Model Testing Of A Deepwater Salm/Tanker System

ABSTRACT The paper describes the results of physical model tests undertaken to investigate the performance of a deepwater SALM/tanker system in a wind, wave and current environment. The system tested is an element of the Esso Deepwater Integrated Production System (EDIPS), for which a conceptual design was completed in 1987 for Esso Exploration and Production UK Limited. The testing program required development of several novel transducers which are described in the paper and necessitated hydroe1astic modelling of the SALM lower riser to ensure that accurate vibration response to wave and flow excitation was obtained. Tests were undertaken in a variety of conditions which included multidirectional waves and oblique wind directions. The test results demonstrate the increased loading and motions caused when the environmental loading is not collinear. The vibration response of the lower riser and the effect of an inertia skirt on the performance of the double articulated SALM are also described in the paper. INTRODUCTION An extensive matrix of wave tank model tests were carried out at the British Maritime Technology (BMT) on a model of a deepwater SALM/Tanker system. The work was funded jointly by Esso Exploration and Production UK Limited and the UK Department of Trade and Industry Marine Technology Committee, and was done under the technical stewardship and coordination of Esso's research affiliate, Exxon Production Research Company. The model tests were conducted with two primary objectives:To act as a comparison for BMT's time domain computer simulation program BMTSPM.To study the dynamic behavior of the SALM/tanker system, which is an element of the Esso Deepwater Integrated Production System (EDIPS) (Reference 1). The SALM system (Figure 1) consists of a buoy moored to the seabed by a single, tensioned riser. The system was designed to operate in a water depth of 610 meters and moor a storage tanker of approximately 250,000 deadweight tonnes capacity. The riser was pin-jointed at both the seabed and the connection with the lower buoy. A removable inertia skirt was fitted to the lower buoy to increase the local added mass and reduce the motions at the mid-water universal joint. The buoy was connected to the tanker by a rigid, pivoted yoke. The SALM buoy, yoke, and tanker models were fabricated conventionally as rigid elements, and were fitted with lead weights to achieve the desired weight, center of gravity and radii of gyration. A flexible model of the riser was designed and built to have the proper scaled bending stiffness. This was a principal challenge of the program, and was done so that the riser's vibration response over the frequency range of predominant wave energy could be measured. Unlike the approach usually taken to model test shallow water SALM systems, the riser cannot be considered a rigid element in deep water systems.