Marine Turbine Research Articles

Experimental analysis of the shear flow effect on tidal turbine blade root force from three-dimensional mean flow reconstruction.

In the main tidal energy sites like Alderney Race, turbulence intensity is high and velocity fluctuations may have a significant impact on marine turbines. To understand such phenomena better, a three-bladed turbine model is positioned in the wake of a generic wall-mounted obstacle, representative of in situ bathymetric variation. From two-dimensional Particle Image Velocimetry planes, the time-averaged velocity in the wake of the obstacle is reconstructed in the three-dimensional space. The reconstruction method is based on Proper Orthogonal Decomposition and enables access to a representation of the mean flow field and the associated shear. Then, the effect of the velocity gradient is observed on the turbine blade root force, for four turbine locations in the wake of the obstacle. The blade root force average decreases whereas its standard deviation increases when the distance to the obstacle increases. The angular distribution of this phase-averaged force is shown to be non-homogeneous, with variation of about 20% of its time-average during a turbine rotation cycle. Such force variations due to velocity shear will have significant consequences in terms of blade fatigue. This article is part of the theme issue 'New insights on tidal dynamics and tidal energy harvesting in the Alderney Race'.

Incorporation of Carbon Nanotubes in Silicone Matrices to Improve Wave Energy Converters Performance’s

The marine energies constitute a strategic sector of the renewable energies to diversify and complete the energy mix. At present, offshore wind energy and the marine turbines are the main approaches. In stages of more upstream research, demonstrators of wave energy converters (WEC) based on a hydraulic conversion have difficulty in developing because of problems of reliability. The harnessing of this field of wave energy could find a new impetus thanks to the development of concepts in break based on innovative and economically technologies: electroactive polymers (EAP). Based on the distortion of an EAP which plays the double role to get the wave energy and to convert it in electrical energy, these generators open interesting perspectives of development because they free themselves from mechanical absorber at the origin of numerous failures of the WEC.Among challenges identified for the realization of performant EAP-WEC, the availability of more successful materials to convert the mechanical energy is at the heart of the concerns. Starting from carbon nanotubes nano-object to end in a viable mechanical structure, we have developed methods and processes which will be implemented in the future technologies of the wave energy but also aim at the manufacture of a functional prototype of laboratory.Our strategy is based on the incorporation of nano/micro hybrid reinforcements of carbon nanotubes within a silicone matrix in order to realize (i) flexible conductive electrodes and (ii) to improve the properties of the active material. A parylene coating of carbon nanotubes has demonstrated to reduce percolation and thus an improvement of the dielectric strength of the active silicone matrix. Finally, mechanical – electrical conversion is undoubtedly improved by this approach as confirmed by mechanical tests, dielectric spectroscopy and dielectric strength.Acknowledgements : The authors thankfully the national French program ANR SEASEA for funding.

Performance of a hydrokinetic turbine using a theoretical approach

Regarding the interest in renewable energies, several sources of energy production have been studied and still under improvement. In this work, we are interested in harnessing marine energy currents exploiting the hydrokinetic turbines. The purpose of this study is to provide a comprehensive assessment of the hydrodynamic loads of a 3-blade horizontal-axis marine turbine using a rotor model adapted to the Moroccan potential. For that, the Blade Element Momentum (BEM) is used to calculate the hydrodynamic loads, to estimate the energetic performance, and to determine the blade optimal parameters for a turbine. In additions, the resulting equations are solved in order to obtain the hydrodynamic loads. For validation, a comparison of pressure coefficients along the chord length was made with the results of the Blade software. The Computations were accomplished for a specific NACA profile.

Optimal Control Design of Generator Systems for Marine Current Turbine Applications Using Economic Model Predictive Control

Economic Model Predictive Control (EMPC) has recently been researched in many areas, especially in terms of energy. The development of advanced control algorithms has promoted the cost reduction of marine energy generation and improved the efficiency and reliability of marine current turbines. By reducing the loss on the marine turbine system, better economic indicators can be achieved. Based on this, the maximum marine power can be captured such that the entire marine current turbine system can obtain maximum economic benefits. In this paper, it is mainly based on the economic model predictive control framework to optimize the ocean current turbine power generation system. The system index is directly used for the objective function of the EMPC problem, as EMPC has the advantage of dealing with system constraints and cost functions. Compare the performance of the proposed control framework with the performance of commonly used basic MPC controllers, simulation results show that the proposed controller can reduce the loss of the turbine system and gearbox, indicating that more energy capture can be obtained for the system to achieve better economic effects.

