Derivation of a multilayer approach to model suspended sediment transport: application to hyperpycnal and hypopycnal plumes

We propose a multi-layer approach to simulate hyperpycnal and hypopycnal plumes in flows with free surface. The model allows to compute the vertical profile of the horizontal and the vertical components of the velocity of the fluid flow. The model can describe as well the vertical profile of the sediment concentration and the velocity components of each one of the sediment species that form the turbidity current. To do so, it takes into account the settling velocity of the particles and their interaction with the fluid. This allows to better describe the phenomena than a single layer approach. It is in better agreement with the physics of the problem and gives promising results. The numerical simulation is carried out by rewriting the multi-layer approach in a compact formulation, which corresponds to a system with non-conservative products, and using path-conservative numerical scheme. Numerical results are presented in order to show the potential of the model

A two-layer shallow water model for bedload sediment transport: convergence to Saint-Venant-Exner model

A two-layer shallow water type model is proposed to describe bedload sediment transport. The upper layer is filled by water and the lower one by sediment. The key point falls on the definition of the friction laws between the two layers, which are a generalization of those introduced in Fern\'andez-Nieto et al. (ESAIM: M2AN, 51:115-145, 2017). This definition allows to apply properly the two-layer shallow water model for the case of intense and slow bedload sediment transport. Moreover, we prove that the two-layer model converges to a Saint-Venant-Exner system (SVE) including gravitational effects when the ratio between the hydrodynamic and morphodynamic time scales is small. The SVE with gravitational effects is a degenerated nonlinear parabolic system. This means that its numerical approximation is very expensive from a computational point of view, see for example T. Morales de Luna et al. (J. Sci. Comp., 48(1): 258-273, 2011). In this work, gravitational effects are introduced into the two-layer system without such extra computational cost. Finally, we also consider a generalization of the model that includes a non-hydrostatic pressure correction for the fluid layer and the boundary condition at the sediment surface. Numerical tests show that the model provides promising results and behave well in low transport rate regimes as well as in many other situations

Formal deduction of the Saint-Venant-Exner model including arbitrarily sloping sediment beds and associated energy

In this work we present a deduction of the Saint-Venant-Exner model through an asymptotic analysis of the Navier-Stokes equations. A multi-scale analysis is performed in order to take into account that the velocity of the sediment layer is smaller than the one of the fluid layer. This leads us to consider a shallow water type system for the fluid layer and a lubrication Reynolds equation for the sediment one. This deduction provides some improvements with respect to the classical Saint-Venant-Exner model: (i) the deduced model has an associated energy. Moreover, it allows us to explain why classical models do not have an associated energy and how to modify them in order to recover a model with this property. (ii) The model incorporates naturally a necessary modification that must be taken into account in order to be applied to arbitrarily sloping beds. Furthermore, we show that this modification is different of the ones considered classically, and that it coincides with a classical one only if the solution has a constant free surface. (iii) The deduced solid transport discharge naturally depends on the thickness of the moving sediment layer, what allows to ensure sediment mass conservation. Moreover, we include a simplified version of the model for the case of quasi-stationary regimes. Some of these simplified models correspond to the generalization of classical ones such as Meyer-Peter$\&$M\"uller and Ashida-Michiue models. Three numerical tests are presented to study the evolution of a dune for several definition of the repose angle, to see the influence of the proposed definition of the effective shear stress in comparison with the classical one, and by comparing with experimental data.Comment: 44 pages, sumbitted to Advances in Water Resources 17 july 201

A robust model for rapidly varying flows over movable bottom with suspended and bedload transport: modelling and numerical approach

We propose a coupled model for suspended and bedload sediment transport in the shallow water framework. The model is deduced under hydrostatic pressure assumptions and will not assume any Bossinesq hypothesis. The numerical resolution is carried out in a segregated way. First the underlying system of conservation laws is solved by using a first order path-conservative Riemann solver. Then, the source terms corresponding with the erosion and depositions rates are approximated in a semi-implicit way. The final scheme preserves the positivity of the density. Several numerical experiments were carried out in order to validate the model and the numerical scheme. The results obtained are in good agreement with the experimental data

