Browsing by Author "Touzon, Imanol"
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Item Mooring System Design Approach: A Case Study for MARMOK-A Floating OWC Wave Energy Converter(American Society of Mechanical Engineers (ASME), 2018) Touzon, Imanol; de Miguel, Borja; Nava, Vincenzo; Petuya, Victor; Mendikoa, Iñigo; Boscolo, Francesco; Tecnalia Research & Innovation; RENOVABLES OFFSHOREThis paper presents a methodology and a flowchart of steps to take for a, consistent and rapidly convergent design of catenary mooring systems. It is subsequently applied for a floating Oscillating Water Column WEC MARMOK-A developed by Oceantec Energías Marinas, in order to fulfill the technical requirements of such dynamic systems. The approach, based on the catenary equations, considers the water depth as a design scale factor for the mooring system, leading to an equivalent static mooring performance. In general, a mooring system configuration is described by the number and distribution of lines; thus, as a preprocess in the herein described procedure, a database is built for different line lengths. The main advantage of the procedure is that once that, after characterizing a mooring system configuration at a specific water depth with a specific line mass and axial stiffness, the database built can be used for any other water depth with any line mass and axial stiffness, accelerating the design optimization process. Mooring static properties are derived for a given material elastic modulus, lines’ mass and water depth. The mean offset and horizontal stiffness are afterwards derived with lines pretension and steady environmental forces (mean wave drift, current and wind) as well as maximum offset and characteristic line tensions. Finally, the process is applied for different lines pretensions to achieve an objective horizontal stiffness of the structure. The introduced procedure is presented through its application to the MARMOK-A device at a 90m depth site moored by means of a Karratu named mooring configuration. Results are presented in terms of total lines mass, device maximum expected excursion and required footprint for different horizontal stiffness and lines mass in order to give an insight of the impact on total plant cost indicators.Item Numerical Approaches for Loads and Motions Assessment of Floating WECs Moored by Means of Catenary Mooring Systems(Springer Science and Business Media B.V., 2022) Touzon, Imanol; Petuya, Victor; Nava, Vincenzo; Alonso-Reig, Maria; Mendikoa, Iñigo; Quaglia, Giuseppe; Gasparetto, Alessandro; Petuya, Victor; Carbone, Giuseppe; Tecnalia Research & Innovation; RENOVABLES OFFSHORETechnologies for harvesting offshore renewable energy based on floating platforms, such as offshore wind, wave and tidal energies, are currently being developed with the purpose of achieving a competitive cost of energy. The economic impact of the mooring system is significant within the total cost of such deployments, and large efforts are being carried out to optimize designs. Analysis of mooring systems at early stages generally require a trade-off between quick analysis methods and accuracy to carry out multi-variate sensitivity analyses. Even though the most accurate approaches are based on the non-linear finite element method in the time domain, these can result in being very time consuming. The most widely used numerical approaches for mooring line load estimates are introduced and discussed in this paper. It is verified that accurate line tension estimates require lines drag and inertia forces to be accounted for. A mooring and floating structure coupled model based on the lumped mass finite element approach is also discussed, and it is confirmed that the differences found in the coupled numerical model are mainly produced by the uncertainty on hydrodynamic force estimates on the floating structure rather than by the lumped mass method. In order to enable quick line tension estimates, a linearization of the structure and mooring coupled model is discussed. It shows accurate results in operational conditions and enables modal analysis of the coupled system.Item Numerical Simulation of Control Strategies at Mutriku Wave Power Plant(American Society of Mechanical Engineers (ASME), 2018) Faÿ, François-Xavier; Kelly, James; Henriques, João; Pujana, Ainhoa; Abusara, Mohammad; Mueller, Markus; Touzon, Imanol; Ruiz-Minguela, Pablo; Tecnalia Research & Innovation; RENOVABLES EFICIENCIA ENERGETICA Y CIRCULARIDAD; DIGITAL ENERGY; RENOVABLES OFFSHOREIn order to de-risk wave energy technologies and bring confidence to the sector, it is necessary to gain experience and collect data from sea trials. As part of the OPERA H2020 project, the Mutriku Wave Power Plant (MWPP) is being used as a real condition laboratory for the experiment of innovative technologies. The plant is situated in the North shore of Spain and has been operating since 2011. It uses the Oscillating Water Column (OWC) principle, which consists in compressing and expanding the air trapped in a chamber due to the inner free-surface oscillation resulting from the incident waves. The pressure difference between the air chamber and the atmosphere is used to drive an air turbine. In that case, a self-rectifying air turbine is the best candidate for the energy conversion, as it produces a unidirectional torque in presence of a bi-directional flow. The power take-off system installed is composed of a biradial turbine connected to a 30kW off-the-shelf squirrel cage generator. One of the novelties of the turbine is a high-speed stop-valve installed close to the rotor. The valve may be used to control the flow rate through the turbine or for latching