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Dispersion characteristics in the Western Mediterranean are analyzed using data from Coastal Ocean Dynamics Experiment (CODE) and Surface Velocity Program (SVP) surface drifters deployed in the period 1986–2017. Results are presented in terms of absolute dispersion A2
(mean-squared displacement of drifter individuals) and of relative dispersion (D2; mean square separation distance of drifter pairs). Moreover, the dispersion characteristics are estimated for different initial separation distances (D0) between particles: smaller, larger,
or comparable with the internal Rossby radius of deformation. Results show the presence of a quasiballistic regime for absolute dispersion at small time scales and the nonlocal relative dispersion regime related to the submesoscale activities for scales smaller than the internal Rossby radius.
At intermediate times, two anomalous absolute dispersion regimes (elliptic and hyperbolic regimes) related with the flow topology are observed, although the relative dispersion involves the Richardson and shear/ballistic regimes only for D0 smaller than the Rossby radius. During
the subsequent 20–30 days, absolute dispersion shows quasirandom walk regime and relative dispersion follows the diffusive regime for scales larger than 100 km for which pair velocities are uncorrelated.

This work presents the main results of the first Lagrangian Particle Tracking challenge, conducted within the framework of the European Union's Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge, jointly organised by the research groups of DLR, ONERA and TU Delft, considered a synthetic experiment reproducing the wall-bounded flow in the wake of a cylinder which was simulated by LES. The participants received the calibration images and sets of particle images acquired by four virtual cameras, and were asked to produce as output the particles positions, velocities and accelerations (when possible) at a specific time instant. Four different image acquisition strategies were addressed, namely two-pulse (TP), four-pulse (FP) and time-resolved (TR) acquisitions, each with varying tracer particle concentrations (or number of particles per pixel, ppp). The participants' outputs were analysed in terms of percentages of correctly reconstructed particles, missed particles, ghost particles, correct tracks and wrong tracks, as well as in terms of position, velocity and acceleration errors, along with their distributions. The analysis of the results showed that the best-performing algorithms allow for a correct reconstruction of more than 99% of the tracer particles with positional errors below 0.1 pixels even at ppp values exceeding 0.15, whereas other algorithms are more prone to the presence of ghost particles already for ppp < 0.1. While the velocity errors remained contained within a small percentage of the bulk velocity, acceleration errors as large as 50% of the actual acceleration magnitude were retrieved.

We investigate tracer transport on random discrete fracture networks that are characterized by the statistics of the fracture geometry and hydraulic conductivity. While it is well known that tracer transport through fractured media can be anomalous and particle injection modes can have major impact on dispersion, the incorporation of injection modes into effective transport modeling has remained an open issue. The fundamental reason behind this challenge is that-even if the Eulerian fluid velocity is steady-the Lagrangian velocity distribution experienced by tracer particles evolves with time from its initial distribution, which is dictated by the injection mode, to a stationary velocity distribution. We quantify this evolution by a Markov model for particle velocities that are equidistantly sampled along trajectories. This stochastic approach allows for the systematic incorporation of the initial velocity distribution and quantifies the interplay between velocity distribution and spatial and temporal correlation. The proposed spatial Markov model is characterized by the initial velocity distribution, which is determined by the particle injection mode, the stationary Lagrangian velocity distribution, which is derived from the Eulerian velocity distribution, and the spatial velocity correlation length, which is related to the characteristic fracture length. This effective model leads to a time-domain random walk for the evolution of particle positions and velocities, whose joint distribution follows a Boltzmann equation. Finally, we demonstrate that the proposed model can successfully predict anomalous transport through discrete fracture networks with different levels of heterogeneity and arbitrary tracer injection modes. © 2017 Elsevier Ltd. ; PKK and SL acknowledge a grant (16AWMP- B066761-04) from the AWMP Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government and the support from Future Research Program (2E27030) funded by the Korea Institute of Science and Technology (KIST). PKK and RJ acknowledge a MISTI Global Seed Funds award. MD acknowledges the support of the European Research Council (ERC) through the project MHetScale (617511). TLB acknowledges the support of European Research Council (ERC) through the project Re- activeFronts (648377). RJ acknowledges the support of the US Department of Energy through a DOE Early Career Award (grant DE-SC0009286). The data to reproduce the work can be obtained from the corresponding author. ; No

