The use of large floating units to operate in deep water appears as a solution adopted by the industry to produce and storage the oil and finally to transfer the oil to shuttle ships. In the particular case of Petrobras the conversion of VLCC to FPSO has been adopted to work in the exploitation of oil in deep water. This has motivated many studies about the dynamics of this kind of structures exposed to the environmental conditions: wind, currents and waves. The present paper deals with the dynamics of ships in the horizontal plane under the action of a current. A maneuvering model is used to express the hydrodynamic forces. Analytical expressions for the eigenvalues of the linear stability analysis are obtained. These expressions are used to analyze the influence of the main dimensions in the design of new structures and the use of some stabilizers.

The paper presents the development of a methodology for the definition of the operational limits for Self-Elevating Units, during the “jack-up” and “jack-down” operations. The methodology is based on the structural analysis of the unit during the impact between the spud can and the soil. The mechanics of the impact is based on the first principle of Momentum Theory and the Virtual Work Theory. The study includes the development of a motion analysis in order to obtain the allowable maximum wave heights that guarantee the integrity of the unit.

Pull-out test and decay tests in still water and in waves for the surge motion of a VLCC in ballast condition are carried out at LabOceano. The pull-out test associated with the mean drift displacement in regular waves is used to determine mean drift force. From the decay tests the damping coefficients are adjusted using the Froude energy method and the procedure based on the logarithm decrement. For the decay test in waves, the response is subdivided in the mean drift contribution, the regular wave response and the transient response. The wave drift damping is considered as an increase on the linear damping in still water. So, we introduce an additional damping to the linear part of the damping coefficient in still water and simulate the decay test in waves. Comparing the results from the simulation with the experiments the wave drift damping contribution is adjusted. Finally, the mean drift results are compared with the results obtained with the potential theory. The wave drift damping coefficients obtained from the experiments are compared with coefficients obtained with a formulation proposed in the literature.

This paper presents a methodology for the positioning of a turret based on the hydrodynamic behavior of the FPSO and the structural behavior of the mooring lines. It is presented a procedure for the simulation of the equilibrium and the dynamics of the FPSO’s for a range of environmental conditions and positions of the turret. The results are studied in order to define the best position for the turret. Experimental results are used in order to calibrate the physical models.

The paper deals with the dynamics of floating systems (FPSO units) moored in deep water in the presence of currents. The offloading operation is carried out in a tandem arrangement from the FPSO to a Shuttle ship of lesser capacity. According to the classical theory of dynamic systems, a study of the behavior of floating units is performed by determining the equilibrium position and then analyzing the stability around this position. The time domain analysis is also used to compare the results. This procedure is extended to the case of systems in a spread mooring configuration and with turret.