On combination formulae for the extremes of wave-frequency and low-frequency responses

One special feature in moored floating platforms is the co-existence of the first-order wave-frequency (WF) response and the second-order low-frequency (LF) resonant response. Non-linear properties inherent in moored floating platforms cause the platform motions and mooring cable tensions to be non-Gaussian (not normal) distributed, both for the WF and for the LF components. As the LF and the WF components are not independent, it is important and necessary to find a simple, reliable and yet physically sound technique to estimate their combination. In this paper, on the basis of some model test results, different combination formulae are compared and a formula considering WF and LF correlation effects is suggested. A simple approach is also proposed to estimate the correlation factor. (C) 1999 Elsevier Science Ltd. All rights reserved.