Ocean Wave Energy Systems Hydrodynamics, Power Takeoff and Control Systems

Preface
Contents
Contributors
1 Wave Energy Potential
	1.1 World Energy Outlook
	1.2 Ocean Energy
	1.3 Environmental Impacts
	1.4 Tidal Datum
	1.5 Importance of Wave Energy
	1.6 Wave Power Potential
		1.6.1 Methods of Evaluation
		1.6.2 Estimated Wave Power Potential
	1.7 Wave Energy Map for INDIA
	References
2 Wave Energy Convertors
	2.1 General
	2.2 Harnessing of Wave Energy
	2.3 Conversion Process
	2.4 Wave Energy Devices
	2.5 Wave Energy Developments and Activities
		2.5.1 General
		2.5.2 Shoreline Wave Energy System
		2.5.3 Near Shore Wave Energy System
		2.5.4 Offshore Wave Energy Systems
	2.6 Onshore/Nearshore OWC Wave Energy Devices
	2.7 Offshore OWC Wave Energy Devices
	2.8 Special Types of Breakwaters with WEC
	2.9 Summary
	References
3 Direct Absorber for Wave Energy Conversion
	3.1 Introduction
		3.1.1 Wave Energy Physics and Resource
	3.2 Theoretical Background and Governing Equations
		3.2.1 Linear Wave Theory of Ocean Surface (LWT)
		3.2.2 Dispersion Relation
		3.2.3 Energy in Water Wave
		3.2.4 Wave Energy Spectrum
		3.2.5 Forces on Floating Bodies
	3.3 Wave Energy Conversion Systems
		3.3.1 Attenuator
		3.3.2 Oscillating Wave Surge Converter
		3.3.3 Oscillating Water Column
		3.3.4 Overtopping Device
		3.3.5 Submerged Pressure
		3.3.6 Point Absorber
	3.4 Conclusion
	References
4 Development of Oscillating Water Column and Wave Overtopping—Wave Energy Converters in Europe Over the Years
	4.1 The Importance of Wave Energy Resources Utilisation
	4.2 A Brief Introduction to Wave Energy Harvesting Mechanism
	4.3 Oscillating Water Column (OWC) Type Wave Energy Converter
		4.3.1 General Introduction of OWC
		4.3.2 Working Principle and Design Analysis of OWC
	4.4 Oscillating Water Column Type WEC Projects Developments History
		4.4.1 Land Installed Marine Power Energy Transmitter (LIMPET)
		4.4.2 Pico Power Plant
		4.4.3 Mutriku Wave Energy Plant
		4.4.4 Resonant Wave Energy Converter (REWEC) or U-OWC
		4.4.5 Siadar Wave Power Project
		4.4.6 Floating OWC Development
	4.5 Brief Summary of Wave Overtopping Devices’ Development Over the years
		4.5.1 General Introduction to Wave Overtopping Mechanism
		4.5.2 Wave Loadings Analysis and Development of Sea-Wave Slot-Cone Generator (SSG)
		4.5.3 Overtopping BReakwater for Energy Conversion (OBREC) Development
	References
5 Performance Characteristics of an OWC in Regular and Random Waves
	5.1 Introduction
	5.2 Experimental Investigations
		5.2.1 OWC Model
		5.2.2 Experimental Program
		5.2.3 Harbour Walls in OWC
		5.2.4 Wave Characteristics for the Study
		5.2.5 Hydrodynamic Factors
	5.3 Results and Discussion
		5.3.1 Regular Wave Tests
		5.3.2 Random Waves
		5.3.3 OWC with Inclined Harbour Walls in Regular and Random Wave Fields
	5.4 Summary and Conclusions
	References
6 Wave Induced Pressures and Forces on an OWC Device
	6.1 Introduction
	6.2 Literature Review
	6.3 Experimental Investigation
		6.3.1 Test Facility
		6.3.2 Test Model and Experimental Set-Up
		6.3.3 Instrumentation
		6.3.4 Wave Characteristics
	6.4 Hydrodynamic Parameters
	6.5 Results and Discussion
		6.5.1 Time Histories of Measured Signatures
		6.5.2 Pressure Distribution in Front of the Lip Wall
		6.5.3 Pressure Distribution at the Rear Wall of OWC Device
		6.5.4 Air Pressure Inside the OWC Caisson
		6.5.5 Horizontal Wave Force
		6.5.6 Vertical Wave Force
		6.5.7 Comparison of Measured and Estimated Horizontal Wave Force
		6.5.8 Total Horizontal and Vertical Wave Forces Due to Random Waves
	6.6 Summary and Conclusions
	References
7 Hydrodynamic Performance Characteristics of U-OWC Devices
	7.1 Introduction
	7.2 Experimental Set-Up
		7.2.1 General
		7.2.2 Details of the Models and Test Set-Up
		7.2.3 Test Facility
		7.2.4 Experimental Procedure
	7.3 Results and Discussion
		7.3.1 Spectral Width Parameter
		7.3.2 Dynamic Pressures
