A Problem Analysis of the Pulau Bukom-SBM offshore Singapore

A Problem Analysis of the Pulau Bukom-SBM offshore Singapore

Slooten, W.

Velsink, H. (mentor)
Massie, W.W. (mentor)
Booij, N. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

1990-06-01

The Pulau Bukom-SBM, situated at about 10 kilometers offshore Singapore, is used as a mooring facility for tankers transporting crude oil for the Shell refineries on the island of Pulau Bukom. The bow hawsers (nylon ropes) which connect the ships with the SBM are frequently subjected to extreme forces excited by the ships. Many similar installations are used over the entire globe and normally these peak loads are due to wave- or current forces working on the tankers in severe weather conditions. Offshore Singapore, however, these loads also occur during apparent calm periods and seem to be independent of the waves. In order to guarantee safe dynamic operations SEPL installed a load monitor recorder on the SBM which measures all the executed forces in the hawsers. The data obtained from the load recordings are compared to the tidal predictions for Singapore area which show that some sort of relation exists between the height of the peak loads and the current velocities present at the time the forces are executed. Because of the suspected inaccuracies in the data the exact relation can not be derived. Investigation of the continuous load monitor recordings give some insight in the physics of the system as is explained in chapter 2. In chapter 3 the dynamics of the system (SBM inclusive moored tanker) are examined. Although the system is a non-linear double mass-spring system, adequate approximations of the resonant frequency can be obtained when the system is simplified to a linear single mass-spring system. Hereby the effects of the simplifications on the natural frequency value are investigated as well. A study on the average occuring wave fields near Singapore (chapter 4) shows that neither first- nor second order wave motions possess enough energy for exciting the moored tankers significantly. Through the establishment of a detailed tidal current model of the area of the SBM the presence of macro eddies is proven (chapter 5). These macro eddies are local current fluctuations in the order of minutes which originate in lee of islands or by other irregularities in the bottom topography. When carried along in the main current they can cover a distance of several kilometers before they are damped out. Since the diameters of the eddies are about two or three times the average ship length they can excite the tankers to peak loads comparable to the recorded forces and are, thus, the most probable cause of the problems. Although the development and testing of load reducing measures fall beyond the scope of this study, it is clear that it will be very difficult to apply adequate measures within limited costs which can lengthen the operational life of the hawser.

single buoy mooring
mooring systems
offshore mooring
offshore loading

http://resolver.tudelft.nl/uuid:966dbcc3-789f-41e7-9d77-68beb7e94519

Student theses

master thesis

(c) 1990 Slooten, W.