Gu, Haoyuan (2016-12). Coupled Mooring Analysis of a CALM Buoy by a CFD Approach. Master's Thesis. Thesis uri icon

abstract

  • The catenary anchor leg mooring (CALM) system is widely used as an efficient and economic single point mooring system in offshore engineering applications. CALM buoys are often connected to FPSOs with large flowlines for offloading function. Compared to other floating structures like FPSOs or TLP, CALM buoy is more sensitive to the responses of mooring lines and oil offloading lines due to its special characteristics. These features for buoy can result in dangerous motions causing fatigue damage in mooring and flowlines systems. Therefore, it is essential to develop advanced numerical methods for accurate estimate of dynamic motion for CALM buoys. In this research thesis, the Finite-Analytic Navier-Stokes (FANS) code is coupled with an in-house MOORING3D code for time-domain simulation of the hydrodynamic response of CALM buoy system. In the FANS code, the fluid domain is decomposed into multi-block overset grids. The Large Eddy Simulation (LES) turbulence model is used to provide accurate prediction of vortex-induced motion of the buoy. The mooring system is simulated with a nonlinear finite element module, MOORING3D. An interface module is established to facilitate interactive coupling between the buoy and mooring lines. The coupled FANS/MOORING3D code is calibrated first for free-decay case and compared with model test data. Then the coupled code is applied for the simulation of two degree-of-freedom vortex-induced motion of a CALM buoy in uniform currents to illustrate the capability of the present CFD approach for coupling mooring analysis of offshore structures. With the study it can be verified that the coupled FANS/MOORING3D method is able to provide an accurate simulation of the hydrodynamic behavior of the CALM buoy system.
  • The catenary anchor leg mooring (CALM) system is widely used as an efficient and economic single point mooring system in offshore engineering applications. CALM buoys are often connected to FPSOs with large flowlines for offloading function. Compared to other floating structures like FPSOs or TLP, CALM buoy is more sensitive to the responses of mooring lines and oil offloading lines due to its special characteristics. These features for buoy can result in dangerous motions causing fatigue damage in mooring and flowlines systems. Therefore, it is essential to develop advanced numerical methods for accurate estimate of dynamic motion for CALM buoys.

    In this research thesis, the Finite-Analytic Navier-Stokes (FANS) code is coupled with an in-house MOORING3D code for time-domain simulation of the hydrodynamic response of CALM buoy system. In the FANS code, the fluid domain is decomposed into multi-block overset grids. The Large Eddy Simulation (LES) turbulence model is used to provide accurate prediction of vortex-induced motion of the buoy. The mooring system is simulated with a nonlinear finite element module, MOORING3D. An interface module is established to facilitate interactive coupling between the buoy and mooring lines. The coupled FANS/MOORING3D code is calibrated first for free-decay case and compared with model test data. Then the coupled code is applied for the simulation of two degree-of-freedom vortex-induced motion of a CALM buoy in uniform currents to illustrate the capability of the present CFD approach for coupling mooring analysis of offshore structures.

    With the study it can be verified that the coupled FANS/MOORING3D method is able to provide an accurate simulation of the hydrodynamic behavior of the CALM buoy system.

publication date

  • December 2016