Response of a Small Array due to Irregular Waves: Comparison to Predictions Based on Measured Regular Wave Response (original) (raw)
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Experimental measurements of irregular wave interaction factors in closely spaced arrays
IET Renewable Power Generation, 2010
Much of the published work concerning the response and power output of closely spaced arrays of heaving wave energy devices concerns behaviour in regular waves only and is based on numerical analysis. To date, limited experimental work has been published and it remains unclear how device interactions predicted in idealised models relate to the response of proposed devices in realistic irregular wave-fields. Experimental measurements of the power absorbed by a small two-dimensional array of heaving devices in both regular and irregular waves in a wide flume are reported. In regular wave conditions, positive interactions (where the average power output of the array exceeds the same number of isolated devices) are measured. These tests indicate that the occurrence of positive interactions is largely dependent on the incident wave period and the performance of adjacent devices. Preliminary tests indicate that float responses tend to be smaller when subjected to short period irregular waves of matching peak frequency and standard deviation of surface elevation. The data presented provide an insight into interactions within irregular wave conditions and forms a basis for evaluating numerical models.
Benchmark Modeling of the Near-Field and Far-Field Wave Effects of Wave Energy Arrays
2013
This project will perform benchmark laboratory experiments and numerical modeling of the near-field and far-field impacts of wave scattering from an array of wave energy devices. We will develop a predictive understanding of the effects of an array of wave energy converters on the wave conditions and the potential for any wave field modifications to change nearshore current and sediment transport patterns 2. Project Scope This project addresses Topic Area 2: "Marine and Hydrokinetic Site-specific Environmental Studies/Information" under FOA Number DE-FOA-0000069 and is an industry-led partnership that will perform environmental testing studies regarding the installation of arrays of wave energy conversion devices. The study will perform benchmark laboratory experiments using an array of 1:33 scale wave energy conversion devices. The experiments will quantify the wave scattering effects of these arrays and be used to develop and test numerical models for wavestructure interaction and far-field hydrodynamic effects. 3. Accomplishments (Task Deliverables) 3.1.
Wave climate investigation for an array of wave power devices
This paper presents the results of a study carried out to determine the change in wave climate around an array of hypothetical wave devices. The main objective of this work is to investigate the change in wave height in the upstream and downstream of the devices for different levels of wave absorption. This is achieved by modeling the wave devices as porous structures with different porosity levels, with the inclusion of partial reflection and partial transmission. The MIKE 21 suite wave models, (i) Spectral wave and (ii) Boussinesq wave are used for this purpose. The former wave model is employed for the estimation of various phase averaged wave parameters for the Orkney Islands. These wave parameters are then used as input to the Boussinesq model to study wave-device array interactions. The results are presented in the form of wave disturbance coefficients defined as a ratio of the significant wave height at a particular location relative to the incoming or input significant wave height. This study illustrates how the variations in wave absorption by the devices affect the degree of wave reflection and transmission around the devices.
Arrays of Point-Absorbing Wave Energy Converters in Short-Crested Irregular Waves
Energies
For most wave energy technology concepts, large-scale electricity production and cost-efficiency require that the devices are installed together in parks. The hydrodynamical interactions between the devices will affect the total performance of the park, and the optimization of the park layout and other park design parameters is a topic of active research. Most studies have considered wave energy parks in long-crested, unidirectional waves. However, real ocean waves can be short-crested, with waves propagating simultaneously in several directions, and some studies have indicated that the wave energy park performance might change in short-crested waves. Here, theory for short-crested waves is integrated in an analytical multiple scattering method, and used to evaluate wave energy park performance in irregular, short-crested waves with different number of wave directions and directional spreading parameters. The results show that the energy absorption is comparable to the situation in ...
A Physical and Numerical Study of an Interconnected Wave Energy Array
University of Plymouth, 2020
K ey to the progression of the wave energy extraction sector is reducing capital costs whilst maintaining or improving energy extraction efficiency. To achieve this, multiple devices in farm configurations, known as arrays, are likely to be developed. Mooring and anchorage systems of large scale arrays have been highlighted as notable contributors to high structural costs. To minimize the number of anchors required, and thus the cost, one option is to interconnect devices within the arrays. The implication on array performance and line tension of this mooring design needs to be understood to realize the true possibility for cost reduction. Large scale physical tests were performed in the COAST Laboratory at the University of Plymouth. An array of five individually moored oscillating water column type wave energy converters (WEC) were initially tested in operational and extreme conditions, followed by four interconnected designs of reducing levels of interconnectivity. Results showed considerable performance implications due to the interconnecting of devices, with a 75% increase in annual yield for all levels of connectivity, relative to the individually moored control case. The performance enhancement was attributed to the interconnecting moorings altering the system resonant frequency, resulting in a beneficial phase difference between the water column and the device. Whilst the overall array performance was not significantly effected by the level of connectivity the spatial variation in power distribution within the array was. The fatigue line loading experienced by the interconnecting lines in operational states showed iv beneficial results compared to that experienced by the individually moored array. However, in extreme sea states, some interconnecting and seabed lines displayed higher extreme loads compared to the individually moored array and so would require a higher strength material, incurring possible higher costs. Due to the improved fatigue characteristics of the interconnected arrays during operational conditions, these higher performance lines required would likely have an increased service life that requires complex cost modelling. This thesis demonstrates a beneficial potential for interconnected WEC arrays worthy of further investigation. v vi T p Peak period [s]. V Volume [m 3 ].
