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Sun H.,Harbin Engineering University | Sun H.,University of Michigan | Ma C.,University of Michigan | Ma C.,Jiangsu Maritime Institute | And 6 more authors.
Renewable Energy | Year: 2017

Flow Induced Motions (FIMs) of rigid circular cylinders, and particularly VIV (Vortex Induced Vibrations) and galloping, are induced by alternating lift. The VIVACE (VIV for Aquatic Clean Energy) Converter uses single or multiple cylinders, in tandem, on elastic end-supports, in synergistic FIM, to convert MHK energy to electricity. Selectively distributed surface roughness is applied to enhance FIM and increase efficiency. In this paper, two cylinders are used in tandem with center-to-center spacing of 1.57, 2.0 and 2.57 diameters, harnessing damping ratio 0.00<ζ < 0.24, for Reynolds number 30,000 ≤ Re ≤ 120,000. The virtual spring-damping system Vck in the Marine Renewable Energy Laboratory (MRELab) enables embedded computer-controlled change of viscous-damping and spring-stiffness for fast and mathematically correct oscillator realization, without including the hydrodynamic force in the closed control loop. Experimental results for oscillatory response, energy harvesting, and efficiency are presented and the envelope of optimal power is derived. All the 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) For the tested cylinder spacing, two cylinders harness power is between 2.56 and 13.49 times the power of a single cylinder, the efficiency of two cylinders is between 2.0 and 6.68 of a single cylinder. (2) The MHK power harnessed by the upstream cylinder is increased by up to 100%, affected by the downstream cylinder. (3) The MHK power harnessed by the downstream cylinder and its FIM are affected to a lesser extent by the interaction. (4) VIVACE can harness energy from flows as slow as 0.4 m/s with no upper limit in flow velocity. (5) Close spacing and high spring stiffness yield highest harnessed power. (6) The optimal harnessed power shifts to softer springs as spacing increases. © 2017 Elsevier Ltd


Kim E.S.,University of Michigan | Kim E.S.,Vortex Hydro Energy, LLC | Bernitsas M.M.,University of Michigan | Bernitsas M.M.,Vortex Hydro Energy, LLC
Applied Energy | Year: 2016

Horizontal hydrokinetic energy can be harnessed using Steady Lift Technology (SLT) like turbines or Alternating Lift Technology (ALT) like the VIVACE Converter. Tidal/current turbines with low mechanical losses typically achieve about 30% peak power efficiency, which is equivalent to 50.6% power efficiency over the Betz limit at flow speed nearly 3.0 m/s. The majority of flows worldwide are slower than 1.0-1.5 m/s. Turbines also require large in-flow spacing resulting in farms of low power-to-volume density. Alternating-lift overcomes these challenges. The purpose of this study is to show that the ALT Converter is a three-dimensional energy absorber that efficiently works in river/ocean currents as slow as 1.0-1.5 m/s a range of velocities presently inaccessible to watermills and turbines. This novel converter utilizes flow-induced motions (FIM), which are potentially destructive phenomena for structures, enhances them, and converts hydrokinetic energy to electricity. It was invented in the Marine Renewable Energy Lab (MRELab) and patented through the University of Michigan. MRELab has been studying the effect of passive turbulence control (PTC) to enhance FIMs and to expand their synchronization range for energy harnessing. This study shows that multiple cylinders in proximity can synergistically work and harness more energy than the same number of a single cylinder in isolation. Estimation based on experiments, shows that a 4 PTC-cylinder Converter can achieve 88.6% peak efficiency of the Betz limit at flow speed slower than 1.0 m/s and power-to-volume density of 875 W/m3 at 1.45 m/s. Thus, the Converter can efficiently harness energy from rivers and ocean current as slow as 0.8-1.5 m/s, with no upper limit in flow velocity. © 2016 Elsevier Ltd.


Sun H.,University of Michigan | Kim E.S.,Vortex Hydro Energy, LLC | Bernitsas M.P.,Vortex Hydro Energy, LLC | Bernitsas M.M.,University of Michigan
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2015

The research objective of the Marine Renewable Energy Lab (MRELab) is to design multi-cylinder VIVACE Converters and optimize their power output for a broad range of velocities. For a given geometric and mass configuration of a school of cylinders, each point on the power envelope, at a given flowspeed, is a function of the spring constant and damping. Conducting tests with real springs and dampers requires lengthy preparation for each set of experiments. A more efficient way to conduct experiments faster and accurately is developed based on a controller embedded virtual springdamping system (Vck) that des not include the hydrodynamic force in the closed loop. Each oscillator consists of one Vck, one interchangeable cylinder moving on submerged roller blocks and driven by the fluid flow, and connected to the controller through belts and pulleys. It is designed to achieve the desired static/dynamic friction through the Vck. An Arduino embedded board controls a servomotor with an optical encoder, which enables real-time position/speed measurement. A system identification (SI) methodology is developed making possible to identify the damping model of any oscillator, which is typically much more complicated than the classical linear viscous model. Upon completion of the SI process for an oscillator, the actual nonlinear damping model is subtracted using the controller and leaving the system with zero damping. Then, a mathematically linear damping model is added, thus, resulting in a system with real linear viscous damping. This process enables changing the spring constant and harnessing damping through the controller instantly. Experiments are then conducted with both real spring dampers and Vck to validate the process. All FIM experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan at 16,000