control. This paper focuses on the development, the implementation and the numerical simulation of five control strategies including turbine speed and generator torque controllers. The algorithms were designed thanks to a numerical model describing one of the OWC chambers of the Mutriku power plant. Numerical results are presented for a variety of sea states and a comparison between the proposed control laws in terms of energy production and power quality is performed.Item A numerical study on the hydrodynamic impact of device slenderness and array size in wave energy farms in realistic wave climates(2017) Penalba, Markel; Touzon, Imanol; Lopez-Mendia, Joseba; Nava, Vincenzo; Tecnalia Research & Innovation; RENOVABLES OFFSHOREThe future of wave energy converters lies in the design and realization of farms comprising of several devices, given the level of actual power flow for the individual devices and because of several operational issues. Therefore, not only the hydrodynamics of individual and isolated devices should be analysed, but interactions among devices within an array must also be carefully evaluated. In this paper, the authors attempt to parameterize the behaviour of small-, medium- and large-arrays of wave energy converters, in a particular staggered configuration, at four different locations characterized by realistic wave climates. The arrays studied in the present paper consist of heaving cylinders of different slenderness ratios. It turns out that for arrays of very short inter-device distances, regardless of the cylinder and array size, interactions are strong and lead to not negligible effects of destructive interference (total power reduction compared to the sum of isolated devices). Under these conditions, the bigger the array, the stronger the interactions and the higher the loss of power. However, a range of inter-device distances, referred to as intermediate region, where the power absorption is consistent and the interaction effect appears to be positive, has been found. This intermediate region is easily detectable for small arrays, but loses its ideal characteristics with the increase of the size of the array.Item Ocean Energy Systems Wave Energy Modelling Task: Modelling, Verification and Validation of Wave Energy Converters: Modelling, verification and validation ofwave energy converters(2019) Wendt, Fabian; Nielsen, Kim; Yu, Yi-Hsiang; Bingham, Harry; Eskilsson, Claes; Kramer, Morten; Babarit, Aurelien; Bunnik, Tim; Costello, Ronan; Crowley, Sarah; Gendron, Bengamin; Giorgi, Giuseppe; Girardin, Samuel; Greaves, Devorah; Heras, Pilar; Hoffman, Johan; Islam, Hafizul; Jakobsen, Ken-Robert; Janson, Carl-Erik; Jansson, Johan; Kim, Hyun Yul; Kurniawan, Adi; Leoni, Massimiliano; Mathai, Thomas; Nam, Bo-Woo; Park, Sewan; Rajagopalan, Krishnakumar; Ransley, Edward; Read, Robert; Ringwood, John V.; Rodrigues, Jose Miguel; Rosenthal, Benjamin; Roy, Andre; Ruehl, Kelley; Schofield, Paul; Sheng, Wanan; Shiri, Abolfazl; Thomas, Sarah; Touzon, Imanol; Yasutaka, Imai; Giorgi, Simone; Kim, Jeong-Seok; Kim, Kyong-Hwan; Gendron, Benjamin; Greaves, Deborah; Schofield, Paul; Tecnalia Research & InnovationThe International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.Item OES Task 10 WEC heaving sphere performance modelling verification(CRC Press, 2018-09-12) Nielsen, K.; Wendt, F.; Yu, Y.-H.; Ruehl, K.; Touzon, Imanol; et al.OES Task 10 Modelling, Verification and Validation of Wave Energy Converters (WECs) is a task under the IEA Technology Collaboration Program for Ocean Energy Systems (OES). The long-term goals are to assess the accuracy of, and establish confidence in, the use of numerical WEC models, to determine a range of validity of existing computational modelling tools, to identify uncertainty related to simulation meth-odologies and finally to define future research. To some extent, this project builds on the experience from a similar effort carried out to verify modelling of wind turbines as part of the IEA Wind Task 30 on wind OC3-OC5.Item A Simplified Modeling Approach of Floating Offshore Wind Turbines for Dynamic Simulations(2022-03-18) López-Queija, Javier; Robles, Eider; Llorente, Jose Ignacio; Touzon, Imanol; López-Mendia, Joseba; Tecnalia Research & Innovation; RENOVABLES OFFSHORECurrently, floating offshore wind is experiencing rapid development towards a commercial scale. However, the research to design new control strategies requires numerical models of low computational cost accounting for the most relevant dynamics. In this paper, a reduced linear time-domain model is presented and validated. The model represents the main floating offshore wind turbine dynamics with four planar degrees of freedom: surge, heave, pitch, first tower foreaft deflection, and rotor speed to account for rotor dynamics. The model relies on multibody and modal theories to develop the equation of motion. Aerodynamic loads are calculated using the wind turbine power performance curves obtained in a preprocessing step. Hydrodynamic loads are precomputed using a panel code solver and the mooring forces are obtained using a look-up table for different system displacements. Without any adjustment, the model accurately predicts the system motions for coupled stochastic wind–wave conditions when it is compared against OpenFAST, with errors below 10% for all the considered load cases. The largest errors occur due to the transient effects during the simulation runtime. The model aims to be used in the early design stages as a dynamic simulation tool in time and frequency domains to validate preliminary designs. Moreover, it could also be used as a control design model due to its simplicity and low modeling order.