Adaptive backstepping control for maximizing marine current power generation based on uncertainty and disturbance estimation

The renewable energy from marine currents is highly promising as a clean, reliable and predictable energy source for the next-generation electricity generation. Therefore, the paper focuses on the design and implementation of the high-efficiency control for maximizing the marine current power generation and hence an adaptive backstepping controller with uncertainty and disturbance estimation is proposed for a generic horizontal marine turbine. The turbine design principle and dynamics modelling are presented and then the control problem is formulated. Consequently, the controller is designed to be composed of a marine turbine speed control loop and a q-axis current control loop while the uncertainty and disturbance is estimated and compensated. A swell filter is also incorporated into the control loop to smooth generator power fluctuations. The stability of the proposed control is verified via the Lyapunov synthesis and all the tracking errors are guaranteed to converge to zero asymptotically. The proposed control is verified and the test results indicate that the generator produces obviously more power (up to 30% more power) when using the proposed control in comparison with a conventional backstepping control.

Incorporation of a Non-Constant Thrust Force Coefficient to Assess Tidal-Stream Energy

A novel method for modelling tidal-stream energy capture at the regional scale is used to evaluate the performance of two marine turbine arrays configured as a fence and a partial fence. These configurations were used to study bounded and unbounded flow scenarios, respectively. The method implemented uses turbine operating conditions (TOC) and the parametrisation of changes produced by power extraction within the turbine near-field to compute a non-constant thrust coefficient, and it is referred to as a momentum sink TOC. Additionally, the effects of using a shock-capture capability to evaluate the resource are studied by comparing the performance of a gradually varying flow (GVF) and a rapidly varying flow (RVF) solver. Tidal-stream energy assessment of bounded flow scenarios through a full fence configuration is better performed using a GVF solver, because the head drop is more accurately simulated; however, the solver underestimates velocity reductions due to power extraction. On the other hand, assessment of unbounded flow scenarios through a partial fence was better performed by the RVF solver. This scheme approximated the head drop and velocity reduction more accurately, thus suggesting that resource assessment with realistic turbine configurations requires the correct solution of the discontinuities produced in the tidal-stream by power extraction.

Hydrodynamic design of rotor blades of marine current turbines

The utilisation of marine current turbines with horizontal axis for electrical power production offers a sustainable and clean option to augment traditional energy technologies and enhance the expansion of renewable energies in the marine field. Some prototypes of these turbines are now available and operating. The advantages of tidal currents for renewable energies when compared with wind resources are that sea water is about 800 times denser that air (and the extracted energy is proportional to density) and the nature of currents that results in a more predictable resource than wind resources. But these advantages set certain limitations and technical problems, some of them related with the hydrodynamic design of rotor blades since the design of a marine turbine is some kind different of the techniques used for wind turbines. Methodologies need be established to describe the physical and operational performance of the turbines, allowing their design to be investigated and performance evaluated. This paper describes the hydrodynamics of rotor design that is projected in order to extract the maximum power from the tide. The blade element momentum theory is used for the rotor modelling, different aspects and limitations of this approach when applied to marine rotor design are commented, and examples are presented.

An improved control-limit-based principal component analysis method for condition monitoring of marine turbine generators

The safe operation of marine turbine generators is a crucial concern in industries and academics. It is always important to monitor the health status of marine turbine generators. The lubricant oil usually carries abundant information on the turbine operation conditions. Various oil parameters of the turbines have been used in the existing monitoring systems. However, many of them conflict with each other by contrary detection results. Hence, it should eliminate the redundant oil parameters for efficient condition monitoring. Although many research studies addressed the redundant feature reduction issue using principal component analysis (PCA), PCA is designed for features with a linear relationship, which is not the case in marine turbine generator monitoring. This paper proposes a new nonlinear analysis method, the improved control-limit based PCA, to extract distinct failure indicators from the oil parameters of marine turbine generators. The contribution of this method is that the Hotelling statistic and Q statistic are combined to calculate a fixed control limit for PCA. The ability of the improved PCA to dealing with nonlinearity has been significantly enhanced by the proposed method. Experimental validation demonstrates that the extracted failure indicator using the proposed method is more effective than existing monitoring indexes with respect to fault detection accuracy.

