235 research outputs found

    Simulation of a Pendulum-Type Wave Energy Converter for Oceanic Drifters

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    Drifters (floating devices) are Lagrangian instrumentation widely used in oceanography and climate research. They are designed to obtain marine data by passively following the water currents, providing information about the ocean surface such as currents or water temperature. One of the main challenges faced at drifter’s design is their autonomy. Therefore, some studies tried to deal with this issue by embedding a Wave Energy Converter (WEC) on the drifter: waves excite the drifter, and its motion is used to generate power through an inner mechanism, so no battery exchange is needed. In this work, a 4 Degree of Freedom (DoF) analytical model has been developed to explain the coupled motion of a floating spherical buoy with an inner single pendulum under realistic sea conditions. Lagrange equations have been used to obtain the motion model while Morrison formulation has been selected to describe the interaction between the buoy and the fluid. The model has been tested considering both a regular and an irregular sea state. Airy’s theory has been chosen to describe the motion of linear waves. The model has been implemented in Matlab to run the simulations and to obtain the drifter’s motion. The validation of the results has been carried out by comparing the model’s output with the one obtained by OrcaFlex (Orcina), the world’s leading package for dynamic analysis of offshore marine systems. In both simulations, considering the sea state regular and irregular, results show a high match between the analytical model and OrcaFlex. Once the analytical model has been validated, we have studied the possibility to increase the pendulum’s rotation which is directly related to the power generation. A pendulum whose articulation has an oscillatory movement is prone to undergo parametric instability. In our case, that oscillatory motion corresponds to the buoy’s vertical motion. We have optimized the pendulum design to operate in resonance with the sea excitation, and increase the rotation and therefore, the energy generated by the device. As a first optimization step of the drifter design, several simulations have been performed covering a large range of pendulum length. Parametric resonance occurs at a pendulum’s length of 155 cm. The pendulum is not directly connected to the drifter’s generator, there is a gear system between them. In this work, the motion of the gear system has been studied separately. An extension of the present work would be the design of a more complex pendulum in order to achieve its parametric resonance at a realistic length, as the common drifter’s diameter is around 10 cm and does not fit that pendulum length.Objectius de Desenvolupament Sostenible::14 - Vida Submarin

    Estimating a mean transport velocity in the marginal ice zone using ice-ocean prediction systems

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    Understanding the transport of objects and material in the marginal ice zone (MIZ) is critical for human operations in polar regions. This can be the transport of pollutants, such as spilled oil, or the transport of objects, such as drifting ships and search and rescue operations. For emergency response, the use of environmental prediction systems are required which predict ice and ocean parameters and are run operationally by many centres in the world. As these prediction systems predict both ice and ocean velocities, as well as ice concentration, it must be chosen how to combine these data to best predict the mean transport velocities. In this paper we present a case study of four drifting buoys in the MIZ deployed at four distinct ice concentrations. We compare short-term trajectories, i.e. up to 48 h lead times, with standard transport models using ice and ocean velocities from two operational prediction systems. A new transport model for the MIZ is developed with two key features aimed to help mitigate uncertainties in ice–ocean prediction systems: first, including both ice and ocean velocities and linearly weighting them by ice concentration, and second, allowing for a non-zero leeway to be added to the ice velocity component. This new transport model is found to reduce the error by a factor of 2 to 3 for drifters furthest in the MIZ using ice-based transport models in trajectory location after 48 h.publishedVersio

    The physical oceanography of the transport of floating marine debris

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    Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales

    Search and rescue at sea aided by hidden flow structures

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    Every year hundreds of people die at sea because of vessel and airplane accidents. A key challenge in reducing the number of these fatalities is to make Search and Rescue (SAR) algorithms more efficient. Here we address this challenge by uncovering hidden TRansient Attracting Profiles (TRAPs) in ocean-surface velocity data. Computable from a single velocity-field snapshot, TRAPs act as short-term attractors for all floating objects. In three different ocean field experiments, we show that TRAPs computed from measured as well as modelled velocities attract deployed drifters and manikins emulating people fallen in the water. TRAPs, which remain hidden to prior flow diagnostics, thus provide critical information for hazard responses, such as SAR and oil spill containment, and hence have the potential to save lives and limit environmental disasters

    Near-Surface Oceanic Kinetic Energy Distributions From Drifter Observations and Numerical Models

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    The geographical variability, frequency content, and vertical structure of near-surface oceanic kinetic energy (KE) are important for air-sea interaction, marine ecosystems, operational oceanography, pollutant tracking, and interpreting remotely sensed velocity measurements. Here, KE in high-resolution global simulations (HYbrid Coordinate Ocean Model; HYCOM, and Massachusetts Institute of Technology general circulation model; MITgcm), at the sea surface (0 m) and at 15 m, are compared with KE from undrogued and drogued surface drifters, respectively. Global maps and zonal averages are computed for low-frequency

