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Mathematical models of biofluid flows in compliant ducts

Kizilova N., Hamadiche M., Gad-el-Hak M.

Archives of Mechanics

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2012

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Vol. 64, nr 1

65-65

EN

A literature review of liquid and gas flows in compliant tubes, ducts and cavities in living bodies is presented. The common features of such flows as determined by fluid–structure interactions and system instabilities are described. The corresponding mathematical models are given and theoretical and numerical results are discussed. Original new results on flow stabilization in layered viscoelastic tubes in biosystems are also presented.

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The art and science of large-scale disasters

Gad-el-Hak M.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2009

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Vol. 57, nr 1

3-34

EN

The subject of large-scale disasters is broadly introduced in this article. Both the art and science of predicting, preventing and mitigating natural and manmade disasters are discussed. A universal, quantitative metric that puts all natural and manmade disasters on a common scale is proposed. Issues of prediction, control and mitigation of catastrophes are presented. The laws of nature govern the evolution of any disaster. In some cases, as for example weather-related disasters, the first-principles laws of classical mechanics could be written in the form of field equations, but exact solutions of these often nonlinear differential equations are impossible to obtain particularly for turbulent flows, and heuristic models together with intensive use of supercomputers are necessary to proceed to a reasonably accurate forecast. In other cases, as for example earthquakes, the precise laws are not even known and prediction becomes more or less a black art. Management of any type of disaster is more art than science. Nevertheless, much can be done to alleviate the resulting pain and suffering. The expansive presentation of the broad field of large-scale disasters precludes a detailed coverage of anyone of the many topics touched upon. Three take-home messages are conveyed, however: a universal metric for all natural and manmade disasters is presented; all facets of the genre are described; and a proposal is made to view all disasters as dynamical systems governed for the most part by the laws of classical mechanics.

3

Differences between liquid and gas transport at the microscale

Gad-el-Hak M.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2005

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Vol. 53, nr 4

301-316

EN

Traditional fluid mechanics edifies the indifference between liquid and gag flows as long as certain similarity parameters - most prominently the Reynolds number - are matched. This may or may not be the case for flows in nano- or microdevices. The customary continuum, Navier-Stokes modelling is ordinarily applicable for both air and water flowing in macrodevices. Even for common fluids such as air or water, such modelling bound to fail at sufficiently small scales, but the onset for such failure is different for the two forms of matter. Moreover, when the no-slip, quasi-equilibrium Navier - Stokes system is no longer applicable, the alternative modelling schemes are different for gases and liquids. For dilute gases, statistical methods are applied and the Boltzmann equation is the cornerstone of such approaches. For liquid flows, the dense nature of the matter prec1udes the use of the kinetic theory of gases, and numerically intensive molecular dynamics simulations are the only alternative rooted in first principles. The present artic1e discusses the above issues, emphasizing the differences between liquid and gag transport at the microscale and the physical phenomena unique to liquid flows in minute devices.