Article

Field Measurements of a Full Scale Tidal Turbine

Authors:
  • Sustainable Marine Energy
  • SCHOTTEL HYDRO
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Abstract

Field testing studies are required for tidal turbine device developers to determine the performance of their turbines in tidal flows. Full-scale testing of the SCHOTTEL tidal turbine has been conducted at Queen’s University Belfast’s tidal site at Strangford Lough, NI. The device was mounted on a floating barge. Testing was conducted over 48 days, for 288 hours, during flood tides in daylight hours. Several instruments were deployed, resulting in an expansive data set. The performance results from this data set are presented here. The device, rated to 50kW at 2.75m/s was tested in flows up to 2.5m/s, producing up to 19kW, when time-averaged. The thrust on the turbine reached 17kN in the maximum flow. The maximum system efficiency of the turbine in these flows reached 35%. The test campaign was very successful and further tests may be conducted at higher flow speeds in a similar tidal environment.

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... In particular, it revealed a large effect of turbulence strength, generated at high current speed, on the flicker level (i.e., the level of rapid fluctuations in the voltage of the power supply). Jeffcoate et al. [13] investigated the performance of a 1/10 scale tidal turbine (1.5 m diameter) in both steady state and real sea flow conditions at the experimental site in Strangford Narrows (UK). A clear decrease and strong variations of the TEC performance in turbulent tidal flow were documented. ...
... A number of experimental studies focusing on assessment of the performance of scaled horizontal axis tidal turbines (HATTs) were conducted recently in the Strangford Lough (Northern Ireland) (e.g., [17,13,10]). Frost et al. [10] assessed the performance of a 1.5 m diameter HATT (designed by SCHOTTEL Hydro Ltd) in a real tidal flow and in a towing tank. ...
... The 13% drop in peak power performance between the laboratory and field results was attributed (i) to the Doppler noise, biasing the velocity data recorded by ADCP, and (ii) to the turbulence modifying the flow regime and producing the flow instability. Similar effect was documented by Jeffcoate et al. [13] during a 1/10 scale Eppler type turbine tests mounted on a moored pontoon in a tidal flow. It was inferred that the performance of the tested turbine was affected by turbulence. ...
Article
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An experiment was performed to study the power production by a Darrieus type turbine of the Dutch company Water2Energy in a tidal estuary. Advanced instrumentation packages, including mechanical sensors, acoustic Doppler current profiler (ADCP), and velocimeter (ADV), were implemented to measure the tidal current velocities in the approaching flow, to estimate the turbine performance and to assess the effect of turbulence on power production. The optimal performance was found to be relatively high (Cp ∼ 0.4). Analysis of the power time history revealed a large increase in magnitude of power fluctuations caused by turbulence as the flow velocity increases between 1 and 1.2 m/s. Turbulence intensity does not alone capture quantitative changes in the turbulent regime of the real flow. The standard deviation of velocity fluctuations was preferred in assessing the effect of turbulence on power production. Assessing the scaling properties of the turbulence, such as dissipation rate, ε, the integral lengthscale, L, helped to understand how the turbulence is spatially organized with respect to turbine dimensions. The magnitude of power fluctuations was found to be proportional to L and the strongest impact of turbulence on power generation is achieved when the size of turbulent eddies matches the turbine size.
... In a more complete experimental program, the author of Refs. [189][190][191] outlined the testing regime of a full-scale, variablespeed, fixed-pitch horizontal axis turbine developed by the German company SCHOTTEL. The composite turbine blades are designed to be passively adaptive in order to reduce thrust in overspeed conditions. ...
... The passively adaptive blade was shown to reduce the thrust by approximately 50% compared to a rigid blade design in overspeed conditions. In Ref. [189], the same turbine is mounted to a moored barge for a stationary test conducted over 48 days during daytime flood tides. This more closely simulated real tidal condition includes turbulence and velocity shear; however, the tidal regime at the test site did not exceed the design flow speed, and therefore, the benefits of the passive adaptive blades were not realized. ...
... The moored and towing tests presented in Refs. [190,189] were compared in Ref. [191]. Though there were substantial differences in the flow conditions of each test, little impact was observed on the power output of the turbine. ...
Article
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In this paper, the advantages, state-of-the-art, and current challenges in the field of adaptive composite marine propulsors and turbines are reviewed. Adaptive composites are used in numerous marine technologies, including propulsive devices and control surfaces for marine vessels, offshore platforms, unmanned surface and underwater vehicles, and renewable energy harvesting devices. In the past, most marine propulsors and turbines have been designed as rigid bodies, simplifying the design and analysis process; however, this can lead to significant performance decay when operating in offdesign conditions or in spatially or temporally varying flows. With recent advances in computational modeling, materials research, and manufacturing, it is possible to take advantage of the flexibility and anisotropic properties of composites to enable passive morphing capabilities to delay cavitation and improve overall energy efficiency, agility, and dynamic stability. Moreover, active materials can be embedded inside composites to enable energy harvesting, in situ health and condition monitoring, mitigation and control of flow-induced vibrations, and further enhancements of system performance. However, care is needed in the design and testing of adaptive composite marine propulsors and turbines to account for the inherent load-dependent deformations and to avoid potential material failures and hydroelastic instabilities (resonance, parametric excitations, divergence, flutter, buffeting, etc.). Here, we provide a summary of recent progress in the modeling, design, and optimization of adaptive composite marine propulsors and turbines, followed by a discussion of current challenges and future research directions.
... The sea state was 1-0, and no precipitation was falling. More details on the turbine setup can be found in Jeffcoate et al. [13]. Measurements were performed in flood tides when the mean flow direction in the channel is northwest. ...
... Measurements were performed at the QUB tidal test site in Portaferry, Northern Ireland, during the Marine Renewables Infrastructure Network (MaRINET) testing campaign of the SCHOTTEL STG turbine. Details of the turbine setup can be found in Jeffcoate et al. [13]. ...
... Predicting the performance of full scale tidal turbines and support systems is critical for effective device development and deployment. Considerable research and industry study has been conducted investigating the performance of tidal turbines themselves, in particular rotors and power-take-off systems [1]; however there has been less investigation into the support structures, such as platforms, that the turbines are mounted upon [2], [3]. The fluid dynamics and system response of the platforms are as critical as the rotor performance itself, as this will affect the amount of extractable power. ...
... A modular turbine operating module (S-TOM) allows for a fully integrated solution of the power conversion system into the PLAT-O platform. Full details of a first generation SIT turbine are available in [1]. The full scale SIT diameters are 3m, 4m or 5m. ...
Conference Paper
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Computational simulations are traditionally used in accompaniment with tank testing to verify the performance of a rotor or support structure. Sustainable Marine Energy's second generation platform PLAT-O#2 has been tested at 1/17 scale at FloWave and using ProteusDS software to predict it's performance in both operating and line failure conditions. The mooring line loads and motion of the platform have been analysed in axial flows up to 4.5m/s full-scale velocities. The loads predicted by ProteusDS are comparable, but the simulations slightly over-predict the loads, due to drag effects at small-scales. This drag discrepancy causes slightly different platform behaviour, though does improve understanding of the effects of pitch, heave and surge on mooring line loads. In a line loss condition these effects are less substantial and the predictions are very comparable to tank testing results. The loads experienced in a line failure are at approximately a factor of 3 from normal operating conditions, which is a typically used factor of safety. Further understanding of the accuracy of ProteusDS PLAT-O performance predictions can be conducted with full-scale assessment of PLAT-O#1.
... Prototype-scale devices in open sea conditions have been tested to a lesser extent due to the inherent up-scaling challenges, e.g., Jeffcoate et al. [12] tested a 4 m diameter, 50 kW turbine and Frost et al. [13] compared the performance of a 1.5 m diameter turbine in both towing tank tests and at a tidal site. It should be noted that there are a significant number of engineering challenges when moving from small-scale prototype tests in controlled conditions to full-scale turbine deployments in open sea sites, particularly in terms of obtaining reliable device and environmental measurements. ...
... This procedure for calculating thrust differs from that typically used in scale-model studies [17] or field testing of smaller rotors [12], where load cells are placed on the turbine support structure and a correction is applied to remove the drag forces acting on the structural elements, leaving only the axial force on the rotor. This involves measuring the drag on the support structure without the rotor, something that was not practical for the turbine in this study and would not provide any information on the individual blade loading and bending moments. ...
