Wave Measurements for the Monitas System

The paper is one of the series of papers about the Advisory Monitoring System for controlling the fatigue lifetime consumption of FPSO hulls. The system has been developed within the Monitas Joint Industry Project (JIP). The name Monitas stands for Monitoring Advisory System. A key factor for proper lifetime prediction is an accurate assessment of the ocean surface wavefield. Therefore, a dedicated wave system analyses tool (XWaves) has been developed within the project that allows for online analysis of the measured wave data. The Monitas project recommends use of navigational radar for measuring waves. This paper compares the wave data obtained from such radar with that obtained from a wave buoy. The differences in obtained wave data from both instruments are illustrated and explained. The effect of these differences on fatigue lifetime consumption has been quantified. The paper also investigates how different wave data formats which are being used by the offshore industry affect the fatigue lifetime calculations. All comparisons and conclusions are based on real data collected from the Monitas system installed on board FPSO Glas Dowr. It has been concluded that navigational radar can be used as the instrument for wave measurements and that different wave data formats are acceptable providing the wave directionality data is preserved.

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