Mancha3D code: Multi-purpose Advanced Non-ideal MHD Code for High resolution simulations in Astrophysics

The Mancha3D code is a versatile tool for numerical simulations of magnetohydrodynamic processes in solar/stellar atmospheres. The code includes non-ideal physics derived from plasma partial ionization, a realistic equation of state and radiative transfer, which allows performing high quality realistic simulations of magneto-convection, as well as idealized simulations of particular processes, such as wave propagation, instabilities or energetic events. The paper summarizes the equations and methods used in the Mancha3D code. It also describes its numerical stability and parallel performance and efficiency. The code is based on a finite difference discretization and memory-saving Runge-Kutta (RK) scheme. It handles non-ideal effects through super-time stepping and Hall diffusion schemes, and takes into account thermal conduction by solving an additional hyperbolic equation for the heat flux. The code is easily configurable to perform different kinds of simulations. Several examples of the code usage are given. It is demonstrated that splitting variables into equilibrium and perturbation parts is essential for simulations of wave propagation in a static background. A perfectly matched layer (PML) boundary condition built into the code greatly facilitates a non-reflective open boundary implementation. Spatial filtering is an important numerical remedy to eliminate grid-size perturbations enhancing the code stability. Parallel performance analysis reveals that the code is strongly memory bound, which is a natural consequence of the numerical techniques used, such as split variables and PML boundary conditions. Both strong and weak scalings show adequate performance up till several thousands of CPUs

Análisis de la relevancia y factibilidad de indicadores de calidad en las unidades de nutrición

Introducción: La evaluación de la calidad en las actividades sanitarias exige la elección de unos indicadores acordes con los resultados que queremos medir. De todos los posibles, debemos priorizar aquellos que nos permitan obtener la información más relevante sin sobrecargar el trabajo habitual de nuestras Unidades. Objetivo: Conocer la opinión de los socios de SENPE respecto a la relevancia y la viabilidad del uso de una selección de indicadores de calidad para su aplicación en nutrición clínica. Métodos: Encuesta remitida mediante correo electrónico a los socios de SENPE solicitando a los mismos su opinión sobre 12 indicadores de calidad, valorándose cada uno en cuanto a su relevancia y factibilidad de la aplicación en su medio. Resultados: Contestaron 40 encuestados de 40 centros diferentes de 12 comunidades autónomas. En general, los indicadores fueron considerados más relevantes que factibles. Los indicadores mejor puntuados fueron: “identificación en las bolsas de nutrición artificial”, “posición semi-incorporada del paciente con nutrición enteral por sonda nasogástrica” y “protocolos clínicos básicos”. Considerando los indicadores por grupos (de estructura, proceso o resultado) los mejor valorados fueron: “identificación del paciente en las bolsas de nutrición artificial” (estructura), “posición semi-incorporada” y “protocolos clínicos básicos” (proceso), y “cumplimiento del objetivo calórico” (resultado). Conclusión: Los resultados de la encuesta permiten seleccionar indicadores prioritarios para su aplicación en las Unidades de NutriciónIntroduction: The quality assessment in health activities requires the choice of indicators in line with the results we want to measure. Of all possible, we should prioritize those that allow us to obtain the most relevant information without overloading the regular work of our units. Objective: To determine the opinion of the members of SENPE regarding the relevance and feasibility of using a selection of quality indicators designed for use in clinical nutrition. Methods: E-mail survey sent to members of SENPE asking them their views on 12 quality indicators, evaluating each in terms of their relevance and feasibility of implementation in their environment. Results: 40 respondents answered from 40 centers in 12 different regions. In general, the indicators were considered more relevant than feasible. The indicators best rated were: “identification in artificial nutrition bags, “semi-recumbent position in patient with nasogastric tube feeding” and “basic clinical protocols”. Considering the type of indicator: “patient identification in the bags of artificial nutrition (structure),” a semi-incorporated “and” basic clinical protocols (process), and “fulfillment of the caloric goal” (result). Conclusion: The results of the survey can make a selection of indicators that could be considered for first-line introduction in a Nutrition Uni

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic