International Journal of Marine Energy最新文献

The Reference Model Project, supported by the U.S. Department of Energy, was developed to provide publically available technical and economic benchmarks for a variety of marine energy converters. The methodology to achieve these benchmarks is to develop public domain designs that incorporate power performance estimates, structural models, anchor and mooring designs, power conversion chain designs, and estimates of the operations and maintenance, installation, and environmental permitting required. The reference model designs are intended to be conservative, robust, and experimentally verified. The Backward Bent Duct Buoy (BBDB) presented in this paper is one of three wave energy conversion devices studied within the Reference Model Project. Comprehensive modeling of the BBDB in a Northern California climate has enabled a full levelized cost of energy (LCOE) analysis to be completed on this device.

A single-layer, quasi-geostrophic (QG), large-scale ocean circulation model is developed in this paper to study available ocean current energy potentials harnessed by using the ocean current turbines. Power extraction is modeled by adding a parameterized Rayleigh friction term in the barotropic vorticity equation. Numerical assessments are performed by simulating a set of mid-latitude ocean basins in the beta plane, which are standard prototypes of more realistic ocean dynamics considering inter-decadal variability in turbulent equilibrium. The third-order Runge–Kutta scheme for the temporal discretization and the second-order conservative Arakawa scheme for the spatial discretization are utilized to perform Munk scale resolving high-resolution computations. A sensitivity analysis with respect to the turbine parameters is performed for various physical conditions. Results show that the proposed model captures the quasi-stationary ocean dynamics and provides the four-gyre circulation patterns in time mean. After an initial spin-up process, the proposed model reaches a statistically steady state at an average maximum speed between 1.5 m/s and 2.5 m/s, which is close to the observed maximum zonal velocities in the western boundary currents. The probability density function of the available power over a long time period is computed for a wide range of parameters. Numerical results shows that 10 GW mean power can be extracted from the turbines distributed over a length scale of 100 km along the western boundaries. However, it is demonstrated that bigger turbine areas would alter the flow patterns and energetics due to excessive dissipation. An increase in the turbine area results in an increase in the available power ranging from 8 to 22 GW depending on the values of turbine modeling parameters. This first step in the numerical assessment of the proposed QG model shows that the present framework could represent a viable tool for evaluating energy potentials in a highly turbulent flow regime.

Power cable failures for offshore marine energy applications are a growing concern since experience from offshore wind has shown repeated failures of inter-array and export cables. These failures may be mitigated by dedicated cable protection systems, such as bend restrictors. This paper presents the rationale and the results for accelerated reliability tests of an articulated bend restrictor. The tests are a collaborative effort between the University of Exeter, CPNL Engineering and NSW, supported by the EU MARINET programme.

The tests have been carried out at full-scale and exposed the static submarine power cable, fitted with an articulated pipe bend restrictor, to mechanical load regimes exceeding the allowable design loads in order to provoke accelerated wear and component failures. The tested load cases combined cyclic bending motions with oscillating tensile forces. A range of acceleration factors have been applied in respect to the 1:50 years load case, subjecting each of the three restrictor samples to 25,000 bending cycles (50,000 tensile cycles). The static power cable was also loaded beyond its intended use, testing the worst case scenario of repeated dynamic loading, purposely inflicting failure modes for investigation. Throughout the test the static submarine power cable sustained over 77,000 bending cycles.

The test demonstrated the integrity of the cable protection system with quantified wear rates obtained through 3D scanning of the individual shells. The static power cable also maintained its integrity throughout the accelerated test regime. None of the failure modes, mainly fatigue cracks and fretting of individual wires, identified by cable dissection would have caused a direct loss of service. The observed failure modes could also be predicted through numerical load analysis, giving confidence in the utilised mechanical modelling and cross-sectional analysis for dynamic applications.

The aim of this investigation was to develop a methodology to characterise the wave climate for offshore, nearshore and onshore locations of interest. The proposed methodology was applied to a domain located off the west coast of Ireland, adjacent to Loop Head, Co. Clare, and this was an area of interest for ocean energy development. A 3rd generation spectral wave model for the domain was developed, calibrated and validated using DHI’s MIKE 21 spectral wave modelling software along with sea state, met-ocean and bathymetric data obtained from a wide range of sources.

The model yielded information on a range of indices including annual mean wave power, exploitable wave power, maximum wave height, percentage occurrence of a range of sea states and wave directionality at off-shore, near-shore, and on-shore locations.

The models predictions were compared with local wave measurements for calibration and validation purposes obtained from a non-directional Datawell Waverider wave measurement buoy. The wave climate model predicted significant wave height and energy period at this location exhibiting a scatter index of less than 0.25 and a correlation coefficient greater than 0.85. The inclusion of a high resolution bathymetry dataset in the on-shore and coastal regions of the domain was the main driver in achieving this level of agreement between the data.

The spectral wave model developed in this research programme will be useful for future wave energy research. Results from this model indicate that the domain off County Clare possesses an exploitable resource with promising levels of energy for potential wave energy projects. They also show that the near-shore and on-shore environment in this domain maintains good levels of power with relative filtering of extreme waves.

Oscillating wave surge converters are a promising technology to harvest ocean wave energy in the near shore region. Although research has been going on for many years, the characteristics of the wave action on the structure and especially the phase relation between the driving force and wave quantities like velocity or surface elevation have not been investigated in detail. The main reason for this is the lack of suitable methods. Experimental investigations using tank tests do not give direct access to overall hydrodynamic loads, only damping torque of a power take off system can be measured directly. Non-linear computational fluid dynamics methods have only recently been applied in the research of this type of devices. This paper presents a new metric named wave torque, which is the total hydrodynamic torque minus the still water pitch stiffness at any given angle of rotation. Changes in characteristics of that metric over a wave cycle and for different power take off settings are investigated using computational fluid dynamics methods. Firstly, it is shown that linearised methods cannot predict optimum damping in typical operating states of OWSCs. We then present phase relationships between main kinetic parameters for different damping levels. Although the flap seems to operate close to resonance, as predicted by linear theory, no obvious condition defining optimum damping is found.

Tidal energy is a renewable resource that can contribute towards meeting growing energy demands, but uncertainties remain about environmental impacts of device installation and operation. Environmental monitoring programs are used to detect and evaluate impacts caused by anthropogenic disturbances and are a mandatory requirement of project operating licenses in the United States. In the United Kingdom, consent conditions require monitoring of any adverse impacts on species of concern. While tidal turbine sites share similar physical characteristics (e.g. strong tidal flows), similarities in their biological characteristics have not been examined. To characterize the generality of biological attributes at tidal energy sites, metrics derived from acoustic backscatter describing temporal and spatial distributions of fish and macrozooplankton at Admiralty Inlet, Washington State and the Fall of Warness, Scotland were compared using t-tests, F-tests, linear regressions, spectral analysis, and extreme value analysis (EVA). EVA was used to characterize metric values that are rare but potentially associated with biological impacts, defined as relevant change as a consequence of human activity. Pelagic nekton densities were similar at both sites, as evidenced by no statistically significant difference in densities, and similar daily density patterns of pelagic nekton between sites. Biological characteristics were similar, suggesting that generic biological monitoring programs could be implemented at these two sites, which would streamline permitting, facilitate site comparison, and enable environmental impact detection associated with tidal energy deployment.