Experimental study of high-speed phenomena involving bubbles and free surfaces: bubble growth in microgravity and fast lifting of a plate from a water surface

Mención Internacional en el título de doctorThis thesis addresses two different problems with a common link: both are experimental studies where the effect of gravity does not play an important role. While the first one is in microgravity conditions, the other one shows an acceleration much greater than gravity. As a consequence, this dissertation is divided into two parts: growing bubbles in gas-supersaturated liquid in microgravity and fast lifting of a plate from a water surface. In the first part, the diffusion-driven growth of a dense bubble cloud is studied in gas-supersaturated liquid in microgravity conditions. Understanding the diffusive-driven dynamics is relevant in several modern technologies such as space manufacturing or chemistry processes as well as in the formation of the small planetary bodies if we move to the geological field. On Earth’s conditions, it is not possible to observe this purely diffusion-driven growth for more than 100 ms since the gravity induces buoyancy effects that affects in these dynamics. Thus, we carried out experiments in which a bubble cloud grows in aCO2-supersaturatedwater in microgravity using of the drop tower of the German Center of Applied Space Technology and Microgravity (ZARM). In the experiments, the evolution of the bubble cloud can be observed for more than 3 s as well as their interactions and competition to access the CO2 available in the bulk liquid outside the cloud. Firstly, we show the details of the experimental setup that we use to perform these experiments and some preliminary results related to the individual growth of large bubbles and the time evolution of the gas volume of the cloud. Then, we report the existence of different regimes where the bubble cloud presents different growth rates in our experiments. Finally, we suggest a model that describes these regimes and their corresponding growth rate, qualitatively. In the second part, we address an experimental research regarding the fast lifting of a circular disc from a water surface. For naval and ocean engineering it is essential to model the force that a structure must withstand when it impacts or exits the water. Since full-scale numerical simulations are usually impractical for this purpose, several analytical or semi-analytical approaches have been developed over the years. Due to the complexity of the free surface flows involving both numerical and analytical computations must be validated against experiments. With this idea in mind, here we report the results of the experimental measurements of the hydrodynamic force acting on a plate that is lifted from the water surface and starts to move upwards suddenly at an acceleration much larger than gravity, a≫g. Furthermore, we include the hydro-elastic effect that we observed in the experiments in the solution of the asymmetric of the water exit problem. Our work focuses on the early stages of the disc motion when the suction and inertial forces are the most relevant. Thus, the experimental set-up is described firstly, then we compare the experimental results against the linearised theory of the water exit proposed by Korobkin (2013). Finally, as a consequence of the experimental observations of the hydroelastic interaction between the disc and the liquid, the problem of the water exit is reformulated and solved taking into account this effect.Esta tesis aborda dos problemas diferentes con un nexo en común: ambos son estudios experimentales donde el efecto de la gravedad no juega un rol importante. El primer problema se estudia en condiciones de microgravedad. En el segundo, la aceleración será mucho mayor que la de la gravedad. Por tanto, esta tesis se dividirá en dos partes: el crecimiento de burbujas en un líquido sobresaturado de gas en condiciones de microgravedad y la salida súbita de una placa circular sobre una superficie de agua. En la primera parte, se estudia el crecimiento difusivo de una nube densa de burbujas en un líquido sobresaturado de gas en condiciones de microgravedad. Entender la dinámica de los mecanismos difusivos es relevante para varias tecnologías, como la fabricación espacial o en procesos químicos, así como en la formación de los pequeños cuerpos planetarios en geológia. Sin embargo, no es posible observar este crecimiento puramente difusivo durante más de 100 ms en condiciones normales. Por ello, hemos llevado a cabo una serie de experimentos en los que una nube de burbujas crece por difusión en un agua sobresaturada de CO2 en microgravedad en la torre de caída del Centro Alemán de Tecnología Espacial Aplicada y Microgravedad (ZARM). En estos experimentos, se puede observar la evolución de la nube de burbujas durante más de 3 s, junto con sus interacciones y la competición entre ellas para acceder al CO2 disponible en el líquido. Primero, se describe la configuración experimental diseñada y puesta en marcha para realizar los experimentos junto con algunos resultados preliminares acerca del crecimiento individual de burbujas grandes y la evolución del volumen de gas de la nube. Más adelante, mostramos la existencia de varios regímenes donde la nube de burbujas presenta diferentes ratios de crecimiento en nuestros experimentos. Finalmente, presentamos un modelo simplificado que describe estos regímenes y su índice de crecimiento correspondiente, de forma cualitativa. En la segunda parte, estudiaremos experimentalmente la salida súbita de un disco circular situado en la superficie del agua. En ingeniería naval y oceánica, resulta esencial modelar la fuerza que debe soportar una estructura cuando impacta o sale del agua. Puesto que las simulaciones numéricas a gran escala generalmente no son prácticas para este propósito, a lo largo de los años se han desarrollado varios modelos analíticos o semianalíticos. Debido a la complejidad de los flujos de superficie libre involucrados, tanto los cálculos numéricos como los analíticos deben validarse experimentalmente. Con esta idea en mente, presentamos los resultados obtenidos de las medidas experimentales de la fuerza hidrodinámica que actúa sobre una placa que se levanta de la superficie del agua y que comienza a moverse hacia arriba repentinamente a una aceleración mucho mayor que la gravedad, a ≫ g. Además, incluiremos el efecto hidroelástico observado en los experimentos en la solución del problema asimétrico de salida rápida del agua. Nuestro trabajo se centra en los primeros instantes del movimiento de la placa, cuando la succión y las fuerzas de inercia son las más relevantes. Por lo tanto, se describirá la configuración experimental, luego compararemos los resultados experimentales con la teoría linealizada del problema de salida rápida del agua propuesta porKorobkin (2013). Finalmente, como consecuencia de las observaciones experimentales acerca de la interación hidroelástica entre el disco y el líquido, el problema de salida rápida del agua se reformula y se resuelve teniendo en cuenta este efecto.Programa de Doctorado en Mecánica de Fluidos por la Universidad Carlos III de Madrid; la Universidad de Jaén; la Universidad de Zaragoza; la Universidad Nacional de Educación a Distancia; la Universidad Politécnica de Madrid y la Universidad Rovira i VirgiliPresidente: Ignacio González Loscertales.- Secretario: Rocío Bolaños Jiménez.- Vocal: Alan Tassi