		7.3.3 Energy Efficiency
		7.3.4 Air Pressure Variation
		7.3.5 Phase Difference
		7.3.6 Wave Amplification
	7.4 Conclusions
	References
8 CFD Modelling of OWC Devices for Wave Energy Harnessing
	8.1 Introduction
	8.2 The Numerical Experiment
		8.2.1 Computational Domain
		8.2.2 Mesh
		8.2.3 Boundary Conditions
	8.3 Governing Equations
		8.3.1 Pressure-Based Solver
		8.3.2 Pressure–Velocity Coupling
		8.3.3 Solution Control Parameters
	8.4 Under-Relaxation Factors
		8.4.1 Spatial Discretization of Equations
		8.4.2 Reconstruction of Gradients
		8.4.3 Time Discretization
	8.5 Multiphase Flow
		8.5.1 The Volume of Fluid (VOF)
	8.6 Explicit Scheme
	8.7 Implicit Scheme
		8.7.1 Interpolation Near the Water–air Interface
		8.7.2 Wave Generation
		8.7.3 Dynamic Mesh
	8.8 Dynamic Mesh Update
	8.9 Elastic Smoothing Method
		8.9.1 Open Channel Boundary Condition
	8.10 PTO System and Configuration of the Porous Medium Region
	8.11 Simulation, Data Saving, and Post-Processing
	8.12 Conclusions
	References
9 Numerical Modelling Techniques for Wave Energy Converters in Arrays
	9.1 Introduction
	9.2 Review of Hydrodynamic Modelling of WEC Arrays
		9.2.1 Point Absorber Method
		9.2.2 Plane-Wave Method
		9.2.3 Multiple Scattering
		9.2.4 Direct Matrix Method
		9.2.5 Geographical Scale Studies
	9.3 Boundary Element Methods
		9.3.1 Problem Definition
		9.3.2 Mathematical Formulation
		9.3.3 Generated Power and Interaction Factor
		9.3.4 Wave Disturbance Under Multi-Directional Sea
	9.4 Verification of the Numerical Model
		9.4.1 Performance of Arrays
	9.5 WEC Array Modelling by Ocean Scale Numerical Models
		9.5.1 Numerical Model Set-Up
		9.5.2 Predictions Without Energy Extraction
		9.5.3 Implementation of Energy Extraction
	9.6 Concluding Remarks
	References
10 Hydrodynamic Performance of an Array of OWC Devices Integrated with Breakwater
	10.1 Introduction
	10.2 Experimental Investigation
		10.2.1 Test Facility
		10.2.2 Data Acquisition Sensors
		10.2.3 Test Model and Experimental Setup
		10.2.4 Instrumentation
		10.2.5 Wave Characteristics and Hydrodynamic Parameters
	10.3 Results and Discussion
		10.3.1 Time Histories
		10.3.2 Effect of Wave Characteristics
		10.3.3 Wave Interaction Between Devices
		10.3.4 Effect of Spacing
		10.3.5 Performance of OWC in an Array
		10.3.6 Total Performance vs. Average Performance
		10.3.7 Reflection Nature of OWCBW System
	10.4 Hydrodynamic Performance of OWCBW System Subjected to Oblique Wave Incidence
	10.5 Summary and Conclusions
		10.5.1 The Salient Conclusions Drawn from the Studies Are
	References
11 Power Take-Off Devices for Wave Energy Converters
	11.1 Introduction to Wave Energy
	11.2 Types of Power Take-Off Mechanisms Used in Point Absorbers
		11.2.1 Air Turbines
		11.2.2 Hydraulic Converters
		11.2.3 Hydro Turbines
		11.2.4 Direct Mechanical Drive Systems
		11.2.5 Direct Electrical Drive Systems
	11.3 Conclusion
	References
12 Wells Turbine as a Power Take-Off Mechanism for Wave Energy Converters
	12.1 Introduction
	12.2 Historical Overview
	12.3 Wells Turbine: Principle of Operation
	12.4 Variations of Wells Turbine
		12.4.1 Monoplane Wells Turbine
	12.5 Turbines with Guide Vane
	12.6 Turbines with Non-zero Pitch Angles
	12.7 Turbines with Variable Pitch Angles
	12.8 Unsteady Flow Analysis
	12.9 Starting Characteristics of Wells Turbine
	12.10 Optimization of Air Turbines
	12.11 Conclusion
	References
13 Experimental Testing of Air Turbines for Wave Energy Conversion
	13.1 Introduction
	13.2 Experimental Setup
	13.3 Instrumentation: Sensors and Data Acquisition Systems
	13.4 Generator Selection
	13.5 Generator Characteristics
	13.6 Experimental Procedure
	13.7 Experimental Testing of an Impulse Turbine
		13.7.1 Design and Fabrication
		13.7.2 No-Load Test
		13.7.3 Performance of the Turbine
		13.7.4 Power Calculation: Load Test
	13.8 Experimental Testing of a Wells Turbine
		13.8.1 Design and Fabrication
