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Scaling of Point-Absorber Wave Energy Converter Hydrodynamics.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Scaling of Point-Absorber Wave Energy Converter Hydrodynamics./
作者:	Rusch, Curtis J.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	104 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-05, Section: B.
Contained By:	Dissertations Abstracts International83-05B.
標題:	Ocean engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28721897
ISBN:	9798480643732

Scaling of Point-Absorber Wave Energy Converter Hydrodynamics.
Rusch, Curtis J.

Scaling of Point-Absorber Wave Energy Converter Hydrodynamics. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 104 p.

Source: Dissertations Abstracts International, Volume: 83-05, Section: B.

Thesis (Ph.D.)--University of Washington, 2021.

This item must not be sold to any third party vendors.

Wave energy converters (WECs) are devices that generate mechanical or electrical power from the motion of ocean waves. Point absorber WECs react to the motion of the ocean waves at or near the surface, and have a characteristic surface expression of less than one tenth of a wavelength. Two-body, point absorber WECs rely on the reaction force produced by a submerged component, usually a heave plate, to capture power from ocean waves. This work is motivated by limited understanding of heave plate hydrodynamics, necessary to produce accurate WEC models.In oscillatory flow, drag and inertial forces experienced by flat plates and cylinders have been shown to vary with the Keulegan-Carpenter number. We demonstrate that this extends to an asymmetric hexagonal conic heave plate suitable for a point absorber WEC. The forces on three geometric scales of this plate were measured by forced oscillation experiments in quiescent water. From these measurements, phase-invariant and phase-dependent coefficients of drag and added mass are calculated using a Morison decomposition. For low amplitude oscillations, the total force experienced by the conic heave plate is well-described by phase-invariant coefficients that scale with the Keulegan-Carpenter number. However, for larger oscillations, maximum forces are better described by phase-dependent coefficients. Flow visualization is used to interpret the phase variations.We explore the role of heave plate topology on fluid reaction forces using three representative shapes: a hexagonal flat plate, a hexagonal conic with an open top, and the same with a closed top that encloses a fluid mass. We force each test article sinusoidally in a quiescent tank and decompose the reaction force using forms of the Morison equation for phase-invariant and phase-dependent parameterizations. We find that a flat plate generates 5.3 % more fluid reaction force than the open conic topology, and 21.4 % more than the enclosed conic. We also show that asymmetric topologies generate asymmetric reaction forces, but the magnitude of asymmetry is limited by nearly symmetric fluid inertia forces, which dominate over drag for these test articles. Additionally, we observe asymmetric vortex dynamics for the flat plate when the Keulegan-Carpenter number is between 1 and 2, accompanied by a shift in the phase of the peak force by about 7 % of the oscillation period. As a consequence of this shift, the hydrodynamic coefficients estimated from the phase-dependent Morison equation decomposition are asymmetric, suggesting that phase-dependent representations may not provide physical insight in some hydrodynamic regimes and that flat plates may have multiple reaction force profiles for a range of Keulegan-Carpenter numbers. Finally, we apply results from heave plate experiments to models of a two-body point absorber WEC. We approximate these hydrodynamics using three parameterizations: (1) as low-fidelity coefficients invariant across sea state, accurate only at the reference sea state, (2) mid-fidelity coefficients dependent on the oscillation amplitude, but invariant in phase, which accurately represent forces for small amplitude motions, and (3) high-fidelity coefficients dependent on both oscillation amplitude and phase, which represent hydrodynamic forces accurately for all oscillation amplitudes. As dynamical models of WECs often rely on a low-fidelity representation, it is important to understand how this practice impacts wave energy converter modelling and whether code bases should be extended to incorporate higher-fidelity representations of heave plate hydrodynamics. Here, we validate an analytical model for a two-body point absorber WEC against field data and a dynamical model. We then use the analytical model to evaluate the effect of these parameterizations on estimates of heave plate motion, tension between the float and heave plate, and electrical power output from the WEC. We find that predictions of electrical power output using mid-fidelity coefficients differ by up to 30 % from models using low-fidelity coefficients for regular waves ranging in height from 0.5 - 1.9 m. High-fidelity coefficients, however, yield less than a 5 % change when compared with mid-fidelity coefficients. This suggests that mid-fidelity coefficients can be important for accurate wave energy converter modeling, but the added complexity of high-fidelity coefficients yields little further benefit. We show similar, though less pronounced, trends in maximum tether tension, while heave plate motion has only a weak dependence on coefficient fidelity. Finally, we emphasize the importance of using experimentally derived added mass over that calculated from boundary element methods (another common practice for dynamical models), which can lead to substantial under-prediction of power output and peak tether tension.In total, this work experimentally characterizes the hydrodynamics of asymmetric heave plates across scale and topology, touches on the intricacies of vortex behavior in these experiments, and models two-body WECs using heave plate hydrodynamic parameterizations of varying fidelity to determine the impact on WEC behavior. This fills a gap in the literature in asymmetric heave plate hydrodynamics. This also provides the first characterization of the impact of enclosed fluid on the reaction force heave plates provide to point absorber WECs. Moreover, we provide guidance on the use of these hydrodynamic parameterizations to WEC modellers, assessing the changes seen in model behavior for low-, mid-, and high-fidelity hydrodynamic representations.

