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Numerical and experimental modelling of tidal range structures with focus on conservation of momentum through hydraulic structures

Coz, Nejc 2019. Numerical and experimental modelling of tidal range structures with focus on conservation of momentum through hydraulic structures. PhD Thesis, Cardiff University.
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Hydrodynamic modelling has an important role in the development of Tidal Range energy Structures (TRS). The aim of this research study was to develop a methodology for the simulation of TRS with Delft3D software. The study has focused on two key issues of the regional–scale hydrodynamic models. Firstly, the majority of studies before the year 2016 have ignored the conservation of momentum of the flow through the hydraulic structures. Secondly, 3D hydrostatic models have been largely underused in TRS simulations to date. The first key objective was to develop a TRS module for Delft3D software. The case study of Severn Barrage was used for validation. Direct comparisons with the past studies showed good agreement between the results, confirming the appropriateness of the developed model. The second key objective was to introduce a novel approach for the treatment of momentum transfer through hydraulic structures. This was achieved by representing the momentum of the discharged water as an additional external force in the momentum equation. The final key objectives were (i) to validate the developed method through a series of physical experiments and (ii) to use it in the regional-scale model with the Swansea Bay tidal lagoon. A good match between measurements and simulation results confirmed that momentum conservation is required for accurately predicting the velocity of the discharged jets. The results without the momentum conservation achieved only 50 per cent of the measured velocity. Extending the 2D model to 3D was found to be more important for the estimation of local bed shear stress, than for predicting the velocity field. The 3D simulations did slightly improve the accuracy of the velocity field, but more importantly, they have produced a more realistic vertical velocity profile. The 3D model can capture the attachment of the jets to the bottom surface, distorting the standard logarithmic profile assumed in depth-averaged shallow water flows. As a result, the bed shear stress increased by 75 per cent from 2D to 3D simulation. The Swansea Bay lagoon case study showed that momentum conservation only affected the area close to the structure. The results were found to be sensitive to the vertical velocity profile of the jet. The simplified velocity distribution had Abstract IV a bigger impact on the hydrodynamics and power output estimation than the realistic distribution. In general, the 2D model with momentum conservation was found to be sufficient for analysing hydrodynamics in most cases. However, the 3D model has proved to be indispensable for accurate predictions of local-scale impacts, especially in an around the lagoon.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Tidal range power; Delft3D; Numerical modelling; Renewable energy; Hydraulic structures; Momentum conservation.
Date of First Compliant Deposit: 30 October 2019
Last Modified: 04 Aug 2022 02:10

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