International Journal of Marine Energy最新文献

A pressure differential sea wave energy converter concept using the forced harmonic motion of a hydraulic water column and hydraulic piston is presented. The mechanical power from the hydraulic piston is converted to electrical power by a linear induction generator. The equation of motion, and electrical power generated are derived in terms of design dimensions and mechanical properties of the wave energy converter. The frequency response of the system is modelled numerically for a variety of wave frequencies, and its time response is modelled using a simple Euler method numerical model. It was found that the wave energy converter yields a maximum conversion efficiency of 27% and a prompt transient response to actuation with waves around its natural frequency. High survivability and reduced visual and water-surface impact are likely advantages of this design concept, since all mechanical components may be incorporated into the sea-floor and shoreline.

Parametric Finite Element Analysis (FEA) modelling is a powerful design tool often used for offshore wind. It is so effective because key design parameters (KDPs) can be modified directly within the python code, to assess their effect on the structure’s integrity, saving time and resources. A parametric FEA model of offshore wind turbine (OWT) support structures (consisting of monopile (MP), soil-structure interaction, transition piece (TP), grouted connection (GC) and tower) has been developed and validated. Furthermore, the different KDPs that impact on the design and scaling-up of OWT support structures were identified. The aim of the analyses is determining how different geometry variations will affect the structural integrity of the unit and if these could contribute to the turbine’s scale-up by either modifying the structure’s modal properties, improving its structural integrity, or reducing capital expenditure (CAPEX). To do so, three design cases, assessing different KDPs, have been developed and presented. Case A investigated how the TP’s and GC’s length influences the structural integrity. Case B evaluated the effect of size and number of stoppers in the TP, keeping a constant volume of steel; and Case C assessed the structure’s response to scour development. It is expected that this paper will provide useful information in the conceptual design and scale-up of OWT support structures, helping in the understanding of how KDPs can affect not only the structure’s health, but also its CAPEX.

An embedded Reynolds-Averaged Navier–Stokes blade element actuator disk model is used to investigate the performance of a closely spaced cross-stream fence of four turbines. The flow characteristics of such fences are found to be dependent on both the local turbine scale flow problem and the array in channel flow scale problem. The mean fence power is found to be less than that predicted for a single turbine with the same local blockage ratio (ratio of turbine swept area to surrounding flow passage area), but greater than that for a single turbine based on the global blockage ratio of the fence (ratio of total fence swept area to the cross-sectional area of the channel). Cross-fence variation in turbine performance is observed as a result of the differing resistance to bypass flow acceleration around the inboard and outboard turbines and depends on the operating condition of the turbines. Reducing turbine thrust, such as by changing the rotational speed of the turbine or by employing a pitch-to-feather power capping mechanism reduces turbine-turbine interactions and turbine performance becomes more uniform across the fence. An approximately 6% increase in the mean fence power can be achieved if a cross-fence differential blade pitch strategy is employed to maximise the lift to drag ratio along the majority of the blade span of each of the turbine blades.

We have investigated wave energy potential near the coast of northern Iran. Our main goal, in this study, was to find a suitable location for installing wave energy conversion systems along the southern coast of the Caspian Sea, within Iran's territorial waters, based on the data obtained from ECMWF (European Centre for Medium-Range Weather Forecasts) between 1999 and 2013. We plotted annual and seasonal diagrams of wave height, period, and energy at 17 different locations. We observed that, despite some minor fluctuations, wave energy generally reaches its peak value in autumn. Based on the analyzed data, we suggest that cities of Noshahr and Babolsar are suitable locations for installation of wave energy conversion systems. We further studied wave roses nearby the aforementioned cities. We found that strongest waves occur in South-southeast (SSE) direction with the maximum magnitude of 8.37 and 9.67 Mwh (per unit length of the wave front) at Babolsar and Noshahr, respectively. Finally based on our study, we suggest an optimal range of significant wave height and period for designing an efficient wave energy converter in these areas.

This paper presents a numerical model that simulates the behaviour of an offshore point absorber wave energy converter (WEC). The model receives 1st order irregular waves as input and delivers instantaneous displacements, velocities and power as output. The model outputs are strongly non-linear due to the nature of some parts of the device, such as the power take off system (PTO), the mooring wires and the drag forces exerted on the wet bodies.

Two different devices are modelled, a two-body device consisting in a floating buoy attached to a linear generator placed at the sea bed and a three-body device, which also includes a submerged sphere located halfway from the float and the generator. For each device, the model takes into account either the heave mode only or the heave and surge modes combined.

