scholarly journals Hydrokinetic Power Conversion Using Vortex-Induced Oscillation with Cubic Restoring Force

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3283
Author(s):  
Mengyu Li ◽  
Christopher Bernitsas ◽  
Guo Jing ◽  
Sun Hai
Keyword(s):  
Reynolds Numbers ◽  
University Of Michigan ◽  
Restoring Force ◽  
High Deformation ◽  
Marine Renewable Energy ◽  
Linear Damping ◽  
Marine Hydrokinetic ◽  
The University ◽  
Current Energy ◽  
Cubic Stiffness

A cubic-spring restoring function with high-deformation stiffening is introduced to passively improve the harnessed marine hydrokinetic power by using flow-induced oscillations/vibrations (FIO/V) of a cylinder. In these FIO/V experiments, a smooth, rigid, single-cylinder on elastic end-supports is tested at Reynolds numbers ranging from 24,000 < Re < 120,000. The parameters of the tested current energy converter (CEC) are cubic stiffness and linear damping. Using the second generation of digital virtual spring-damping (Vck) controller developed by the Marine Renewable Energy Laboratory (MRELab), the cubic modeling of the oscillator stiffness is tested. Experimental results show the influence of the parameter variation on the amplitude, frequency, energy conversion, energy efficiency, and power of the converter. All experiments are conducted in the low turbulence-free surface water (LTFSW) channel of the MRELab of the University of Michigan. The main conclusions are: (1) The nonlinearity in the cubic oscillator is an effective way to extend the vortex-induced vibration (VIV) upper branch, which results in higher harnessing power and efficiency compared to the linear stiffness cylinder converter. (2) Compared to the linear converter, the overall power increase is substantial. The nonlinear power optimum, occurring at the end of the VIV upper branch, is 63% higher than its linear counterpart. (3) The cubic stiffness converter with low harnessing damping achieves consistently good performance in all the VIV regions because of the hardening restoring force, especially at higher flow velocity.

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.

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

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Omer Kemal Kinaci ◽  
Sami Lakka ◽  
Hai Sun ◽  
Ethan Fassezke ◽  
Michael M. Bernitsas
Keyword(s):  
University Of Michigan ◽  
Amplitude Response ◽  
Turbulence Control ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Highly Nonlinear ◽  
Invaluable Tool ◽  
Induced Motion ◽  
The University ◽  
Passive Turbulence Control

Vortex-induced vibrations (VIVs) are highly nonlinear and it is hard to approach the problem analytically or computationally. Experimental investigation is therefore essential to address the problem and reveal some physical aspects of VIV. Although computational fluid dynamics (CFDs) offers powerful methods to generate solutions, it cannot replace experiments as yet. When used as a supplement to experiments, however, CFD can be an invaluable tool to explore some underlying issues associated with such complicated flows that could otherwise be impossible or very expensive to visualize or measure experimentally. In this paper, VIVs and galloping of a cylinder with selectively distributed surface roughness—termed passive turbulence control (PTC)—are investigated experimentally and computationally. The computational approach is first validated with benchmark experiments on smooth cylinders available in the literature. Then, experiments conducted in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan are replicated computationally to visualize the flow and understand the effects of thickness and width of roughness strips placed selectively on the cylinder. The major outcomes of this work are: (a) Thicker PTC initiates earlier galloping but wider PTC does not have a major impact on the response of the cylinder and (b) The amplitude response is restricted in VIV due to the dead fluid zone attached to the cylinder, which is not observed in galloping.

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.

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.

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.

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.

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.

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

2013 ◽  
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 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. The two identical cylinders are rigid, suspended by springs, and allowed to move transversely to the flow direction and their own axis. 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 the 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. In addition the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Novae in the Magellanic Clouds

1979 ◽  
Vol 46 ◽  
pp. 96-101
Author(s):  
J.A. Graham
Keyword(s):  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
University Of Michigan ◽  
The Past ◽  
Spectroscopic Information ◽  
Objective Prism ◽  
The University ◽  
Small Cloud ◽  
Low Dispersion

During the past several years, a systematic search for novae in the Magellanic Clouds has been carried out at Cerro Tololo Inter-American Observatory. The Curtis Schmidt telescope, on loan to CTIO from the University of Michigan is used to obtain plates every two weeks during the observing season. An objective prism is used on the telescope. This provides additional low-dispersion spectroscopic information when a nova is discovered. The plates cover an area of 5°x5°. One plate is sufficient to cover the Small Magellanic Cloud and four are taken of the Large Magellanic Cloud with an overlap so that the central bar is included on each plate. The methods used in the search have been described by Graham and Araya (1971). In the CTIO survey, 8 novae have been discovered in the Large Cloud but none in the Small Cloud. The survey was not carried out in 1974 or 1976. During 1974, one nova was discovered in the Small Cloud by MacConnell and Sanduleak (1974).

Sign in / Sign up

Export Citation Format

Share Document