An heuristic hydrodynamic model for the analysis of moored ships under current action.

Author(s)

Alexandre Nicolaos Simos

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica
• Defense date: 03 set. 2001

Examining board members

Celso Pupo Pesce; Jose Augusto Penteado Aranha; Marcos Donato Auler da Silva Ferreira; Clodoaldo Grotta Ragazzo; Sergio Hamilton Sphaier

• Advisor: Celso Pupo Pesce

Abstract

A new hydrodynamic model for the analysis of current forces acting on moored tanker ships is proposed. The theoretical model is valid for any angle of attack of the current and is intended, primarily, for the analysis of FPSO (Floating Production Storage and Offloading) systems, although its application may be easily extended to other correlated problems in ocean engineering. The model depends basically on the ship main dimensions and requires few external parameters to be derived. This quasi-explicit nature certainly constitutes the model main advantage and it was only possible due to the more restricted context it was derived for. The extended heuristic model, as it is called, was based on a previous static version presented by Leite et al. (1998). The hydrodynamic effects arising from the ship yaw motion were now incorporated, making the model able to cope with the problem of combined drift-yaw motions. Yaw velocity influence was determined by means of a heuristic combination of semi-empirical formulations of force and moment components, resultant from distinct fluid flow patterns, each one related to a different range of angles of attack. Force predictions were validated through confrontation with yaw-rotating experimental results, obtained for different tanker models in distinct loading conditions. It was also verified experimentally that the model is capable of predicting the hydrodynamic forces involved in the unstable dynamic behavior of asingle-point moored tanker, when subjected to a steady ocean current, known as fisthailing phenomenon. A critical revision of the different theoretical models at hand represents a supplementary purpose of this work. This revision was performed based on the main hydrodynamic aspects involved in common offshore applications of moored tanker ships. ) Therefore, instead of a passionate defense of any particular theoretical procedure, the work aims to provide a consistent orientation in order to help the offshore system designer to choose, between the various hydrodynamic models, the one that is more suitable for the analysis of a specific project, confident on its advantages and aware of its eventual limitations. (AU)

• FAPESP's process: 97/14091-3 - Modelagem hidrodinâmica de sistemas FPSO (floating production storage and Offloading systems) em configuração turret
• Grantee: Alexandre Nicolaos Simos
• Support type: Scholarships in Brazil - Doctorate