Quartier, Nicolas

Stratigaki, Vicky

Troch, Peter

Ghent University Academic Bibliography

Nicolas Quartier (Nicolas.Quartier@UGent.be)Ghent University, Ghent, BelgiumFuture work• Add a drag coefficient in WEC-Sim to consider theeffect of viscous drag.• Compare the modified wave field with both PTO-systems in DualSPHysics with the results fromlinear calculationsComparison WEC-Sim vs. DualSPHysicsHeaving WEC• Flat shape increases radiation effect• Based on commercialWECs: Carnegie, SINN PowerModelled WECs and PTO-systems DualSPHysics• DualSPHysics applies theSmoothed Particle Hydrodynamicsmethod (SPH), a Lagrangianmeshless method.• DualSPHysics discretizes the fluidin particles: physical quantities arecomputed as an interpolation ofthe values of neighbouringparticles.• Allows calculations of WECs inextreme sea states.Using the numerical model, WEC-Sim• Model PTO-system• Time domain• Calculate absorbed powerUsing the numerical model, DualSPHysics• Coupled with Chrono Engine: allows modelling effect of PTO-system• Time domainEffect of the PTO-system on the non-linear effectsFig. 1: Sketch of the modelled heaving WEC.Fig. 2: Heaving WEC in extreme wave conditions.Vicky Stratigaki (Vicky.Stratigaki@UGent.be)Peter Troch (Peter.Troch@UGent.be)How can a heaving wave energy converter (WEC) be modelled accurately in operational and extreme sea states?  This research is being supported by the Research Foundation Flanders (FWO), Belgium -330 FWO.OPR.2.0 - FWO research project No. 3G029114 Comparative study of the hydrodynamics of a heaving wave energy converter using linear and non-linear wave theoryINORE European Symposium 25 - 31 August 2019 Nocera Umbra, Italy-0.05-0.04-0.03-0.02-0.010.000.010.020.030.040.050.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00Position [m]Time [s]SPH WECSim• WEC-Sim overestimates heave motion of WEC atresonance due to non-linear effects.• Vorticity in close proximity of the WEC is visible inDualSPHysics. This vorticity increases with increasingrelative velocities and causes energy losses.• DualSPHysics applies correct wave-shape accordingto Stokes 2nd order theory.• Optimal PTO-damping for linear or Coulomb PTO-system seems to be larger in DualSPHysics than inWEC-Sim.• DualSPHysics can be used to estimate the dragcoefficient of the WEC. Viscous drag can be includedin WEC-Sim, resulting in more realistic results.PTO-system• Linear PTO-system• Coulomb damping, as a simplified model of a hydraulic PTO-system• Adding a PTO-system causes a phase shift of theWEC’s heave motion relative to the wave elevation.This increases the relative velocities between WECand water particles, resulting in higher vorticity.• Difference between linear damping and Coulombdamping still to be further investigated.Fig. 3: Dimensions of numerical wave tank in DualSPHysics for T = 1.2 s, H = 0.15 m.Fig. 4: Heave displacement of the WEC with linear PTO-system, T = 1.2 s, H = 0.15 m.Fig. 5: Vorticity  in the proximity of the WEC [1/s].

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Comparative study of the hydrodynamics of a heaving wave energy converter using linear and non-linear wave theory

