Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
STUDY OF THE INTEGRITY OF MOORING SYSTEMS FOR OIL EXPLORATION PLATFORMS
Submission Author:
Felipe Hansen , DF , Brazil
Co-Authors:
Felipe Hansen, Lucival Malcher
Presenter: Felipe Hansen
doi://10.26678/ABCM.COBEM2021.COB2021-1401
Abstract
This project proposes the application of the finite element method, using the software called ABAQUS, version 6.14 for the study and analysis of chain links without mallet belonging to the FPSO ship anchoring system. For the purpose of this analysis, it was considered the cyclical flexion that occurred outside the main plane of the links, known as OPB (Out of Plane Bending) and IPB (In Plane Bending). The OPB generates a considerably greater influence on fatigue life compared to the IPB. For this reason, only bending moments from that plane were considered. According to the API (American Petroleum Institute) design recommendations, the dimensioning of the chain links of the FPSO ship anchoring system considers only the normal stress generated by axial loads arising from the contact between the links, disregarding any bending moment. Nevertheless, this moment occurs, because large loads raise the resulting frictional force in the contact between the links, making it behave like a bezel and, consequently, the action of transverse forces would result in a flexion of the link in the main plane. As a result, FPSO platform ships that are designed to last more than 20 years, supporting various factors of nature, as well as operating conditions of the platform itself, supporting transport loads and elevation of the oil, reported cases of failure in the anchoring system in less than 2 years. As a way of validating this study, the full scale mooring-fairlead set was modeled on the ABAQUS, a simplified model of the anchoring system containing only a set of 5 links and 2 semi-links, guided through the fairlead. In this modeling, the material of the links was defined as offshore steel belonging to grade R4, a material capable of withstanding very high loads, whereas the fairlead was defined as a rigid body, since it was not deemed necessary to analyze its stress and deformation fields. Finally, the modeling went through several simulations considering the distribution of stress generated in the links from the different working angles of the moorings, more specifically analyzing the winding angles of 17°, 30°, 45° and 60°, being applied on currents, normal stresses oscillating between 200 ton and 400 ton. With the result of this analysis it is possible to identify the hotspots in the links and to identify the effect that the degree of winding of the mooring-fairlead set has on the life of the link.
Keywords
anchoring system, mooring-fairlead, Hotspots, OPB
