Numerical simulation of ship performance in level ice: evaluation, framework and modelling

Shipping activities in ice-covered areas such as Arctic, sub-Arctic and Antarctic regions rely on ice-going ships with adequate icebreaking capacity. To ensure safe and efficient voyages, ship performance in ice needs to be estimated in the design stage in order to meet the requirements of the operational area. The performance of a ship in level ice is an important index in the design of ice-going ships. Model-scale testing is currently the most reliable method to estimate ship performance in level ice. However, model-scale testing is relatively expensive and thus is not suitable in early design stage. Theoretical approaches, including analytical formulae and numerical simulations, can be used in early design stage to optimize hull lines and select the optimal concept. In recent years, numerical methods get more attention over analytical methods due to the capability to solve more complex problems. Although several numerical models have been proposed in the literature, there lacks a systematic evaluation of numerical methods for the estimation of ship performance in level ice. Since the interaction between ship and ice is a complex process involving extensive aspects, there needs a well-defined framework to guide the development of numerical models. The primary aim of this thesis is to evaluate numerical simulation as a tool to estimate ship performance in level ice, and establish a framework to formulate future modelling work. Following this framework, this thesis attempts to build several local-scale ship-ice interaction models and include them in a ship performance model, which can be used to simulate ships' attainable speed and maneuverability in level ice. In this thesis, the full-scale measurement data of the ship S.A. Agulhas II are utilized to evaluate the accuracy of a numerical model and two analytical methods. The uncertainties associated with the numerical model are quantified. It is found that numerical methods have not demonstrated clear advantage over analytical methods for ships following a straight course. To advance the state-of-the-art, a framework is proposed to cover a wide range of modelling aspects, including modelling purposes, model elements, modelling strategies and methods, as well as methodology of validation. Following the framework and motivated by the evaluation, several local-scale models are developed to model ice breaking and rotation processes. These models are based on first-principle approaches and can simulate the breaking and rotation processes with fast computation. A global-scale numerical model for the simulation of ship performance in level ice is finally developed based on the local-scale models. This model can simulate ships going straight and turning in level ice for ship design purposes. The data of the S.A. Agulhas II turning in level ice is used to benchmark the numerical simulation results. It is found that the model gives reasonable estimation of the ship's turning performance.