Generation of Offshore Environments in the Numerical Wave Tank to Model Metocean Conditions Interaction with Offshore Structure Near the Free Surface

Offshore structures play a vital role in the economy of offshore oil-producing countries, where mostly fixed jacket type structures are used to produce oil and gas installed in shallow water. In an offshore environment where structures are installed, there exist met ocean forces such as wind, waves, and currents. These met ocean conditions when interacting with offshore structures near the free surface, generate loads. The estimation of such loads is very much important for the proper design of these structures. The primary aim of this study is to investigate the interaction of waves with a jacket platform by generating offshore environments in the numerical wave tank (NWT). To achieve this goal, ANSYS Fluent is used for the flow analysis by using continuity and Navier Stokes equation. Results are verified and validated with the analytical work. Wave crests under operating condition generate a force of 1.3 MN which is the lowest in magnitude as compared to wave crest which produces 4.5 MN force under extreme conditions. Unlike operating wave crest, the operating wave trough generates a higher force of 1 MN than extreme conditions which account for 1.5 MN forces. Forces produced by the extreme offshore environment are 30% higher than those generated under operating conditions. It is concluded from the results that a positive force is exerted onto the structure during the water entry phase while a negative force is observed when the water leaves the structure.

Focused Plunging Breaking Waves Impact on Pile Group in Finite Water Depth

Accuracy estimation of wave loading on cylinders in a pile group under different impact scenarios is essential for both the structural safety and cost of coastal and offshore structures. Differing from the interaction of waves with a single cylinder, less attention has been paid to pile groups under different arrangements. Numerical simulations of interactions between plunging breaking waves and pile group in finite water depth are performed using the two-phase flow model in REEF3D, an open-source computational fluid dynamics program to investigate the wave loads and flow kinematics characteristics. The Reynolds-averaged Navier-Stokes equation with the two equation k − ω turbulence model is adopted to resolve the numerical wave tank. The model is validated by comparing the numerical wave forces and free surface elevation with measurements from experiments. The computational results show fairly good agreement with experimental data. Four cases are simulated with different relative distances, numbers of cylinders and arrangements. Results show that the wave forces on cylinders in the pile group are effected by the relative distance between cylinders. The staggered arrangement has a significant influence on the wave forces on the first and second cylinder. The interaction inside a pile group mostly happens between the neighboring cylinders.

Numerical Investigation of the Motion Characteristics of Cylindrical Floating Body in Waves Using the Volume of Fluid Method

In this paper, a numerical hydrodynamic performance assessment of a full scale cylindrical floating body with different damping devices is presented. The motion characteristics of the full scale cylindrical floating body are investigated in regular and irregular wave conditions with different wave heights and periods. A numerical wave tank based on the two-phase Volume of Fluid (VOF) model was established. Approaches to the computational domain and overset-grids were investigated and were found to be suitable. Grid convergence was undertaken for the simulations. The numerical wave tank was performed to analyse the motion characteristics of the cylindrical floating body with arbitrary devices under different wave conditions by using the VOF method with an overset-grid technique. The motion characteristics of the cylindrical floating body with different damping devices were numerically investigated to provide more information on the effect of damping devices on the hydrodynamic performance. The conclusions of this paper give guidance in the motion characteristics and the damping device prototype design to be adopted under the specified wave conditions.