Direct numerical simulation of the oscillatory flow around a sphere resting on a rough bottom

The oscillatory flow around a spherical object lying on a rough bottom is investigated by means of direct numerical simulations of continuity and Navier-Stokes equations. The rough bottom is simulated by a layer/multiple layers of spherical particles, the size of which is much smaller that the size of the object. The period and amplitude of the velocity oscillations of the free stream are chosen to mimic the flow at the bottom of sea waves and the size of the small spherical particles falls in the range of coarse sand/very fine gravel. Even though the computational costs allow only the simulation of moderate values of the Reynolds number characterizing the bottom boundary layer, the results show that the coherent vortex structures, shed by the spherical object, can break-up and generate turbulence, if the Reynolds number of the object is sufficiently large. The knowledge of the velocity field allows the dynamics of the large scale coherent vortices shed by the object to be determined and turbulence characteristics to be evaluated. Moreover, the forces and torques acting on both the large spherical object and the small particles, simulating sediment grains, can be determined and analysed, thus laying the groundwork for the investigation of sediment dynamics and scour developments.Comment: 35 pages, 21 figure

Direct Numerical Simulation of Oscillatory Flow Over a Wavy, Rough, and Permeable Bottom

The results of a direct numerical simulation of oscillatory flow over a wavy bottom composed of different layers of spherical particles are described. The amplitude of wavy bottom is much smaller in scale than typical bed forms such as sand ripples. The spherical particles are packed in such a way to reproduce a bottom profile observed during an experiment conducted in a laboratory flow tunnel with well-sorted coarse sand. The amplitude and period of the external forcing flow as well as the size of the particles are set equal to the experimental values and the computed velocity field is compared with the measured velocity profiles. The direct numerical simulation allows for the evaluation of quantities, which are difficult to measure in a laboratory experiment (e.g., vorticity, seepage flow velocity, and hydrodynamic force acting on sediment particles). In particular, attention is focused on the coherent vortex structures generated by the vorticity shed by both the spherical particles and the bottom waviness. Results show that the wavy bottom triggers transition to turbulence. Moreover, the forces acting on the spherical particles are computed to investigate the mechanisms through which they are possibly mobilized by the oscillatory flow. It was found that forces capable of mobilizing surface particles are strongly correlated with the particle position above the mean bed elevation and the passage of coherent vortices above them

Eddy interaction model for turbulent suspension in Reynolds-averaged Euler-Lagrange simulations of steady sheet flow

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Advances in Water Resources 111 (2018): 435-451, doi:10.1016/j.advwatres.2017.11.019.A Reynolds-averaged Euler–Lagrange sediment transport model (CFDEM-EIM) was developed for steady sheet flow, where the inter-granular interactions were resolved and the flow turbulence was modeled with a low Reynolds number corrected turbulence closure modified for two-phase flows. To model the effect of turbulence on the sediment suspension, the interaction between the turbulent eddies and particles was simulated with an eddy interaction model (EIM). The EIM was first calibrated with measurements from dilute suspension experiments. We demonstrated that the eddy-interaction model was able to reproduce the well-known Rouse profile for suspended sediment concentration. The model results were found to be sensitive to the choice of the coefficient, C0, associated with the turbulence-sediment interaction time. A value was suggested to match the measured concentration in the dilute suspension. The calibrated CFDEM-EIM was used to model a steady sheet flow experiment of lightweight coarse particles and yielded reasonable agreements with measured velocity, concentration and turbulence kinetic energy profiles. Further numerical experiments for sheet flow suggested that when C0 was decreased to C0  1.0). Additional simulations for a range of Shields parameters between 0.3 and 1.2 confirmed that CFDEM-EIM was capable of predicting sediment transport rates similar to empirical formulations. Based on the analysis of sediment transport rate and transport layer thickness, the EIM and the resulting suspended load were shown to be important when the fall parameter is less than 1.25.Z. Cheng and T.-J. Hsu were supported by the U.S. Office of Naval Research (N00014- 16-1-2853) and National Science Foundation (OCE- 1537231). J. Chauchat was supported by the Région Rhones-Alpes (COOPERA project and Explora Pro grant) and the French national programme EC2CO-LEFE MODSED. J. Calantoni was supported under base funding to the U.S. Naval Research Laboratory from the U.S. Office of Naval Research. The authors would also like to acknowledge the support from the program on "Fluid- Mediated Particle Transport in Geophysical Flows" at the Kavli Institute for Theoretical Physics, Santa Barbara, USA

