Article

Strength and Reliability of Wood for the Components of Low-Cost Wind Turbines: Computational and Experimental Analysis and Applications

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Abstract

This paper reports the latest results of the comprehensive program of experimental and computational analysis of strength and reliability of wooden parts of low cost wind turbines. The possibilities of prediction of strength and reliability of different types of wood are studied in the series of experiments and computational investigations. Low cost testing machines have been designed, and employed for the systematic analysis of different sorts of Nepali wood, to be used for the wind turbine construction. At the same time, computational micromechanical models of deformation and strength of wood are developed, which should provide the basis for microstructure-based correlating of observable and service properties of wood. Some correlations between microstructure, strength and service properties of wood have been established.

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... Experiences from projects across multiple countries suggest that self-made SWTs are more error-prone than commercial systems (Kamp and Vanheule, 2015) and that users should expect problems requiring substantial maintenance to arise at least once a year (Neves et al., 2015;Sumanik-Leary et al., 2014). This is problematic, because Mishnaevsky et al. (2009), based on a number of project experiences in Nepal, report that product reliability is a key user requirement for adoption. While studies from the early 2010s state that open-source SWTs have only undergone limited quality testing (Hosman, 2012;Sumanik-Leary et al., 2012a), our publication snowballing method has identified a variety of technical assessments of whole turbines or components thereof that have been conducted since then (see Table 1). ...
... While studies from the early 2010s state that open-source SWTs have only undergone limited quality testing (Hosman, 2012;Sumanik-Leary et al., 2012a), our publication snowballing method has identified a variety of technical assessments of whole turbines or components thereof that have been conducted since then (see Table 1). However, comparatively few publications discuss procedures for field-based quality-testing, which is critical for allowing users to assess their self-fabricated turbines and, therefore, can increase the confidence of potential users in the reliability of the machinery (Corbyn and Little, 2008;Latoufis et al., 2015b;Mishnaevsky et al., 2009). ...
... To address these issues, there appears to be a need for robust but inexpensive procedures to conduct field-based quality testing of user-manufactured machines. Our findings suggest that only few researchers and practitioners focusing on open-source SWTs have addressed this issue (Corbyn and Little, 2008;Latoufis et al., 2015b;Mishnaevsky et al., 2009). Pearce (2017 studies the case of scientific hardware based on OSH and makes a similar point about the importance of quality testing, stressing that the lack of procedures for product validation and calibration has been one of the key features holding back the further adoption of such equipment (p. ...
Article
The successes of open-source software raise the question of whether technological hardware that has been developed based on an open and collaborative mode of innovation can achieve similar levels of diffusion. While some expect such open-source hardware (OSH) to lead to transformational changes in the ways technologies are produced, the available empirical evidence suggests that, to date, the diffusion of most OSH applications has been modest. In this paper, we focus on the limited uptake of OSH and study factors that help explain its adoption by users who replicate available open-source designs. Given our limited understanding of this topic, we present an in-depth study of small wind turbines based on open designs. Through a systematic review of the case-specific literature, we identify and analyse 60 documents, including case studies, construction manuals, market analyses, and technical assessments. We find that the adoption of available open-source wind turbine designs by technology users depends on a number of factors that are currently underemphasized in discussions on the potential of OSH. This includes the quality of OSH self-manufactured products, the particular motivations of adopters to engage with OSH, the availability of adequate production inputs for local manufacturing, and the resources available through open-source communities.
... In a number of works, the strength and damage mechanisms of hybrid composites were studied [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. It was reported, among others, that the incorporation of glass fibers in carbon fiber reinforced composites allows the improvement of their impact properties and tensile strain to failure of the carbon fibers. ...
... An interesting option for developing countries is small turbines, producible on-site, and made from "natural composites", i.e., from locally available timber [47]. In a series of investigations, a group of Nepali, Danish and Australian scientists studied the applicability of different timbers for wind turbines, and demonstrated that the turbines with wooden blades represent a reliable and low cost option for the developing countries [48][49][50][51]. Figure 5 shows a test of a timber wind turbine blade and small wind turbines installed in a village school in Nepal. blades instead of common composites. ...
