Statistical moments predictions for a moored floating body oscillating in random waves

Two statistical techniques are developed to predict the statistical moments of the horizontal motion of a floating moored dock, known as catenary anchor leg mooring (CALM), loaded by hydrodynamic random forces. The dock is represented by a lumped mass, the mooring cables by equivalent nonlinear springs and the hydrodynamic forces are modelled by a modified Morison equation. The model of the floating dock leads to a nonlinear ordinary differential equation. Although the problem could be approached by a direct numerical integration, e.g. by Monte-Carlo simulations, because of the stochastic nature of the excitation, this would imply a large number of runs to produce results of some statistical significance. In the present paper an alternative solution is based on the development of two more efficient techniques to predict the relevant statistical moments of the dock response. The first method, called CPSP (conventional perturbation-statistical perturbation), is based on the application of two subsequent perturbation techniques, the first relying on a classical perturbation method, the second on a statistical perturbation approach. The second method, called SLSP (statistical linearization-statistical perturbation), combines indeed a statistical linearization approach together with a statistical perturbation approach. The procedures allow the linearization of the cables restoring forces as well as of the hydrodynamic load and they can be easily generalized to be applied to different dock configurations or to systems of different physical nature. The results, compared with those obtained by a Monte-Carlo simulations, show, in terms of statistical moments of the dock response, a satisfactory agreement

Energy flow uncertainties in vibrating systems: definition of a statistical confidence factor

A method for evaluating the energy flow confidence level in vibrating systems with randomly perturbed parameters is presented. The energy flow is predicted in terms of the mobilities of resonant subsystems or by the solution of the velocity wave field for non-resonant subsystems. The statistical moments of the energy flow are calculated by a perturbation technique and a confidence factor is defined as the ratio between mean and standard deviation. The properties of the confidence factor are investigated by a theoretical analysis as a function of frequency. Three cases are studied to compare the confidence factor obtained theoretically with a prediction provided by a Monte-Carlo simulation

The role of biomechanics in the assessment of carotid atherosclerosis severity: a numerical approach

Numerical fluid biomechanics has been proved to be an efficient tool for understanding vascular diseases including atherosclerosis. There are many evidences that atherosclerosis plaque formation and rupture are associated with blood flow behavior. In fact, zones of low wall shear stress are vivid areas of proliferation of atherosclerosis, and in particular, in the carotid artery. In this paper a model is presented for investigating how the presence of the plaque influences the distribution of the wall shear stress. In complement to a first approach with rigid walls, an FSI model is developed as well to simulate the coupling between the blood flow and the carotid artery deformation. The results show that the presence of the plaque causes an attenuation of the WSS in the after-plaque region as well as the emergence of recirculation areas

Renormalization group study of marginal ferromagnetism

When studying the collective motion of biological groups a useful theoretical framework is that of ferromagnetic systems, in which the alignment interactions are a surrogate of the effective imitation among the individuals. In this context, the experimental discovery of scale-free correlations of speed fluctuations in starling flocks poses a challenge to the common statistical physics wisdom, as in the ordered phase of standard ferromagnetic models with $\mathrm{O}(n)$ symmetry, the modulus of the order parameter has finite correlation length. To make sense of this anomaly a novel ferromagnetic theory has been proposed, where the bare confining potential has zero second derivative (i.e.\ it is marginal) along the modulus of the order parameter. The marginal model exhibits a zero-temperature critical point, where the modulus correlation length diverges, hence allowing to boost both correlation and collective order by simply reducing the temperature. Here, we derive an effective field theory describing the marginal model close to the $T=0$ critical point and calculate the renormalization group equations at one loop within a momentum shell approach. We discover a non-trivial scenario, as the cubic and quartic vertices do not vanish in the infrared limit, while the coupling constants effectively regulating the exponents $\nu$ and $\eta$ have upper critical dimension $d_c=2$, so that in three dimensions the critical exponents acquire their free values, $\nu=1/2$ and $\eta=0$. This theoretical scenario is verified by a Monte Carlo study of the modulus susceptibility in three dimensions, where the standard finite-size scaling relations have to be adapted to the case of $d>d_c$. The numerical data fully confirm our theoretical results.Comment: 13 pages, 6 figures. Added numerical simulation

Vibroacoustic optimization using a statistical energy analysis model

In this paper, an optimization technique for medium-high frequency dynamic problems based on Statistical Energy Analysis (SEA) method is presented. Using a SEA model, the subsystem energies are controlled by internal loss factors (ILF) and coupling loss factors (CLF), which in turn depend on the physical parameters of the subsystems. A preliminary sensitivity analysis of subsystem energy to CLFs is performed to select CLFs that are most effective on subsystem energies. Since the injected power depends not only on the external loads but on the physical parameters of the subsystems as well, it must be taken into account under certain conditions. This is accomplished in the optimization procedure, where approximate relationships between CLFs, injected power and physical parameters are derived. The approach is applied on a typical aeronautical structure: the cabin of a helicopter