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 1 page, 1 figure ; Maps of velocity vectors and streamlines, calculated after integration from some reference contour, can be very useful to illustrate the gross characteristics of the changing velocities. Nevertheless, they are only snapshots of the velocity field that cannot be used to directly infer exchange between different oceanic regions. In order to do so, we must use of a Lagrangian approach, where we actually track water parcels as they move under the influence of the spatially and temporally changing velocity fields. Here we present a simple model that integrates monthly velocity fields in time, either forward or backward, in order to track the origin or fate of water parcels. In our case, the velocity fields are inferred from the positions of Argo floats. We illustrate the model by examining the recirculation of intermediate waters in the southern South Atlantic Ocean. The model allows us tracking whether and how the water parcels at these intermediate depths recirculate zonally or drift meridionally. In this application, we carefully explore the important role of the Brazil-Malvinas Confluence and the Agulhas Leakage. We estimate that most of the intermediate waters recirculate across the ocean in time periods between about 15 and 30 years, eventually meeting at the Brazil-Malvinas Confluence region. Our results show no water transfer from the Indian Ocean, i.e. they show no Agulhas Leakage, although this may be an artefact caused by the absence of rings in the mean fields. A remarkable feature is the presence of a meridionally pulsating behaviour in the transoceanic trajectories, best visible in an accompanying video ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through project VA-DE-RETRO (CTM2014-56987-P) ; Peer Reviewed

We study the sea surface transport in the Western Mediterranean Sea from a Lagrangian point of view, in particular the Alboran and the North-Western subbasins. The study is carried out through the analysis of 3 years of surface velocity model data through Finite Size Lyapunov Exponents, Residence Time, and virtual particle trajectories complementing the classical Eulerian approach. The spatiotemporal variability of the main transport processes is inferred from the Empirical Orthogonal Function modes of the Lyapunov Exponents, being the most relevant modes discussed and physically interpreted. Results indicate that some of the variability in the surface transport patterns in the Western Mediterranean can be explained by specific modes which provide an indication of connectivity among subbasins, like the inflow of Atlantic waters through the Ibiza Channel (JGR) ; J.M.S. is supported by the PhD CSIC-JAE program cofunded by the European Social Fund (ESF). G.S. is supported by the Spanish government through the "Ramón y Cajal" program. Authors would like to thank financial support from MED Projects TOSCA (G-MED09-425) and MEDESS-4MS funded by FEDER Funds. The authors also thank financial support from MICINN through Project 289 445 CGL2011-22964. Authors strongly thank the Government of the Balearic Islands and FEDER through the "Grups Competitius" program. C.L. acknowledges Spanish MINECO and FEDER through project ESCOLA (CTM2012-39025-C02-01). ; Peer reviewed

16 pages, 6 figures.-- ArXiv pre-print available at: http://arxiv.org/abs/physics/0608105 ; With the tools of lobe dynamics, the authors analyze the structures present in the velocity field obtained from a numerical simulation of the surface circulation in the northwestern Mediterranean Sea. In particular, focus is placed on the North Balearic Front, the westernmost part of the transition zone between saltier and fresher waters in the western Mediterranean, which is here interpreted in terms of the presence of a semipermanent "Lagrangian barrier," across which little transport occurs. Identified are relevant hyperbolic trajectories and their manifolds, and it is shown that the transport mechanism known as the turnstile, previously identified in abstract dynamical systems and simplified model flows, is also at work in this complex and realistic ocean flow. In addition, nonlinear dynamics techniques are shown to be powerful enough to identify the key geometric structures in this part of the Mediterranean. The construction also reveals the spatiotemporal routes along which this transport happens. Topological changes in that picture, which are associated with the crossing by eddies and may be interpreted as the breakdown of the front, are also observed during the simulation. ; A.M.M. acknowledges the MCyT (Spanish Government) for a Ramón y Cajal Research Fellowship and financial support from MEC (Spanish Government) reference MTM2004-00797 and the Royal Society-CSIC cooperation agreement reference B2003GB03. E.H.-G. acknowledges financial support from MEC and FEDER through Project CONOCE2 (FIS2004-00953). We also acknowledge M. Emelianov for communicating us results from a recent cruise before publication. D.S. and S. W. acknowledge financial support from ONR Grant No. N00014-01-1-0769. ; Peer reviewed

