Tidal turbine Research Papers - Academia.edu (original) (raw)

As tidal turbine farms grow they interact with the larger scale flow along a channel by increasing the channel's drag coefficient. This interaction limits a channel's potential to produce power. A 1D model for a tidal channel is combined with a theory for turbines in a channel to show that the tuning of the flow through the turbines and the density of turbines in a channel's cross-section also interact with the larger scale flow, via the drag coefficient, to determine the power available for production. To maximise turbine efficiency, i.e. the power available per turbine, farms must occupy the largest fraction of a channel's cross-section permitted by navigational and environmental constraints. Maximising of power available with these necessarily densely packed farms requires turbines to be tuned for a particular channel and turbine density. The optimal through-flow tuning fraction varies from near 1/3 for small farms occupying a small fraction of the cross-section, to near 1 for large farms occupying most of the cross-section. Consequently, tunings are higher than the optimal through-flow tuning of 1/3 for an isolated turbine from the classic turbine theory. Large optimally tuned farms can realise most of a channel's potential. Optimal tunings are dependent on the number of turbines per row, the number of rows, as well as the channel geometry, the background bottom friction coefficient and the tidal forcing.

- by
- •
- Marine Renewable Energy, Tidal Stream Energy, Tidal Stream Turbine Modelling, Tidal turbine

Today, the world is heavily dependent on fossil fuels, as most of the energy requirements are being met through conventional methods of burning these fuels. The energy demand is increasing day with growing population. Consequently, fossil fuel reserves are depleting continuously and will soon run out in coming years. Therefore, renewable energy resources have gained enormous attention in recent years. The growing interest in exploring tidal current technologies has many compelling reasons such as its renewable nature, tidal energy is cleaner than fossil fuels, intermittent but predictable, security and diversity of supply, and limited social and environmental impacts. Tidal current technologies are still in development phase, yet need some time to mature to prove their full potential. Tidal current turbine is an important tidal current technology. The purpose of this paper is to present a comprehensive review of tidal current turbine, its potential and associated challenges. The pap...

- by Nasir Mehmood
- •
- Environmental Science, Wave Energy, Tidal Stream Energy, Tidal turbine

This paper presents a combined theoretical and CFD study on the fluid-mechanical limit of power extraction by a closely-spaced lateral array of wind turbines. The idea of this study originates in recent studies on the array optimisation of tidal/marine turbines, for which the power coefficient of each turbine is known to increase significantly if the lateral spacing between turbines, or the local blockage, is optimised. The present study, using 3D Reynolds-averaged Navier-Stokes (RANS) simulations of a boundary-layer flow over a closely-spaced lateral array of up to 9 actuator discs, suggests that a similar—albeit less significant—power increase due to the effect of local blockage can be achieved even for wind turbines. A possible theoretical approach to estimating this power increase is also discussed.

- by Takafumi Nishino
- •
- Fluid Mechanics, Wind Energy, Tidal Stream Energy, Aerodynamics

Blade boundary layer resolved simulations of two different tidal turbine rotor designs are presented. The first rotor was designed to achieve its maximum power coefficient at tip speed ratio of 5 in unblocked conditions and the other was designed to achieve its maximum power coefficient at a tip speed ratio of 5 but at a higher local blockage ratio of 0.197. Both designs achieve their maximum power coefficient close to a tip-speed-ratio of 5 for which they were originally designed. In addition, the maximum power coefficients for both rotors operating in an unblocked domain compare favourably with full-scale deployed horizontal axis tidal turbines. With increasing blockage ratio, it is observed that greater power coefficients can be achieved, 0.62 to 0.63, but that this requires an increased thrust. The blockage designed rotor can provide this extra thrust naturally , primarily as it is designed with greater solidity. In contrast, the rotor designed for unblocked flow must be made to operate at a significantly higher tip-speed-ratio to achieve the required thrust.

— With the rising concerns over global climate change associated with rapid depletion of limited fossil fuel resources, worldwide attention has intensified towards the potentials and possibilities of renewable energy sources. In the context of Bangladesh, among multifarious sources of renewables (solar, wind, biomass, tidal and wave power and ocean thermal energy) harnessing of energy from ocean tides, that cogitates both kinetic and potential energy, is a promising option. The former deals with tidal current energy conversion technologies while the latter concept focuses on the tidal barrage approach-similar to hydropower technique. This paper presents an assessment of the potential of tidal barrage technology through the development of a laboratory scale prototype model. The prototype energy extractor is constructed to study and verify the one-way generation method of tidal barrage technology. The model is scaled down to actual generation. A laboratory flume is used to generate a hydraulic head across a sluice gate, considering the upstream as basin side and downstream as the seaside. Water on the basin side is retained by the sluice, creating maximum head difference and thereby generates electricity while traversing through the turbine and rotating the generator. The generated power in the downstream end is measured by an ammeter. The amount of energy generated through the turbine is then compared to the theoretical energy generation. The findings of this study are discussed in relation to the prospects of tidal potential energy and identifies this technology as a preferable option for electricity generation in the suitable locations of the Bay of Bengal.

