International Journal of Marine Energy最新文献

The study focuses on a high resolution coastal assessment for the Libyan Sea at the South-West Mediterranean. To date majority of information for the area, are based on large scale oceanic models with coarse resolutions not adequate for nearshore assessments. This dataset and analysis provides an in-depth wave energy resource assessment and detail dissemination of sites according to their metocean characteristics. Identification for wave energy is based on the database constructed, allowing the quantification of energy levels and resource implications at sites.

Mean values of wave heights around the coastlines are $\approx 1\text{m}$, though high storm events exceed 5 m at several areas. Highest wave energy resources are located at open coastal areas, with energetic months reaching up to 10 kW/m. Low energy seasons are found throughout summer months, where energy content is reduced threefold. The resource can be classified as low, however the coefficient of variation suggests a predictable resource with extreme events not expected to surpass 10 m.

Although, resource is not as energetic as open oceanic regions the low variations may assist wave energy as a supporting renewable energy option. Assessing the wave climate around the coasts for a long period of time can also provide confident and robust suggestions on the selection for wave energy converters. In addition, lower extreme events are expected to reduce potential installations costs by lowering structural expenditure and strengthening works to facilitate operation at milder environments.

This paper deals with an energy characterization method of tidal sites. This method is illustrated by the study of a typical tidal site close to the Ouessant (Ushant) Island of the Bretagne region in France. The main objective of this study is to find the optimal location of a tidal turbine including the effect of using or not a yaw drive system.

After presenting the different data used in this work, the marine current velocity is first evaluated at different specific locations and times of the studied zone. Afterwords, the tidal energy is evaluated for different systems (tidal turbine with a yaw and bidirectional tidal turbine with fixed axis) and presented in terms of energy distribution maps.

This article presents a practical method for predicting the power output of cross-flow tidal/river turbines with wake interaction and channel blockage effects. In a turbine farm, the power generated by each rotor depends on the cube of the local velocity, which is influenced by the bottom topology, by other turbines’ wakes and also by finite channel cross sectional areas restricting wake expansion. Therefore, the accuracy of power predictions depends strongly on proper modelling of rotor wakes and the influence of the channel/river boundaries. This is a critical issue for the tidal and river kinetic turbine power industries because best practise for predicting energy yield has yet to be established, while project revenue streams are primarily a function of yield.

This article introduces a simulation-based method to predict individual turbine and total farm power output with modest computational expense, named the tuned actuator cylinder approach (TACA). Rotors are represented in the simulations as momentum sink terms, using approximately 21 elements across their diameter, allowing for very fast simulations of multiple rotors. The model is tuned to match known (from experiments or high-fidelity blade-resolved simulation) thrust and power operational profiles for a particular turbine, with known inflow conditions. Once tuned, the TACA model can be applied to a wide range of turbine array configurations, and arbitrary flow environments. Thus, TACA is an appropriate tool for case-studies and/or optimization of turbine array layout at real-world tidal/river energy sites.

The purpose of this work is to provide an innovative tool based on the classic Levelised Cost of Energy (LCOE) which gives an overview of the limits for the technical parameters of Wave Energy Converters (WECs). In this case, the LCOE calculation procedure is reversed: the LCOE target is set in the first instance, followed by the calculation of the Average Energy Production (AEP) based on different scenarios. Then, the Capital and Operating Expenditures (CAPEX and OPEX) are calculated and percentages per cost centre are assigned in order to find the cost of each technical parameter, e.g. the structure, Power Take-Off (PTO), connections, mooring and installation costs. With this reversed LCOE the upper costs limits for a WEC were obtained. Moreover, an approximation of parameters such as the maximum mass of steel, mooring length or number of interventions per year are given. Five WECs classes are analysed in this paper: Oscillating Water Column (OWC), overtopping devices, heaving devices, fixed Oscillating Wave Surge Converter (OWSC) and floating OWSC. An extensive comparison with actual devices is made. Finally, a comparison with the limits in the Offshore Wind Energy sector is given as a check of the cost-reduction potential of Wave Energy. As a conclusion, although in a primary stage of development, commercial WEC projects have the potential to be competitive with the Offshore Wind Energy industry.

