Interdependence of Flow and Shape Morphological Dynamics For Flow-Induced Erosion of Bluff Bodies

Flow-induced erosion encompasses all processes in which fluid-solid interactions result in the removal and transport of material from the solid. The removed material may change its physical state and/or chemical composition and may be redeposited onto the solid body or advected away by the fluid and deposited elsewhere. Common to all flow induced erosion processes is that they involve an eroding surface, and eroding agent, and a fluid flow which delivers the eroding agent to the eroding surface. Consequently, the study of erosion is difficult as it requires detailed knowledge of the material, mechanical, and/or thermophysical properties of the eroding surface; the transport mechanisms that deliver the eroding agent to the eroding surface; and the transport mechanisms that entrain and advect the eroded material into and within the fluid flow. This difficulty is compounded by the fact that that there is a feedback coupling between the eroding surface and the fluid dynamics that control the transport mechanisms important to erosion. Specifically, during erosion, surface morphological changes to the eroding surface will alter the flow field thereby increasing or decreasing the rate at which the eroding agent is delivered to the eroding surface. This in turn alters the surface morphology. Thus a complex feedback cycle exists between the fluid and surface dynamics. The study of this feedback cycle has received little attention in the fluid mechanics community. This relative neglect is understandable due to its non-equilibrium nature, yet surprising when one considers how much erosion by the action of a flow is an integral part of major scientific and engineering fields, for example geophysics, environmental, manufacturing, and aerospace. The underlying research objective of this dissertation is to better understand the two-way coupling between an eroding body and the surface flux of the eroding agent by evaluating the shape dynamics of eroding bluff bodies through the erosion process. The problem is challenging since, as described above, the surface flux of the eroding agent will vary as the surface morphology of the eroding body evolves. In order to investigate the complex interdependence between the flow and surface morphology of an eroding body during flow-induced erosion, physical ablation and dissolution experiments will be performed and existing numerical datasets will be analyzed to: (i) re-evaluate existing scaling laws regarding geometric properties (cross-sectional area, wetted perimeter, and curvature) of bluff bodies undergoing erosion in (a) uniform, unidirectional flow, (b) in spatially and temporally varying flow, and (c) in convectively driven flow; (ii) identify a shape parameter of the eroding surface that is well-correlated with local evolutional changes to the eroding agent surface flux; and (iii) develop a simple feedback erosion model that bypasses the fluid dynamics and adjusts the local eroding agent surface flux based on the evaluation of the identified shape parameter. The focus on the erosion of bluff bodies was chosen because, in principle, it is more amenable to the study of the erosion feedback cycle as the evolution of the shape dynamics and morphological changes to the surface of the eroding bluff body are a direct result of the, unknown, instantaneous magnitude of the local eroding agent surface flux. Since the evolution of the local eroding agent surface flux is a direct consequence of the feedback from the eroding surface on the flow dynamics, an improved understanding of the erosion feedback cycle is possible by evaluating only the morphological changes to the surface of the eroding bluff body

Managing the environment and metamorphoses of the State: the French experience

This article examines the evolution of the State’s role in management of the environment. The French experience, characterised by a highly-centralised State, presents researchers with a situation where anypermanence, like any change, tends to be extreme. Therefore it acts as a starting point for our analysis of changes in the State’s role in the management of nature, which was formerly considered as a resource to be exploited, and is now redefined as an environment to be protected. In particular, diachronic analysis enables us to grasp the dynamics of these social changes. On the basis of an interdisciplinary exchange between a historian and a sociologist, this article suggests that we should qualify theories of the disappearance of the State by giving ourselves the means to differentiate, in management of theenvironment, what is new and what is not, by highlighting the capacity for “integration of criticism” (BOLTANSKI; CHIAPELLO, 1999) by institutions. The environment is an instrument of hybridisation that questions old dichotomies: between nature and culture, between local and national, between the particular and the general, between vernacular knowledge and scientific knowledge. This questioning tends to deprive science and politics of their respective monopolies as representatives of nature and of society. Against this background, the central State becomes a manager of socio-natural diversity, thetechnocratic State gives a voice to local know-how, and the State concedes a certain plurality to the general public interest of which it no longer has quite a complete monopoly. The State is no longer quite what it was, in its role and its functioning, but the State endures. Thus, the society is changing, but the categories of the XX° century are not totally obsolete yet

