Showing papers on "Vortex-induced vibration published in 2019"

A cross-coupled dual-beam for multi-directional energy harvesting from vortex induced vibrations

Abstract: This study proposes a cross-coupled dual-beam structure for energy harvesting from vortexinduced vibrations (VIV) induced by wind flows in different directions. A series of wind tunnel tests are conducted to investigate the performance of the proposed energy harvester subjected to the wind load with various speeds and directions. The upper and bottom piezoelectric beams can generate a maximum power output of 6.77 μW and 56.64 μW, respectively. The dominant operation frequencies in different directions are different which indicates a potential broadband capability. A parametric study is performed to reveal the effect of the dimension of the bluff body on the performance of the proposed energy harvester.

Active control of vortex-induced vibration of a circular cylinder using machine learning

Abstract: We demonstrate the use of high-fidelity computational fluid dynamics simulations in machine-learning based active flow control. More specifically, for the first time, we adopt the genetic programming (GP) to select explicit control laws, in a data-driven and unsupervised manner, for the suppression of vortex-induced vibration (VIV) of a circular cylinder in a low-Reynolds-number flow (Re = 100), using blowing/suction at fixed locations. A cost function that balances both VIV suppression and energy consumption for the control is carefully chosen according to the knowledge obtained from pure blowing/suction open-loop controls. By implementing reasonable constraints to VIV amplitude and actuation strength during the GP evolution, the GP-selected best ten control laws all point to suction-type actuation. The best control law suggests that the suction strength should be nonzero when the cylinder is at its equilibrium position and should increase nonlinearly with the cylinder’s transverse displacement. Applying this control law suppresses 94.2% of the VIV amplitude and achieves 21.4% better overall performance than the best open-loop controls. Furthermore, it is found that the GP-selected control law is robust, being effective in flows ranging from Re = 100 to 400. On the contrary, although the P-control can achieve similar performance as the GP-selected control at Re = 100, it deteriorates in higher Reynolds number flows. Although for demonstration purpose the chosen control problem is relatively simple, the training experience and insights obtained from this study can shed some light on future GP-based control of more complicated problems.

Vortex-induced vibration wind energy harvesting by piezoelectric MEMS device in formation.

Abstract: A silicon chip integrated microelectromechanical (MEMS) wind energy harvester, based on the vortex-induced vibration (VIV) concept, has been designed, fabricated, and tested as a proof-of-concept demonstration. The harvester comprises of a cylindrical oscillator attached to a piezoelectric MEMS device. Wind tunnel experiments are conducted to measure the power output of the energy harvester. Additionally, the energy harvester is placed within a formation of up to 25 cylinders to test whether the vortex interactions of multiple cylinders in formation can enhance the power output. Experiments show power output in the nanowatt range, and the energy harvester within a formation of cylinders yield noticeably higher power output compared to the energy harvester in isolation. A more detailed investigation conducted using computational fluid dynamics simulations indicates that vortices shed from upstream cylinders introduce large periodic transverse velocity component on the incoming flow encountered by the downstream cylinders, hence increasing VIV response. For the first time, the use of formation effect to enhance the wind energy harvesting at microscale has been demonstrated. This proof-of-concept demonstrates a potential means of powering small off-grid sensors in a cost-effective manner due to the easy integration of the energy harvester and sensor on the same silicon chip.

Vortex-induced vibration of a cooled circular cylinder

Abstract: We numerically investigate vortex-induced vibration of a cooled circular cylinder in the presence of thermal buoyancy. We employ an in-house fluid-structure interaction solver based on a sharp-interface immersed boundary method. The cylinder is elastically mounted and is free to vibrate transversely to the flow direction. The surface of the cylinder is prescribed at a temperature lower than that of the fluid, and the gravity is aligned opposite to the flow direction. Numerical simulations are carried out for the following parameters: Reynolds number, Re = 150, Prandtl number, Pr = 7.1, Richardson number, Ri = [−1, 0], mass ratio, m = 2, and reduced velocity, UR = [3, 20]. The oscillation amplitude of the cylinder is larger in the presence of the thermal buoyancy for 4 < UR < 15. The amplitude is maximum at UR = 11 and is around ≈1D* in the presence of the thermal buoyancy, where D* is the diameter of the cylinder. However, this amplitude is ≈0.6D* at UR = 4 in the absence of the thermal buoyancy. The lock-in (synchronization) region is obtained for a wider range of UR in the presence of the thermal buoyancy. In the presence of the thermal buoyancy, along with a dominating vortex shedding frequency, we obtain multiple weak as well as strong even and odd harmonics along with subharmonics of the fundamental frequency in the lift signal. However, the secondary frequencies are limited to only a weak third harmonic of the fundamental frequency in the absence of the thermal buoyancy. We observe elongated as well as wider vortices and isotherms in the presence of the thermal buoyancy although the vortex shedding mode remains “2S.” Our results show that there exists a critical minimum absolute value of Ri in order to achieve the lock-in and this value increases with UR.

