Overtopping breakwater for energy conversion (OBREC) is integration between breakwater and wave energy converter (WEC) that allows incoming waves to be stored in the reservoir. The higher the overtopping amount collected in a reservoir, the greater the energy generated will be. Hence, most of the overtopping concept has attempted to maximize the inclusion of water in the reservoir by optimizing geometrical parameters, particularly the ramp angle. However, the studies corresponding to ramp shapes geometries have not been adequately reviewed. Most studies only focused on the usage of linear overtopping ramp shape. There is still limited knowledge on the influence of different ramp shape parameters towards the overtopping wave. Thus, this paper aimed to push the border of available knowledge by investigating the influence of the ramp shape parameters to the overtopping wave discharge through simulation and experimenting approaches. Seven different ramp shapes have been tested under Malaysia’s wave condition and a new ramp shape parameter allowing for maximized overtopping wave on OBREC is presented.

Drilling risers used in oil and gas operations are subjected to external loads such as wave and current. One of the phenomena that arise from the external loads is the Vortex-Induced Vibration (VIV), which affects the performance of the riser due to excessive vibration from the vortex shedding. A significant factor influencing the VIV is the design of the drilling riser and its auxiliary lines. Until now, the optimum geometrical size and gap between the auxiliary and the main riser are still very scarcely studied. In this paper, the main objective is to study the effects of the gap ratio (G/D) on the vortex shedding phenomenon on a fixed and freely vibrating riser. The riser system was modelled with a main drilling riser and six auxiliary lines with a constant diameter ratio (d/D) of 0.45 and gap ratio (G/D) = 0 to 2.0 in the laminar flow regime with Reynold Number, Re = 200. The simulations were conducted for Single Degree of Freedom (SDOF) using Computational Fluid Dynamics (CFD) software, Altair AcuSolve. It was found that the freely vibrating riser experienced higher lift and drag forces as compared to the fixed riser due to the synchronization (lock-in) of the shedding vibration and the natural frequencies. The lock-in phenomenon is normally observed on the drilling riser at different current directions. The forces are reduced when G/D is higher. The vortex shedding was significantly reduced for auxiliaries between 0.3 to 1.4. It is confirmed that by modifying the interaction of the vortices in the wake region with auxiliary lines, the hydrodynamic forces will be decreased. Finally, this fundamental study could potentially be used in the designing stage of an optimum drilling riser system by considering significant governing factors.

An excessive trim by stern on a high-speed craft is vulnerable to decrease comfortable ride incorporated with the large pitch motion. To prevent such problem, the craft is then equipped with a device known as “trim-tabs” providing a lift force at the stern region, which leads to reduce pitch angle/trim of the craft. This paper presents computational modelling of trim-tabs on high-speed craft towards reducing the pitch motion in the calm water condition. Here, the commercial Computational Fluid Dynamic (CFD) software; called Numeca Fine Marine has been accordingly utilised to evaluate several effects of Froude numbers (Fr) and angle of the trim-tabs into characteristics of the lift force of the high-speed craft. The results revealed that the pitch motion of the high-speed craft equipped with the trim-tabs (5o) has significantly reduced up to 76% at Fr = 1.0. This can be explained that the installed trim-tabs has increased the negative trim moment, which inherently creates the restoring moment pushing the stern up along the pitch-axis. Meanwhile, this may cause involuntary the total ship’s resistance increased. In general, this simulation pointed out the advantage of the trim-tabs to increase the comfortability of the high-speed craft.

The Wave Energy Converters (WECs) have become the main attraction in producing electricity by converting the wave's energy to electricity. The focus of the WECs is the overtopping of the wave. The higher of overtopping water collected in the basin, the higher the power produced. Producing the higher overtopping also requires higher wave flow rate entry. In the Wave Dragon system, the rate of wave flow entering the reservoir is influenced by the guiding wall (reflector) angles and wave height. Hence, most overtopping concepts have tried to increase the water addition into the pool studying their geometrical parameter, mainly on the guiding wall of Wave Dragon. The unknown effect of the guiding wall angles on the overtopping and effect of the wave characteristic remained. Thus, this study aims to investigate the appropriate guiding wall angle on the influence of different wave heights affecting the performance of the Wave Dragon unit. Then, using FLOW 3D software to apply different guiding wall angles and wave characteristics to the device parameters for investigation. The numerical result highlights that the higher overtopping discharge is obtained during the upper limit of wave height and guiding wall angle. Besides, percentage different between the simulations model and experimental observation, was found at 15%. The result of this study will be beneficial to the industry related to wave potential energy, especially Wave Dragon, and it will also help them improve their device performance.

Prediction of ship’s total resistance of a pusher-barge system has become enormous complexity involving nonlinear-hydrodynamic flows behaviour along their hull forms. Both of empirical and simplified numerical solutions may still lead into inaccurate results due to presence of nonlinear characteristics of the pressure and viscous resistances. The use of a more sophisticated method would obviously necessitate to solve the above problem. This paper presents a Computational Fluid Dynamics (CFD) approach to predict the total ship’s resistance of a pusher-barge system at various barge’s configurations. To achieve such objective, four different configurations of the barge models incorporated with various Froude numbers have been taken into account in the computational simulation. In general, the results revealed that the increase of Froude number (Fr = 0.182 to 0.312) was proportional to the magnitude of RT, RP and RV. Regardless of the various Froude number, the pusher-barge system with a 13BP configuration provides the highest resistance compared to the 12BP and 11BP. In addition, the arrangement of barges in the longitudinal (12BP) and lateral (21BP) configurations produced a significant effect with increases in RT, RP and RV values of 110%, 167.5% and 77.6%, respectively. The possible reason for this is that the increase of the total wetted surface area for 21BP has produced to a proportionally higher amount of the pressure and viscous resistance. Overall study, the numerical results were presented and analysed based on few aspects involved the total resistance and resistance coefficient in terms of pressure and viscous resistance of the pusher-barge system. This analysis provides very valuable information on choosing the most reliable arrangement of pusher-barge system. This analysis provides very valuable information on choosing the most reliable arrangement of pusher-barge system