Éléments pour une problématique de l'histoire du risque. Du risque accepté au risque maîtrisé. Représentations et gestion du risque d'inondation en Camargue, XVIIIe-XIXe siècles

La recherche de la sécurité des biens et des personnes nous est si familière qu'elle paraît aller de soi et ne dépendre que de l'évolution des techniques qui permettent des protections plus ou moins efficaces. Or, dès 1956, dans un article des Annales, Lucien Febvre préconisait de se pencher sur l'histoire du sentiment de sécurité. Pour lui la perception de la sécurité variait dans le temps et il montrait que sous l'Ancien Régime elle résidait essentiellement dans la confiance en Dieu...

Éléments pour une problématique de l’histoire du risque. Du risque accepté au risque maîtrisé. Représentations et gestion du risque d’inondation en Camargue, XVIIIe-XIXe siècles. Mémoire pour l’Habilitation à la direction de recherches

La recherche de la sécurité des biens et des personnes nous est si familière qu’elle paraît aller de soi et ne dépendre que de l’évolution des techniques qui permettent des protections plus ou moins efficaces. Or, dès 1956, dans un article des Annales, Lucien Febvre préconisait de se pencher sur l’histoire du sentiment de sécurité. Pour lui la perception de la sécurité variait dans le temps et il montrait que sous l’Ancien Régime elle résidait essentiellement dans la confiance en Dieu. Plus r..

Management of COVID-19 in the community and the role of primary care: how the pandemic has shone light on a fragmented health system

[Extract] The Australian health care system is well regarded on the global stage in terms of the balance between investment in health care and outcomes delivered, particularly in terms of universal access, quality and safety.1 However, there is considerable fragmentation and poor coordination of care and communication between hospitals and primary care, which limits further improvement.2, 3 Geographical barriers, workforce shortages and issues relating to acceptability of services limit health care access for residents of rural, regional and remote communities, Aboriginal peoples and Torres Strait Islanders, and together with an inadequate focus on prevention, limit progress towards health equity. Australian responses to the coronavirus disease 2019 (COVID-19) pandemic through both public health responses and the acute health sector have been viewed as among the best in the world. Nevertheless, challenges in the structure, organisatIon and financing of the Australian health care system have been brought into stark relief by the evolution of responses to the pandemic

Dependability of Aggregated Objects, a pervasive integrity checking architecture

International audienceRFID-enabled security solutions are becoming ubiquitous; for example in access control and tracking applications. Well known solutions typically use one tag per physical object architecture to track or control, and a central database of these objects. This architecture often requires a communication infrastructure between RFID readers and the database information system. Aggregated objects is a different approach presented in this paper, where a group of physical objects use a set of RFID tags to implement a self-contained security solution. This distributed approach offers original advantages, in particular autonomous operation without an infrastructure support, and enhanced security

Measurement errors in body size of sea scallops (Placopecten magellanicus) and their effect on stock assessment models

Body-size measurement errors are usually ignored in stock assessments, but may be important when body-size data (e.g., from visual sur veys) are imprecise. We used experiments and models to quantify measurement errors and their effects on assessment models for sea scallops (Placopecten magellanicus). Errors in size data obscured modes from strong year classes and increased frequency and size of the largest and smallest sizes, potentially biasing growth, mortality, and biomass estimates. Modeling techniques for errors in age data proved useful for errors in size data. In terms of a goodness of model fit to the assessment data, it was more important to accommodate variance than bias. Models that accommodated size errors fitted size data substantially better. We recommend experimental quantification of errors along with a modeling approach that accommodates measurement errors because a direct algebraic approach was not robust and because error parameters were diff icult to estimate in our assessment model. The importance of measurement errors depends on many factors and should be evaluated on a case by case basis