Coalesced effect of cavitation and silt erosion in hydro turbines—A review

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Pannkaj P. Gohil and R.P. Saini – Renewable and Sustainable Energy Reviews, May 2014

Abstract

Cavitation is a phenomenon which manifests itself in the pitting of the metallic surfaces of turbine parts because of the formation of cavities. However, silt erosion is caused by the dynamic action of silt flowing along with water, impacting against a solid surface. The erosion and abrasive wear not only reduce the efficiency and the life of the turbine but also cause problems in operation and maintenance, which ultimately lead to economic losses. Researchers have studied that the cavitation in silt flow is more serious than in pure water. However, the coalesced effect of silt erosion and cavitation is found to be more pronounced than their individual effects.

In the present paper the studies in this field carried out by various investigators are discussed and presented. Parameters related to the combined effect of cavitation and silt erosion which are responsible for efficiency loss due to erosion as investigated by researchers have also been discussed.

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In-tank tests of a dielectric elastomer generator for wave energy harvesting

R. Vertechy, M. Fontana, G. P. Rosati Papini, and D. Forehand – Proc. SPIE Electroactive Polymer Actuators and Devices (EAPAD), March 2014

Abstract

Wave energy harvesting is one of the most promising applications for Dielectric Elastomer Generators. A simple and interesting concept of a Wave Energy Converter based on Dielectric Elastomers is the Polymeric Oscillating Water Column (Poly-OWC). In this paper, preliminary experimental results on the assessment of a small-scale Poly-OWC prototype are presented. The scale of the considered prototype is 1:50. Tests are conducted in a wave-flume by considering sea state conditions with different wave amplitudes and frequencies. The obtained experimental results confirm the viability of the Poly-OWC device.

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Oscillating-water-column wave-energy-converter based on dielectric elastomer generator

R. Vertechy, M. Fontana, G.P. Rosati Papini, and M. Bergamasco – SPIE Smart Structures and Materials+ Nondestructive Evaluation and Health Monitoring, April 2013

Abstract

Dielectric Elastomers (DE) have been largely studied as actuators and sensors. Fewer researches have addressed their application in the field of energy harvesting. Their light weightiness, low cost, high corrosion resistance, and their intrinsic high-voltage and cyclical-way of operation make DE suited for harvesting mechanical energy from sea waves. To date, the development of cost-effective Wave Energy Converters (WECs) is hindered by inherent limitations of available material technologies.

Passive Control of Marine Hydrokinetic Turbine Blades

Michael R. Motley and Ramona B. Barber – Composite Structures, December 2013

Abstract

Marine hydrokinetic (MHK) turbine blades are generally constructed from fiber reinforced polymer composites and are subject to large, highly dynamic fluid forces. The bend-twist deformation coupling behavior of these materials can be hydroelastically tailored to improve system performance over the expected life of the turbine by way of rapid, passive pitch control that can increase lifetime power generation, reduce hydrodynamic instabilities, and improve load shedding and structural performance.

Accelerated Aging Tests for Marine Energy Applications

Peter Davies – Solid Mechanics and its Applications, 2014

Abstract

Polymer matrix fibre reinforced composites have been employed in marine applications for over 50 years, and there is considerable experience of their long term behaviour. However, the recent development of systems designed to recover ocean energy, such as tidal turbines and wave energy generators, imposes much more severe constraints on materials than traditional structures. The requirements in terms of sea water aging and fatigue resistance require specific test programmes; this presentation will describe some of these applications and the tests needed to guarantee long term behavior of composites for these structures. Some results from studies performed in this area at Ifremer over the last 5 years will be discussed.

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A review on potential applications of carbon nanotubes in marine current turbines

Kai-Wern Ng, Wei-Haur Lam, and Saravanan Pichiah – Renewable and Sustainable Energy Reviews, December 2013

Abstract

Marine current turbine is one of the promising marine renewable energy technologies that could provide clean and sustainable energy. This field has undergone rapid growth in both industry and academia during the last decade. However, there was no study being done in incorporating nanotechnology into marine current turbines. Carbon nanotubes, as one of the most studied nanomaterials, are a potential candidate to be incorporated into marine current turbines. This paper aims to review some of the researches done on carbon nanotubes to date, and proposed some potential applications in marine current turbines based on the review. The potential applications proposed are based on the need of marine current turbines. Apart from that, it also aims to act as a starting point to connect the two research areas (marine renewable energy and nanotechnology) together. The proposed applications include: structural reinforcement, fouling release coating, structural health monitoring, high performance wires/cables and lubrication.