The collector of an oscillating water column system (OWC) for wave energy utilization requires a bidirectional turbine that copes with pneumatic power while providing specified impedance or, in terms of an OWC designer, “damping”. Damping is realized by keeping to a specific flow rate through the turbine at a given pressure head due to the individual performance characteristic of the turbine. With the number of turbine designs increasing designers of OWC systems are facing more options to select and dimension a bidirectional turbine. Energy yield, size and hence cost of the turbine and electric generator, operational behaviour, envisaged control strategy and noise emitted by the turbine are possible criteria for selection.

The primary objective of this paper is to describe a simple procedure for making a first choice of a turbine for a particular OWC application. Here we confine ourselves to a family of reaction type of turbines (axial-flow Wells and mixed-flow turbines by Moisel) with their approximately linear pressure head/volume flow rate characteristics. Starting point is the set of non-dimensional steady-state characteristics of each turbine in the family. Utilizing standard scaling laws and a very simple time domain model for the cyclic turbine operation (i.e. based one single sea state and turbine operation assumed to be fixed rotational speed), first estimates of turbine size and rotor speed, number for stages or flows, and performance curves can be determined. The resulting turbine may also serve as a starting configuration for a refined analysis, e.g. the optimization of the turbine and the complete OWC system, utilizing more complex stochastic models. Three case studies illustrate the application of the method: selection and scaling of turbines, effect of collector parameters, turbines in series and parallel.

The well-known dispersion relation links the length and period of a water wave with the depth in which it propagates. When model testing in tanks, the water depth should be consistently scaled to correctly replicate the waves. While this is done routinely by scaling foreshore bathymetry in coastal engineering physical model studies, and is not significant for deep water scenarios, this is not always considered when testing marine renewable energy devices, which are often in intermediate depth. Where water depth is not scaled consistently there will be resulting errors in wave parameters including wavelength, steepness, celerity, group velocity, and power. Design diagrams are presented to quantify and visualise these discrepancies over a typical range for testing offshore renewable energy devices. This design tool will facilitate experimental planning, quantification of uncertainties, and correlation of model test results with field data.

The need for increasing the share of sea resources in the global renewable energy market requires a specialized design of wave energy converters and Power Take-Off units that, in turn, may be capable of maximising power production and minimizing extraction costs. In this respect, as optimization of wave energy converter performances, by properly tuning relevant hydrodynamic parameters and controlling the motion in waves, reveals a basic issue to reduce energy production charges, a new cost-based design procedure for heaving point absorber type devices is developed, with the main aim of accounting for wave climate at deployment site, reliable device operational profiles and design restraint criteria for both floating buoy and Power Take-Off unit. The newly proposed cost-based procedure is applied to detect the optimum configuration of heaving point absorber devices at several candidate deployment sites. Finally, the incidence of wave climate and available energy resources, on detecting the optimum device configuration and assessing relevant energy production costs, is investigated and fully discussed.

Wave energy is expected to play an important role in the forthcoming years for the de-carbonisation of Scottish and British electricity production. This study underlines the importance of resource assessment and attempts to improve the quantifiable wave power resource, with use of a validated numerical model. While levels of wave flux are high for an area that may not always constitute the best option for wave energy applications. In this study, a long-term hindcast for the Scottish coastlines run from 2004 to 2014 (11 years) improving the existing wave maps and resource estimations. Spatial and physical considerations of a third generation spectral model allow examination at locations of immediate interest for the ocean energy community. Utilising numerical wave models of finer resolution allows for the detailed coupling of potential wave energy converters (WECs) and site characterization. Such detail energy results allow for improved financial analysis that take into account the severity of local resource and its energy potential.

An approach for numerically representing turbulence effects in the simulation of ocean current turbines (OCT)s is described. Ambient turbulence intensity and mean flow velocity are utilized to develop analytic expressions for flow velocities at a grid of nodes that are a function of time. This approach is integrated into the numerical simulation of an OCT to evaluate effects of turbulence on performance. For a case study a moored OCT with a 20 m rotor diameter is used. Mean power in the presence of ambient turbulence intensities (TI)s of 5% and 20% are found to be 370 kW and 384 kW, with standard deviations of 17.2 kW and 74.6 kW respectively. Similarly, the axial loads on a single blade of the three-bladed rotor are found to be 139 kN and 140 kN, with standard deviations of 3 kN and 12 kN respectively for these TIs.