Seakeeping calculations with FineMarine

Abstract

Using computational fluid dynamics (CFD), Seakeeping tests aim to obtain the ship's response, avoiding or validating experimental tests. Still, this conventional process is costly in computational time, even with supercomputers. Fortunately, applying an infinite number of superimposed harmonic factors, Transient Wave Group (TWG) facilitates to reduce simulation time, using the Gaussian wave packages model recommended by Clauss and Bergmann in 1986. This project uses FineMarine (CFD software) to evaluate simulation with TWG in three steps of simulations. The first stage is dealing with 2D simulations without any solid to verify the input wave generation. The followed step includes the response measurement of a mid-ship section in beam seas. Finally, the seakeeping response evaluation of an 80 meters patrol boat in beam and head seas in 3D dimension. The results generated by the simulation have a level of acceptance. For the first stage (TWG without solid body), the simulation obtains the input proposed spectrum and free surface elevation (FSE). In the step with the midsection, the results became acceptable but with certain discrepancies due to lack of simulation time due to the low value of roll inertia which generates prolonged movement. As the last stage, the results differences disappeared with the 3D model in head seas due to the high inertia value incidence in pitch motion. In general, inertia helps to obtain fast response stability. In addition, ship velocity seakeeping simulations in head seas assert the use of TWG compared to experimental data and Qship potential flow solver. Conventional seakeeping test takes long simulations for irregular waves such as JONSWAP, ITTC, Pierson-Moskovitz. Otherwise, for a regular wave, it is manageable but not efficient in terms of acquisition data. That is why TWG is a method to optimize the simulation time in terms of irregular waves. Overall, TWG is splendidly suited for ships on Head Seas, with values close to experimental. However, using TWG in beam seas requires a longer simulation time until its movements stabilize, even with low wave steepness wave excitation.