PTO-Sim: Development of a power take off modeling tool for ocean wave energy conversion

So, Ratanak; Casey, Sean M.; Kanner, Sam; Simmons, Asher; Brekken, Ted K. A.

doi:10.1109/pesgm.2015.7285735

Cited by 11 publications

(13 citation statements)

References 6 publications

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“…This fluid flow is translated in rotational energy by the variable displacement motor. The motor's axle is connected to a generator's axle, which generates electricity [20]. The provided model calculates the hydraulic PTO force, f PTO,h with:…”

Section: Hydraulic Pto Systemmentioning

confidence: 99%

“…with Q motor originating from the hydraulic motor -see Equation (20). The total fluid volume inside the accumulator at time t j equals V in (t j ) and is calculated with:…”

Section: Hydraulic Pto Systemmentioning

confidence: 99%

“…A particular concern with many existing PTO modelling efforts is that the most common PTO system type developed for commercial WEC prototypes, a hydraulic PTO system, is inherently non-linear [17,18]. A few recent studies, notably [16][17][18][19][20][21][22] have implemented realistic hydraulic PTO models with non-linear dynamics. However, these studies were limited in their scope to single WECs and not WEC farms, furthermore, many of the models quite complicated in their implementation.…”

Section: Introductionmentioning

confidence: 99%

“…Previously, a similar approach was presented in [25][26][27] for the case of a wave-structure interaction solver coupled to a wave propagation model using a basic linear PTO model. WEC-Sim has been used in modelling hydraulic PTOs in several recent studies [20,22]. In the present paper, only the near-field zone is simulated with a future goal of coupling to a wave propagation model to model the impact of a WEC farm (consisting of one or multiple WEC arrays) in the 'far-field'.…”

Section: Introductionmentioning

confidence: 99%

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Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model

et al. 2018

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The Power Take-Off (PTO) system is the key component of a Wave Energy Converter (WEC) that distinguishes it from a simple floating body because the uptake of the energy by the PTO system modifies the wave field surrounding the WEC. Consequently, the choice of a proper PTO model of a WEC is a key factor in the accuracy of a numerical model that serves to validate the economic impact of a wave energy project. Simultaneously, the given numerical model needs to simulate many WEC units operating in close proximity in a WEC farm, as such conglomerations are seen by the wave energy industry as the path to economic viability. A balance must therefore be struck between an accurate PTO model and the numerical cost of running it for various WEC farm configurations to test the viability of any given WEC farm project. Because hydrodynamic interaction between the WECs in a farm modifies the incoming wave field, both the power output of a WEC farm and the surface elevations in the ‘near field’ area will be affected. For certain types of WECs, namely heaving cylindrical WECs, the PTO system strongly modifies the motion of the WECs. Consequently, the choice of a PTO system affects both the power production and the surface elevations in the ‘near field’ of a WEC farm. In this paper, we investigate the effect of a PTO system for a small wave farm that we term ‘WEC array’ of 5 WECs of two types: a heaving cylindrical WEC and an Oscillating Surge Wave Energy Converter (OSWEC). These WECs are positioned in a staggered array configuration designed to extract the maximum power from the incident waves. The PTO system is modelled in WEC-Sim, a purpose-built WEC dynamics simulator. The PTO system is coupled to the open-source wave structure interaction solver NEMOH to calculate the average wave field η in the ‘near-field’. Using a WEC-specific novel PTO system model, the effect of a hydraulic PTO system on the WEC array power production and the near-field is compared to that of a linear PTO system. Results are given for a series of regular wave conditions for a single WEC and subsequently extended to a 5-WEC array. We demonstrate the quantitative and qualitative differences in the power and the ‘near-field’ effects between a 5-heaving cylindrical WEC array and a 5-OSWEC array. Furthermore, we show that modeling a hydraulic PTO system as a linear PTO system in the case of a heaving cylindrical WEC leads to considerable inaccuracies in the calculation of average absorbed power, but not in the near-field surface elevations. Yet, in the case of an OSWEC, a hydraulic PTO system cannot be reduced to a linear PTO coefficient without introducing substantial inaccuracies into both the array power output and the near-field effects. We discuss the implications of our results compared to previous research on WEC arrays which used simplified linear coefficients as a proxy for PTO systems.

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Section: Hydraulic Pto Systemmentioning

confidence: 99%

“…with Q motor originating from the hydraulic motor -see Equation (20). The total fluid volume inside the accumulator at time t j equals V in (t j ) and is calculated with:…”

Section: Hydraulic Pto Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model

et al. 2018

View full text Add to dashboard Cite

show abstract

“…A particular concern with many existing PTO modelling approaches is that the most common PTO system type developed for commercial WEC prototypes, a hydraulic PTO system, is inherently nonlinear [30][31][32]. A few recent studies, notably [29,30,[32][33][34][35][36], have achieved realistic hydraulic PTO models with nonlinear dynamics. However, these investigations were limited in their scope to single WECs and not WEC arrays.…”

Section: Introductionmentioning

confidence: 99%

Analysing the Near-Field Effects and the Power Production of Near-Shore WEC Array Using a New Wave-to-Wire Model

Balitsky

Quartier

Stratigaki

et al. 2019

Water

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In this study, a series of modules is integrated into a wave-to-wire (W2W) model that links a Boundary Element Method (BEM) solver to a Wave Energy Converter (WEC) motion solver which are in turn coupled to a wave propagation model. The hydrodynamics of the WECs are resolved in the wave structure interaction solver NEMOH, the Power Take-off (PTO) is simulated in the WEC simulation tool WEC-Sim, and the resulting perturbed wave field is coupled to the mild-slope propagation model MILDwave. The W2W model is run for verified for a realistic wave energy project consisting of a WEC farm composed of 10 5-WEC arrays of Oscillating Surging Wave Energy Converters (OSWECs). The investigated WEC farm is modelled for a real wave climate and a sloping bathymetry based on a proposed OSWEC array project off the coast of Bretagne, France. Each WEC array is arranged in a power-maximizing 2-row configuration that also minimizes the inter-array separation distance d x and d y and the arrays are located in a staggered energy maximizing configuration that also decreases the along-shore WEC farm extent. The WEC farm power output and the near and far-field effects are simulated for irregular waves with various significant wave heights wave peak periods and mean wave incidence directions β based on the modelled site wave climatology. The PTO system of each WEC in each farm is modelled as a closed-circuit hydraulic PTO system optimized for each set of incident wave conditions, mimicking the proposed site technology, namely the WaveRoller® OSWEC developed by AW Energy Ltd. The investigation in this study provides a proof of concept of the proposed W2W model in investigating potential commercial WEC projects.

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Numerical Modelling

Vyzikas

Greaves

2018

Wave and Tidal Energy

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PTO-Sim: Development of a power take off modeling tool for ocean wave energy conversion

Cited by 11 publications

References 6 publications

Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model

Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model

Analysing the Near-Field Effects and the Power Production of Near-Shore WEC Array Using a New Wave-to-Wire Model

Numerical Modelling

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