International audience This article shows how to consistently and accurately manage the Lagrangian formulation of chemical reaction equations coupled with the superficial velocity formalism introduced in the late 80s by Quintard and Whitaker. Lagrangian methods prove very helpful in problems in which transport effects are strong or dominant, but they need to be periodically put back in a regular lattice, a process called remeshing. In the context of digital rock physics, we need to ensure positive concentrations and regularity to accurately handle stagnation point neighborhoods. These two conditions lead to the use of kernels resulting in extra-diffusion, which can be prohibitively high when the diffusion coefficient is small. This is the case especially for reactive porous media, and the phenomenon is reinforced in porous rock matrices due to Archie's law. This article shows how to overcome this difficulty in the context of a two-scale porosity model applied in the Darcy-Brinkman-Stokes equations, and how to obtain simultaneous sign preservation, regularity and accurate diffusion, and apply it to dissolution processes at the pore scale of actual rocks.

High-frequency radar, HFR, is a cost-effective monitoring technique that allows us to obtain high-resolution continuous surface currents, providing new insights for understanding small-scale transport processes in the coastal ocean. In the last years, the use of Lagrangian metrics to study mixing and transport properties has been growing in importance. A common condition among all the Lagrangian techniques is that complete spatial and temporal velocity data are required to compute trajectories of virtual particles in the flow. However, hardware or software failures in the HFR system can compromise the availability of data, resulting in incomplete spatial coverage fields or periods without data. In this regard, several methods have been widely used to fill spatiotemporal gaps in HFR measurements. Despite the growing relevance of these systems there are still many open questions concerning the reliability of gap-filling methods for the Lagrangian assessment of coastal ocean dynamics. In this paper, we first develop a new methodology to reconstruct HFR velocity fields based on self-organizing maps (SOMs). Then, a comparative analysis of this method with other available gap-filling techniques is performed, i.e., open-boundary modal analysis (OMA) and data interpolating empirical orthogonal functions (DINEOFs). The performance of each approach is quantified in the Lagrangian frame through the computation of finite-size Lyapunov exponents, Lagrangian coherent structures and residence times. We determine the limit of applicability of each method regarding four experiments based on the typical temporal and spatial gap distributions observed in HFR systems unveiled by a K-means clustering analysis. Our results show that even when a large number of data are missing, the Lagrangian diagnoses still give an accurate description of oceanic transport properties. ; This study has been supported by the JERICO-NEXT project funded by the European Union's Horizon 2020 research and innovation program under grant agreement no. 654410. Ismael Hernández-Carrasco acknowledges the Juan de la Cierva contract funded by the Spanish government. The work of Anna Rubio was partially supported by the LIFE-LEMA project (LIFE15 ENV/ES/000252), the Directorate of Emergency Attention and Meteorology of the Basque Government and the Department of Environment, Regional Planning, Agriculture and Fisheries of the Basque Government (Marco Program).