		13.8.2 Starting Characteristics
		13.8.3 No-Load Test
		13.8.4 Test with Resistive Loading
	13.9 Uncertainty Analysis
	13.10 Conclusions
	References
14 Passive Flow Control Methods for Performance Augmentation in Air Turbines Used for Wave Energy Conversion—A Review
	14.1 Wave Energy
	14.2 Oscillating Water Column
	14.3 Air Turbines for Wave Energy Conversion
		14.3.1 Wells Turbine
		14.3.2 Axial Impulse Turbine
	14.4 Flow Control Methods
	14.5 Passive Flow Control Methods in Wells Turbine
		14.5.1 Blade Sweep
		14.5.2 Blade Setting Angle
		14.5.3 Penetrating Ring and Endplate at the Blade Tip
		14.5.4 Non-uniform Tip Clearance
		14.5.5 Variable Chord Blade
		14.5.6 Casing Groove
		14.5.7 Suction Slots
		14.5.8 Variable Thickness Blade
		14.5.9 Leading-Edge Undulation
		14.5.10 Radiused Edge Tip Blade
		14.5.11 Static Extended Trailing Edge (SETE)
		14.5.12 Gurney Flap
		14.5.13 Combined Radiused Edge Tip, Static Extended Trailing Edge, and Variable Thickness Blade
	14.6 Passive Flow Control Methods in Axial Impulse Turbine
		14.6.1 Endplates
		14.6.2 Blade Setting Angle
		14.6.3 Penetration Ring
		14.6.4 Leaned Blade
	14.7 Conclusions
	References
15 Optimization of an Impulse Turbine  for Efficient Wave Energy Extraction
	15.1 Introduction
	15.2 Oscillating Water Column
	15.3 Turbine Selection for OWC
	15.4 Numerical Studies on Impulse Turbine
		15.4.1 Background Study
		15.4.2 Steps Involved in Performing CFD Simulations
		15.4.3 Case Study on CFD Simulations for an Impulse Turbine for Wave Energy Extraction
	15.5 Optimization
		15.5.1 Design Variable and Objective Function
		15.5.2 Design Space
		15.5.3 Use of Surrogates Method to Populate Sampling Points
		15.5.4 Genetic Algorithm as an Optimizer
	15.6 Results and Discussions Based on Optimization of Impulse Turbine
		15.6.1 Design Space
		15.6.2 Sensitivity of Design Variable
		15.6.3 Results from Optimization Algorithm
		15.6.4 Results for Optimized Turbine Over Wide Flow Range
		15.6.5 Parametric Sensitivity Analysis
	15.7 Closure
	References
16 Control of Wave Energy Converters
	16.1 Introduction
	16.2 Control Techniques Applied to WECs
		16.2.1 Control of WEC Primary Parameters
		16.2.2 Airflow Control
		16.2.3 Control of Secondary Converters
	16.3 Conclusion
	References
17 Recent Advances in Direct-Drive Power Take-Off (DDPTO) Systems for Wave Energy Converters Based on Switched Reluctance Machines (SRM)
	17.1 Introduction
	17.2 Power Take-Off (PTO) in Wave Energy Converters
		17.2.1 Introduction to PTO-Concept
		17.2.2 Introduction to the Different Types of PTOs
	17.3 Direct-Drive Power Take-Off: SRM Topology
		17.3.1 Introductory Aspects
		17.3.2 Example of an Analysis of a WEC with a DDPTO
		17.3.3 The Linear Switched Reluctance Machine (LSRM)
		17.3.4 SRM Power Electronics and Control
	17.4 Superconducting Linear Switched Reluctance Machine (LSRM)
		17.4.1 Introduction
		17.4.2 The Importance of High Force/High Efficiency PTOs
		17.4.3 Some Simple Concepts on Superconductivity and Cryogenics
		17.4.4 Options for Superconducting Machines: A Superconducting PTO
	17.5 Concluding Remarks
	References
18 Grid Integration of Wave Energy Devices
	18.1 Introduction: Wave Energy Impacts in Electric Grid
		18.1.1 Impact in the Power Grid of Renewable Energy
		18.1.2 Current Status and Perspectives of Ocean Energy
		18.1.3 Problems with the Grid Integration of Wave Energy Converters
	18.2 Power Oscillations in Wave Energy Generation
		18.2.1 Wave Energy Resource: Characterization of Oscillations
		18.2.2 Evaluation of Electric Power Oscillations in Wave Energy Converters
		18.2.3 Evaluation of Impacts on the Electric Grid
	18.3 Analysis of Smoothing Power Solutions
		18.3.1 Introduction: Relevant Solutions for Wave Power Smoothing
		18.3.2 Analysis of Energy Storage as Power Smoothing Solution
	18.4 Integration of Energy Storage System in Wave Energy Converters: Industrial Examples
	References