- by Myisha Ahmad and +1
- •
- Renewable Energy, Tidal Stream Turbine Modelling, Tidal turbine, Tidal Power: An Effective Method of Generating Power

The Betz limit sets a theoretical upper limit for the power production by turbines expressed as a maximum power coefficient of 16/27. While power production by wind turbines falls short of the Betz limit, tidal turbines in a channel can theoretically have a power coefficient several times larger than 16/27. However, power extraction by turbines in large tidal farms also reduces the flow along the channel, limiting their maximum output. Despite this flow reduction, turbines in tidal farms can produce enough power to meet a stricter definition of what it means to exceed the Betz limit, one where the maximum power output of a turbine at the reduced flow exceeds the maximum output from a single Betz turbine operating in the unreduced flow. While having a power coefficient > 16/27 is easily achieved by turbines in a channel, generating enough power to meet this stricter definition of exceedance is much more difficult. Whether turbines meet this stricter definition depends on their number, how they are arranged and tuned, and the dynamical balance of the channel. Arranging a tidal turbine farm so that the turbines within it exceed the stricter Betz limit would give tidal turbine farms an economic advantage over similarly sized wind farms. However, exceeding the stricter limit comes at a cost of both higher structural loads on the tidal turbines and the need to produce power from weaker flows. Farms in a channel loosely based on the Pentland Firth are used to discuss exceedance and structural loads.

- by Ross Vennell
- •
- Renewable Energy, Wind Energy, Marine Renewable Energy, Tidal Stream Energy

— This work presents a numerical simulation of a Vertical Axis Marine Current Turbines (VAMCT) in both steady and unsteady current velocities. Three different turbines were examined in this study in order to investigate the relationship between the current fluctuation frequency, the number of turbine blades and turbine frequency. Three, four and five blades turbines were numerically simulated. Fluent is used to solve the 2-D model using the time-accurate incompressible Unsteady Reynolds-averaged Navier-Stokes (URANS) equation with k-ω SST turbulence mode. The simulation results showed that there existed a significant relationship between the number of turbine blades, the turbine Tip Speed Ratio and the current fluctuation frequency. In an unsteady current the increase in the number of blades led to a reduction in the turbine's instability; however it might not increase the power performance especially at high TSR..

The greatest increase in demand for energy coming from newly industrialized countries where large-scale electricity generation will be required, the environmental requirements for zero or low CO2 emission sources and the need to invest in a sustainable energy mix, involve the development of new energy sources. Wave, tidal and marine current energy could be available as a future energy option and should be able to acquire a significant role in providing a sustainable, secure and safe solution to tackle European and global energy needs. Sun and wind are predictable, but not constant: photovoltaic panels and eolic turbines could barely support alone the peaks of the power request from the grid, and the contribution of hydroelectric seems to have already reached its limits in some European countries. For this reasons, in order to become independent from fossil fuels, it will be fundamental to harvest energy from the largest number of natural phenomena, especially ones that are predictale with high precision, as tides, and ones that are almost constant, as ocean currents.

- by Riccardo Novo
- •
- Renewable Energy, Wave Energy, Tidal Stream Energy, Green Energy

Sustainable energy generation through renewable sources is a rapidly expanding industry within the energy sector and as part of that industry tidal power creates the potential to tap into a previously untapped resource. Existing tidal barrage schemes are leading the way in exploiting tidal energy resources but are only producing a very small percentage of the world's generated electricity. Further development and expansion of this technology has been somewhat hindered by opposition from green political parties whom believe that the environmental impact of such a scheme is too great.
Tidal stream devices have therefore been developed as an alternative method of extracting the energy from the tides. This form of tidal power technology poses less threat to the environment and does not face the same limiting factors associated with tidal barrage schemes, therefore making it a more feasible method of electricity generation.
This paper describes work involved with modelling, using the CFD package SolidWorks Flow Simulation, a contra-rotating double row bladed tidal turbines. The first rotor has three blades rotating in a anti-clockwise direction while the second rotor, located directly behind the first, has four blades rotating in an clockwise direction. A contra-rotating marine current turbine has a number of attractive features: near zero reactive torque on the support structure, near-zero swirl in the wake, and high relative inter-rotor rotational speeds. The design of these turbines is to assess the potential increase in the power, torque and axial thrust generated over a conventional single row propeller.
The results from the CFD models show that there is a negligible increase in the power generated but an increase in the axial load on the turbine. The nett torque acting on the device is, however, considerably reduced, and potentially negated, so potentially helping the turbine to align to the tidal flow. Flow visualization of the wake verified the lack of swirl behind the turbine.

Calvert K and Simandan D (2010) Energy, space, and society: a reassessment of the changing landscape of energy production, distribution, and use Journal of Economics and Business Research XVI(1), pp. 13-37.
ABSTRACT: While geography has always mattered for the energy sector, the relative effects of location and distance on the economics of energy regimes are increasing as we begin to deploy more renewable energy technologies. This reintroduction of the friction of distance is leading to an energy landscape that is far different from fossil-based regimes. The new energy paradigm, based as it is upon the physics and the economics of renewable energy, is being reflected in the landscape as distributed, decentralized, and diversified patterns of energy generation. Because the increased use of renewable energy technologies is beginning to change the spatial patterns of political and socioeconomic activities, a thorough understanding of these patterns is crucial to increasing the socio-political acceptability of new technologies and to avoiding the socially costly unintended consequences of policy and investment decisions. This paper proposes a theoretical foundation upon which economists and economic geographers could scaffold their analyses of the spatial characteristics of the economics of energy use. To this end, we bring together two complementary conceptualizations of economic geography: firstly, as the study of the effects of location and distance on energy economics, and secondly, as the study of the ways in which political, economic, and technological energy-related practices give rise to particular spatial patterns of socio-economic welfare. We end the paper by developing the concept of energy rationality and showing how it relates to discussions of metarationality, common sense, and wisdom.

