Large Blades Research Articles

Preparation of Mg2Ni Hydrogen Storage Alloy Materials by High Energy Ball Milling

In this paper, Mg2Ni hydrogen storage alloy powder was prepared by high-energy ball milling mechanical alloying method, and the influence of stirring shaft rotation speed, ball milling time, and different sizes of ball mills on the formation time, powder morphology, and crystal structure of Mg2Ni alloy during ball milling was studied. The results show that the Mg2Ni alloy was obtained by high-energy ball milling in this work, and the efficiency was increased by about 76% compared with the traditional ball milling method. In the case of higher rotational speed or larger blades, the time to generate Mg2Ni alloy can be advanced, the alloying process can be shortened, and Mg2Ni alloy with a particle size of less than 10 um can be obtained. However, after the ball milling reaches a certain time, the cold welding and crushing of the alloy powder reach a balance, and the particle size is basically unchanged. The hydrogen storage alloy was activated, the hydrogen storage PCT curve was detected, and the hydrogen absorption kinetic curve and the PCT curve were analyzed. After ball milling at 900/1100 rpm for 13 hours, a Mg2Ni alloy with a single composition, extremely low impurity content, and partially amorphous and nanocrystalline coexistence was obtained. Its mass hydrogen storage density also reached the theoretical value of 3.6 wt%.

Dynamic Characteristics Monitoring of Large Wind Turbine Blades Based on Target-Free DSST Vision Algorithm and UAV

The structural condition of blades is mainly evaluated using manual inspection methods. However, these methods are time-consuming, labor-intensive, and costly, and the detection results significantly depend on the experience of inspectors, often resulting in lower precision. Focusing on the dynamic characteristics (i.e., natural frequencies) of large wind turbine blades, this study proposes a monitoring method based on the target-free DSST (Discriminative Scale Space Tracker) vision algorithm and UAV. First, the displacement drift of UAV during hovering is studied. Accordingly, a displacement compensation method based on high-pass filtering is proposed herein, and the scale factor is adaptive. Then, the machine learning is employed to map the position and scale filters of the DSST algorithm to highlight the features of the target image. Subsequently, a target-free DSST vision algorithm is proposed, in which illumination changes and complex backgrounds are considered. Additionally, the algorithm is verified using traditional computer vision algorithms. Finally, the UAV and the target-free DSST vision algorithm are used to extract the dynamic characteristic of the wind turbine blades under shutdown. Results show that the proposed method can accurately identify the dynamic characteristics of the wind turbine blade. This study can serve as a reference for assessment of the condition of wind turbine blades.

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

AbstractApplication of large blade impellers to turbulent single‐phase and two‐phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three‐dimensional velocity fields collected in a single‐phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two‐phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear‐rate controlled and bulk‐motion controlled processes.

Early Neolithic Large Blades from Crno Vrilo (Dalmatia, Croatia): Preliminary Techno-Functional Analysis

Abstract The excavation of Crno Vrilo site (Zadar, Dalmatia, Croatia), carried out by B. Marijanović, has unearthed the vestiges of an Early Neolithic village dating back to ca. 5800–5600 cal BC. The lithic assemblage, with more than 4000 pieces, represents the biggest Impressed Ware assemblage of littoral Croatia. Lithic production at Crno Vrilo is characterised by the pressure Blade flaking on high-quality exogenous cherts (Gargano, southern Italy) reflecting important socio-economic and technical aspects that are specific to the Neolithic. The presence of some débitage elements such as flakes, debris, cortical and technological pieces indicates that standard pressure flaking occured at the site, while the presence of large Blades (with widths exceeding 20 mm) suggests production by lever pressure, a technique that required specialized knowledge and equipment. This article questions whether the lever pressure technique was used in the production of large Blades and examines the status of these Blades in the Crno Vrilo lithic assemblage by examining their technological and functional aspects.