Large Eddy Simulation of Flow around Marine Turbine

Renewable energy usually refers to those natural resources of energy whose availability does not decrease with its usage. Various sources of renewable energy are there such as solar energy, wind energy, marine energy. The Marine Current Turbine (MCT), is an exciting proposition for the extraction of tidal and marine current power. CFD simulation is being widely used in the research on marine current turbines. The present research also represents a step in this direction. Solution of incompressible unsteady Navier-Stokes (N-S) equations is required in the numerical simulation of flow around MCT. Large Eddy Simulation (LES) has been opted which fully resolves the energetic turbulent flow structures and models only the sub-grid scale turbulence. IB method has been used to enforce the boundary conditions on complex geometry. Due to computational limitations we have been able to perform only a coarse grid LES of the marine turbine for specific operating conditions. Nevertheless, the results provide insights into the flow structures around the marine turbine. Analysis shows that the effect of vorticity diminishes after 11R from the turbine rotor blade. However, the velocity deficit region remains until the end of the domain used in our simulations which is 10D distance downstream of the rotor blades.

Efficiency Analysis of Methanol Usage for Marine Turbine Power Plant Operation Based on Waste Heat Chemical Regeneration

Efficiency Analysis of Methanol Usage for Marine Turbine Power Plant Operation Based on Waste Heat Chemical Regeneration

Development of ocean current marine turbine

Owing to huge amount of kinematic energy, ocean current has the potential to be a base power source, it’s also source for huge and steady flow energy. Moreover, Japan has potential ocean area -which can be used for large scale power production. One example is Kuroshio which is one of the strongest ocean current. However, since the flow velocity of a steady ocean current is low compared with the velocity of the tidal current, development of a system which can efficiently generate power in the low flow velocity is needed. Prototype testing is complicated because the area where Kuroshio current located is far from on shore. In this study, development of blades, water bearing, and a drive train suitable for a generation of electrical energy at the low flow velocity and towing test was carried out.

Large eddy simulation of a marine turbine in a stable stratified flow condition

The present study focuses on the evaluation of the impact of marine stable stratification on turbine performance and wake characteristics. Stratification is usually present in regions where marine turbines are installed; this is the case of estuarine basins and shelf seas. Stratification influences the turbine efficiency and rotor wake development; on the other hand, the turbine wake may increase vertical mixing and reduce stratification in the water basin. To evaluate mutual interaction between a marine turbine and vertical stratification, two types of stable stratified conditions are simulated, a weak and a strong stratified condition, respectively. The numerical analysis is carried out using Large Eddy Simulation (LES) coupled with a Blade Element Momentum (BEM) turbine module. The capability of the model in reproducing power and thrust characteristics of a turbine is proved by comparison with experimental data. Results show that stratification has a remarkable impact on wake development: concerning power performance, as the stratification intensifies, it increases due to the growth of streamwise velocity; meanwhile, the power coefficient slightly increases. Also, the recovery of wake velocity deficit is faster in case of strong stratification, thus reducing the extension of the downward region affected by the presence of the turbine. Results also show that the turbine modifies stratification, specifically the mixing effect is higher in case of strong stratification; this phenomenon is ascribed to the strong vertical meandering of the wake and the development of an eddy that overturns high-density fluid over lower-density fluid.