- by Dragos Simandan
- •
- Critical Theory, Environmental Engineering, Economic History, Landscape Ecology

Why we have to be addictive to rotary turbine for tide or wind energy harvest? Perhaps we are not smart enough to find a new way. Now I propose a rectangular cross section turbine that works in reciprocation mode to harvest energy from any flowing fluid. In a sense, fluid flows in similar way of electric DC (Direct Current), but reciprocal motion of device's ram behaves in similar way of AC (Alternating Current), thus a DC-AC mechanic inverter is needed. Of course, inverse utilization of same mechanism renders an AC-DC mechanic rectifier, i.e. an exotic pump.

- by Yanming Wei
- •
- Fluid Mechanics, Wind Energy, Tidal turbine, Pumps

The International Energy Agency (IEA) concludes in The World Energy Outlook 2008 that the current energy consumption and production is “patently unsustainable environmentally, economically, and socially”. Social concern and international agreements (e.g. Kyoto 1997, Copenhagen 2009 or Durban 2011) are pushing forward the development of renewable energy technologies for sustainable and renewable energy generation.
In particular, offshore wind and tidal turbines have seen increasing interest from academia, industry and government bodies, during recent years, as offshore sites present huge energy potential. The new engineering challenges presented by these technologies, together with the difficulty to undertake experimental test under offshore environments, have raised the interest on Computational Fluid Dynamics (CFD) to design appropriate turbines and blades, understand fluid flow physical phenomena associated with offshore environments and predict power production,
among others.
This book encompasses novel CFD techniques to compute offshore wind and tidal applications. All the included papers have been presented at the 11th World Congress on Computational Mechanics (WCCM XI) organised together with the 6th European Conference on Computational Fluid Dynamics (ECFD VI) in Barcelona 2014. The book includes contributions of researchers from academia and industry.

- by adeline Montlaur and +1
- •
- Computational Fluid Dynamics, Fluid Mechanics, Wind Energy, Tidal Stream Energy

It is fact that we are in the world where almost 80%
of the demanding energy is furnished by coal, oil, gas and hydro
power plant. Now this is a time for renewable energy resource to
fulfil our country needs.Pakistan nearly consists of 1545 km of
coastal length. We can generate electricity through different
method as world is utilizing this energy. Now it’s time to
implement some modern technique and expertise on these
explored sites to generate electricity. Harnessing Tidal energy is
one the modern techniques.In this study we compare small scale
model with large creek. by using our simulation model we can
generate 200 MW at 30% efficiency. Using modern techniques
and efficient turbine installation can increase sites efficiency.We
explore three of these sites but there are many sites available to
harness tidal energy. In this study the complete design to install
number of turbines and length for installing turbines is
illustrated.

- by amir shahbaz
- •
- Hydrography, Tidal turbine, Hydrographic Surveying

This thesis talks about the development, design, and Evaluation of a horizontal-axis hydrokinetic rotor using NACA (National Advisory Committee for Aeronautics), as well as NREL (National Renewable Energy Laboratory) selected profiles. Different profile’s configuration along the blades of the propeller are used in order design these rotors. These
configurations are assessed in terms of: efficiency, structural integrity, and the possibility of generating cavitation, all this under strict conditions of operation. In order to select the design, which allows determining the most suitable configuration, in other words, the configuration
that most closely fulfills the requirements of the established design, an optimization process has been defined.

- by Claudio Troncoso
- •
- Tidal turbine

This work investigates the performance of ducted wind turbines (DWTs) through the axial momentum theory (AMT) as well as through a semi-analytical approach. Although the AMT points out that the duct thrust plays a key role in the enhancement of the power extraction, it does not allow for the evaluation of the flow field around the duct. For this reason, a semi-analytical model is also used to investigate the local and global features of the flow through a DWT. In comparison to the AMT, the proposed semi-analytical method can properly evaluate the performance of the device for each prescribed rotor load distribution and duct geometry. Moreover, in comparison to other linearised methods, this approach fully takes into account the wake rotation and divergence, and the mutual interaction between the turbine and the shroud. The analysis shows the opportunity to significantly increase the power output by enclosing the turbine in a duct and that the growth in the duct thrust has a beneficial effect onto the device performance. Finally, some insights on the changes occurring to the performance coefficients with the rotor thrust and the duct camber are obtained through a close inspection of the local features of the flow field.