La percussion lancée dans l’Aurignacien ancien du Bergeracois : quelques exemples issus des sites de Barbas III, Vieux Coutets, Les Garris et Cantalouette II (Dordogne, France)

In order to illustrate the launched percussion activities during the Early Aurignacian, we have selected four of the 15 sites appertaining to this technocomplex in the Bergerac region, in Southwestern France. The occupation of this territory, very rich in good quality flint nodules, some of which display imposing morphologies and dimensions, shows a certain functional complementarity between the different Aurignacian occupations, from the specialized occupation to the habitat site. In addition to technological particularities, such as the production of large blades (greater than 20 cm) or the coexistence of curved and straight lamellar production systems, this Early Aurignacian also illustrates some remarkable symbolic behavior expressed in body ornaments and artistic depictions. In these sites, the tools used in launched percussion, although always present, represent a marginal tool category, showing also a great diversity of functions. Three major classes of tools have been recognized: blunt impact tools, sharp impact tools, and linear blunt tools (an intermediate form between the other two). Each of these groups is oriented towards complementary uses within the range of activities made in these occupations. The blunt impact tools comprise a wide range of hammer-stones that take part in different phases of knapping activities, such as the opening of new blocks or the reconfiguration of cores, according to their physical and mechanical properties. Also, the traces left by these hammers are visible on other artifacts left on the sites, such as notches of carinated end-­scrapers. The sharp impact tools comprises a diversified range of cutting tools made on different blanks (preforms, cortical flakes, blades) obtained in laminar production. These tools present a particular morpho-functional structure of active or prehensive parts, natural or made, that improves an ergonomy essentially based on mass. This ergonomy, combined with the kinetics of launched percussion, gives these tools a great efficiency in chopping medium and hard organic materials. Finally, the linear blunt tools is represented by a single tool with blunt linear active zones, formed by open dihedrals with angles between 85 and 115°. The kind of activity made with this tool seems different, it bears traces of recurrent impacts similar to those present on tools used for grinding, pounding or crushing, suggesting also the presence of an anvil. These tools are very often associated with the transformation of plants. This panoply of diversified percussive tools complements the activities perceived on the other cutting and scrapping tools. This, again, illustrates the variety of activities made at this sites, basically the acquisition and transformation of organic perishable materials (of plant and animal origins), contributing to demonstrate that the Early Aurignacian occupations of the Bergeracois are much more complex thansimple flint workshops.

Effects of swirler blade angle and actuator applied voltage on combustion characteristics and cooling effectiveness

This paper investigated effects of swirlers with blade angles and applied voltage of plasma actuators on combustion and wall temperature of a Can - type gas turbine combustor. Results show that large blade angle of the swirler is beneficial for the mixing of fuel and air, which improves uniformity of the outlet temperature distribution and reduces CO emission but results in temperature rise of the wall. Pattern factor reflects uniformity of the temperature distribution at the outlet of the combustion chamber, and a small value of the pattern factor means a good distribution uniformity. In this paper, the minimum pattern factor is 0.45 when the blade angle of the swirler is 55°, which means the best uniformity of temperature distribution at combustor outlet. Compared with the worst results with a 40° blade angle, the pattern factor for the blade angle of 55° decreases by 66.4%. CO emission decreases with the increase of the blade angle. Compared with the maximum value of CO emission for a 40° blade angle, reductions of CO emission are 67.6%, 95.9% and 99.6% with the blade angles of 45°, 50° and 55°. It is found that CO emission decreases by 1.3% and pattern factor increases by 2.2%, when the blade angle of the swirler changes from 55° to 60°. When the applied voltage changes from 0 kV to 8 kV and 16 kV, cooling effectiveness increases by 3.2% and 0.7%. Cooling effectiveness decreases by 2.9% when the applied voltage increases from 0 kV to 24 kV.