Drop tower setup to study the diffusion-driven growth of a foam ball in supersaturated liquids in microgravity conditions

The diffusion-driven growth of a foam ball is a phenomenon that appears in many manufacturing process as well as in a variety of geological phenomena. Usually these processes are greatly affected by gravity, as foam is much lighter than the surrounding liquid. However, the growth of the foam free of gravity effects is still very relevant, as it is connected to manufacturing in space and to the forma- tion of rocks in meteorites and other small celestial bodies. The aim of this research is to investigate experimentally the growth of a bubble cloud growing in a gas-supersaturated liquid in microgravity conditions. Here, we describe the ex- periments carried out in the drop tower of the Center of Ap- plied Space Technology and Microgravity (ZARM). In few words, a foam seed is formed with spark-induced cavitation in carbonated water, whose time evolution is recorded with two high-speed cameras. Our preliminary results shed some light on how the size of the foam ball scales with time, in particular at times much longer than what could be studied in normal conditions, i.e. on the surface of the Earth, where the dynamics of the foam is already dominated by gravity after several milliseconds

A separação natureza / cultura em crise O barequeo: R-e-existindo pela permanência no canyon do rio Cauca

Este escrito es el resultado de reflexiones realizadas desde una mirada compleja entre la geográfica critica, la ecología política y la antropología ecológica, lo cual implica tener una perspectiva de análisis sobre las interrelaciones y reciprocidades entre seres humanos y no humanos. Esto, en contextos específicos, donde se han generado conocimientos de acuerdo a las situaciones particulares que ha desatado la imposición del modelo capitalista y las luchas por su re-existencia. El mismo, trata sobre la configuración de subjetividades de las comunidades del cañón del río Cauca, en Antioquia, Colombia, especialmente en la búsqueda de patrimonialización como herramienta para salvaguardar el Barequeo como modo de vida. Esta búsqueda se produce durante el proceso de instalación de la hidroeléctrica Hidroituango, apoyada en la transición energética. Para la elaboración del trabajo, primero se hizo necesario realizar un breve análisis de la noción de naturaleza y la diferencia con el concepto de medio ambiente, categoría que, desde el esquema dual, irrumpe la vida de las poblaciones. Posteriormente, se abordó la estrategia glocal desde una perspectiva de lugar, la cual se ha generado en la defensa de la vida y el territorio; siendo el lugar quien dota de significado y permite pensar más allá del desarrollo impuesto. Finalmente, se realizó un acercamiento a lo que ha sido el proceso de pedido de patrimonialización, como articulación con el proyecto político de la organización en movimiento. La solicitud fue rechazada, pero en el proceso quedaron en evidencia las continuidades moderno/coloniales, que siguen gestionando la vida a partir de las clasificaciones eurocéntricas, raciales y patriarcales.Fil: Martínez Vega, Aimée Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Catamarca. Universidad Nacional de Catamarca. Centro de Investigaciones y Transferencia de Catamarca; Argentin

