The analysis of model measurements concerning the behaviour of moored ships in long waves

Abstract

When designing a new port it is important to predict the operation efficiency of the port. In this respect, it is desirable to predict the possible downtime of a new port in an early phase of the design process. Downtime depends strongly on the moored ship motions. In the past decades several numerical models were developed to predict the behaviour of moored ships in waves. They are referred to as Six Degree of Freedom (SDF) models. These models, such as TERMSIM and BAS, are complex and require quite detailed input data. This detailed information is not available in the planning phase of a new port. Consequently, it is desirable to estimate possible downtime by means of a simple model that estimates the ship's behaviour without detailed input data. With this in mind Delft University of Technology started a research programme that consists of a number ofMSc- projects possibly leading to a PhD-project. The research objective of the programme is to investigate the possibilities of simplification of the models used nowadays. In this respect the aim is to find straightforward relationships to describe the behaviour of moored ships subjected to incident waves. It is emphasized that this simplified model is not meant to replace the Six Degree of Freedom models. The simple model is a valuable design tool, to be used in an early stage of the port development process. This report covers one of the MSc-projects defined as "The analysis of model measurements concerning the behaviour ofmoored ships in long wave ". It concerns the model tests of the planned "Coega Harbour" in South Africa. Part of this project is carried out in South Africa, at CSIR (Council for Scientific and Industrial Research), where data of the model tests are available. The aim of the project is to gain insight in the importance of the various parameters and their mutual relations. An important issue is the validation of relationships mentioned in the literature. The main objective is to derive straightforward relations between motions of a moored ship and the wave field near the ship. Hypotheses with regard to the surge, sway and roll motion are derived from the theory of a moored ship. These hypotheses are verified using the data measured in the physical model. This data is limited to one type of ship moored with one type of mooring system inside one specific harbour. Consequently, the conclusions do not contain general validity. Nonetheless, the results present tools that contribute to the understanding of the response of a moored ship to incident waves.