Experimental investigation of mini Gurney flaps in combination with vortex generators for improved wind turbine blade performance

Abstract. This wind tunnel study investigates the aerodynamic effects of mini Gurney flaps (MGFs) and their combination with vortex generators (VGs) on the performance of airfoils and wind turbine rotor blades. VGs are installed on the suction side aiming at stall delay and increased maximum lift. MGFs are thin angle profiles that are attached at the trailing edge in order to increase lift at pre-stall operation. The implementation of both these passive flow control devices is accompanied by a certain drag penalty. The wind tunnel tests are conducted at the Hermann-Föttinger Institut of the Technische Universität Berlin based on two airfoils that are characteristic of different sections of large rotor blades. Lift and drag are determined using a force balance and a wake rake, respectively, for static angles of attack between −5 and 17∘ at a Reynolds number of 1.5 million. The impact of different MGF heights including 0.25 %, 0.5 % and 1.0 % and a VG height of 1.1 % of the chord length is tested and evaluated. Furthermore, the clean and the tripped baseline cases are considered. In the latter, leading-edge transition is forced with Zig Zag (ZZ) turbulator tape. The preferred configurations are the smallest MGF on the NACA63(3)618 and the medium-sized MGF combined with VGs on the DU97W300. Next, the experimental lift and drag polar data are imported into the software QBlade in order to design a generic rotor blade. The blade performance is simulated with and without the add-ons by means of two case studies. In the first case, the retrofit application on an existing blade mitigates the adverse effects of the ZZ tape. Stall is delayed and the aerodynamic efficiency is partly recovered leading to an improvement of the power curve. In the second case, the new design application allows for the design of a more slender blade while maintaining the rotor power. This alternative blade appears to be more resistant against the adverse effects of forced leading-edge transition.

Numerical Assessment of a BAY-Type Model for different Vortex Generator Shapes Applied on a Wind Turbine Airfoil

Modern wind turbines are increasingly equipped with vortex generators in the inner part of the rotor blade. On large blades it is usual to install hundreds of these small passive devices to delay flow separation. Therefore, affordable numerical methods to include vortex generators in the design process are required. One very promising method based on the addition of source terms in the flow equations is the BAY model. In this work a BAY-type model is presented and assessed for three different vortex generator shapes (rectangular, delta and cropped-delta) placed on a DU 97-W-300 airfoil and computed with steady-state Reynolds-averaged Navier-Stokes numerical methods. In order to quantify the circulation of the main streamwise vortex, a method to identify the vortex core based on the λ2-criterion is presented and shows good results. The computations reveal very good agreement with the experimental data for attached flow in terms of lift and pressure distribution while drag is inherently underestimated by the BAY model due to the inviscid modelling of the vortex generators. It is displayed that this underestimation is proportional to the vortex generator surface area. Concerning the different shapes, it is shown that the delta shape reveals larger deviations from the fully resolved case than the other geometries and therefore requires higher mesh resolution.

Identification of torsional frequencies of a large rotor blade based on measurement and simulation data

With increasing size of wind turbines, the aerodynamic and structural properties of the rotor blades become more and more important. However, studies investigating the torsional properties using measurement data and simulation results on full-size turbines are still scarce. In this study, torsional measurements are carried out on a large wind turbine with a rotor diameter of 180 m and compared with model results. In this study, torsional measurements on a large wind turbine with a rotor diameter of 180 m are conducted and compared with model results. Torsional parameters of a rotor blade are identified using two different measurement methods, the first based on strain gauges and the second based on accelerometers. Both methods show frequencies that can be associated with the natural frequencies of the two first torsional modes of the rotor blade. To extract the natural frequencies and to reduce external effects, a manual pitching procedure is evaluated. Here, the first two natural frequencies associated with torsional modes can be identified. In a second step, the behaviour of the blade during power production is investigated and compared with the simulation results.