... An interesting option for developing countries is small turbines, producible on-site, and made from "natural composites", i.e., from locally available timber [47]. In a series of investigations, a group of Nepali, Danish and Australian scientists studied the applicability of different timbers for wind turbines, and demonstrated that the turbines with wooden blades represent a reliable and low cost option for the developing countries [48][49][50][51]. Figure 5 shows a test of a timber wind turbine blade and small wind turbines installed in a village school in Nepal. ...
Article
Full-text available
A short overview of composite materials for wind turbine applications is presented here. Requirements toward the wind turbine materials, loads, as well as available materials are reviewed. Apart from the traditional composites for wind turbine blades (glass fibers/epoxy matrix composites), natural composites, hybrid and nanoengineered composites are discussed. Manufacturing technologies for wind turbine composites, as well their testing and modelling approaches are reviewed.
... As shown in Fig. 1, many attempts at bringing down the cost of SWTs have been made in different sectors. Several components of SWTs especially the mechanical parts can be provided from local resources [4]. For instance, employing natural timber resources for towers and blades could noticeably reduce the production cost. ...
... Of particular interest of the proposed configuration is that the blades twist at the root is transferred to the hub by the trapezoidal transition section which is not the case in the conventional hubs (Figs. [2][3][4][5]. In fact, by replacing the cube shape with the "twisted" trapezoidal one, the need for large-thickness blanks is avoided (see Fig. 6b). ...
Article
The study puts forward a new and economic rotor hub configuration for small wind turbines. With the use of the proposed idea, the required size of timber blanks from which the blades are cut is reduced, leading to the reduction in blanks cost as well as machining process cost. To investigate the presented scheme from the structural aspect, the finite-element analysis was done on a 1 kW turbine rotor hub. The results reveal the applicability of the proposed hub as it could withstand the aerodynamic and centrifugal loadings. From the economic perspective, the cost reduction in the timber blanks and machining process is about 33% and 58% respectively compared to the conventional hub used in small turbines. This would be of interest in promoting the use of small turbines in developing countries where the cost of renewable energies is not competitive with non-renewable ones. Moreover, by using this new hub, the subtraction (machining) mass of timber during the machining process is reduced noticeably, rendering the presented hub configuration interesting from the environmental aspect. Also provided by this new configuration is the starting improvement of the turbine thanks to the lower value of the rotor inertia compared to the conventional configuration.
... We acquire short-length fibers using the pneumatic approach, which is called Veranne, in which the lengthening is achieved by pushing the fibers under the operation of a pressured air jet. Just the first procedure allows for the production of materials with excellent mechanical properties [6]. ...
Article
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In light of rising energy demand, solar and wind power are popular renewable energy sources. A need for the hour is for reliable little wind power at a reasonable price. The materials needed the cost of continuance and function, and the cost of fuel influences the cost of energy production. Material costs are inversely related to energy costs. The blade design is critical in any wind turbine design. The choice of material is a critical element in blade design if the blade is to have a long predicted life. For smaller wind turbine blades, several materials such as wood, fiber glass, carbon fiber, natural fiber, and sandwiched composite items are provided. The main features to consider while choosing a blade material include hardness, toughness, density, price, and affordability. The materials for a wind turbine blade are indeed an essential part of the design process. These articles present numerous materials as potential blade options and use ANSYS computational modeling to select the best one.
... For these reasons, over the last few decays attempts are being made on lingocellulose materials for next-generation structural applications [19], which are readily available in plants, animal products, or other minerals [20]. These materials are interestingly reliable and cost-effective especially for developing countries [21,22], to capture on-site wind power by manufacturing the blades from local composite materials [23,24]. The important characteristics of natural fibers include good mechanical properties, noenvironmental impacts, non-corrosive, biologically degradable, cost-effectiveness, etc [25]. ...
