In an earlier work Leite et al (1998) developed a heuristic hydrodynamic model, based on the shrtwing theory, for the horizontal current forces on an FPSO system. The proposed model was quasi-explicit in the sense that it depends on the ship's main dimensions and on only three hydrodynamic coefficients, namely, the friction coefficient Cf for head on incidence, the drag coefficient CY for a cross-flow, and the related yaw moment coefficient lCY. As discussed in Leite et al (1998), these coefficients could even be estimated from the ITTC friction curve and from Hoerner's sectional results, which would then turn the hydrodynamic model explicit. The model has been tested against experimental results for the horizontal force coefficients, obtained both at IPT and at the Marin wave tank, and it has also been confronted with bifurcation experiments for a turret configuration realized at IPT. The agreement rendered good results in all cases tested. The heuristic approach has now been extended to incorporate the yaw velocity terms while preserving the quasi-explicit feature of the original model. The main purpose of the work herein is to present such a development together with some experimental validation. Using Froude scaling of different ships in distinct ballast conditions, the horizontal forces and moment in the yaw rotating tests were measured at IPT and at Marin and compared with those predicted by the heuristic model, the observed agreement again being fair enough. In an accompanying paper in this issue, the derived mathematical model is tested against experiments that emulate a single-point mooring of a tanker ship in order to disclose the model's ability to cope with the main dynamic features of the fishtailing instability problem.
Development and Experimental Validation of an Underwater Manipulator Hydrodynamic Model