Numerical study of flow-induced vibration of a circular cylinder with attached flexible splitter plate at low

Abstract: Flow-induced vibration (FIV) of an elastically mounted circular cylinder with an attached splitter plate in uniform flow is studied numerically via a stabilized space–time finite element method. The Reynolds number based on the cylinder diameter to choose the appropriate flexibility of the attached splitter plate to minimize FIV.

Vortex-induced vibration and galloping of a circular cylinder in presence of cross-flow thermal buoyancy

Abstract: The effect of cross-flow thermal buoyancy on vortex-induced vibration (VIV) of a circular cylinder is numerically investigated. An in-house fluid-structure solver based on the sharp-interface immersed boundary method is employed. The cylinder is kept in the uniform flow stream and is mounted elastically such that it is constrained to move in the transverse direction to the flow. The surface of the cylinder is heated at a prescribed temperature, and the thermal buoyancy is imposed in the transverse direction to the flow. Simulations are performed for the following parameters: Reynolds number Re = (50, 150), Prandtl number Pr = 7.1, mass ratio m = 2, reduced velocity UR = [4–15], and Richardson number Ri = [0–4]. We found that the thermal buoyancy could suppress or agitate the VIV. At lower Re (=50) and Ri = (1, 2), we observe the suppression in the VIV; however, there is no suppression for higher Re (=150) for these values of Ri. Galloping is observed for higher values of Ri = (3, 4) for Re = (50, 150). The galloping has been reported for rotationally asymmetric bluff bodies (e.g., D-section cylinder) in previous studies in isothermal flows. We show that a circular cylinder, a rotationally symmetric body, exhibits galloping due to the transversely acting thermal buoyancy at higher Ri.

Numerical investigation of vortex-induced vibration of an elastically mounted circular cylinder with One-degree of freedom at high Reynolds number using different turbulent models:

Abstract: This study presents numerical investigation for flow around cylinder at Reynolds number = 104 using different turbulent models. Numerical simulations have been conducted for fixed cylinder case at ...

Effect of vortex-induced vibration of finned cylinders on heat transfer enhancement

Abstract: Two-degree-of-freedom vortex-induced vibration (VIV) of a finned cylinder with heat transfer is studied numerically at the Reynolds number Re = 150. The governing equations in the Arbitrary Lagrangian-Eulerian frame are solved by the finite volume method. The dynamics of the oscillating cylinder (with or without fins) in the fluid flow was approximated as a mass-spring system. The effects of the number and arrangement of the fins (14 different cases) on the vortex shedding pattern, vibration amplitude, and frequency and heat transfer of the cylinder are investigated and discussed. The results indicate that in comparison with the stationary state, the effects of the number and arrangement of the fins on the wake pattern and the heat transfer enhancement in the VIV state are significant. Different vortex shedding pattern like 2S, P, 2P, S + P and combination of them with stable or unstable interactions between vortices and cylinders are observed in an oscillating cylinder. In the vibration state of finned cylinders, the heat transfer enhances up to 50.4% with respect to the stationary state and increases up to 64% with respect to the stationary smooth cylinder.Two-degree-of-freedom vortex-induced vibration (VIV) of a finned cylinder with heat transfer is studied numerically at the Reynolds number Re = 150. The governing equations in the Arbitrary Lagrangian-Eulerian frame are solved by the finite volume method. The dynamics of the oscillating cylinder (with or without fins) in the fluid flow was approximated as a mass-spring system. The effects of the number and arrangement of the fins (14 different cases) on the vortex shedding pattern, vibration amplitude, and frequency and heat transfer of the cylinder are investigated and discussed. The results indicate that in comparison with the stationary state, the effects of the number and arrangement of the fins on the wake pattern and the heat transfer enhancement in the VIV state are significant. Different vortex shedding pattern like 2S, P, 2P, S + P and combination of them with stable or unstable interactions between vortices and cylinders are observed in an oscillating cylinder. In the vibration state of finned c...