    Building a Maxey--Riley framework for surface ocean inertial particle dynamics

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    A framework for the study of surface ocean inertial particle motion is built from the Maxey--Riley set. A new set is obtained by vertically averaging each term of the original set, adapted to account for Earth's rotation effects, across the extent of a sufficiently small spherical particle that floats at an assumed unperturbed air--sea interface with unsteady nonuniform winds and ocean currents above and below, respectively. The inertial particle velocity is shown to exponentially decay in time to a velocity that lies close to an average of seawater and air velocities, weighted by a function of the seawater-to-particle density ratio. Such a weighted average velocity turns out to fortuitously be of the type commonly discussed in the search-and-rescue literature, which alone cannot explain the observed role of anticyclonic mesoscale eddies as traps for marine debris or the formation of great garbage patches in the subtropical gyres, phenomena dominated by finite-size effects. A heuristic extension of the theory is proposed to describe the motion of nonspherical particles by means of a simple shape factor correction, and recommendations are made for incorporating wave-induced Stokes drift, and allowing for inhomogeneities of the carrying fluid density. The new Maxey--Riley set outperforms an ocean adaptation that ignored wind drag effects and the first reported adaption that attempted to incorporate them.Comment: To appear in Phys. Fluid

    Contributions to the design of energy harvesting systems for autonomous sensors in low power marine applications

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    Tesi en modalitat de compendi de publicacionsOceanographic sensor platforms provide biological and meteorological data to help understand changes in marine environment and help to preserve it. Lagrangian drifters are autonomous passive floating platforms used in climate research to obtain surface marine data. They are low-cost, versatile, easy-to-deploy and can cover large extensions of the ocean when deployed in group. These deployments can last for years, so one of the main design challenges is the autonomy of the drifter. Several energy harvesting (EH) sources are being explored to reduce costs in battery replacement maintenance efforts such as solar panels. Drifters must avoid the impact of the wind because this may compromise proper surface current tracking and therefore, should ideally be mostly submerged. This interferes with the feasibility of solar harvesting, so other EH sources are being explored such as the oscillatory movement of the drifter caused by ocean waves. Wave energy converters (WEC) are the devices that turn this movement into energy. The motion of the drifter can principally be described by 3 oscillatory degrees of freedom (DoF); surge, heave and pitch. The heave motion includes the buoyancy’s response of the drifter, which can be explained by a mass-spring-damping model. By including the wave’s hydrodynamic load in this model, it is converted into a nonlinear system whose frequency response includes the wave’s frequency and the natural frequencies from the linear system. A smart option to maximize the captured energy is to design the inner WEC with a natural frequency similar to that of the drifter's movement. In this thesis, a 4 DoF model is obtained. This model includes the heave, the surge and the pitch motion of the drifter in addition to the inner pendulum motion relative to the buoy. Simultaneously, different pendulum-type WECs for small-size oceanic drifters are proposed. One of these converters consists of an articulated double-pendulum arm with a proof mass that generates energy through its relative motion with the buoy. Different experimental tests are carried out, with a prototype below 10 cm in diameter and 300 g of total mass, proving the capability of harvesting hundreds of microwatts in standard sea conditions EH sources require an additional power management unit (PMU) to convert their variable output into a constant and clean source to be able to feed the sensor electronics. PMUs should also ensure that the maximum available energy is harvested with a maximum power point tracking (MPPT) algorithm. Some sources, such as WECs, require fast MPPT as its output can show relatively rapid variations. However, increasing the sampling rate may reduce the harvested energy. In this thesis, this trade-off is analyzed using the resistor-based fractional open circuit voltage-MPPT technique, which is appropriate for low-power EH sources. Several experiments carried out in marine environments demonstrate the need for increasing the sampling rate. For this purpose, the use of a commercial PMU IC with additional low-power circuitry is proposed. Three novel circuits with a sampling period of 60 ms are manufactured and experimentally evaluated with a small-scale and low-power WEC. Results show that these configurations improve the harvested energy by 26% in comparison to slow sampling rate configurations. Finally, an EH-powered oceanographic monitoring system with a custom wave measuring algorithm is designed. By using the energy collected by a small-size WEC, this system is capable of transmitting up to 22 messages per day containing data on its location and measured wave parameters.Les plataformes d’observaciĂł oceanogrĂ fiques integren sensors que proporcionen dades fĂ­siques i biogeoquĂ­miques de l’oceĂ  que ajuden a entendre canvis en l’entorn marĂ­. Un exemple d’aquestes plataformes sĂłn les boies de deriva (drifters), que sĂłn dispositius autĂČnoms i passius utilitzats en l’àmbit de la recerca climĂ tica per obtenir dades in-situ de la superfĂ­cie marina. Aquests instruments sĂłn de baix cost, versĂ tils, fĂ cils de desplegar i poden cobrir grans superfĂ­cies quan s’utilitzen en grup. L’autonomia Ă©s un dels principals desafiaments en el disseny de drifters. Per tal d’evitar els costos en la substituciĂł de bateries, s’estudien diferents fonts de captaciĂł d’energia com per exemple la solar. Els drifters utilitzats per l’estudi dels corrents marins superficials han d’evitar l’impacte directe del vent ja que afecta al correcte seguiment de les corrents i, per tant, cal que estiguin majoritĂ riament submergides. AixĂČ compromet la viabilitat de l’energia solar, fet que requereix l’estudi d’altres fonts de captaciĂł com el propi moviment de la boia causat per les onades. Els convertidors d’energia de les onades (WEC, wave energy converters) compleixen aquesta funciĂł. El moviment dels drifters pot explicar-se bĂ sicament a travĂ©s de 3 graus de llibertat oscil·latoris: la translaciĂł vertical i la horitzontal i el balanceig. La translaciĂł vertical inclou la flotabilitat del dispositiu, que es pot descriure mitjançant el model massamolla- amortidor. Incloure la cĂ rrega hidrodinĂ mica de l’onada en aquest model el converteix en un sistema no lineal amb una resposta freqĂŒencial que inclou la de l’onada i les naturals del sistema lineal. Una opciĂł per maximitzar l’energia captada Ă©s dissenyar el WEC amb una freqĂŒĂšncia natural similar a la del moviment de la boia. En aquesta tesis es proposa un model de 4 graus de llibertat per a l’estudi del moviment del drifter. Aquest inclou els 3 graus de llibertat de la boia i el moviment del pĂšndul relatiu a ella. En paral·lel, es proposen diferents WEC del tipus pendular per drifters de reduĂŻdes dimensions. Un d’aquests WEC consisteix en un doble braç articulat amb massa flotant que genera energia a travĂ©s del seu moviment relatiu al drifter. S’han dut a terme diferents proves experimentals amb un prototip inferior a 10 cm de diĂ metre i 300 g de massa, les quals demostren la seva capacitat de captar centenars de microwatts en condicions marines estĂ ndard. Utilitzar fonts de captaciĂł d’energia requereix incloure una unitat gestora de potĂšncia (PMU, power management unit) per tal de convertir la seva sortida variable en una font constant i neta que alimenti l’electrĂČnica dels sensors. Les PMU tambĂ© tenen la funciĂł d’assegurar que es recull la mĂ xima energia mitjançant un algoritme de seguiment del punt de mĂ xima potĂšncia. Els WEC requereixen un seguiment d’aquest punt rĂ pid perquĂš la seva sortida consta de variacions relativament rĂ pides. Tanmateix, augmentar la freqĂŒĂšncia de mostreig pot reduir l’energia captada. En aquesta tesi, s'analitza a fons aquesta relaciĂł utilitzant la tĂšcnica de seguiment de la tensiĂł en circuit obert fraccionada basada en resistĂšncies, que Ă©s molt adequada per a fonts de baixa potĂšncia. Diversos experiments realitzats en el medi marĂ­ mostren la necessitat d'augmentar la freqĂŒĂšncia de mostreig, aixĂ­ que es proposa l'Ășs de PMU comercials amb una electrĂČnica addicional de baix consum. S’han fabricat tres circuits diferents amb un perĂ­ode de mostreig de 60 ms i s’han avaluat experimentalment en un WEC de reduĂŻdes dimensions. Els resultats mostren que aquestes configuracions milloren l'energia recollida en un 26% en comparaciĂł a PMU amb mostreig mĂ©s lent. Finalment, s’ha dissenyat un sistema autĂČnom de monitoritzaciĂł marina que inclou un algoritme de mesura d'ones propi. Aquest sistema Ă©s capaç de transmetre fins a 22 missatges al diaPostprint (published version

