Numerical Investigation of Ship Responses in Calm Water and Regular Head Waves

Licentiatavhandling, 2022

In order to design fuel efficient ships and install right machinery onboard, ship designers need to know the interaction effects between hull, propeller and appendages in realistic operating conditions. Neglecting the interaction effects may result in under/over-prediction of the required power. Moreover, with the current strict regulations for reducing CO2 footprint from shipping different type of solutions should be implemented to comply with the  regulations. Developing accurate and reliable engineering methods that can predict ship resistance and power in realistic operating conditions, such as in waves, can be an important contribution to achieve the aforementioned needs of the shipping industry.

Traditionally, ships power prediction has been carried out for the ships operating in calm water rather than more realistic environmental conditions. However, waves can play a significant role on ship performance at sea. In this thesis, as a first step towards prediction of interaction effects in waves, bare hull performance prediction in calm water and regular head waves is carried out using two distinct numerical methods. First, a Fully Nonlinear Potential Flow (FNPF) method is used to investigate a ship performance in a broad range of operational conditions. The analysis of results provided a valuable insight into the ship hydrodynamic responses and the correlation between them. Subsequently, a state-of-the-art Computational Fluid Dynamics (CFD) method is employed using a Reynolds-Averaged Navier-Stokes (RANS) approach. Besides ship hydrodynamic responses, the results from this method provided a detailed information about the flow field around the hull, including its transient nominal wake. In addition, a formal verification and validation (V&V) procedure is applied to understand and control the numerical and modeling error in the RANS computations.

Generally, the results of the employed numerical methods were in a good agreement with the experimental data. The prediction of ship motions and to some extend resistance in the FNPF method were rather accurate, however, due to the higher level of simplifications and approximations in this method, the RANS method deemed a better candidate for prediction of ship wake. The computational costs of RANS methods are 2-3 order of magnitude higher than that of FNPF. The ship hydrodynamic responses and the flow field analyses from this thesis can shed more light onto the hull wave interaction effects and help the ship/propeller designers to optimize their designs for more realistic conditions than only calm water.