bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear hydrodynamics of a heaving sphere in diffraction, radiation, and combined tests
Authors: Orszaghova Jana , Wolgamot Hugh , Kurniawan Adi , Ho Daniel , Tan Bryan , McCauley Guy , Hals Todalshaug Jørgen
Published: September 2023

We report on an experimental campaign designed to shed light on critical nonlinear hydrodynamic effects of heaving wave energy converter (WEC) buoys undergoing large-amplitude motions in operational conditions. The experiments carried out with a spherical model comprised radiation, diffraction and combined tests, where the vertical motion was prescribed and delivered via an actuator. As such, we had independent control of incident waves and motions, enabling isolation of different nonlinear terms by combining recordings from multiple phase- and amplitude-manipulated runs. All tests utilised short-duration wave groups and/or corresponding transient motion signals.
We focus on analysis of nonlinear changes in the hydrodynamic forces, and free surface, in the first-harmonic frequency range - this is of most importance to WECs. In a series of radiation experiments, with progressively increasing imposed motions, the radiated wave field and the force in phase with the body velocity are found to decrease nonlinearly, pointing to the WEC's reduced ability to radiate waves under larger oscillations. In the combined tests, we are able to isolate various high-order cross-terms. We attempt to explain the observed trends through third-order potential flow interactions and consider a simple method to approximately describe these.
Experimental measurements of two elastic taut-slack mooring configurations for the multi-float M4 WEC
Authors: Draycott Samuel , Stansby Peter , Li Gangqiang
Published: September 2023

Moorings are a vital and often problematic component of any floating offshore renewable energy system, whether for wind or wave energy conversion, and here we consider the multi-float WEC system M4 in a 122 configuration. Previous experimental work has shown elastic cables to reduce extreme snap loads by a factor of about 6 when considering single cables between the bow float and a mooring buoy, and between the mooring buoy and the bed [1]. Here we compare results for two alternative configurations designed to reduce the mooring footprint as well as extreme snap loads. The first system, shown in Figure 1 (a), consists of a large surface buoy connected to the seabed with three equi-spaced elastic cables in pre-tension, with a single elastic cable to the bow float. The second system, shown in Figure 1 (b) has a smaller submerged buoy, again connected to the seabed with three equi-spaced elastic cables in pre-tension, however, this is connected to a smaller surface buoy which is subsequently connected to the bow float. Both systems are taut-slack. In this paper we present experimental measurements taken at the COAST laboratory at the University of Plymouth. Both configurations are tested in irregular (JONSWAP) wave conditions up to limiting steepness, with run times of 35 mins at 1:40 scale or about 3.5 hours full scale. Peak, mean and rms bed loads for both configurations are presented along with rms and peak relative angular pitch response with drive train disengaged (free hinge between mid and stern floats).

References[1] P. Stansby et al., “Experimental study of mooring forces on the multi-float WEC M4 in large waves with buoy and elastic cables,” Ocean Eng., vol. 266, no. P4, p. 113049, 2022.
Hydrodynamic studies of a 15 MW semi-submersible FOWT to assess the suitability of the inclusion of a damper system
Authors: Gao Yu , Zhao Chenyu , Johanning Lars , Pillai Ajit C
Published: September 2023

Floating Offshore Wind Turbines (FOWT) can exploit the high energy density found in the offshore environment, with turbines now reaching up to 15 MW in size. At the same time, however, the energetic environment and the massive size of the device present significant challenges in the motion stabilization and mooring system. To overcome these challenges, a tuned mass damper (TMD) has been considered for integration in the FOWT for peak motion reduction. This paper investigates the baseline responses including motion, dynamic response, and tensile loading of the mooring line for a 15MW FOWT on a semi-submersible platform without TMD to identify the damageable motion and the impacts of the TMD on the motion response under wave-wind environmental loadings. The comprehensive analysis is conducted in a package for the dynamic analysis of offshore marine systems, named as Orcaflex. The dynamic and motion characteristics of the 15MW FOWT are analysed and compared under different environmental parameters. The wave and wind parameters are quantified by the 20-years statistical data of the Celtic Sea including both operational and extreme conditions (with a 50-year return period).
Subsequently, the key parameters of TMD are investigated by configuring different combinations of mass, damping coefficients and stiffnesses. The preliminary results of the study show that the TMD system can successfully mitigate extreme motion characteristics, however this is strongly dependent on damping properties. Unsuitable TMD designs may increase the motion responses of FOWT and the tensile loading on the mooring line. Therefore, the TMD properties have to be adjusted based onsite environmental conditions). With this consideration, an active TMD with changeable damping properties will be conducted in future research.
Experimental comparison of the flow-induced loading between a ducted bottom-mounted twin vertical axis tidal turbine at still and an unducted prototype
Authors: Saouli  , Coquet  , Facq  , Gaurier  , Germain Grégory , Gomez  , Marcon  , Maurice  , Moreau
Published: September 2023

The FloWatt project aims to demonstrate the efficiency of the HydroQuest’s 2.5 MW-rated turbine for commercial farm deployment. The project is dedicated to develop an innovative design of a turbine for high energetic sites and to deploy seven vertical axis tidal turbines on the Raz Blanchard site, France. This technology has already been successfully developed in a previous project at a smaller scale on the Paimpol-Bréhat test site.

