Thermal Analysis of Inorganic Materials

Traballo presentado ao seminario internacional: Thermal Analysis and Rheology (1. 2003. Ferrol)

Tracer particle transport dynamics in the diffusive sandpile cellular automaton

The confinement properties of the diffusive running sandpile are characterized by tracking the motion of a population of marked grains of sand. It is found that, as the relative strength of the avalanching to the diffusive transport channel is varied, a point is reached at which the particle global confinement time and the probability density functions of the jump-sizes and waiting-times of the tracked grains experience a sudden change, thus revealing a dynamical transition, that is consistent with previous studies (Newman DE et al., Phys Rev Lett 2002;88(20):204304). Across this transition, the sandpile moves from a regime characterized by self-similarity and memory, where avalanches of all possible sizes dominate transport across the system, to another regime where transport is taken over by near system-size, quasi-periodic avalanches. Values for the fractional transport exponents that quantify effective transport across the sandpile prior to the transition are also obtained.This research has been sponsored in part by Ministerio de Economía y Competitividad of Spain under Projects No. ENE2015- 68265-P and No. ENE2015-66444-R. Research also supported in part by DOE-OFES Grant No. DE-FG02-04ER5741 at University of Alaska. Sandpile simulations have been run in Uranus, a supercomputer cluster at Universidad Carlos III de Madrid (Spain) that has been funded by the Spanish Government via the national projects UNC313-4E-2361, ENE2009-12213-C03-03, ENE2012-33219 and ENE2012-31753

Experimental analysis of flow and turbulence characteristics in oscillatory boundary layers from LDV measurements

The oscillatory boundary layer represents a particular case of unsteady wall-bounded flows in which fluid particles follow a periodic sinusoidal motion. Unlike steady boundary layer flows, the flow regime and bed roughness character of oscillatory flows change in time during the oscillation, a characteristic that introduces a high degree of complexity in the analysis. Experimental work in this topic started in the 1960s followed by numerical work in the late 1980s, yet it is not completely understood, particularly in the transitional regimes. In this work, several oscillatory flow experiments were performed in the Large Oscillatory Water and Sediment Tunnel (LOWST) facility at the Ven Te Chow Hydrosystems Laboratory. A custom PVC floor was built inside the tunnel to obtain a flat and smooth bed. The range of wave Reynolds numbers tested spanned all along the transition regime of the oscillatory boundary layer between the upper limit of the laminar regime and the lower limit of the turbulent regime (3x104 < Rew < 9x105). A 3D laser Doppler velocimetry (LDV) system was used to measure instantaneous flow velocities with high spatial and temporal resolution, which allowed capturing flow features with great detail inside the boundary layer and even inside the viscous sublayer in some cases. A special set-up was built involving two LDV probes and a refraction-correcting device to be able to measure all three velocity components (u, v, w) simultaneously. From the velocity measurements, flow characteristics were obtained through the analysis of different variables including mean flow velocities, boundary layer thickness, turbulence intensities, turbulent kinetic energy, viscous and Reynolds stresses, turbulence production, eddy viscosity, quadrant analysis, bed shear stresses, shear velocity, wave friction factor and viscous sublayer thickness. In particular, the results of this work provide detailed evidence of the competition between laminar and turbulent effects taking place in the transition regime of the oscillatory boundary layer as Rew increased. A surprising behavior was observed in the phase of the peak bed shear stress, which changed dramatically with Rew: first leading about 40º ahead of the outer flow for low Rew, then lagging up to 25º behind for the transitional Rew experiments, and finally returning slightly ahead about 5º for high Rew. This finding is expected to have significant implications for the entrainment and transport of sediment near the bed. Also, investigation of the viscous sublayer revealed that the classic steady flow threshold of z+ = 5 doesn’t work well for oscillatory flows. A new method was developed to calculate the thickness of the viscous sublayer taking into account the ratio of viscous to turbulent forces near the bed. These results can be directly applied to better understand sediment transport in the ocean under the action of waves and currents. Furthermore, they will be also useful for a variety of engineering applications related to fluid mechanics including aerospace, biomedical research, engine design, turbines, industrial machinery, pumping systems, pipe transport, marine hydrokinetics, wave dynamics, and river, coastal and estuarine processes

The Wear Responses of the Welded Joints of ASTM A335 Gr. P11 Steels Affected by Accelerated Flow Corrosion