Effect of Wake Alignment on Turbine Blade Loading Distribution and Power Coefficient

This paper describes the use of a lifting line model in order to determine the optimum loading on a marine turbine's blades. The influence of the wake and its geometry is represented though the use of a full wake alignment model. The effects of viscous drag are included through a drag-to-lift ratio. Results for different number of blades and tip speed ratios are presented. Various types of constraints are imposed in the optimization method in order to avoid abrupt changes in the designed blade shape. The effect of the constraints on the power coefficients of the turbines is studied. Once the optimum loading has been determined, the blade geometry is generated for a given chord and camber distributions. Finally, a vortex-lattice method is used to verify the power coefficient of the designed turbines.

Hydrodynamic Assessment of a Dual-Rotor Horizontal Axis Marine Current Turbine

The hydrodynamic performance of a dual-rotor horizontal axis marine turbine (HAMCT) is investigated for the power gain in operating the rear rotor without blade-pitch control. This kind of turbine can be advantageous for a rectilinear tidal current of reversing directions, where each rotor blade is optimally fixed-pitched towards its upstream velocity. The blade element momentum (BEM) method is coupled with the Park wake model. A generic three-blade turbine is shown to gain up to 20% in the coefficient of power CP as relative to the front rotor CP when operating the rear rotor at the same tip speed ratio (TSR) as the front one, gaining overall CP up to 0.55. Analytic model is derived to backup the estimate of power gain. Plots for turbine performance variation with TSR and profile hydrodynamic efficiency are given, and analysed for lab and small-medium size turbines.

Accelerated life testing study of a novel tidal turbine blade attachment

This paper describes the setup and some results of an accelerated life testing study of a tidal turbine blade attachment, which involved high-cycle fatigue testing of a tidal turbine subsystem at the Large Structure Laboratory of the National University of Ireland Galway (NUI Galway). Tidal turbines are in an early stage of development, which implies that there is no standard design and many different approaches are emerging in the market. The subsystem described in this paper is a 3/8 scaled down part of a 10-blade hubless turbine, developed by OpenHydro, a company specialising in the design, manufacture, installation, and maintenance of marine turbines generating renewable energy from tidal streams. The subsystem consists of a blade and a sector of the rotating ring. The sample was installed on an existing 10 m × 6 m × 6 m reconfigurable test frame and was loaded with a servo-hydraulic actuator controlled by an advanced software system, which allowed for an accurate sinusoidal load-controlled high-cycle fatigue test. The sample was loaded at four different levels to accumulate damage representative of a typical tidal turbine deployment life. The main objective of the test was to analyse the structural behaviour of the attachment system solution (blade-rotating ring) under fatigue load, particularly the internal structural welds, and to validate previously developed numerical models. To address all the requirements and to obtain valuable data, a large experimental test was set up. A total of 110 channels in a multi-channel data acquisition system were used to simultaneously acquire strain, displacement, and load data. Accurate measurements of temporal deformations and movement in a 3D field at the rear side of the ring were also acquired using a Digital Image Correlation system. The mechanism of failure was expected to be fatigue crack propagation at locations pre-determined in a structural analysis of the system.

Marine Turbine Hydrodynamics by a Boundary Element Method with Viscous Flow Correction

A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. For this purpose, semi-analytical trailing wake and viscous flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tends to reduce in cases where turbine blades operate in off-design conditions.

Simulation model of darrieus turbine using software CFD (Computating Fluid Dinamyc) in Bedono Village of Demak district

One area in Central Java that has the potential to develop a tidal power plant is the village Bedono, of Demak regency. In the area there are places with sea currents accelerating as sea water moves towards the mouth of the river which is then used for this study site with coordinates 6 ° 55'29.0 "S 110 ° 29'11.4" E. In this study, the Darrieus type H type offshore turbine, developed by NACA (National Advisory Committee for Aeronautics), is NACA 0018 which is a special blade for marine turbine applications. Simulation using Computational Fluid Dynamics (CFD) program with the condition of research location such as sea depth, sea water velocity, gravity force and seawater period used as the variable. From the simulation results using CFD obtained the highest sea water flow velocity in Bedono village occurred at 14-16 at 2.5m / sec and the lowest at 22-24 at 0,530m / s. The greatest boost of simulation results was obtained at the highest current velocity of 2.5 m / s from 631,115N and torque was 315,558 Nm.