ЛАДЕЙКИ: ЗАБЫТЫЕ ПАМЯТНИКИ ПАЛЕОЛИТА КРАСНОЯРСКА

Ladeyki is the first famous Paleolithic site in the Enisiey valley (nowadays it is Kamenny Kvartal district in Kras- noyarsk) that was discovered by Savenkov I.T. in summer 1884, some days before the artifacts from Afontova Gora had been found. Later on, collection in blowouts on the outskirts of Ladeyki village were carried on by Elenev A. S., Ermolaev A. P., Merhart G., Sosnovski G. P. The analysis of archival and literary sources of the late XIX — early XX century allows us to trace in detail the history of the study of the site. The funds of the Krasnoyarsk Regional Museum of Local Lore contain a small collection of Paleolithic (?) items from Ladeyki site, which includes a pebble tool, fragments of a points on a large blade with retouched, fragments of small side-scrapers, large-sized chisel-like tools with their distinctive characteristic of so-called "dull lustre". It is known that the fauna fossils which are attributed to the Paleolithic included the bones of a reindeer, a mammoth and a bison. According to researches of the first part of XIX century (Merhart G., Gromov V. I., Sosnovskiy G. P.), the site, that was destroyed and partly redeposited in the blowouts, could be attributed ti the end of the Late Paleolithic as well as Pereselencheskiy Punkt. Cultural affiliation of Ladeyki is still discussed. Nowadays Ladeyki is better known as the site of the early Iron Age and the early Middle Ages (Ladeyskoe settlement, site Ladeyskaia-2). Exploration survey carried out in 2012 on the territory of the Kamenny Kvartal did not help to reveal traces of the Late Paleolithic site.

Design and structural responses of a 38-meter sectional wind turbine blade under extreme static loads

The structural reliability of large sectional blades has always been a challenging issue with regard to the mild cost increment incurred compared with corresponding non-segmented blades. The use of excellent connection configurations and optimized composite layouts are cost-efficient approaches to achieve this goal as well as better understanding of the structural responses of sectional blades under extreme loads. This work presents the design and fabrication of a sectional blade, based on a 38-meter typical commercial wind turbine blade, with unique connections and a composite layout. The prototype blade is experimentally studied under extreme static loads according to international standards. The strains of the spar caps, sandwich structures, and shear webs are collected, and the contact status of adjacent segments and bolt loads are also monitored as well. The results revealed that the sectional blade successfully sustained the extremely static loads with only a moderate manufacturing cost increment compared with the corresponding non-segmented blade. The advantages of the proposed strategies are validated for sectional blades. Regarding the structural integrity of the sectional blade, blade buckling, composite failure and residual deflection were not observed. Flap-wise loads are more critical for the bolted joint of segment connections than edge-wise loads, as detrimental bolt load increases tend to occur due to the prying effect at the leading and trailing edges. An improved analysis based on the load factor from multi-bolted joint box-beam models and experiments could predict the bolt loads of segmented connections with desirable accuracy and could be suitable for the multi-bolted joint design of sectional blades.

Paleolithic Site Tri Skaly in Western Transbaikalia as a Hunter-Gatherers’ Base Camp

Purpose. In 2015 a new archaeological site Tri Skaly were found in the lower part of the Khilock River basin (Western Transbaikalia). This site is of a large interest in the sense of investigations concerned early stages of the Upper Palaeolithic in Transbaikal, because it is westernmost among similar sites and located in the area where such sites were not known earlier. The purpose of this investigation is defining the functional purpose of the ancient settlement. Discrete approach to the data analysis lead to the controversial conclusions. The article presents the results of the complex approach to the investigations of palaeolithic cultural horizons at Tri Skaly archaeological site.Results. In the Tri Skaly collection the most representative and various part of the archaeological finds consists of the stone artifacts typical for the early Upper Paleolithic period. On the basis of the stone industry consideration the affinity with the Tolbaga culture’s Paleolithic sites is proposed; it is reflected in the production of tools on the large blades. The well-investigated sites of this culture show the representative toolkit and the multi-way economic activity at the ancient settlement. The obvious predominance of primary knapping products over retouched items suggests the use of the area as a workshop, or camp workshop if we take into consideration the presence of some structural elements of the cultural horizon. Paleontological materials demonstrate the overwhelming majority of the Equus Ferus bones, the distal ends of the legs. This fact leads to the conclusion that this area was used as the kill and butchering site. At the same time, we have evidence that allows us to interpret bones as possible kitchen debris, not only wastes from butchering. In addition, a toolkit includes various types of tools related to different activities.Conclusion. The detailed analysis and synthesis of all available components from the Paleolithic site Tri Skaly (stone industry, palaeontological finds) evidence about multi-way economic activity here in Upper Palaeolithic. Based on this we conclude Tri Skaly site is a periodically used base hunting camp with a full cycle of stone processing and tool production and evidences of non-utilitarian activity.