Along the past three years, an important amount of work has been achieved to widely characterise the behaviour of the 1/20 scale 2-VATT similar to the 1MW-rated demonstrator. The turbine was tested in many different operating conditions in the Ifremer’s wave and current flume tank to reproduce full-scale conditions and turbine response (wide range of operating points and incident velocities, facing aligned and misaligned currents, with and without vertical velocity shear, with and without bathymetry generated turbulence, with and without surface waves following and against the current). Based on that experience, we gain confidence in the design process by comparing those experimental results to numerical and in-situ ones.

 

After a quick presentation of the industrial development for the deployment of a pilot farm with the manufacture, installation and operation of 7 turbines on the Raz-Blanchard site, we will focus on the scientific development aiming to prepare large-scale deployments of the next generation of turbine. One important step is to compare the flow-induced loading between the 2 kinds of turbine (ducted and unducted) and to analyse environmental loads during survival conditions. To investigate those points, the behaviour of a 1/20 scale 2-VATT similar to the 2.5 MW-rated demonstrator is experimentally studied in a wide range of operating conditions: with and without vertical velocity shear, and with and without surface waves following and against the current.

In the paper, we will compare at 1/20 scale the behaviour of the two kinds of turbine: 1 MW-rated and 2.5 MW-rated turbines. The experiments have been done in the same basin, under the same experimental conditions. The databases are being processed before launching a fine physical analysis.
Integrated hydrodynamic-electrical hardware model for wave energy conversion with M4 ocean demonstrator
Authors: Apsley Judith , Zhang Xiaotao , Iacchetti Matteo , Damian Iñaki Erazo , Liao Zhijing , Li Gangqiang , Stansby Peter , Li Guang , Wolgamot Hugh , Gaudin Christophe , Kurniawan Adi , Zhang Xinan , Lin Zifan , Fernando Nuwantha , Shearer Chris , Saunders Brad
Published: September 2023

Wave energy is well known to be a renewable energy resource with worldwide capacity similar to wind. However there is to date negligible generation of electricity from wave. Many devices have been proposed without convergence on a particular design as there has been for wind. We are here concerned with a multi-float attenuator type M4 which has been widely tested in wave basins and modelled by linear diffraction/radiation methods. Potential of MW capacity for grid supply has been demonstrated at many sites. To advance development, small scale ocean tests are being planned for Albany, Western Australia where summer wind-wave conditions in King George Sound will excite the device giving principal absorption with mean periods in the range 2 - 3.5  seconds (or peak periods of 2.5 – 4.5 s). The aim is to learn about most aspects of ocean deployment from wave climate and environment planning to realistic electricity generation, albeit at kW scale. In this paper the emphasis is on the specification of electrical drive train (power take off) which requires the input of torque time variation for the wave conditions on the site, as described by a scatter diagram. First a linear time domain wave multi-float model (Fortran) is set up for the particular 121 configuration, shown in Fig. 1. Such models have been used and validated against wave basin tests for similar configurations. This is then converted into state-space form in Matlab. This is highly efficient and suited for real time PTO control in Simulink. Fig. 2 shows the main components of the electrical drive train, including the gearbox, generator, super-capacitors, power electronic converters and resistor bank to dissipate electricity. Bespoke Matlab models will be run for the wave conditions in the scatter diagram to check that components are suitably rated for normal sea-states, and are safely protected through electrical power-limiting control in high sea states. Simulated electrical generator results will be shown for typical sea states, with some power-limiting. Instrumentation will be specified. Only uni-directional waves are considered in this paper. Ultimately the efficacy of the system will be demonstrated in ocean conditions.
methodology to capture the single blade loads on a cross-flow tidal turbine flume model
Authors: Bennecke Timo , Ruiz-Hussmann Karla , Joedecke Paul , Abbaszadeh Shokoofeh , Delafin Pierre-Luc , Weber Christian-Toralf , Hoerner Stefan
Published: September 2023