Article
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Tidal turbines are subject to highly dynamic mechanical loading through operation in some of the most energetic waters. If these loads cannot be accurately quantified at the design stage, turbine developers run the risk of a major failure, or must choose to conservatively over-engineer the device at additional cost. Both of these scenarios have consequences on the expected return from the project. Despite an extensive amount of research on the mechanical loading of model scale tidal turbines, very little is known from full-scale devices operating in real sea conditions. This paper addresses this by reporting on the rotor loads measured on a 400 kW tidal turbine. The results obtained during ebb tidal conditions were found to agree well with theoretical predictions of rotor loading, but the measurements during flood were lower than expected. This is believed to be due to a disturbance in the approaching flood flow created by the turbine frame geometry, and, to a lesser extent, the non-typical vertical flow profile during this tidal phase. These findings outline the necessity to quantify the characteristics of the turbulent flows at sea sites during the entire tidal cycle to ensure the long-term integrity of the deployed tidal turbines.
... Whilst similar methodologies are applicable [6], the IEC methodology addresses the power weighted velocity as appose to the volumetric weighted velocity, making it more suitable for this specification. The specification has been taken up and used in research and industry [7], [8]. ...
... The laboratory and field test sites used in this research have been used in previous research by Queens University Belfast (QUB) and other research institutes [2], [4], [8], [10]. The first site is in a laboratory at CNR-INSEAN, Italy. ...
Conference Paper
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The paper presents data from two experimental campaigns at CNR-INSEAN's towing tank in Italy and Strangford Lough tidal test site in Northern Ireland. The experiments maintained identical instrumentation between the campaigns allowing the comparison of steady uniform flow with unsteady non-uniform conditions, respectively. The rotor is a 3 blades designed by Schottel Hydro Ltd for the SIT250 device, scaled to 1.5m diameter. The flow instrumentation used in this paper are Nortek's Aquadopp 2 MHz Acoustic Doppler Current Profiler (ADCP). The comparison between controlled laboratory and uncontrolled tidal environment is made by adopting a methodology for assessing turbine power performance using ADCP inflow data. The method allows the inflow velocity to be equated to a single measurement, using the power and area-weighted velocities across the swept area of the turbine's rotor. The method has been expanded to include uncertainties and significant factors contributing to uncertainty have been identified. The carriage velocity was used to calibrate the inflow measurements in the laboratory environment, providing confidence intervals for performance. The Schottel SIT250 scaled blades had a peak hydrodynamic performance of CP=0.44 and 0.38 at CNR-INSEAN and Strangford Lough respectively. The difference between the performance in the towing tank and at the tidal test site are discussed with attributed causes presented as a result of Doppler noise biasing and the non-uniform, turbulent inflow velocity at Strangford Lough.
... The specification provides the methodology for determining an average value for velocity at a site, enabling the time average performance of a turbine to be captured and reported to a common standard. The IEC specification has been used in other research projects and across the industry [10,13,24] and will be used to guide the data analysis in this paper. ...
Article
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The first aim of the research presented here is to examine the effect of turbine control by comparing a passive open-loop control strategy with a constant rotational speed proportional–integral–derivative (PID) feedback loop control applied to the same experimental turbine. The second aim is to evaluate the effect of unsteady inflow on turbine performance by comparing results from a towing-tank, in the absence of turbulence, with results from the identical machine in a tidal test site. The results will also inform the reader of: (i) the challenges of testing tidal turbines in unsteady tidal flow conditions in comparison to the controlled laboratory environment; (ii) calibration of acoustic Doppler flow measurement instruments; (iii) characterising the inflow to a turbine and identifying the uncertainties from unsteady inflow conditions by adaptation of the International Electrotechnical Commission technical specification (IEC TS): 62600-200. The research shows that maintaining a constant rotational speed with a control strategy yields a 13.7% higher peak power performance curve in the unsteady flow environment, in comparison to an open-loop control strategy. The research also shows an 8.0% higher peak power performance in the lab compared to the field, demonstrating the effect of unsteady flow conditions on power performance. The research highlights the importance of a tidal turbines control strategy when designing experiments.
... The kite is attached to a foundation on the seabed, at a depth of approximately 20 m, by a 27 m long moving tether. The schottel turbine is a fixed horizontal-axis stationary device, mounted from a moored barge at a depth of 3.4 m below the sea surface over an approximate total water depth of 12 m (see [31] for more details on the schottel device). The ambient soundscape of the Narrows was recorded for 2 weeks during a summer (July 2016) and a winter (January 2017) deployment, respectively. ...
Article
The deployment of tidal energy arrays is gaining momentum to provide marine renewable energy (MRE) to the global market. However, there are concerns over the potential impacts underwater noise emissions from operational devices may have on marine fauna. Auditory masking (the interference of important biological signals by anthropogenic noise) is a highly pervasive impact to marine fauna. We used a relatively new approach to evaluate the effects of noise from operational tidal energy devices on the listening space of marine mammals. Here, listening space reductions (LSR) for harbour porpoises (Phocoena phocoena) and harbour seals (Phoca vitulina) were assessed in winter and summer for two tidal energy devices of different designs. Results demonstrated that LSR was influenced by type of turbine, species, and season. For instance, LSRs for harbour seals were in excess of 80% within 60 m, whilst for harbour porpoises they were in excess of 55% within 10 m of the devices. For both species, LSRs were highest during winter, characterised by low ambient noise conditions. These findings highlight the importance of assessing masking over seasons, as masking effects are highly influenced by ambient noise conditions. Understanding the natural variation within seasons is also particularly relevant for tidal turbine noise assessments as devices are typically situated in highly dynamic environments. Since masking effects occur at the lower level of behavioural impacts in marine mammals, assessing the spatial extent of masking as part of environmental impact assessments is recommended. The listening space formula, which is largely based on measurable environmental factors (device and ambient noise), is transferable to any MRE device, or arrays, for any species (for which an audiogram can be assumed) and therefore provides an effective method to better inform MRE pre-and post-consenting processes.
... Similarly, to Frost et al., Ahmed et al. [33] presented results for the fluctuation in T h , C p and bending moment on the HATCT blade. Besides, significant fluctuations in T h and T have been considered by Jeffcoate et al. [34] during trials of a HATCT. ...
Article
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One of the most essential parameters contributing to the performance of hydrokinetic tidal current turbine is its geometry. In this study, the effect of curvature, thickness, and blade pitch angle (BPA⁰) with a glimpse at the turbine performance considering the probability of fatigue loading presence are investigated. Six different airfoils based on possessing the acceptable lift to drag ratio were selected and used to design turbine blades using the blade element momentum theory. Computational fluid dynamic was employed for simulation the performance of turbines at diverse tip speed ratios (TSR)s and BPA⁰s so that the condition for obtaining the maximum performance was determined. An experimental setup was fabricated to validate the computational results. The question is: To what extent this maximum performance condition is possible to be implemented in practice? To answer this question, a parameter called superiority of maximum power coefficient (SCPmax) was introduced to assess the usefulness of employment of each airfoil based on maximum power coefficient (CPmax), thrust coefficient (CTh), and the percentage of airfoil thickness (%t) and exhibit the utility of maximum performance against the probability of fatigue hazard. Results indicated that at higher values of BPA⁰s, by increasing the thickness, the maximum amount of torque enhances. Furthermore, the augmentation in the TSR leads to increase in CPmax at the lower value of BPA⁰ so that the difference between the lowest (for NACA 65(3)-618) and highest (for NACA 4412) CPmax is around 66%. In contrast, the maximum value of SCPmax belonged to the NACA65(3)-618 due to lower CTh and more %t, while the minimum amount of SCPmax appertained to the NACA2410 which has the minimum %t.
... The hub height of PLAT-I and the Schottel Instream Turbines (SIT) 4m rotor power curves were utilised for calculations of generated power (Jeffcoate et al. 2015). An estimate of flow velocity at this depth was calculated from VD by splitting the depth at each point in the domain into 1m bins and assuming a 1/7th Law profile (Legrand et al. 2009). ...
Conference Paper
Full-text available
This paper examines the impact of MetOcean conditions on weather window availability and subsequent maintenance costs for a floating tidal energy converter. Understanding these impacts and costs at the initial planning stage will give a better estimation of project lifetime costs and ensure that these expenses are factored into the site selection methodology. Several sources of freely available data were input into the Delft3D modelling suite to produce spatially and temporally varying estimates of MetOcean data for the Surigao Strait in the Philippines. A Dijkstra’s Algorithm was used to generate an optimum route to shore for cabling and vessels. The Weibull Persistence Method was successfully applied to MetOcean characteristics at each point along this route, to calculate the probability of operational limitations being exceeded. The number of probable access and waiting hours within a month was calculated, and costs were assigned to each task. These costs were then contrasted against the potential revenue at each point within the domain, to provide a first-pass estimate of the optimum deployment location within the Surigao Strait.
