1,721,080 research outputs found
Aerodinamica
No full textQuesto testo è rivolto agli studenti del secondo anno del Corso di Laurea in Ingegneria Aerospaziale (Nuovo Ordinamento).
I capitoli iniziali del libro descrivono alcuni aspetti teorici generali della fluidodinamica fino alla definizione delle equazioni per lo studio del moto di un fluido newtoniano. Il capitolo 4 e' dedicato ai moti irrotazionali mentre i successivi 5 e 6 descrivono rispettivamente l'applicazione della teoria potenziale al flusso intorno ad un profilo alare sottile e ad un'ala finita. Il capitolo 7 illustra alcuni aspetti di base della teoria dello strato limite. Gli ultimi tre capitoli sono invece dedicati allo studio dei flussi comprimibili e ne illustrano elementi fondamentali come l'onda d'urto, il moto all'interno di ugelli oppure intorno a profili alari.
Al termine di ciascun capitolo sono proposti alcuni esercizi per la verifica dell'apprendimento degli argomenti trattati
Green's function method for axisymmetric flows: analysis of the Taylor-Couette flow
No full textA numerical method for the solution of the Navier-Stokes equations in rotationally symmetric flow problems is presented. The numerical procedure is based on a boundary integral equation formulation with the fundamental solution of the Stokes' equation accounting for the rotational symmetry. The proposed methodology has been applied to the study of the Taylor-Couette flow between two concentric rotating cylinders of infinite axial length. A comparison with the available theoretical, experimental or numerical findings is performed to evaluate the accuracy of the present results. As predicted by the analytical theory and confirmed by the experiments, multiple solutions that are found for Reynolds numbers higher than the critical value, indicate the proposed methodology as a useful tool to get physical insight on the instabilities occurring in the solution of the Navier-Stokes equations. © 1990 Springer-Verlag
A boundary integral equation method for axisymmetric viscous flows
No full textA boundary integral equation formulation is presented in this paper for the analysis of steady viscous flows whose velocity fields possess rotational symmetry. For flows described by linear equations the BIE method results particularly well suited the flowfield variables being expressed in terms of some quantities on the domain contour. The integral representation for the axisymmetric Stokes' flow is reported and the Green's functions needed to accomplish the solution are derived and discussed. Finally further examples of applications are given when the nonlinear terms play a relevant role in defining the structure of the motion
Application of multipole expansion technique to two-dimensional nonlinear free surface flows.
No full textThe original idea by Rokhlin (1985) to rapidly solve the Laplace equation is applied here for studying nonlinear free-surface flows. The boundary integral equations for the velocity field are discretized through the Euler-McLaurin quadrature formula, which, in spite of its simplicity, displays spectral convergence properties for regular boundary data. In order to solve the discretized boundary integral equations, an iterative solver for algebraic systems is coupled to a fast summation technique based on the multipoles expansion of the influence coefficients. The resulting algorithm allows for a small size of the code (O(N)) and fast computation (O(Nlog N)) without affecting the original convergence properties. Typical long-time evolution and large-scale computations, which often arise in nonlinear free-surface flows, are discussed to show the effectiveness of the developed approach
Unsteady viscous flows about bodies: vorticity release and forces
No full textThe force (drag and lift) exerted on a body moving in a viscous fluid is expressed via the 'free' and 'bound' vorticity moments, and the role of vortex shedding is discussed. The formulation encompasses classical, inviscid flows, and leads to efficient computational methods. Numerical results for a few prototype flows are presented
Aquatic locomotion for self-propelled fishlike bodies and different styles of swimming
No full textFish swimming is an intriguing subject of interest in fluid mechanics at the border with other disciplines in the field of environmental sciences. The main complexity is given by the interaction between the fish body and the unbounded fluid domain, otherwise at rest. The theoretical approach has to consider the full body-fluid system to obtain from the exchanged internal forces the whole motion, i.e. locomotion plus recoil displacements, which define, together with the prescribed body deformation, the free swimming behavior. The impulse formulation allows for an easy calculation of the potential contribution, related to the added mass, and of the vortical contribution related to bound and released vorticity. A simple two- dimensional and non-diffusive model is adopted for the numerical simulations to generate neat results able to clarify several physical phenomena. The aim is a unified procedure for both undulatory and oscillatory swimming to obtain valid answers for cruising speed and expended energy, hence for the performance in terms of the cost of transport. The paper describes the theoretical aspects of the model within the context of the relevant literature and summarizes the more significant results obtained recently by the research group of the authors
Wave impact with air entrapped in shallow water sloshing flow
No full textLNG carriers with prismatic membrane tanks are more exposed than other carriers to violent sloshing phenomena resulting large impact loads [1]. Because of the large and clean tanks used in LNG ship, low lling depth conditions are of concern for the maximum loads occurring on the walls
Structural study of magnesioaxinite and its crystal-chemical relations with axinite-group minerals.
No full textThe magnesium end-member of the axinite mineral group was studied by single-crystal X-ray diffraction and refined in the P (1) over bar space group (R = 2.2 %). Cell parameters are a = 7.1381(3) Angstrom, b = 9.1626(4) Angstrom, c = 8.9421(4) Angstrom, alpha = 91.903(4)degrees beta = 98.105(3)degrees gamma = 77.468(4)degrees, V = 565.21(4) Angstrom (3). Magnesioaxinite is isostructural with (Mn,Fe)axinites, but shows structural features which may account for the compositional gap observed between magnesioaxinite and manganaxinite. Electron and ion microprobe analyses and refined site occupancies gave the following crystal chemical formula: ([6])[Ca-2.00(Ca1.95Mn0.03)(Mg1.92Mn0.04V0.03Cr0.01)Al2.00Al2.00]([4])[B-2.00Si8.02O30](OH1.9O0.1), very close to the ideal Mg end-member. The octahedron occupied by Mg ([Mg-O] = 2.17 Angstrom) is distorted and closely connected with both tetrahedral and octahedral structure components. Its modification (when Mg substitutes for Fe2+ and Mn) causes lattice deformations and also influences T-O-T angles and geometry of octahedral sheets
Effect of free surface radiation in axisymmetric thermocapillary flows
No full textA theoretical and computational model which considers the interface boundary conditions with the required accuracy, has been previously presented for plane two dimensional flows. The model is here applied to axisymmetric flows and physical conditions simulating the experiments conducted by other authors at ground level for very small characteristic dimensions of the floating zones. In particular the effect of the free surface radiation, coupled with several different imposed temperature gradients between the solid walls, has been considered. The influence of the free surface diffusivity coefficients on the bulk convective flows is also analyzed in the case of pure radiation
Site distribution of Fe2+ and Fe3+ in elbaite-schorl-dravite tourmalines by 57Fe Mössbauer Spectroscopy.
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