A new well-balanced non-oscillatory central scheme for the shallow water equations on rectangular meshes

This paper is concerned with the development of high-order well-balanced central schemes to solve the shallow water equations in two spatial dimensions. A Runge Kutta scheme is applied for time discretization. A Gaussian quadrature rule is used to evaluate time integrals and a three-degree polynomial which calculates point-values or flux values. A new procedure has been defined to evaluate the flux integrals and to approach the 2D source term integrals in order to verify the exact C-property, using the water surface elevation instead of the water depth as a variable. Numerical experiments have confirmed the high-resolution properties of our numerical scheme in 2D test problems.This work was partially funded by the "Programa de Apoyo a la Investigacion y Desarrollo" (PAID-06-10) and (PAID-05-12) of the Universidad Politecnica de Valencia. Angel Balaguer-Beser thanks the support of the Spanish Ministry of Education and Science in the framework of the Projects CGL2009-14220-C02-01 and CGL2010-19591. The authors express their gratitude to the anonymous reviewers for their helpful comments.Capilla Romá, MT.; Balaguer Beser, ÁA. (2013). A new well-balanced non-oscillatory central scheme for the shallow water equations on rectangular meshes. Journal of Computational and Applied Mathematics. 252:62-74. https://doi.org/10.1016/j.cam.2013.01.014S627425

Estudio comparativo de métodos de regresión para la predicción de variables de estructura y combustibilidad a partir de datos LiDAR full-waveform

Revista oficial de la Asociación Española de Teledetección[EN] Regression methods are widely employed in forestry to predict and map structure and canopy fuel variables. We present a study where several regression models (linear, non-linear, regression trees and ensemble) were assessed. Independent variables were calculated using metrics extracted from full-waveform LiDAR data, while the reference data used to generate the dependent variables for the prediction models were obtained from fieldwork in 78 plots of 16 m radius. Transformations of dependent and independent variables with feature selection were carried out to assess their influence in the prediction of response variables. In order to evaluate significant differences and rank regression models we used the non-parametric tests Wilcoxon and Friedman, and post-hoc analysis or post-hoc pairwise multiple comparison tests, such as Nemenyi, for Friedman test. Regressions using transformation of the dependent variable, like square-root or logarithmic, or the independent variable, increased R2 up to 6% with respect to linear regression using unprocessed response variables. CART (Classification and Regression Tree) method provided poor results, but it may be interesting for categorisation purposes. Square-root transformation of the dependent variable is the method having the best overall results, except for stand volume. However, not always has a significant improvement with respect to other regression methods.[ES] Los métodos de regresión se utilizan ampliamente en el ámbito forestal para la predicción y el cartografiado de las variables de estructura y combustibilidad. En este artículo se evalúan diferentes modelos de regresión (lineal, no lineal, árboles de regresión y ensemble). Como variables independientes se utilizaron métricas extraídas de datos LiDAR full-waveform, mientras que los valores de las variables dependientes se generaron a partir de modelos basados en datos de campo obtenidos para 78 parcelas de 16 m de radio. Se llevaron a cabo transformaciones de las variables dependientes e independientes con selección de atributos para evaluar su influencia en la predicción de la variable respuesta. Con el fin de verificar diferencias significativas y ordenar los modelos de regresión se emplearon los tests no paramétricos de Wilcoxon y Friedman, y el análisis post-hoc o los tests de comparación post-hoc por pares, como el de Nemenyi, para el test de Friedman. Las regresiones basadas en la transformación de la variable dependiente, como raíz cuadrada o logaritmo, o en la transformación de las variables independientes, obtuvieron un incremento de la R2 de hasta un 6% con respecto a la regresión lineal. Mediante el método CART (Classification and Regression Tree) se obtuvieron resultados discretos, si bien su uso puede estar indicado para la categorización o estratificación. Con el método basado en la transformación de la variable dependiente mediante raíz cuadrada se consiguieron los mejores resultados comparativos en la predicción de variables forestales, excepto para el volumen. Sin embargo, su uso no siempre implica una mejora significativa con respecto a los otros métodos de regresión usados en este trabajo.This research has been funded by the Spanish Ministerio de Economía y Competitividad and FEDER, in the framework of the project CGL2013-46387-C2-1-R.Crespo-Peremarch, P.; Ruiz, L.; Balaguer-Beser, A. (2016). A comparative study of regression methods to predict forest structure and canopy fuel variables from LiDAR full-waveform data. Revista de Teledetección. (Special Issue):27-40. https://doi.org/10.4995/raet.2016.4066SWORD2740Special Issu

Using remote sensing to assess the relationship between crime and the urban layout