- by Marcello Manna and +1
- •
- Wind Energy, Tidal Stream Energy, Wind Engineering, Wind Energy (Engineering)

h i g h l i g h t s " A new series of bi-directional HATT rotors was developed. " A generic wind/tidal turbine rotor design and optimization procedure was developed. " An unsteady, time-domain, and efficient panel method was developed and validated. " The code finished over 15,000 runs in 3 months while a RANS CFD will take 50 years. " A 53% power efficiency was achieved to produce extra energy of 1230 MW h/year. a b s t r a c t A series of bi-directional horizontal axis tidal turbine (HATT) rotors was prototyped. The geometry and motion parameters of the turbine series cover a wide range of tidal turbine operating conditions targeted to the tidal flow speed probability distribution of the Bay of Fundy, NS Canada. A generic yet novel wind/ tidal turbine rotor design and optimization procedure was developed and used for the optimization process. In the process, optimum annual energy production, as a benchmark, was obtained and used for comparison by taking into account both rotor hydrodynamic power production performance characteristics and annual tidal inflow speed probability distribution. The diameter of the full-scale bi-directional HATT rotor series developed is 20-m. Optimum values of various variables were obtained for maximum annual energy production. These optimum values include: uniform pitch-diameter-ratio (p/D) distributions, nominal pitch values with different curve forms of non-uniform p/D distributions, shaft rotational speeds under fixed rotor diameter, diameter at fixed tip-speed-ratio (TSR), a combination of optimum shaft speeds at corresponding inflow speeds and optimum uniform p/D distribution at a fixed rotor diameter, number of rotor blades at fixed chord length, rotor solidity at fixed number of blades, and the combination of number of blades and solidity for both optimum constant pitch distribution and optimum linear pitch distribution. For the 20-m bi-directional HATT, a substantial improvement in power coefficient C pow was obtained, from 0.28, as a result of the primary optimization process (for both optimum uniform p/D distribution and shaft speed n), to the final maximum of 0.43. This corresponds to a 56% increase in annual energy production of 1230 MW h, from 2188 to 3418 MW h, an improved energy production equivalent to the energy generated from 600 tonnes of coal (at 2 kW h per 1 kg coal from a standard thermal power plant). The annual energy production from the optimized 20-m bi-directional HATT before the deduction of mechanical and electrical conversion loses, is 3418 MW h, equivalent to the electric energy generated from 1550 tonnes of coal.

- by Neil Bose
- •
- Engineering, Economics, Tidal turbine, Tidal power

— This paper investigates the effects of Tidal Energy Converter (TEC) array size at a tidal channel on flood/ebb discharges at multi-inlet coastal lagoon by applying numerical modelling. The paper presents a case study for the Faro-Olhão inlet in the Ria Formosa (Portugal), a potential site for tidal in-stream energy extraction. Arrays of up to 11 rows with 5 TECs each were studied to assess impacts on inlets discharges changes. For the particular cases assessed the results show that tidal energy extraction will have a greater impact on Ancão and Armona inlets discharges together with the Faro-Olhão inlet. Future work is directed to include impacts on sediment dynamics and optimise TEC array size as a function of multiple design variables subject to environmental constraints.
Keywords— Tidal stream energy, hydrodynamic modelling, flood/ebb discharges impact, array size, multi-inlet coastal lagoon.

- by Eduardo González-Gorbeña and +1
- •
- Marine Renewable Energy, Tidal Stream Energy, Tidal Stream Turbine Modelling, Tidal turbine

 There are many areas of Europe in which extreme tidal currents are observed.

- by Mahrez AIT and +1
- •
- Composite Materials and Structures, Damage Mechanics, Tidal turbine, Hydrodynamics

A metamodel simulation based optimisation approach for the tidal turbine location problem is introduced. The method comprises design of experiments, computational simulations, metamodel construction and formulation of a mathematical optimisation model. Sample plans with different number of data points are used to fit 2nd and 3rd order polynomial as a function of two design parameters: longitudinal and lateral spacing, with a view to approximating the power output of tidal turbine farms with inline and staggered layouts, each Aquatic Science and Technology ISSN 2168-9148 2015 34 of them with a fixed number of turbines. The major advantage this method has, in comparison to those reported in the literature, is the capability to analyse different design parameter combinations that satisfy optimality criteria in reasonable computational time, while taking into account complex flow-turbine interactions.

- by Paulo Rosman and +1
- •
- Renewable Energy, Marine Renewable Energy, Tidal Stream Energy, Design of Experiments

Abstract
The renewable energy route map for Wales outlines ambitious targets for 50% renewables by 2025. The Welsh coast, subject to tidal ranges of the order of 13m and tidal flows in excess of 3 m/s, is thus in an ideal position to
significantly contribute to these targets. Tidal stream energy is an emerging energy sector and a relatively small number of devices are at various stages of development in Wales. However, before such demonstration devices or
arrays can be applied at a larger scale, a number of consents and permissions must be obtained to ensure safe and environmentally responsible deployment. This paper describes the multidisciplinary work that has been undertaken on an area of ocean that could be used for the
deployment of a tidal stream turbine. The paper aims to put the scientific work undertaken into the context of device deployment in a complex marine environment and to provide an overview of the surveying and modelling
required for the deployment of a single demonstration device off the Welsh coast. The Bristol Channel was chosen as a case study because of its high tidal flows and proximity to national grid connections and support
infrastructure. This paper provides an overview of the research carried out during the project; the details of each discipline will be provided in individual papers by the respective subject authors

- by Roger A Falconer
- •
- Tidal Stream Turbine Modelling, Tidal turbine, Tidal Barrages

Tuning wind and tidal turbines is critical to maximizing their power output. Adopting a wind turbine tuning strategy of maximizing the output at any given time is shown to be an extremely poor strategy for large arrays of tidal turbines in channels. This impatient-tuning strategy results in far lower power output, much higher structural loads and greater environmental impacts due to ow reduction, than an existing patient-tuning strategy which maximizes the power output averaged over the tidal cycle. This paper presents a smart patient tuning strategy, which can increase array output by up to 35% over the existing strategy. This smart strategy forgoes some power generation early in the half tidal cycle in order to allow stronger flows to develop later in the cycle. It extracts enough power from these stronger flows to produce more power from the cycle as a whole than the existing strategy. Surprisingly, the smart strategy can often extract more power without increasing maximum structural loads on the turbines, while also maintaining stronger flows along the channel. This paper also shows, that counter-intuitively, for some tuning strategies imposing a cap on turbine power output to limit loads can increase in a turbine's average power output.

