Numerical simulation of ship motion due to waves and manoeuvring
This is a master thesis conducted at KTH Centre for Naval Architecture in collaboration with Seaware AB and Wallenius Marine AB.Traditionally simulation of ship motion is divided into manoeuvring and seakeeping. In manoeuvring the plane motion in surge, sway and yaw degrees of freedom for a ship considered moving in calm water is simulated. For increased accuracy the roll degree of freedom can be included as it affects the plane motion. In seakeeping ship motion due to waves at a specific speed and course in 3 to 6 DOF (degrees of freedom), depending on the area of interest, is simulated.The motion that a ship undergoes at sea is however dependent on the interaction between the forces and moments due to waves as well as the forces and moments related to ship manoeuvring. Furthermore, analysis on e.g. methods for counteracting roll motion in waves with rudder movement requires the modelling of forces and moments due to waves and manoeuvring in several DOF. It is therefore desirable to develop a unified model that describes ship motion in several DOF with respect to waves and the effects of manoeuvring.To create a mathematical model, written in MATLAB script, for simulation of ship motion due to waves and the manoeuvring related forces in 5 DOF, a wave induced (Ovegård 2009) and manoeuvrability (Zachrissson 2011) ship motion model were integrated.The code was validated against a linear strip theory, a non-linear ship motion model as well as model experimental results. Results have shown that whilst the heave and pitch motions agree with the models and tank tests the roll motion is seen, in some cases, as creating larger response in comparison to other models and experimental tank tests.
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