Selection of Interface DoFs in Hub-blade(s) Coupling of Ampair Wind Turbine Test Bed

International audienceSubstructure coupling is an important tool in several applications ofmodal analysis. It is particularly relevant in virtual prototyping of complex systems and responds to actual industrial needs, especially in an experimental context. Furthermore, the reverse problem, the decoupling of a substructure from an assembled system, arises when a substructure cannot be tested separately but only when coupled to neighboring substructures, a situation often encountered in practice. In this paper, the dynamic behavior of the Ampair test bed wind turbine rotor, made by three blades - each one bolted to the hub at three points - is analyzed. The aim is both to identify the dynamic behavior of the rotor starting from the frequency response functions (FRFs) of blades and hub, and to select a reduced set of relevant DoFs to represent the interface between blades and hub. FRFs to be used in the coupling procedure are obtained starting from FE model of each substructure, by using a super-element based computational approach. The decoupling problem, with the aim of identifying the dynamic behavior of each blade from the FRFs of the assembled rotor and of the hub, is also considered

Le ferromagnétisme marginal à basse température explique les corrélations à longue portée dans les essaims d'oiseaux

We introduce a new ferromagnetic model capable of reproducing one of the most intriguing properties of collective behaviour in starling flocks, namely the fact that strong collective order coexists with scale-free correlations of the modulus of the microscopic degrees of freedom, that is, the birds´ speeds. The key idea of the new theory is that the single-particle potential needed to bound the modulus of the microscopic degrees of freedom around a finite value is marginal, that is, it has zero curvature. We study the model by using mean-field approximation and Monte Carlo simulations in three dimensions, complemented by finite-size scaling analysis. While at the standard critical temperature, Tc, the properties of the marginal model are exactly the same as a normal ferromagnet with continuous symmetry breaking, our results show that a novel zero-temperature critical point emerges, so that in its deeply ordered phase the marginal model develops divergent susceptibility and correlation length of the modulus of the microscopic degrees of freedom, in complete analogy with experimental data on natural flocks of starlings.Nous introduisons un nouveau modèle ferromagnétique capable de reproduire l'une des propriétés les plus intrigantes du comportement collectif des essaims d'oiseaux, à savoir le fait qu'un ordre collectif fort coexiste avec des corrélations sans échelle du module des degrés de liberté microscopiques, à savoir les vitesses des oiseaux. L'idée-clé de la nouvelle théorie est que le potentiel à un corps nécessaire pour lier le module des degrés de liberté microscopiques autour d'une valeur finie est marginal, c'est-à-dire qu'il a une courbure nulle. Nous étudions le modèle en utilisant l'approximation du champ moyen et les simulations de Monte-Carlo en trois dimensions, complétées par l'analyse à l'échelle finie. Alors qu'à la température critique standard, Tc , les propriétés du modèle marginal sont exactement les mêmes que celles d'un ferromagnétique normal avec rupture de symétrie continue, nos résultats montrent qu'un nouveau point critique à température nulle émerge, de sorte que, dans sa phase profondément ordonnée, le modèle marginal développe une susceptibilité divergente et une longueur de corrélation du module des degrés de liberté microscopiques, en analogie complète avec les données expérimentales sur des essaims naturels d'oiseaux.Fil: Cavagna, Andrea. Consiglio Nazionale delle Ricerche; ItaliaFil: Culla, Antonio. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; ItaliaFil: Di Carlo, Luca. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; ItaliaFil: Giardina, Irene. Consiglio Nazionale delle Ricerche; Italia. Università Degli Studi Di Roma "la Sapienza". Dipartimento Di Sanita Publica E Malattie Infetive.; Italia. Istituto Nazionale Di Fisica Nucleare.; ItaliaFil: Grigera, Tomas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; Argentin

Surface unmanned multipurpose research marine vehicle: SUNMARE Project

This paper presents the preliminary activities undertaken for the research project SUNMARE (Surface UNmanned multipurpose research MARine vEhicle), which aims at the development of an innovative autonomous platform for marine, oceanographic, lacustrine, and submerged/semi-submerged cultural heritage monitoring/measurements. SUNMARE is a modular ship comprising of a mother unmanned ship and a smaller autonomous vehicle. Through an innovative fully autonomous launch and recovery system (LARS), the Unmanned surface vehicle (USV) can detach and reconnect to the mother ship. The architecture of the LARS and the on-purposely designed control algorithms are here presented together with statistical recovery success analysis concerning the autonomous dynamic connection of the vehicles, so to assess the reliability of the system

[Montreal 1976] [Material gráfico]

Contiene fotografías pertenecientes al archivo fotográfico del diario "Región", publicadas entre 1974 y 1976, aunque la mayoría en 1976Todas las fotografías firmadas por Foto E. Gar (Oviedo), Cifra Gráfica, y EF