A Semi-Lagrangian Particle Level Set Finite Element Method for Interface Problems

We present a quasi-monotone semi-Lagrangian particle level set (QMSL-PLS) method for moving interfaces. The QMSL method is a blend of first order monotone and second order semi-Lagrangian methods. The QMSL-PLS method is easy to implement, efficient, and well adapted for unstructured, either simplicial or hexahedral, meshes. We prove that it is unconditionally stable in the maximum discrete norm, � · �h,∞, and the error analysis shows that when the level set solution u(t) is in the Sobolev space Wr+1,∞(D), r ≥ 0, the convergence in the maximum norm is of the form (KT/Δt)min(1,Δt � v �h,∞ /h)((1 − α)hp + hq), p = min(2, r + 1), and q = min(3, r + 1),where v is a velocity. This means that at high CFL numbers, that is, when Δt > h, the error is O( (1−α)hp+hq) Δt ), whereas at CFL numbers less than 1, the error is O((1 − α)hp−1 + hq−1)). We have tested our method with satisfactory results in benchmark problems such as the Zalesak’s slotted disk, the single vortex flow, and the rising bubble

Matematización y trabajo matemático en la elaboración de simuladores con GeoGebra

El artículo se centra en los procesos de modelación a través de los cuales un grupo de estudiantes aprenden matemática mientras participan en una experiencia de simulación con GeoGebra. Específicamente, se asume una perspectiva cognitiva para analizar los procesos de matematización y trabajo matemático llevados a cabo por estos alumnos al representar una pieza que compone al mecanismo de una máquina de vapor tipo Newcomen. Tal perspectiva se refiere al “ciclo de modelación” de Blum, Leiβ (2007), específicamente en lo que respecta al tránsito por las fases modelo real, modelo matemático y resultados matemáticos. El análisis de los procesos cognitivos contribuyó a identificar ocho episodios que revelan cómo los estudiantes, con la orientación de un profesor, generaron un modelo matemático útil para representar la pieza en el GeoGebra y construyeron un dibujo dinámico asociado con este modelo. Los resultados obtenidos dan cuenta de la existencia de tipos de modelos matemáticos generados en la matematización, diferentes niveles de análisis en el trabajo matemático y características del rol que cumple el profesor al orientar el desarrollo de la actividad

Multiscale modeling of viscoelastic fluids: an up-to-date CONNFFESSIT

The present communication introduces an up-to-date version of the CONNFFESSIT method in the field of micro-macro simulations of non-Newtonian fluids. The ‘macro’ section employs a semi-Lagrangian method in order to reduce the Navier-Stokes equations to a Stokes-like subproblem. Linear systems arising from the finite element formulation are solved via the ‘Incomplete Cholesky Conjugate Gradient’ iterative algorithm, wherein the sparsity pattern of the matrices is taking into account. As to the ‘micro’ part, the stochastic formulation simplifies the Fokker-Planck equations in the configuration space to stochastic differential equations for the internal degrees of freedom of the particles (‘dumbbells’) conveying the rheological information of the kinetic model, their integration being accomplished by means of a semi-implicit, PredictorCorrector algorithm. The ‘micro-macro’ coupling involves the polymer stress tensor, which is computed through a mixed ‘Finite Element / Natural Element’ method.An extended, search-and-locate method for unstructured meshes and non-connected domains has been implemented. The robustness and efficiency of the method is highlighted on a benchmark problem (10:1 planar contraction)

Stochastic semi-Lagrangian micro–macro calculations of liquid crystalline solutions in complex flows

