Browsing by Subject "steel catenary riser"
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Item Assessment of Global Buckling and Fatigue Life for Steel Catenary RIser by Hull-Riser-Mooring Coupled Dynamic Analysis Program(2013-08-01) Eom, TaesungSteel Catenary Riser (SCR) is a popular solution for a floating production facility in the deep and ultra-deep ocean. In the analysis of SCR, the behavioral characteristics are investigated to check the failure modes by assessing the magnitude and the frequency of the stress and strain which SCR goes through in time series. SCR is affected by the motions of connected floating production facility and exciting environmental loads. The driven force and motion of SCR has an interaction with seabed soil which represents the stiffness and friction force where SCR touches the seabed. Dynamic response of SCR is primarily caused by the coupled motion of floating structure. The displacement of floating structure is often large and fast enough to cause short cycles of negative and positive tension on SCR. The interaction between SCR and seabed is concentrated at the touchdown zone resulting into the compression and corresponding deformation of pipeline at the position. This paper presents models of floating production facilities and connected mooring lines and SCRs in 100-year hurricane environmental loads and seabed, focusing on the motional characteristics of SCR at the touchdown zone. In time series simulation, the model of SCR is first analyzed as a pipeline with indefinite elasticity so that the SCR does not fail even if the exciting loads exceed the property limit of SCR. Then the SCR design is manually checked using criteria for each failure mode to estimate the integrity.Item Non-linear load-deflection models for seafloor interaction with steel catenary risers(2009-05-15) Jiao, YaguangThe simulation of seafloor-steel catenary interaction and prediction of riser fatigue life required an accurate characterization of seafloor stiffness as well as realistic description of riser load-deflection (P-y) response. This thesis presents two load-deflection (P-y) models (non-degradating and degradating models) to simulate seafloor-riser interaction. These two models considered the seafloor-riser system in terms of an elastic steel pipe supported on non-linear soil springs with vertical motions. These two models were formulated in terms of a backbone curve describing self-embedment of the riser, bounding curves describing P-y behavior under extremely large deflections, and a series of rules for describing P-y behavior within the bounding loop. The non-degradating P-y model was capable of simulating the riser behavior under very complex loading conditions, including unloading (uplift) and re-loading (downwards) cycles under conditions of partial and full separation of soils and riser. In the non-degradating model, there was a series of model parameters which included three riser properties, two trench geometry parameters and one trench roughness parameter, two backbone curve model parameters, and four bounding loop model parameters. To capture the seafloor stiffness degradation effect due to cyclic loading, a degradating P-y model was also developed. The degradating model proposes three degradation control parameters, which consider the effects of the number of cycles and cyclic unloading-reloading paths. Accumulated deflections serve as a measure of energy dissipation. The degradating model was also made up of three components. The first one was the backbone curve, same as the non-degradating model. The bounding loops define the P-y behavior of extreme loading deflections. The elastic rebound curve and partial separation stage were in the same formation as the non-degradating model. However, for the re-contact and re-loading curve, degradation effects were taken into the calculation. These two models were verified through comparisons with laboratory basin tests. Computer codes were also developed to implement these models for seafloor-riser interaction response.Item Optimized Design of Statically Equivalent Mooring and Catenary Ryser Systems(2015-03-03) Felix Gonzalez, IvanDue to size limitations of wave basins worldwide it is necessary to employ statically equivalent truncated mooring and riser systems to test floating systems to be deployed in deep and ultra-deep waters. A procedure for the optimized design of the statically equivalent truncated mooring and riser system was developed using a Genetic Algorithm, considering that the equivalent mooring/system needs to reproduce the net static forces and moments exerted by the prototype mooring/riser system on the floater in its six rigid body degrees of freedom (surge, sway, heave, roll, pitch and yaw). A fit-for-purpose program was developed to evaluate the three-dimensional static equilibrium of floating structures, considering the attached mooring and steel catenary riser systems. The static response is calculated for a set of offsets in the surge direction from the calm water equilibrium position up to a maximum user defined offset. Four study cases were considered to demonstrate the effectiveness and robustness of a Genetic Algorithm procedure developed for the optimize design of the statically equivalent mooring and riser system. The four study cases were a semisubmersible with a symmetric polyester mooring system, a semisubmersible with a symmetric steel wire mooring system, a semisubmersible with a non-symmetric polyester mooring and steel catenary riser system attached, and a spar with a non-symmetric polyester mooring and a steel catenary riser system attached. To gain insight on the distortion of the dynamic mooring forces exerted on the floater when dynamic effects are ignored in the design, a procedure to assess the mooring system inertia and damping force contributions to the floater was developed. The application of the procedure was demonstrated using two study cases corresponding to deepwater polyester and steel mooring systems.