Modeling the geometry of the overtopping ramp and the Archimedes screw turbine of a wave-energy converter

• Compare various geometries to select the optimal configurations with respect to overtopping for a waveenergy converter. • Predict performance under real-world conditions for the ramp. • Compare the effect of porosity on the lift forces acting on the ramp. • Visualize the velocity fields and compare the results with those from another software. • Defining a wave energy spectrum as a boundary condition should be done carefully to avoid incorrect simulations. It is suggested to remove short-wave components from the energy spectrum, as these shorter wavelengths cannot be properly resolved by the code. Modeling the geometry of the overtopping ramp and the Archimedes screw turbine of a wave-energy converter. Saeed OSOULI1,2, Matteo POSTACCHINI1, Ivan SABBIONI2, Maurizio BROCCHINI1 1Department of Ingegneria Civile, Edile e Architettura, Università Politecnica delle Marche, Ancona, Italy 2 Mentucci Aldo Costruzioni, Senigallia, Italy Fig.1 – A numerical simulation estimating wave forces on a plate in a porous structure (left) and the geometries used to simulate the turbine and ramp in FLOW-3D Numerical Setups (Figs.2 and 3) •2D-Wave flume:72𝑚 × 1𝑚 × 10𝑚 • Different frontal slopes. • Wave characteristics based on energy spectrum 𝐻𝑠, 𝑇, ℎ = 1 𝑚, 7𝑠, 6𝑚 • 3 energy spectrums with different angular frequencies. •The setup follows Zitti et al. (2020) but differs in the top boundary condition. • The flow velocity was set to 0.2 m/s in a free-surface water channel. • Prescribed motions were imposed on the turbine. Archimedes TurbineArchimedes Turbine Wave energy converter Wave energy converter Turbulence Models and Size of Cells Two Turbulence Transport Models: RNG k-epsilon for the WEC k-omega for the Turbine 0.05 m in x and z direction for WEC 2 mesh blocks for the Turbine, uniformly 0.01 and 0.005 m. Methodology Inspiration and motivations Results Effect of input Spectrum and Ramp slope Short-wave components in the energy spectrum result in a large overtopping volume (Figs. 4a and 4b). Based on estimates from the EurOtop manual and Iuppa et al. (2019), this setup should yield less than 2 m³, the closest observed value is 2.95 m³ for Model 1. This energy model includes only waves with frequencies up to 0.3 Hz. A 26° slope produces the highest overtopping volume (Fig. 4c). Fig.2 – Mesh blocks for Turbine (top) and WEC’s BCs (bottom) References Eurotop, J.W. van der Meer, N.W.H. Allsop, T. Bruce, A. Kortenhaus, , T. Pullen, H. Schüttrumpf, (Eds.), 2018 Assessment Manual www.overtopping-manual.com. Iuppa, C., Cavallaro, L., Musumeci, R. E., Vicinanza, D., & Foti, E. (2019). Empirical overtopping volume statistics at an OBREC. Coastal Engineering, 152, 103524. https://doi.org/10.1016/j.coastaleng.2019.103524 Zitti, G., Fattore, F., Brunori, A., Brunori, B., & Brocchini, M. (2020). Efficiency evaluation of a ductless Archimedes turbine: Laboratory experiments and numerical simulations. Renewable Energy, 146, 867–879. Fig.3 –Energy Spectrums All have the same Wave characteristics: the spectral peaks and the area under the spectrum are nearly identical, but they cover different wave periods. Conclusions Fig.4 – a) water volume. b) free surface at 30m from the toe. c) different slopes with Model 1 as input. Wave force on different conditions Fig.6 illustrates the effect of porosity. While shear and lift forces are negligible in the solid configuration (Right), introducing a volumetric porosity of 0.5 leads to a sharp increase in both lift and shear forces (Left). Fig.5 –Turbine torque comparison: Zitti et al. (top) vs. current study (bottom). Turbine performance In Fig. 5, a comparison between FLOW-3D and ANSYS Fluent is presented. In both software packages, increasing the rotation speed decreases the torque; however, FLOW-3D exhibits larger oscillations. This behaviour may be due to differences in numerical approach, cell type/size, and the boundary conditions applied at the free surface. Probes Wave maker Pressure Wall (a) (b) (c) Fig.6 –Wave force on a ramp in a porous structure (Left) and solid (Right). 0.005 m cells 0.01 m cells Convey systems with Turbines