Estimates of fracture density and uncertainties from well data

International audienceThis paper aims at building a method to estimate the probability law governing the 3D fracture density of a fractured rock conditioned to the number of traces observed on a borehole image when the spatial distribution of fracture centers is assumed to follow a Poisson process. A closed-form expression of this law, allowing to calculate its mean value as well as a confidence interval, is derived in both cases of a lineic well (scanline) and a cylindrical well. The latter is better adapted to the situation of fracture size of the same order of magnitude as the well radius, which enables the presence of partial traces. In particular, the method takes into account the bias in the density estimate due to the fact that a fracture may cut the well along two distinct traces according to the considered fracture size. Monte Carlo simulations finally show a good agreement with the theoretical results of mean density and confidence interval

Un modèle éléments finis avec contact et frottement en petits glissements pour la tension et la flexion d'un câble spiralé monotoron

National audienceEn considérant que les glissements au sein d’un câble restent petits, même lors de flexion avec des rayons de courbure d’une dizaine de mètres, nous proposons un nouveau modèle formulant le contact et le frottement entre des poutres, sans réactualisation de l’appariement de contact défini à l’état initial. Cette particularité offre un gain de 25 en temps de calcul et en robustesse par rapport aux modèles proposés dans la littérature. La distribution des tensions au sein du câble reste comparable à celle déterminée par des modèles poutre-poutre formulés en grand glissement

Robust implementation of contact under friction and large sliding with the eXtended finite element method

International audienceAn X-FEM formulation is proposed for the case of large sliding frictional interfaces. A continuous augmented Lagrangian framework is adopted for contact and friction. We provide an algorithm for the selection of an appropriate discrete space for the Lagrange multipliers, accounting for the transition between contact and free zones, and also between sliding and adherent zones. A 3D numerical test is realized with Code_Aster free software for the compression of a cylinder cut along a radial section and shows the ability of the model to capture such transitions

A New Finite Element Model of Spiral Strand Wire Ropes for Fatigue Life Estimate of a Mooring Line

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A New Fully Detailed Finite Element Model of Wire Rope for Fatigue Life Estimate of a Mooring Line

International audienceSpiral strand wire ropes are commonly used in the mooring system of offshore structures. When dealing with the fatigue limit state, engineers have to consider many different load cases, according to the variability of the environmental state. This usually prevents the use of any detailed numerical model of the mooring lines. In this paper, we propose a new method to evaluate with an affordable computational cost the detailed mechanical stress state in different parts of the wire ropes used for mooring a floating offshore wind turbine. We first compute tension and bending history in the mooring, with the hydrodynamic software Deeplines, assuming for simplification stationary aerodynamic loads on the floater. These time series are then accounted for in a novel Finite Element Model of the spiral strand, with small sliding among the wires. The obtained kinematics and stress state of the wires can then feed a fatigue law based on fretting fatigue, which has been experimentally evidenced to condition the fatigue life of spiral strand wire ropes. The potential of this method is illustrated with an application to a cylinder-like shape floater equipped with 3 pairs of catenary mooring lines. It is shown that bending and tension histories do not significantly depend on the wire rope bending stiffness