Park H.,University of Michigan | Kumar R.A.,University of Michigan | Kumar R.A.,Kerala University | Bernitsas M.M.,University of Michigan | Bernitsas M.M.,Vortex Hydro Energy, LLC
Ocean Engineering | Year: 2013

Passive turbulence control (PTC) in the form of selectively distributed surface roughness is applied on a rigid circular cylinder on two end-springs. The cylinder is placed perpendicular to a uniform steady flow and the cylinder response is measured experimentally for 3×104≤Re≤1. 2×105 and broad ranges of the main PTC parameters. PTC consists of two roughness strips placed parallel to the cylinder axis and symmetrically to the flow with thickness on the order of the boundary layer thickness. Different flow-induced motion (FIM) is observed depending primarily on the circumferential location of the two strips. FIM enhancement is studied in this paper in the soft galloping and the two hard galloping zones identified in the PTC-to-FIM Map. In galloping, amplitudes of oscillation reach 2.9 times the cylinder diameter limited only by the free-surface and bottom-boundary effects of the experimental facility. The galloping range follows the VIV range thus expanding dramatically the FIM range. Enhancement of FIM is needed to convert more hydrokinetic energy to mechanical and subsequently to electrical energy over broad velocity range. Use of laser broad field-of-view visualization reveals very different vortex structures between VIV and galloping confirming the fundamentally different driving mechanism of these two FIM kinds. © 2013 Elsevier Ltd.


Park H.,University of Michigan | Ajith Kumar R.,University of Michigan | Ajith Kumar R.,Amrita University | Bernitsas M.M.,University of Michigan | Bernitsas M.M.,Vortex Hydro Energy, LLC
Ocean Engineering | Year: 2016

Suppression of vortex-induced vibrations (VIV) of an elastically mounted circular cylinder in a steady flow is studied experimentally using localized surface roughness, called Passive Turbulence Control (PTC). PTC consists of two roughness strips with thickness on the order of the boundary layer thickness and placed parallel to the cylinder axis symmetrically with respect to the flow. The range of Reynolds number (3×104≤Re≤1.2×105) considered covers primarily the Transition to Shear Layer3, high-lift, flow regime. For the smooth cylinder, the broad synchronization range and higher peak amplitude in the upper branch and unstable oscillations in the lower branch are characteristic of VIV at higher Reynolds numbers and distinctive from those of lower Reynolds numbers. From the PTC-cylinder results with systematic variation of the PTC location, one strong-suppression zone and two weak-suppression zones are identified based on the location of the PTC. These zones are part of the Map that established the relation between PTC and Flow-Induced Motions in previous work. In the strong suppression zone, reduction of 30-80% is achieved while in the weak suppression zones reduction of less than 30% is achieved. Broad field-of-view flow visualization shows that smooth cylinder vortex structures change with PTC and between zones. © 2015 Elsevier Ltd. All rights reserved.


Ding L.,Chongqing University | Zhang L.,Chongqing University | Kim E.S.,University of Michigan | Bernitsas M.M.,University of Michigan | Bernitsas M.M.,Vortex Hydro Energy, LLC
Journal of Fluids and Structures | Year: 2015

Two-dimensional Unsteady Reynolds-Average Navier-Stokes equations with the Spalart-Allmaras turbulence model are used to simulate the flow induced motions of multiple circular cylinders with passive turbulence control (PTC) in steady uniform flow. Four configurations with 1, 2, 3, and 4 cylinders in tandem are simulated and studied at a series of Reynolds numbers in the range of 30 000


Sun H.,University of Michigan | Kim E.S.,University of Michigan | Nowakowski G.,U.S. Department of Energy | Mauer E.,U.S. Department of Energy | And 2 more authors.
Renewable Energy | Year: 2016