Marine turbine system directly connected to electrical grid: Experimental implementations using a nonlinear and robust control

This paper deals with real-time implementations of a nonlinear and robust control applied on a marine turbine system. For the experimental validation which uses real data from Raz de Sein site (Brittany, France), the DC motor drives a wound rotor synchronous generator. A computer pilots this DC motor in order to stand in for the marine turbine behavior. Experimental results show the control successful of both outputs (terminal voltage and speed) making possible direct connection to electrical grid. In addition, we verify the robustness properties of the complete system under hard mechanical and electrical perturbations. Finally, a comparative study highlight the proposed control performances compared with conventional AVR-PSS which is one of the most widely adopted controller in industry for electrical grid stabilization.

Inverse method for hydrodynamic load reconstruction on a flexible surface-piercing hydrofoil in multi-phase flow

An inverse method for reconstruction of the in situ steady-state hydrodynamic load distribution using limited strain measurements is developed and validated on a rectangular, flexible surface-piercing hydrofoil in fully-wetted (FW) and fully-ventilated (FV) flows. The hydrofoil is used as a canonical proxy to more complex hydrodynamic lifting surfaces such as marine propulsors and turbines. The approach involves using a forward fluid–structure interaction (FSI) model to predict the hydroelastic response for given operating conditions. The inverse problem is solved as an optimization problem to determine unknown operating conditions. The forward FSI model consists of a nonlinear lifting line (LL) fluid solver with considerations for free surface, ventilation, and viscous effects, and a solid finite element method (FEM) solver using 1-D beam elements representing the spanwise bending and twisting deformations.The coupled FSI model was validated using data collected during towing tank experiments at the University of Michigan. Predictions of the lift and moment coefficients, as well as spanwise bending and twisting deformations agreed well with experimental results in FW and in FV flows.The inverse problem is formulated as an optimization problem to determine the unknown operating conditions that will minimize the difference between the measured and predicted deformations. To avoid non-uniqueness problems often encountered by inverse problems, a dynamic constraint using the measured wetted natural frequencies was added to help regularize the problem and speed up the solution process. A sequential quadratic programming algorithm was used as the optimizer for the inverse problem. The experimental studies showed that the inverse FSI model accurately determined the unknown operating conditions (angle of attack and immersed aspect ratio) for a given a known flow speed and a limited number of strain measurements in both FW and FV conditions. The converged results were used to reconstruct a 3-D hydrodynamic load distribution on the foil and to predict the cavity shape for FV operating conditions, which were found to agree well with experimental measurements and observations.

Prospects for the domestic production of large-sized cast blades and vanes for industrial gas turbines

Russian experience in the production of large-sized cast blades and vanes for industrial gas turbines is analyzed for the past decades. It is noted that the production of small- and medium-sized blades and vanes made of Russian alloys using technologies for aviation, marine, and gas-pumping turbines cannot be scaled for industrial gas turbines. It is shown that, in order to provide manufacturability under large-scale casting from domestic nickel alloys, it is necessary to solve complex problems in changing their chemical composition, to develop new casting technologies and to optimize the heat treatment modes. An experience of PAO NPO Saturn in manufacturing the blades and vanes made of ChS88U-VI and IN738-LC foundry nickel alloys for the turbines of the GTE-110 gas turbine unit is considered in detail. Potentialities for achieving adopted target parameters for the mechanical properties of working blades cast from ChS88UM-VI modified alloy are established. For the blades made of IN738-LC alloy manufactured using the existing foundry technology, a complete compliance with the requirements of normative and technical documentation has been established. Currently, in Russia, the basis of the fleet of gas turbine plants is composed by foreign turbines, and, for the implementation of the import substitution program, one can use the positive experience of PAO NPO Saturn in casting blades from IN738-LC alloy based on a reverse engineering technique. A preliminary complex of studies of the original manufacturer’s blades should be carried out, involving, first of all, the determination of geometric size using modern measurement methods as well as the studies on the chemical compositions of the used materials (base metal and protective coatings). Further, verifying the constructed calculation models based on the obtained data, one could choose available domestic materials that would meet the operating conditions of the blades according to their heat resistance and corrosion resistance.