Top Tensioned Riser (TTR) and Steel Catenary Riser (SCR) are often used in a floating oil/gas production system deployed in deep water for oil transport. This study focuses on the improvements to the existing numerical code, known as CABLE3D, to allow for static and dynamic simulation of a TTR connected to a floating structure through a tensioner system or buoyancy can, and a SCR connected to a floating structure through a flex joint. A tensioner system usually consists of three to four cylindrical tensioners. Although the stiffness of individual tensioner is assumed to be linear, the resultant stiffness of a tensioner system may be nonlinear. The vertical friction at a riser guide is neglected assuming a roller is installed there. Near the water surface, a TTR is forced to move due to the motion of the upper deck of a floating structure as well as related riser guides. Using the up-dated CABLE3D, the dynamic simulation of TTRs will be made to reveal their motion, tension, and bending moment, which is important for the design. A flex joint is approximated by a rotational spring with linear stiffness, which is used as a connection between a SCR and a floating structure or a connection between a TTR and the sea floor. The improved CABLE3D will be integrated into a numerical code, known as COUPLE, for the simulation of the dynamic interaction among the hull of a floating structure, such as SPAR or TLP, its mooring system and riser system under the impact of wind, current and waves. To demonstrate the application of the improved CABLE3D and its integration with COUPLE, the related simulation is made for ‘Constitution’ SPAR under the met-ocean conditions of hurricane ‘Ike’. The mooring system of the Spar consists of nine mooring lines and the riser system consists of six TTRs and two SCRs.

Orientador: Prof. Dr. Juan Pablo Julca Ávila / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Mecânica, 2016. / Os risers de produção são estruturas tubulares cilíndricas usadas para o escoamento de petróleo e gás desde os poços de petróleo localizados no chão marinho até uma unidade flutuante de produção de petróleo. Quando imersos em correntezas, estas estruturas vibram devido à excitação no topo, ao escoamento interno e ao desprendimento alternado de vórtices à jusante. Este fenômeno é conhecido como Vibração Induzida por Vórtices (VIV). Quando a frequência de emissão dos vórtices se aproxima de uma das frequências naturais do riser, este começa a oscilar tomando controle do processo de emissão de vórtices e, subsequentemente, quando a frequência de emissão de vórtices coincide com a frequência natural do riser, este entra em ressonância. Na última condição, os riser vibram a amplitudes da ordem de 1 a 2 vezes o seu diâmetro e são submetidos a elevadas tensões fletoras cíclicas podendo conduzir à falha prematura por fadiga. Este trabalho de mestrado tem como principal objetivo o desenvolvimento e implementação de uma ferramenta computacional, escrita em FORTRAN, capaz de simular a VIV em risers verticais longos tracionados no topo para águas profundas. Um riser tracionado no topo é modelado como uma viga vertical de Euler-Bernoulli. Um código para análise estática e dinâmica por elementos finitos é desenvolvido. O escoamento tridimensional em torno do riser é substituído por um número de planos de escoamento bidimensional transversais ao eixo do riser. Em cada plano hidrodinâmico, o escoamento é calculado pelo método dos vórtices discretos para fornecer as forças de arrasto e sustentação. As equações de dinâmica estrutural são resolvidas usando as forças hidrodinâmicas calculadas previamente para obter o movimento do vertical riser. A ferramenta computacional desenvolvida foi implementada no cluster de processadores de alto desempenho da UFABC. / Risers are offshore cylindrical tubular structures used for transporting oil and gas from the wells located on the seabed up to a floating offshore production platform at the surface. When they are subjected to seawaters currents, these structures oscillate due to movement at the top, internal flows and alternating vortex shedding in the downstream region of riser. This phenomenon is known as Vortex-Induced Vibration (VIV). When the vortex-shedding frequency is close to one of the riser natural frequencies, it begins to oscillate taking control of vortex-shedding process and thereafter when the vortex-shedding frequency coincides with the natural frequency of the riser, this enters into resonance. At last, risers oscillate with amplitudes of once to twice their diameter and are subjected to high cyclic bending stress which can lead to premature fatigue failure. This work of master's degree has as main aim the development and implementation of a computational tool, written in FORTRAN, capable of simulating VIV in deepwater top tensioned long vertical risers. A top tensioned riser is modeled as a vertical Euler-Bernoulli beam. A code for the static and dynamic analysis by Finite Element Method is developed. The 3D fluid flow around the riser is replaced by a determinated number of 2D cross-sections. In each hydrodynamic cross-section, fluid flow is calculated by the Discrete Vortex Method to obtain drag and lift forces. Dynamics equations are solved using hydrodynamic forces previously calculated to get the dynamics-time response of vertical riser. The developed computational tool was implemented in the UFABC's cluster using High-Performance Computing techniques.