Development of Offshore Structures (Mooring/Riser) Performance Assessment and Monitoring using Computer Simulations and Numerical Sensors
Abstract
In this dissertation, five subjects which are related to offshore structure (mooring lines and risers) performance assessment and monitoring will discuss mainly such as chain mooring OPB-induced failure and riser structure health monitoring with numerical sensors.
First, a multi-scale approach concept is introduced to estimate OPB (out of plane bending)-induced failure considering time-varying interlink bending stiffness by using both high-fidelity nonlinear-FEM (finite element method)-based local structural analysis and low-fidelity global-system-simulation program so that they can mutually be interfaced during the time-stepping procedure.
Second, the effects of underwater-chain-stopper (UCS) bearing friction at fairlead connection and time-varying interlink EI (bending stiffness) at the UCS exit on the OPB-fatigue-induced chain failure are investigated. To demonstrate their effects through numerical simulations, three different approaches, such as only considering time-varying EI, considering both time-varying EI and fairlead bearing friction, and neither considered, are modeled and the results are systematically compared.
Third, a new algorithm for the real-time structural health monitoring of TLP (tension-leg platform) tendons is presented. The algorithm is based on bi-axial sensors installed along the tendon and top tension-meter. Then, the tension and bending moment along the tendon can be estimated by using the developed algorithm. For bending moment, a generalized-coordinate-based FEA (Finite Element Analysis) formulas with cubic interpolation are derived. For tension, analytical formulas with small angle assumption are derived.
Fourth, the methodology for the real-time tracing of riser profile and bending moment by multiple inclinometers along the riser is presented with the assumption that its top (by GPS; global positioning system) and bottom (anchoring) points are known. For riser x-y-z displacement and bending-moment tracing, quadratic and cubic interpolation functions for each line element between two neighboring bi-axial inclinometers are employed with respect to the global and generalized coordinate systems to derive analytical solutions.
Lastly, the monitoring methodology with minimum top sensors using digital twin with assumption that there is a significantly wave excitation loads reduction below certain water depth (last sensor attached) is presented. Also, multivariate regression can be applied to predict current profile at the remaining water depth.
Citation
Chung, Woo Chul (2021). Development of Offshore Structures (Mooring/Riser) Performance Assessment and Monitoring using Computer Simulations and Numerical Sensors. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /195619.