Lagrangian particle tracking and Large-Eddy simulation were used to assess the effect of different fuels on spray characteristics. In such a two-way coupled modeling scenario, spray momentum accelerates the gaseous phase into an intense, multiphase jet near the nozzle. To assess fuel property effects on liquid spray formation, the non-reacting Engine Combustion Network Spray A baseline condition was chosen as the reference case. The validated Spray A case was modified by replacing n-dodecane with diesel, methanol, dimethyl ether, or propane assuming 150 MPa injection pressure. The model features and performance for various fuels in the under-resolved near-nozzle region are discussed. The main findings of the paper are as follows. (1) We show that, in addition to the well-known liquid penetration (Formula presented.), and vapor penetration (Formula presented.), for all the investigated fuels, the modeled multiphase jets exhibit also a third length scale (Formula presented.), with discussed correspondence to a potential core part common to single phase jets. (2) As a characteristic feature of the present model, (Formula presented.) is noted to correlate linearly with (Formula presented.) and (Formula presented.) for all the fuels. (3) A separate sensitivity test on density variation indicated that the liquid density had a relatively minor role on (Formula presented.). (4) Significant dependency between fuel oxygen content and the equivalence ratio (Formula presented.) distribution was observed. (5) Repeated simulations indicated injection-to-injection variations below 2% for (Formula presented.) and 4% for (Formula presented.). In the absence of experimental and fully resolved numerical near-nozzle velocity data, the exact details of (Formula presented.) remain as an open question. In contrast, fuel property effects on spray development have been consistently explained herein. ; The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the European Union HERCULES-2 project within Horizon 2020 research and innovation program under grant agreement no. 634135. The present study has also been financially supported by the Academy of Finland (grant nos 289592 and 318024) and by the King Abdullah University of Science and Technology, Office of Sponsored Research (OSR) under Award OSR-2017-3319. The simulations presented above were performed using computer resources within the Aalto University School of Science "Science-IT" project.

Accurate models of turbulent dispersion are required for simulating the near-field concentration distribution of pollutants. However, high-resolution measurements of turbulent dispersion in the atmospheric boundary layer are sparse. This thesis describes the three artificial release experiments in the summers of 2017-2019 within the comtessa (Camera Observation and Modelling of 4D Tracer Dispersion in the Atmosphere)project and presents derived results for the turbulent dispersion of tracer puffs. Instantaneous puffs of sulfur dioxide (SO2) were released from a tower on a military site in Norway. Column-integrated SO2 concentrations were observed with SO2 cameras from up to six viewing directions while the atmospheric flow was characterised by eddy covariance measurements at different altitudes along the release tower. A novel simplified tomographic approach was applied to reconstruct the dispersion of tracer puffs separated into their centre of mass trajectories and their dispersion around the centre of mass. Using ensembles of puff releases, the meandering, relative and absolute dispersion as well as the Lagrangian velocity autocorrelations were measured. The ratio of Lagrangian and Eulerian time scales was estimated to a lower bound of TL/TE = 0.33 * 1/i where i is the turbulence intensity; agreeing with previous studies.

Special volume: Advances in Spanish physical oceanography. Scientia Marina 76(Suppl.1) 2012.-- 16 pages, 10 figures, 1 table ; [EN] The regional ocean circulation within the Canary Upwelling System between 31°N and 35°N is studied using numerical tools. Seasonal mean and near-instantaneous velocity fields from a previously-generated climatological Regional Ocean Modelling System (ROMS) solution of the Canary Basin are used to force a series of offline Lagrangian particle-tracking experiments. The primary objective is to identify the pathways through which water parcels arrive at the upwelling region north of Cape Ghir. Examining year-long pathways, the Azores Current contributes over 80% of particles annually, of which a large proportion arrive directly from offshore (from the northwest), while others travel along the shelf and slope from the Gulf of Cadiz. The remaining ~20% originate within the Gulf of Cadiz or come from the south, although the southern contribution is only significant in autumn and winter. When season-long pathways are considered, the alongshore contributions become increasingly important: northern contributions reach 40% in spring and summer, while southern values exceed 35% in winter. This study also shows that coastal upwelling changes both spatially and temporally. Upwelling becomes intensified near Cape Beddouza, with most upwelling occurring within ~40 km from shore although significant values may reach as far as 120 km offshore north of Cape Beddouza; at these locations the offshore integrated upwelling reaches as much as 4 times the offshore Ekman transport. In the Cape Beddouza area (32°N to 33°N), upwelling is negligible in February but intensifies in autumn, reaching as much as 3 times the offshore Ekman transport ; [ES] Se estudia la circulación oceánica regional en el Sistema de Afloramiento de Canarias entre 31 y 35°N mediante herramientas numéricas. Con este fin se realizan una serie de experimentos de seguimientos de partículas Lagrangianas mediante los campos de velocidad, tanto los medios estacionales como los cuasi-instantáneos, obtenidos a partir de una solución previamente generada del Sistema de Modelado Oceánico Regional (ROMS). El objetivo principal es identificar las rutas mediante las cuales las parcelas de agua llegan a la región de afloramiento al norte de Cabo Ghir. Al examinar las rutas anuales se aprecia que la Corriente de Azores contribuye con más del 80% de las partículas, una gran proporción de las cuales llega directamente desde costa afuera (desde el noroeste) mientras que otras siguen la plataforma y el talud continental desde el Golfo de Cádiz. Las restantes ~20% se originan en el Golfo de Cádiz o vienen desde el sur, aunque la contribución sureña solo es significativa en otoño e invierno. Al examinar las rutas estacionales se observa que las contribuciones a lo largo de la costa se tornan más importantes: la contribución norteña alcanza el 40% en primavera y verano mientras que las partículas originadas al sur exceden un 35% en invierno. Este estudio también muestra que el afloramiento costero cambia temporal y espacialmente. El afloramiento se intensifica cerca de Cabo Beddouza, con la mayor parte del afloramiento teniendo lugar en unos ~40 km desde la costa, aunque se obtienen valores significativos a distancias de hasta 120 km fuera de costa al norte de Cabo Beddouza; en estas mismas localidades el afloramiento integrado costa afuera alcanza hasta 4 veces el transporte de Ekman perpendicular a costa. En el área de Cabo Beddouza (32 a 33°N), el afloramiento es despreciable en febrero pero se intensifica en otoño, alcanzando hasta 3 veces el transporte de Ekman perpendicular a costa ; This research was supported by the Spanish government through projects MOC2 (CTM2008-06438-C02-01) and TIC-MOC (CTM2011-28867) ; Peer reviewed