Effect of Delay on Control of Direct Resonance of Ships in Beam Waves Using a Proportional–Derivative Controller With Delay

Abstract A harmonically excited, single-degree-of-freedom time-delay system with cubic and quintic nonlinearities is studied. This system describes the direct resonance of a ship with an actively controlled antiroll tank (ART) that is subjected to beam waves. We consider low-, medium-, and high-freeboard ship models. A proportional–derivative (PD) controller with a constant time delay is assumed to operate the pump in the active ART system. The delay originates from the time required to pump fluid from one container to another, the inertia of large impeller blades and linkages, and the measurement and processing time of the roll-sensing unit. The stability boundary of the system, in the parametric space of the control gain and the delay, is derived analytically from the characteristic equation of the linearized system. We show that the area of the zero equilibrium region is inversely related to the derivative time constant of the PD controller; thus, we focus on a strictly proportional-gain controller. The spectral Tau method is used to identify the eigenvalues associated with the zero equilibrium since the rightmost eigenvalues determine the system's robustness to perturbations in the initial conditions. We use the method of multiple scales and harmonic balance to obtain the global bifurcation diagram in the space of the applied frequency and the amplitude of the response. Numerical simulations verify our analytical expressions. Study of the dynamics, stability, and control of the roll motion of ships is critical to avoid dynamic instabilities and capsizing.

Development of three-dimensional co-rotational beam model for nonlinear dynamic analysis of highly flexible slender composite blades

The main purpose of this work is to introduce a novel method analyzing the dynamic response of a highly flexible slender composite beam having anisotropic property and variable cross-section. A three-dimensional co-rotational model is developed. The beam deformation in dynamic conditions is obtained by applying HHT-α method as dynamic analysis tool. Validation studies with various boundary conditions, multiple external loads and pre-curved structures are performed. Furthermore, dynamic analysis with a large, flexible, and slender composite blade is performed with and without structural couplings. It is shown the developed beam model accurately predicts nonlinear three-dimensional response and anisotropic structural coupling effects.

A comprehensive three-dimensional study on Darrieus vertical axis wind turbine with slotted blade to reduce flow separation

Aerodynamic performance of different designs of slotted blade of a straight blade Darrieus vertical axis wind turbine and their corresponding flow structure are precisely analyzed using three-dimensional numerical simulation. The slots aim to transfer flow from the blade pressure side to its suction side and eventually improve the blade output torque by procrastination of flow separation, especially at low tip speed ratios (TSRs). Investigations on slot width and blade height reveal that the slot should be wide enough to successfully pass flow to confront higher volume of flow separation in larger blades. Having changed the outflow location of the slot from 2C/3 to C/6 from the blade leading edge, the location of C/3 is found to be the best by noticeable alleviation in flow separation and suppressing its development toward the blade leading edge. As a result, significant improvement in average torque coefficient is achieved. This means that at TSRs of 0.5, 1.0, and 1.5, average torque coefficient increases for the slotted blade by 93.4%, 66.1%, and 10.5%, respectively. In addition, a delay of up to 15.5° occurs in the azimuth angle of torque coefficient peak with respect to that of the base blade (without slot).

Выбор высоты лопаток рабочего колеса центробежного компрессора при первичном проектировании

In the preliminary designing of industrial centrifugal compressors using the universal modeling method, the relative blade heights at the exit of the impeller of a centrifugal compressor are determined only by the dimensionless compressor performance parameter— a conditional flow rate in the design mode. The second main design parameter, the theoretical head factor, is not taken into account. This rule is formulated on the basis that the relative height of the blades has relatively little effect on the slowing down the flow on the suction side of the blades, where separation can occur. The article considers another negative aspect of the large blade height. Increasing the height of the blades reduces their exit angle at a given theoretical head coefficient. The rotation of the flow by the blades decreases (which helps to reduce losses), but their length increases. With a larger area of the blades, friction losses increase. The computational research was carried out on the example of impellers with a moderate flow rate = 0.0518 in the theoretical head coefficient range = 0.475–0.70. Mathematical models of the Universal Modeling Method and calculations of an inviscid quasi-three-dimensional flow were selected as a tool for research. The results show that the existing primary design methodology can be refined.