HAL (Le Centre pour la Communication Scientifique Directe), 2012
Wave energy from ocean waves is absorbed by using Wave Energy Converters (WECs). In order to extract a considerable amount of wave power at a location, in a cost-effective way, large numbers of WECs have to be arranged in arrays using a particular geometric configuration. Interactions between the individual WECs ("near field effects") affect the overall power production of the array. In addition, the wave height reduction behind an entire WEC array ("far field effects") may affect other users in the sea, the environment or even the coastline. Several numerical studies on large WEC arrays have already been performed, but large scale experimental studies, focussing on "near-field" and "far-field" wake effects of large WEC arrays are not available in literature. Within the HYDRALAB IV FP7 European programme, the WECwakes research project has been introduced, in order to perform experiments on large arrays of point absorber WECs, using different geometric configurations and inter-WEC spacings. The selected facility is the Shallow Water Wave Basin of the Danish Hydraulic Institute (DHI), in Denmark. The results from the WECwakes experimental tests will be useful in the validation and extension of the recently developed numerical models, as well as in providing insight to optimizing the geometric configurations of WEC arrays for real applications. The latter, also, aims at cost-effective configurations of WEC arrays for power production, and at quantifying the related environmental impact. The present paper focuses on the preparation of the WECwakes project and the development of the used WEC models.
Wave energy from ocean waves is absorbed by using Wave Energy Converters (WECs). In order to extract a considerable amount of wave power at a location, in a cost-effective way, large numbers of WECs have to be arranged in arrays using a particular geometric configuration. Interactions between the individual WECs ("near field effects") affect the overall power production of the array. In addition, the wave height reduction behind an entire WEC array ("far field effects") may affect other users in the sea, the environment or even the coastline. Several numerical studies on large WEC arrays have already been performed, but large scale experimental studies, focussing on "near-field" and "far-field" wake effects of large WEC arrays are not available in literature. Within the HYDRALAB IV FP7 European programme, the WECwakes research project has been introduced, in order to perform experiments on large arrays of point absorber WECs, using different geometric configurations and inter-WEC spacings. The selected facility is the Shallow Water Wave Basin of the Danish Hydraulic Institute (DHI), in Denmark. The results from the WECwakes experimental tests will be useful in the validation and extension of the recently developed numerical models, as well as in providing insight to optimizing the geometric configurations of WEC arrays for real applications. The latter, also, aims at cost-effective configurations of WEC arrays for power production, and at quantifying the related environmental impact. The present paper focuses on the preparation of the WECwakes project and the development of the used WEC models.
Estimation and Forecasting of Excitation Force for Arrays of Wave Energy Devices
IEEE Transactions on Sustainable Energy, 2018
To maximise energy conversion, real-time control of a Wave Energy Converter (WEC) requires knowledge of the present and future excitation force (Fex) acting on the device, which is a non-measurable quantity. The problem of estimation and forecasting of Fex becomes more challenging when arrays of WECs are considered, due to the hydrodynamic interactions in the array. In this paper, a global Fex estimator for a complete WEC array is developed and compared to a set of independent estimators which utilise information local only to each device. A significant question is whether the array of measurements is sufficient to compensate for the greater complexity of the wave field, compared to the isolated body case. The paper shows that the global estimator is always more accurate than the independent estimator, improving up to 45% the estimation accuracy of the independent estimator. Regarding prediction, two different Fex forecasters for a WEC array are compared: a global forecaster, utilising Fex estimates from the full set of array devices, and an independent forecaster, utilising only a local Fex estimate. We demonstrate that the global forecaster achieves more accurate results, not only compared to the independent forecaster, but also compared to the isolated body case.
2017
Wave Energy Converters (WECs) are devices used to capture ocean energy into useable electricity. In order to produce a large amount of electricity at a competitive cost, arrays composed of large numbers of WECs will need to be deployed in the ocean. Due to hydrodynamic interaction between the WECs (near field effects), the geometric layout of the array is a key parameter in maximizing the overall array power production and minimizing far field array effects on the surrounding area and wave field. Consequently, it is essential to model both the near field and far field effects of a WEC array. Modeling both effects by employing a single numerical model that offers the desired precision at a reasonable computational cost, is, however, still a great challenge.
Laboratory Observations and Numerical Modeling of the Effects of an Array of Wave Energy Converters
Coastal Engineering Proceedings, 2012
This paper investigates the effects of wave energy converters (WECs) on water waves through the analysis of extensive laboratory experiments, as well as subsequent numerical simulations. Data for the analysis was collected during the WEC-Array Experiments performed at the O.H. Hinsdale Wave Research Laboratory at Oregon State University, in collaboration with Columbia Power Technologies, using five 1:33 scale point-absorbing WECs. The observed wave measurement and WEC performance data sets allowed for a direct computation of power removed from the wave field for a large suite of incident wave conditions and WEC array sizes. Using measured power absorption characteristics as a WEC parameterization for SWAN was developed. This parameterization was verified by comparison to the observational data set. Considering the complexity of the problem, the parameterization of WECs by only power absorption is a reasonable predictor of the effect of WECs on the far field.