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This study examines how motion influences turbulent velocity fluctuations utilizing measurements obtained from a wind lidar profiler. Onshore tests were performed using a WindCube v2.1 lidar, which was mobile and mounted on a hexapod to simulate buoy motion. Additionally, a fixed WindCube v2.1 lidar was used as a reference during these tests. To assess the motion-induced effects on velocity fluctuations measured by floating lidar systems, the root-mean-square error (RMSE) of velocity fluctuations obtained from the fixed and mobile lidars was calculated. A comprehensive wind dataset spanning 22.5 h was analyzed, with a focus on regular motions involving single-axis rotations and combinations of rotations around multiple axes. The investigation of single-axis rotations revealed that the primary influencing factor on the results was the alignment between the tilt direction of the mobile lidar and the wind direction. The highest RMSE values occurred when the tilt of the mobile lidar leans in the wind direction, resulting in pitch motion, whereas the lowest RMSE values were observed when the tilt of the mobile lidar leans perpendicular to the wind direction, resulting in roll motion. Moreover, the addition of motion around extra axes of rotation was found to increase RMSE.

The resourcecode Marine Data Toolbox is a python package developed within the Resource- CODE project, to facilitate the access to a recently developed Metocean hindcast database (Accensi et al., 2021), and to a set of state-of-the-art methods for data analysis. This toolbox provides developers with a set of standard functions for resource assessment and operations planning. The advanced statistical modelling tools provided together with the embedded high resolution wave hindcast database provide the developers with a set of standard functions for resource assessment, extreme values modelling and operations and maintenance planning. Suitable for users not familiar with netCDF files handling or statistical analysis development, it is however designed to fulfil expert metocean analysis requirements. The advanced statistical modelling tools provided allow the developers of Offshore Renewable Energy (ORE) devices to conduct the necessary assessments to reduce uncertainty in expected environmental conditions, and de-risk investment in future technology design.

This study investigates the impact of motion on the line-of-sight (LOS) turbulent velocity fluctuations derived from lidar profiler measurements. Onshore tests were conducted using a WindCube v2.1 lidar, referred to as the mobile lidar, mounted on a hexapod to simulate buoy motion, with a fixed lidar used as a reference. To assess the motion-induced effects on turbulent velocity fluctuations measured by floating lidar systems, the root-mean-square error (RMSE) of LOS velocity fluctuations obtained from the fixed and mobile lidars was calculated. A comprehensive wind dataset spanning 45 hours was analyzed, with a focus on regular motions involving single-axis rotations and combinations of rotations around multiple axes. The investigation of single-axis rotations revealed that the primary influencing factor on the results was the alignment between wind direction and the axis of rotation. The highest RMSE values occurred when winds propagated perpendicular to the rotation axis, resulting in pitch motion, whereas the lowest RMSE values were observed when wind propagated along the rotation axis, leading to roll motion. Furthermore, yaw motion was found to increase the RMSE compared to scenarios without yaw motion. Moreover, the addition of motion around extra axes of rotation was found to increase RMSE. High wind speed emerged as a significant driver of RMSE, with higher velocities leading to higher RMSE values. The study also indicated that the role of wind shear in influencing RMSE of LOS velocity fluctuations requires further investigation. Additionally, the study explored the impact of motion period, revealing that motion frequencies affect the LOS velocity spectra within the expected inertial sub-range. However, the impact on RMSE was found to be limited in comparison to the amplitude, wind direction, and wind speed.

The RESOURCECODE wave database was developed at Ifremer by the Laboratory of Ocean Physics and Satellite remote sensing (LOPS by its acronym in French). The generated hindcast was also primarily validated at Ifremer by LOPS and the Marine Structures Laboratory (LCSM by its acronym in French), and further analyzed at the Laboratory of Hydrodynamics, Energy and Atmospheric Environment at Ecole Centrale Nantes. This high-resolution regional hindcast includes the evolution in time (hourly) and space of the directional spectrum and several integrated wave parameters, which allow to have a detailed description of the sea states. The modelled area extends from 12°W to 13.5°E longitude, and from 36°N to 63°N latitude, hence, the European and UK's North Atlantic coast, Irish sea, the Northern Sea, and La Manche are included within the domain. On its first version (March 2021), this data-set covers 27 years from 1994 to 2020. The primary aim of the RESOURCECODE project is the creation of a marine data toolbox to enable developers of ocean energy devices and arrays, and their suppliers, to make optimized technical and commercial decisions, but the open nature of the wave database created allows its use in diverse research and/or engineering applications.

