Nonlinear Piecewise Restoring Force in Hydrokinetic Power Conversion Using Flow-Induced Vibrations of Two Tandem Cylinders

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Chunhui Ma ◽  
Hai Sun ◽  
Marinos M. Bernitsas
Keyword(s):  
Positive Impact ◽  
Clean Energy ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Restoring Force ◽  
Nonlinear Spring ◽  
Hydrokinetic Energy ◽  
Spacing Ratio ◽  
Flow Induced Vibrations ◽  
The University

Flow-induced vibrations (FIVs) of two tandem, rigid, circular cylinders with piecewise continuous restoring force are investigated for Reynolds number 24,000 ≤ Re ≤ 120,000 with damping, and restoring force function as parameters. Selective roughness is applied to enhance FIV and increase the hydrokinetic energy captured by the vortex-induced vibration for aquatic clean energy (VIVACE) converter. Experimental results for amplitude response, frequency response, interactions between cylinders, energy harvesting, and efficiency are presented and discussed. All experiments were conducted in the low-turbulence free-surface water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are as follows: (1) the nonlinear-spring converter can harness energy from flows as slow as 0.33 m/s with no upper limit; (2) the nonlinear-spring converter has better performance at initial galloping than its linear-spring counterpart; (3) the FIV response is predominantly periodic for all nonlinear spring functions used; (4) the influence from the upstream cylinder is becoming more dominant as damping increases; (5) optimal power harnessing is achieved by changing the linear viscous damping and tandem spacing L/D; (6) close spacing ratio L/D = 1.57 has a positive impact on the harnessed power in VIV to galloping transition; and (7) the interactions between two cylinders have a positive impact on the upstream cylinder regardless of the spacing and harness damping.

Nonlinear Piecewise Restoring Force in Hydrokinetic Power Conversion Using Flow Induced Motions of Two Tandem Cylinders

2017 ◽  
Author(s):  
Chunhui Ma ◽  
Hai Sun ◽  
Marinos M. Bernitsas
Keyword(s):  
Positive Impact ◽  
Clean Energy ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Restoring Force ◽  
Nonlinear Spring ◽  
Hydrokinetic Energy ◽  
Spacing Ratio ◽  
Linear Spring ◽  
The University

Flow Induced Motions (FIMs) of two tandem, rigid, circular cylinders with piecewise continuous restoring force are investigated for Reynolds number 24,000≤Re≤120,000 with damping, and restoring force function as parameters. Selective roughness is applied to enhance FIM and increase the hydrokinetic energy captured by the VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) Converter. Experimental results for amplitude response, frequency response, interactions between cylinders, energy harvesting, and efficiency are presented and discussed. All experiments were conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are: (1) The nonlinear-spring, Converter can harness energy from flows as slow as 0.33 m/s with no upper limit. (2) The nonlinear-spring Converter has better performance at initial galloping than its linear-spring counterpart. (3) The FIM response is predominantly periodic for all nonlinear spring functions used. (4) The influence from the upstream cylinder is becoming more dominant as damping increases. (5) Optimal power harnessing is achieved by changing the linear viscous damping and tandem spacing L/D. (6) Close spacing ratio L/D = 1.57 has a positive impact on the harnessed power in VIV to galloping transition. (7) The interactions between two cylinders have a positive impact on the upstream cylinder regardless of the spacing and harness damping.

Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000 < Re < 120,000

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations (VIV) of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. Two identical rigid cylinders suspended by springs with their axes perpendicular to the flow are allowed one degree of freedom motion transverse to the flow direction. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth cylinder is similar to that of an isolated smooth cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. Galloping is suppressed in both cylinders. In addition, the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Effect of Bottom Boundary on VIV for Energy Harnessing at 8×103

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
K. Raghavan ◽  
Michael M. Bernitsas ◽  
D. E. Maroulis
Keyword(s):  
Strong Dependence ◽  
Clean Energy ◽  
Reynolds Numbers ◽  
Strong Impact ◽  
University Of Michigan ◽  
Vortex Induced Vibration ◽  
Bottom Boundary ◽  
The University ◽  
Energy Harnessing ◽  
First Time

