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This article presents the development of a numerical tool for seakeeping simulations of marine systems using a time domain boundary element method based on Rankine sources. The formulation considers two initial boundary value problems defined for the velocity and acceleration potentials, the last being used to avoid numerical problems in calculating the time derivatives of the velocity potential. A fourth-order Runge-Kutta method is used for the time marching of the problem, which consists in the integration of the free surface conditions and body equations of motion. Numerical test cases are presented for bodies with simplified geometries, such as an hemisphere and a circular section cylinder. Exciting forces, added mass and radiation damping coefficients, and motions response amplitude operators are compared to analytical and numerical data, presenting a very good agreement. Furthermore, the numerical method is applied to a floating production storage and Off-loading unit and the results are verified with experimental data carried out in the hydrodynamic calibrator of the University of Sao Paulo. By means of these investigations, we have verified that the developments performed so far are correct and new extensions, therefore, may be planned for more complex applications.

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The development of a numerical method for the computation of the linear and weakly non-linear wave effects on floating bodies is presented. The method is formulated in terms of a higher order time-domain boundary elements method based on the Rankine sources. The higher order approach is assumed for both body geometry (using NURBS) and computed function (using B-splines), the former in a standard CAD geometry format to provide more flexibility. In this paper, the procedures adopted for the numerical solution of the main mathematical problems involved are thoroughly described and discussed, with the purpose of documenting important aspects of these methods that are often absent in the literature. Several verification cases are presented, including first-order quantities (motion RAOs, velocity field, and free-surface elevation) and second-order loads (mean drift, sum, and difference components). Regarding the latter, at the present stage of the development, the numerical method is able to compute the so-called quadratic components of forces and moments. For these loads, steady-state solutions in both monochromatic and bichromatic waves are compared to the results obtained with a well-known frequency-domain code. Keywords Higher order boundary element method Á Time-domain Á Rankine sources Á Seakeeping Á Quadratic second-order loads.

The determination of hydrodynamic coefficients of full scale underwater vehicles using system identification (SI) is an extremely powerful technique. The procedure is based on experimental runs and on the analysis of on-board sensors and thrusters signals. The technique is cost effective and it has high repeatability; however, for open-frame underwater vehicles, it lacks accuracy due to the sensors’ noise and the poor modeling of thruster-hull and thruster-thruster interaction effects. In this work, forced oscillation tests were undertaken with a full scale open-frame underwater vehicle. These conducted tests are unique in the sense that there are not many examples in the literature taking advantage of a PMM installation for testing a prototype and; consequently, allowing the comparison between the experimental results and the ones estimated by parameter identification. The Morison’s equation inertia and drag coefficients were estimated with two parameter identification methods, that is, the weighted and the ordinary least-squares procedures. It was verified that the in-line force estimated from Morison’s equation agrees well with the measured one except in the region around the motion inversion points. On the other hand, the error analysis showed that the ordinary least-squares provided better accuracy and, therefore, was used to evaluate the ratio between inertia and drag forces for a range of Keulegan–Carpenter and Reynolds numbers. It was concluded that, although both experimental and estimation techniques proved to be powerful tools for evaluation of an open-frame underwater vehicle’s hydrodynamic coefficients, the research provided a rich amount of reference data for comparison with reduced models as well as for dynamic motion simulation of ROVs.

The fuel consumption analysis of a Suezmax tanker customized to the offloading operation in the brazilian coast is performed in order to verify the possible savings produced by the so-called ''slow steaming'' technique during navigation. This ship is equipped of a single engine/propeller but there is a trend of building new vessels considering an equivalent two engines-two propellers for better safety during navigation and offloading operations, therefore a comparison regarding the propulsive efficiency, fuel consumption, and operational conditions (max engine power, rotation, and cavitation limitations) is performed in order to verify the benefits of this new concept. The methodology applied is based on a mixed approach considering numerical simulations using CFD (computational fluid dynamics) and regression models available in the literature: the first one applied to compute the ship resistance and nominal wake fraction in the propeller plane and the second one applied for the propulsive efficiency prediction, as the propeller curves based on Wageningen B-series. The specific fuel oil consumption curves were obtained from the engine manufacturer catalogue.

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