- by Ross Vennell
- •
- Renewable Energy, Tidal Stream Energy, Tidal Stream Turbine Modelling, Tidal turbine

Marine current power is a significant energy resource yet to be exploited for electricity production. Several novel turbine technologies can be found on the market, and new ones emerge every year. This study found that the most popular choice seems to be the axial flow three-bladed turbine, although the industry has not yet converged to one preferred technology. An overview of the turbine technologies is presented with drive train layout for each device, if this information is obtainable. The majority of manufacturers use geared (mechanical or hydraulic) solutions, and an induction or a synchronous generator. The few direct drive systems all use PM synchronous generators. For prototype turbines there is a trade-off between choosing a proven generator technology that is not optimised for the application, and using a prototype machine that may reduce the number of design iterations.

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s−1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime.

- by Paul Evans and +4
- •
- Oceanography, Hydrodynamics (Physics), Hydrography, Coastal Management

Much of the global tidal current energy resource lies in the accelerated flows along narrow channels. These channels have the potential to produce 10s -1000s of MW of electricity. However, realizing 100 MW of a channel's potential is much more complex than installing 100 one MW turbines because large scale power extraction reduces tidal currents throughout the channel, changing the resource. This synthesis and review gives an overview of the issues and compromises in designing the layout of the large tidal turbine arrays required to realize this potential. The paper focuses on macro- and micro-design of arrays. Macro-design relates to the total number of turbines and their gross arrangement into rows, while micro-design adjusts the relative positions of the turbines within a grid and the spacing between rows. Interdependent macro-design compromises balance the total number of turbines, array power output, the power output of each turbine, the loads turbines experience, turbine construction costs, maintaining navigability along the channel and any environmental impacts due to flow reduction. A strong emphasis is placed on providing physical insights about how “channel-scale dynamics” and the “duct-effect” impact on the compromises in array design. This work is relevant to the design of any “large” array which blocks more than 2%-5% of a channel's cross-section, be it 2 turbines in a small channel or 100 turbines in a large channel.

Due to the low current speeds associated with Malaysian tidal currents, Savonius turbine was
chosen as a device in extracting this energy. However, this turbine suffers from poor efficiency. The present paper describes some works carried out to improve the turbine. The effect of speeds on performance was found to be minimal while the use of deflectors improved flow into the rotor and contributes significantly to the coefficient of performance improvement. The use of ducts was also studied, indicating improved flow characteristics.

This book encompasses novel CFD techniques to compute offshore wind and tidal applications. All included papers have been presented at the6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) (ECCM 6) and the 7th European Conference on Computational Fluid Dynamics (ECFD 7)that was held in Glasgow in 2018. The book includes contributions of researchers from academia and industry.

The world is heavily dependent on fossil fuels since most of its energy requirements are fulfilled by conventional methods of burning these fuels. The energy demand is increasing by day with growing population. The energy production by fossil fuels is devastating the environment and survival of life on globe is endangered. The renewal energy technologies are vital to ensure future energy sustenance and environmental issues. Ocean is a vast resource of renewable energy. The technology today makes it possible to extract energy from tides. The growing interest in exploring tidal current technologies has compelling reasons such as security and diversity of supply, intermittent but predictable and limited social and environmental impacts. The purpose of this study is to present a comprehensive review of tidal current technologies to harness ocean energy. The ocean energy resources are presented. The author discusses tidal energy technologies. The tidal current turbines are discussed in d...

- by jawad khan
- •
- Tidal Stream Energy, Tidal turbine, Applied Sciences, Tidal Renewable Energy

Having very strong current on the west coast with up to 10 m tidal range, there are many suitable sites for the application of tidal current power (TCP) in Korea. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. To extract a significant quantity of power, a tidal current farm with a multi-arrangement is necessary in the ocean. The interactions between devices contribute significantly to the total power capacity. Thus, the study of wake propagation is necessary to understand the evolution of the wake behind a turbine. This paper introduces configuration design of horizontal axis tidal current turbine based on the blade element theory, and evaluating its performance with CFD. The maximum efficiency of the designed turbine was calculated as 40% at a tip speed ratio (TSR) of 5. The target capacity of 300 kW was generated at the design velocity, and the performance was stable over a wide range of rotating speeds. To investigate the wakes behind the turbine, unsteady simulation was carried out. The wake velocity distribution was obtained, and velocity deficit was calculated. A large and rapid recovery was observed from 2D to 8D downstream, followed by a much slower recovery beyond. The velocity was recovered up to 86% at 18D downstream.

- by 강희 이
- •
- Tidal turbine, Wind turbine

Abstract: The renewal energy technologies are increasingly popular to ensure future energy sustenance and address environmental issues. The tides are enormous and consistent untapped resource of renewable energy. The growing interest in exploring tidal energy has compelling reasons such as security and diversity of supply, intermittent but predictable and limited social and environmental impacts. The tidal energy industry is undergoing an increasing shift towards diffuser augmented turbines. The reason is the higher power ...