Flow Induced Motions (FIMs) of a single, rigid, circular cylinder with end-springs are investigated for Reynolds number 30,000 ≤ Re ≤ 120,000 with mass ratio, damping, and stiffness 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 at higher Reynolds numbers. The second generation of virtual spring-damping system Vck, recently developed in the Marine Renewable Energy Laboratory (MRELab), enables embedded computer-controlled change of viscous-damping and spring-stiffness for fast and precise oscillator modeling. Experimental results for amplitude response, frequency response, 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 oscillator can harness energy from flows as slow as 0.3946 m/s with no upper limit. (2) Increasing the spring stiffness, shifts the VIV synchronization range to higher flow velocities, resulting in reduced gap between VIV and galloping, where the harnessed power drops. (3) In galloping, the harnessed power increases with the mass ratio. (4) Local optima in energy conversion efficiency appear at the beginning of the VIV upper branch and at the beginning of galloping. (5) Local optima in power appear at the end VIV upper branch and at the beginning of galloping. © 2016 Elsevier Ltd


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 500.00K | Year: 2010

This Small Business Technology Transfer (STTR) Phase II project will advance the development and prototype testing necessary to transition an innovative large scale generating system from concept to commercialization. The underwater energy generation system is based on the naturally occurring phenomenon of vortex induced vibration (VIV). This device harvests hydrokinetic energy via a system of cylinders that oscillate due to water currents at velocities as low as 2-3 knots (water turbines require 5-7 knots). This system captures energy from water currents - unlike hydroelectric power there are no dams or turbines. The proposed research and development includes: (a) Application of Passive Turbulence Control (PTC) to enhance the hydrodynamic effect of VIV and increase hydrokinetic harvested energy for large scale cylinders; (b) Identification of optimal cylinder spacing as a result of using PTC; (c) Installation of a large 4-cylinder module in the St. Clair River in Port Huron, MI; (d) Classification and research of appropriate materials to extend period between maintenance cycles in harsh marine environments.

The broader impact/commercial potential of this project is that it taps into a vast new source of clean and renewable energy - water currents as slow as 2 to 3 knots. Currently, there are only pilot devices for harnessing horizontal hydrokinetic energy (currents, tides). All devices considered are conventional propeller/turbines that target speeds around 5-7 knots (only seven locations with these conditions exist in the US). The vast majority of river/ocean currents in the United States are slower than 3 knots. This leaves the vast majority of rivers and bodies of water in the country untapped for power generation. Renewable energy generation is one of today?s most challenging global dilemmas. The energy crisis requires tapping into every source of energy and developing every technology that can generate energy at a competitive cost within the next 50 years. Development of this technology will bolster domestic energy security and mitigate global climate change. There are numerous commercial and military applications from small scale (1-5kW) to large scale (100MW). Applications span from small portable devices, to direct water pumping for irrigation, direct pumping for desalination, off-shore stations, idle ships, coastal naval bases, etc.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2013

Renewable energy generation is one of todays most challenging global dilemmas. The energy crisis requires tapping into every source of energy and developing every technology that can generate energy at a competitive cost within the next 50 years. Development of the FiSH-MHK transformative technology on top of the verified and pilot-tested VIVACE technology will bolster domestic energy security and mitigate global climate change. There are numerous commercial and military applications for a fully developed system, which could generate clean/renewable energy from small scale (1-5kW) to medium scale (500kW) to large scale (100MW). Applications span from small portable devices, to direct water pumping for irrigation, direct pumping for desalination, to powering off-shore stations, idle ships, coastal naval bases, and coastal communities, to powering utility-scale companies. Large areas with no natural resources such as the Caribbean or the Polynesia, sparsely populated areas like Alaska, long slow flows like the Netherlands channels, and areas that need desalinated water would benefit from FiSH-VIVACE converter as a reliable and environmentally compatible technology to generate MHK Power. The objectives of the proposed work pertain to building a high power-density and high efficiency device to harness MHK energy by mimicking fish-school kinematics. Vortex Hydro Energy is collaborating with a concept formed and undergone preliminary testing at the University of Michigan to complete this task. The objectives of the proposed work pertain to achieving synergistic kinematics of a school of fish-shaped bodies to maximize conversion of hydrokinetic power to electricity. This will be done by designing a school of bluff bodies with fish-body cross-section, fish-surface roughness, and fish-school spacing to optimize the lift-to-drag ratio of the oscillators as a group. The plan has three major objectives stated next. Objectives of Phase I SBIR: 1. Design the cross-section fish-shape of each individual school member (converter) to maximize its oscillatory lift-to-drag ratio using the dedicated CFD code developed, verified, and experimentally validated in the MRELab. 2. Test the optimized fish-shape experimentally in the Low Turbulence Free Surface Water Channel of the MRELab in comparison to a circular cylinder. 3. Perform preliminary CFD simulations for multiple cylinders with the fish-shaped cross section to identify synergistic operation. Objectives of Phase II SBIR: 1. Implement the optimal body-shape in a CFD search for optimal three-dimensional body distribution in a school of converters. 2. Test the optimized configuration experimentally. 3. Build/test/deploy the designed system in the St. Clair River.

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