A design of Darrieus vertical axis tidal turbine using modified airfoil was studied numerically in this work. The turbine design was evaluated in 2D CFD model using kω turbulence model, upwind interpolation scheme and simulated using OpenFOAM. The turbine had three blades which were arranged symmetrically. The blades were of NACA 0012 airfoil which had been modified in the trailing edge region to increase its lift performance. The modification was made by truncating the trailing edge at the 15% of chord length from the trailing edge. Single normal and blunt airfoil were modelled and investigated prior to the turbine design evaluation. For generating the mesh, Cstructured grid was employed to the single airfoil model and hybrid mesh to the vertical axis tidal turbine model. From the single airfoil simulations, it was found that blunt NACA0012 had 12% higher lift coefficient than normal airfoil and the pressure coefficient magnitude of blunt vertical axis tidal turbine significantly rise two times from vertical axis tidal turbine using normal NACA0012 airfoil.  Index Terms-vertical axis tidal turbine, Darrieus turbine, truncated Naca0012, blunt airfoil

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Improving the reliability of marine renewable energy devices such as wave and tidal energy convertors is an important task, primarily to minimize the perceived risks and reduce the associated cost for operation and maintenance. Marine systems involve a wide range of uncertainties, due to the complexity of failure mechanism of the marine components, scarcity of data, human interactions and randomness of the sea environment. The fundamental element of a probabilistic risk analysis necessarily needs to rely on operational information and observation data to quantify the performance of the system. However, in reality it is difficult to ascertain observation of the precursor data according to the number of component failures that have occurred, mainly as a result of imprecision in the failure criterion, record keeping, or experimental and physical modelling of the process. Traditional reliability estimation approaches such as Fault Tree, Event Tree and Reliability Block Diagram analysis offer simplified, rarely realistic models of this complex reliability problem. The main reason is that they all rely on accurate prior information as a perquisite for performing reliability assessment. In this paper, a hierarchical Bayesian framework is developed for modelling marine renewable component failures encountered the uncertainty. The proposed approach is capable to incorporate the conditions, which lack reliable observation data (e.g. unknown/uncertain failure rate of a component). The hierarchical Bayesian framework provides a platform for the propagation of uncertainties through the reliability assessment of the system, via Markov Chain Monte Carlo (MCMC) sampling. The advantages of using MCMC sampling has proliferated Bayesian inference for conducting risk and reliability assessment of engineering system. It is able to use hyper-priors to represent prior parameters as a subjective observations for probability estimation of the failure events and enable an updating process for quantitative reasoning of interdependence between parameters. The developed framework will be an assistive tool for a better monitoring of the operation in terms of evaluating performance of marine renewable system under the risk of failure. The paper illustrates the approach using a tidal energy convertor as a case study for estimating components failure rates and representing the uncertainties of system reliability. The paper will be of interest to reliability practitioners and researchers, as well as tidal energy technology and project developers, seeking a more accurate reliability estimation framework.

The depletion of fossil fuels and the worsening environment motivate engineers and researchers to explore renewable energy resources. One of the promising renewable energy is wind energy. The wind turbine extracts wind energy to generate electricity. This study aims to modify a wind turbine blade using Clark Y foil to improve the lift force. The modification is employed by forming a winglet profile with a 30° angle on the foils tip. The result shows that the 30° winglet enlarges the lift coefficient to 1.3253 from 1.2795 of the original blade lift coefficient.