The OPTIDE project aims to improve the efficiency and durability of Hydro-kinetic cross-flow tidal turbines (CFTT). These turbines are attractive for the exploitation of tidal energy, as the area-based power density of such turbine arrays is higher in comparison to those from horizontal-axis turbines. CFTT also generally feature a simpler design and the ability to operate under varying flow conditions. Nevertheless, the efficiency of single CFTT is lower relative to the most commonly used axial turbine type. Furthermore the life time can be affected by alternating and pulsating stresses, caused by continuous variations of the angle of attack and hydraulic loads during the rotation. These stresses may lead to structural damage and fatigue-induced material failures. A promising approach to overcome these drawbacks is intracycle blade pitching. In this case the angle of attack is continuously adjusted individually for each blade during the rotation. The consequence is smoothed peaks of the load alternations and a higher power coefficient CP . The project aims to explore the influence of active blade pitching on CFTTs and to optimize it with numerical and experimental means. Therefore, a lab-scaled three-bladed experimental turbine with embedded pitch actuators is developed. The model will subsequently be tested in the lab flume of the Institute of Fluid Dynamics and Thermodynamics of the Otto-von-Guericke University Magdeburg. Blade forces in tangential and radial components as well as the machine torque and the rotational speed are measured during the experiments. The turbine is equipped with two full-bridges of strain gauges for the detection of the blade loads, from which the structural stress is calculated subsequently. To ensure the turbine model’s mechanical durability, weakly coupled fluid-solid-interaction (FSI) simulations have been performed and will be presented. To this purpose, a 2D flow analysis, employing the open-source CFD toolkit OpenFOAM (v2206), has been coupled with a 3D structural analysis, using the Mechanical module of the commercial software package Ansys Workbench (2020 R2). The FSI simulations show that the current setup only allows for the measurement of the radial blade load component, because the pitching moment at blade level interferes with the measurements as soon as the profile stalls. The measurements are further distorted by secondary force paths from the loads on the other rotor blades. Possible measures for an improved instrumentation strategy on the flume model will be presented and discussed. It is shown that multiple equipment options allow for a decent investigation of the forces on blade level.
Large-eddy simulations of interaction between surface waves and a tidal turbine wake in a turbulent channel
Authors: Stallard Tim , Mullings Hannah , Draycott Sam , Ouro Pablo
Published: September 2023

Tidal stream turbines are now being developed for array deployments, largely at sites with relatively shallow water depths on either bed-supported, or floating support structures. Proximity to the free-surface presents design challenges with increased exposure to wave-induced kinematics leading to potential for increased peak- and fatigue-loads. Free surface proximity can also alter wake recovery rates which can influence the siting, and operation, of further turbines. To-date the impact of waves on turbine loading and on wake recovery has receivedlimited attention, generally for specific combinations of conditions reproducible in experimen tal facilities [1-2] or numerical models [3]. Improved understanding of how waves affect both turbine loading, and wake dynamics is necessary to inform the development of appropriate load prediction and mitigation methods and to further parameterise wake recovery to inform array siting.

This work presents CFD analysis of the loading and wake of a three-bladed horizontal axis tidal turbine within a wide, shallow channel with a turbulent inflow developed using a synthetic eddy method and free surface waves modelled using a Level-Set Method (LSM). The turbine and wave conditions considered are based on prior experimental studies [1] within a channel depth h = 0.45 m and mean flow U = 0.47 m/s. The simulated channel is width 3.67h and length 88h and long-crested regular waves are imposed, with the focus of this study on waves with non-dimensional wavenumber kh = 2.8, comparable with experimental conditions. Simulations are accomplished using the in-house large-eddy simulation (LES) code DOFAS(Digital Offshore Farms Simulator) [4], which adopts an Actuator Line Method (ALM) to resolve the turbine blades. LSM is used to model the air-water interface in an accurate manner [5] with waves can be generated in DOFAS using linear or second-order Stokes theories with an absorption layer placed at the outlet of the domain to avoid wave reflections. At the inlet a mean logarithmic velocity profile is imposed over which artificial turbulence is added. Simulations were run for 400 s of physical time on 8,000 cores using ARCHER2.

The waves studied are shown to alter the rate of wake recovery, increasing the rate in the near-wake of the turbine and slightly reducing the rate beyond eight diameters downstream. Analysis of turbulence characteristics indicates a significant variation across the water column due to wave action. Propagation over the turbine wake also introduces directionality to the wave field, which is associated with the change of wave-speed over the wake region. Modal decomposition analysis of the velocity fluctuations with Proper Orthogonal Decomposition(POD) reveals that the wake dynamics behind the turbine change due to the waves.
System Identification for Modelling M4 Wave Energy Converter
Authors: Wang Xuefei , Liang Danni , Li Mengxiao , Stansby Peter , Zhang Long
Published: September 2023

As one of the renewable energy resources, wave energy has the potential to be one of the major electricity generation resources in the long term. However, the industrial-scale implementation of wave energy is still at an early stage and requires deeper research and development.  Currently, only several different wave energy conversion techniques such as oscillating bodies, oscillating water columns, and over-topping modules, are available. Among these energy converters, the 6-float, multi-mode, moored wave energy converter (WEC) M4 has been developed by the University of Manchester.  M4 consists of a bow float, three mid floats and two stern floats with beams hinged above the outer mid floats. The mooring to the bow float includes an elastic cable from the bed to a spherical buoy and an inelastic cable linking the buoy to the bow float. The M4 converter has been modelled numerically. However, these numerical methods often require large computational resources and therefore they can only be used offline and they cannot be implemented in real-time applications. It is highly desirable to develop a computationally efficient model for the M4 system. 

