WORKSTREAM 2: Wave and tidal stream modelling (Lead Edinburgh University)
This workstream will increase our knowledge, confidence and understanding of coupled hydrodynamic models of wave and tidal systems. The research incorporates the physical impacts of marine renewable developments within these. Enhanced hydrodynamic models will examine various development scenarios based upon the PFOW leasing round. These scenarios will provide a framework for examining the response of the underlying hydrodynamic system in the region to harvesting of wave and tidal energy. The model set-up and required outputs will feed through to WS3 and WS4 to facilitate assessment of the impact of hydrodynamic alterations due to energy harvesting on sediment and ecosystem dynamics.
Task WS2.1 Parameterisation of wave and tidal energy harvesting: In conjunction with WS1.2, the definition of appropriate parameterisations that can be implemented in numerical modelling frameworks will be a key output. These parameterisations must consider (i) the energy harvested by a wave or tidal device, (ii) energy losses due to the device support structure impinging on the flow, (iii) energy losses due to mixing of the wake generated by the device with free-stream flow (tidal only) (iv) alterations of the flow field due to flow-structure interaction (e.g. waves radiated from a device, or turbulence and vorticity generation in the wake of a device). Once applied in fine-scale models, appropriate for considering inter-array effects, these parameterisations can then be further developed for incorporation in larger (regional and shelf) scale hydrodynamic simulations, using the more detailed description and interactions observed at higher spatial resolutions.
Task WS2.2 Development of combined wave-tidal energy resource assessment: Publically available resource estimation is at best based upon coarse grid models/satellite measurements. Applying results or values extracted from such databases to a specific project development provides
highly inaccurate power estimates due to the relative scale of the data resolution (Cornett, 2008) and project extent. Coarse representations are also deficient in capturing smaller scale spatial and temporal features (Bento et al., 2011, Venugopal et al., 2011) of wave and tidal propagation that will have a significant impact on extraction technology design, operation and energy yield assessment. The industry standard commercial hydrodynamic MIKE21/3 modelling suite (DHI, 2011) and Delft 3D suite software (Delft, 2011) will be employed for hindcasting/forecasting the combined wave-tidal current resource. Both of these model frameworks already incorporate wave-current interaction capabilities and an inter-comparison study will be carried with these models wherever necessary. The appropriateness of these formulations and the underlying assumptions invoked will be analysed and reported on. Adopting two different numerical model codes to conduct the assessment will ensure reliability of application of the energy harvesting parameterisations developed in WS2.1. The selection of these two model frameworks was established by extensive discussion with device and field developers and the regulator, in preliminary TeraWatt consortium discussions. Wave buoys/ADCP measurements compiled by WS1.1 will be used for calibration and validation of numerical models outputs. The models will then be used to estimate the theoretical wave and tidal energy resource in the PFOW system by hindcasting application to enable comparison against the identified existing datasets. The model runs necessary to inform assessment of theoretical energy resource potential will form the basis for comparison with the scenarios to be investigated in WS2.3.
Task WS2.3 Development of combined wave-tidal energy resource harvesting scenarios: Parameterisations developed in WS2.1 in conjunction with the scenario outputs from WS1.2, will be used in the model framework validated in WS2.2 to consider the impacts of energy harvesting on the regional, local and fine-scale hydrodynamic system. These scenarios will enable assessment of both the individual and cumulative impact of the developments included in the PFOW leasing round. These assessments will examine the altered flow physics observed due to differing development scenarios and consider the impact of build order on the potential resource and economic impacts of developments on each other. Assessments of mean and extreme variability observed, in comparison with the WS2.2 pre-development model simulations, relating to wave and tidal statistics, will be detailed both graphically and numerically for each of the identified scenarios. Hypothetical energy converter arrays will be modelled within MIKE21/3 and the effect upon energy extraction (for different energy absorption levels) on the surrounding wave and tidal climate will be studied. The wave-current transformation and effect of energy extraction by one type of device array (e.g., nearshore wave/tidal energy converters) on another type of array (e.g. coastal or shallow water converters) will be investigated. Also the wave reflection from near coastal arrays towards seaward arrays will be examined. The outputs from these assessments, and the model runs feed directly into WS3 and WS4. Task WS2.4 Site-specific fatigue and extreme wave estimation by numerical wave simulation: This task will specify design methodologies for extreme wave simulations. A procedure will be developed to estimate the extreme design wave conditions at potential wave and tidal energy sites, using numerical models. Using the ERA-40 Reanalysis (ERA, 2011) data the extreme wave (e.g. 20. or 50 or 100 year wave climate) estimation will be carried out using a proven method (e.g. the modified Battjes method or a Peak Over Threshold method (Tucker and Pitt, 2001) at desirable grid points. The extreme wave conditions from these grids will then be transferred to potential energy sites using fine grid modelling. Guidelines to perform this operation for a higher degree of accuracy with uncertainty quantification will be provided.
WS2 Deliverables:
DW2.1. Parameterisations of energy harvesting impacts for application in hydrodynamic models applicable at various scales of interest (fine, array, regional and shelf).
DW2.2. Assessment of the impact of coupled wave-current hydrodynamics on model simulations in comparison with individual application of wave and current development.
DW2.3. Assessment of the theoretical wave and tidal energy resource potential of the modelled PFOW system using calibrated and validated hindcast simulations.
DW2.4. Assessment of the impact of planned developments in the PFOW system and its potential to host additional developments. This will include sensitivity analysis of the hydrodynamic
system for various proposed developments, individually, in various configurations, and finally in total.
DW2.5. Provision of appropriate model output data and statistics in a format as required by WS3 and WS4.
