This paper presents a novel method for the identification of the parameters governing Fickian moisture diffusion in composite materials. In the first part of the manuscript, the theoretical background is given and closed-form solutions are produced for 3D Fickian diffusion. Then, the different existing identification alternatives are reviewed and a novel procedure is proposed that takes advantage of all the gravimetric curve data points instead of just initial slope and saturation. The method relies on the solution of an optimization problem. In the second part of the paper, validation of this identification technique is performed from simulated gravimetric curves. The main advantage of the method when compared to previously published materials is that diffusion coefficients and saturation level can be identified from gravimetric curves obtained from unsaturated coupons. This is particularly useful when considering thick coupons that will take a long time to saturate or when non-Fickian diffusion mechanisms occur after some time. Finally, the method is applied to experimental results obtained from glass/epoxy composites. It is shown that although the diffusion of moisture in the composite is basically non-Fickian, it can be considered Fickian up to about 10 days and that these data are sufficient to retrieve the 3D diffusion coefficients as well as the Fickian saturation level.

Floating offshore wind offers a promising potential in the development of renewable energies. One of the key component of offshore wind farms projects is the inter-array power cable. Additionally, the dynamic behavior of floating support under offshore environmental conditions requires dynamic power cable structures which have to withstand both fatigue and extreme loads over its lifetime. Both global and local analyses are required to properly design a dynamic power cable. Indeed, the axial, bending and torsion loads due to environmental conditions (waves and current) and the floating support motion are calculated from a global model by using a dedicated software. Then, the global loading has to be transferred to local sub-models in order to calculate stresses acting on the different components of the power cable. This paper describes a 3D finite elements (FE) model dedicated to a detailed prediction of stresses in an armoured power cable. The loads under extreme environmental conditions are first evaluated from a global analysis. The local model, developed in a commercial FE software, uses periodic boundary conditions to reduce the computational costs and accurately model cables with constant curvatures in space. The model includes contact pressure and friction effects between all cable components, as well as potential lateral contacts between adjacent armour wires, and the radial stiffness of the cable core. The applicative example, focusing on the amour layers, illustrates the potential of the model.

A novel concept of wind turbine floater based on tension-leg technology is introduced. This floater, dedicated to support wind turbines up to 10 MW, aims at minimizing weight and operations while decreasing the level of motions at the nacelle, hence reducing the loading on the turbine and the need for maintenance. The lightness and modularity of the concept allows for use of typical construction means, flexible procurement and building. The self-installability, meaning towing on site by means of standard anchor handling vessel (AHV) with the turbine already installed, facilitates and accelerates the towing and maintenance procedures. Regarding motions, especially tilt angle and nacelle accelerations, excellent floater performance in both operational and extreme conditions, is ensured through an innovative mooring system and reduced wave loads. The latter are kept low thanks to a high transparency of the floater to wave excitation.

Use of composite materials in the deep sea oil production riser systems may allow a dramatic decrease in weight, as well as improved fatigue resistance to loads induced by environmental conditions. Many concepts have been developed by the industry and could be available in the next years. However, the cost of composite components will always be higher than the one of steel components, and only significant advantages for particular applications will justify their use by the industry. Up to now, cost comparisons have been made essentially for TLP or SPAR riser systems. This paper presents a study that has been carried out to compare steel and composite riser solutions for catenary risers, submerged export lines, and hybrid riser towers in ultra deep water. Specifications were first proposed, following which steel and composite solutions were designed and compared. This was done both from the feasibility point of view as well as from consideration of the operational advantages resulting from the lightweight and the fatigue resistance of the composite. Acceptable costs of composite risers were then deduced. The main conclusions are that in the mild conditions of the Gulf of Guinea or of Brazil, both steel and composite solutions are technically feasible, although steel solutions come close to their limits. Composite riser joints fabricated in moderately long lengths seem to be the most interesting solution for transportation and laying purposes. Large cost advantages may be obtained, particularly during the laying phase, which can justify using the composite solution. INTRODUCTION: During the nineties, the oil industry proceeded to exploit offshore fields in 1000 metres water depths and beyond. This has been done generally by simple extrapolation of existing architectural floating concepts, such as TLPs and FPSOs, or by using new ones such as SPAR systems. A significant new development has been the introduction of Steel Catenary Risers. Also the exploitation of new lightweight materials has begun with the introduction of the first mooring systems made out of polyester ropes. New problems have also arisen such as the necessity for significant thermal insulation of pipes. With increasing water depth, and particularly in Ultra Deep Water (between 2000 - 3000 m), the need to decrease the weight of the risers and mooring lines will become stronger. The introduction of lightweight materials may become the best economic option, or possibly the only technically available option. Among such materials, high strength composites have been the subject of intensive industrial research and may become commercially available for operational purposes in the present decade. Up to now attention has been generally focused on weight sensitive floating systems, such as TLPs, on which the balance of weight and the advantages induced can be easily deduced. The objectives of the present study were to evaluate the technical and economic interest of other pipe systems, such as catenary risers, export lines, or hybrid towers, where the balance of weight is only part of the interest, and where steel solutions have run into barriers including fatigue behaviour, stiffness, installation loads, thermal insulation, etc.