 

 

In this paper, system identification methods are used to model the M4 WEC system with the experimental data. First, two linear models including autoregressive with exogenous inputs (ARX) and the Box-Jenkins (BJ) model are used to build three different types of models for 6 float M4 WEC system using three different input and output variables: wave surface wave surface elevation, the mooring forces (top and bed forces) and the bow float motions (pitch, surge and heave). Further, when constructing the model of the M4 system, the impacts of both sampling rate and model orders are considered. The modelling results are compared and analysed using three selected criteria including fitting percentage, mean squared error and final prediction error. Finally, the performance of identified models are validated by wave basin experiments which covers seven major wave conditions including different wave heights and mean wave periods. Results show that both ARX and BJ models are feasible to model the M4 WEC system, with low orders and sampling rates for high short-term prediction accuracy. These models could be potentially used for real-time applications.
Discussions on Wave energy period in higher wave energy potential marine waters of Taiwan
Authors: Tzang Shiaw-Yih , Zhang Z.-X.
Published: September 2023

For evaluating wave energy, wave energy period Te is commonly adopted. However, the in-charge government agencies in Taiwan traditionally provided with peak frequency Tp without giving information on the transferring relationship between Te and Tp. This results in difficulties on correctly evaluating wave energy potentials at certain marine waters. Thus, existing spectrum data need to be derived to calculate values of Tp and Te so as to derive representative transferring coefficient Cep for long-term evaluations on wave energy. This study aims at deriving values of Cep at relatively higher potential marine waters of Taiwan. As shown in Figure 1, the data were collected from two stations in Keelung marine waters and one station within marine waters for offshore wind of Changhua. By choosing different criteria for Cep, selected data were regressed for obtaining representative Cep in different seasons. For conservative point of views, the values of Cep ranging from 0.85~0.87 from data in northeaster monsoon months, as shown in Figure 2, being generally slightly smaller than those of the whole year, were adopted at the three stations. It is also found that the representative values of Cep were derived mainly from data comprising of exploitable wave power densities of between 2~80 kW/m2. Data collection instruments, selection criteria and associated outcomes shall be detailed in the full paper.
Comparison of Actuator Line Modelling of Tidal Power Kites with ADCP Measurements
Authors: Saravana Prabahar Nimal Sudhan , Fredriksson Sam , Broström Göran
Published: September 2023

The potential for tidal energy to be a part of future renewable energy systems is expanding. Tidal turbines deployed in open waters or channels are effective methods to harness energy from tidal currents. Sharing similar functionality with wind turbines, horizontally mounted tidal turbines require a minimum tidal current velocity to operate effectively. The Deep Green (DG) power plant which is based on a tethered kite model aims, however, to operate efficiently in tidal current velocities as low as 1.2 m/s. The kite wing is steered in a lemniscate trajectory ( ) almost perpendicular to the tidal current. In the trajectory, the relative flow velocity through the turbine attached to the wing reaches several times the tidal current velocity, enabling efficient operation of the turbine in relatively low-velocity tidal currents. This could reduce geographical limitations in installing large-scale tidal power arrays.

In a previous project, numerical modelling of the DG was carried out in a tidal flow using Large Eddy Simulations (LES) and Actuator Line Modelling (ALM) implemented in OpenFOAM solver. ALM using momentum sources has been used in modelling wind turbines and has been validated against experimental data and observations. The ALM has been further developed in order to be able to model wings (here the kite) that move in arbitrary paths compared to horizontally mounted turbines with rotational paths. This numerical model for the DG kite in a tidal flow has, however, up to now not been validated against observations, which is beneficial before further analyses are made, e.g., optimization studies.

In this study, Acoustic Doppler Current Profiler (ADCP) observations taken in the wake of a DG are compared to the results from the numerical model under similar conditions. Comparing the numerical results directly with the observations leads to discrepancies, hence the model data is resampled in a similar way that the ADCP would measure and process data using a virtual ADCP for the model. Flow properties such as the instantaneous and time-averaged stream velocities are in turn compared for both the tidal flow without the DG and with a DG. The effect of the DG on the tidal flow is analysed using the model and the observations. After resampling the model data, the model and observations show good agreement. This suggests 1) that the DG model using ALM can be used for further analysis and 2) that whilst comparing model data with ADCP observations for studying the small-scale effects of tidal turbine wakes, care should be taken to sample the model data consistently with observations.
Preliminary performance assessment from towing tank testing of a horizontal-axis turbine
Authors: Lande-Sudall David , Tolleifsen Sondre , Gravelsæter Kjetil , Moen Harald , Bartl Jan
Published: September 2023

Following the Norwegian government’s goal to be a ‘low emission society’ by 2050, there is a significant push to develop offshore renewable energy; principally offshore wind, but also wave and tidal stream. The MarinLab towing tank at the Western Norway University of Applied Sciences, Norway is 50 m long with a 3.0×2.2 m section and was inaugurated in 2016 as an educational and research facility, supporting local industry to achieve a low-carbon transition.

