Current Energy Harnessing using Synergistic Kinematics of Schools of Fish-Shaped Bodies
This report details the design, fabrication, lab-testing, field-testing, performance, deployment and retrieval of Oscylator-4, a 4kW model of the VIVACE Converter. 1. THE TECHNOLOGY is a current/tide MHK energy Converter, named VIVACE, consisting of 1-4 cylinders with surface roughness, in school formation. Each rigid cylinder oscillates on end-springs forced by Fluid-Structure Interaction instabilities referred to as Flow-Induced Oscillations (FIO): Vortex Induced Vibrations (VIV), transition from VIV to galloping, and galloping. FIO are catastrophic phenomena, omnipresent in cylinders in flows from fishnets to buildings, bridges and offshore platforms, starting at very slow speeds with no upper limit. When controlled they generate electric power. Each cylinder is control-connected to PTO. Uniqueness and innovation: The Converter provides efficient access to slow currents (slower than 3kn), which constitute the vast majorityThe underlying physical phenomena are natural and scalableAlternating lift is compatible with fish kinematicsSynergistic FIO harness much more power than isolated cylinders enabling compact designs with high power-to-volume density. 2. STATE OF THE ART: VIVACE has established the following:High power density with up to 4 cylinders in close proximity.Efficiency reaching 88% of Betz limit.Adaptive damping increasing power 51%-95% in single-cylinder and 50% in two-cylinder synergistic FIO.Applicable understanding of synergistic hydrodynamics FIO.Simple geometry and durable structure.Real 3-D converter as opposed to point, line, or area converters. Field-operation at slow flows, about 2.3kn. 3. PROJECT OBJECTIVES:#1 Lab-testing to identify optimal 3-D converter distribution in a school.#2 Build and dry-test Oscylator-4 during the first year. #3 Build and install a full-scale commercial-size 4-cylinder Oscylator-4 in the St. Clair River. 4. LABORATORY TESTS with 1-4 cylinders. Conclusions:Alternating lift provides an environmentally compatible way to harness MHK energy from flows as slow as 0.274m/s. Adaptive damping increases harnessed power by 51% to 95%. For two cylinders, the converted power is 2.56-7.5 times the power of a single cylinder. The highest efficiency reached for two cylinders was 63% of the Betz limit. Adaptive damping improves harnessed power by two cylinders in synergistic FIO by 25%. Synergy between multiple cylinders results in efficiency of over 80% of the Betz limit. 5. RIVER TEST: Results Hydrodynamics: The results were a real breakthrough as not only the power increased with cylinder synergy, but the volume of the device reduced dramatically. Weight and Volume: Both reduced more than expected. Cost: Deployment/retrieval cost was high. Thus, the desired LCOE was not reached. Oscylator-4 can be redesigned for self-deployment to nearly eliminate the cost of deployment/retrieval and reduce CAPEX dramatically. 6. TEST RESULTS: All cylinders were over-buoyed (m*=mass/buoyancy<1). Thus, cylinders were subjected to a component of the buoyance pushing the cylinder to the highest point in the structure. The control for Oscylator-4 was designed to compensate for buoyance effects. 7. PRODUCTS DEVELOPED Lab testing with up to four cylinders in tandem. Synergy between cylinders has been proven, by two cylinders in proximity generating 2.6-7.5 times the power of a single cylinder. Similar amplification was found using 3/4 cylinders. This combination of higher power and smaller volume resulted in an order of magnitude increase in power-to-volume density. A full-scale prototype, Oscylator-4, was built and tested in the St. Clair River for three months - the duration of the permit. The full-scale tests confirmed the model predictions. Testing revealed strengths and weaknesses of Oscylator-4 and how it can be redesigned to reduce the LCOE. Calculations showed that LCOE strongly depends on flow velocity and the target of $0.15/kWh can be achieved with improvements to the Oscylator-4 and at higher flow speeds. Extensive footage of interaction of fish with Oscylator-4 has been recorded. 8. CONCLUSIONS An ALT (Alternating-Lift Technology) providing an alternative to SLT (Steady-Lift Technology) can be developed. That is, a MHK energy converter that does not use impoundments or turbines is feasible. The VIVACE concept and its application, Oscylator-4, enhance fluid-structure interactions and, by controlling the response, harness power. ALT is environmentally compatible because it uses alternating-lift like fish. ALT can achieve high power- to-volume density by synergy between cylinders – like fish in schools. This enables the Oscylator-4 to become a real three-dimensional converter that can be distributed in compact formations in fluid space. The Converter can operate in low flow speeds, which represent the vast majority of flows in rivers, tides, and ocean currents. 9. FUTURE RECOMMENDATIONS In the next design cycle, the following remaining challenges will be addressed: (A) Advanced nonlinear control of FIO to improve power harnessing without suppressing FIO. (B) Reduce friction in the transmission mechanism (bearings) of the PTO. (C) Redesign deployment/retrieval for cost reduction. All three have major impact on the LCOE. Benefits to the public: An environmentally compatible technology can be developed to harness MHK energy even from slow current/river/ocean flows.
- Research Organization:
- Vortex Hydro Energy, Ann Arbor, MI (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Water Power Technologies Office
- DOE Contract Number:
- EE0006780
- OSTI ID:
- 1479197
- Type / Phase:
- SBIR (Phase III)
- Report Number(s):
- DOE-VHE-0006780
- Country of Publication:
- United States
- Language:
- English
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