[EN] The link between place and crime is at the base of social ecology theories of crime that focus in the relationship of the characteristics of geographical areas and crime rates. The broken windows theory states that visible cues of physical and social disorder in a neighborhood can lead to an increase in more serious crime. The crime prevention through environmental design (CPTED) planning approach seeks to deter criminal behavior by creating defensible spaces. Based on the premise that a settlement's appearance is a reflection of the society, we ask whether a neighborhood's design has a quantifiable imprint when seen from space using urban fabric descriptors computed from very high spatial-resolution imagery. We tested which land cover, structure and texture descriptors were significantly related to intra-urban homicide rates in Medellin, Colombia, while controlling for socioeconomic confounders. The percentage of impervious surfaces other than clay roofs, the fraction of clay roofs to impervious surfaces, two structure descriptors related to the homogeneity of the urban layout, and the uniformity texture descriptor were all statistically significant. Areas with higher homicide rates tended to have higher local variation and less general homogeneity; that is, the urban layouts were more crowded and cluttered, with small dwellings with different roofing materials located in close proximity to one another, and these regions often lacked other homogeneous surfaces such as open green spaces, wide roads, or large facilities. These results seem to be in agreement with the broken windows theory and CPTED in the sense that more heterogeneous and disordered urban layouts are associated with higher homicide rates.This research was made possible by funding from EAFIT University (EAFIT-435-000060) and the Medellin City Hall EnlazaMundos program. The authors thank the anonymous reviewers and Hermilson Velazquez, Andr es Ramírez Hassan and Gustavo Canavire for their insightful observations and suggestions during the different stages of this projectPatiño Quinchía, JE.; Duque, JC.; Pardo Pascual, JE.; Ruiz Fernández, LÁ. (2014). Using remote sensing to assess the relationship between crime and the urban layout. Applied Geography. 55:48-60. https://doi.org/10.1016/j.apgeog.2014.08.016S48605

ANALYSIS OF THE SIDE-LAP EFFECT ON FULL-WAVEFORM LIDAR DATA ACQUISITION FOR THE ESTIMATION OF FOREST STRUCTURE VARIABLES

LiDAR full-waveform provides a better description of the physical and forest vertical structure properties than discrete LiDAR since it registers the full wave that interacts with the canopy. In this paper, the effect of flight line side-lap is analysed on forest structure and canopy fuel variables estimations. Differences are related to pulse density changes between flight stripe side-lap areas, varying the point density between 2.65 m−2 and 33.77 m−2 in our study area. These differences modify metrics extracted from data and therefore variable values estimated from these metrics such as forest stand variables. In order to assess this effect, 64 pairwise samples were selected in adjacent areas with similar canopy structure, but having different point densities. Two parameters were tested and evaluated to minimise this effect: voxel size and voxel value assignation testing maximum, mean, median, mode, percentiles 90 and 95. Student’s t-test or Wilcoxon test were used for the comparison of paired samples. Moreover, the absolute value of standardised paired samples was calculated to quantify dissimilarities. It was concluded that optimizing voxel size and voxel value assignation minimised the effect of point density variations and homogenised full-waveform metrics. Height/median ratio (HTMR) and Vertical distribution ratio (VDR) had the lowest variability between different densities, and Return waveform energy (RWE) reached the best improvement with respect to initial data, being the difference between standardised paired samples 1.28 before and 0.69 after modification

MODELLING LANDSCAPE MORPHODYNAMICS BY TERRESTRIAL PHOTOGRAMMETRY: AN APPLICATION TO BEACH AND FLUVIAL SYSTEMS

Beach and fluvial systems are highly dynamic environments, being constantly modified by the action of different natural and anthropic phenomena. To understand their behaviour and to support a sustainable management of these fragile environments, it is very important to have access to cost-effective tools. These methods should be supported on cutting-edge technologies that allow monitoring the dynamics of the natural systems with high periodicity and repeatability at different temporal and spatial scales instead the tedious and expensive field-work that has been carried out up to date. The work herein presented analyses the potential of terrestrial photogrammetry to describe beach morphology. Data processing and generation of high resolution 3D point clouds and derived DEMs is supported by the commercial Agisoft PhotoScan. Model validation is done by comparison of the differences in the elevation among the photogrammetric point cloud and the GPS data along different beach profiles. Results obtained denote the potential that the photogrammetry 3D modelling has to monitor morphological changes and natural events getting differences between 6 and 25 cm. Furthermore, the usefulness of these techniques to control the layout of a fluvial system is tested by the performance of some modeling essays in a hydraulic pilot channel

Numerical-experimental contrast of a mathematical model that simulates the movement of a uid under shallow water conditions including energy losses.