COMPARATIVE STUDY OF THE HYDRODYNAMICS OF A HEAVING WAVE ENERGY CONVERTER USING LINEAR AND NON-LINEAR WAVE THEORYDEPARTMENT OF CIVIL ENGINEERINGNicolas Quartier, Peter Troch, Vasiliki StratigakiContact: Nicolas.Quartier@ugent.beawww.ugent.beProblem statementHow can a heaving wave energy converter (WEC) accurately be modelled in operational and extreme sea states?Scientific backgroundUsing the numerical model, NEMOH• Frequency domain• Applies linear potential flow theory – small wave and body amplitudes assumed• Allows fast calculationsUsing the numerical model, WEC-Sim• Availability to accurately model PTO system• Time domain• Enables calculation of average absorbed power and hydrodynamic forcesUsing the numerical model, DualSPHysics• DualSPHysics applies the Smoothed Particle Hydrodynamics method (SPH), a Lagrangian meshless method.• DualSPHysics discretizes the fluid in particles –physical quantities are computed as an interpolation of the values of neighbour-particles [1].• Allows calculations of WECs in extreme sea states.PTO system modelling• DualSPHysics – Chrono-Engine coupling allows accurate modelling of realPTO systems [2]. Chrono-Engine is an open-source multi-physics simulationplatform, suited for the numerical modelling of mechanical systems such asjoints, springs, hinges... [3].Numerical research• DualSPHysics has successfully been coupled to Chrono-Engine for the numericalmodelling of a linear PTO system [2].• Previous research shows that linear models lead to overestimations of theabsorbed wave power up to 150 % [4].Research objectives• Develop an accurate numerical model of a heaving WEC with DualSPHysics,coupled to Chrono-Engine used for the PTO system modelling.• Compare the hydrodynamic forces and absorbed power calculated using WEC-Sim with the results obtained with DualSPHysics and evaluate in whichconditions non-linearities become significant.• Calculate the wave field modified due to the presence of the heaving WEC(near-field effects).MethodologyDevelopmentAcknowledgementsThis research is being supported by the Research Foundation Flanders (FWO), Belgium -330 FWO.OPR.2.0 - FWO research project No. 1SC5419N References[1] A. J. C. Crespo, J. M. Domínguez, B. D. Rogers, M. GómezGesteira, S. Longshaw, R. Canelas, R. Vacondio, A. Barreiro, O. García-Feal, “DualSPHysics: open-source parallel CFD solver on Smoothed Particle Hydrodynamics (SPH)”, Computer Physics Communications, vol. 187, pp. 204-216, 2015. [2] R.B.C. Canelas, A.J.C. Crespo, M. Brito, J.M. Domínguez, O. García-Feal, “Extending DualSPHysics with a Differential Variational Inequality: modeling fluid-mechanism interaction”, Applied Ocean Research, vol.76, pp. 88-97, 2018. [3] H. Mazhar et al., “CHRONO: a parallel multi-physics library for rigid-body, flexible-body, and fluid dynamics,” Mechanical Sciences, vol. 4, no. 1, pp. 49-64, 2013[4] C. Windt, “A high-fidelity wave-to-wire simulation platform for wave energy converters: Coupled numerical wave tank and power take-off models”, Applied Energy vol.226, pp.655-669, 2018[5] Verbrugghe, T., 2018. “Coupling Methodologies for Numerical Modelling of Floating Wave Energy Converters”, PhD Thesis, Ghent university. Ghent, Belgium[6] Crespo, A.J.C et al., 2018. “Floating moored oscillating water column with meshless SPH method”. OMAE 2018, Madrid, Spain[7] P. Balitsky, “Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model”, Energies 2018, 11, 3489Linear modelsFig. 1: WEC in operational conditions.Smoothed Particle HydrodynamicsFig. 2: WEC in operational conditions.Fig. 3: DualSPHysics coupled to Chrono-Engine. (Brito et al., 2016)• A WEC-Sim model for the heavingWEC with a linear and a hydraulic PTOsystem has been developed – see Fig.4. Besides the forces and the absorbedpower, the modified wave field wascalculated (Fig. 5) and a comparisonbetween the linear and hydraulic PTOsystem was made.• It was concluded that for a heavingWEC the type of PTO system has asignificant influence on the averageabsorbed power, but less on themodified wave field [7].Future work• Develop numerical wave basin in DualSPHysics ableto generate the required wave conditions.The heaving WEC will be coupled to Chrono-Engine,enabling the PTO system modelling.• After modelling a heaving WEC with a linear PTOsystem, a model of a more accurate PTO system, suchas a hydraulic PTO, will be modelled with the Chrono-Engine.Fig. 5: Amplitude of total wave field surrounding a single heaving WEC .Fig. 6: Coupling between DualSPHysics and OceanWave3D.• The modified wave field surrounding the WEC will be determined using theestablished DualSPHysics – OceanWave3D coupling , Fig. 6 [5]. OceanWave3D is anon-linear potential flow wave propagation model.• In the future , the influence of the mooring lines will be investigated as well, using therecently developed coupling between DualSPHysics and MoorDyn [6].Fig. 4: Schematic representation of the hydraulic PTO system for a heaving cylindrical WEC [7].Validation• A first numerical validation will be done in smallwaves by checking the results of DualSPHysicswith those of WEC-Sim.• Experiments with heaving WEC arrays will beconducted in 2020 in the Coastal and Ocean Basin(COB) in Ostend, Belgium. This ‘WECfarm’ projectwill allow validation of the developed numericalmodels.

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Comparative study of the hydrodynamics of a heaving wave energy converter using linear and non-linear wave theory

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Ghent University Academic Bibliography

Ghent University Academic Bibliography