- by jawad khan
- •
- Tidal Stream Energy, Tidal turbine, Applied Sciences, Tidal Renewable Energy

- by nasir mehmood
- •
- Tidal Stream Energy, Tidal turbine, Applied Sciences, Tidal Renewable Energy

In order to avoid a reduction in energy supply for power distribution, it is important to have a control technique to achieve maximum power output from a tidal farm. It is of paramount importance to checkmate the performance of ocean tides inflow dynamics, due to its effect on power generated from a tidal farm. The functional environment of tidal turbines is important for its performance and the recovery of tidal wake. Therefore, an optimization algorithm is proposed using a gradient-based optimization method is used to optimize the minimum power generated from a tidal turbine array of 36 turbines. The minimum power production from a tidal farm with 36 turbines at a tidal speed of 5m/s was optimized to achieve 49.28 MW which is a 76 percent increase. The simulation results and the tidal farm composition were done using Finite Volume Community Ocean Model (FVCOM) software.

- by Daniel Obaleye
- •
- Electrical Engineering, Renewable Energy, Optimization, Tidal turbine

Diffuser-augmented wind-turbines are drawing increasing attention since they can beat the Betz-limit referred to the rotor-area. However, their diffusion is still prevented by some issues including: 1) the attainable power has not yet been shown to be larger than that of an open-turbine with the same frontal-area, 2) the classical analysis methods rely on the one-dimensional-flow and no-tip-gap assumptions whose impact has never been quantified. The paper addresses these two items investigating the potential of ideal diffuser-augmented wind-turbines using a newly-developed Axial-Momentum-Theory approach, and an extended version of a free-wake ring-vortex actuator-disk model. In comparison with similar methods, the novelty of the first approach is that it accounts for the two-dimensional effects and the tip-gap presence. Since this approach cannot evaluate the performance of a turbine for a given duct-geometry, a ring-vortex method is also developed. This is the first low-computational-cost method relying on the exact solution of the inviscid-flow through a uniformly-loaded ducted-turbine with a finite-size tip-gap. It strongly couples the flow induced by the duct and the wake which are modelled as the superposition of ring-vortices. The combined use of axial-momentum and ring-vortex methods leads to the following results. Firstly, it is clearly shown that an ideal diffuser-augmented turbine can extract more power than a Betz disk with the same frontal-area. To strengthen this statement, a new duct geometry with a remarkable value of the exit-area power-coefficient equal to 0.6098 is presented. This value is significantly higher than that of a base-line NACA5415 duct profile, i.e. 0.4800. Secondly, the impact of the one-dimensional-flow and no-tip-gap assumptions is evaluated. It is also shown that the tip-gap has negligible effects. Moreover, the one-dimensional-flow hypothesis has a low impact for high values of the rotor load, while the errors grow up decreasing the rotor thrust.

- by Rodolfo Bontempo and +1
- •
- Wind Energy, Tidal Stream Energy, Wind Engineering, Tidal Stream Turbine Modelling

Despite the large resource of tidal and wave energy, the marine energy industry is still lag-
ging far behind the wind industry. Much of the knowledge required to develop reliable and prof-
itable marine energy systems is available in the wind energy sector. A novel marine energy
technology developed by Ecofys Netherlands BV, dubbed the C-Energy project, uses the
knowledge of both vertical and horizontal axis wind turbines by combining a Darrieus and a
Wells type rotor. The use of these two unidirectional rotor types enables the system to extract
energy from both tidal currents and waves. During the summer of 2009 the 30kWp turbine was
installed as a demonstration project in the Westerschelde River, The Netherlands.
With use of blade element momentum theories for horizontal and vertical axis turbines, a
hydrodynamic model has been developed for this turbine to predict its performance and the
loads on the turbine blades. Measurements from the C-Energy demonstration project have been
used to validate this computational model. A finite element model provides the strain data re-
quired for the validation process and is also used to estimate the fatigue life.
The combination of the hydrodynamic model and the finite element model gives reliable es-
timates for the occurring stresses. With this result, the structural design of the turbine blades
can be optimized for any site condition and expected life time.

- by Turaj Ashuri
- •
- Mechanical Engineering, Structural Engineering, Fluid Mechanics, Renewable Energy

VI International Conference on Computational Methods in Marine Engineering. Marine 2015, Rome, Italy.

Tidal energy is on the verge of commercial viability and full scale prototypes are meeting the challenges of the marine environment. The primary focus of the sector has concerned Horizontal Axis Tidal Turbines (HATTs); comprising a turbine supported by a tubular stanchion operating on a bi-directional, or yaw system. The direction of tidal flow, however, varies over the ebb or flood phases of a tidal cycle. This pa-per utilises tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), a macrotidal strait and proposed HATT installation site and combines with Computational Fluid Dynamics (CFD) to assess the impact of misalignment between a HATT and its surrounding free stream velocity. The majority of the veloci-ties within the northern area of Ramsey Sound tend to fall within a misalignment of ±20° for velocities greater than the economic viable threshold of 2 ms-1. However, bathymetry and coastline configuration influence both flow magnitude and direction. At the outer margins for the Sound, the velocities are acted upon by various promontories, reefs and shelving areas, which deflect and retard the flow, resulting in a flow direction greater than 20°, particularly towards the outer edges of the Sound. Utilising field data for numerical simulations will help inform the industry and increase investor confidence in this technology, whilst avoiding costly scaled ex-perimentation. It was found that an axial flow misalignment of ±10° results in approximately a 7% reduction in peak power, 3% in peak torque and 5% in peak thrust. The axial wake recovery length was shorter for the ±10° cases, recovering to 90% by 7D downstream, as opposed to 10D downstream for the aligned turbine.

