Extensive model test measurements augmented by analytical studies have provided a quantitative understanding of the mechanisms by which loading is induced by wave action on a floating hose-string attached to a catenary anchor 1eg buoy. The loading is markedly influenced by the dynamic response of the buoy and the wave climate.
The most common single point mooring (SPM) is the catenary anchor leg mooring (CALM). The distinctive feature of this system is a floating buoy moored by catenary chains which are anchored to the seafloor (Figure 1). Four, six or eight chains are used. The tanker is moored to the buoy at the bow. Oil is transported between the sea-bed pipeline and the buoy via flexible submarine hoses and between the buoy and tanker vi a one or more flexible floating hose-strings.
Recent research, O'Donoghue (1987), at Heriot-Watt University, Edinburgh, U.K. has concentrated on the floating hose string component of an SPM installation. This component, between the tanker and the mooring buoy of a CALM SPM, consists of a number of individual hose lengths, each 10m long, bolted together by means of steel flanges built into the ends of the hose lengths.
The floating hose link is a vital one in an SPM terminal system. Failure or damage to any part of a floating hose-string may cause oil spillage and terminal downtime with serious pollution and financial consequences. Ziccardi (1970) points out that the selection of a hose system for an SPM terminal depends on both operational and environmental conditions. Operational requirements such as working pressure, desired through-put, nature of products to be transported, are generally well-defined. However there is a serious lack of knowledge of the forces and moments induced on floating hose-strings in the ocean environment. This has meant that the design of floating hose-strings has, for the most part, been based on trial and error.
The objective of this study is a quantitative understanding of the mechanism by which forces and moments are induced in floating hose-strings attached to a CALM buoy by the combined action of waves and buoy motions. The study is based primarily on physical-model tests in which the buoy motions and the forces and moments along the hose-string are measured in various sea conditions.
The authors are aware of only four pub1i shed papers which address the behaviour of floating hose-strings in the ocean environment and the contents of these are summarised in what follows:
Brady et al (1974) report on load measurements recorded at a CALM buoy off Nigeria. The straingauged load-measuring spool was fitted between the 24 inch first-off-the-buoy hose and the buoy manifold. Measurements of axial load, torsion and bending moments in two orthogonal planes were recorded. From the statistical analysis of the 60 second records and from vi sua1 records of the sea conditions, attempts were made to correlate the measured loads with the environmental data but the desired correlation is severely limited due to the lack of accurate wave records.
