This paper presents developments in numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on rotor-performance prediction and hydrodynamic loads for structural design calculations. This study initially used theoretical double-multiple-streamtube models, followed by physical testing on a scaled-down model turbine and primarily numerical simulations. Numerical investigations of a proposed full-scale turbine (power coefficient, blade loads and flow behaviour) were undertaken using the developed computational models. The turbine design was studied using a time-accurate Reynolds-averaged Navier–Stokes (RANS) commercial solver. A transient-rotor-stator model with a moving mesh technique was used to capture the change in flow field at a particular time step. A shear stress-transport [ ] turbulence model was used to model turbulent features of the flow. The numerical results show good agreement with experimental measurements and the theoretical double-multiple-streamtube model. Turbine sensitivity to parametric variations was also demonstrated in the full-scale numerical study. This work concludes that the developed model can effectively predict hydrodynamic performance and structural design blade loads of a vertical-axis marine current turbine.

This paper develops a geometrical construction of a shortest Dubins path in a discontinuous orientation restricted environment. The method proposed here builds the shortest path from one pose to the other while avoiding a no-go zone in terms of orientation, and being constrained to move forward. Finally, an application to autonomous sailboats is then provided to validate the feasibility of the planned shortest path in a position keeping scenario.

Wave and current energy can be harnessed in the East China Sea and South China Sea; however, both areas are subject to high frequencies of typhoon events. To improve the safety of the ocean energy conversion device, a Floating Ocean Energy Conversion Device (FOECD) with a single mooring system is proposed, which can be towed to avoid severe ocean conditions or for regular maintenance. In this paper, the structure of the FOECD is introduced, and it includes a catamaran platform, an oscillating buoy part, a current turbine blade, hydraulic energy storage and an electrical generation part. The numerical study models the large catamaran platform as a single, large buoy, while the four floating buoys were modeled simply as small buoys. Theoretical models on wave energy power capture and efficiency were established. To improve the suitability of the buoy for use in the FOECD and its power harvesting capability, a numerical simulation of the four buoy geometries was undertaken. The shape profiles examined in this paper are cylindrical, turbinate (V-shaped and U-shaped cone with cylinder), and combined cylinder-hemisphere buoys. Simulation results reveal that the suitability of a turbinate buoy is the best of the four types. Further simulation models were carried out by adjusting the tip radius of the turbinate buoy. Three performance criteria including suitability, power harvesting capability and energy capture efficiency were analyzed. It reveals that the turbinate buoy has almost the same power harvesting capabilities and energy capture efficiency, while its suitability is far better than that of a cylindrical buoy.

This work reviews hydrodynamic analysis models developed for the design of Darrieus-type vertical axis marine current turbines, with particular emphasis on the prediction of hydrodynamic rotor performance, as well as their suitability for aiding the optimization process, either directly, or as a fast filter of potential blade profiles. In order to improve the performance of a marine current turbine it is necessary accurately to model the flow passing the turbine’s blades. Several types of models exist for Darrieus-type turbines, from momentum-based streamtube models to complex computational fluids dynamics (CFD) simulations. With continuously varying large angles of attack on the blades, the main issue is accurate prediction of the flow field around the rotor and thus its loads and torque. This is further complicated by the significant inherent unsteady hydrodynamic characteristics and potential for dynamic stall. Comparisons of the analytical results with experimental data are presented to compare these different models and thus illustrate their areas of suitability in this context. In conclusion, vertical axis machines have the potential of high power capture compared with that of their horizontal counterparts but this will depend on blade profile and design configuration, solidity, and tip speed ratio. None of the existing theoretical methods really captures the actual performance of the machines except for detailed CFD simulations, which are inevitably computational time intensive.

Scour induced by a Darrieus-type tidal current turbine was investigated by using a joint numerical and experimental method with emphasis on the scour process of a full-scale turbine. This work proposes a new numerical method to estimate turbine scour developments, followed by model validation through experimental data in the initial stage. The small-scale numerical model was further extended to a full-scale model for the prediction of turbine scour. The numerical model consists of (1) k- $\omega$ turbulence closure, (2) a sediment transport model, and (3) a sediment slide model. The transient-state model was coupled with a morphologic model to calculate scour development. A dynamic mesh updating technique was implemented, enabling the autoupdate of data for the grid nodes of the seabed at each time step. Comparisons between the numerical results and the experimental measurements showed that the proposed model was able to capture the main features of the scour process. However, the numerical model underestimated about 15–20% of the equilibrium scour depth than experimental data. An investigation of the temporal and spatial development of seabed scour around a full-scale Darrieus-type tidal current turbine is demonstrated. This work concludes that the proposed numerical model can effectively predict the scour process of tidal current turbines, and the rotating rotor has a significant impact on the equilibrium scour depth for full-scale turbines.

The oscillating water column wave energy converter (OWCWEC) is an established device which produces electricity by causing an ocean wave to drive air through a turbine. A system to control the operation can improve the device's performance. In varying sea conditions, different objectives for control may be appropriate. For example, in some seas the controller might shut off the plant because the waves could damage the structure, while in others the controller should operate purely to maximise the energy passed to the electricity grid. The fundamentally nonlinear dynamics of the OWC-WEC influence the choice of control algorithm for the WEC. Different outcomes in performance may be caused by very small changes in controller action. This is especially true for those OWC-WECs whose characteristics include stalling under certain conditions for optimal performance. Robustness to uncertainty in inputs and prevention of damage to the structure are necessary. However, too much conservatism will lead to unnecessarily low extracted powers. In the present paper, the advantages and disadvantages of feed-forward controllers and artificial neural networks previously used on OWC-WECs are discussed, as well as the testing of model predictive control and fuzzy logic controllers in the OWC-WEC context