... The turbines can be operated upstream or downstream and the blades are interchangeable on the drivetrain. The turbines are hosted by SME's tidal platforms, which currently use SIT250s [5], [6]. ...
Conference Paper
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Sustainable Marine Energy and SCHOTTEL Hydro have developed a taut-moored mid-water column tidal energy platform, PLAT-O, and a semi-catenary moored floating surface platform, PLAT-I, that each host between two and four turbines. The combined platform rated power is up to 280kW. Each platform is suitable for different environmental conditions, with PLAT-I intended for low wave climates and PLAT-O for more extreme offshore conditions. This provides the basis for site selection criteria for each system. Site criteria include flow velocity, wave conditions, water depth and bathymetry, power requirements, and station keeping requirements. These have been designated into a Site Classification System for identifying sites suitable for each of SME's platforms. Site assessment must be conducted to find these sites. Whilst in developed and more easily accessible locations the equipment, vessels, and expertise used are readily available, in more remote areas and off-grid communities the traditional assessment techniques must be modified for the equipment available and for the cost associated with different survey methods. SME have developed a site assessment technique for their platform systems which is divided into four stages: Desktop Study, Visual Survey, Initial Survey, and Detailed Survey. Each stage increases complexity and cost. This allows sites to be discounted at early stages if unsuitable for further development before unnecessary money is spent. This system leads to a cost saving of up to 47% when assessing two sites using SME's method rather than two ADP surveys, and discounting one for inadequate velocity, as an example. The assessment technique, relevance to SME's tidal energy platforms, cost implications, and suggested modifications for applicability to other systems is presented.
... Comprehensive testing has been carried out and published for the first generation SCHOTTEL Instream Turbine (SIT). These include full-scale pushing tests in Rotterdam harbour [4] and moored tests using a floating platform at Queen's University Belfast's Tidal Test Site in Strangford Lough [5]. A comparison of both data sets showed comparable power output and performance curves for both the steady and turbulent tidal tests [6]. ...
Conference Paper
Full-text available
SCHOTTEL HYDRO has developed the SCHOTTEL Instream Turbine (SIT). Four SITs had been mounted on Sustainable Marine Energy's floating surface platform PLAT-I, with a combined platform rated power of 280kW. The PLAT-I platform has been undergoing field performance testing in Scotland to determine the power performance of the individual turbines according to IEC62600-200. Time series as well as processed performance data shows a high spatial variation of the inflow across the platform and hence a high dependency on the flow speed measurement location. The turbines power performance is found to be in line with design predictions, whereas the thrust loads measured are lower than the predictions. NOMENCLATURE ADCP Acoustic Doppler Current Profiler ECM Electromagentic Current Meter IEC International Electrotechnical Commission PLAT-I PLATform for Inshore Energy PLAT-O PLATform for Offshore Energy TSR Tip speed ratio TEC Tidal Energy Converter SIT SCHOTTEL Instream Turbine SDM SIT Deployment Module I. INTRODUCTION Validating the power performance of a tidal turbine is a key element in moving forward towards commercialisation for the tidal energy sector. This includes both performance prediction during the design phase as well as field measurements. During the design phase of turbine development blade-element momentum models and model scale tank tests are widely used [1]. For full-scale operational tests guidelines and test methodology are set out in IEC62600-200, the technical specification for Tidal Energy Converter (TEC) power performance assessment [2]; this standard has been used previously to assess the performance of seabed mounted tidal turbines [3]. Comprehensive testing has been carried out and published for the first generation SCHOTTEL Instream Turbine (SIT). These include full-scale pushing tests in Rotterdam harbour [4] and moored tests using a floating platform at Queen's University Belfast's Tidal Test Site in Strangford Lough [5]. A comparison of both data sets showed comparable power output and performance curves for both the steady and turbulent tidal tests [6]. Performance prediction using a blade-element momentum model has been validated for the second generation SIT 250 blade geometry. This included towing tank as well as cavitation tunnel data and showed very good agreement for power and thrust coefficients, as well as the cavitation inception bucket over a wide range of tip speed ratios [1]. This paper presents results for SCHOTTEL HYDRO´s current SIT 250 turbine design at full-scale in a tidal environment. Sustainable Marine Energy's PLAT-I platform has four SIT250 turbines and was recently deployed in a field test. The testing method and analysis of turbine performance characterisation were guided by the IEC62600-200 Technical Specification for Tidal Energy Converter (TEC) power performance assessment [2]. The overall objective of this work is a full-scale assessment of the turbines during the Sea Acceptance Tests of PLAT-I at Connel, Oban, Scotland. Further information on the platform results can be found in Part 2 [7].
... The turbine is installed on a frame hinged to the back of the barge and can be lifted out of the water, Figure 3. The barge and tidal turbine have been presented in more detail in [5,6]. The inflow velocity was measured using an Aquadopp Profiler ADP at the bow of the barge, set to a sampling frequency of 1 Hz and providing data over 10 m with resolution of 0.2 m. ...
... prototypes deployed in open water [9]. The assessment of tidal turbines operating in array has 7 largely been done numerically using simplified Blade Element Momentum theory (BEMT) 8 through fully resolved three dimensional computational fluid dynamics (CFD) to large scale 9 ...
Article
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For the successful deployment of large scale tidal turbine arrays occupying a large part of tidal channels, understanding the effects of wake interaction in densely spaced arrays is of importance. A comprehensive set of experiments has been conducted with scaled tidal turbines to investigate the resulting wake characteristics in a number of different staggered array configurations with up to four turbines on a designated support frame. Wake velocity deficits and turbulence intensities at a number of locations within and downstream of the array are presented and in addition the flow field recordings from Particle Image Velocimetry (PIV) measurements are presented for visual investigation of the resulting wake field and wake characteristics along the array centre line. The experiments show that lateral and longitudinal spacing variations of the individual devices vary the resulting flow field downstream of the array section significantly. Lateral spacing can be optimised to result in beneficial flow effects that accelerate the downstream wake recovery. Very close spacing however leads to significantly reduced velocity recovery. Longitudinal spacing shows less significant influence, especially for configurations with wide lateral distances. Differences in wake velocity deficit of up to 10% have been identified and suggest array wake recovery in and downstream of staggered sections, in areas of lower ambient turbulence levels, to be more significantly influenced by the lateral spacing especially towards the front rows of the array. With every additional array section the increasing turbulence intensity within the array is anticipated to reduce this effect.
... Bahaj et al., 2007, Chamorro et al., 2013 ou in situ (e.g. Jeffcoate et al., 2015) (1,2 MW) est montée sur un pieu ( Fig. 0.5). ...
Thesis
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Malgré l'intérêt suscité, l'exploitation de l'énergie hydrolienne accuse toujours un sérieux retard par rapport à d'autres ressoures renouvelables. Ce développement tardif s'explique d'une part par l'absence d'une méthodologie pertinente de quantification du potentiel hydrocinétique, d'autre part, par le milieu marin, jugé hostile, au sein duquel des phénomènes turbulents,appliquent des contraintes sur la structure des hydroliennes. Offrant une vision précise de l'écoulement et de son hétérogénéité spatiale et temporelle, la courantographie radar, présentée dans la première partie de cette thèse, constitue un outil puissant d'analyse de la dynamique de la marée. Inédite dans le domaine des énergies renouvelables, elle offre une alternative probante à la modélisation numérique, souvent privilégiée bien que générant des résultats contestables compte tenu de sa conceptualisation simpliste des phénomènes réels. L'étude d'impact d'un écoulement turbulent pleinement développé sur la performance énergétique de prototypes d'hydroliennes de type Darrieus constitue la seconde partie de cette thèse. L'analyse spectrale des signaux temporels de vitesse de courant a permis de révéler les propriétés scalaires de l'écoulement. La caractérisation multi-échelle a montré que l'écoulement est animé par un processus dynamique de brisures successives des structures fluides imbriquées de taille allant de l'échelle d'injection à l'échelle de diffusion moléculaire. Enfin, le partitionnement en échelles dynamiques de la turbulence des spectres de vitesse et de puissance générée par l'hydrolienne a mis en évidence une certaine similarité entre la taille des structures tourbillonnaires qui régissent l'écoulement et les dimensions de la turbine.