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Static and Fatigue Analysis of Composite Turbine Blades Under Random Ocean Current Loading

Fang Zhou, H. Mahfuz, G. Alsenas, H. Hanson – Marine Technology Society Journal, April, 2013

Abstract

The objective of this paper is to investigate how U.S. National Renewable Energy Laboratory (NREL)-designed modeling tools commonly used for wind turbine blade design and analysis can be applied to the design of ocean current turbines (OCT). Design, static analysis, and fatigue life predictions of a horizontal-axis, ocean current turbine composite blade were investigated using NREL’s PreCom, BModes, AeroDyn, FAST with seawater conditions. PreComp was used to compute section properties of this OCT blade. BModes calculated mode shapes and frequencies of the blade. Loading on a turbine blade in the Gulf Stream at a South Florida location (26^o4.3’N 79^o50.5’W, 25-m depth) was calculated with AeroDyn. FAST was then used to obtain the dynamic response of the blade, including flap and edge bending moment distribution with respect to blade rotation. Static analysis was performed by using a combination of Sandia’s NuMAD and ANSYS. Palmgren-Miner’s cumulative fatigue damage model was employed with damage estimation based on the material fatigue property data in DOE/MSU Composite Material Fatigue Database. During service life, OCT blades are subjected to cyclic loads and random ocean current loading. Hence, the blades experience repeated and alternating stresses, which can lead to fatigue failure. These loads were weighted by rate of occurrence from a histogram analysis of in situ measurements conducted by the Southeast National Marine Renewable Energy Center (SNMREC).

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Consistent ocean wave energy harvesting using electroactive polymer (dielectric elastomer) artificial muscle generators

S. Chiba, M. Waki, T. Wada, Y. Hirakawa, K. Masuda, and T. Ikoma – Applied Energy, April, 2013

Abstract

An energy transduction technology that operates efficiently over a range of frequencies is important for practical energy harvesting devices such as ocean wave power generators. Dielectric elastomer is based on the change in capacitive energy of a deformable dielectric and is a candidate for such applications. A simple scale model of EPAM-based wave energy harvesting system was tested in a wave tank over a range of wave periods from 0.7 to 3 s and wave heights from 2 cm to 6 cm. The energy output was found to be largely independent of wave period.

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Evaluation of the durability of composite tidal turbine blades

P. Davies, G. Germain, B. Gaurier, A. Boisseau, and D Perreux – Phil. Trans. R. Soc. A, 2013

Abstract

The long-term reliability of tidal turbines is critical if these structures are to be cost effective. Optimized design requires a combination of material durability models and structural analyses. Composites are a natural choice for turbine blades, but there are few data available to predict material behaviour under coupled environmental and cycling loading. The present study addresses this problem, by introducing a multi-level framework for turbine blade qualification. At the material scale, static and cyclic tests have been performed, both in air and in sea water. The influence of ageing in sea water on fatigue performance is then quantified, and much lower fatigue lives are measured after ageing. At a higher level, flume tank tests have been performed on three-blade tidal turbines. Strain gauging of blades has provided data to compare with numerical models.

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Polycrystalline diamond bearing testing for marine hydrokinetic application

B.A. Lingwall, T.N. Sexton, C.H. Cooley – Technical Report submitted to DOE EERE Wind & Water Power Program, December, 2012

Abstract

Polycrstalline diamond (PCD) bearings were designed, fabricated and tested for marine-hydro-kinetic (MHK) application. Bearing efficiency and life were evaluated using the US Synthetic bearing test facility. Three iterations of design, build and test were conducted to arrive at the best bearing design. In addition life testing that simulated the starting and stopping and the loading of real MHK applications were performed. Results showed polycrystalline diamond bearings are well suited for MHK applications and that diamond bearing technology is TRL4 ready. Based on life tests results bearing life is estimated to be at least 11.5 years. A calculation method for evaluating the performance of diamond bearings of round geometry was also investigated and developed. Finally, as part of this effort test bearings were supplied free of charge to the University of Alaska for further evaluation. The University of Alaska test program will subject the diamond bearings to sediment laden lubricating fluid.

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