International Journal of Marine Energy最新文献

Oscillating Water Column (OWC) devices are one of the most promising technologies to be implemented into already existing or in-development ocean structures, such as breakwaters. All moving components to retrieve power from the waves are well above the waterline and the still structure can be easily incorporated within solid edifices. In this paper, we investigate the hydrodynamic response of two types of Bent Duct OWC devices with different inlet geometries, both in isolation and when implemented in a flat-faced breakwater. A rectangular and circular cross-sectional shaped OWC device are used for comparison. Numerical method using a FEM based frequency domain model and experimental investigation using the Australian Maritime College wave basin are applied and the results evaluated across a range of frequencies, 0.5 Hz–1.2 Hz. Both the capture width and volume flux resulting from the numerical method match accurately with those resulting from the experiment. Discrepancies only arise around the natural resonance frequency where the assumptions of small amplitudes become erroneous. The implementation of the device within the breakwater was found to significantly enhance the capture width of each device, while the variation in inlet geometry provided low deviations in the results.

Chacao Channel is an energetic tidal channel located at the northernmost part of the Chilean Patagonia. The channel has been previously identified as a prospective site for tidal energy extraction, however there has been only a limited understanding of the tidal flows. A new set of field measurements distributed along Chacao Channel is presented here for tidal energy resource characterization, including tidal elevations, tidal currents (in space and time), and turbulence. The field data also are used to calibrate and validate a FVCOM hydrodynamic numerical model of the entire channel, which is then used for tidal energy resource assessment. Field measurements indicate that tidal elevation range increases eastward along the channel, that tidal currents exceed 4 ${\text{ms}}^{-1}$ at some points within the channel, and that turbulence intensity ranges between 5 and $20\%$. The data and numerical model results are used to estimate the kinetic power density of the tidal currents at Chacao Channel, which is in average 5 ${\text{kWm}}^{-2}$.

Quantifying and mitigating environmental risks presented by marine energy conversion systems requires a variety of sensors (active acoustic, passive acoustic, and optical). The operation of these sensors must satisfy three directives to be effective: (1) do not alter the environment through operation of sensors; (2) capture rare events; and (3) do not accrue unmanageable volumes of low-value data. This requires integrating sensors into a single package, rather than operating them independently. The Adaptable Monitoring Package is an integrated instrumentation package that combines a multibeam sonar, acoustic camera, current profiler, optical cameras, and an array of hydrophones. The capabilities and limitations of the AMP sensors were benchmarked using cooperative targets, and real-time target tracking and detection was used to detect opportunistic targets (e.g., diving birds, seals). During an initial deployment, automatic detection of opportunistic targets achieved a 58% true positive rate and a 99% true negative rate (100% corresponding to an ideal system in both cases). In post-processing, target tracking data were used to evaluate automatic target classification capabilities using a k-nearest neighbor algorithm. Results suggest that real-time target classification should be possible and enable integrated instrumentation systems to meet the monitoring needs of marine energy deployments.

Wave energy converters (WECs) range significantly in respect of concepts, technologies and design maturation, with the majority of devices at an early commercial stage. To date, most large scale deployments have been conducted with a single WEC. However, there is a necessity to expand these to ‘arrays’ or ‘farms’ in the future in order to reduce both installation and maintenance cost per unit as well as harnessing maximum energy at a given site. There are complex hydrodynamic and environmental implications which require consideration when moving from a single device installation to an array of devices. Many theoretical and numerical studies exist in this domain, however, limited experimental investigations have been performed due to the cost and size related to testing facilities as well as the complexity of the experiment and related instrumentation.

This paper presents a novel experimental approach, performed as part of a larger project, aiming to address a critical knowledge gap: understanding the performance of WEC arrays, and to develop a methodology to accurately model an array of WECs. The experimental investigation utilised Australia’s most technically advanced wave basin at the Australian Maritime College, specialist institute of the University of Tasmania. For the first time, it applied the phenomenological theory to experimental hydrodynamic investigation of array of generic WECs by separating the problem into its diffraction and radiation problems. Such approach removes the need of power-take-off modelling and control. Using a post-processing analytical model, the q-factor, the parameter representative of the array performance, for several configurations can be derived. Furthermore a bespoke stereo-videogrammetry method was developed to measure the wave field around and in the lee of the array. This paper describes the hydrodynamic approach and experimental methods developed as part of this project and presents preliminary results related to array q-factor and wave field measurements.