To advance knowledge of aero- or hydrodynamic interaction of future turbines for both wind and tidal stream energy, a model scale test-bed horizontal axis turbine has been developed. This turbine will enable testing of rotor diameters typically in the range of 500-600 mm. The turbine is instrumented with a torque-thrust sensor of 5 Nm/100 N capacity, custom-manufactured by Marin in the Netherlands. The turbine is speed regulated via a 4096 counts angular encoder connected to a 200 W Maxon EC-i brushless motor.

Before testing new rotor geometries, a benchmarking study is being undertaken with an existing known geometry. The benchmark rotor has diameter, D=700 mm and employs the same NACA 63418 airfoil as Mycek et al. (2014), allowing comparison. Unlike Mycek et al. (2014), the nacelle has a nominal diameter of 90 mm and length 760 mm. The size of the rotor risks exceeding the capacity of the torque sensor, such that maximum tow-speed is limited to 0.8 m/s. The benchmark blades are machined from solid aluminium in a four-axis CNC milling machine, following a method similar to Payne et al. (2017). Due to machining limitations, the minimum trailing edge thickness is specified as 0.2 mm. The final surface finish is achieved by manual polishing, and the final dimensions, quantified using a Hexagon ROMER Absolute laser scanner, are found to be within ±0.2 mm accuracy. Future blade sets will typically have a smaller diameter, allowing for 3D printing and consistency of surface finish.

A blade-element momentum model has been run with Prandtl tip and hub losses and 0° pitch (Fig. I). Lift and drag coefficients were calculated for a range of chord Reynolds numbers using XFOIL, for angles of attack between -5 to 16° and extrapolated to ±180° with Viterna’s method. Due to difficulties in estimating laminar-turbulent transition around critical Reynolds numbers, there is uncertainty in the XFOIL coefficients. At peak TSR, the chord-based Reynolds number is approximately 280k at 3/4 span. Curves for both Rec =250k (solid) and 500k (dashed) with Ncrit = 9 are presented, showing a significant drop in performance for lower Reynolds numbers, due to a collapse in Cl/Cd. Initial tests were conducted in near- zero ambient turbulence, though passive turbulence grids are available for future testing. Reasonable agreement on CT is observed when corrected for blockage according to Bahaj (2007), and further assessment will provide results on CP, tower loads and wake recovery.
Experimental investigation on the hydrodynamic performance of a pile-supported OWC-type breakwater
Authors: ALMALKI YUSUF , KARMPADAKIS IOANNIS , SWAN CHRIS
Published: September 2023

The present study considers the design optimisation of an Oscillating Water Column (OWC) incorporated into a pile-supported breakwater structure. This has been achieved by performing a substantial number of scaled physical model tests and a methodical variation of key device parameters within multiple configurations. The key aspects that have been investigated include: (a) the geometric characteristics of the breakwater structure, (b) the pneumatic efficiency of the OWC, (c) the geometry of the OWC chamber and (d) the relative position of the OWC chamber within the breakwater. The present work considers (monochromatic) regular waves of varying steepness and effective water depth as incident wave conditions. The efficiency of the designed structure in terms of shore protection capacity and wave energy extraction was assessed by quantifying relevant transmission coefficients and the power output metrics. This has been achieved by using a combination of collocated and complementary measuring devices, such as arrays of wave gauges, pressure transducers and a high-definition video camera. The study concluded that systematic refinement of the geometrical parameters can substantially enhance the overall hydrodynamic efficiency of a pile-supported OWC breakwater. Additionally, it was found that a configuration featuring a chamber positioned in front of the breakwater, with a relative chamber breadth of 0.67, outperforms wider breadth configurations in terms of both energy extraction efficiency and reduction of the transmission coefficient. Taken together, the present study provides an in-depth analysis of the effects of key design parameters of a breakwater-integrated OWC, its efficiency and shore protection potential.
Dimensioning and optimization of multi-source offshore renewable energy parks
Authors: Schaap Anton , Van der Zant Hinne
Published: September 2023

