Wave Loading On A Prototype Cylinder Available to Purchase

This paper presents the results of wave forces acting on a slender vertical cylinder installed on a floating offshore structure. The experiment project was conducted by using the prototype floating structure "POSEIDON", under the deck of which the test cylinder with 0.406 m diameter was installed vertically. The cylinder was made in three separates parts (upper, middle and lower sections). In the middle section which is a.6m high, the force transducers and three components accelerometers were mounted. The immersed depth of centre of the middle section was 2.5m. The experiment had been conducted from September, 7 to November, 11 in 1989. Wave forces, wave surface elevation, current, accelerations of the cylinder and motions of POSEIDON were measured. Not only the frequency domain analysis but also time series fitting analysis are carried out to identify the force coefficients. As for the frequency domain analysis, a multi-input/single-outpu t model is used to directly identify frequency dependent inertia and drag coefficients. And for the time series analysis, a least square fit of instantaneous inline force is used to identify the constant force coefficients. And after the at-sea experiment, a forced surging test was also done at the laboratory basin of Ship Research Institute in order to investigate a basic characteristics of the inertia and drag coefficients. Furthermore the statistical analysis was carried out to study whether the extreme value of the inline force is estimated from the linear noise theory or not. The main results are as follows: The inertia coefficient strongly depends on wave frequencies. Particularly the variation of the coefficient in the frequency range greater than 0.1 Hz ia large. However, if the frequency dependent Keulegan Carpenter number, defined by each frequency components of relative velocity spectrum,