... MacEnri et al. [10] documented a determining effect of tidal current speed and turbulence strength on the flicker performance of the MCT SeaGen 1.2 MW tidal energy converter. Jeffcoate et al. [11] investigated the performance of a 1/10 scale tidal turbine (1.5 m diameter) in both steady state and real sea flow conditions. They documented a global decrease and strong variations of the performance in turbulent tidal flow at the experimental site in Strangford Narrows (UK). ...
... where C C is a coefficient that represents the conversion losses between kinetic energy in the flow and electricity. A value of 0.5 was assigned to C C based on experimental results reported by Jeffcoate et al. [16]. The chosen values of C T = 0.85 and C C = 0.5 are equivalent to a power coefficient of C P = 0.425. ...
Conference Paper
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Lashy Sound is a small channel in Orkney, Scotland, where a tidal stream energy development is planned. This study uses numerical modelling to investigate the energy resource of the Sound and the effects on the flow of removing this power. A new 3D regional-scale hydrodynamic model of the area was built using the MIKE software and was used to study Lashy Sound. A standard momentum sink approach was used to represent tidal energy converters. It is estimated that the maximum possible yield from this channel from the M2 tidal constituent alone is 23 MW mean and 61 MW peak power, although this would require an unrealistic and uneconomic arrangement of tidal turbines. The 30 MW capacity that is planned is predicted to be feasible, and the environmental effects of both large and small arrays are discussed.
... The results indicated that the flexible blades operated at a higher efficiency than the rigid blade, especially at low flow or off-design conditions. In a more complete experimental program, [14][15][16] outline the testing regime of the full scale variable speed, fixed pitch horizontal axis turbine developed by the company SCHOTTEL. The composite turbine blades presented were designed to be passively adaptive in order to reduce loading in overspeed conditions, and were shown to reduce thrust by approximately 50% compared to a rigid blade design in overspeed conditions. ...
Article
Modern marine hydrokinetic turbine blades are typically constructed from fiber reinforced polymer (FRP) composites, which provide superior strength- and stiffness-to-weight ratios and improved fatigue and corrosion resistance compared to traditional metallic alloys. Furthermore, numerical studies have demonstrated the possibility of tailoring the anisotropic properties of FRP composites to create an adaptive pitch mechanism that can improve system performance, especially in off-design or varying flow conditions. Potential benefits of an adaptive pitch system include increased lifetime energy capture, reduced hydro-elastic instabilities, reduced risk of mechanical failure, and improved efficiency, load shedding, fatigue life, and structural integrity. In this work, static and dynamic testing results for a flume-scale marine hydrokinetic turbine system are presented. Two sets of adaptive composite blades are compared to neutral pitch composite and rigid aluminum designs. Static testing was used to quantify the mechanical load-deformation response of each blade type. Additionally, instantaneous blade and full system loading was measured during dynamic flume testing, allowing a multilevel analysis of adaptive blade performance. Experimental results show notable shifts in the power and thrust coefficients and significant load adjustments induced through passive pitch adaptation, suggesting that adaptive pitch composite blades could be a valuable addition to marine hydrokinetic turbine technology.
... McLaughlin and Harvey, 2016), piled foundations (e.g. Whittaker et al., 2007;Spagnoli et al., 2013), moored foundation solutions (Jeffcoate et al., 2015;Scotrenewables, 2016;), tripods with buckets and suction buckets. The advantages and disadvantages of each of these systems have previously been established (IEA -RETD, 2012). ...
Article
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One of the biggest challenges faced by the offshore wave and tidal energy industry is the high cost of constructing and installing offshore foundations. Foundations based on post tensioned pile anchors can be effectively proposed to tackle this issue. A series of full-scale direct shear tests were performed on-shore to evaluate the shear resistance of post-tensioned pile anchor foundations designed for securing tidal turbine devices to a rock seabed. We focused, in particular, on the primary shear resistance mechanism of post-tensioned anchors, by applying a vertical force which mobilizes, a frictional force able to resist horizontal thrusts. Different load paths, involving monotonic or cyclic loading, were applied; several configurations for the footing of the foundation were tested. The footing stress-displacement behavior and the stress conditions at sliding failure from a number of different testing configurations were compared and analyzed. A marked consistency with the shear performance of natural rock joints was identified. This allows the behavior of tension pile foundations subjected to substantial horizontal loads to be modeled using relationships developed for rock joints, widely available in the literature. Additionally, the results obtained from different tests were also collated considering the various configurations adopted for the foundation-rock system and the applied load paths, to identify the factors that affect the shear resistance of the foundation.
... Over-speed power regulation is a complimentary control scheme for a turbine with BT blades. For example, Schottel applies an over-speed control methodology to a turbine that utilizes passively adaptive blades for load mitigation [59]. The implementation of over-speed control for flow speeds beyond design conditions was investigated using the design tool. ...
Article
Fixed pitch passively adaptive tidal turbine blades made of non-homogeneous composite materials have the potential to reduce blade and structural loads, shed power above design conditions, reduce cavitation inception, and reduce the effects of fatigue loading. Due to the flexibility of these blades, a fluid–structure interaction design methodology is required. This paper outlines the development of a coupled finite element (FEM)-blade element momentum theory (BEMT) design tool developed to iterate between the structural (deformation and stresses) and hydrodynamic (power and thrust loads) responses of passively adaptive blades. Such a FEM–BEMT design methodology provides an early stage tool with minimal computational requirements compared to computational fluid dynamics-FEM coupled codes. Both the BEMT and FEM components of the design code have been verified independently, with results presented here. Results using the design tool in a case study of a small-scale turbine with three pre-twisted fixed pitch passively adaptive blades, operated using variable speed control, showed load mitigation and power shedding at flow speeds above design conditions, and increased overall power capture between the cut-in speed and the design speed.
... It is acknowledged that some inaccuracy is inherent in using the same value of juj, representing an entire mesh element, in both of the equations above (more correctly, the velocity in (1) should be the free-stream velocity and that in (4) should be the velocity at the turbine, but neither of these values is known to the model), and correction for this is implicitly included in the value of C C . A value of 0.5 was assigned to C C based on experimental results with a Schottel turbine reported by Jeffcoate et al. [23]. This two-stage approach is equivalent, below the rated speed, to a power coefficient of 0.425, which is within the range shown by Bahaj et al. [24] from tank testing. ...
Article
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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.
... MacEnri et al. [9] documented a determining effect of tidal current speed and turbulence strength on the flicker performance of the MCT SeaGen 1.2 MW tidal energy converter. Jeffcoate et al. [10] investigated the performance of a 1/10 scale tidal turbine (1.5 m diameter) in both steady state and real sea flow conditions. They documented a global decrease and strong variations of the performance in turbulent tidal flow at the experimental site in Strangford Narrows (UK). ...
Conference Paper
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A vertical axis tidal turbine (VATT) of the Dutch company "Water2Energy", mounted on a surface platform , was tested during several weeks in real sea conditions in a tidal estuary-the Sea Scheldt, Belgium. Velocity measurements were performed to estimate the major turbulent properties of the tidal flow at the experimental site, to evaluate the tidal turbine performance, and to quantify the effect of turbulence on the output power. The optimal performance (C p) of the turbine was founded to be 0.42 in the velocity range 1.1−1.2 m/s. Results show that the dissipation rate, ε, and turbulent strength, σ u are tightly related with the magnitude of the output power variability. It was demonstrated that tidal turbine responds more actively to turbulence on scales similar to the rotor diameter.
... Power Generated (PG) was calculated by utilising a powerweighted average velocity over the swept area of the turbines, and the power curves of the SCHOTTEL Hydro 4m rotors [21] (Figure 9). An estimate of flow velocities swept by the rotors assuming a 4m hub depth, was calculated using the 1/7 th Law Profile. ...
Conference Paper
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estimated and included in the choice of ultimate deployment position. Another advantage of this approach is that it uses freely available data, allowing site assessments to determine project feasibility, without high upfront investment. Freely available astronomic, bathymetric and meteorological data was therefore input into a Delft3D-FM simulation of the Bay of Fundy. Models were calibrated with tide gauge, flowmeter and wave buoy data to output spatially and temporally varying estimates of tidal height, flow velocity and significant wave height. Results demonstrate that areas of highest resource are the most profitable, but sheltered areas with lower flow speeds are also highly economically viable. For an emerging technology sector with relatively limited operational experience, it is recommended that these areas of less risky investment opportunity should be targeted by tidal energy developers.
