No abstract

DP crane barges operate in close proximity to FPSO (Floating Production Storage and Offloading) during lifting operations. This operation is critical since small variations of the relative position may result in collision between the bodies or large motion of the lifting load. The hydrodynamic interactions between the units are an important effect that must be considered in the analysis of those operations. The interactions are an intricate problem that cannot be modeled analytically in an appropriate way. Hence, experimental and numerical tools are applied for the definition of the environmental conditions for a safe operation or the optimal relative positioning between the vessels. A research project conducted by Petrobras in cooperation with Brazilian universities aims to develop and to validate numerical tools for aiding the design and analysis of the DP lifting operations. They are based on dynamical time-domain simulations of the operation and can be used for predicting several parameters of the operations. The experimental tests that will be used for validating this numerical model, concerning the DP performance when the crane barge is close to a FPSO, are presented in this paper. The tests were conducted in an ocean basin using the model of a moored FPSO and the DP crane barge. The station keeping ability (relative motion) and the performance of the propulsive subsystem of the DP crane barge (power and thrust utilization parameters) are measured. Several relative positions and wave conditions were considered.

The coupled hydrodynamic of a DP Barge operating close to a FPSO is evaluated. Experimental tests in a wave basin were performed to obtain the system dynamic behavior for several relative positions and environmental incidences. Two small scale models with factor 1:48 were tested in three different relative positions, five incidence angles and two irregular seas. The industry experience in operating barges was used to provide the insight to select these configurations. The DP Barge model was equipped with a dynamic positioning (DP) system, in order to keep its position relative to the FPSO. The FPSO model uses a scaled spread mooring system. Motions for DP Barge only were also obtained. Discussions are centered in reduction or amplification of DP Barge motions due the FPSO presence. Results are presented in terms of motions significant amplitude and RAO curves. A numerical model was evaluated and its results compared with the experiments. Some considerations, problems and conclusions about the operation were also obtained. These discussions complement the study presented by Vieira et al. (2011), which explored this operation numerically. A companion paper (Tannuri et al., 2012) will discuss the effects of the hydrodynamic coupling on the DP performance of the barge.