Effect of added mass and damping on the response of subsea structure installation

Date on title page is 2021. Degree awarded in 2022Remotely located deepwater fields with challenging environmental conditions are now being explored and developed because of their good energy resource. This means technology advancement in marine operations is required to influence the field development cost. This is hindered by the difficulty in estimating the added mass and damping parameters which are important influencing factors in the installation process of subsea structures required for the field development. These issues are addressed by developing an analytical calculation and Fluent simulation method to estimate the hydrodynamic coefficients of complicated subsea structures far from boundaries and in close proximity to the seabed at different KC numbers. The analytical method is developed from standard hydrodynamic theory, and the CFD analysis is based on estimating the hydrodynamic force on the structure and then splitting the force into its added mass component, while the equivalent linearized damping is derived from the sinusoidal varying force over a time record by fitting a line that touches the peak of these forces. The results from the analytical method and CFD analysis were found to be satisfactory after validating with existing literature and through numerical flow visualisation. The added mass and damping of the structure show KC dependency. As KC increases, the flow field around the vertically oscillating structure and the vortex shedding pattern changes. The increase in KC leads to an independent and interactive vortex shedding regime for the different heights above seabed. The installation analysis performed, showed increasing response of the subsea protective structure at different KC as it progresses to the seabed, which is useful in understanding the influence of submergence on the added mass and damping of subsea structures oscillating in heave direction at various KC number.Remotely located deepwater fields with challenging environmental conditions are now being explored and developed because of their good energy resource. This means technology advancement in marine operations is required to influence the field development cost. This is hindered by the difficulty in estimating the added mass and damping parameters which are important influencing factors in the installation process of subsea structures required for the field development. These issues are addressed by developing an analytical calculation and Fluent simulation method to estimate the hydrodynamic coefficients of complicated subsea structures far from boundaries and in close proximity to the seabed at different KC numbers. The analytical method is developed from standard hydrodynamic theory, and the CFD analysis is based on estimating the hydrodynamic force on the structure and then splitting the force into its added mass component, while the equivalent linearized damping is derived from the sinusoidal varying force over a time record by fitting a line that touches the peak of these forces. The results from the analytical method and CFD analysis were found to be satisfactory after validating with existing literature and through numerical flow visualisation. The added mass and damping of the structure show KC dependency. As KC increases, the flow field around the vertically oscillating structure and the vortex shedding pattern changes. The increase in KC leads to an independent and interactive vortex shedding regime for the different heights above seabed. The installation analysis performed, showed increasing response of the subsea protective structure at different KC as it progresses to the seabed, which is useful in understanding the influence of submergence on the added mass and damping of subsea structures oscillating in heave direction at various KC number