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Ocean Systems Engineering
  Volume 12, Number 1, March 2022 , pages 87-142
DOI: https://doi.org/10.12989/ose.2022.12.1.087
 

A computer based simulation model for the fatigue damage assessment of deep water marine riser
Chirag A. Pallan and Rajiv Sharma

 
Abstract
    An analysis for the computation of Fatigue Damage Index (FDI) under the effects of the various combination of the ocean loads like random waves, current, platform motion and VIV (Vortex Induced Vibration) for a certain design water depth is a critically important part of the analysis and design of the marine riser platform integrated system. Herein, a 'Computer Simulation Model (CSM)' is developed to combine the advantages of the frequency domain and time domain. A case study considering a steel catenary riser operating in 1000 m water depth has been conducted with semi-submersible. The riser is subjected to extreme environmental conditions and static and dynamic response analyses are performed and the Response Amplitude Operators (RAOs) of the offshore platform are computed with the frequency domain solution. Later the frequency domain results are integrated with time domain analysis system for the dynamic analysis in time domain. After that an extensive post processing is done to compute the FDI of the marine riser. In the present paper importance is given to the nature of the current profile and the VIV. At the end we have reported the detail results of the FDI comparison with VIV and without VIV under the linear current velocity and the FDI comparison with linear and power law current velocity with and without VIV. We have also reported the design recommendations for the marine riser in the regions where the higher fatigue damage is observed and the proposed CSM is implemented in industrially used standard soft solution systems (i.e., OrcaFlex*TM and Ansys AQWA**TM), Ms-Excel***TM, and C++ programming language using its object oriented features.
 
Key Words
    computer simulation model; current velocity; deep water marine riser; fatigue damage; linear law; power law; random waves; vortex induced vibration
 
Address
Chirag A. Pallan and Rajiv Sharma: Design and Simulation Laboratory, Department of Ocean Engineering, IIT Madras,
Chennai (TN) - 600036, India
 

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