Experimental investigation of Reynolds number and spring stiffness effects on vortex induced vibrations of a rigid circular cylinder

Abstract: The Vortex Induced Vibration for Aquatic Clean Energy (VIVACE) is a breakthrough technology, which harvests the hydrokinetic energy of ocean currents through enhancing Vortex Induced Vibration (VIV). In this paper, the VIV of an elastically mounted circular cylinder in a towing tank water channel is studied experimentally to investigate the effect of natural frequency, by using five different springs in a wide range of stiffness (125 N/m × 104 × 104) with high mass-damping parameter (m* ζ = 0 .11). Results demonstrated the strong dependency of VIV on natural frequency and lock-in observed in a broad range of spring stiffness. Moreover, the studied Re range showed the gradual transition between two distinct turbulence shear layers from previously published works at Re ≈ 4,000 to Re ≈ 100,000. The amplitude ratio and range of synchronization in the upper branch increases by spring stiffness. The lower branch of response disappeared due to the high mass-damping parameter in conducted experiments. These observations suggested to employ an adjustable natural frequency system to have an optimum energy harvesting in VIV-based ocean energy converters in an expanded range of operation.

Eigen-Solution for Flow Induced Oscillations (VIV and Galloping) Revealed at the Fluid-Structure Interface

Abstract: Consistent rather than heuristic nondimensionalization of the fluid and oscillator dynamics in fluid-structure interaction, leads to decoupling of amplitude from frequency response. Further, recognizing that the number of governing dimensionless parameters should decrease, rather than increase, due to the fluid-structure synergy at the interface, an eigen-relation is revealed for a cylinder in Flow Induced Oscillations (FIO), including VIV and galloping: mA/mbod = CA/m* = 1/f*2-1. It shows that, for a given dimensionless oscillation frequency f*, the ratio of real added-mass to oscillating-mass is fully defined. Amplitude decoupling and the eigen-relation, lead to explicit expressions for coefficients, phases, and magnitudes of total, added-mass, and in-phase-with-velocity forces; revealing their dependence on the generic Strouhal number (Stn = fn*), damping, and Reynolds. Heuristic dimensionless parameters, (mass-damping, reduced velocity, mass-ratio, force coefficients) used in VIV data presentation are not needed. Theoretical derivations and force reconstruction match nearly perfectly with extensive experimental data collected over a decade in the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan using four different oscillator test-models. Beyond the single frequency response model, the residuary force is derived by comparison to experiments. Established facts regarding VIV and galloping and new important observations are readily explained: (1) The effects of Strouhal, damping-ratio, mass-ratio, Reynolds, reduced velocity, and stagnation pressure. (2) The cause of expansion/contraction of the VIV range of synchronization. (3) The corresponding slope-change in oscillation frequency with respect to the Strouhal frequency of a stationary-cylinder. (4) The critical mass-ratio m* implying perpetual VIV. (5) The significance of the natural frequency of the oscillator in vacuo. (6) The effect of vortices on VIV and galloping. (7) The magnitude of vortex forces. (8) The indirect and direct vortex effects. (9) The unification of VIV and galloping onset. (10) Defining the next step in higher order theories for VIV and galloping beyond the eigen-relation.

Optimization of Galloping Piezoelectric Energy Harvester with V-Shaped Groove in Low Wind Speed

Abstract: A square cylinder with a V-shaped groove on the windward side in the piezoelectric cantilever flow-induced vibration energy harvester (FIVEH) is presented to improve the output power of the energy harvester and reduce the critical velocity of the system, aiming at the self-powered supply of low energy consumption devices in the natural environment with low wind speed. Seven groups of galloping piezoelectric energy harvesters (GPEHs) were designed and tested in a wind tunnel by gradually changing the angle of two symmetrical sharp angles of the V-groove. The GPEH with a sharp angle of 45° was selected as the optimal energy harvester. Its output power was 61% more than the GPEH without the V-shaped groove. The more accurate mathematical model was made by using the sparse identification method to calculate the empirical parameters of fluid based on the experimental data and the theoretical model. The critical velocity of the galloping system was calculated by analyzing the local Hopf bifurcation of the model. The minimum critical velocity was 2.53 m/s smaller than the maximum critical velocity at 4.69 m/s. These results make the GPEH with a V-shaped groove (GPEH-V) more suitable to harvest wind energy efficiently in a low wind speed environment.