A general method for the simulation of complex flows of liquid crystalline polymers (LCPs) using a stochastic semi-Lagrangian micro–macro method is introduced. The macroscopic part uses a spatial-temporal second order accurate semi-Lagrangian algorithm, where ideas from the finite element and natural element methods are mixed in order to compute average quantities. The microscopic part employs a stochastic interpretation of the Doi–Hess LCP model, which is discretized with a second order Richardson extrapolated Euler–Maruyama scheme. The new method is validated and tested using the benchmark problem of flow between rotating eccentric cylinders. In a decoupled analysis, a discussion on the sensibility of the scalar order parameter to the macroscopic flow is offered. For the coupled situation, the proposed method predicts disclinations at certain regions of the geometry, as well as an accentuated abatement of the flow as the strength of the micro–macro interaction increases. Further examples are provided at different Peclet and concentration numbers to gain insight on the behavior of complex flows of LCPs in the eccentric cylinder geometry. The generality and robustness of the method, as well as its accurate prediction of LCP behavior under complex flows are main features of the implementatio

Un esquema adaptativo semilagrangiano con elementos finitos anisótropos para la resolución de problemas de combustión.

En este trabajo se presenta un método numérico adaptativo para la resolución de problemas temporales de Combustión en la Mecánica de Fluidos. La dis- cretización espacial de las ecuaciones está basada en el método de los elementos finitos y la discretización temporal se realiza con un esquema semilagrangiano para tratar de forma eficiente los términos convectivos. La caracteística principal de la adaptación local, es que el mallado que se construye es anisótropo, lo que le capacita para adaptarse mejor a capas límitee con un reducido coste computacional. Para ello, se define un tensor métrico en cada paso de tiempo, basado en indicadores de error construidos a priori y a posteriori. Ilustraremos el buen comportamiento del código numérico con la modelización de un problema de combustión en 2D y 3D, donde se analilzará la interacción de llamas de difusión de Hidrógeno y vórtices que pueden ser generados en un flujo turbulento

Efecto de las estelas en los parques eólicos

Para el diseño de parques eólicos es de interés conocer la producción de energía eléctrica de las turbinas eólicas, o aeroturbinas, así como las cargas que pueden sufrir las mismas limitando su vida útil. La producción de energía está ligada a la intensidad del viento incidente, y la vida útil de las aeroturbinas al grado de agitación turbulenta del viento. El grupo de Mecánica de Fluidos Aplicado a la Ingeniería Industrial de la UPM, ha desarrollado programas informáticos para estimar la magnitud del viento y la intensidad de la turbulencia, en función de las características del terreno y de la distribución de las turbinas en el parque eólico, utilizando para ello modelos numéricos que simulan el movimiento turbulento de los fluidos

Efectos topográficos en el recurso eólico.

Para el diseño de parques eólicos es de interés conocer la producción de energía eléctrica de las turbinas eólicas, o aeroturbinas, así como las cargas que pueden sufrir las mismas limitando su vida útil. La producción de energía está ligada a la intensidad del viento incidente, y la vida útil de las aeroturbinas al grado de agitación turbulenta del viento. El grupo de Mecánica de Fluidos Aplicado a la Ingeniería Industrial de la UPM, ha desarrollado programas informáticos para estimar la magnitud del viento y la intensidad de la turbulencia, en función de las características del terreno y de la distribución de las turbinas en el parque eólico, utilizando para ello modelos numéricos que simulan el movimiento turbulento de los fluido

Study of isolated wakes and their superposition in wind farms, using different turbulence models