[Abstract] This study shows the efects of wear on welded joints of ASTM A355 Gr. P11 “Seamless Ferritic Alloy-Steel Pipe for High Temperature Service” steels subjected to the welding procedures established by codes B31.1 and ASME III. The standard welding procedure establishes the following steps: a preheating process, welding and post-weld heat treatment. This generates a wear behavior that depends on the thermal cycles to which the diferent areas of the joint are subjected. The objective of this article was the study of the behavior against the flow-accelerated corrosion of the welded joints of a low alloy steel. There is the possibility of establishing welding procedures other than those established, while maintaining the safety ranges, depending on the field of application for the steel

Fatigue Study of the Pre-Corroded 6082-T6 Aluminum Alloy in Saline Atmosphere

[Abstract] This work studies the influence of the saline atmospheric corrosion on the fatigue strength of 6061-T6 aluminum alloy. For this purpose, this alloy was subjected to tests in a salt spray corrosion chamber at different exposure times (1, 2, and 3 months) according to ASTM B117 standard. The morphological study of the pits was carried out by confocal microscopy. Subsequently, fatigue tests were performed at variable stresses whose maximum stress (Smax) was between 30% and 95% of the yield strength (S0) in order to keep them within the zone of elastic behavior of the material. Data were analyzed using the Basquin equation and the maximum likelihood function method. The results show a similar decrease in the conventional fatigue limit (2 × 106 cycles) after one month (98 MPa) and two months (91 MPa) of corrosion. After three months of corrosion, the material showed a very important reduction in the fatigue limit (68 MPa) with respect to the uncorroded material (131 MPa). The data of Se/S0 (fatigue limit/yield strength) versus the ratio Pm/Dm (pit average depth/pit diameter at zero depth) can be fitted to a logarithmic curve

Estudio y Evaluación del Riego por Aspersión de la Granja de la Universidad Tecnológica del Magdalena

Este trabajo se efectuó en los terrenos de la Universidad Tecnológica del Magdalena, que se encuentra situada en la región de Mamatoco al Oriente de la ciudad de Santa Marta. Este estudio tuvo su comienzo en el mes de septiembre de 1.972 y se concluyó en abril de 1.973. El objetivo principal fue estudiar el riego por aspersión y determinar si es factible la utilización de este riego en las labores agrícolas de la granja. Para su desarrollo se usaron los laboratorios de suelos, de química además de diferentes implementos pertenecientes a la Universidad Tecnológica del Magdalena. Las prácticas de campo se efectuaron en todo el terreno ocupado por la granja, en el tiempo previsto para su ejecución. Se comenzó con pruebas de infiltración en lotes escogidos previamente, siguiendo en su orden las pruebas de capacidad de campo, punto de marchitez, determinación de perfiles hídricos, texturas, estructuras, etc. Se utilizó el equipo comprado por la Universidad del Magdalena, cuyos resultados se van a conocer en este estudio y se aconsejó comprar un equipo de mayor capacidad que suplirá las necesidades de la granja, cuyas características del equipo aconsejado son las siguientes: 89 Equipo portátil, con 16 aspersores con una presión de trabajo de 3 atmósferas, sin tuberías principales, ya que éstas fueron reemplazadas por los canales de riego; con laterales de 200 metros de longitud. El sistema de riego adoptado es el de cobertura total de gran eficiencia, ya que permite regar la zona con mayor facilidad y un mínimo de desplazamientos, lo que permite la conservación del material por más tiempo. La prueba efectuada de distribución del agua resultó buena dando una lámina bastante uniforme y bien distribuida. Para el sistema empleado se utiliza una distancia entre laterales de 15 metros y entre aspersores 12 metros. Los laterales deben ser colocados perpendicularmente a la dirección de los vientos, ya que éstos son un factor limitante en la eficiencia del riego por aspersión

Finding Respondents from Minority Groups

The recruitment of respondents belonging to ethnic minorities poses important challenges in social and health research. This paper reflects on the enablers and barriers to recruitment that we encountered in our research work with persons belonging to ethnic minorities. Additionally, we applied the Matching Model of Recruitment, a theoretical framework concerning minority recruitment, to guide our reflection. We also explored its applicability as a research design tool. In assessing our research experience, we learned that minority recruitment in social and health research is influenced by the social context of all key players involved in the research. Also, there are enablers and barriers within that social context facilitating or delaying the recruitment process. The main enablers to recruit respondents belonging to ethnic minorities include working with community agencies and gatekeepers who share a common vision with researchers and the latter’s ability to gain the trust of potential respondents. The main barriers include demanding too much from these same community agencies and gatekeepers and ignoring factors that could delay the completion of the research. Although we found the Matching Model of Recruitment to be an effective tool in assessing the processes of recruiting respondents belonging to ethnic minorities, further empirical research is needed to explore its usefulness during the research planning phase