DW2.6. Estimation of extreme waves for potential development sites.
This workstream will increase our knowledge, confidence and understanding of coupled hydrodynamic models of wave and tidal systems. The research incorporates the physical impacts of marine renewable developments within these. Enhanced hydrodynamic models will examine various development scenarios based upon the PFOW leasing round. These scenarios will provide a framework for examining the response of the underlying hydrodynamic system in the region to harvesting of wave and tidal energy. The model set-up and required outputs will feed through to WS3 and WS4 to facilitate assessment of the impact of hydrodynamic alterations due to energy harvesting on sediment and ecosystem dynamics.
Task WS2.1 Parameterisation of wave and tidal energy harvesting: In conjunction with WS1.2, the definition of appropriate parameterisations that can be implemented in numerical modelling frameworks will be a key output. These parameterisations must consider (i) the energy harvested by a wave or tidal device, (ii) energy losses due to the device support structure impinging on the flow, (iii) energy losses due to mixing of the wake generated by the device with free-stream flow (tidal only) (iv) alterations of the flow field due to flow-structure interaction (e.g. waves radiated from a device, or turbulence and vorticity generation in the wake of a device). Once applied in fine-scale models, appropriate for considering inter-array effects, these parameterisations can then be further developed for incorporation in larger (regional and shelf) scale hydrodynamic simulations, using the more detailed description and interactions observed at higher spatial resolutions.
Task WS2.2 Development of combined wave-tidal energy resource assessment: Publically available resource estimation is at best based upon coarse grid models/satellite measurements. Applying results or values extracted from such databases to a specific project development provides
highly inaccurate power estimates due to the relative scale of the data resolution (Cornett, 2008) and project extent. Coarse representations are also deficient in capturing smaller scale spatial and temporal features (Bento et al., 2011, Venugopal et al., 2011) of wave and tidal propagation that will have a significant impact on extraction technology design, operation and energy yield assessment. The industry standard commercial hydrodynamic MIKE21/3 modelling suite (DHI, 2011) and Delft 3D suite software (Delft, 2011) will be employed for hindcasting/forecasting the combined wave-tidal current resource. Both of these model frameworks already incorporate wave-current interaction capabilities and an inter-comparison study will be carried with these models wherever necessary. The appropriateness of these formulations and the underlying assumptions invoked will be analysed and reported on. Adopting two different numerical model codes to conduct the assessment will ensure reliability of application of the energy harvesting parameterisations developed in WS2.1. The selection of these two model frameworks was established by extensive discussion with device and field developers and the regulator, in preliminary TeraWatt consortium discussions. Wave buoys/ADCP measurements compiled by WS1.1 will be used for calibration and validation of numerical models outputs. The models will then be used to estimate the theoretical wave and tidal energy resource in the PFOW system by hindcasting application to enable comparison against the identified existing datasets. The model runs necessary to inform assessment of theoretical energy resource potential will form the basis for comparison with the scenarios to be investigated in WS2.3.
Task WS2.3 Development of combined wave-tidal energy resource harvesting scenarios: Parameterisations developed in WS2.1 in conjunction with the scenario outputs from WS1.2, will be used in the model framework validated in WS2.2 to consider the impacts of energy harvesting on the regional, local and fine-scale hydrodynamic system. These scenarios will enable assessment of both the individual and cumulative impact of the developments included in the PFOW leasing round. These assessments will examine the altered flow physics observed due to differing development scenarios and consider the impact of build order on the potential resource and economic impacts of developments on each other. Assessments of mean and extreme variability observed, in comparison with the WS2.2 pre-development model simulations, relating to wave and tidal statistics, will be detailed both graphically and numerically for each of the identified scenarios. Hypothetical energy converter arrays will be modelled within MIKE21/3 and the effect upon energy extraction (for different energy absorption levels) on the surrounding wave and tidal climate will be studied. The wave-current transformation and effect of energy extraction by one type of device array (e.g., nearshore wave/tidal energy converters) on another type of array (e.g. coastal or shallow water converters) will be investigated. Also the wave reflection from near coastal arrays towards seaward arrays will be examined. The outputs from these assessments, and the model runs feed directly into WS3 and WS4. Task WS2.4 Site-specific fatigue and extreme wave estimation by numerical wave simulation: This task will specify design methodologies for extreme wave simulations. A procedure will be developed to estimate the extreme design wave conditions at potential wave and tidal energy sites, using numerical models. Using the ERA-40 Reanalysis (ERA, 2011) data the extreme wave (e.g. 20. or 50 or 100 year wave climate) estimation will be carried out using a proven method (e.g. the modified Battjes method or a Peak Over Threshold method (Tucker and Pitt, 2001) at desirable grid points. The extreme wave conditions from these grids will then be transferred to potential energy sites using fine grid modelling. Guidelines to perform this operation for a higher degree of accuracy with uncertainty quantification will be provided.
WS2 Deliverables:
DW2.1. Parameterisations of energy harvesting impacts for application in hydrodynamic models applicable at various scales of interest (fine, array, regional and shelf).
DW2.2. Assessment of the impact of coupled wave-current hydrodynamics on model simulations in comparison with individual application of wave and current development.
DW2.3. Assessment of the theoretical wave and tidal energy resource potential of the modelled PFOW system using calibrated and validated hindcast simulations.
DW2.4. Assessment of the impact of planned developments in the PFOW system and its potential to host additional developments. This will include sensitivity analysis of the hydrodynamic
system for various proposed developments, individually, in various configurations, and finally in total.
DW2.5. Provision of appropriate model output data and statistics in a format as required by WS3 and WS4.
DW2.6. Estimation of extreme waves for potential development sites.