Gonzalo Simarro

A Lagrangian model for tracking surface spills and SaR operations in the ocean

An operational model for tracking surface objects in the ocean is presented. Contrary to most of traditional Lagrangian Particle Tracking Algorithms, the presented approach computes the probability density function from the final position of a set of neutrally buoyant particles deployed in the flow providing the area of accumulated probability. The model departs from daily predictions of ocean surface currents, winds and waves provided by an Operational Forecasting System, and integrates the Eulerian velocities to obtain the trajectory of each particle forward in time. A random walk term is added to simulate numerical diffusivity. Several tests are performed in order to determine the optimal numerical scheme as well as the computational time step. To show the performance of the model we simulate the trajectories of a set of SVP-drifters deployed in the Balearic Sea. For these experiments, the final position of the drifters laid within the modeled contour of 50% of accumulated probability for the first 24?h forecast. An operational model for oil spill and SaR Operations is presented.The model includes advection from currents, waves and wind.Numerical diffusivity is computed from model simulations.The system provides areas of accumulated probability.The model is tested against the trajectory of three SVP-drifters.

Fully Nonlinear Model for Water Wave Propagation from Deep to Shallow Waters

AbstractA set of fully nonlinear Boussinessq-type equations (BTEs) with improved linear and nonlinear dispersive performance is presented. The highest order of the derivatives is three in the equations, and they use the minimum number of unknowns: the free surface elevation and the horizontal velocity at a certain depth. The equations allow reduction of the errors both in linear frequency dispersion and shoaling below 0.30% for kh≤5, and below 2.2% for kh≤10, with k as the wave number and h as the water depth. The weakly nonlinear performance is also improved for kh≤2. A simple fourth-order explicit numerical scheme is presented to test the linear and nonlinear behavior of the model equations against analytical and experimental results.

Sea surface transport in the Western Mediterranean Sea : A Lagrangian perspective

[2] 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.

Estimating Final Scour Depth under Clear-Water Flood Waves

AbstractIn this paper we experimentally investigate the final scour depth around cylindrical piers under flood waves. Only clear-water conditions are considered. An approach to estimate the final scour depth under a flood wave is proposed, based on the local scour depth calculated with steady flow equations under peak flow conditions. The new experimental results are also used to investigate the performance of existing expressions or approaches to predict time evolution under steady and unsteady flow conditions.

Wave mixing rise inferred from Lyapunov exponents

We study the horizontal surface mixing and the transport induced by waves in a coastal environment. A comparative study is addressed by computing the Lagrangian coherent structures, via Finite Size Lyapunov Exponents, that arise in two different numerical settings: with and without wave coupled to currents. In general, we observe that mixing is increased in the area due to waves. Besides, the methodology presented here is tested by deploying a set of eight Lagrangian drifters at different locations. This dynamical approach is shown as a valuable tool to extract information about transport, mixing and residence embedded in the Eulerian time dependent velocity fields obtained from numerical models.

An eddy tracking algorithm based on dynamical systems theory

This work introduces a new method for ocean eddy detection that applies concepts from stationary dynamical systems theory. The method is composed of three steps: first, the centers of eddies are obtained from fixed points and their linear stability analysis; second, the size of the eddies is estimated from the vorticity between the eddy center and its neighboring fixed points, and, third, a tracking algorithm connects the different time frames. The tracking algorithm has been designed to avoid mismatching connections between eddies at different frames. Eddies are detected for the period between 1992 and 2012 using geostrophic velocities derived from AVISO altimetry and a new database is provided for the global ocean.

SAND RIDGES IN THE MID-OUTER SHELF AS POTENTIAL SAND BORROWS AREAS (NW MEDITERRANEAN)

The Coastal Sediments ’15 conference, Understanding and Working with Nature, 11-15 May 2015, San Diego, California.-- 13 pages, 6 figures

A non-hydrostatic global spectral dynamical core using a height-based vertical coordinate

Most of the dynamical cores of operational global models can be broadly classified according to the spatial discretisation into two categories: spectral models with mass-based vertical coordinate and grid point models with height-based vertical coordinate. This article describes a new non-hydrostatic dynamical core for a global model that uses the spectral transform method for the horizontal directions and a height-based vertical coordinate. Velocity is expressed in the contravariant basis (instead of the geographical orthonormal basis pointing to the East, North and Zenith directions) so that the expressions of the boundary conditions and the divergence of the velocity are simpler. Prognostic variables in our model are the contravariant components of the velocity, the logarithm of pressure and the logarithm of temperature. Covariant tensor analysis is used to derive the differential operators of the prognostic equations, such as the curl, gradient, divergence and covariant derivative of the contravariant velocity. A Lorenz type grid is used in the vertical direction, with the vertical contravariant velocity staggered with respect to the other prognostic variables. High-order vertical operators are constructed following the finite difference technique. Time stepping is semi-implicit because it allows for long time steps that compensates the cost of the spectral transformations. A set of experiments reported in the literature is implemented so as to confirm the accuracy and efficiency of the new dynamical core.

Toe protection for spill-through and vertical-wall abutments

This study addresses the design of riprap aprons as a scour countermeasure near abutments under clear-water conditions. It deals with the lateral extent of riprap aprons and the geometry of the scour hole prevailing at the apron edge. The study applies to riprap aprons acting as granular filters. The scour depth appears to be independent for a sufficiently long relative abutment length. Scour holes develop farther away from spill-through abutments than from vertical-wall abutments; the distance between the point of maximum scour depth and the abutment increases with the relative abutment length. The effect of contraction on this distance was not identified. The angle defining the position of the deepest scour point is close to 30°. Neither the abutment shape nor the flow contraction seems to influence the minimum stable apron width.

Effect of Viscosity on the Equilibrium Scour Depth at Single Cylindrical Piers

AbstractMost studies on scouring seem to have overlooked the effect of viscosity, the assumption being that the flow is free of viscous effects inside the scour hole because of the presence of highly turbulent flow structures such as down-flow, horseshoe vortex, and wake vortices irrespective of the approach flow regime. The present work reports the results of experiments conceived to revisit the effect of viscosity on scouring. The experiments were performed by changing the Reynolds-like numbers for two flow shallowness values and keeping constant the remaining dimensionless parameters that control the scour process. The values of the Reynolds number corresponded to transitional approach flows. The experimental results indicate that scouring does depend on viscosity in usual laboratory conditions, the viscous effect leading to scour depths in the safety side.