NewWave-type focused wave groups are commonly used to simulate the design wave for a given sea state. These extreme wave events are challenging to reproduce numerically by the various Numerical Wave Tanks (NWTs), due to the high steepness of the wave group and the occurring wave-wave interactions. For such complex problems, the validation of NWTs against experimental results is vital for confirming the applicability of the models. Intercomparisons among different solvers are also important for selecting the most appropriate model in terms of balancing between accuracy and computational cost. The present study compares three open-source NWTs in OpenFOAM, SWASH and HOS-NWT, with experimental results for limiting breaking focused wave groups. The comparison is performed by analysing the propagation of steep wave groups and their extracted harmonics after employing an accurate focusing methodology. The scope is to investigate the capabilities of the solvers for simulating extreme NewWave-type groups, which can be used as the “design wave” for ocean and coastal engineering applications. The results demonstrate the very good performance of the numerical models and provide valuable insights to the design of the NWTs, while highlighting potential limitations in the reproduction of specific harmonics of the wave group.

Resource mapping is a key element in the planning and consequent deployment of Offshore Renewable Energy (ORE) converters. A proper characterization of the environmental forcing enables the optimization of energy extraction and a more accurate assessment of the structural loading. This contributes to improving reliability and extending the operational life of devices at a given extraction site. Providing an accurate characterisation of the environmental loading is subjected to the availability and quality of relevant datasets, which are either obtained from measurements, in-situ or via remote sensing, or from numerical models. Then, the adequate use of these datasets relies on the analysis’ tools and selected methods which allow an appropriate description of the underlying physics. This paper presents the high-resolution wave hindcast database extending across European waters and developed to be the reference dataset of the ResourceCODE Marine Data Toolbox, designed to provide a full suite of tools to support ocean energy analytics.

A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulence measurements over a 36-h period at a highly energetic tidal energy site in Alderney Race. This system enables the evaluation of the six components of the Reynolds stress tensor throughout a large proportion of the water column. The present study provides mean vertical profiles of the velocity, the turbulence intensity and the integral lengthscale along the streamwise, spanwise and vertical direction of the tidal current. Based on our results and considering a tidal-stream energy convertor (TEC) aligned with the current main direction, the main elements of turbulence prone to affect the structure (material fatigue) and to alter power generation would likely be: (i) the streamwise turbulence intensity (Ix), (ii) the shear stress, (iii) the normal stress, and (iv) the vertical integral lengthscale (Lz). The streamwise turbulence intensity, (Ix), was found to be higher than that estimated at other tidal energy sites across the world for similar height above bottom. Along the vertical direction, the length (Lz) of the large-scale turbulence eddies was found to be equivalent to the rotor diameter of the TEC Sabella D10. It is considered that the turbulence metrics presented in this paper will be valuable for TECs designers, helping them optimize their designs as well as improve loading prediction through the lifetime of the machines. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

Tidal turbine will be installed in area with high current and high turbulence level. A characterisation of this last is required. The aim of the project THYMOTE is to characterize and understand the generation of eddies from smaller to several tens of meters. Three technics are used: Numerical modelling, Physical modelling, field measurements. Physical and numerical modelling show clearly the appearance of the eddies close to the bottom in presence of dunes or rocks and their motion towards the free surface.

La base de données de rejeu d'états de mer HOMERE a été mise en place par les équipes de l'Ifremer du laboratoire de Comportement des Structures en Mer (RDT/LCSM) et du Laboratoire d'Océanographie Physique et Spatiale (LOPS). Cette base de données consiste en un ensemble de paramètres permettant de décrire les caractéristiques principales et l'évolution des conditions d'états de mer sur la zone de la Manche et du Golfe de Gascogne. Initialement développée pour répondre aux besoins liés aux études sur la caractérisation de la ressource et du comportement des structures en mer, en particulier dans le domaine des énergies marines renouvelables, son champ d’application est en fait, de par l’ensemble des paramètres et l’information spectrale disponibles, mais aussi de par la haute résolution de la grille de calcul, bien plus étendu. Des applications liées à l’étude du transport sédimentaire ou des échanges océan-atmosphère tout comme à la gestion des opérations et campagnes à la mer, par exemple, peuvent ainsi être envisagées. La première version de cette base de données couvrant la période 1994 - 2012 a été créée en 2012 et mise à disposition à partir de Janvier 2013. En 2017 une mise à jour du jeu de données a été créée pour prendre en compte : - La correction des données de forçage pour deux années (1996 et 2001) - L’extension du jeu de données au-delà de 2012 et jusqu’à 2016 inclus - La réécriture des paramètres de sortie dans un format NetCDF plus performant en lecture - La mise à jour des noms de paramètres selon la nomenclature en vigueur - Le portage de la base de données sur le nouveau serveur DATARMOR opérationnel depuis Mars 2017. L'objectif de cette note est de présenter la base de données HOMERE dans sa nouvelle version HOMERE 2017 en précisant en particulier les modifications apportées. Cette note s’appuie en partie sur la notice publique (Janvier 2014 - RDT/LCSM/C&R14LCSM301/EB/CM), manuel de l’utilisateur de la première version du jeu de données.

