José Luiz Lima de Azevedo

Uma revisão sobre a turbulência e sua modelagem

The movements are characterized by turbulent fluctuations in instantaneous speed, temperature and other scalars. As a consequence of these fluctuations, the turbulent state in fluid contributes significantly to transport momentum, heat and mass. Turbulence is defined as a state of the flow in which the time dependent variables exhibit irregular fluctuations which are seemingly random such that, in practice, only statistical properties can be recognized and subjected to analysis. The study of transport phenomena is greatly hampered by the presence of these fluctuations. Any simplification in the analysis of the effects of turbulence is extremely advantageous in physical, mathematical and numerical terms. The constant search for such simplifications is one of the main goals in the developing of new models of turbulence. This article aims to review the phenomenon of turbulence and its modeling, focusing on its theoretical foundations and on the main technical approaches used in the modeling of the phenomenon.

Os processos de conversão de energia nos oceanos: uma revisão do Diagrama de Lorenz

The energetic analysis is an important diagnostic tool for the identification of dynamic processes associated with events of energy conversion in the ocean. In brief, that analysis shows the energetic interactions which are taking place among the mean and eddy fields of a certain geophysical flow, as well as the transfers involved between the reservoirs of energy in the oceans. Those processes are detailed in the Lorenz Diagram which links, through four boxes, the reservoirs of the mean kinetic energy, eddy kinetic energy, mean potential energy and eddy potential energy of the flow. Moreover, the Diagram identifies the interactions that occur between those four energy forms, as well as the exchanges through the boundaries (sources and sinks). After an extensive review, we have identified that the specialized literature lacks in texts which detail the several mechanisms of energetic conversion among the main forms of energy in the oceans, with most publications detailing only part of those components. This article presents a detailed review on this subject, gathering information of several sources and having as main objective the step by step construction of the Lorenz Diagram, with their respective formulations. The discussion of each term of the Diagram is presented objectively thus enabling a better understanding of this tool, which is instrumental in summarizing the energy processes at a given area of the ocean.

O mecanismo de autopropulsão de vórtices oceânicos: uma revisão

Oceanic eddies are effective carriers of momentum, mass, heat, of chemical and biological characteristics associated generally with their place of origin. These features exercise influence on global circulation, in the distribution of large-scale water masses and in the biology of the oceans. This influence does not only involve the transfer of energy and properties associated with the place of origin of the eddy but also their strong performance in mixing processes. The motion of eddies across the oceans are primarily driven by three factors: the self-propulsion which is intrinsic to the feature and moves it towards the west; the advection by others currents and the influence of eddies nearby. This work focuses on the first point, where the self-propulsion of isolated eddies is widely reviewed and discussed. The expression that allows the approximate calculation of the translation speed of isolated vortices is deduced. The basic equations (shallow water, the Bernoulli function and integrated meridional momentum) required for this development are presented and discussed as well as the meridional forces that act on these features in motion, where the mathematical formalism associated with each of them is also reviewed. This review shows that all isolated vortices are self-propelled towards the west, regardless of the hemisphere considered. It also shows that three meridional forces act on the eddies in motion: (1) the β force, due to the difference of the Coriolis parameter between the northern and southern hemispheres of the eddy, (2) the Coriolis force and the (3) ambient force, due to the action of the external fluid on the isolated eddy. Several analyses can be made with respect to these forces and this review also presents, as an example, a comparison of the β forces acting in anticyclonic and cyclonic eddies, with the same characteristics, moving in the southern hemisphere. It is concluded that the β force in the former is greater than the force in the latter. This study also comments aspects related with the balance of forces on particles rotating inside the eddy, where the gradient, geostrophic, quasi-geostrophic and cyclostrophic balances are discussed.