Papers by Michael Togneri
Energy Procedia, Sep 1, 2017
Acoustic Doppler current profilers (ADCPs) are commonly used to assess mean currents and turbulen... more Acoustic Doppler current profilers (ADCPs) are commonly used to assess mean currents and turbulence at energetic sites. Since 2014, five-beam ADCP configurations have become more common, but conventional analysis of turbulence properties is still based on the four-beam Janus configuration. We use measurements from a single site to investigate whether improved estimates of turbulent kinetic energy (TKE)are made possible by the addition of a fifth vertical beam. We conclude that four-beam estimates of TKE are suitable in most cases, and exhibit lower variance than five-beam estimates, but are more prone to contamination by wave activity.
MARINE VI : proceedings of the VI International Conference on Computational Methods in Marine Engineering, 2015
To fully understand the performance of tidal stream turbines for the development of ocean renewab... more To fully understand the performance of tidal stream turbines for the development of ocean renewable energy, a range of computational models is required. We review and compare results from several models of horizontal axis turbines at different spatial scales. Models under review include blade element momentum theory (BEMT), blade element actuator disk, Reynolds averaged Navier Stokes (RANS) CFD (BEM-CFD), blade-resolved moving reference frame and coastal models based on the shallow water equations. To evaluate the BEMT, a comparison is made to experiments with three different rotors. We demonstrate that, apart from the near-field wake, there are similarities in the results between the BEM-CFD approach and a coastal area model using a simplified turbine fence at a headland case.
EGU General Assembly Conference Abstracts, Apr 1, 2018
Ocean Engineering, Oct 1, 2021
Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at ... more Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at tidal stream energy sites; they are used to estimate several parameters, including turbulent kinetic energy (TKE). However, estimates of TKE from ADCPs are often swamped by wave action. We surmise that this bias can be detected as a data mode: to test this, we present an empirical orthogonal function (EOF) analysis of two months of TKE estimates from ADCP measurements at a tidal energy site with significant wave activity. The results of the analysis were compared with linear wave theory, using data from a wave buoy. The first data mode identified from EOF analysis agrees well with the wave bias predicted by linear theory, and the resulting decomposition of the data set into wave and turbulent components appears realistic. This decomposition is possible from ADCP data alone, and therefore offers a novel and widely applicable analysis technique for simultaneous assessment of turbulence and waves at highly-energetic tidal sites. The method can also be applied retrospectively to historical data sets. We also show that the decomposition can be improved by including higher EOF modes, but this requires an independent measurement of waves to determine the optimum number of modes.
Proceedings of the European Wave and Tidal Energy Conference
Accurate assessment of marine currents is critical for meaningful planning of tidal stream energy... more Accurate assessment of marine currents is critical for meaningful planning of tidal stream energy deployments. Methods for assessing mean flow speed are well-established, but the issue of assessing phenomena that vary over much shorter time scales than the semidiurnal tide (principally turbulence and waves) is not as settled. This is in part due to the limitations of the standard instruments used for surveying currents at potential tidal stream sites i.e., acoustic Doppler current profilers (ADCPs). Because ADCPs use multiple acoustic beams to sample single components of velocity at widely-separated spatial locations, a reliable analysis of the mean flow can be obtained by a suitable average over measurements from all beams: this approach works well for determining mean flow properties, but is less well-suited for the smaller and faster variations associated with waves and turbulence. In particular, conventional analysis approaches such as the variance method do not meaningfully dis...
This upload contains data related to the publication 'The Use of Unmanned Aerial Systems to M... more This upload contains data related to the publication 'The Use of Unmanned Aerial Systems to Map Intertidal Sediment' by Fairley, I., Mendzil, A., Togneri, M., Reeve, D.E., Remote Sensing, 2018, accepted.<br> Any use of the data should cite the above publication. The data was collected through the DST-UAV project, funded by the UK NERC, project reference NE/R014485/1 The .zip folder data is organised in subfolders for each flight date. Each subfolder is named in the following way 'siteName-ddmmyy.'<br> Within each subfolder are RGB orthomosaics and multispectral reflectance maps as geotiffs.