ISBN: 9798480643732Subjects--Topical Terms:

660731
Ocean engineering.
Subjects--Index Terms:

Added mass

Scaling of Point-Absorber Wave Energy Converter Hydrodynamics.
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300 $a 104 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-05, Section: B.
500 $a Advisor: Polagye, Brian L.
502 $a Thesis (Ph.D.)--University of Washington, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Wave energy converters (WECs) are devices that generate mechanical or electrical power from the motion of ocean waves. Point absorber WECs react to the motion of the ocean waves at or near the surface, and have a characteristic surface expression of less than one tenth of a wavelength. Two-body, point absorber WECs rely on the reaction force produced by a submerged component, usually a heave plate, to capture power from ocean waves. This work is motivated by limited understanding of heave plate hydrodynamics, necessary to produce accurate WEC models.In oscillatory flow, drag and inertial forces experienced by flat plates and cylinders have been shown to vary with the Keulegan-Carpenter number. We demonstrate that this extends to an asymmetric hexagonal conic heave plate suitable for a point absorber WEC. The forces on three geometric scales of this plate were measured by forced oscillation experiments in quiescent water. From these measurements, phase-invariant and phase-dependent coefficients of drag and added mass are calculated using a Morison decomposition. For low amplitude oscillations, the total force experienced by the conic heave plate is well-described by phase-invariant coefficients that scale with the Keulegan-Carpenter number. However, for larger oscillations, maximum forces are better described by phase-dependent coefficients. Flow visualization is used to interpret the phase variations.We explore the role of heave plate topology on fluid reaction forces using three representative shapes: a hexagonal flat plate, a hexagonal conic with an open top, and the same with a closed top that encloses a fluid mass. We force each test article sinusoidally in a quiescent tank and decompose the reaction force using forms of the Morison equation for phase-invariant and phase-dependent parameterizations. We find that a flat plate generates 5.3 % more fluid reaction force than the open conic topology, and 21.4 % more than the enclosed conic. We also show that asymmetric topologies generate asymmetric reaction forces, but the magnitude of asymmetry is limited by nearly symmetric fluid inertia forces, which dominate over drag for these test articles. Additionally, we observe asymmetric vortex dynamics for the flat plate when the Keulegan-Carpenter number is between 1 and 2, accompanied by a shift in the phase of the peak force by about 7 % of the oscillation period. As a consequence of this shift, the hydrodynamic coefficients estimated from the phase-dependent Morison equation decomposition are asymmetric, suggesting that phase-dependent representations may not provide physical insight in some hydrodynamic regimes and that flat plates may have multiple reaction force profiles for a range of Keulegan-Carpenter numbers. Finally, we apply results from heave plate experiments to models of a two-body point absorber WEC. We approximate these hydrodynamics using three parameterizations: (1) as low-fidelity coefficients invariant across sea state, accurate only at the reference sea state, (2) mid-fidelity coefficients dependent on the oscillation amplitude, but invariant in phase, which accurately represent forces for small amplitude motions, and (3) high-fidelity coefficients dependent on both oscillation amplitude and phase, which represent hydrodynamic forces accurately for all oscillation amplitudes. As dynamical models of WECs often rely on a low-fidelity representation, it is important to understand how this practice impacts wave energy converter modelling and whether code bases should be extended to incorporate higher-fidelity representations of heave plate hydrodynamics. Here, we validate an analytical model for a two-body point absorber WEC against field data and a dynamical model. We then use the analytical model to evaluate the effect of these parameterizations on estimates of heave plate motion, tension between the float and heave plate, and electrical power output from the WEC. We find that predictions of electrical power output using mid-fidelity coefficients differ by up to 30 % from models using low-fidelity coefficients for regular waves ranging in height from 0.5 - 1.9 m. High-fidelity coefficients, however, yield less than a 5 % change when compared with mid-fidelity coefficients. This suggests that mid-fidelity coefficients can be important for accurate wave energy converter modeling, but the added complexity of high-fidelity coefficients yields little further benefit. We show similar, though less pronounced, trends in maximum tether tension, while heave plate motion has only a weak dependence on coefficient fidelity. Finally, we emphasize the importance of using experimentally derived added mass over that calculated from boundary element methods (another common practice for dynamical models), which can lead to substantial under-prediction of power output and peak tether tension.In total, this work experimentally characterizes the hydrodynamics of asymmetric heave plates across scale and topology, touches on the intricacies of vortex behavior in these experiments, and models two-body WECs using heave plate hydrodynamic parameterizations of varying fidelity to determine the impact on WEC behavior. This fills a gap in the literature in asymmetric heave plate hydrodynamics. This also provides the first characterization of the impact of enclosed fluid on the reaction force heave plates provide to point absorber WECs. Moreover, we provide guidance on the use of these hydrodynamic parameterizations to WEC modellers, assessing the changes seen in model behavior for low-, mid-, and high-fidelity hydrodynamic representations.
590 $a School code: 0250.
650 4 $a Ocean engineering. $3 660731
650 4 $a Fluid mechanics. $3 528155
650 4 $a Mechanical engineering. $3 649730
653 $a Added mass
653 $a Drag
653 $a Heave plate
653 $a Keulegan-Carpenter number
653 $a Morison
653 $a Wave energy
653 $a Wave energy converters
690 $a 0547
690 $a 0204
690 $a 0548
710 2 $a University of Washington. $b Mechanical Engineering. $3 2092993
773 0 $t Dissertations Abstracts International $g 83-05B.
790 $a 0250
791 $a Ph.D.
792 $a 2021
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28721897