Multi-source offshore renewable energy parks, consisting of wind, solar and wave converters, can utilize the available offshore area much more efficiently than single source wind parks. They can also produce power with a higher capacity factor than single source parks, utilizing the available grid connection more efficiently. Dimensioning and financial optimization of such parks will be driven by geographic constraints like available area, water depths, shipping lanes, exclusion zones etc., but also by the available resources of wind, solar and wave power. Another major driver in the optimization will be the electricity price. With the raising share of weather dependent renewables in the electricity mix, the electricity price will become more volatile. Therefore, an optimized design process of a multi-source park should also incorporate a pricing mechanism that can produce hourly electricity prices based on actual weather conditions. The paper will present the results of a numerical model that can integrate solar and wave power in a wind park area as well as optimize the export cable capacity. Battery storage can be added to this multi-source park to shift part of the production to hours with higher electricity prices. A case study has been performed for the planned offshore wind park TNW, North of the Dutch  Waddeneilanden. Since such a multi-source park will have an expected lifetime of about 30 years, it will even reach the year 2050, in which weather dependent renewable energy will be much more dominant than today, with far stronger electricity price volatility. For the electricity price calculation, assumptions are made for the installed base of solar, wind and wave power in the whole of The Netherlands, as well as the geographic spread of this installed base over the land area and the offshore exclusive economic zone in the North Sea. This installed base is simplified by concentrating it in about ten locations divided over this area. Other necessary assumptions are the future electricity demand pattern, the future capacity of the interconnections with the surrounding countries and the capacity of the flexible load that will be available at that time (electric cars, electric heaters etc.). From literature, the cost of conventional power fueled by natural gas and/or hydrogen is derived which serves as back up power for hours with low wind, solar and wave power production. Based on all these assumptions, a pricing curve is constructed reaching from sub zero at abundant renewable supply to a maximum value at zero renewable supply. With the model, scenarios of future developments in installed wind, solar and wave power, but also in e.g. electric cars, electric heaters and other flexible loads, can be examined and the sensitivity of the optimization of the multi-source park design can be determined. The relevance of wave power can be determined from the average price per MWh that wave power can earn compared to wind and solar.
Geometrical Design of the L-shaped Oscillating Water Column Using Artificial Neural Network
Authors: LIN CHEN-CHOU , CHOW YI-CHIH , NGUYEN DUY TONG
Published: September 2023

Among the various wave energy converters available, the oscillating water column (OWC) shows a number of advantages in terms of implementation and maintenance. In dealing with the survivability issues, incorporating OWCs into reinforced concrete constructions, like breakwaters, is more cost-effective and can endure the effects of seawater impact and erosion.
This paper focuses on optimizing the geometrical design of a novel OWC type, the L-shaped OWC, by establishing a general design procedure to achieve higher energy-capturing efficiency. The performance of the OWC is influenced significantly by the OWC’s geometry under a specified wave condition. It is found that the dimension of the air chamber and water duct is critical in determining OWC’s performance. We develop the chamber and duct design procedure based on the artificial neural network approach by establishing a collection of two-dimensional RANS simulations as the training database. In the end, the performance of the optimal design is compared with the design of a previous paper. The result shows that the capture factor of the optimized chamber geometry of the L-shaped OWC is 12% more than the former design.
Assessment of tidal energy resources in the Strait of Magellan in southern Chile
Authors: Suarez Atias Leandro , Escauriaza Cristian , Williams Megan , Guerra Maricarmen
Published: September 2023

The Strait of Magellan in the Chilean Patagonia (Lat: 53.5°S) connects the Atlantic and Pacific oceans through a narrow passage. Historic and current pressures from navigation, oil and coal industries combined with changes due to anthropogenic climate change and local population growth make the region both complex and relevant. A large tidal range on the Atlantic side of the strait produces very strong currents in the first and second narrows that have a significant potential for hydrokinetic energy. Maximum currents have been measured up to 5 m/s.
 
With the goal of performing a detailed assessment of the marine energy potential of the strait, field measurements combined with an FVCOM numerical simulations are being used to assess the tidal potential and understand the complex coastal physics of the system. Field observations were carried out in short field campaigns in 2018 and 2019 to characterize the flow in one of the channel narrows. We deployed a moored ADCP for currents and turbulence characterization, measured salinity and temperature, sea-surface elevations with pressure sensors, and made velocity transects with a vessel-mounted ADCP. These characterizations will also help to inform the role of the flow through the Strait of Magellan on the continental shelf.
 
The field data we collected is critical to understand the factors that control the dynamics of the flow in this section of the channel, and understand its marine energy potential. Measured velocities are being used to validate an FVCOM numerical model which will expand our spatially and temporally limited measurements, to estimate the tidal energy resources in the Magellan strait and evaluate the impacts of varying climatic conditions. The numerical model will also allow to predict the complementarity of tidal energy with other renewable resources, in the context of green hydrogen in the Strait of Magellan.
 
