Математичне моделювання роботи буксира з азимутними рушіями на тросі

Use of harbor tugs to assist vessels in berthing operations is a common practice. More often nowadays tugs are used also to provide escort service to large vessels, which cannot maneuver safely in constrained harbor waters without assistance due to their size, or to provide back-up steering ability if the vessel propulsion fails. High level of risk usually inherent to these operations stipulates the study of the tug and ship interaction dynamics. This research deals with mathematical modeling of the towing process, with the focus on azimuthal stern drive, tug maneuvering characteristics and its transverse stability. A mathematical model of an ASD tug in four degrees of freedom is presented in the paper. Following features were specifically considered: thrust degradation due to propeller interaction, transverse stability on large angles of heel, interaction via a hawser with an independently steered vessel, and the hawser tension in a dynamically unstable situation. Software developed on the basis of the proposed mathematical model allows modelling girting and capsizing of a tug. In addition, it gives an opportunity to access dangerous tug handling modes, which can be presented during tug masters training or used in the towing operations risk analysis.