Structural response analysis of the hydraulic pneumatic tensioner under its local failure based on a fully coupled TLP-TTR system

The presented work studied the structural response of the hydraulic pneumatic tensioner (HPT) in a TLP-TTR system with failure of the tensioner cylinder. A fully coupled hull-tendon-TTR-tensioner model was established in AQWA to simulate the failure numerically. A specific HPT was modeled by considering 4 cylinders and the real-time stroke of each piston. A set of formulas was proposed to calculate the real-time tension including different components, e.g. Stribeck friction, in the tensioner. A riser array including 6 independent production TTRs and their tensioners was also modeled. The production TTR model was stacked up by different specific riser joints. The hydrodynamic force acting on the hull was obtained by using the 3D potential flow theory. The real-time tensions on different tensioner cylinders were obtained by using an in-house-developed program. Different environmental conditions, including a calm sea, regular waves, and extreme sea states, were considered in the simulations. In the results, the behaviors of different cylinders of the failed tensioner were presented. The results show that when an accidental local failure of the HPT occurs, the tension and stroke responses are still far from the designed-limits to induce a progressive failure

Buckling analysis of subsea pipeline with integral buckle arrestor using vector form intrinsic finite thin shell element

Buckling damage is one of the biggest safety issues for subsea pipelines. Buckling behaviors of the subsea pipeline with integral buckle arrestors under external pressure are studied experimentally and numerically herein. Pressure chamber tests of four full-sized pipeline with identical thickness and different diameters are presented. An emerging vector form intrinsic finite element method (VFIFE) is introduced to simulate the whole buckling process both in dynamic and quasi-static cases, including local collapse, propagation, buckling prevention, and crossover. Numerical schemes for multifold nonlinearities and multithreaded computation are proposed and tested. Results of experiments and numerical simulations, as well as computations of the traditional finite element method and DNV specifications, are compared. Thusly it is indicated that the VFIFE model can accurately (within +/- 1.5%) predict the buckling loads that initiate local collapse, propagation and crossover, and simulate the dynamic and quasi-static buckling modes for pipelines with practical range of diameter-to-thickness ratios greater than 20. For thick parts where integral arrestor with diameter-to-thickness ratios smaller than 20 located, the VFIFE thin shell element may underestimate the structural strength about 8.0%. The VFIFE can directly simulate the pipeline buckling behavior without special processing for the iterative calculation and the stiffness matrix convergence, and achieve the parallel efficiency over 90% for a common computer (12 threads, 4G RAM). Thus, the VFIFE can provide a new, practical and universal analytic strategy for subsea pipeline buckling analysis

Design and Performance Assessment of Multi-Use Offshore Tension Leg Platform Equipped with an Embedded Wave Energy Converter System

In this study, a new multi-use offshore tension leg platform (TLP) was designed for wave energy production through an embedded wave energy converter (EWEC) system. The proposed EWEC system consists of four built-in tuned liquid column dampers for absorbing the hull motion energy and eight Wells turbines as the power take-off devices. A multifold nonlinear analytical model of this multibody system was developed considering the hydrodynamics of theTLP-EWEC system during large motions and the aerohydrodynamics of the chamber-turbine groups. A comprehensive assessment, including an evaluation of motion responses and preliminary generating capacity, was performed for different wave-load directions using the numerical time integration method. The results indicated that the multi-use platform can generate a considerable amount of turbine power for the offshore platform energy mix as well as serve for offshore oil and gas production in the target oil fields. Such additional benefits and profitability were proven effective and worthy for further exploration and practical application