This is the first study aimed at predicting the tidal energy resources in the Strait of Magellan, combining field observations and numerical models. Future work will focus on the interactions of physical and environmental processes that can help to promote a sustainable development of marine energies in the southern part of the continent.
Tidal Turbine Benchmarking Project: Stage I - Steady Flow Blind Predictions
Authors: Willden R.H.J. , Chen Xiaosheng , Tucker Harvey S.W. , Edwards H. , Vogel C.R. , Bhavsar K. , Allsop T. , Gilbert J. , Mullings H. , Ghobrial M. , Ouro P. , Apsley D. , Stallard T. , Benson I. , Young A. , Schmitt P. , Zilic de Arcos F. , Dufour M.-A. , Choma Bex C. , Pinon G. , Evans A.I. , Togneri M. , Masters I. , Da Silva Ignacio L.H. , Duarte C.A.R. , Souza F.J. , Gambuzza S. , Liu Y. , Viola I.M. , Rentschler M. , Gomes T. , Vaz G. , Azcueta R. , Ward H. , Salvatore F. , Sarichloo Z. , Calcagni D. , Tran T.T. , Ross H. , Oliveira M. , Puraca R. , Carmo B.S.
Published: September 2023

This paper presents the first blind prediction stage of the Tidal Turbine Benchmarking Project being conducted and funded by the UK's EPSRC and Supergen ORE Hub. In this first stage, only steady flow conditions, at low and elevated turbulence (3.1%) levels, were considered. Prior to the blind prediction stage, a large laboratory scale experiment was conducted in which a highly instrumented 1.6m diameter tidal rotor was towed through a large towing tank in well-defined flow conditions with and without an upstream turbulence grid.
Details of the test campaign and rotor design were released as part of this community blind prediction exercise. Participants were invited to use a range of engineering modelling approaches to simulate the performance and loads of the turbine. 26 submissions were received from 12 groups from across academia and industry using solution techniques ranging from blade resolved computational fluid dynamics through actuator line, boundary integral element methods, vortex methods to engineering Blade Element Momentum methods.
The comparisons between experiments and blind predictions were extremely positive helping to provide validation and uncertainty estimates for the models, but also validating the experimental tests themselves. The exercise demonstrated that the experimental turbine data provides a robust data set against which researchers and design engineers can test their models and implementations to ensure robustness in their processes, helping to reduce uncertainty and provide increased confidence in engineering processes. Furthermore, the data set provides the basis by which modellers can evaluate and refine approaches.
Hydrodynamic Response of Mocean Wave Energy Converter in Extreme Waves
Authors: Samuel John Ashlin , Venugopal Vengatesan , Retzler Christopher , Ma Qingwei
Published: September 2023

The design of moored floating wave energy converters (WECs) must take into account extreme responses and mooring line loads in order to ensure their survival and continued wave power generation in the ocean environment. This study focuses on Mocean Energy's hinged raft WEC and aims to provide a comprehensive understanding of its hydrodynamic characteristics in survival wave conditions. To achieve this, a physical model study was conducted on a Froude scale of 1 in 50 at the FloWave Ocean Energy Research Facility, University of Edinburgh.

The experiments involved the use of NewWaves focusing of crest and trough at the model hinge location, as well as long irregular waves. Motion responses of the fore and aft bodies of the WEC were measured using a Qualisys camera, and single component load cells were used to measure the forces in the 3-point catenary mooring line. The hydrodynamic characteristics of the WEC were evaluated in terms of response amplitude operators and non-dimensional mooring line loads.

Results indicate that the fore and aft bodies of the WEC exhibit similar motion responses, except for the pitch motion. The aft body has a pitch response 2 to 3 times higher than the fore body. Concerning the moorings, the wave load on the mooring line in line with the wave direction was found to be higher than the other two mooring lines which were arranged at an angle to the wave direction.

In this paper, a brief discussion of the model set-up, parameters, test procedure, analysis of results, and discussion will be reported. The results will provide insight into the behaviour of the Mocean device in survival wave conditions and will aid with the determination of appropriate design parameters for optimal performance and survival in the ocean environment.
Numerical Study on Overtopping Performance of Multi-stage Overtopping Wave Energy Converters
Authors: Zhang Guoliang , Zhang Xiaoxia , Xu Chuanli , Dong Xiaochen , Liu Zhen
Published: September 2023

The characteristics of wave conditions with large tidal ranges and small wave heights in China's coastal waters limit the operation time of traditional single-stage overtopping devices, while the multi-stage overtopping wave energy converters can increase the overall operation time of the device by distributing the upper and lower reservoirs. To study the overtopping performance of the multi-stage overtopping wave energy converter under real sea conditions, a two-dimensional numerical model of the device is developed and verified by physical model tests. The effects of the lower reservoir opening width, slope angle combination, and slope inundation length on the overtopping performance are investigated under regular wave conditions. It is found that a smaller opening width and two 30° slope angles improve the overtopping performance of the device, while the slope inundation depth has less effect. Further, based on the full-scale prototype device, the database of overtopping in a complete tidal cycle (12h) were constructed under real sea conditions in different seasons to provide the basic data for the Wave-to-wire model of power generation simulation.
On spatial interpolation of ocean energy source variables: A comparative analysis
Authors: Gambarelli Leonardo , Pasta Edoardo , Giorgi Giuseppe
Published: September 2023