... Supplement Bshowing the evolution of the vortical structures for l ¼ 2 and 6.15 can be obtained from authors upon request.3 For isotropic decaying turbulence, jp 0 j 2 is expected to show k À7/3 scaling in the inertial subrange[80], where k is the wavenumber (which is same as frequency for homogeneous turbulence).O. ...
Article
The predictive capabilities of blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and detached eddy simulation (DES), the most commonly used hybrid RANS/large eddy simulation (LES) model, are assessed for hydrokinetic turbine performance and mean and turbulent flows in the intermediate-wake region, and results for a range of tip-speed ratio encompassing design and off-design conditions are analyzed to understand the wake recovery mechanism. The performance predictions compared within 5% of the experimental data. Both URANS and DES models performed reasonably well for the near wake predictions, where the errors were <15%. DES outperformed URANS for both mean wake deficit and turbulence predictions in the intermediate-wake region and both quantities compared within 10% of the experiments. The improved prediction by DES is because of its ability to predict the tip vortex breakdown, which plays a critical role in the wake recovery, especially for higher tip speed ratios (λ). However, DES significantly underpredicted the turbulence predictions in the near-wake region, which could be partly due to the negligence of free-surface effects and partly due to modeling issues, namely modeled stress depletion. The study reveals that the tip vortex breakdown mechanism depends on λ. For lower values of λ, instabilities generated in the root vortex core are identified to be the cause of breakdown. For higher values, the breakdown occurred because of the instabilities generated during the vortex filament entanglement. Future work should focus on investigation of other hybrid RANS/LES models to address the limitations of the DES models, and extension of the study to include free-surface effects.
... The turbine operational states analysed for this paper are power production, stop and idling (freewheeling). Basis are data gathered from a measurement campaign that deployed an Acoustic Doppler Current Profiler at the installation site in the Minas Passage of the Bay of Fundy, Canada [14]. For each load case 10 min of samples are simulated. ...
Article
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As a regenerative energy source, tidal energy can significantly contribute to greenhouse gas reduction, even though the potentially achievable energy output is lower than that of wind or solar energy. The decisive advantage of tidal turbines lies in the simply and reliably predictable energy output. However, their commercial use has so far been impeded by the fact that on the one hand complex mechanical systems are required to convert energy of tidal currents and on the other hand multi-axial loading conditions caused by turbulent ocean currents act on the turbine. For this reason, field tests on prototypes are an essential part of the development strategy to ensure operational reliability. However, in-field tests do not allow for accelerated lifetime testing, so that test bench experiments are becoming an increasingly important alternative. Today, established procedures for testing the turbines main bearings and gearing system are already available, both for setting up the required test configuration and for determining the corresponding test loads. However, the use of advanced calculation methods, such as the finite element method for stress calculation, requires a deep understanding of the examined components and hinders the transfer of the approaches to other components. To simplify the process of test loads determination, a general methodology is presented, which relies exclusively on standardized empirical calculation rules. Doing this, fatigue equivalent loads can be determined for any component in a simple process. It was shown that the achieved reduction in complexity opens further potential for test acceleration, since several components can be tested simultaneously.
... Optimal efficiency can be obtained when waves are in normal conditions. This can be obtained by using a special valve that prevents the turbine from over speed (Jeffcoate et al., 2015). ...
Article
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This paper aims to review the potential of wave energy in several countries, the wave energy converter technology that has been developed, and the impact of the installation of wave energy converter technology devices on the environment. In addition, it discusses the theoretical formulations and challenges in the development of energy converter technology in the future. Based on the detail analysis, the potential of ocean wave energy for alternative energy is very large but cannot be used optimally because the technology of wave energy converter that has been developed is still on a prototype scale. In addition, the impact of the use of ocean wave converters on the environment is insignificant compared with conventional energy. Finally, this study informs and recommends the government and the private sector to start investing in the ocean wave energy industry optimally in order to achieve a sustainable future.
... Dai and Lam [15] proposed a 1-MW full-scale turbine model and completed a numerical investigation for its power coefficient and structural loading. Penny et al. [16] conducted full-scale testing of the SCHOTTEL tidal turbine at Queen's University Belfast's tidal site and found that the maximum system efficiency of the turbine reached 35% in flows up to 2.5 m/s. Gonzalez-Gorbeña et al. [17] presented a study for the optimization of an instream tidal energy converter array layout and showed that large amounts of energy extraction may cause significant erosion. ...
Article
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Scour induced by a Darrieus-type tidal current turbine was investigated by using a joint numerical and experimental method with emphasis on the scour process of a full-scale turbine. This work proposes a new numerical method to estimate turbine scour developments, followed by model validation through experimental data in the initial stage. The small-scale numerical model was further extended to a full-scale model for the prediction of turbine scour. The numerical model consists of (1) k-ω turbulence closure, (2) a sediment transport model, and (3) a sediment slide model. The transient-state model was coupled with a morphologic model to calculate scour development. A dynamic mesh updating technique was implemented, enabling the autoupdate of data for the grid nodes of the seabed at each time step. Comparisons between the numerical results and the experimental measurements showed that the proposed model was able to capture the main features of the scour process. However, the numerical model underestimated about 15%–20% of the equilibrium scour depth than experimental data. An investigation of the temporal and spatial development of seabed scour around a full-scale Darrieus-type tidal current turbine is demonstrated. This work concludes that the proposed numerical model can effectively predict the scour process of tidal current turbines, and the rotating rotor has a significant impact on the equilibrium scour depth for full-scale turbines.
... As examples, the rotor design of the horizontal axis fixed-pitch SIT250 turbine and its prede- cessor STG50 from SCHOTTEL HYDRO purposefully aims for an elastic deformation -in particular torsion -to reduce the thrust loads in off-design conditions (cp. [1] and [2] ). The full-scale testing of the 4 m diameter STG50 turbine showed a significant decrease of the thrust due to the elastic deformation of the blades [3]. ...
Conference Paper
During the model scale testing of a newly de- signed 6.3 m horizontal axis fixed-pitch tidal turbine, a distinct - undesired - deformation of the 1:12.6 brass model was observed. The objective of this contribution is a nu- merical and experimental assessment of a potential per- formance modification due to the observed deformation. To simulate the bending and twisting an extended and validated blade element momentum (BEM) model, predicting the turbine performance including the cavita- tion characteristics, was coupled to the finite element method (FEM) solver from ANSYS Mechanicals®. The deformation was predicted for a wide operating range utilizing the BEM-FEM coupling. It was found that the axial bending of the blades was accompanied by a distinctive torsion which led to increased pitch angels. Comparing the performance predictions for the rigid and flexible rotor blades showed that the obtained variation in pitch angle distribution led to i) a decreased power output, ii) reduced thrust loads and iii) somewhat lower critical cavitation numbers. Experimental performance characteristics of the - una- voidably flexible - model scale turbine were obtained in comprehensive towing tank and cavitation tunnel tests. A comparison with the prediction strongly suggests, that the model-scale turbine experienced the performance changing deformation as simulated from the FEM model.
... The sites at which devices are tested and deployed are highly energetic (by necessity -there needs to be enough energy present in the water flowing through the area to be extracted), with both spatial and temporal variations present, ranging from turbulent fluctuations [1e3] to larger bathymetry dependent flow features [4,5], vertical flow profiles and asymmetric flood/ebb flow speeds and direction [6,7]. These flow variations lead to fluctuations in the loads on the devices, which is then reflected in operational performance [8,9] as well as repeated load cycling that may lead to fatigue damage. Work in the wind sector suggests that typical wind turbines are "fatigue critical" -parts are more likely to fail through fatigue than through over loading and need to be designed accordingly [10], and while loadings on tidal devices will be different (and are likely to be higher), it is likely that the survivability and reliability will also require careful consideration of the unsteady nature of the forces acting upon them [9,11]. ...
Article
Full-text available
The development of tidal energy converters, and particularly floating tidal energy converters, is an area of increased development in recent years. Testing of a floating tidal energy device over winter 2017/18 led to an opportunity to record and examine strain of a full scale composite turbine blade under operational conditions, with comparison of generating and parked behaviours. Comparison of the recorded data shows that blade strain correlates well with both torque and thrust over the averaging periods specified in IEC62600-200, although examination of frequency spectra generated from the strain data show that higher frequency fluctuations in strain are not necessarily detectable in the larger scale thrust and torque recordings with this particular measurement arrangement. The need for well synchronised clocks on recording systems is also highlighted, along with a cross-correlation method used to recover the alignment of data from different systems to allow comparison between them over periods of a similar order of magnitude to the clock skew between the systems.