The concept of extracting energy from ocean/river currents using vortex induced vibration was introduced at the OMAE2006 Conference. The vortex induced vibration aquatic clean energy (VIVACE) converter, implementing this concept, was designed and model tested; VIV amplitudes of two diameters were achieved for Reynolds numbers around 105 even for currents as slow as 1.6 kn. To harness energy using VIV, high damping was added. VIV amplitude of 1.3 diameters was maintained while extracting energy at a rate of PVIVACE=0.22×0.5×pU3DL at 1.6 kn. Strong dependence of VIV on Reynolds number was proven for the first time due to the range of Reynolds numbers achieved at the Low-Turbulence Free Surface Water (LTFSW) Channel of the University of Michigan. In this paper, proximity of VIVACE cylinders in VIV to a bottom boundary is studied in consideration of its impact on VIV, potential loss of harnessable energy, and effect on soft sediments. VIV tests are performed in the LTFSW Channel spanning the following ranges of parameters: Re∊[8×103–1.5×105], m∗∊[1.0–3.14], U∊[0.35–1.15 m/s], L/D∊[6–36], closest distance to bottom boundary (G/D)∊[4−0.1], and m∗ζ∊[0.14–0.26]. Test results show strong impact for gap to diameter ratio of G/D<3 on VIV, amplitude of VIV, range of synchronization, onset of synchronization, frequency of oscillation, hysteresis at the onset of synchronization, and hysteresis at the end of synchronization.

Synergistic Flow-Induced Oscillation of Multiple Cylinders in Harvesting Marine Hydrokinetic Energy

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Mengyu Li ◽  
Christopher C. Bernitsas ◽  
Jing Guo ◽  
Hai Sun
Keyword(s):  
Negative Impact ◽  
Flow Speed ◽  
Shielding Effect ◽  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Close Proximity ◽  
Marine Hydrokinetic ◽  
The University ◽  
Energy Harnessing

Abstract Flow-induced oscillations/vibrations (FIO/V) of cylinders in tandem can be enhanced by proper in-flow spacing to increase hydrokinetic energy harnessing. In a farm of multiple cylinders in tandem, the effect of interference on harnessing efficiency arises. Three years of systematic experiments in the Marine Renewable Laboratory (MRELab) of the University of Michigan, on an isolated cylinder, and two and three cylinders in tandem have revealed that synergistic FIO can enhance oscillations of cylinders in close proximity. Two cylinders in tandem can harness 2.5–13.5 times the hydrokinetic power of one isolated cylinder. Three cylinders in tandem can harness 3.4–26.4 times the hydrokinetic power of one isolated cylinder. Negative impact on the harnessed energy by multiple cylinders, such as the shielding effect for the downstream cylinder/s, is possible. Specifically for the three-cylinder configuration, at a certain flow speed, the decrease in the power of the middle cylinder can be overcome by adjusting its stiffness and/or damping.

scholarly journals Virtual Spring–Damping System for Flow-Induced Motion Experiments

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Hai Sun ◽  
Eun Soo Kim ◽  
Marinos P. Bernitsas ◽  
Michael M. Bernitsas
Keyword(s):  
First Generation ◽  
Closed Loop ◽  
Hydrodynamic Force ◽  
Circular Cross Section ◽  
Data Generation ◽  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Vortex Induced Vibrations ◽  
Induced Motion ◽  
The University

Flow-induced motion (FIM) experiments of a single circular cylinder or multiple cylinders in an array involve several configuration and hydrodynamic parameters, such as diameter, mass, damping, stiffness, spacing, Reynolds number, and flow regime, and deviation from circular cross section. Due to the importance of the FIM both in suppression for structural robustness and in enhancement for hydrokinetic energy conversion, systematic experiments are being conducted since the early 1960s and several more decades of experimentation are required. Change of springs and dampers is time consuming and requires frequent recalibration. Emulating springs and dampers with a controller makes parameter change efficient and accurate. There are two approaches to this problem: The first involves the hydrodynamic force in the closed-loop and is easier to implement. The second called virtual damping and spring (Vck) does not involve the hydrodynamic force in the closed-loop but requires an elaborate system identification (SI) process. Vck was developed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan for the first time in 2009 and resulted in extensive data generation. In this paper, the second generation of Vck is developed and validated by comparison of the FIM experiments between a Vck emulated oscillator and an oscillator with physical springs and dampers. The main findings are: (a) the Vck system developed keeps the hydrodynamic force out of the control-loop and, thus, does not bias the FIM, (b) The controller-induced lag is minimal and significantly reduced compared to the first generation of Vck built in the MRELab due to use of an Arduino embedded board to control a servomotor instead of Labview, (c) The SI process revealed a static, third-order, nonlinear viscous model but no need for dynamic terms with memory, and (d) The agreement between real and virtual springs and dampers is excellent in FIM including vortex-induced vibrations (VIVs) and galloping measurements over the entire range of spring constants and velocities tested (16,000 < Re < 140,000).