Historia de las ideas latinoamericanas en Colombia, motivo para repensar un proyecto de Valorización e Integración

El presente trabajo tiene como objetivo discutir que el desarrollo reciente de la historia de las ideas latinoamericanas en Colombia no facilita una auténtica apropiación de lo latinoamericano por dos motivos: a) considerar las fronteras "nacionales" como obstáculo para emancipar el cuerpo, la tierra y el intelecto y b) evitar la reflexión imprescindible acerca de las condiciones materiales, políticas y culturales que hacen posible la subsistencia de la población hasta sus aspiraciones educativas. El individualismo, el desconocimiento de la historia en Colombia, la integración regional considerada solo desde el terreno económico, la comparación comercial euro-norteamericana son factores que no permiten el dialogo intercultural basados en procesos de subjetivación, reconocimiento, memoria, valoración, concertación, promoción de diversidad de saberes y sentires y reivindicación de derechos individuales y colectivos. El método propuesto por el maestro Arturo Roig para el estudio de la historia de las ideas permitiría generar un "nosotros" que favorezca la apropiación de la historia de las ideas latinoamericanas, en un proceso de desintegración, valoración y reintegración, para ello se recurre a ejemplificar con los movimientos altermundistas ante el despojo y el extractivismo a gran escala. Ellos constituyen una alternativa capaz de generar cambios sociales a partir de la descolonización del cuerpo, la mente y el espíritu, reivindicando los aportes de los intelectuales nacidos y formados en "Nuestra América" que permitan reflexiones y acciones de integración latinoamericana.   In this paper we posit that the recent development of the history of Latin American ideas in Colombia hinders a real apprehension of the Latin American question due to: a) the consideration of the national boundaries as an obstacle in the emancipation of the body, the land, and the intellect; and b) the lack of fundamental reflection regarding material, political, and cultural conditions that make possible the existence of people and their educative aspirations. Individualism, ignorance of Colombian history, the belief that regional integration is solely an economical issue, and the commercial European-North American comparison are factors that impede an intercultural dialogue based on processes of subjetivation, acknowledgement, memory, valorization, agreement, promotion of knowledge and feelings diversity, and the claim of individual and collective rights. The method proposed by Arturo Roig for the study of history of ideas can generate a collective "us" that fosters the appropriation of the history of Latin American ideas within a process of disintegration-valorization-reintegration; to illustrate this we consider the "anti-globalization" movement in the face of plundering and large-scale extractivism, which constitutes an alternative possibility of social change based on the decolonization of body, mind, and spirit, vindicating the contributions of intellectuals born and raised in "Our America" while encouraging reflections and actions toward Latin American integration

Air entrapment and its effect on pressure impulses in the slamming of a flat disc on water

The presence of ambient air in liquid-slamming events plays a crucial role in influencing the shape of the liquid surface prior to the impact, and the distribution of loads created upon impact. We study the effect of trapped air on impact loads in a simplified geometry, by slamming a horizontal flat disc onto a stationary water bath at a well-controlled velocity. We show how air trapping influences pressure peaks at different radial locations on the disc, how the pressure impulses are affected and how local pressure impulses differ from those obtained from area-integrated (force) impulses at impact. More specifically, we find that the air layer causes a gradual buildup of the load before the peak value is reached, and show that this buildup follows inertial scaling. Further, the same localised pressure impulse at the disc centre is found to be lower than the corresponding (area-integrated) force impulse on the entire disc. While the (area-integrated) force impulses are close to the classical result of Batchelor (An Introduction to Fluid Dynamics, Cambridge University Press, 1967, § 6.10) and Glasheen & McMahon (Phys. Fluids, vol. 8, issue 8, 1996, pp. 2078-2083), the localised pressure impulses at the disc centre, where the trapped air layer is at its thickest, lie closer to the theoretical estimation by Peters et al. (J. Fluid Mech., vol. 724, 2013, pp. 553-580) for an air-cushioned impact.We acknowledge financial support from SLING (project number P14-10.1), which is partly financed by the Netherlands Organisation for Scientific Research (NWO). P.V.-M. acknowledges the support of the Spanish Ministry of Economy and Competitiveness through grants DPI2017-88201-C3-3-R and DPI2018-102829-REDT, partly funded with European funds

