Study On Elaborate Assessment Of Tidal Current Energy Resource And Micro-siting Of Tidal Farm

The development and utilization of tidal current energy is an effective method to alleviate energy crisis and climate change.The tidal current energy technology has the advantages of highly predictable,less environmental impact and high technology readiness level.According to recent large-scale surveys and resource assessments,Bohai Strait,Zhoushan Archipelago area of Zhejiang,many sea bays in Fujian and Qiongzhou Strait contain a vast tidal current energy resource that has broad prospects for exploitation.Due to the spatiotemporal nature of tidal current energy,it is fundamental to establish an assessment method to help site selection and design that can predict the spatial and temporal distribution of the resource.Tidal farm siting process can be divided into two phases which are macro-siting and micro-siting.The former means the process to find a suitable area for utilization according to the characteristics of tidal current energy,depth and marine spatial plan,etc.The latter is to find the best layout of tidal turbines array at a specific channel determined from macro-siting process.Micrositing for tidal current farm directly affects economic performance of the plant.Regular layout of the tidal current turbines(TCT)array is usually not optimal due to the influence of bathymetry,shoreline and morphology.Therefore,it has both scientific and practical importance to study the resource assessment method of tidal current energy,to find an analytical expression of TCT's wake by studying the spatiotemporal characteristics of its wake,as well as to develop an array layout optimization method for large-scale exploitation of tidal current energy.Firstly,to accommodate the needs of exploiting tidal current energy resource,this dissertation introduced the characterization parameters for presenting fluctuation of flow direction and time available for power generation.A new index called Marcositting Index for Tidal Current Plant is proposed to quantify the spatiotemporal distribution characteristics of the resource,velocity profile and water depth of a site.This index,combined with conventional assessment parameters such as flow velocity and power density,formed a comprehensive framework for tidal current energy resources assessment.Using the FVCOM ocean numerical model,tidal current around Zhoushan Archipelago area and Putuoshan-Huludao Waterway(referred to as PH Waterway)was well simulated.By applying the above-mentioned resource assessment methods to the modelling result,a site with abundant tidal current energy resource and good exploitation condition was selected.Secondly,in order to study the influence of TCTs on surrounding flow field,the hydrodynamic characteristics of a two-blade horizontal axis TCT was investigated through experiments.The turbulence intensity(TI)of the experimental flume and the attenuation characteristics of the turbine wake were analysed.Using numerical modelling technology,the virtual tank for prototype TCT was established and the flow field characteristics around the turbine were investigated.The characteristics of wake structure under different blockage ratio scenarios was studied based on the numerical simulation.Based on a Gaussian probability distribution,an analytical wake model which considering the blockage ratio effect for TCT was proposed.The model can predict the patterns of velocity deficit,expansion and recovery of flow in the middle and far wake field accurately.Finally,a particle swarm optimization algorithm was used to find the optimal layouts of TCT array,in which the constraint conditions were modified in terms of the wake model we proposed.A case study of PH Waterway showed that the total power generation of the optimized layout using this method significantly outperformed the traditional staggered layout,which proved this method is able to assist the design and micro-siting of tidal current project,and it improved the economic performance of the tidal current energy plant.This study of this dissertation provide scientific support for elaborate assessment of tidal current energy resource and micro-siting of tidal farm.