reconstructed based on the experimental strain data processed by modal superposition method. In this paper, the traveling wave characteristics, the spatial-temporal distribution characteristics of frequency and fatigue damage of the BUC and UBUC under VIV are studied. The experimental results show that there are obvious differences between BUC and UBUC in the response characteristics of VIV. The UBUC appears the traveling wave sooner than BUC, but its standing wave characteristics are more obvious than those of BUC at high velocities. Compared with BUC, the spatial-temporal distribution of UBUC frequencies appears wide-band distribution sooner, but has narrower bandwidth in the “lock-in” state. The level of fatigue damage of BUC was approximately the same as that of UBUC.

We investigate the closed-loop control of a circular cylinder showing lock-in phenomena due to vortex-induced vibrations (VIV). The control action was implemented by a sampled-data proportional-integral-derivative (PID) controller to suppress the large amplitudes due to lock-in. The controller was first applied to a linearized system to observe its stability characteristics based on the eigenvalues of the system. Another method was also proposed, which employs a novel, time-dependent Lyapunov function that is positive definite at sampling times but not necessarily between the sampling times. A new set of sufficient conditions in terms of linear matrix inequalities is derived to obtain the sampled-data PID control gains for the VIV system. The PID controller tuned with these gains for various delays was applied to control the nonlinear responses of the circular cylinder during the lock-in. The results showed that the PID controller significantly reduced the rise in lock-in amplitude compared to only proportional control and for certain delays was able to completely mitigate the effects of lock-in. It was also observed that for delays ranging from 0.1 to 0.14 s, the nonlinear system was destabilized with increasing proportional gains as indicated by the eigenvalue analysis of the linearized system. Even under such situations, properly tuned integral and derivative gains could significantly reduce the amplitude rise otherwise observed due to lock-in of the uncontrolled system. Finally, an on-off control scheme was also proposed, which, if optimized properly, can restrict the lock-in amplitude to some prescribed limit by only using the control for some fraction of the total operational time. Thus, it can potentially save control power.

Helical strakes have been widely applied for suppressing the vibration of flexible cylinders undergoing vortex-shedding in offshore engineering. However, most research works have concerned on the application of helical strakes for the isolated flexible cylinder subjected to vortex-induced vibration (VIV). The effectiveness of helical strakes attached to side-by-side flexible cylinders in vibration reduction is still unclear. In this paper, the response characteristics of two side-by-side flexible cylinders with and without helical strakes were experimentally investigated in a towing tank. The configuration of the helical strakes used in the experiment had a pitch of 17.5D and a height of 0.25D (where D is the cylinder diameter), which is usually considered the most effective for VIV suppression of isolated marine risers and tendons. The center-to-center distance of the two cylinders was 3.0D. The uniform flow with a velocity ranging from 0.05 m/s to 1.0 m/s was generated by towing the cylinder models along the tank. Experimental results, including the displacement amplitude, the dominant frequency, the dominant mode, and the mean drag force coefficient, were summarized and discussed. For the case where only one cylinder in the two-cylinder system had helical strakes, the experimental results indicated that helical strakes can remarkably reduce the flow-induced vibration (FIV) of the staked cylinder. For the case of two straked cylinders in a side-by-side arrangement, it was found that the performance of helical strakes in suppressing the FIV is as good as that for the isolated cylinder.

Nanofluids are used in heat exchanger system as efficient heat transfer fluids to improve heat transfer performance by passive method. Besides, another special active technique by implementing the low or high frequency vibration, which was used in heat exchanger to enhance the heat transfer performance. This paper reviews the heat transfer augmentation in heat exchanger by using nanofluids, vibration excitation of low and high frequency vibration. The use of nanofluids in heat exchanger system can provide better effective thermal conductivity compared to the conventional coolants. The presence of nanosize particles in nanofluids performed better mixing flow with higher thermal properties compared to pure fluids. Additionally, the active method by inducing low and high frequency vibration technology was applied in heat exchanger system. The heat transfer augmentation by vibration excitation was resulted from the mitigation of the fouling resistance on the surface of the tube wall. It was found that vibration excitation not only increase the heat transfer rate, but also might be a solution for fouling reduction. Hence, there is a great potential of using nanofluids together with vibration excitation simultaneously in heat exchanger system to improve the heat transfer performance.

Vortex-induced vibration of two tandem circular cylinders with different diameters under low Reynolds number (Re = 200) is investigated numerically by solving the uncompressible two-dimensional Navier–Stokes equations. The arbitrary Lagrange–Euler method is used to simulate the movement of mesh. Effects of diameters and gap ratios are considered. Numerical results show that diameter ratios and gap ratios have little effect on maximum vibration amplitude. Four different vortex shedding modes are detected in this study.

The vortex-induced vibration (VIV) of the downstream cylinder of two cylinders in tandem at low Reynolds number of 150 was numerically studied. In all cases, the upstream elliptical cylinder with aspect ratios (AR = 1, 2.3, 2.8, 4, corresponding to an inclined angle of 0°, 30°, 45°, 60° in three-dimensional) was fixed and the downstream cylinder was allowed to freely vibrate in both transverse and streamwise directions. The effects of varying the aspect ratios of the upstream elliptical cylinder on the force coefficients, response amplitude and frequency, motion trajectory, and vortex shedding patterns of the downstream cylinder were studied in detail. The results show that the VIV response is very different from that of an isolated cylinder due to flow interference between the two cylinders. As the aspect ratios increase, the upstream elliptical cylinder becomes more streamlined, which acts analogous to a flow rectifier. Not only does it shorten the distance between the two cylinders, but also it reduces the turbulence intensity of the wake. For this tandem arrangement, the cylinder response in the streamwise direction is more sensitive to the reduced velocity as compared to that in the transverse direction.

Top tension riser is one of the most frequently used and vulnerable equipment in deep-sea petroleum engineering. With experiments and CFD simulations, researchers have found some hysteresis phenomenon and bistable behavior in vortex-induced vibration of the cylinders. However, there is still insufficient research on the bifurcation phenomenon and the multi-stable behavior of the riser vortex-induced vibration. In this study, based on the Van der Pol wake oscillator model, the vortex-induced vibration cross-flow governing equations of the riser fluid structure–coupled system in linear shear flow are established. Then the simplified multi-degrees-of-freedom model with 15-order modes is derived by the Galerkin method. Poincare map is utilized to obtain bifurcation diagram and identify the dynamic property of the top tension riser in a wide flow velocity range. Nonlinear dynamic behavior such as bistable behavior and even tristable behavior are discovered from the bifurcation diagram. Combined with the riser coupled system’s eigen analysis and the three-dimensional spectrum contour, it is found that there are various phenomena of mode interaction in the riser system, including 1:3 internal resonance phenomenon. Such study can provide reference and guide the design and optimization of riser structural parameters.