In the context of wave energy systems development, the estimation of wave parameters such as significant wave height (Hs) and energy period (Te) over the entire ocean surface is of paramount importance. These information are crucial for estimating the energy harvesting potential of deployment sites, designing wave energy converters (WECs), planning optimal maintenance intervention frequency, and assessing the impact of waves on coastal communities. However, measuring Hs and the Te at every point in the ocean is impossible due to the vastness of the ocean and due to the cost and difficulties of installing and maintaining wave instrumentation buoys, since these have to survive in marine environment, which is particularly hostile. As a consequence, the amount of data is too limited and sparse in space for the practical and precise performance of these analyses. To address such data scarcity and sparsity, we analyse in this paper various spatial interpolation techniques employed to fill the spatial gaps in the wave parameter datasets. These techniques are compared in their performances in estimating the wave parameters in space given a set of known measurements in limited sampling locations. Three types of interpolators are considered: linear interpolator, spline interpolator, and radial basis functions (RBFs) interpolator. These algorithms are trained and tested on a public dataset of wave parameters from Copernicus Marine Service in an area between the coastlines of South England and North France. To simulate the available data scarcity and sparsity, only limited percentages of the ocean area are considered covered and available in the training stage (from 0.01% to 1%). The performance of each interpolator is evaluated on the remainder of the considered area in terms of Normalized Root Mean Square Error (NRMSE) and on the Normalized Mean Absolute Error (NMAE) achieved by the algorithm in reconstructing the parameters at these unsampled locations. The results of this study demonstrate the feasibility of spatial gap-filling of wave parameters, and demonstrates that the RBF algorithm outperforms the other  two algorithms both in performances and, even more, in terms of robustness to different training points sampling.
SUSTAINABLE HUMAN DEVELOPMENT: ISSUES AND CHALLENGES
Authors: Dr. Santosh R  , Smt. Deepa D
Published: September 2023

The research paper examines sustainable human development by addressing its definitions and nature. It delves into key challenges such as governance, economic violence, corruption, terrorism, and various forms of security including human, political, economic, food, health, and environmental. It also analyzes challenges like deforestation, climate change, pollution, groundwater depletion, low literacy, poor health, and extreme poverty. The study concludes by summarizing the discussed sustainable development challenges.
KEYWORDS: Governance, Literacy, Health, Poverty, Climate Change
INFLUENCE OF PROVISION OF INCENTIVES BY HEAD TEACHERS ON TEACHERS’ WORK PERFORMANCE IN PUBLIC PRIMARY SCHOOLS IN NAKURU COUNTY, KENYA
Authors: Christine Kamba Malebe  , Dr. Emily Nyabisi  , Prof. Pamela Ochieng
Published: September 2023

Recent reports on education in Kenya underscore the importance of head teachers adopting effective instructional leadership practices and teachers enhancing their pedagogical knowledge and skills in order to guarantee high-quality education and academic achievement within the countrys school systems. Giving teachers incentives is one of the instructional leadership strategies that headteachers can use. This studys goal was to ascertain how the head teachers incentives affected teachers work performance in Kenyas Nakuru County public elementary schools. The study was informed by the Hallinger and Murphy (1985) Model of Instructional Leadership and the Campbell et al. (1993) Theory of Job Performance. The study employed a convergent parallel design and a mixed methods research methodology. In order to gather and analyze data from a target population of 57,800 students, 7,741 teachers, 680 head teachers from 680 schools, and 11 Quality Assurance and Standards Officers (QASOs), the study simultaneously used quantitative and qualitative research methodologies. Cluster sampling was used to choose a sample of 68 elementary schools for the investigation. Through simple random sampling, 60 students and 329 teachers were chosen from these sampled schools. Additionally, 68 head teachers and 9 QASOs were chosen through the use of a purposeful sample. A focus group discussion guide, questionnaire, interview schedule, and document analysis checklist were the research tools employed. A pilot research with a sample size of 35 teachers was carried out in 7 public elementary schools in Baringo County. The quantitative data were analyzed using descriptive and inferential statistics, notably frequency counts, percentages, Spearman rank correlation, and regression analysis. The Statistical Package for Social Sciences (SPSS) version 25 was used to test the hypothesis at a significance level of 0.05. Tables were used to depict the results as frequencies and percentages. Thematic analysis and story presentations were used to display qualitative data. According to the study, head teachers incentives had a statistically significant positive effect on teachers job performance in Nakuru Countys public elementary schools. The study emphasizes the value of teachers work performance for overall school outcomes, giving head teachers and other education stakeholders important information to consider while focusing on efforts for providing incentives for teachers and legislation that support such programs. This would foster an environment where teachers may work as efficiently and effectively as possible, enhancing student achievement in KCPE examinations in public primary schools.

KEY WORDS: Provision of Incentives, Teachers Work Performance, Instructional Leadership, Public Primary Schools