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The DeepCwind floating wind turbine platform has become one of the most successful structures for accommercial floating wind farms, and the stability of it is crucial for survivability. Hence, this paper studies an anti-oscillation device with the purpose of reducing the heave and surge effects of the platform. The influence of various chamfered perforations at different sizes of the anti-heave device on the floating platform was further studied by numerical and experimental methods. Furthermore, through an analysis of the surge and heave of the pedestal with anti-heave devices with different chamfered perforations under different wave heights and wave periods, the effects on the hydrodynamic performance of the pedestal were studied. Physical experiments were conducted on a pedestal with anti-heave devices with chamfered perforations under the working conditions of different wave heights and wave periods to verify the reliability of the numerical simulation. The results show that the anti-heave effect of the anti-oscillation device is obvious under the small wave period and large wave height. Under the working conditions of different wave heights and wave periods, different perforated chamfers have different effects on reducing the oscillation of the pedestal, and its effect does not change linearly with an increasing chamfer. Under most working conditions, the anti-heave effect of the 35° chamfered perforated model was found to be the most obvious. [ABSTRACT FROM AUTHOR]

Abstract Two dimensional freely floating body motion responses induced by wave and current are investigated in seabed conditions. This problem is solved by boundary integral method, which is formulated by a combination of steady, diffraction/radiation and reflection potential problems accounting for current, incoming wave and seabed effects respectively. All the three potential problems are solved using a boundary element model involving a continuous Rankine source method subject to appropriate boundary conditions. The presence of incoming wave, current and seabed causes an asymmetric fluid domain. Numerical simulations show that water depth, seabed slope angle, current speed, current direction and cross coupling effects are significantly important for surge, heave and roll motion responses. Highlights 1 Both coupled and uncoupled body motion equations are developed. 2 Steady potential, diffraction/radiation potential and reflection potential are included in the numerical model 3 Roll viscous damping is interpolated into the potential theory model. 4 Mathematical model is validated by comparing with published numerical and model test data. All the three body motion modes (surge, heave and roll) are investigated. [ABSTRACT FROM AUTHOR]

The unsteady vortex-induced forces on a multi-column platform in current from subcritical up to supercritical Reynolds numbers have been investigated using three-dimensional numerical simulations. Two different current incidences, 0 ∘ and 45 ∘ , are considered. The results show that for 0 ∘ current incidence, the mean streamwise force coefficients ( C ¯ x) increase with the rise of R e when R e < 2. 2 × 1 0 5 , while they grow slightly when R e ≥ 2. 2 × 1 0 5 . For 45 ∘ current incidence, a decrease of streamwise force with increasing R e is observed. Similar to a single cylinder, the fluctuating transverse force coefficients (C y ′) of the multi-column platform drop at R e = 1 × 1 0 5 for 0 ∘ and 45 ∘ current incidences. In addition, it is found that for 0 ∘ current incidence, the C y ′ values of the downstream columns are much larger than those of the upstream columns, while for 45 ∘ current incidence, the C y ′ values of each column are similar. Furthermore, the results of correlations between the forces on each column and total forces indicates that for 0 ∘ current incidence, the fluctuating transverse forces on the downstream columns are mainly responsible for the total fluctuating transverse force on the multi-column platform. [ABSTRACT FROM AUTHOR]

Based on a Lagrangian integral technique and Lagrangian particle-tracking technique, a numerical model was developed to simulate the underwater transport of oil from a deepwater spill. This model comprises two submodels: a plume dynamics model and an advection-diffusion model. The former is used to simulate the stages dominated by the initial jet momentum and plume buoyancy of the spilled oil, while the latter is used to simulate the stage dominated by the ambient current and turbulence. The model validity was verified through comparisons of the model predictions with experimental data from several laboratory flume experiments and a field experiment. To demonstrate the capability of the model further, it was applied to the simulation of a hypothetical oil spill occurring at the seabed of a deepwater oil/gas field in the South China Sea. The results of the simulation would be useful for contingency planning with regard to the emergency response to an underwater oil spill. [ABSTRACT FROM AUTHOR]

Three dimensional Rankine source model is utilized to investigate the hydrodynamic responses for wave radiation problems under arbitrary seabed condition in time domain. The free surface, seabed surface and body surface are presented by layer of continuous panels rather than a discretization by isolated points. These panels are positioned exactly on the fluid boundary surfaces and no desingularization technique required. To accommodate the sloping seabed profile, a straightforward source panel distribution on seabed surface is newly developed with two parameters determined by numerical tests. The accuracy and efficiency of the numerical solutions are validated by comparison with published data. The influences of flat seabed, uneven seabed and sloping seabeds are examined. Numerical simulations demonstrate that various seabed profiles have significant and complicated effects on the body hydrodynamic response characteristics. • Layer of Rankine source panel is applied to simulate free surface, body surface and seabed surface respectively. • A straightforward seabed source distribution is newly developed to accommodate sloping seabed profiles. • The proposed model is validated extensively by comparison with published data. • Effect of sloping sebed on wave radiation is studied by Rankine source panel method. [ABSTRACT FROM AUTHOR]

This paper presents numerical studies on vortex-induced motions (VIM) of a multi-column floating oil and gas exploration platform. Numerical computations are performed using an improved delayed detached eddy simulation (IDDES) together with a moving grid approach. The transverse (sway) and yaw motion responses, motion trajectories, motion frequencies and power spectral density of motions are computed and analyzed systematically. After extensive comparisons with experiments, it is confirmed that the present numerical solutions using IDDES agree well with the experimental results and are better than those via delayed detached eddy simulation (DDES). The differences of transverse motion responses between computational results and experiments are less than 10% in the lock-in region. The numerical simulations reveal that the transverse VIM responses occur in a range of reduced velocities from 7.0 to 14.0 at H / D = 1.44 ( H and D are the column height and width, respectively). The largest nominal transverse amplitude, around 35 % of the column width, occurs for 22 . 5 ∘ current incidence. It is found that the VIM responses mainly perform along the platform diagonals for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences. The transverse and yaw motion frequencies for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences are higher than those for 0 ∘ current incidence. The energy levels of the yaw motion responses for 1 5 ∘ , 22 . 5 ∘ and 4 5 ∘ current incidences are about 10% of that for 0 ∘ current incidence. Moreover, parametric studies have been performed to examine the effect of submerged column height on VIM. It demonstrates that VIM in transverse direction grows significantly when submerged column height H / D is greater than 1.0. To be more specific, compared to the case with H / D = 1.44, VIM in transverse direction at H / D = 3.0 increase by around 120%. [ABSTRACT FROM AUTHOR]