Different models to simulate wakes in wind farms are reviewed [1], [2]. Special emphasis is put in those elaborated by the authors. First, kinematic models, based on self-similar velocity deficit profiles and global momentum conservation, are briefly revisited. Then, field models of a different degree of complexity, which solve numerically the flow equations with several types of simplifications and turbulence closure models, are analyzed and compared. Models like Ainslie´s that uses a simple algebraic expression for the eddy viscosity, and are still widely used, are compared to other more complete models like UPMWAKE, which uses a k-ε turbulence closure. Ground effect, simulation of atmospheric conditions, atmospheric stability, simulation of turbulence characteristics, wake superposition and computer time consumed, will be used as terms of comparison. Results of an algebraic Reynolds Stress Model will also be presented, and compared with those of the k-ε turbulence closure. Then a comparison will follow of elliptic and parabolic models, and how boundary conditions at the disk are imposed. A discussion on the displacement of the wake origin for parabolic models will be made. The simplicity and computer time consumed to simulate wake superposition in whole large wind farms of the elliptic and parabolic models will be analyzed and compared. Results of a large eddy simulation model will also be presented and compared to those of previously mentioned models [3]. Wake meandering, and its role in wake turbulence generation when using simpler eddy viscosity models will be analyzed, and compared with other mechanisms of turbulence generation. The possibility and convenience of introducing unsteady terms in parabolic field models of wind farms, like UPMPARK, and thus simulate wake meandering will be discussed. Results of UPMPARK with and without meandering will be compared with available experimental data

The MANGUA Project : A Population-Based HIV Cohort in Guatemala

Introduction. The MANGUA cohort is an ongoing multicenter, observational study of people living with HIV/AIDS in Guatemala. The cohort is based on the MANGUA application which is an electronic database to capture essential data from the medical records of HIV patients in care. Methods. The cohort enrolls HIV-positive adults ≥16 years of age. A predefined set of sociodemographic, behavioral, clinical, and laboratory data are registered at entry to the cohort study. Results. As of October 1st, 2012, 21 697 patients had been included in the MANGUA cohort (median age: 33 years, 40.3% female). At enrollment 74.1% had signs of advanced HIV infection and only 56.3% had baseline CD4 cell counts. In the first 12 months after starting antiretroviral treatment 26.9% (n = 3938) of the patients were lost to the program. Conclusions. The implementation of a cohort of HIV-positive patients in care in Guatemala is feasible and has provided national HIV indicators to monitor and evaluate the HIV epidemic. The identified percentages of late presenters and high rates of LTFU will help the Ministry to target their current efforts in improving access to diagnosis and care

Chemometrics and elemental mapping by portable LIBS to identify the impact of volcanogenic and non-volcanogenic degradation sources on the mural paintings of Pompeii

Crystallization of soluble salts is a common degradation phenomenon that threatens the mural paintings of Pompeii. There are many elements that contribute to the crystallization of salts on the walls of this archaeological site. Notably, the leachates of the pyroclastic materials ejected in 79 AD by Mount Vesuvius and local groundwater, rich in ions from the erosion of volcanic rocks. Both sources could contribute to increase the concentration of halides (fluorides and chlorides) and other salts in these walls. The distribution of volcanogenic salts and their impact on the conservation of Pompeian mural paintings have however not yet been fully disclosed. In this work, an analytical methodology useful to determine the impact of the main sources of degradation affecting the mural paintings of Pompeii is presented. This methodology combines the creation of qualitative distribution maps of the halogens (CaF and CaCl) and related alkali metals (Na and K) by portable Laser Induced Breakdown Spectroscopy (LIBS) and a subsequent Principal Component Analysis of these data. Such maps, together with the in-situ identification of sulfate salts by portable Raman spectroscopy, provided information about the migration and distribution of volcanogenic halides and the influence of ions coming from additional sources (marine aerosol and modern consolidation mortars). Additionally, the thermodynamic modeling developed using the experimentally determined ionic content of Pompeian rain- and groundwater allowed to determine their specific role in the formation of soluble salts in the mural paintings of Pompeii.The research leading to these results has received funding from “la Caixa” Foundation (Silvia P erez-Diez, ID 100010434, Fellowship code LCF/BQ/ES18/11670017). This work has been supported by the Spanish Agency for Research AEI (MINECO- FEDER /UE) through the projects MADyLIN (BIA2017-87063-P) and MINECO-17-CTQ2016-77887-C2-1-R, and the Government of the Principality of Asturias (GRUPIN IDI/2018/000186). The authors thank for technical and human support provided by the laboratory Raman-LASPEA of SGIker (UPV/EHU/ ERDF, EU)