2015 Progress Report: Ocean Wave Energy Harvester with a Novel Power Takeoff MechanismEPA Grant Number: SU835734
Title: Ocean Wave Energy Harvester with a Novel Power Takeoff Mechanism
Investigators: Zuo, Lei , Liang, Changwei
Current Investigators: Zuo, Lei , Liang, Changwei , Ai, Junxiao , Li, Xiaofan , Wise, Adam , Lee, Rosaline , House, Evan , Boontanom, Jedhathai , Capindo, Carl Matthew , Mizrahi, Coby , Palencia, Gabriel , Fernandez, Luis , Sim, Duncan , Heyde, Keith , Ding, Josh
Institution: Virginia Tech
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2014 through August 14, 2016
Project Period Covered by this Report: August 15, 2014 through August 14,2015
Project Amount: $90,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2014) Recipients Lists
Research Category: P3 Challenge Area - Air Quality , Sustainable and Healthy Communities
In this report period we designed and prototyped a wave energy converter with mechanical motion rectifier as the power takeoff mechanism. The power takeoff has been tested in the lab and the overall system was tested in the ocean of Long Island Sound. The peak power in one phase of the generator is 205w while the average power is 21W when the significant wave height is about 0.2m.In addition, the dynamics and design of a two-body wave energy converter is also studied based on the linear frequency model.
Lab Test for the Power Takeoff System
Lab testing for the power takeoff mechanism was conducted to verify feasibility of converting bidirectional motion into unidirectional rotation, and to estimate the output power under external excitation. The power takeoff system was driven manually.
Figure 6 shows the output voltage and output power of the power takeoff system when the external electrical load is 50 Ohms. The output voltage in Figure 6 is always large than zero, which verifies the concept of mechanical motion rectifier mechanism.
Figure 6: Output power and voltage of the power takeoff system in the lab test.
Ocean Test for the Overall system
The ocean test of the designed wave energy converter prototype was conducted in Long Island Sound. The research boat Seawolf (Figure 7(a)) was used to bring the prototype to the middle of Long Island Sound (41°02'20"N 73°11'06"W), which is about 5 miles to the coast. The purpose of this testing is to verify the feasibility of wave energy harvesting in the ocean. The depth of the sea is about 25 meters. As a preliminary study, instead of anchoring the shaft to the seabed, the shaft of the wave converter is connected to the boom on Seawolf boat.
Figure 7. In-ocean test of the MMR-based ocean wave converter.
(a) Seawolf research vessel; (b) Assembled buoy; (c)Location of experiment; (d) buoy connected with the boom with tensioning weight
Figure 8: (a) Recorded voltage, current and output power from one of the three phases of the generator; (b) Zoomed figure for the output power
A tensioning weight of 80kg was used at the end of the boom to provide a reaction force to the buoy in both upward and downward motions. As shown in Figure 7(d), the upper shaft was attached to the bottom of the tensioning weight.
An extension power cord was used to connect the generator in the wave converter to electrical loads in the Sealwolf dry lab.
From NOAA’s Buoy Station 44039 (41°8'15" N 72°39'17" W), the wave height was 0.2m and dominated wave period was 4s. Figure 8 shows the recorded current and voltage and output power from one of the three phases of the generator. The peak of the output power in one phase is 205W while the average power is only 21W. Totally 63W average power was generated from the three phases. Such a number is less than the rated power in the concept design. The ocean wave test does verify the feasibility of harvesting the power from the wave motion with mechanical motion rectifier. The disengagement can be found in Figure 8(b)
Modelling and Analysis of a Two-body Wave energy Converter
A frequency domain model of a two-body wave energy converter is considered (Figure 9) by accounting for the linearized viscous damping due to viscous effect. The closed-form solution of the suboptimal and optimal absorption power and corresponding power takeoff parameters are obtained. The suboptimal and optimal designs of the two-body wave energy converter are defined based on the obtained closed -form solutions. Despite the linearized drag damping and hydrodynamic simplification considered in the simulation, the results are useful to understand the dynamics and design of a two-body wave energy converter.
Figure 9. Schematic of two-body wave energy converter
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 Oceanlinx Company. URL: http://www.oceanlinx.com, last accessed data 2015.
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 Lejerskog E, Gravråkmo H, Savin A, Strömstedt E, Tyrberg S, Haikonen K, Krishna R, Boström C, Rahm M, Ekström R and Svensson O. Lysekil research site, Sweden: a status update. In 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 2 publications||2 publications in selected types||All 2 journal articles|
||Xie J, Zuo L. On the Dynamics and Design of A Two-body Wave Energy Converters. Renewable Energy 2017;1(101):265-74.||
||Liang Changwei, Ai Junxiao Zuo Lei. Design, fabrication, simulation and testing of an ocean wave energy converter with mechanical motion rectifier. Ocean Engineering 2017;136:190-200.||