Interface-resolved direct numerical simulations of sediment transport in a turbulent oscillatory boundary layer

The flow within an oscillatory boundary layer, which approximates the flow generated by propagating sea waves of small amplitude close to the bottom, is simulated numerically by integrating the Navier-Stokes and continuity equations. The bottom is made up of spherical particles, free to move, which mimic sediment grains. The approach allows one to fully resolve the flow around the particles and to evaluate the forces and torques that the fluid exerts on their surface. Then, the dynamics of sediments is explicitly computed by means of the Newton-Euler equations. For the smallest value of the flow Reynolds number presently simulated, the flow regime turns out to fall in the intermittently turbulent regime such that turbulence appears when the free-stream velocity is close to its largest value but the flow recovers a laminar-like behaviour during the remaining phases of the cycle. For the largest value of the Reynolds number, turbulence is significant during almost the whole flow cycle. The evaluation of the sediment transport rate allows one to estimate the reliability of the empirical predictors commonly used to estimate the amount of sediments transported by sea waves. For large values of the Shields parameter, the sediment flow rate during the accelerating phases does not differ from that observed during the decelerating phases. However, for relatively small values of the Shields parameter, the amount of moving particles depends not only on the bottom shear stress but also on flow acceleration. Moreover, the numerical results provide information on the role that turbulent eddies have on sediment dynamics

Three-dimensional spatial variations of suspended sediment concentration over vortex ripples

Abstract A three-dimensional mixture theory model (SedMix3D) was used to simulate the flow and sediment transport over vortex ripples for scaled laboratory conditions. SedMix3D treats the fluid-sediment mixture as a continuum of varying density and viscosity with the concentration of sediment and velocity of the mixture calculated using a sediment flux equation coupled to the Navier-Stokes equations for the mixture. Mixture theory allows the model to simulate the three-dimensional flow and sediment concentration within and above an evolving sediment bed. Grid spacing was on the order of a sediment grain diameter and time steps were O(10 -5 s). The simulation was forced with a time series of free-stream velocity measured in a free-surface laboratory flume. Spatial variations in the simulated suspended sediment concentration were primarily associated with the non-uniform generation of vortex structures over the ripple flanks. The suspended sediment was initially picked up in regions of high vorticity, and then caused a damping of the vorticity while being advected through the water column

Development and Evaluation of an Autonomous Sensor for the Observation of Sediment Motion

Abstract Measurements within the mobile bed layer have been limited by previous Eulerian-based technologies. A microelectromechanical system device, called a smart sediment grain (SSG), that can measure and record Lagrangian observations of coastal sediments at incipient motion has been developed. These sensors have the potential to resolve fundamental hypotheses regarding the incipient motion of coastal sediments. Angle of repose experiments verified that the sensor enclosure has mobility characteristics similar to coarse gravel. Experiments conducted in a small oscillating flow tunnel verified that the sensors detect incipient motion under various hydrodynamic conditions. Evidence suggests the influence of pressure-gradient-induced sediment motion, contrary to the more commonly assumed bed shear stress criterion. Lagrangian measurements of rotation measured with the newly developed SSG agreed to within 5% of the rotation estimates made simultaneously with high-speed video cameras

Protocolo de profilaxis de úlcera por estrés

1 recurso en línea 3 p.La profilaxis de la úlcera por estrés (PUE) es una práctica universalmente extendida y como medicación ampliamente prescripta en pacientes hospitalizados. Se ha mostrado su eficacia para la prevención de la hemorragia digestiva en pacientes críticos de Unidades de Terapia Intensiva (UTI) con factores de riesgo. Sin embargo, actualmente esta patología es un evento relativamente infrecuente y el riesgo de sangrado clínicamente significativo es bajo.Fil: Bustos Fierro, Carolina. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Herrera Comoglio, Raquel. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Calantoni, Miguel Alberto. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina

Protocolo de uso del Cateter Venoso Central

6 p.Se entiende por PRODUCTO MÉDICO (PM) de uso restringido a aquel para el que, mediante un procedimiento participativo, multidisciplinar y representativo del hospital, su uso ha sido restringido a determinados grupos de pacientes o a determinadas situaciones clínicas por motivos epidemiológicos, económicos o para evitar complicaciones. El Hospital Nacional de Clínicas (HNC) cuenta con PM de uso restringido como es el CATETER VENOSO CENTRAL (CVC).Fil: Bustos Fierro, Carolina. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Herrera Comoglio, Raquel. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Calantoni, Miguel Alberto. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina

A storm driven turbidity maximum in a microtidal estuary

Many macro- and mesotidal estuaries are characterized by Turbidity Maxima Zones (TMZs), regions with suspended solid concentrations that are much higher than those found throughout the rest of the estuary. Such regions are located near the upriver limit of salt intrusion and their position and extent are modulated and driven by tidal oscillations, especially in estuaries where tidal forcing is large. Hence, pronounced TMZs are not typically expected in micro-tidal estuaries. Field experiments were carried out in the microtidal estuary of the Misa River (northeast coast of Italy) with the aim to analyze riverine-coastal ocean interactions during different climatic conditions, freshwater discharge and tidal forcing. The goal was also that of identifying factors and episodic conditions that could lead to the evolution of ephemeral TMZs in this microtidal estuarine system. Observational results, combined to a flocculation model suite, describe the hydrodynamics, morphological bed evolution, water chemistry and floc dynamics within the estuary during wintertime quiescent and stormy periods. Pronounced TMZs with different location and extent were observed during two storms with different intensities, when enhanced freshwater discharge, wave action and tidal oscillation generated significant stratification of the lower estuarine water column. Higher turbidity values were observed throughout the TMZ during the smaller/weaker storm, while stronger surface mixing during the stronger storm led to greater dispersion of the (re-)suspended particulate load throughout the upper water column, providing a less pronounced TMZ along the bed of the lower estuary. Observations in the Misa River, potentially valid for other microtidal estuaries, show that: 1) episodic storm conditions that significantly increase freshwater discharge can lead to the evolution of an ephemeral TMZ that is modulated, but not controlled, by tidal oscillations and surface mixing conditions; 2) ephemeral TMZ localization, intensity, and extent during episodic storm events is a function of storm intensity; 3) moderately enhanced freshwater flow during an episodic storm event promotes a high degree of stratification, allowing for the formation of large flocs with great settling rates, leading to a pronounced TMZ forming downriver of the landward limit of seawater intrusion; whereas higher freshwater flows during stronger storm events lead to less stratification, greater bottom turbulence and potential TMZ suppression near the riverbed, with shear conditions promoting smaller flocs with lower settling and a greater potential for suspended particulate export from the lower estuary to coastal waters

Protocolo de uso de Nutrición Parenteral

7 pSe entiende por MEDICAMENTO DE USO RESTRINGIDO a aquel para el que, mediante un procedimiento participativo, multidisciplinar y representativo del hospital, su uso ha sido restringido a determinados grupos de pacientes o a determinadas situaciones clínicas para asegurar una mayor eficacia, evitar efectos adversos, por motivos epidemiológicos o por motivos económicos. El Hospital Nacional de Clínicas (HNC) cuenta con un listado de medicamentos de uso restringido entre los que se encuentra la NUTRICIÓN PARENTERAL (NP).Fil: Bustos Fierro, Carolina. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Calantoni, Miguel Alberto. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina.Fil: Herrera Comoglio, Raquel. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Hospital Nacional de Clínicas; Argentina