A Contribution to Time-Dependent Damage Modeling of Composite Structures

International audienceThe paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite 2 material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue

Caractérisation et analyse de tubes composites carbone / époxyde = Characterization and Analysis of Carbon Fibre / Epoxy Composite Tubes

National audienceLes propriétés mécaniques d'un matériau composite de type résine époxyde renforcée par des fibres de carbone sont déterminées par des essais sur des éprouvettes tubulaires. Trois empilements - [±15°], [±45°], et [±75°] - sont utilisés pour caractériser le comportement dans la direction des fibres, dans la direction transverse, et en cisaillement. Des essais quasi-statiques et en fluage sont effectués. Les résultats sont comparés aux approches analytiques

An Optimization method for the Configuration of Inter Array Cables for Floating Offshore Wind Farm.

International audienceIFP Energies nouvelles (IFPEN) is involved for many years in various projects for the development of floating offshore wind turbines. The commercial deployment of such technologies is planned for 2020. The present paper proposes a methodology for the numerical optimization of the inter array cable configuration. To illustrate the potential of such an optimization, results are presented for a case study with a specific floating foundation concept [1]. The optimization study performed aims to define the least expensive configuration satisfying mechanical constraints under extreme environmental conditions. The parameters to be optimized are the total length, the armoring, the stiffener geometry and the buoyancy modules. The insulated electrical conductors and overall sheath are not concerned by this optimization. The simulations are carried out using DeepLines TM , a Finite Element software dedicated to simulate offshore floating structures in their marine environment. The optimization problem is solved using an IFPEN in-house tool, which integrates a state of the art derivative-free trust region optimization method extended to nonlinear constrained problems. The latter functionality is essential for this type of optimization problem where nonlinear constraints are introduced such as maximum tension, no compression, maximum curvature and elongation, and the aero-hydrodynamic simulation solver does not provide any gradient information. The optimization tool is able to find various local feasible extrema thanks to a multi-start approach, which leads to several solutions of the cable configuration. The sensitivity to the choice of the initial point is demonstrated, illustrating the complexity of the feasible domain and the resulting difficulty in finding the global optimum configuration

CONTRIBUTION A L'ETUDE DE DURABILITE D'UNE STRUCTURE TRAVAILLANTE EPAISSE EN COMPOSITES DANS LE DOMAINE DU TRANSPORT FERROVIAIRE

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

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

Influence of Hydrodynamic Modeling Assumptions on Floating Wind Turbine Behaviour

This paper aims to highlight the key physical aspects that govern the dynamic behavior of a trifloater based floating wind turbine and the modeling assumptions- with a focus on hydrodynamics modeling and platform/tower interface flexibility- required to properly take into account the coupled hydrodynamics and aerodynamics effects in the fatigue analysis. Three selected load cases are simulated with different hydrodynamics models and the results are compared to each other. On this specific floating structure, Morison formulation seems to provide very similar results compared to other hydrodynamic modeling approaches based on potential flow theory and a more consistent way to model the floater damping. The use of a hybrid formulation including Morison damping on the columns instead of a quadratic damping matrix is an interesting alternative since it gathers the advantages of the different models

Comparaison de modèles FEM à un essai de tension-flexion d'un câble d'ancrage offshore

International audienceUne piste de simplification des designs de lignes d’ancrage dans l’ingénierie offshore consiste à remplacer les chaines en tête de ligne par des câbles monotorons acier. Cette étude documente les simulations d’un essai de cycles de flexion d’un câble en tension avec 3 modèles éléments finis différents capables de prendre en compte les interactions de contact et frottement entre les fils. Nous comparons les réponses du calcul implicite avec MULTIFIL, d’Abaqus Explicit avec le contact Edge/Edge et de la routine utilisateur de la thèse de F. Bussolati [1] avec Abaqus/Standard