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Fluid structure response of vertical axis tidal turbine blades using NACA 0012 and periodic inflow equivalence model is predicted in this work. The response is investigated numerically by developing a 2D CFD model at high Reynolds number (3.07x10 6 ). The periodic inflow equivalence model is conducted by modelling the rotation of the turbine as time dependent unsteady incoming fluid velocity and angle of attack variation entering the 2D CFD domain. The blade response is modeled by a vibrational system with spring damper components which are attached at the blade fluid dynamic center point. The aim of this study is to predict a resonant condition or a lock-in frequency induced by wake generation at a vertical axis turbine blade during the turbine operation. The model is generated using a dynamic mesh construction in OpenFOAM 2.2 and the mesh is refined using snappyHexMesh utility. The mesh has seven added boundary layers around the blade surface and simulated using k-ω SST turbulence model. Drag, lift and moment force coefficient are observed during 12 seconds which is equal to 3.3 revolutions and extracted using Fast Fourier Transform method to obtain its predominant frequency. The predominant frequency determines the dynamic condition of the blade and is used for predicting a resonance based on the turbine's natural frequency. The result shows that the vertical axis tidal turbine which is manufactured from a composite with material pitch stiffness of 200 Nm/radians, heave stiffness of 1000 N/s, and operates at tidal velocity of 0.656 m/s is found to experience a resonance or lock-in phenomena induced by wake generation in the pitch mode response. IntroductionRenewable energy has been widely used as an energy alternative not only because of the depletion of fossil fuel but also because it is environmental friendly. However some devices still needs to be developed including vertical axis tidal turbines. Although a vertical axis tidal turbine has been examined for decades but its interaction with the fluid passing through the turbine has not been explored and understood. Therefore the aim of this work is to investigate in 2D the fluid structure response (FSI) of a vertical axis tidal turbine blade using a time varying incoming velocity and angle of attack model which is equivalent to the vertical axis tidal turbine periodic revolution. This allows the development of a strip theory based approach for estimating the vertical axis tidal turbine blade fatigue and the influence of structure design solutions. The aim is accomplished by developing a suitable CFD model for the time varying angle of attack and incoming velocity for a typical vertical axis tidal turbine and hence to evaluate the FSI response for a representative set of damping constant for a typical composite material.A vertical axis tidal turbine extracts energy from the kinetic energy of tides and converts it to mechanical energy form by turbine rotations. Unlike wind turbines which have been developed thoroughly, vertical axis tidal turbines...

The wind energy is one of the renewable energy which is extracted the most amongst other resources. However, the performance still required to be improved by modifying the wind turbine blade. In this study, the modification is employed at the tip of the blade using 30° winglet. The aim of this paper is to investigate numerically the lift of force of the modified Clark Y foil in various pitch angles and predict the pitch angle at which the maximum lift is found to be maximum. There are five pitch angle variations, and they are 0°, 12°, 22°, 32°, and 42°. 3D CFD models are used using OpenFOAM 8. From the results, it can be seen that the maximum lift force was achieved at the pitch angle variation of 32° with the value of 1.245 and the maximum drag force was achieved at the pitch angle variation of 22° with the value of 1.325. While the maximum C l /C d that represents aerodynamic efficiency was achieved at the variation of 12° with the value of 2.915.

Solar air heater (SAH) is a renewable energy application for the drying process. SAH has a challenge to produce high performance under uncertain weather. The performance of SAH can be enhanced by providing the absorber plate by adding the fins. This study aims to evaluate the thermal performance of SAH with rectangular fins SAH at low air velocity. This study compares the performance of SAH without fins and SAH with rectangular fins. Two variations of a tilt angle of SAH are 0° and 30° which are observed in this study. The SAH uses a ventilator turbine to suck air into the collector box. The air velocity is 0.01 m/s. The method is experimental. The SAH is tested under real condition from 9 a.m. to 4 p.m. The measurement tools consist of  a pyranometer, an anemometer, a temperature sensor in the inlet section, 3 sensors in the absorber plate, a sensor in the outlet section,  6 temperature sensors in the drying cabinet. The result showed the thermal efficiency of SAH with rectangular fins is 29.67 % higher than SAH without fins at 0˚ tilt of angle at noon. The thermal efficiency of SAH with rectangular fins is 25.26 % higher than  that of without fins at 30˚ tilt of angle at noon.