Research on dynamic aerodynamic performance of wind turbine airfoil under large blade deformation

With the increase of wind power blades, the amount of blade design pre-bending and deformation in motion has increased significantly. Under the condition of large deformation of the wind turbine blade, the pitch axis deviates greatly from the centerline of the airfoil. At this point, the pitch movement of the wind turbine blade will lead to the dynamic change of the airfoil angle of attack and the horizontal movement of the airfoil at the same time. Concerning this problem, the dynamic stall characteristic of the S809 airfoil under the condition of large deformation was studied using CFD technology. The results show that the horizontal motion caused by the deviation of the pitch axis from the airfoil center can significantly change the stall characteristic of the airfoil. Based on this, the fatigue load changes caused by changes in dynamic stall characteristics under typical operating conditions are studied.

Uncertainty quantification of modal parameter estimates obtained from subspace identification: An experimental validation on a laboratory test of a large-scale wind turbine blade

The uncertainty afflicting modal parameter estimates stems from e.g., the finite data length, unknown, or partly measured inputs and the choice of the identification algorithm. Quantification of the related errors with the statistical Delta method is a recent tool, useful in many modern modal analysis applications e.g., damage diagnosis, reliability analysis, model calibration. In this paper, the Delta method-based uncertainty quantification methodology is validated for obtaining the uncertainty of the modal parameter and the modal indicator estimates in the context of several well-known subspace identification algorithms. The focus of this study is to validate the quality of each Delta method-based approximation with respect to the experimental Monte Carlo distributions of parameter estimates using a statistical distance measure. On top of that, the accuracy in obtaining the related confidence intervals is empirically assessed. The case study is based on data obtained from an extensive experimental campaign of a large scale wind turbine blade tested in a laboratory environment. The results confirm that the Delta method is, on average, adequate to characterize the distribution of the considered estimates solely based on the quantities obtained from one data set, validating the use of this statistical framework for uncertainty quantification in practice.

Study on surface roughness of large size TiAl intermetallic blade in electrochemical machining

Large size TiAl alloy blades as a core component in aero-engines have received a lot of attention due to their light weight and superior performance. However, precision manufacturing of such blades is very difficult using traditional mechanical cutting methods because of the large size, super twisted profile and typical difficult-to-cut materials. Electrochemical machining (ECM) is a preferred method for such blades due to its inherent characteristics. In this work, the surface quality of such blades is studied in detail and some defects on the surface of the blade are overcome. Exploratory experiments of DC ECM and pulse ECM at different pulse frequencies are carried out, and the results show that pulse ECM at low pulse frequency is more likely to obtain blade with high surface quality. A two-step variable parameter ECM strategy is proposed based on low pulse frequency, which completely removed the “patchy” morphology and raised defects on the blade surface, and reduced the surface roughness from about Ra 5.5 μm to about Ra 1.8 μm. A control method of multi-channel pressure difference at the inlet is proposed based on the direction of the flow mark, which effectively eliminated the flow mark defect on the blade surface, further reduced the surface roughness to about Ra 0.9 μm, and obtained the blade with high surface quality.

Fault Detection of Wind Turbine Blades Using Multi-Channel CNN

This study utilized the multi-channel convolutional neural network (MCNN) and applied it to wind turbine blade and blade angle fault detection. The proposed approach automatically and effectively captures fault characteristics from the imported original vibration signals and identifies their state in multiple convolutional neural network (CNN) models. The result obtained from each model is sent to the output layer, which is a maximum output network (MAXNET), to compute the most accurate state. First, in terms of wind turbine blade state detection, this paper builds blade models based on the normal state and three common fault types, including blade angle anomaly, blade surface damage, and blade breakage. Vibration signals are employed for fault detection. The proposed wind turbine fault diagnosis approach adopts a triaxial vibration transducer and frame grabber to capture vibration signals and then applies the new MCNN algorithm to identify the state. The test results show that the proposed approach could deliver up to 87.8% identification accuracy for four fault types of large wind turbine blades.