... The sensors are also utilised in tidal channel applications to measure mean flow [3,4] and turbulence [5,6] and investigate turbulence predictions from hydrodynamic models [7]. ADCPs are used in tidal energy applications to inform resource assessment [8], evaluate the performance of tidal turbines in the field [9,10] and investigate turbine blade loading [11]. ...
... where TI is known as the turbulence index of the flow and α is an empirical parameter employed to fit the velocity profile, as in reference [17], given measured data. The polynomial approximation is plotted in Fig. 2, where it should be noted that the reference employed is from the seabed, keeping the conventions of references [17,18]. The spatial and temporal components of the correlation are modelled in the following way: ...
Chapter
For a model of offshore structure standing in a fluid, we derived the cumulative distribution function of the extreme base shear and the extreme bending moment, that is, the extreme value produced by the weighted sum of a spatially continuous non-Gaussian stochastic horizontal force field produced by current and turbulence, in a given time interval it is assumed to be stationary. In the proposed methodology, the theory of translated processes is used to solve the problem of finding the extreme of non-Gaussian stochastic processes. The application is carried out on a thick column whereas the stochastic field of turbulence is supposed to be Gaussian but not necessarily narrow-band. The cumulative distribution functions obtained are in good agreement with statistical results derived from simulations in the time domain.
... We analyzed the industrial three-bladed tidal turbine STG 50 [26]. The turbine rotor blades, made of carbon fibre composite material, were optimized based on size, giving them a high power to weight ratio and a low power to cost ratio. ...
Article
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Numerical investigation of the flow around an axial tidal turbine were investigated. Two different methods to model the flow around the tidal turbine, the multiple reference frame method and the actuator disk momentum method, were used and compared in terms of accuracy and computational efficiency. Discretization errors were performed for Power and Thrust coefficients. Numerical prediction compared favourably to the experimental measurements from physical tests of the tidal turbine in homogenous flow. The Multiple Reference Frame method was used to compute power coefficient and thrust of a tidal turbine at different tip speed ratios, the forces that act on the turbine blades, and the pressure distributions at each blade cross sections. we performed all our simulations at the best efficient point. We found that the maximum stresses on the turbine blade occurred at turbines radius between 0.8 and 0.9Ro, where Ro is the turbine bald radius. The optimum radial and longitudinal distances were studied for installing other turbines to produce optimum power output. We conclude that a farm of our presented turbines, which gives the maximum output power for each turbine, can be arranged with the turbines being separated by three times the turbine's radius.
... Similarly to Frost et al., Ahmed et al. [13] presented results for the fluctuation in thrust force, power coefficient and bending moment on the tidal turbine blade as it rotates through 360⁰. Furthermore, significant fluctuations in thrust force and torque have been observed by Jeffcoate et al. [14] during full-scale trials of a 50kW tidal turbine. There are four main aspects that that have been identified by tidal turbine developers that contribute to unsteady loadings on tidal turbine blades: ...
Article
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As the world moves to a greater reliance on renewable energy, a vital component will be the predictability and dependability of the energy source; tidal energy provides such a solution. Horizontal axis tidal turbines are the most mature technology of all the marine renewable energy devices currently under development, as full-scale porotypes are already being tested and operated. As the industry develops and strives for commercial viability, it is becoming increasingly vital to develop a robust understanding of the complex interaction between the tidal flow, turbine blades and the support structure. This study uses an advanced computational fluid dynamics model to explore the operational fatigue loadings induced on tidal turbine blades. Two factors are considered, the presence of a support structure and varying vertical velocity profile of the tidal current. In order to perform the investigation, a model of a concept 16 m diameter horizontal axis tidal turbine with a monopile support structure is created. An investigation of the operational fatigue loadings due to variations in the positioning and the diameter of the support structure, the tidal turbine blade loads were found to varying by up to 43% of the maximum total thrust force.
... The SIT 250 is a horizontal axis instream turbine. The first generation SIT 250 was presented by SCHOTTEL in 2012 (Jeffcoate et al. 2015). It is designed as a modular turbine system utilizing one drivetrain for two rotor diameters, 4 m and 6.3 m, which can be selected based upon the varying velocity frequency distributions of different deployment sites. ...
Article
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Tidal energy has seen a surge of interest in recent years with several companies developing technology to harness the power of the world’s oceans where the operational capacity in Europe was over 11 MW in 2020. One such developer is the partnership of SCHOTTEL Hydro (Germany) and Sustainable Marine (UK) who have developed a scalable multi-turbine device equipped with 70 kW turbines and capable of operating in arrays at sites around the world. The technology to harness tidal energy is still at a relatively early stage of development; hence, de-risking of component parts plays a vital role on the road to commercialisation. Despite this, the number of tidal energy blades undergoing test programmes remains small. Two different rotor diameters have been developed for the aforementioned device such that it can be optimised for sites of varying potential. In this paper, a blade from each of the 4.0 m and 6.3 m diameter devices was tested for their responses in natural frequency, static loading and fatigue loading under test standards IEC 62600-3:2020 and DNVGL-ST-0164. Testing saw the survival of a blade in fatigue at a lifetime-equivalent load and the generation of natural frequency, strain and displacement results for both blades. Data generated from the testing as a whole will contribute to the modelling and validation of future tidal blades.
... Zhou et al. summarized that the performance of the major industrialized large tidal turbines is about 40% [27]. Jeffcoate et al. conducted vessel-mounted full-scale testing of the SCHOTTEL tidal generator (STG) turbine, and the results show that the system efficiency reached 35% [28]. Therefore, in this study, efficiency of tidal device is assumed as 35% from a conservative point of view in order to not overestimate the tidal current energy potential. ...
Article
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Korea is a very well-known country for having abundant tidal current energy resources. There are many attractive coastal areas for the tidal current power that have very strong currents due to the high tidal range and the acceleration through the narrow channels between islands in the west and south coasts of the Korean peninsula. Recently, the Korean government announced a plan that aims to increase the portion of electricity generated from renewable energy to 20% by 2030. Korea has abundant tidal current energy resources; however, as reliable resource assessment results of tidal current energy are not sufficient, the portion of tidal current power is very small in the plan. Therefore, a reliable resource assessment should be conducted in order to provide a basis for the development plan. This paper describes the resource assessment of tidal current energy in Korea based on the observational data provided by KHOA (Korean Hydrographic and Oceanographic Agency) and numerical simulation of water circulation. As the observational data were unable to present the detailed distribution of the complicated tidal current between islands, numerical simulation of water circulation was used to describe the detailed distribution of tidal current in Incheon-Gyeonggi and Jeollanam-do, where the tidal energy potentials are abundant. The west and south coastal areas of Korea were divided into seven regions according to the administrative district, and the theoretical tidal current potential was calculated using average power intercepted. The results of this research can provide the insight of the tidal current energy development plan in Korea.
Thesis
The tidal current energy is highly predictable, and it can provide a stable output to the grid. Especially in the coastal regions, it might enhance the diversity of the energy mix, contribute to the decarbonization of electricity production, increase energy security by exploiting indigenous resources, and fuel economic growth. Due to their advanced technological readiness levels, tidal energy conversion systems are likely to become commercially attractive within a decade, with the potential for a significant market share in future energy systems. Indonesia, with a significant potential for tidal current energy, is one of the many countries aiming to increase the contribution of the tidal currents in their national energy mix. Hence, the country intensifies the research and development efforts to reach this goal. The presented study stresses fundamental research issues regarding the characterization of tidal current energy resources with a focus on Indonesia, leading to a concluding overview of the country’s potentials for tidal current energy. Developed approaches and tools such as high-resolution, three-dimensional numerical models validated by state-of-the-art measurements, are presented. Analyses of the tidal current energy potentials of several promising straits between the Indian Ocean and inner Indonesian Seas are performed. A resource assessment methodology is developed to define energy hotspots within the target domains and to estimate technically extractable powers from each of them. The influence of density-induced flow on tidal stream power generation for the Sunda Strait, located between Java and Sumatra islands, is investigated. Physical impacts of tidal current energy extraction on hydro-environment and performance of tidal turbine arrays are presented in detail for the Strait of Larantuka, which divides East Flores and Adunara islands in eastern Indonesia. Changes in the local flow field due to the operation of turbines as well as the turbine performances for various dissipation levels and array configurations are evaluated. The results underline the potentials of the Indonesian straits of Bali, Larantuka, Boling, Alas, Lombok, Sunda, and Badung for the production of renewable electricity from tidal currents. While the currents with the highest power densities are observed in the straits of Bali and Larantuka, Alas Strait was found to have the biggest potential for tidal current energy extraction due to the larger size of its energy hotspot. The technically extractable power potential of all the investigated straits is estimated to exceed a total of 5,000MW. It is found that in the Sunda Strait, the density gradients caused by the water exchange between the Java Sea and the Indian Ocean can seasonally amplify tidal current speeds by up to 100% at the free sea surface. During both northwest and southeast monsoonal seasons, electricity production in Sunda Strait rated for the baroclinic mode resulted in more than twice the electricity production estimated for the barotropic mode. Concerning the impacts of tidal energy extraction, an overall change is observed in the flow fields, which have been simulated due to different dissipation levels and array configurations. Up to 30 – 40% decrease in current speeds is observed downstream of the turbine arrays. On the contrary, within the adjacent nearshore shallow waters, up to an 80% increase in current speeds was observed mainly due to the blockage effect. Turbines seemed to reach their rated capacities for short periods and to operate with a maximum of 60% efficiency compared to their rated power. The findings emphasize the importance of high-resolution modelling tools for a comprehensive assessment of tidal current energy resources, for optimizing the layout of multi-turbine arrays, and for the assessment of potential physical impacts due to tidal current energy extraction.