Article
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Performances of hybrid Natural Fiber-Reinforced Composites (NFRCs) from E-glass, Nacha (Hibiscus macranthus Hochst. Ex-A . Rich.), and Sisal (Agave sisalana) fibers are investigated for wind turbine blades applications. The process of composite manufacturing was getting started with harvesting and extracting the fibers from undesired constituents. To improve the interfacial interaction between fibers, it was further treated with 5% of NaOH and remnants removal. The experiment was performed based on the Taguchi method, specifically with L16 orthogonal array. Four levels of a natural fiber weight ratio (i.e. 5%, 10%, 15 %, and 20%) were considered during the composite preparations process while the weight of glass fiber was maintained at 5% and 10%. The composites are manufactured using the hand lay-up method, and the test specimens are as per American Society for Testing and Materials (ASTM) standards. Then, tensile, compressive, and flexural tests were carried out using a universal testing machine (UTM). Analysis of variance (ANOVA) was employed to determine the factors which affect the experimental responses. Hence, in the main effect, it was confirmed that Nacha fiber (%wt of N) significantly contributes to tensile, compressive, and flexural strength at a 95% level of confidence. Furthermore, the optimal fiber compositions of composites are determined based on a higher signal-to-noise ratio (S/N) for the corresponding strengths.
... Although the original requirement of Australian industry was for pulp quality improvement, the primary data is more directly applicable to the uses of solid wood [180][181][182][183][184][185][186][187][188][189][190][191][192][193][194][195][196][197][198]. In some of these studies, the ability of SilviScan to analyze large numbers of samples in great detail has been used to map the interior structure of stems to give a more comprehensive understanding of wood property variation over a wide range of scales. ...
Article
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To maximize utilization of our forest resources, detailed knowledge of wood property variation and the impacts this has on end-product performance is required at multiple scales (within and among trees, regionally). As many wood properties are difficult and time-consuming to measure our knowledge regarding their variation is often inadequate as is our understanding of their responses to genetic and silvicultural manipulation. The emergence of many non-destructive evaluation (NDE) methodologies offers the potential to greatly enhance our understanding of the forest resource; however, it is critical to recognize that any technique has its limitations and it is important to select the appropriate technique for a given application. In this review, we will discuss the following technologies for assessing wood properties both in the field: acoustics, Pilodyn, Resistograph and Rigidimeter and the lab: computer tomography (CT) scanning, DiscBot, near infrared (NIR) spectroscopy, radial sample acoustics and SilviScan. We will discuss these techniques, explore their utilization, and list applications that best suit each methodology. As an end goal, NDE technologies will help researchers worldwide characterize wood properties, develop accurate models for prediction, and utilize field equipment that can validate the predictions. The continued advancement of NDE technologies will also allow researchers to better understand the impact on wood properties on product performance.
... An alternative is timber which could come from sustainable plantations. It was historically used in boats and windmills and is still employed in a variety of applications including ultralight aircraft propellers and small wind turbine (SWT) blades and towers [1][2][3][15][16][17][18]. ...
Article
Despite the use of composite materials, timber is still widely used in the wind energy industry and especially in small wind turbine blades. Four species of timber namely alder, ash, beech and hornbeam which are grown in Iran were tested for their suitability for use in small blades. A solid blade is easiest to manufacture and is interesting from the structural aspect but its high inertia could delay starting since small turbines have no pitch mechanism to optimize the blade angles of attack during starting. We describe the design and optimization of solid and hollow blades for a small horizontal axis turbine via genetic algorithms. In order to maximize the power coefficient and minimize the starting time, the optimization algorithm tries to find the external/internal geometry of the blades while the resultant stresses do not exceed the allowable stress of the timbers. Regardless of the type of timbers, the optimization results show that the power coefficient of all the optimal blades is sufficiently high but the starting performance requires choosing an appropriate timber. More specifically, the alder solid blade would be better than the beech, hornbeam and ash. For the hollow blades, the alder and beech timbers could be used for windy areas and all four timbers are very promising for operation in low wind speed regions where starting behavior is more important.