This paper presents the propagation longitudinal nonlinear plastic stress in thin semi-infinite rod or in wire. The rod is characterized by a nonlinear strain hardening model within the scope a plastic strain. The modulus of strain hardening is a decreasing function of the strain. The frontal bar end is suddenly launching to the velocity V, and subsequently moves with this one. General solution of this boundary value problem of the Lagrangian coordinate (material description) and of the Eulerian one (spatial description) has been presented. There has been carried out the physical interpretation of the obtained results by means of Lagrangian and Eulerian methods. The results of this paper may be utilized in scientific researches and in engineering practice.

The total force exerted on a small rigid body by an acoustic field in a viscous fluid is addressed analytically in the limit where the typical size of the particle is smaller than both the viscous diffusion length scale and the acoustic wavelength. In this low-frequency limit, such a force can be calculated provided the effect of the acoustic steady streaming is negligible. Using the Eulerian linear expansion of Lagrangian hydrodynamic quantities (velocity and pressure), the force on a small solid sphere free to move in an acoustic field is first calculated in the case of progressive and standing waves, and it is compared to past results. The proposed method is then extended to the case of more complex shapes with three planes of symmetry. For a symmetric body oriented with one of its axis along the wave direction, the acoustic force exerted by a progressive wave is affected by the particle shape at leading order. In contrast, for a standing wave (with the same orientation), the force experienced by the particle at leading order is the same as the one experienced by a sphere of same volume and density. ; This work was funded in part by the European Union through a Marie-Curie CIG grant to E.L. and by the Direction Générale de l'Armement (project ERE 12C0020, contract 2012600091) to F.N. ; This is the author accepted manuscript. The final version is available from the American Institue of Physics via http://dx.doi.org/10.1121/1.4942592

Abstract. Experiments on extremely steep deterministic waves generated in a large wave tank by focusing of a broad-banded wave train serve as a motivation for the theoretical analysis of the conditions leading to wave breaking. Particular attention is given to the crest of the steepest wave where both the horizontal velocity and the vertical acceleration attain their maxima. Analysis is carried out up to the third order in wave steepness. The apparent, Eulerian and Lagrangian accelerations are computed for wave parameters observed in experiments. It is demonstrated that for a wave group with a wide spectrum, the crest propagation velocity differs significantly from both the phase and the group velocities of the peak wave. Conclusions are drawn regarding the applicability of various criteria for wave breaking.