In-situ riser structural monitoring has been used by a number of operators and drilling contractors to support drilling operations. The measurements have been used to understand the level of accuracy present in the up-front fatigue analysis and to confirm the integrity of the drilling systems, especially during extreme environmental events. However, the field data analysis requires detailed understanding of drilling riser modeling, loading conditions, operations, sensor characteristics and signal processing. Several methods have been developed to calculate stresses and fatigue damages in the riser using measured motion data. Careful selection of the analysis approach will determine the system configuration and validity of the measured results.
Mode shape matching has been widely used for the data analysis where riser response is dominated by Vortex Induced Vibration (VIV). Another riser fatigue method has been recently developed and is based on analytical transfer functions used to convert measured accelerations into curvature. Another method considers FEA-based transfer functions. Some of these methods perform fatigue calculations in time domain while some others in frequency domain.
Each method exhibits benefits and limitations depending on the characteristics of the measured riser response. Selecting the most appropriate fatigue methodology depends on the riser response and instrumentation system design.
In this paper, three fundamentally different riser fatigue methods utilizing measured motion data are described and compared with each other. The advantages and disadvantages of each approach are evaluated and recommendations are provided for when each method should be considered.
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