- by Tim O'Doherty and +3
- •
- Mechanical Engineering, Oceanography, Tidal Stream Energy, Marine Science

A proposal is made for the use of a traditional stream waterwheel suspended between two floating catamaran NPL series demi-hulls as means of generating electrical power. Two prototype devices, of lengths 1.6m and 4.5m, have been developed, constructed and tested. It was found that the concept is sound although greater investment is required with regards to the materials and both hydrodynamic and aerodynamic design of the waterwheel to ensure an economically viable system. The work presented concentrates on practical aspects associated with design, construction and trial testing in Southampton water of the 4.5m prototype. The relatively low cost, ease of deployment, and the fact that conventional boat mooring systems are effective, combine to make this an attractive alternative energy solution for remote communities.

- by cat fahmi
- •
- Mechanical Engineering, Civil Engineering, Structural Engineering, Renewable Energy

Researchers and engineers around the globe are striving to improve green energy technologies. Among green energy technologies, diffuser augmented tidal turbines are attracting focus due to enormous potential for producing energy. The power output by a tidal turbine is directly proportional to the cube of velocity of incoming fluid flow. Thus, even a minor increase in velocity considerably increases the power output. The diffuser helps accelerate the velocity of incoming fluid flow. Hence, the efficiency of the turbine is significantly increased by using a diffuser. It is challenging to accelerate the incoming flow by a diffuser due to its shape, geometry and fabrication limitations. The diffuser design requires great deal of innovation and time investment. The research community is investing considerable time and financial resources in this arena. However, limited research results are available for diffuser augmented tidal turbines due to their emerging nature, large and costly research & development setup, startup cost and proprietary issues. The purpose of this paper is to present the numerical simulation of 2D model of diffuser for tidal turbine. Numerical simulation results of velocity profile for fifteen models with different mesh sizes is presented in detail. The effect of mesh density on coefficient of velocity is discussed. Predicted results are then compared to experimental results and found in reasonable agreement. The research is essential for utilizing CFD tools for diffuser design for tidal turbine.

The dependence on fossil fuels for energy production has come to an alarming stage. Energy demand continues to increase with growing population. Consequently fossil fuel reserves are continuously draining and the world is confronted with their extinction in near future. Burning fossil fuels has also put our environment on the edge of destruction. Energy resource depletion and devastation of environment has compelled researchers to explore renewable and green resources of energy. Tidal current technologies have salient advantages such as cleaner than fossil fuels, intermittent but predictable, security and diversity of supply, and limited social and environmental impacts. Tidal current technologies continue to develop and expand, yet needs time to prove their full potential. This paper presents the background for shift towards renewable energy, especially tidal energy. It outlines classification of ocean energy resources and tidal energy. This paper also documents today’s popular tidal current devices and reports on the present status of ocean energy development.

Concern over global climate change has led policy makers to accept the importance of reducing greenhouse gas emissions. This in turn has led to a large growth in clean renewable generation for electricity production. Much emphasis has been on wind generation as it is among the most advanced forms of renewable generation, however, its variable and relatively unpredictable nature result in increased challenges for electricity system operators. Tidal generation on the other hand is almost perfectly forecastable and as such may be a viable alternative to wind generation. This thesis paper shows the important of Tidal power over other sources and it’s generation using DFIG. This thesis is analyzed based on the following configuration; A 6 MW tidal power site having four, 1.5 MW tidal turbines connected to a 25 kV distribution system which ensures power to a 120 kV grid through a 30 km, 25 kV feeder line. A 2300V, 2 MVA plant with a motor load (1.68 MW induction motor at 0.93 pf) and of a 200 kW resistive load which is also linked into the same feeder. Both tidal turbine and motor is attached to a protection system which was used to monitor voltage, current and machine speed. DFIG DC link voltage is also monitored. Tidal turbines used an induction generator having a wound rotor and an AC/DC/AC IGBT based PWM converter. The stator winding is also linked directly to the 50 Hz grid and the rotor is fed at variable frequency through the AC/DC/AC converter. DFIG technology was also used for extraction of maximum energy from the tides for low tidal speeds through optimization of turbine speed, while lowering turbine mechanical stresses during heavy tides. The turbine’s optimum speed used to produce maximum mechanical energy for a given tidal speed which is directly proportional to tidal speed. The rotor runs at sub synchronous speed for tidal speeds will also be lowered at 10 m/s and at super synchronous speeds for higher tidal speeds. The simulation of 6MW tidal site was carried out for normal condition and at different types of faults introduced on the 25kV line. They are carried out as follows; a) For normal conditions, at a tidal speed of 13m/s. b) For a phase A to ground fault in the 25 kV line for t=5 to 5.1 seconds. c) For a phase A and B fault in the 25 kV line t=5 to 5.1 seconds. d) For a phase A and B to ground fault in the 25 kV line t=5 to 5.1 seconds. e) For a symmetric fault in the 25kV line for t=5 to 5.1 seconds

Computations of the blade loading and the local flow field around the Model Rotor Experiments In Controlled Conditions (MEXICO) rotor are presented using an actuator line method, implemented within the open source code OpenFOAM. The nacelle and near wake mesh refinement are shown to have little influence on the computed blade loads but a significant impact on the near wake flow field. In addition, the blade loads and near wake flow field calculated with 3 different distributions of the Gaussian smearing parameter ǫ are compared with experimental measurements. Local chord and lift coefficient scaled smearing distributions are shown to yield a significant improvement in the representation of the computed tip vortices and also a small improvement in the blade loading prediction, when compared with a spanwise constant smearing distribution. Despite these improvements in performance prediction, the performance of the rotor is shown to be more strongly influenced by the tip correction fac...

