ANALYZING THE EFFECT OF INTEGRATING RISER/MOORING LINE DESIGN
Partha Chakrabarti, Zentech Inc., Houston, TX, USA,
Ramesh Cbandwani and lan Larsen, Zentech Intl., Surrey, UK
ABSTRACT
The design of riser and mooring systems for a floating production system usually assumes uncoupled behavior of the two systems, and each system is analyzed for the effects of the vessel response given as input. In certain situations, such as for a floating production system, the presence of the risers can affect natural periods, damping, and slow drift response of the vessel thereby influencing the system design. This paper discusses a method for analyzing the coupled riser/mooring system with emphasis on the effect of the risers on the total system behavior.
DYNAMIC ANALYSIS OF RISERS SUBJECTED TO RANDOM WAVES
Saadat Mirza, Engineering Research and Development Dept., Agip S.p.A., Milan, Italy Roberto Bruschi and Paolo Simantiras, Subsea, R&D, Snamprogetti S.p.A., Fano, Italy
ABSTRACT
The paper presents the results of a series of measurements performed on a full scale instrumented riser. The test set up is comprehensively described in a previous paper by Campelli et al. (1992). In particular, in this paper vortex shedding induced vibrations (VIV) under oscillatory flow conditions, are discussed. Response trajectories and hydrodynamic loads are analyzed at two locations, 53% and 62% of the riser length from the bottom hinge. Maximum orbital velocities measured at the two sections, correspond to Keulegan-Carpenter number (KC)of 12 and Reynolds number (Re) of 5x104. In time series, VIV are characterised by excitation during half wave cycles overcoming a certain KC threshold, which is followed by decaying oscillations as a consequence of structural and fluid dynamic damping during half wave cycles characterised by smaller KC. Results are compared with Bearman (1988), using the equivalent KC method proposed by Srinivasan (1990). Response trajectories of cross sections are in accordance with the observations of Sarpkaya (1995).
Presented results are preliminary and further analyses are in progress.
