Numerical modeling of internal waves and their influence on deepwater floating systems
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Copyright 2016, Offshore Technology Conference. Internal waves occur due to a combination of density stratification, bathymetry, and tidal effects and have been observed in many parts of the world. Recent discoveries of oil and gas reserves in areas where these phenomena are prominent have caused concern for field development. There have been several incidents where adverse effects were reported due to the effect of these waves on offshore platforms. This paper studies the effects of these waves on tension leg platforms (TLPs) and semi-submersible platforms within a coupled analysis framework. The physics is modeled by the second order Korteweg-de Vries (KdV) equation obtained by simplification and scaling of the Boussinesq approximation. A solution involving Jacobian elliptic functions coupled with a structure function that captures the effect of the pycnocline is utilized to model the wave. The model is implemented in a coupled analysis framework, and time domain simulations are performed to study the effects on a TLP and Semi configured to the developmental requirements and environmental conditions of an internal wave prominent area. Previous results showing the effects of internal waves on Spar platforms are also presented for comparison purposes. Two different internal waves with heights of 90m and 170m are utilized for the study. The impact of these waves on platform motion, tendon and mooring line tension are presented in this paper. The study could provide guidance on platform selection in areas where the phenomenon is prominent. In addition the model adopted in this study has the advantage of capturing temporal effects of internal wave trains making it an effective model for advance warning systems with real time monitoring.
