A new method and implementation of ship motion computation is described. An existing zero speed method is extended for forward speed calculations by using same kind of speed correction terms as in the Modified Strip Theory. Validation calculation results are shown for two hull forms. Good agreement is achieved for heave and pitch motions in most studied cases. The new method is computationally efficient and is intended for practical ship design work.


Ship motion response in waves, seakeeping characteristics, are of interest during the design work. It can be to ensure that the ship motions do not exceed the limits set by the operational requirements, passenger comfort or other reasons. Especially in the concept design stage a number of ship parameters including the main dimensions, distribution of mass and the hull form can still vary. The designer should be able to check the seakeeping characteristics for a number of different design variations. The timeframe and the resources at this stage are often limited. For these reasons, the seakeeping tools, the design software should be efficient, both in terms of the calculation time as well as in terms of flexibility of hull and other variations of the ship design.

Ship design software NAPA uses parametric representation of the hull form. Potential theory based three-dimensional panel method for seakeeping calculations, described in this paper, was initially implemented in this software for zero-speed calculations. In this paper the extension and the validation of the method for forward speed cases is described.

Potential theory based solvers have been developed since 1950s, but regardless of the relevantly mature stage of the methods, the implementation still remains challenging (Guha and Falzarano 2015), and the benchmark study by Bunnik et al. (2010) show that the results obtained by similar methods may vary depending on the implementation. According to Bertram (2012) the potential flow solvers still dominate in seakeeping analyses.

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