A computer program is developed for the dynamic analysis of a spar platform coupled with mooring lines and risers in waves, winds, and currents. The new multi-contact analysis program is developed for the nonlinear multi-contact coupling between vertical risers and guide frames inside of the spar moon-pool. The program extends capability of the current coupled dynamic analysis program, WINPOST, by adding the capability of analyzing riser effects caused by the contact forces and moments from buoyancy-cans inside the spar moon-pool on the global spar motions. The gap between the buoyancy can and riser guide frames are modeled using three different types of nonlinear gap springs. The new riser model also considers the Coulomb damping between the buoyancy-cans and riser guide frames, and it also calculates the impact force on risers for use in fatigue analysis. The spar platform generally uses vertical risers with dry trees. However, as the water depth increases, the size of the buoyancy-can increases, and it makes installation more difficult. The pneumatic riser support system does not use buoyancy-cans and is an alternative solution to the buoyancy-can approach. The dynamic characteristics of pneumatic riser support system are studied by using the newly developed numerical analysis program. The damped Mathieu instability diagram for the damped Mathieu's equation is developed. Due to spar heave and pitch coupling, Mathieu's instability may become excited in long period waves. In the numerical analysis program, pitch and roll hydrostatic stiffness are recalculated for heave motion in every time step to check Mathieu's instability for the spar platform. Simplified vortex-induced vibration effects on the spar platform are considered in newly developed numerical analysis program, and the results are systematically compared with those of the original program WINPOST. The results in this paper show that the buoyancy-can effect significantly reduces the spar pitch motion, and the Coulomb damping effect also significantly reduces the spar heave motion. The buoyancy-can effect also plays an important role in Mathieu instability. The results also show that a pneumatic riser support system increases the spar heave motion and payload.

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.