Maneuvering of two interacting ships in waves

Abstract

This thesis describes the development of a module based maneuvering prediction system for one ship or two interacting ships in calm water or waves. The work is a continuation and generalization of the previous work of Skejic (2008).

The thesis tries to describe as complete as possible the module based maneuvering system for the sake of making the thesis a more organized piece of work. However, this does not mean that we try to include everything present in detail. The parts of maneuvering system that are consistent with those used by Skejic (2008) are just briefly introduced. While a very detailed description of the formulation and implementation of the developed hydrodynamic models in the system are presented by the main part of the thesis.

These main outcomes of the present research are formulation and implementation of hydrodynamic models to account for 3D hydrodynamic loads and especially the hydrodynamic interaction effects when two ships are present, in both calm water and waves. For the calm water loads a new method was developed to estimate the hydrodynamic interaction loads up to the collision of two ships. In order to estimate the wave effects, a Rankine-source-based method was developed to solve the first order problem of two interacting ships advancing side-by-side in waves. The linear solution is then transformed into frequency domain for evaluating the mean wave loads on each ship based on a method of conservation of momentum. For each ship, a control surface just a few panels away from the ship is applied for calculation of mean wave loads. In this way the present method can have both fast convergence and be capable of evaluating 6-degree-of-freedom mean wave loads.

The hydrodynamic models were implemented applying a constant panel method. Numerical solutions were validated through comparing with analytical solutions, model tests and published numerical predictions. Then the validated solvers are integrated to the maneuvering system for simulating maneuvers of one or two ships in calm water or waves. The predictions were also compared with the published numerical and model test results. It was shown that 3D hydrodynamic models are improving the prediction; it was also shown that hydrodynamic interactions are important especially when two ships are operating in each other’s vicinity, which is common in real underway replacement or lightering operations.