Growth of a bubble cloud in CO2-saturated water under microgravity

The diffusion-driven growth of a dense cloud of bubbles immersed in a gas-supersaturated liquid is a problem that finds applications in several modern technologies such as solvent-exchange micro-reactors, nanotechnology or the manufacturing of foamy materials. However, under Earth's gravity conditions, these dynamics can only be observed for a very limited time if the cloud is not attached to a surface, due to the action of buoyancy, i.e. of gravity effects. Here, we present experimental observations of the time evolution of dense bubble clouds growing in CO2-supersaturated water under microgravity conditions. We report the existence of three regimes where the bubble cloud exhibits different growth rates. At short times, each bubble grows independently following the Epstein–Plesset equation. Later on, bubbles start to interact with each other and their growth rate diminishes as they compete for the available CO2. When this happens, the growth rate slows down. This occurs earlier the deeper the bubble is in the cloud. Finally, at long times, only those bubbles on the husk continue growing. These regimes may be qualitatively described by a mathematical model where each individual bubble grows in the presence of a constellation of point mass sinks. Despite the model being only valid for dilute bubble clouds, its predictions are consistent with the experimental observations, even though the bubble clouds we observe are rather dense

Mapping the Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Banded Spherulites by Nanoindentation

Nanoindentation provides clear evidence that spherulite banding can be associated with a continuous modulation of mechanical properties from the more compliant peaks to the stiffer valleys. The structural arrangement in polymer-banded spherulites has intrigued scientists for many decades, and the debate has been recently intensified with the advent of new experimental evidence. The present paper approaches this issue by exploring the local mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-ringed spherulites via nanoindentation and discussing the confidence of the results. It was found that storage modulus and hardness across the banding morphology can be described as a sequence of regular oscillations with a periodicity that exactly matches the one observed using optical and atomic force microscopy. Results are consistent with the model of regular twisting of the lamellae, with flat-on arrangement in the low regions and edge-on lamellae in the crests.The authors wish to thank the MINECO (Ministerio de Economía y Competitividad), Spain, for funding the research reported under grants MAT2013-47898-C2-1-R (covering the costs to publish in open access) and MAT2012-36341. Patricia Enrique-Jimenez acknowledges MINECO for a FPI (Formación Personal Investigador) studentship. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Pouvoir et Action Publique: Cristallisation des Politiques Publiques et Prélude à la Solution des Problèmes Publics

Les politiques publiques ne sont pas des outils ambigus, mais plutôt la mise en œuvre de certaines orientations et styles de gouvernement; ceci est d'une importance transcendantale car, dans leur dimension fondamentalement empirique, les politiques publiques ont le pouvoir d’inverser, de renforcer ou d'inhiber la capacité d'autres mécanismes qui conduisent au bien-être individuel et collectif. En ce sens, l’objectif de cet article est d´analyser les aléas des variables de pouvoir et d'action publiques afin de  chercher les solutions aux problèmes publics à travers l’idéation, la formulation et la mise en œuvre des politiques publiques. Dans le cadre de cet article, nous n’entrerons pas dans des études de cas particuliers pour exemplifier notre argumentation. Utilisant une méthode d'analyse qualitative, l'article soutient que le pouvoir et l'action publique cristallisent la nature des solutions aux problèmes publics. Cela indique que les politiques publiques constituent de plus en plus, le cordon ombilical entre la société et l’État à travers l’exercice du pouvoir par le gouvernement. Nous concluons que les politiques publiques nécessitent d’une vision holistique, plus alignée sur les compétences multidimensionnelles, individuelles et collectives, tant du gouvernement que des citoyens.   Public policies are not ambiguous tools, but rather the implementation of certain directions and styles of government; this is of transcendental importance because, in their fundamentally empirical dimension, public policies have the power to reverse, enhance or inhibit the capacity of other mechanisms that lead to individual and collective well-being. In this sense, the objective of this article is to analyze the vagaries of the variables of power and public action in order to seek solutions to public problems through the ideation, formulation and implementation of public policies. In the context of this article, we will not go into specific case studies to exemplify our argument. Using a qualitative method of analysis, the article argues that power and public action crystallize the nature of the solutions to public problems. This indicates that public policy increasingly constitutes the umbilical cord between society and the state through the exercise of power by government. We conclude that public policies require a holistic vision, more aligned with the multidimensional, individual and collective skills of both government and citizens