- by Aidan Wimshurst
- •
- Geology, Computational Fluid Dynamics, Tidal Stream Energy, Rotordynamics

Tulisan ini menjelaskan tentang sistem instrumentasi yang dapat diaplikasikan pada turbin arus pasang surut laut.
Sistem instrumentasi pada turbin arus pasang surut laut ini meliputi seperangkat sensor pembaca parameter kinerja
turbin, perekam data untuk mencatat dan menyimpan data yang dihasilkan sensor, dan sistem telemetri untuk mengirim
data ke operator turbin. Sistem instrumentasi tersebut digunakan agar kinerja turbin arus pasang surut laut yang
dipasang di suatu tempat dapat dipantau dari jarak jauh secara kontinu dan real time.Tujuan penelitian instrumentasi
pengukuran kinerja turbin arus pasang surut laut adalah untuk merancang dan menguji sistem instrumentasi dalam
mencatat, menyimpan, dan mengirimkan data parameter kinerja turbin. Pengujian dilakukan di perairan Muara Karang,
Jakarta pada 15 November - 25 Desember 2012. Data parameter kinerja turbin yang diambil meliputi teganganlistrik
generator, arus listrik generator, putaran turbin, serta tegangan baterai. Data tersebut akan tersimpan pada perekam data
dengan kerapatan data(sampling rate) setiap 8 detik. Data tersebut juga akan dikirim ke operator turbin, dengan waktu
pengiriman data setiap satu jam, yang berisi data parameter kinerja turbin setiap 5 menit. Dari data hasil uji coba, dapat
dibuat grafik hubungan antara putaran turbin dengan tegangan generator dan putaran turbin dengan daya generator.
Pada grafik putaran turbin dengan tegangan generator dan putaran turbin dengan daya generator, diperoleh hasil bahwa
secara umum tegangan generator dan daya generator akan naik seiring dengan kenaikan putaran turbin, dengan
kenaikan bersifat fluktuatif. Dari data pengujian, dapat disimpulkan bahwa perangkat keras instrumentasi turbin arus
pasang surut laut telah berhasil dibuat dan dapat berfungsi dengan baik dalam mencatat, menyimpan, dan mengirimkan
data parameter kinerja turbin.
Kata kunci: instrumentasi, telemetri, turbin

- by Hadhi Nugroho
- •
- Tidal turbine, Electronics and Instrumentation

Hydrokinetic turbines can recover the kinetic energy of marine or river currents. The Hydrofluv research and development project (funded by FUI with the support of the Tenerrdis, DERBI and DREAM clusters) aims to demonstrate the feasibility and acceptability of vertical-axis and transverse-flow turbines. Members of the Hydrofluv project, Hydroquest, FOC Transmissions, ERNEO, Biotope, EDF, Artelia and the LEGI laboratory are working both on improving the machines and on a more complete commercial offer (administrative authorizations, impact studies and profitability). Numerical modeling conducted by the LEGI laboratory and Hydroquest has led to the definition of the machine’s characteristics and main parameters. The incorporation of these terms in a larger three-dimensional numerical model has enabled other parameters to be analyzed, such as head loss around the machine (variation in the free surface and current), the interactions between machines and hydrosedimentary impacts. Several academic studies have validated the developments made by comparing the models. The practical application concerns a study of the prototype scheduled to be placed in the Loire at Orleans at the end of 2014. The model accurately represents the impacts of a machine on its environment and has proved to be highly representative compared to more specific local models, which are for the moment two-dimensional and require longer calculation times.

- by Olivier Bertrand and +1
- •
- Tidal Stream Energy, Tidal turbine, Renewable Energy (Marine hydrokinetics)

Computations of the blade loading and local flow field around the Model Rotor Experiments In Controlled Conditions (MEXICO) rotor are presented using an actuator line method, implemented within the open source code OpenFOAM. The nacelle and near wake mesh refinement are shown to have little influence on the computed blade loads but a significant impact on the near wake flow field. In addition, the blade loads and near wake flow field calculated with 3 different distributions of the Gaussian smearing parameter are compared with experimental measurements. Local chord and lift coefficient based smearing distributions are shown to yield a significant improvement in the representation of the computed tip vortices and also a small improvement in the blade loading prediction, when compared with a spanwise constant smearing distribution. Despite these improvements in performance prediction, the performance of the rotor is shown to be more strongly influenced by the tip correction factor, where considerable improvement is still required before actuator line methods can represent real rotors with sufficient accuracy.

- by Gerald Muller
- •
- Mechanical Engineering, Civil Engineering, Structural Engineering, Renewable Energy