At-sea Experiment of a Floating Offshore Structure

Abstract

The at-sea experiment of the moored floating structure, which is called POSEIDON, has been done at the Japan sea since september in 1986.This paper deals with the characteristics of wind speeds measured at the test field. Especially, we concentrate upon varying wind speed spectrum, 1/nth highest expected values, and gust factors.As an anemometer, a sonic anemometer was used and it was installed at the top of mast of POSEIDON, at which is the position of 19.5 m height above sea surface.The main results are as follows.i) A new formula of varying wind speed spectrum is developed under physical considerations. The presented spectrum can be determined by two parameters, i. e. the peak frequency and the power, those are prescribed by the friction coefficient between air and sea surface.The measured spectra do not agree with the well-known spectra (Davenport's and Hino's spectra) but accord with the presented spectra.ii) 1/nth highest expected values and gust factors can be estimated by using the well-known statistical estimation theory (i. e. Longuet-Higgins theory) and the presented spectrum.