ABSTRACT We present the results of simulations carried out with a robust blade element momentum t... more ABSTRACT We present the results of simulations carried out with a robust blade element momentum theory (BEMT) model. This model includes several modifications to classical BEMT, including the addition of tip/hub losses, high induction effects and, most importantly for this work, the ability to deal with arbitrary inflow conditions (i.e., including time variation and spatial non-uniformity). We use this capacity to simulate the response of tidal stream turbines (TSTs) to turbulent inflow conditions. The discussion presented centres firstly on the method of generating these inflow conditions, and secondly on how the simulation results can be used both to diagnose fault conditions during TST operation, and to prognose the fatigue lifespan of gearbox components.
Renewable Energy, 2021
The development of tidal energy converters, and particularly floating tidal energy converters, is... more 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.
Ocean Engineering, 2021
Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at ... more Acoustic Doppler current profilers (ADCPs) are the standard tool for measuring tidal currents at tidal stream energy sites; they are used to estimate several parameters, including turbulent kinetic energy (TKE). However, estimates of TKE from ADCPs are often swamped by wave action. We surmise that this bias can be detected as a data mode: to test this, we present an empirical orthogonal function (EOF) analysis of two months of TKE estimates from ADCP measurements at a tidal energy site with significant wave activity. The results of the analysis were compared with linear wave theory, using data from a wave buoy. The first data mode identified from EOF analysis agrees well with the wave bias predicted by linear theory, and the resulting decomposition of the data set into wave and turbulent components appears realistic. This decomposition is possible from ADCP data alone, and therefore offers a novel and widely applicable analysis technique for simultaneous assessment of turbulence and waves at highly-energetic tidal sites. The method can also be applied retrospectively to historical data sets. We also show that the decomposition can be improved by including higher EOF modes, but this requires an independent measurement of waves to determine the optimum number of modes.
Energy, 2019
Temporal variability in renewable energy presents a major challenge for electrical grid systems. ... more Temporal variability in renewable energy presents a major challenge for electrical grid systems. Tides are considered predictable due to their regular periodicity; however, the persistence and quality of tidal-stream generated electricity is unknown. This paper is the first study that attempts to address this knowledge gap through direct measurements of rotor-shaft power and shore-side voltage from a 1MW, rated at grid-connection, tidal turbine (Orkney Islands, UK). Tidal asymmetry in turbulence parameters, flow speed and power variability were observed. Variability in the power at 0.5Hz, associated with the 10-minute running mean, was low (standard deviation 10-12% of rated power), with lower variability associated with higher flow speed and reduced turbulence intensity. Variability of shore-side measured voltage was well within acceptable levels (~0.3% at 0.5Hz). Variability in turbine power had <1% difference in energy yield calculation, even with a skewed power variability distribution. Finally, using a "t-location" distribution of observed fine-scale power variability, in combination with an idealised power curve, a synthetic power variability model reliably downscaled 30 minute tidal velocity simulations to power at 0.5Hz (R 2 = 85% and ~14% error). Therefore, the predictability and quality of tidal-stream energy may be undervalued in a future, high-penetration renewable energy, electricity grid.
Renewable Energy, 2019
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Remote Sensing, 2018
This paper describes a new methodology to map intertidal sediment using a commercially available ... more This paper describes a new methodology to map intertidal sediment using a commercially available unmanned aerial system (UAS). A fixed-wing UAS was flown with both thermal and multispectral cameras over three study sites comprising of sandy and muddy areas. Thermal signatures of sediment type were not observable in the recorded data and therefore only the multispectral results were used in the sediment classification. The multispectral camera consisted of a Red–Green–Blue (RGB) camera and four multispectral sensors covering the green, red, red edge and near-infrared bands. Statistically significant correlations (>99%) were noted between the multispectral reflectance and both moisture content and median grain size. The best correlation against median grain size was found with the near-infrared band. Three classification methodologies were tested to split the intertidal area into sand and mud: k-means clustering, artificial neural networks, and the random forest approach. Classific...
Energy Procedia, 2017
Acoustic Doppler current profilers (ADCPs) are commonly used to assess mean currents and turbulen... more Acoustic Doppler current profilers (ADCPs) are commonly used to assess mean currents and turbulence at energetic sites. Since 2014, five-beam ADCP configurations have become more common, but conventional analysis of turbulence properties is still based on the four-beam Janus configuration. We use measurements from a single site to investigate whether improved estimates of turbulent kinetic energy (TKE)are made possible by the addition of a fifth vertical beam. We conclude that four-beam estimates of TKE are suitable in most cases, and exhibit lower variance than five-beam estimates, but are more prone to contamination by wave activity.
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Papers by Michael Togneri