Ships Maneuvering Simulations in a Seaway

Abstract

This paper provides overview of the currently available theoretical methods and their capabilities in relation to simulations of the maneuvering behavior of displacement type of ships in a seaway. It has been considered that the ships are engaged in typical type of maneuvers such are for example Zig-Zag and Turning maneuvers according to IMO maneuvering standard and requirements (Faltinsen, 2005) while operating in the same time in deep and open, i.e. unconfined waters and encountering irregular wave field described by long- or short crested wave spectral formulation. Nowadays, most of the maneuvering simulation models, with an exception of limited number of the computational fluid dynamics (CFD) models, are traditionally developed on the potential fluid flow theory with partial inclusion of the viscosity effects. Although their applicability and reliability is already well proven fact through the series of carried out validation and verification procedures related to maneuvering ships in calm water situations, their capabilities in recent years start to be questioned when it comes to maneuvering simulations of ships in a seaway. In this context, a unified maneuvering and seakeeping analysis appears to have a significant role. From the perspective of a maneuvering ship which advances through the wave field and may occasionally experience the wind loading effects it can be recognized that the maneuvering and seakeeping analysis are mutually interconnected. Furthermore, due to fact that their combination represents a complex problem the approach to its solution from the side of related research communities developed gradually. Commonly accepted formulation of a seaway through the linear superposition of regular waves on a certain way dictated approach to combined maneuvering and seakeeping problem having consequence that the problem should be studied mainly in two phases. Usually, in the first phase one will address the regular wave field scenarios while the second phase will account for the irregular wave field scenarios. Theoretical methods capable of combined maneuvering and seakeeping analysis in regular waves are mainly classified in two groups; one based on the (linear) convolution integral approach (Bailey et al., 1997; Fossen, 2005) and the second one based on two-time scale approach where the wave effects upon the maneuvering ship are estimated by the mean 2nd order wave loads (Skejic and Faltinsen, 2008). Present work describes both mentioned methods with focus on their capabilities from the context of a ship executing maneuvers in regular waves. The problem of a maneuvering ship in irregular wave environment started to be analyzed recently in works by Seo and Kim (2011), Prpiæ-Oršiæ and Faltinsen (2012). The mentioned authors focused on a special case of a maneuvering ship in a seaway where it was assumed that the maneuvering ship is advancing on the straight line course, i.e. the ship has the constant heading and zero rudder angle. Mentioned special case is further generalized to arbitrary ship headings and rudder angles by Skejic and Faltinsen (2013). In conclusion, and based on the above described theoretical methods, the present paper discusses the analysis of the propulsive coefficients in the single hull-propeller-rudder arrangement from the wave environment point of view.