The dynamics of mooring lines for deep water applications with submerged buoys attached to them are studied both experimentally and numerically. The experimental setup, as well as the data acquisition procedures are first detailed. This is followed by a presentation of the obtained results and their comparison with numerical predictions using both time and frequency domain computer codes. Very good correlation is obtained. Finally, the beneficial effects of buoys in reducing the mooring line dynamic tension is shown, provided that proper selection of their size, number and location is performed.
The need for incorporating dynamic considerations in a rational design procedure for deep water mooring applications has been addressed in several recent publications (Tein et aI, 1987; Kwok and Huang, 1988; Bergdahl and Rask, 1987; Taylor et aI, 1987; Fylling et aI, 1987; Kwan, 1990). This has led to a modification of the design rules and guidelines of various organizations. The quasi-static design approach, which has been proven to be a proper design tool for mooring systems in shallow water, is generally considered inadequate for the case of deep water applications. In such cases the maximum attainable value of the dynamic tension amplification, which is approximately equal to the elastic stiffness of the line, is shifted within the wave frequency range, thus causing large dynamic tension values due to the vessel's firstorder motions (Triantafyllou et aI, 1985). It is therefore evident that the elastic stiffness of the cable represents the principal parameter affecting the mooring line's dynamic response and, hence, that its reduction would improve the dynamic performance of the line. It has been recently shown both numerically and experimentally (Mavrakos et aI, 1989a and 1989b; Papazoglou et aI, 1990b), that this reduction can be achieved by inserting submerged buoys along the mooring line.
