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In this paper, a linear mathematical and numerical model for analysing the dynamic response of a flexible electroactive wave energy converter is de- Finally, estimates are made for the energy performance of a possible prototype.

Since 2009, SBM Offshore has been developing the S3 Wave Energy Converter (S3 WEC). It consists in a long flexible tube made of an Electro-Active Polymer (EAP). Thus, the structural material is also the Power Take Off (PTO). In order to optimize the S3 WEC, a hydro-elastic numerical model able to predict the device dynamic response has been developed. The inner flow, elastic wall deformations and outer flow are taken into account in the model under the following assumptions: Euler equation is used for the inner flow. The flow is also assumed to be uniform. Elastic deformation of the wall tube is linearized. The outer flow is modeled using linear potential theory. These equations have been combined in order to build the numerical model. First, they are solved in the absence of the outer fluid in order to obtain the modes of response of the device. Secondly, the outer fluid is taken into account and the equation of motion is solved by making use of modal expansion. Meanwhile, experimental validation tests were conducted in the ocean basin at Ecole Centrale De Nantes. The scale model is 10m long tube made of EAP. The tube deformations were measured using the electro-active polymer. The model was also equipped with sensors in order to measure the inner pressure. Comparisons of the deformation rate between the numerical model and experimental results show good agreement, provided that the wall damping is calibrated. Eventually, results of a technico-economical parametric study of the dimensions of the device are presented.

MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. This paper highlights the challenges and solutions associated with the engineering and execution of the 188 nautical mile tow of the GAP from the SBM construction site in Bintulu (Malaysia) to the Kikeh Field. Substantial effort was invested at the engineering stage to study the tow-induced fatigue, including influence of wave direction, tow speed, trailing tug back tension, current and submergence of towheads in order to develop a tow strategy which was a compromise between fatigue damage reduction and realistic and cost effective marine operations. This process is detailed in the paper. Finally, all tasks associated with tow from the point at which the beach hold-back rigging was abandoned to the point at which field pre-entry tasks were carried out are also described in the paper.

MURPHY Sabah Oil Co. Ltd. has developed the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids are transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system. The GAP is an interesting combination of mooring (tether chains), dynamic steel riser (carrier pipe and flowlines) and steel structures (towheads). Design codes and standards usually address the design of these components separately. One of the challenges of the GAP project is to have a consistent design philosophy for all the components so that the GAP can be treated as an integrated system with homogeneous quality and safety levels. GAP component fatigue analysis is a good example of integrated system design. In the GAP, fatigue loading is applied by the floaters, through the tether chains, to the towheads into the carrier pipe. The fatigue analysis of individual GAP components cannot be performed in isolation — it must be the result of an integrated GAP fatigue analysis. A global model of the GAP is built with towheads modelled as rigid bodies and tether chains and carrier pipe modelled as dynamic lines. This model is used to obtain time series of loads on all components of the GAP. The fatigue of each component is calculated using the same methodology based on stress Response Amplitude Operators (RAOs) for a selected number of combinations of FPSO headings, wave directions, FPSO drafts and fluid densities. This methodology is classical for chains and steel pipes. It is less classical to apply such a detailed methodology for large structures like towheads. The towhead structures are key components that provide connection between tether chains and carrier pipe, flexible jumpers and steel flow lines, carrier pipe and decoupling overhead buoyancy tank. As such, the fatigue analysis of the towhead is as critical as for the tether chains and the carrier pipe. Finite element models of the towheads have been subjected to unit loads from all components attached to them and from the dynamic fluid pressures generated by unit towhead accelerations. Using the loads extracted from hydrodynamics calculations on the global GAP model and the matrix of stress for unit loads, the time domain approach is kept throughout the complete structural assessment of the towheads. This is in order to maintain a high degree of accuracy in the stress prediction. Given the criticality of the carrier pipe, a very detailed Engineering Criticality Assessment (ECA) is performed to define flaw acceptance criteria to be used during the Non Destructive Examination (NDE) campaign.