... Figure 1 shows the graph of different mechanical properties such as Young's Modulus, maximum breaking strength, maximum strain before failure and minimum Brinelle's Hardness number with respect to density for eight different types of commonly available Nepalese timber. Laboratory equipments used for four point bending test rig to determine stress strain properties and Brinell's hardness tester for measuring harness number are locally designed and constructed [1], [2]. Table 1 shows the types of timber selected for laboratory investigation along with their density measured at 10-15% moisture content. ...
Article
The paper describes the selection of Nepalese timber for development of small wind turbine blades on the basis of locally based low cost timbers, along with the selection of coatings to protect the timber from weathering. The selection criterion of timber includes timber mechanical properties, weathering effect on coatings, price, growth and availability of the timber. Mechanical properties such as Young's modulus of elasticity, breaking strength, breaking strain and Brinell's hardness of selected Nepalese timbers are presented. The effects of weathering on timbers without coating, and with different coatings, are analysed on the basis of the change in weight of the timber due to the effect of humidity and rainfall over a period of nineteen months. Degradation of different coatings of timber are compared.
... First, the list of practically and economically available timber sorts which have a potential to be used for wind turbines was made (the numbers in the brackets show the botanical name of the timber, average time to grow, in years, and the price on the market in Nepal, in EUR/m 3 ): uttish (botanical name: Alnus nepalensis, 8e15 yrs, 90), lakuri (Fraxinus floribunda, 15e20 yrs, 125), saur (Betula alnoides, 15e20 yrs, 70), tuni (Tuna Ciliata, 15e20 yrs, 210), pine (Pinus roxburghii, 20e30 yrs, 200), sisau (Dalbergia sissoo, 15e50 yrs, 850), okhar (Juglans regia, 30e40 yrs, 710), sal (Shorea robusta, 100e200, 590) [8,9]. For the selected timbers, laboratory investigations of the elastic properties, density, stiffness, breaking strength, strain before failure, hardness, fatigue behavior and microstructures were carried out [7,8]. ...
Article
The low cost wind turbines with timber blades represent a good solution for the decentralized energy production in off-grid regions of developing countries. This paper summarizes the results of investigations on the mechanical testing and choice of timber for wind blades, testing of different coatings and blades as well as installation and practical experience with wooden wind turbines in Nepal. The recommendations on the optimal choice of Nepali timber and coatings for low cost wind blades are summarized. The timber wood blades were designed and tested. On the basis of the recommendations, the wind turbines with timber (lakuri) wind blades were produced, and tested. The turbines with timber wind blades were installed on several locations around Nepal, and their usability was studied. It was demonstrated that the appropriate choice of timber and coatings ensures necessary reliability of the blades and turbines. It was further demonstrated that the low cost wind turbines with timber blades represent a promising and viable option for the decentralized energy production in developing countries, which also opens new areas for businesses.Research highlights► Small wind turbines with timber blades are a good solution for the decentralized energy production in developing countries. ► Properly chosen timber represents a good, strong, reliable and cheap alternative to the traditional composites as the materials for wind blades. ► A program of timber choice for building reliable wind turbines can be realized successfully in a developing country.
Chapter
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Chapter
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The Halpin-Tsai equations are based upon the ″self-consistent micromechanics method″ developed by Hill. Hermans employed this model to obtain a solution in terms of Hill's ″reduced moduli″ . Halpin and Tsai have reduced Hermans' solution to a simpler analytical form and extended its use for a variety of filament geometries. The development of these micromechanics relationships, which form the operational bases for the composite analogy of Halpin and Kardos for semi-crystalline polymers are reviewed.