    Oil Spill Modeling in Sea Ice Covered Ocean

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    The ongoing reduction in extent and thickness of sea ice in the Arctic allows the expansion of shipping activity and oil exploration in the high north, and with that a potential increased risk of oil spill in ice covered areas. This thesis asses the response of two oil-in-ice surface drift models implemented in an open-source Lagrangian framework and forced by four dif- ferent ice-ocean products (RIOPS, TOPAZ4 real-time forecast system, TOPAZ4 reanalysis and SVIM). Both approaches were evaluated over three sets of simulations: (I) a field experiment conducted in the Barents Sea marginal ice zone in 2009; (II) observed trajectories of buoys in the ice pack and in the Barents Sea marginal ice zone; and (III) stochastic simulations (960 runs, from 1998 to 2017) to reproduce a hypothetical oil spill in the Kara Sea. Results from experiments (I) and (II) indicate that the two drift models provide similar response both in the ice pack and the marginal ice zone under the same forcing. It was also found that finer horizontal resolution ice-ocean products (RIOPS and SVIM) did not reproduce better the ob- served drifts. The experiment (III) revealed that the sea ice concentration (%) field dictates the spread, the predominant direction of trajectories and the distance (km) traveled by the cloud of particles (SVIM: -1.41 km/% and TOPAZ4 reanalysis: -1.24 km/%).Master's Thesis in Meteorology and OceanographyGEOF399MAMN-GEO
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