The aim of this paper is the study of the Allowable VCG in monocolumn offshore platforms. As study case the MonoBR — an innovative conceptual unit developed by a partnership of PETROBRAS/CENPES and University of Sa˜o Paulo — was analyzed. The studies were carried out during the design of MonoBR for the Walker Ridge area, Gulf of Mexico. The effect on the stability of the unit caused by a damaged tank depends on its loading condition, since there is lost of both, buoyancy and mass, modifying unit’s displacement and center of gravity. In other words, depending of the tank loading, the amount of water that enters or leaves the unit in a damage case may vary widely. In this paper is presented the methodology adopted in the study of influence of the ballast tanks loading in the Allowable VCG curve in MonoBR, introducing this other variable beyond the draft, the usual single variable in AVCG curves. At the end are presented the main results for the study case, whose AVCG can vary by 50% for the same draft depending of the tank loading.
The MonoBR is a MPSO — mono-column floater, production, storage and offloading unit — a unique platform designed to handle steel catenary risers (SCR) in a depth of 1800 m in Gulf of Mexico oil fields whose target scenario is the ultra-deep water of the Walker Ridge. In this project, special concern was given to sea keeping behavior, constructability and security. Stability Analyses were carried out to ensure the system security and reliability. This paper describes the development carried out by The University of Sa˜o Paulo and PETROBRAS team, in order to analyze the main stability parameters of this new conceptual design for oil production and storage, the MonoBR. The main topics referred on the text are the damaged and intact stability analyses, the tank arrangement, wind influence, rules discussions, the AVCG (Allowable Vertical Center of Gravity) and damage compensation through ballast rearrangement.
The aim of this paper is to present validation studies of a CFD code based on MPS (Moving Particle Semi-implicit Method). In MPS method the fluid is represented by particles, and the particle interactions are governed by continuity and Navier-Stokes equations. It is a meshless method to simulate incompressible flow and it is able to simulate large surface distortion, fluid fragmentation and non-linear dynamics. For the validation studies, two cases with complex hydrodynamic phenomena were selected for experimental measurements in towing tank. The first one is the dynamics of a floating body in waves with an internal tank partial filled with water. In this way sloshing effects on the motion of the model can be evaluated. Usually, dynamics of the floating body and sloshing are calculated separately, by neglecting their coupling effects; the body’s motion is determined without sloshing and that motion is used to excite the liquid tank. Since the sloshing generates forces and moments, which may change the movement of the hull, sloshing forces and moments may act as a roll absorption device or can enlarger it. In MPS this coupled phenomena can be easily simulated, just by using particles representing water of the internal tank, water of the towing tank and structural particles representing the hull, the walls and the wave maker. The second phenomenon is the motions of a damaged hull from the moment soon after suffering damage until reaches the equilibrium position. This is an initial step of a validation study of the motion of a damage hull in waves, which will be compared with physical experiments. The comparisons between the numerical results obtained by the MPS with the experimental and theoretical ones show very good agreement, reinforcing the potential of MPS.
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