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This paper explores technical and other issues arising from using shaped timber for a 1 metre long high efficiency blade for a small 600 W wind turbine. Two readily available Australian grown softwood timber species, radiata pine and hoop pine, were selected. Reasons for selecting these timbers are detailed in the paper. The fatigue life of the both timbers was determined using four point flexural testing. Results show that hoop pine is 25% stronger and 6% more fatigue resistant than radiata pine. A fatigue test procedure for the 1 m blade has been created based on the aeroelastic response of a 2.5 m long composite wind turbine blade and wind data from the Australian Bureau of Meteorology. Blade fatigue-life predictions, using Miners rule for fatigue damage accumulation, indicated effectively unlimited fatigue-life for a blade constructed from hoop pine, with the turbine operating at design performance in wind speeds up to 20 m/s. The blade's life was reduced to a few months when it was constructed from radiata pine for the same operating conditions to 20 m/s. However for an upper wind speed of 17 m/s, the predicted blade fatigue-life is effectively unlimited for both species. Test blades were machined in both radiata pine and hoop pine on a 3-axis milling machine with tool paths created using Pro/Manufacture software. Some of the important issues with respect to creating the blades out of timber are discussed.
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The fatigue properties of wood laminates have been investigated in tension, compression and shear. Fatigue lives in compression are significantly less than in tension, and S-N data at five R ratios has yielded a set of constant-life lines, the form of which is related to the failure mode of the wood observed by scanning electron microscopy. A point of inflection in the constant-life lines at the transition between all compressive and partially tensile fatigue loading is a new observation. S-N curves for wood laminates have been produced for shear across the radial-longitudinal and tangential-longitudinal planes, and the latter plane is observed to be more resistant to fatigue loads. Samples with four times the cross-sectional area of standard-sized samples have been fatigued at R=−1 and no significant difference in fatigue life is apparent. It appears that the absence of a size effect in tension-compression results from the orthotropic structure of wood which is insensitive to variations in the density of surface flaws.
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An overview of the micromechanical theoretical and numerical models of wood is presented. Different methods of analysis of the effects of wood microstructures at different scale levels on the mechanical behaviour, deformation and strength of wood are discussed and compared. Micromechanical models of deformation and strength of wood are divided into three groups: cellular models (applied most often to the mesoscale or cell scale analysis of the wood deformation), continuum micromechanics and homogenization based methods, models which consider wood as a composite and are applied mainly to the analysis of wood at the microscale (cell wall scale) level and multiscale models. Lattice and composite models, which are used to analyze the damage and fracture of wood, are considered in a separate section. The areas of applicability and strong sides of each approach are discussed.
Mechanical properties, strength and fatigue resistance of Nepalese timbers for small wind turbine applications
  • R Sharma
  • R Sinha
  • P Acharya
  • L Mishnaevsky
  • P Freere
R. Sharma, R. Sinha, P. Acharya, L. Mishnaevsky Jr., P. Freere, Mechanical properties, strength and fatigue resistance of Nepalese timbers for small wind turbine applications (in preparation).
Fracture and fatigue in Wood
  • I Smith
  • E Landis
  • M Gong
Smith, I., Landis, E. and Gong, M. (2003) Fracture and fatigue in Wood, John Wiley & Sons.
3D microstructural model of wood: analysis of microscale mechanisms of deformation
  • H Qing
  • Mishnaevsky
H Qing, L Mishnaevsky Jr., 3D microstructural model of wood: analysis of microscale mechanisms of deformation (submitted).
Micromechanical modelling of mechanical behavior and strength of softwood: state-of-the-art review
  • L Mishnaevsky
  • H Qing
L Mishnaevsky Jr., H. Qing, Micromechanical modelling of mechanical behavior and strength of softwood: state-of-the-art review, Computational Materials Science, 2008, doi:10.1016/j.commatsci.2008.03.043
Nutrient contents of feeds and fodder in Nepal
  • Chet Raj Upreti
Chet Raj Upreti, 'Nutrient contents of feeds and fodder in Nepal', November '06