Detecting parametric resonance in a floating oscillating water column device for wave energy conversion: Numerical simulations and validation with physical model tests

conditions contributes to estimating turbine performance, power stability, and power delivered to the grid. Water tunnel tests using a 19.8 cm diameter horizontal axis model turbine in yaw operation show the performance reduction using three designs: no shroud, a convergent-divergent shroud, and a diffuser shroud. Experimental results obtained at three Reynolds numbers of 1.38 × 10 5 , 1.77 × 10 5 , and 2.17 × 10 5 show that the output power decreases in off-axis flows for all designs investigated. The reduction is initially negligible up to a 10° yaw angle, but then increases with increasing the yaw angle.


Upcoming Workshop
The Dutch Marine Energy Centre (DMEC) and European Space Agency (ESA) will be hosting a virtual workshop, "Marine Energy meets Space", on 8 September 2020 at 11:00am CEST (9:00am UTC). The workshop is the first opportunity for marine energy and space companies to explore cross-sectoral cooperation opportunities within an upcoming tender. DMEC and ESA will also be hosting a webinar on 15 September 2020 at 11:00am CEST (9:00am UTC) to inform participants on how to apply to the tender. Both events are online and free to register here.

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The Economist Events' World Ocean Tech and Innovation Summit, hosted by Canada's Ocean Supercluster in collaboration with the Province of Nova Scotia and the Halifax Partnership, will take place in Halifax, Canada from 14-15 October 2020. Register your interest here.

New Documents on Tethys Engineering
Performance characteristics of shrouded horizontal axis hydrokinetic turbines in yawed conditions -Shahsavarifard and Bibeau 2020 During operations, river and tidal hydrokinetic turbines encounter changes in flow direction that decrease their performance. Evaluating hydrokinetic turbines in yaw conditions contributes to estimating turbine performance, power stability, and power delivered to the grid. Water tunnel tests using a 19.8 cm diameter horizontal axis model turbine in yaw operation show the performance reduction using three designs: no shroud, a convergent-divergent shroud, and a diffuser shroud. Experimental results obtained at three Reynolds numbers of 1.38 × 10 5 , 1.77 × 10 5 , and 2.17 × 10 5 show that the output power decreases in off-axis flows for all designs investigated. The reduction is initially negligible up to a 10° yaw angle, but then increases with increasing the yaw angle.

Detecting parametric resonance in a floating oscillating water column device for wave energy conversion: Numerical simulations and validation with physical model tests -Giorgi et al. 2020
The wave energy sector has faced enormous technological improvements over the last five decades, however, due to the complexity of the hydrodynamic processes, current numerical models still have limitations in predicting relevant phenomena. In particular, floating spar-type wave energy converters are prone to large undesirable roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. This paper presents the validation of results from a numerical model, capable of detecting parametric resonance, using experimental data. Experiments were carried out for a scaled model of the Spar-buoy OWC (Oscillating Water Column) device at a large ocean basin.

A New Seafloor Hydrothermal Power Generation Device Based on Waterproof Thermoelectric Modules -Xie et al. 2020
Submarine hydrothermal fluids contain substantial energy, and temperature differences with the surrounding cold seawater can provide energy for seabed observations and submarine operations. This study proposes a novel hydrothermal power generation device comprising a thermoelectric converter and an energy management system. Herein, a waterproof module with high-temperature and high-pressure resistance was designed. Heating and pressurization tests were performed to verify the structure's feasibility. The overall structure of the system based on the module was then designed, and laboratory performance tests were conducted.

Design and comparative survey of high torque coaxial permanent magnet coupling for tidal current generator -Park et al. 2020
This paper presents design and comparative study of high torque coaxial permanent magnet couplings (CPMC) for the use in a tidal current generation (TCG) system. Two different models such as a radial flux-CPMC (RF-CPMC) with magnet retaining rings and a flux concentrating-CPMC (FC-CPMC) with inner and outer rotor yoke changed by retaining rings are analyzed to find the best model under certain design constraint conditions to achieve a minimum pull-out torque of 1.0 kNm. Moreover, the effect of the electromechanical characteristics such as the radial force, stress and deformation are analyzed for both models.

Experimental Investigation of the Mooring System of a Wave Energy Converter in Operating and Extreme Wave Conditions -Sirigu et al. 2020
A proper design of the mooring systems for Wave Energy Converters (WECs) requires an accurate investigation of both operating and extreme wave conditions. A careful analysis of these systems is required to design a mooring configuration that ensures station keeping, reliability, maintainability, and low costs, without affecting the WEC dynamics. In this context, an experimental campaign on a 1:20 scaled prototype of the ISWEC (Inertial Sea Wave Energy Converter), focusing on the influence of the mooring layout on loads in extreme wave conditions, is presented and discussed. Two mooring configurations composed of multiple slack catenaries with sub-surface buoys, with or without clump-weights, have been designed and investigated experimentally.

Hydrodynamic slip enhanced nanofluidic reverse electrodialysis for salinity gradient energy harvesting -Long et al. 2020
Nanofluidic reverse electrodialysis offers an alternative way to harvest the widelyexisting salinity gradient energy. In this study, we investigate the impacts of surface hydrodynamic slip modification on the ionic current rectification and salinity gradient energy conversion via a conical nanopore by thermodynamic analysis and numerical simulation. Results reveal that in the configuration where hydrodynamic slip modification is employed on the surface near the tip side, a small modification fraction contributes to the ionic current rectification due to significantly enhanced ion enrichment, while a larger hydrodynamic slip modification fraction goes against the ionic current rectification for deteriorated ion enhancement and induced counter-electric field concentration gradient near the base side.

News & Press Releases EMEC Achieves World's First Ocean Energy RETL Designation -European Marine Energy Centre (EMEC)
EMEC has been designated with Renewable Energy Testing Laboratory (RETL) status, the highest international designation for marine energy test laboratories. EMEC is the first RETL for ocean energy in the world. RETL designation is awarded by the International Electrotechnical Commission (IEC) -Renewable Energy System which operates a global certification system addressing three renewable energy sectors: solar photovoltaic, wind energy, and marine energy. RETL designation enables EMEC to perform tests to assess the power performance of tidal energy converters anywhere in the world in compliance with IEC Technical Committee 114 Technical Specifications.