Conference Paper
Acoustic Doppler Current Profilers (ADCPs) are commonly used across a range of disciplines for flow measure- ments in fluvial, coastal and offshore environments. As with any measurement instrument, calibration and assessment of the accuracy of ADCP outputs is of high interest to many users, but in most cases the data is not independently verified. The accuracy of the measurements is of particular importance to the emerging tidal stream energy industry, since available power is proportional to velocity cubed. This paper describes the methodology of a field study conducted to compare flow velocity measurements from five collocated ADCPs. The velocity magnitude and direction results from four of the ADCPs are compared and contrasted in the paper. The most significant result from this study is the mean pairwise difference of depth and time averaged speed of up to 0.19 m s −1 between two collocated instruments on one frame. The differences in results between instruments highlight the issues of instrument accuracy and of spatial variability of flow conditions.
Conference Paper
Tidal stream energy has the potential to make a significant contribution to energy mix in the future. Accurate modelling and visualisation of both tidal resource and array layout enhances understanding of in-stream tidal behaviour leading to improvements in site identification and optimal positioning of individual turbines. A realistic representation of blade loading conditions will aid designers and manufacturers in creating more robust devices and improve survivability. The main barriers to large scale deployments of tidal arrays are the costs associated with manufacturing, installation and maintenance. Therefore, presently tidal energy is not competitive on cost with more established renewable technologies. The current position paper investigates and reports on resource modelling, site selection, selecting optimal array configurations and the design and manufacture of devices for tidal stream renewable energy generation. This is aimed at developing models to reliably simulate real conditions, enhance understanding of tidal processes, flow regimes and device survivability issues.
Article
There are many problems in the fields of flow modelling around structures and tidal stream energy yield analysis which require a thorough understanding of the turbulent and time-averaged flow speeds in marine environments. In this paper we examine the relationship between the turbulence intensity and mean tidal flow speed at a potential tidal stream power site. We report data from the Humber Estuary wherein an Acoustic Doppler Current Profiler were used to capture vertical profiles of the high frequency and mean tidal flow speeds throughout Spring and Neap, Flood and Ebb cycles. We show not only that our results extend earlier work but also suggest that the turbulence intensity, IT, can be described parametrically in terms of the mean flow, U, by an inverse power function where the coefficient appears to be dependent upon the anisotropic nature of the turbulence. For the data reported here, the coefficient has value of about 17–18 and the exponent lies between −0.6 and −1.0. Confirmation of this relationship should not only improve engineering design work and energy yield analyses in turbulent tidal flows but also be applicable to other problems such as the prediction of sediment mass transport and pollution dispersal in estuarine management studies.
Conference Paper
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Inflow turbulence can impact a turbine's power performance and load conditions and also affects wake recovery. At array scale, changes in flow conditions across a site impact the energy yield, performance and load conditions of turbines. Understanding the variation of flow conditions in time and space at deployment sites is therefore important to the tidal stream energy industry. Tidal flow field data of sufficient detail to allow turbulence characterisation remains relatively scarce. Traditional three or four beam Acoustic Doppler Current Profilers (ADCPs), which are commonly used for tidal flow resource characterisation, are limited by their spatial and temporal resolution and by the assumption of flow homogeneity across their beams. Higher resolution methods of measurement must therefore be implemented. This paper presents flow measurements that were conducted concurrently from two moored platforms in Strangford Narrows, an energetic tidal channel, separated by approximately 500m. Between the two locations a rocky outcrop exists in the channel and the characteristics of the flow vary significantly. Two collocated instruments were used to measure the flow characteristics at each location: a five beam ADCP (Nortek Signature 1000) and an ADV (Nortek Vector). This paper compares and contrasts both the flow characteristics at each location and the turbulence measurements using the different instrumentation types. The combination of instrumentation enables improved characterisation of the flow.
Conference Paper
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Costa Rica has a great potential for the production of electricity from waves, especially in the Pacific coast. Currently, 99% of the country’s electric energy is produced by renewable sources such as hydropower, wind and geothermal; the extractable energy potential from waves in the Pacific coast equals the combined energy of all these sources. The iMARES group of the University of Costa Rica has carried out a continuous measurement of the Pacific waves of Costa Rica, from which wave characteristics have been determined and how these can influence the production of electrical energy. The arriving waves at the Pacific Coast of Costa Rica are originated mainly in the east side zone of New Zealand and they travel more than 10000 km through the Pacific Ocean basin to the Central American coast. E-BOOK edited and publicated by : Rojas M., J.; Meza, C. (2020). Pan American Marine Energy Conference 2020 Book of Abstracts, paper presented at Pan American Marine Energy Conference (PAMEC 2020), San Jose, Costa Rica.
Thesis
Full-text available
This thesis investigated the non-dimensional performance characteristics of a tidal stream turbine and how they varied in response to changes in flow direction. The problem was considered from an industrial perspective and used the commercial software package ANSYS CFX and a 1:20th scale experimental turbine. Initial considerations analysed the performance of the turbine in an ‘upstream’ or ‘downstream’ configuration relative to the turbines support structure. The conclusions resulting from this were that up to a point by increasing separation between an upstream turbine and its support structure the greater average non- dimensional performance characteristics became. Also, more significantly, it was identified that this orientation and clearance reduced the blade stanchion interaction considerably relative to the downstream orientation. The study made justification for the inclusion of a yaw mechanism to rotate the turbine to face the flow for flood and ebb phases of the tide. In an operational environment this would be expected to enhance the life of the turbine’s blades, thrust bearings, and gearbox - which are known to be prone to fatigue failure, due to highly dynamic loads. The thesis continued to expand into the potential uses of a yaw mechanism to address flow misalignment experienced throughout the tidal cycle. In order to justify this, the non-dimensional performance characteristics of the same turbine were compared for a series of flow misalignment cases. The CFD analysis showed that increased flow misalignment in either the positive and negative direction had the effect of reducing turbine torque and power performance characteristics, and also significantly increases the out-of- plane bending moments. A distinction between the positive yaw angles and negative yaw angles was identified in the turbine’s performance. The negative flow misalignment showed more favorable performance changes than the positive flow misalignment, this was due to the turbines rotational direction. The subsequent recommendations to industry were included making use of the turbines rotational direction and yaw mechanism, to experience lower performance reductions in the case of flow misalignment. Experimental results from tow tank testing at CNR-INSEAN using the 0.5 m diameter turbine validated the non- dimensional performance characteristics of the CFD results. It was identified that steady state CFD results did not capture the performance characteristics of flow misalignment cases as well as the transient CFD results. The experimental turbine captured temporal features identified in the CFD analysis. Recommendations to industry include the careful consideration of steady state CFD analysis in non-idealised flow conditions.
Book
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The Pan American Marine Energy Conference is intended to bring together researchers in marine renewable energy in the Americas (including the Caribbean). This new research conference is part of a global network of conferences that includes the European Wave and Tidal Energy Conference (EWTEC) and the Asian Wave and Tidal Energy Conference (AWTEC). This book includes the contributions presented at the First Pan American Marine Energy Conference that ran from January 26th to the evening of the 28th. PAMEC is intended to foster the development of marine renewable energy through collaboration among researchers, developers, and suppliers. The contributions are collected in the following topics: Resource assessment, Environment, Current technology, Emerging technology, Storage and integration, Building social and policy support.
