{"title":"Time Domain and Frequency Domain Analyses of Measured Metocean Data for Malaysian Waters","authors":"Duong Vannak, Mohd Shahir Liew, Guo Zheng Yew","volume":80,"journal":"International Journal of Geological and Environmental Engineering","pagesStart":549,"pagesEnd":555,"ISSN":"1307-6892","URL":"https:\/\/publications.waset.org\/pdf\/16180","abstract":"Data of wave height and wind speed were collected \r\nfrom three existing oil fields in South China Sea – offshore \r\nPeninsular Malaysia, Sarawak and Sabah regions. Extreme values \r\nand other significant data were employed for analysis. The data were \r\nrecorded from 1999 until 2008. The results show that offshore \r\nstructures are susceptible to unacceptable motions initiated by wind \r\nand waves with worst structural impacts caused by extreme wave \r\nheights. To protect offshore structures from damage, there is a need \r\nto quantify descriptive statistics and determine spectra envelope of \r\nwind speed and wave height, and to ascertain the frequency content \r\nof each spectrum for offshore structures in the South China Sea \r\nshallow waters using measured time series. The results indicate that \r\nthe process is nonstationary; it is converted to stationary process by \r\nfirst differencing the time series. For descriptive statistical analysis, \r\nboth wind speed and wave height have significant influence on the \r\noffshore structure during the northeast monsoon with high mean wind \r\nspeed of 13.5195 knots (\u0001 = 6.3566 knots) and the high mean wave \r\nheight of 2.3597 m (\u0001 = 0.8690 m). Through observation of the \r\nspectra, there is no clear dominant peak and the peaks fluctuate \r\nrandomly. Each wind speed spectrum and wave height spectrum has \r\nits individual identifiable pattern. The wind speed spectrum tends to \r\ngrow gradually at the lower frequency range and increasing till it \r\ndoubles at the higher frequency range with the mean peak frequency \r\nrange of 0.4104 Hz to 0.4721 Hz, while the wave height tends to \r\ngrow drastically at the low frequency range, which then fluctuates \r\nand decreases slightly at the high frequency range with the mean \r\npeak frequency range of 0.2911 Hz to 0.3425 Hz.<\/p>\r\n","references":"[1] Toshio Atsut, Shoji Toma and Kawasaki, 1976, "Fatigue Design of an\r\nOffshore Structure", Offshore Technology Conference, Houston, Texas,\r\n3-6 May 1976.\r\n[2] Peter S. 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