[EN] In this paper, a comparison between the results obtained in laboratory experiments and those calculated by anumerical simulation of shallow water equations in an open channel is performed, considering the energy lossesthat occur as it passes through a local narrowing of the cross section. The mathematical model that simulatesthis physical phenomenon is governed by a partial di erential equations system whose solution provides the waterdepth and the ow rate per unit of width, which is related to the velocity of the water. Such movement is controlledprimarily by the force of gravity, being fundamental the relationship between it and the inertial forces. In thepresent study we have also taken into account energy losses caused by friction of the water with the contours andlocal losses caused by obstacles or changes in the width of the channel. A numerical scheme based on a high-order nite volume method has been used for obtaining the solutions of such model. Two type of laboratory tests havebeen simulated. The rst type represents a slow transition regime, upstream and downstream of a narrowing inthe channel. The second type represents a subcritical ow upstream, a narrowing that works as a control (regimechange) and a downstream supercritical ow. Numerical-experimental comparison demonstrates the importance ofadequately modeling of the di erent physical phenomena involved in the process, and the proper imposition of theboundary conditions of the problem.[ES] En este trabajo se efectúa una comparación entre los resultados obtenidos en experimentos de laboratorio y aquellos calculados mediante una simulación numérica del movimiento de aguas someras en un canal abierto, considerando las pérdidas de energía que tienen lugar a su paso por un estrechamiento localizado. El modelo matemático que simula dicho fenómeno físico se rige mediante un sistema de ecuaciones en derivadas parciales cuya solución proporciona el calado (profundidad del agua) y el caudal por unidad de ancho, el cual está relacionado con la velocidad del agua. Dicho movimiento, está controlado básicamente por la fuerza de la gravedad siendo fundamental la relación entre ésta y las fuerzas inerciales. En el presente estudio se han tenido también en cuenta las pérdidas de energía originadas por la fricción del agua con los contornos así como las pérdidas locales por obstáculos o cambios de ancho. Para obtener las soluciones de dicho modelo se ha usado un esquema numérico basado en el método de volúmenes finitos de alta resolución. Se han efectuado dos tipos de ensayos en un canal de laboratorio. Los del primer tipo representan una transición en régimen lento, aguas arriba y aguas abajo de un estrechamiento en el canal. Los del segundo tipo representan un régimen lento aguas arriba, un estrechamiento que funciona como control (cambio de régimen) y un régimen rápido aguas abajo. La comparativa numérico-experimental demuestra la importancia de modelizar adecuadamente los distintos fenómenos físicos que intervienen en el proceso, así como la correcta imposición de las condiciones de contorno del problema.Los autores agradecen la financiaci´on por parte de la Generalitat Valenciana en el marco del proyecto AICO/2015/098. Beatriz Nacher-Rodr´ıguez agradece la ayuda Val-I+D Predoctoral que le ha sido concedida (ACIF/2015/074) por parte de la Generalitat Valenciana.Balaguer-Beser, A.; Rodríguez-Benlloch, FJ.; Nácher-Rodríguez, B.; Vallés-Morán, FJ. (2017). Contraste numérico-experimental de un modelo matemático que simula el movimiento del flujo en condiciones de aguas someras incluyendo las pérdidas de energía. Modelling in Science Education and Learning. 10(2):85-94. doi:10.4995/msel.2017.6676SWORD8594102Balaguer-Beser, A., Capilla, M.T., Nácher-Rodríguez, B., Vallés-Morán, F.J., Andrés-Doménech, I. (2013). Un esquema centrado de alto orden que resuelve el problema del transporte de sedimentos en canales con geometría irregular. Actas XXIII CEDYA, XIII CMA, pp. 479-487.Balaguer-Beser, Á., Capilla, M. T., Nácher-Rodríguez, B., Vallés-Morán, F. J., & Andrés-Doménech, I. (2014). A High-Order Well-Balanced Central Scheme for the Shallow Water Equations in Channels with Irregular Geometry. SEMA SIMAI Springer Series, 229-237. doi:10.1007/978-3-319-06953-1_22Caleffi, V., Valiani, A., & Bernini, A. (2006). Fourth-order balanced source term treatment in central WENO schemes for shallow water equations. Journal of Computational Physics, 218(1), 228-245. doi:10.1016/j.jcp.2006.02.001Gallardo, J. M., Parés, C., & Castro, M. (2007). On a well-balanced high-order finite volume scheme for shallow water equations with topography and dry areas. Journal of Computational Physics, 227(1), 574-601. doi:10.1016/j.jcp.2007.08.007Te Chow V. (1959). Open channel hydraulics. McGraw-Hill Book Company. New York.Toro, E.F. (2001). Shock-capturing methods for free-surface shallow flows. John Wiley & Sons.Vázquez-Cendón, M. E. (1999). Improved Treatment of Source Terms in Upwind Schemes for the Shallow Water Equations in Channels with Irregular Geometry. Journal of Computational Physics, 148(2), 497-526. doi:10.1006/jcph.1998.612

El poder de mercado en industrias minoristas de gas natural vehicular

La alta concentración del mercado minorista de Gas Natural Vehicular (GNV) en Colombia permite el ejercicio de poder de mercado