Article
With the expansion of intermittent renewable energy sources, and the development of economical and scalable energy storage technologies, the management of the electrical grid has the potential to fundamentally change. Under the current grid management paradigm, balancing and stabilizing a grid with a large penetration of intermittent renewables tends to require that those balancing resources ramp power output up and down more rapidly and more frequently to compensate for output variations of intermittent resources, as well as those of load. This paper describes a strategy of combined wind, solar, and in-stream tidal intermittent generation with energy storage. The new control strategy operates dispatchable generation with the objective of keeping the energy storage at a neutral state of charge in preparation for unpredicted upcoming imbalances between intermittent generation output and system load, while limiting power ramp rates within an acceptable envelope. A case study in Nova Scotia, Canada is examined. The model reveals that approximately 4 h of storage is sufficient to permit up to 70% intermittent generation contribution to the grid at a cost about 50% higher than that of the least cost renewable generation alone.
Article
Combining intermittent renewable generation with energy storage in the electricity grid has become a preferred route to maintaining stability and reliability while decarbonizing. The effects of combining three uncorrelated intermittent resources with energy storage are not well understood. This study reports on a data-driven model and control strategy that optimizes relative installed capacities of wind, solar, and in-stream tidal generation with energy storage for smoothing and shaping to follow electrical load perturbations. The model is applied to a case study in Nova Scotia, Canada which has strong wind and tidal resources, and moderate solar resources. For load-perturbation control on hour shaping timescales the total system capital costs are approximately 20% greater than the costs of the renewable generation without energy storage and output shaping. Shaping timescales of days and weeks favour greater installed wind, solar, and tidal generating capacity and the use of curtailment for economic optimization, with less installed energy storage capacity. Hour-timescale shaping uses the energy storage to mitigate power variability in intermittent generation, which benefits short-term electricity generation dispatch and reliability. Day-timescales shaping uses the energy storage to supply the load's variable energy needs using for day-ahead or future electricity generation scheduling.
Article
The measurement of power performance is an important procedure in the de-sign verification and ongoing health monitoring of a tidal turbine. Standardisedmethods state that the performance should be measured relative to two inde-pendently located flow sensors, the arrangement of which is often non-trivialand necessitates additional cost. Recent interest in the usage of flow sensorsmounted on the turbine has demonstrated their capabilities in profiling the ro-tor approach flow, but this instrument configuration is not recognised in theperformance assessment standard. This study evaluates the merits of the tur-bine mounted configuration by measuring the performance of a tidal turbinerelative to this reference and to a conventional seabed placed instrument. Theturbine mounted sensor is found to provide a better reference of the free-streamconditions, evident from an improved agreement with theoretical predictions ofdevice performance and a reduced amount of variation in the results. This newmethod could reduce both the costs and uncertainty associated with existingperformance assessment best practices
Thesis
The main aim of this study is to create an easy-to-reproduce knowledge unit wherein the digital-filter method-based (DFM) and forward-stepwise method-based (FSM) synthetic inflow generator classes are conceptualised, explored, and improved for large eddy simulation applications (LES). To this end, the following novelties were introduced: [ i ] both classes were abstracted and documented into four non-CFD and five CFD model stages, [ ii ] two new DFM variants were derived, [ iii ] with these two, four preexisting DFM-FSM variants were code implemented, [ iv ] a new analytic function that can transform the skewness-kurtosis of synthetic inflow to target values without changing existing statistics was derived and verified, [ v ] two other skewness-kurtosis transformation approaches were derived and proved ineffectual, [ vi ] five easy-to-code computational speedup techniques for DFM-FSM were introduced and quantified, [ vii ] two new methods to enable DFM-FSM to be computed on nonuniformly-discretized arbitrary boundary geometries were developed, [ viii ] a preliminary method to ensure the divergence freeness in DFM-FSM was studied, [ ix ] each DFM-FSM model stage was evaluated by controlled studies of extensive-than-the-literature range of input variables and output statistics within non-CFD and LES environments through decaying homogeneous isotropic turbulence, homogeneous shear turbulence and smooth-wall plane channel flow, [ x ] five LES post-solution verification approaches were reviewed and compared via these building-block flows. In addition, horizontal axis wind and marine turbine flows were explored by various means including DFM-FSM: [ xi ] for these explorations, in-house codes were written and verified for the blade element momentum theory (BEMT), the time-accurate Euler-Bernoulli beam theory, a BEMT-CFD coupling through the actuator disk method, and the actuator line method, [xii] hydrodynamics of a marine turbine under decaying homogeneous isotropic turbulence with four different turbulence intensities were investigated by wall-modelled & actuator-line modelled LES computations, and twelve analytical wake models, [ xiii ] the arbitrary mesh interface technique under turbulent inflows was quantitatively assessed, and lastly, [ xiv ] considerable amount of for-the-first-time observations and remarks were quantified and reported.
Conference Paper
Full-text available
Performance characteristics are presented for a two-bladed horizontal axis tidal turbine, representing a 1/25th scale operational turbine. The tests were conducted in a 116 m long tow tank facility at the United States Naval Academy. The performance characteristics of power and thrust coefficient are measured for the turbine for a range of tip speed ratios. The results of the model test are applicable to full scale due to Re number independence of the rotor blades for the tested conditions. A full uncertainty analysis is performed and major sources of uncertainty are identified. Uncertainty levels are 4% and 1% for power and thrust coefficient respectively, and 3% for the tip speed ratio.
Thesis
The oceans are a huge resource of untapped energy. There are many marine renewable energy sources however tidal energy has the advantage of being highly predictable. The range of devices for tidal energy extraction is extensive with power being generated either by extracting potential or kinetic energy. Due to environmental concerns regarding potential devices it is thought that a breakthrough will occur in the area of kinetic energy devices, most likely horizontal axis tidal turbines (HATTs). No HATT technology is yet commercial and further research into the field is required to advance the concepts, improve the feasibility of maintenance and make devices more efficient and economic. The blades of a HATT are the source of energy extraction for the device and are required to operate in a harsh subsea environment for a long (20 year) life cycle with minimal need for maintenance. Choice of an appropriate foil section for the blade is integral. A novel bi-directional section has been developed for use on a HATT and compared to a variable pitch device. The concept of using adaptive composite blades in order to improve energy capture but also decrease design complexity has been considered. Preliminary analysis was undertaken and it suggested that a 2.5% increase in annual energy capture and a 10% decrease in thrust loading could be expected through the use of a bend-twist coupled adaptive HATT blade. An experimental method was developed for the assessment of bend and induced twist in a coupled spar, and the results compared well to numerical analysis with the conclusion that the numerical model is very sensitive to manufacturing accuracy. A design tool for the development of adaptive composite bend-twist coupled HATT blades has been developed. The tool couples finite element analysis, computational fluid dynamics and blade element theory to create optimal blades. Coupling the passively adaptive bend-twist coupled spar with actively adaptive snap-through asymmetric laminates to create an efficient blade that works optimally in both directions of tidal flow has been considered. A comparison between four arrays of 4 turbines in a staggered grid, one each with standard fixed pitch, bi-directional, passively adaptive and actively adaptive blades illustrated that annual energy capture could be increased by up to 120% with the use of actively adaptive blades when compared to a base fixed bladed rotor
Article
This paper presents a current and turbulence measurement campaign conducted at a test site in an energetic tidal channel known as Strangford Narrows, Northern Ireland. The data was collected as part of the MaRINET project funded by the EU under their FP7 framework. It was a collaborative effort between Queen's University Belfast, SCHOTTEL and Fraunhofer IWES. The site is highly turbulent with a strong shear flow. Longer term measurements of the flow regime were made using a bottom mounted Acoustic Doppler Profiler (ADP). During a specific turbulence measurement campaign, two collocated instruments were used to measure incoming flow characteristics: an ADP (Aquadopp, Nortek) and a turbulence profiler (MicroRider, Rockland Scientific International). The instruments recorded the same incoming flow, so that direct comparisons between the data can be made. In this study the methodology adopted to deploy the instruments is presented. The resulting turbulence measurements using the different types of instrumentation are compared and the usefulness of each instrument for the relevant range of applications is discussed. The paper shows the ranges of the frequency spectra obtained using the different instruments, with the combined measurements providing insight into the structure of the turbulence across a wide range of scales.
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Full-Scale Testing 515 of a Tidal Energy Converter Using a Tug Boat
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Current and Turbulence 529 Measurement with Collocated ADP and Turbulence Profiler Data, Presented at IEEE/OES 530 11 th Current, Wave and Turbulence Measurement Workshop
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