The compromise between Wave Energy Converter (WEC) performance, cost and survival is both a delicate and critical one. A successful WEC design must effectively address the exploitable wave energy, but survive the climate extremes. Bombora Wave Power has focussed on designing a WEC that performs well in less extreme nearshore climates and is able to decouple its working surfaces from extreme waves. Numerical modelling of the performance of their submerged, pneumatic, flexible membrane WEC, the mWave, is presented. The mWave power matrix is found to provide good performance over a broad range of wave periods, with a broad peak in performance at wave periods of 9 s for the assumed design parameters. This broad peak corresponds favourably to the sea-state probabilities in an assumed near-shore shallow water wave climate on the coast of Portugal, yielding a predicted mean annual electrical power production of 240 kW in such conditions. Small scale physical modelling of the relationship between the initial level of inflation of the mWave cell membranes and the system’s power capture has confirmed the possibility of an mWave survival strategy that can potentially allow safe, de-rated performance in extreme conditions. Future work is planned to further improve predicted mWave performance by refinement of power take-off damping and to physically validate these performance modelling results at full scale.

Air turbines are commonly used in Oscillating Water Column (OWC) devices for wave energy conversion. The purpose of this paper is to simulate the performance of an OWC turbine through the implementation of an Actuator Disk Model (ADM) in Fluent®. A set of different regular wave tests are developed in a 2D numerical wave flume. The model is tested using the information analysed from experimental tests on a Wells type turbine, carried out in wind tunnel. Linear response is achieved in terms of pressure drop and air flow in all cases, proving effectively the actuator disk model applicability to OWC devices.

In this study, we employ a numerical model to compare the performance of a number of wave energy converter control strategies. The controllers selected for evaluation span a wide range in their requirements for implementation. Each control strategy is evaluated using a single numerical model with a set of sea states to represent a deployment site off the coast of Newport, OR. A number of metrics, ranging from power absorption to kinematics, are employed to provide a comparison of each control strategy’s performance that accounts for both relative benefits and costs. The results show a wide range of performances from the different controllers and highlight the need for a holistic design approach which considers control design as a parallel component within the larger process WEC design.

In small-scale testing of wave energy converters (WECs), a key focus is on characterising the interdependent relationship between the primary converter and simulated power take-off system. If primary conversion is via the deformation of a flexible material, this task often requires non-contact measurement. In this paper, we introduce the development of an underwater non-contact measurement technique called videogrammetry, and its novel application to characterise the primary converter operation of a flexible membrane WEC. The work was part of Bombora Wave Power’s concept validation wave tank tests at 1:15 scale. Details of the WEC and how it works is followed by an in depth description on applying underwater videogrammetry. A qualitative and quantitative analysis of membrane operation in a regular wave case is provided and discussed in terms of absorbed energy and power production. Two data sets are compared in this analysis. One data set is from videogrammetry and the other is airflow measurement data (airflow induced in the system due to membrane deformation converts wave energy to mechanical energy). This comparison quantifies the accuracy of videogrammetry, and also serves to verify airflow measurements that were used to determine performance indicators of the WEC throughout the entire test campaign. The results compare reasonably well. Sources of uncertainty for videogrammetry are discussed and improvements suggested. Preliminary best practices for applying videogrammetry in wave energy experiments are provided.

A general method for predicting and evaluating the performance of three candidate cross-flow turbine power-maximizing controllers is presented using low-order dynamic simulation, scaled laboratory experiments, and full-scale field testing. For each testing mode and candidate controller, performance metrics quantifying energy capture (ability of a controller to maximize power), variation in torque and rotation rate (related to drive train fatigue), and variation in thrust loads (related to structural fatigue) are quantified for two purposes. First, for metrics that could be evaluated across all testing modes, we considered the accuracy with which simulation or laboratory experiments could predict performance at full scale. Second, we explored the utility of these metrics to contrast candidate controller performance. For these turbines and set of candidate controllers, energy capture was found to only differentiate controller performance in simulation, while the other explored metrics were able to predict performance of the full-scale turbine in the field with various degrees of success. Effects of scale between laboratory and full-scale testing are considered, along with recommendations for future improvements to dynamic simulations and controller evaluation.

The National Renewable Energy Laboratory and Ocean Power Technologies (OPT) conducted a collaborative code validation and design optimization study for OPT’s PowerBuoy wave energy converter (WEC). NREL utilized WEC-Sim, an open-source WEC simulator, to compare four design variations of OPT’s PowerBuoy. As an input to the WEC-Sim models, viscous drag coefficients for the PowerBuoy floats were first evaluated using computational fluid dynamics. The resulting WEC-Sim PowerBuoy models were then validated with experimental power output and fatigue load data provided by OPT. The validated WEC-Sim models were then used to simulate the power performance and loads for operational conditions, extreme conditions, and directional waves, for each of the four PowerBuoy design variations, assuming the wave environment of Humboldt Bay, California. And finally, ratios of power-to-weight, power-to-fatigue-load, power-to-maximum-extreme-load, power-to-water-plane-area, and power-to-wetted-surface-area were used to make a final comparison of the potential PowerBuoy WEC designs. The design comparison methodologies developed and presented in this study are applicable to other WEC devices and may be useful as a framework for future WEC design development projects.