The devices have been tuned to the Mediterranean wave climate, taking particular attention to the floater dimensions and to the geometrical design of the PTO, which has been redesigned to adapt to the newly introduced surge conditions.

For the two-body device, although the dynamic behaviour changes when the surge is included, no relevant differences are observed regarding the power production. When studying the three-body device, results show two clear trends. For high waves, the surge leads to a decrease in the production, whereas for smaller waves it affects positively the power absorption. Overall, the negative contribution is more relevant but also less frequent, leading to no substantial change in the power production.

Including the surge mode in the model does not give significant variations in production rates and therefore, may be neglected only for energy production assessment. However, it should always be taken into account at the design stage.

The effect of the idealized design parameters, the natural period of oscillation and damping, on the performance of a generic Wave Energy Converter (WEC) model is investigated. Other studies have been conducted on specific WEC technologies, overlooking the impact of these design parameters. Australia has been used as a case study. The consequences of the damping parameter are highlighted. A broad range of ocean wave climates are investigated across different seasons to determine the idealized values of the parameters appropriate for a location, to assist planning for extensive WEC deployments. Swell and wind-sea wave systems were studied; the response of generic model was used to determine the theoretical power generated. It was found that WECs should be selected for a location based on their damping as well as their natural period of oscillation so that the ocean wave resource is optimally utilized.

The Goto Islands in Nagasaki Prefecture, Japan, contain three parallel channels that are suitable for tidal energy development and are the planned location for a tidal energy test centre. Energy extraction is added to a 3D numerical hydrodynamic model of the region, using a sub-grid momentum sink approach, to predict the effects of tidal development.

The available resource with first-generation turbines is estimated at 50–107 MW peak output. Spreading turbine thrust across the whole cross-section to prevent bypass flow results in a 64% increase in peak power in one channel, highlighting the importance of 3D over 2D modelling.

The energy available for extraction in each strait appears to be independent of the level of extraction in other straits. This contrasts with theoretical and numerical studies of other multi-channel systems. The weak interactions found in this study can be traced to the hydraulic effects of energy extraction not extending to neighbouring channels due to their geometry.

In this work, air compressibility effects are investigated during wave interaction with an Oscillating Water Column (OWC) Wave Energy Converter (WEC). Mathematical modelling includes a thermodynamic equation for the air phase and potential flow equations for the water phase. A simple three dimensional OWC geometry with a linear Power Take Off (PTO) response is considered and both the thermodynamic and potential flow equations are linearised. Analysis of the linearised system of equations reveals a nondimensional coefficient which we name “compression number”. The flow potential is decomposed into scattering and radiation components, using an analogue of spring-dashpot response and taking into account the additional effects of air compressibility to wave interaction processes. We use these concepts to characterise the relative importance of the air compressibility effects inside the OWC and to derive novel scaling relations for further investigation of scaling effects in OWC physical modelling. The predictions of the methodology are validated against large scale experimental data, where compressibility effects are evident and further application of the methodology to a realistic OWC geometry is used to demonstrate the importance of these effects to prototype scale.

Many marine mammal populations worldwide are in decline due to stresses from climate change and interactions with anthropogenic activities such as fishing, coastal construction petroleum extraction, and commercial shipping. The advent of the marine renewable energy industry has raised questions, particularly for tidal turbines. However, it is technically very difficult to observe close interactions of marine mammals and underwater turbines, and the likelihood of viewing a rare event such as a collision, is very small. This research seeks to understand the potential risk to a marine mammal from the presence of a tidal turbine by examining the sequence of behavioral events that could lead to a potential collision with the turbine, and the likely consequences to the marine mammal if such a collision were to occur. We examine this potential risk within the context of the physical environment into which a turbine might be deployed, and the attributes of one tidal device, and investigate the biomechanical properties of a marine mammal that may allow the animal to resist injury from a tidal blade collision. The data examined in this research (likelihood of a marine mammal being in close proximity to a tidal turbine, biomechanics of marine mammal tissues, and engineering models) provide insight into the interaction.

A runaway marine current turbine will typically overshoot the runaway speed significantly before it settles at that speed. Numerical simulations of an experimental turbine indicate that the peak forces experienced by the turbine during runaway are up to 2.7 times those seen during nominal operation, and 2.1 times those at asymptotic runaway speed, making peak runaway force an important consideration in turbine design. The main contribution to the force increase is found to originate from the increased rotational speed, but a significant part is also due to the temporal lag in turbine wake development. A parameter study further shows that turbines with low inertia, turbines that have low losses, and turbines designed for low tip speed ratios will experience larger increases in forces.