International Conference on Advances in Structural, Civil and Environmental Engineering - SCEE 2013
Author(s) : DUONG VANNAK, MOHD SHAHIR LIEW
In this research, the data of wave height and wind speed are collected from metocean data of the three existing oil fields in South China Sea – Terengganu, Sarawak and Sabah regions by getting their extreme values and significant data for analysis. The data consist of actual data which were recorded from year 1999 until 2008. From observation, the offshore structures are particularly at risk with any unacceptable motions initiated by wind and waves, which can lead to impact and capsize events, whereas the worst impact comes from the extreme wave height. To prevent the offshore structure from any damage, there is a need to study their descriptive statistics and spectra envelope of wind speed and wave height, and to ascertain the frequency content of each spectrum for offshore structures in the South China Sea shallow waters from actual time series. The results indicate that the process is nonstationary; it is converted to stationary process by first difference method to develop the normalized power spectral density envelope. For descriptive statistics analysis, it illustrates that both wind speed and wave height have significant influence to the offshore structure during northeast monsoon with the high mean wind speed of 13.5195 knots ( = 6.3566 knots) and the high mean wave height of 2.3597 m ( = 0.8690 m). For spectral density analysis, it shows that there is no clearly dominant peak and the peaks seem to fluctuate at random. Each wind speed spectrum and wave height spectrum has its own individual identifiable pattern. The wind speed spectrum tends to grow gradually at lower frequency range and increasing significantly till it doubles at the higher frequency range with the mean peak frequency range of 0.4104 Hz - 0.4721 Hz, while the wave height tends to grow drastically at low frequency range, and fluctuates and decreases slightly at the high frequency range with the mean peak frequency range of 0.2911 Hz - 0.3425 Hz.