Abstract

The Henry problem has played a key role in our understanding of seawater intrusion into coastal aquifers and in benchmarking density dependent flow codes. This paper seeks to modify Henry’s problem to ensure sensitivity to density variations and vertical salinity profiles that resemble field observations. In the proposed problem, the “dispersive Henry problem”, mixing is represented by means of the traditional Scheidegger dispersion tensor (dispersivity times water flux). Anisotropy in the hydraulic conductivity is acknowledged and Henry’s seaside boundary condition of prescribed salt concentration is replaced by a flux dependent boundary condition, which represents more realistically salt transport across the seaside boundary. This problem turns out to be very sensitive to density variations and its solution gets closer to reality. However, an improvement in the traditional Henry problem (gain in sensitivity and realism) can be also achieved if the value of the Peclet number is significantly reduced.

Although the dispersive problem lacks an analytical solution, it can shed light on flow in coastal aquifers. It provides significant information about the factors controlling seawater penetration, width of the mixing zone and influx of seawater. The width of the mixing zone depends basically on dispersion with longitudinal and transverse dispersion controlling different parts of the mixing zone but displaying similar overall effects. Toe penetration is mainly controlled by the horizontal permeability and by the geometric mean of the dispersivities. Finally, transverse dispersivity and the geometric mean of the hydraulic conductivity are the leading parameters controlling the amount of saltwater that enters the aquifer

Abstract

Abstract

In this paper we analyze time marching schemes for the wave equation in mixed form. The problem is discretized in space using stabilized finite elements. On the one hand, stability and convergence analyses of the fully discrete numerical schemes are presented using different time integration schemes and appropriate functional settings. On the other hand, we use Fourier techniques (also known as von Neumann analysis) in order to analyze stability, dispersion and dissipation. Numerical convergence tests are presented for various time integration schemes, polynomial interpolations (for the spatial discretization), stabilization methods, and variational forms. To analyze the behavior of the different schemes considered, a 1D wave propagation problem is solved.

Abstract

Abstract

La adición de nanopartículas puede mejorar notablemente las propiedades de los polímeros. Sin embargo, la producción industrializada de nanocompuestos presenta el desafío tecnológico de dispersar correctamente las nanopartículas en la matriz polimérica. EURECAT ha desarrollado un dispositivo que puede conectarse a extrusoras de doble usillo estándar y proporcionar vibración ultrasónica al material fundido, pretendiendo de esta manera mejorar el grado de dispersión de nanopartículas. El presente trabajo presenta la validación experimental de esta tecnología, incluyendo la construcción de ventanas de procesamiento y la comparación de nanocompuestos obtenidos mediante extrusión compounding tradicional y asistida con ultrasonidos. Los nanocompuestos producidos consisten en 94% polipropileno y 6% nanoarcillas (Cloisite 20A). Las propiedades analizadas son: fluidez (MFI), propiedades mecánicas (tracción), propiedades de barrera al O₂ y microestructura (TEM). Los resultados de MFI y el aumento en la rigidez del material sugirieron una mejora en la dispersión de nanopartículas al utilizar el dispositivo de ultrasonidos, especialmente cuando la intensidad se ajustó al 60%. Estas apreciaciones fueron verificadas con los resultados de los ensayos de barrera (al O₂), los cuales demostraron que el tratamiento de ultrasonidos fue eficaz en disminuir la permeabilidad al O₂ de los compounds.