scholarly journals Flow-Induced Vibrations of Single and Multiple Heated Circular Cylinders: A Review

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8496
Author(s):  
Ussama Ali ◽  
Md. Islam ◽  
Isam Janajreh ◽  
Yap Fatt ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Heat Exchangers ◽  
Power Plants ◽  
Bluff Body ◽  
The Body ◽  
Circular Cylinders ◽  
Fluid Forces ◽  
Spacing Ratio ◽  
Flow Induced Vibrations

This study is an effort to encapsulate the fundamentals and major findings in the area of fluid-solid interaction, particularly the flow-induced vibrations (FIV). Periodic flow separation and vortex shedding stretching downstream induce dynamic fluid forces on the bluff body and results in oscillatory motion of the body. The motion is generally referred to as flow-induced vibrations. FIV is a dynamic phenomenon as the motion, or the vibration of the body is subjected to the continuously changing fluid forces. Sometimes FIV is modeled as forced vibrations to mimic the vibration response due to the fluid forces. FIV is a deep concern of engineers for the design of modern heat exchangers, particularly the shell-and-tube type, as it is the major cause for the tube failures. Effect of important parameters such as Reynolds number, spacing ratio, damping coefficient, mass ratio and reduced velocity on the vibration characteristics (such as Strouhal number, vortex shedding, vibration frequency and amplitude, etc.) is summarized. Flow over a bluff body with wakes developed has been studied widely in the past decades. Several review articles are available in the literature on the area of vortex shedding and FIV. None of them, however, discusses the cases of FIV with heat transfer. In particular systems, FIV is often coupled to heat transfer, e.g., in nuclear power plants, FIV causes wear and tear to heat exchangers, which can eventually lead to catastrophic failure. As the circular shape is the most common shape for tubes and pipes encountered in practice, this review will only focus on the FIV of circular cylinders. In this attempt, FIV of single and multiple cylinders in staggered arrangement, including tandem and side-by-side arrangement is summarized for heated and unheated cylinder(s) in the one- and two-degree of freedom. The review also synthesizes the effect of fouling on heat transfer and flow characteristics. Finally, research prospects for heated circular cylinders are also stated.

scholarly journals Prediction of Dynamic Responses of Flow-Induced Vibration Using Deep Learning

2021 ◽  
Vol 11 (15) ◽  
pp. 7163
Author(s):  
Gi-yong Kim ◽  
Chaeog Lim ◽  
Eun Soo Kim ◽  
Sung-chul Shin
Keyword(s):  
Experimental Data ◽  
Electrical Energy ◽  
Clean Energy ◽  
Flow Speed ◽  
Dynamic Responses ◽  
University Of Michigan ◽  
Flow Induced Vibration ◽  
Marine Renewable Energy ◽  
The University ◽  
Good Agreement

Flow-induced vibration (FIV) is a phenomenon in which the flow passing through a structure exerts periodic forces on the structure. Most studies on FIVs focus on suppressing this phenomenon. However, the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan, USA, has developed a technology called the vortex-induced vibration for aquatic clean energy (VIVACE) converters that reinforces FIV and converts the energy in tidal currents to electrical energy. This study introduces the experimental data of the VIVACE converter and the associated method using deep neural networks (DNNs) to predict the dynamic responses of the converter. The DNN was trained and verified with experimental data from the MRELab, and the findings show that the amplitudes and frequencies of a single cylinder in the FIV predicted by the DNN under various test conditions were in good agreement with the experimental data. Finally, based on both the predicted and experimental data, the optimal power envelope of the VIVACE converter was generated as a function of the flow speed. The predictions using DNNs are expected to be more accurate as they can be trained with more experimental data in the future and will help to substantially reduce the number of experiments on FIVs.