When considering deployment of wave energy converters at a given site, it is of prime importance from both a technical and an economical point of view to accurately assess the total yearly energy that can be extracted by the given device. Especially, to be considered is the assessment of the efficiency of the device over the widest span of the sea-states spectral bandwidth. Hence, the aim of this study is to assess the biases and errors introduced on extracted power classically computed using spectral data derived from analytical functions such as a JONSWAP spectrum, compared to the power derived using actual wave spectra obtained from a spectral hindcast database.

This work presents the analysis of wave and turbulence measurements collected at a tidal energy site. A new method is introduced to produce more consistent and rigorous estimations of the velocity fluctuations power spectral densities. An analytical function is further proposed to fit the observed spectra and could be input to the numerical models predicting power production and structural loading on tidal turbines. Another new approach is developed to correct for the effect of the Doppler noise on the high frequencies power spectral densities. The analysis of velocity time series combining wave and turbulent contributions demonstrates that the turbulent motions are coherent throughout the water column, rendering the wave coherence-based methods not applicable to our dataset. To avoid this problem, an alternative approach relying on the pressure data collected by the ADCP is introduced and shows appreciable improvement in the wave-turbulence separation.

This report is a deliverable of MERiFIC Work Package 3.6: ‘Operation and Maintenance requirements’ and has been produced as a cross border collaboration between IFREMER and the University of Exeter. The report provides an overview of guidelines and recommendations for the management of O&M operations necessary for an optimal exploitation of Marine energy plants, with a focus on the specific areas of South West Cornwall, UK and Iroise sea, Brittany, France. An overview of the onshore infrastructures and ports possibly suitable for management of such O&M operations is also provided. Management of scheduled and unscheduled maintenance operations are discussed in their various aspects including site accessibility. It should be noted that this topic, including weather window assessment for operations is discussed in more detail in the additional MERIFIC report D3.6.2: Best Practice for installation procedures.

This report is a deliverable of MERiFIC Task 3. 6: ‘Installation Procedures’ and has been produced in a cross border collaboration between IFREMER and the University of Exeter. In this report different elements are presented for the planning and organisation of installation operations for the deployment of Marine energy plants. The optimization of installation procedures are discussed and brought in a context to potential costs optimization and the availability of suitable vessels is considered. Installation procedures, which were also investigated, should include pre-installation surveys so as to optimize the design of moorings and secure laying of the power cable, a specific feature of the commissioning of such Marine energy plants. Attention should also be given to the Health and Safety procedures. Finally, the influence of the weather conditions on the success of these installation operations was discussed and studied. Especially, "Access time" and "Waiting time" weather windows were assessed for different sites in both areas of south west Cornwall and the Iroise Sea, pointing out the importance of the seasonal variability of the wave climate for the planning of installation operations.

This report provides an overview of resource assessment techniques for marine energy developments and the requirements at different stages of project development. It then details the studies that have been completed in Cornwall and the Isles of Scilly (Section 3) and Finistère and PNMI (Section 4). These studies combine shorter-term in situ measurements, using a range of measurement technologies, and numerical modelling to provide long-term and geographically diverse records.

This paper presents an analysis of sea states carried out from extended wave measurements realized near the Wave Hub wave energy test facility in Cornwall (UK). The space directional information is derived from the spectro-directional processing of time-domain data provided by an array of four independent SEAWATCH Mini II displacement buoys separated by an approximate average distance of 500 m. It is observed that, even though the size of the array is small compared to the local wave trains' length, the estimation of the directional spectra - using maximum entropy and likelihood methods - may sometimes exhibit certain space variability over the array. It was also observed that the tidal currents variations produced a significant influence upon the wave directional estimation and wave spectral parameters. Spectro-directional partitioning and wave system tracking were subsequently applied and this emphasized the influence of tide variations upon the individual swells and wind-seas as measured by the buoys. This paper, therefore, also illustrates the relevance of applying partitioning and tracking procedures for the identification of wave systems in oceanographic and wave energy studies. (C) 2012 Elsevier Ltd. All rights reserved.