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dc.contributor.advisorJohanning, Lars
dc.contributor.advisorRace, Julia
dc.contributor.advisorVenugopal, Vengatesan
dc.contributor.authorBivol, Ilie
dc.date.accessioned2021-06-18T16:24:00Z
dc.date.available2021-06-18T16:24:00Z
dc.date.issued2020-12-10
dc.identifier.urihttps://hdl.handle.net/1842/37705
dc.identifier.urihttp://dx.doi.org/10.7488/era/982
dc.description.abstractTo tackle climate change and pursue a more sustainable future, humanity ought to shift the means of electricity generation from burning hydrocarbons to renewable sources such as tidal currents. Tidal current convertors generate electricity from moving water using turbines that operate in a similar manner to wind turbines. Unlike the wind, tidal currents are fully predictable and can therefore provide a reliable source of power. At present, this technology has a limited track record and there is limited knowledge of how these devices behave. Floating-type TECs incorporate a mooring system that provides vital function of station-keeping and stability. When designing mooring systems, engineers are faced with the challenge of accurately predicting line loads in order to prescribe sufficient design capacity and ensure that load-bearing strength is not exceeded by peak loads in service. Mooring line loads are interdependent on the coupled behaviour of platform, turbines and mooring system in the turbulent flow environment. For mooring load analysis, standards recommend 1) the use of a fully-coupled dynamic analysis model and 2) the inclusion of flow turbulence in the current sub-model. For this purpose, tools are being developed such as ProteusDS, a dynamic analysis software, and TurbSim, a stochastic turbulent flow field generator. These tools have not been extensively validated or rigorously tested for the TEC application; therefore, their evaluation would be highly beneficial for improved mooring load analysis of TEC devices. Sustainable Marine Energy has been developing device concepts PLAT-I and PLAT-O. PLAT-I #1 is a surface variant with a catenary mooring that undergone initial sea trials in the Connel Sound, Scotland, at a highly turbulent site. PLAT-O #2 is a subsea platform with a taut mooring that was tested in the FloWave tank. Past a certain inflow speed, the platform was observed in the tank to descend to a stable elevation about the upstream mooring members whilst tension is lost in the downstream lines - a behaviour referred to as ‘squatting’. Based on provided data from these tests, this thesis investigates the mooring line loads of these devices in current-only environments. To this end, field data is analysed to obtain flow characteristics at site including turbulence. Device load characteristics are derived such as mean and peak mooring loads and contributions to these from device hydrodynamic loadings. In the case of PLAT-I, device load performance is analysed from the perspective of various flow instruments to identify the most suitable flow instrumentation set-up for such deployments. Methodology is informed by standard guidelines such as from the IEC. In parallel to field studies, numerical studies are conducted based on dynamic analysis tool ProteusDS, which for the deployment of PLAT-I at Connel uses input from TurbSim, that will help understand device behaviour and inform the robustness of these tools for this application. It is found that flow characteristics at site show non-logarithmic vertical shear, substantial horizontal flow gradients and extraordinarily high turbulence intensities. In these conditions, the peak loads of PLAT-I were measured to be higher by a factor of 2 or more than corresponding mean loads at the same sustained inflow speed. Numerical models based on ProteusDS and TurbSim generally overestimate peak loads however these provide comparable predictions of peak-to-mean ratios which are promising results that call for continuing development of these models and tools. From tank-testing of PLAT-O #2, the platform lift force was identified as a significant contributor to squatting motion, besides platform drag and turbine thrust. When this lift force is accounted for, the ProteusDS model accurately reproduced the squatting behaviour. Thus, research in this thesis contributes to knowledge on areas of device behaviour and mooring loads, flow conditions and turbulence at tidal sites, flow instrumentation strategy for field deployments, and evaluation of mooring load analysis tools ProteusDS and TurbSim for TEC devices in current-only environmental load casesen
dc.contributor.sponsorEngineering and Physical Sciences Research Council (EPSRC)en
dc.language.isoenen
dc.publisherThe University of Edinburghen
dc.relation.hasversionlie Bivol, Penny Jeffcoate, Lars Johanning, and Ryan Nicoll. PLAT-O #2 at FloWave: A tank-scale validation of ProteusDS dynamic analysis tool for floating tidal, In Proceedings of 12th (2017) European Wave and Tidal Energy Conference (EWTEC)en
dc.relation.hasversionIlie Bivol, Penny Jeffcoate, Lars Johanning, Ryan Nicoll, Jeffrey Steynor, and Vengatesan Venugopal. A tank-scale validation of ProteusDS at modelling the response of a tidal device to currents, In Proceedings of the 4th (2018) Asian Wave and Tidal Energy Conference (AWTEC)en
dc.subjecttidal current convertorsen
dc.subjectfloating-type TECsen
dc.subjectmooring load analysisen
dc.subjectmooring line loadsen
dc.subjectpeak-to-mean ratiosen
dc.subjectplatform lift forceen
dc.subjectsquatting behaviouren
dc.subjectmooring load analysis toolsen
dc.titleInvestigation of mooring line loads of tidal current convertors in current-only environmentsen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnameEngD Doctor of Engineeringen
dc.rights.embargodate2025-12-10en
dcterms.accessRightsRestricted Accessen


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