Session: 09-03-02 Tidal Energy: Hydrodynamics

Paper Number: 129792

129792 - Hydrokinetic Energy Harnessing Using Turbulence Stimulation and Nonlinear Damping on Flow-Induced Oscillations of Two-Cylinders in Tandem 

Background: Passive Turbulence Control (PTC) and nonlinear adaptive damping are used in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan to improve efficiency and power-to-volume ratio of the VIVACE converter. Redesigned PTC induces higher oscillatory response and earlier shifting from VIV to galloping. Implementing adaptive damping enhances amplitude response in all Flow Induced Oscillation (FIO) regimes and prevents amplitude drop in VIV to galloping transition. Implementing both large PTC and adaptive damping, two tandem cylinders respond with constant phase difference emulating fish-body undulation. 

Problem Definition: Marine Hydrokinetic (MHK) energy technologies require a minimum of 2 m/s water speed to operate optimally, while most ocean currents, rivers, and tides are slower than 1-1.5m/s. VIVACE has been proved in the MRELab to start harvesting energy at flow speed of 0.3 m/s. However, there are still slower currents omnipresent in oceans, tides, and rivers.

Objective: The MRELab seeks to improve efficiency of the VIVAVE converter by initiating FIO’s earlier and gaining higher power conversion without controlling the motion of cylinders which would bias the underlying phenomenon. In our approach, the oscillator properties are redesigned and/or controlled rather than the oscillator motion. Specifically:  

1. Modify cylinder geometry by turbulence stimulation

2. Implement damping adjusting itself according to oscillation speed.

3. Change distance between cylinders in tandem.

Solution Approach:  The cylinder geometry is changed by bigger turbulence stimulation up to 29% of the cylinder’s diameter. Linear damping is replaced by nonlinear damping proportional to cylinder speed. This nonlinear, speed-adaptive damping is achieved by feeding a sensor reading into an Arduino board to calculate the appropriate damping, and then implementing it into the servo motor used to emulate spring and damping outside the control loop. To study the effects of these modifications, the following parameters were used in the experiments:

A)   Two cylinders in tandem with spacing of 2.57D, for D=8.89 cm and mass ratio m*=1.326.

B)    Each cylinder is equipped with symmetric turbulence stimulation of 2.54 cm height, located at  from the stagnation point.

C)    The leading cylinder has linear damping ratio .

D)   The trailing cylinder has speed proportional damping  .

E)    Spring stiffness K=400-800n/m

F)    Flow speed V=0.36-1.16 m/s.

Selective experiments are CFD-simulated for visualization and explanation of phenomena observed. Specially, the following data are plotted and compared: 

(a)   Response amplitude ratio A/D vs. Reynolds number, flow speed, and reduced velocity.

(b)   Frequency ratio vs. Reynolds number, flow speed, and reduced velocity.

(c)   Time history of displacement, speed, and total force of each cylinder to establish relation to high-power response patterns.

(d)   Extensive experiments and observations point to the conclusion that the maximum output of MHK energy conversion corresponds to oscillatory patterns mimicking the fish-body undulation. 

 

Finding: 

(1)   Regardless of damping and stiffness, the amplitude response of the leading cylinders shifts to galloping at U=0.36 m/s and the amplitude ratio A/D keeps increasing linearly with water speed.

(2)   VIV and galloping coexist before U=0.9 m/s.

(3)   The amplitude response of the trailing cylinder shows characteristics of VIV at low speed and then quickly changes to galloping. Increasing of both stiffness and adaptive damping shifts its response to galloping earlier.

(4)   Amplitude response in galloping becomes less stable as water speed increases. This is quantified by the increased standard deviation of the amplitude ratio.

(5)   Total mechanical power converted of cylinders in FIOs increases quadratically with increasing stiffness and damping.

(6)   Regardless of the stiffness and damping, the efficiency of system reaches the peak value when reduced velocity is in the range of .

(7)   The phase difference between leading and trailing cylinders are consistent with flow speed regardless of stiffness and damping. Specifically:

a.     The second cylinder leads the first cylinder before flow speed reaches the transition range.

b.     The phase difference between two cylinders is almost 180^o in the transition range.

c.     The first cylinder leads the second cylinder after flow speed reached the transition range.

Presenting Author: Nipit Congpuong University of Michigan

Presenting Author Biography: Nipit Congpuong, M.S. in Mechanical Engineering, is a current Ph.D. candidate in Mechanical Engineering at the University of Michigan, Ann Arbor, MI 48015; Tel: 706-888-0253; cnipit@umich.edu. Education: Virginia Polytechnic Institute and State University BS ME 2020, University of Michigan MS ME 2022.

He was awarded the Thai Government scholarship to study aboard for bachelor’s degree, Master’s degree and Doctorate’s degree. He is working in the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan under the supervision of Dr Michael M. Bernitsas. His research involves (1) Flow Induced Oscillations, Vortex Induced Vibration, and Galloping. (2) Multibody interaction in Flow Induced Oscillations. (3) Renewable energy from ocean currents, rivers, and tides. (4) Fish biomimetics in the design of the VIVACE Converter.

Authors:

Nipit Congpuong University of Michigan
Salman Sadiq University of Michigan
Hai Sun Harbin Engineering University
Michael Bernitsas Univ Of Michigan