Computational and Experimental Assessment of Turbulence Stimulation on Flow Induced Motion of Circular Cylinder

2015 ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Michael M. Bernitsas
Keyword(s):  
Parametric Design ◽  
Fluid Dynamic ◽  
Circular Cylinders ◽  
Design Parameters ◽  
Turbulence Control ◽  
Hydrokinetic Energy ◽  
Flow Features ◽  
Induced Motion ◽  
Marine Hydrokinetic ◽  
The University

In the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan, Flow Induced Motion (FIM) is studied as a means to convert marine hydrokinetic energy to electricity using the VIVACE energy harvester [1–4]. Turbulence stimulation in the form of sand-strips, referred to as Passive Turbulence Control (PTC), were added to oscillating cylinders in 2008 [5]. PTC enabled VIVACE to harness hydrokinetic energy from currents/tides over the entire range of FIM including VIV and galloping. In 2011, the MRELab produced experimentally the PTC-to-FIM Map defining the induced cylinder motion based on the location of PTC [6]. In 2013, the robustness of the map was tested and dominant zones were identified [7]. Even though the PTC-to-FIM Map has become a powerful tool in inducing specific motions of circular cylinders, several parameters remain unexplored. Experiments, though the ultimate verification tool, are time consuming and hard to provide all needed information. A computational tool that could predict the FIM of a cylinder correctly would be invaluable to study the full parametric design space. A major side-benefit of PTC was the fact that PTC enabled computational fluid dynamic (CFD) simulations to generate results in good agreement with experiments by forcing the location of the separation point [8]. This valuable tool, along with experiments, is used in this paper to investigate PTC design parameters such as width and thickness and their impact on flow features with the intent of maximizing FIM and, thus, hydrokinetic energy conversion.

Synergistic Flow Induced Oscillation of Multiple Cylinders in Harvesting Marine Hydrokinetic Energy

2019 ◽  
Author(s):  
Sun Hai ◽  
Michael M. Bernitsas ◽  
Chen Zhiyun
Keyword(s):  
University Of Michigan ◽  
Hydrokinetic Energy ◽  
Close Proximity ◽  
Marine Hydrokinetic ◽  
The University ◽  
Energy Harnessing

Abstract Flow Induced Oscillations (FIO) of cylinders in tandem can be enhanced by proper spacing to increase hydrokinetic energy harnessing. In a farm of multiple cylinders in tandem, the issue of the effect of interference on harnessing efficiency arises. Over the course of three years of development in the Marine Renewable Laboratory of the University of Michigan, systematic experiments on an isolated cylinder, and two and three cylinders in tandem have revealed that synergistic FIO can actually enhance oscillations of cylinders in close proximity. Two cylinders in tandem can harness 2.5–13.5 times the hydrokinetic power of one isolated cylinder. Three cylinders in tandem can harness 3.4–26.4 times the hydrokinetic power of one isolated cylinder.

Free vibrations of two tandem elastically mounted cylinders in crossflow

2018 ◽  
Vol 861 ◽  
pp. 349-381 ◽  
Author(s):  
Bin Qin ◽  
Md. Mahbub Alam ◽  
Yu Zhou
Keyword(s):  
Shear Layers ◽  
Free Vibrations ◽  
Circular Cylinders ◽  
Laser Vibrometer ◽  
Base Surface ◽  
Frequency Responses ◽  
Spacing Ratio ◽  
Flow Induced Vibrations ◽  
Generation Mechanisms ◽  
Positive Work

The paper presents an experimental investigation on the flow-induced vibrations of two tandem circular cylinders for spacing ratio $L/D=1.2{-}6.0$ and reduced velocity $U_{r}=3.8{-}47.8$, where $L$ is the cylinder centre-to-centre spacing and $D$ is the cylinder diameter. Both cylinders are allowed to vibrate only laterally. Extensive measurements are conducted to capture the cylinder vibration and frequency responses, surface pressures, shedding frequencies and flow fields using laser vibrometer, hotwire, pressure scanner and PIV techniques. Four vibration regimes are identified based on the characteristics and generation mechanisms of the cylinder galloping vibrations. Several findings are made on the mechanisms of vibration generation and sustainability. First, the initial states (vibrating or fixed) of a cylinder may have a pronounced impact on the vibration of the other. Second, alternating reattachment, detachment, rolling up and shedding of the upper and lower gap shear layers all contribute to the vibrations. Third, the gap vortices around the base surface of the upstream cylinder produce positive work on the cylinder, sustaining the upstream cylinder vibration. Fourth, reattachment, detachment and switching of the gap shear layers result in largely positive work on the downstream cylinder, playing an important role in sustaining its vibration.

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