Abstract—Data of wave height and wind speed were collected from three existing oil fields in South China Sea – offshore Peninsular Malaysia, Sarawak and Sabah regions. Extreme values and other significant data were employed for analysis. The data were recorded from 1999 until 2008. The results show that offshore structures are susceptible to unacceptable motions initiated by wind and waves with worst structural impacts caused by extreme wave heights. To protect offshore structures from damage, there is a need to quantify descriptive statistics and determine 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 using measured time series. The results indicate that the process is nonstationary; it is converted to stationary process by first differencing the time series. For descriptive statistical analysis, both wind speed and wave height have significant influence on the offshore structure during the northeast monsoon with high mean wind speed of 13.5195 knots (࣌ = 6.3566 knots) and the high mean wave height of 2.3597m (࣌ = 0.8690m). Through observation of the spectra, there is no clear dominant peak and the peaks fluctuate randomly. Each wind speed spectrum and wave height spectrum has its individual identifiable pattern. The wind speed spectrum tends to grow gradually at the lower frequency range and increasing till it doubles at the higher frequency range with the mean peak frequency range of 0.4104 Hz to 0.4721 Hz, while the wave height tends to grow drastically at the low frequency range, which then fluctuates and decreases slightly at the high frequency range with the mean peak frequency range of 0.2911 Hz to 0.3425 Hz. Keywords—Metocean, Offshore Engineering, Time Series, Descriptive Statistics, Autospectral Density Function, Wind, Wave. I. INTRODUCTION T present, there are more than 10,000 offshore production structures worldwide and more than 250 fixed platforms located in offshore Peninsular Malaysia, Sarawak and Sabah regions. The numbers will increase with world energy demand. The design life of a platform is 25 years; the majority of the structures are going to exceed the designed life period. With increasing energy demand, oil-and-gas companies are eager to explore other areas for a new source of hydrocarbons. To determine the sites for exploratory drilling, regional sea state condition surveys are done to ensure that operations will have no disruption from any extreme event and the design of offshore platform will be scrutinized for its design efficiency and economics due to escalating material costs. In deepwater regions, offshore structures are often exposed to critical states due to severe metocean conditions. Damage Duong Vannak, Mohd Shahir Liew, and Guo Zheng Yew are with the Civil Engineering Department, Universiti Teknologi Petronas, Perak, Malaysia (e- mail: duongvannak@gmail.com, shahir_liew@petronas.com.my, henry.yew88@gmail.com). has been reported on offshore drilling platforms due to wave forces. The periodicity of loads has two phases on structural damage, the first being the dynamic resonance of the structure and the other is the fatigue failure of the material [1]. Generally, the overall design of the offshore structure depends on the environmental loads, with wind speed and wave height being the most critical loads considered, which are applied to the structure from various directions. The environmental load data are obtained from a hindcast database which provides significant wave heights, wave directions, spectral information, current amplitude and direction, and wind speed and direction over a long time period. Hindcast data are far more comprehensive than any measured time history [2]. If there is insufficient or missing measured data for the location, the standard practice is to use hindcast data to derive metocean design criteria [3]. II. METOCEAN Responses of selected offshore structures, due to metocean forces, are monitored in real-time and full scale, providing essential information and knowledge for the design of offshore structures and offshore installations. Measured metocean data is used to produce customized domains to get high resolution prediction of ocean and coastal conditions, and also can be configured to whatever scale required – for instance to resolve the wave energy gradients behind an island, throughout an oil field or along a shipping channel and into a harbor entrance [4]. Metocean data help to reduce construction costs with accurate and less conservative design conditions besides avoiding high costs for installation and operation. It is necessary to support offshore operational planning for the optimal design of offshore installations and to ensure offshore safety and environmental protection as there is no universal wave spectral model which can be applied to all storms in the world. The environmental study at the exposed installation area is important and is required for all stages of offshore oil- and-gas exploration and production [5]. However, other parameters must also be considered at some locations and specific types of operations, such as sea temperature, visibility and ice conditions [6]. The response or resistance of offshore structural facilities to environmental loads is usually dependent on the load application, which is critical to ensure reliability of offshore structures. The use of wind and wave statistics in the design and operation of offshore facilities provides the engineer with a source of information on output or response statistics for key design parameters, rather than only single-value input statistics. Although it is not practical to analyze each and every facility exposure event during its Duong Vannak, Mohd Shahir Liew, and Guo Zheng Yew Time Domain and Frequency Domain Analyses of Measured Metocean Data for Malaysian Waters A World Academy of Science, Engineering and Technology International Journal of Geological and Environmental Engineering Vol:7, No:8, 2013 549 International Scholarly and Scientific Research & Innovation 7(8) 2013 scholar.waset.org/1307-6892/16180 International Science Index, Geological and Environmental Engineering Vol:7, No:8, 2013 waset.org/Publication/16180