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1
Thresher, R. W., A. D. Wright i E. L. Hershberg. "A Computer Analysis of Wind Turbine Blade Dynamic Loads". Journal of Solar Energy Engineering 108, nr 1 (1.02.1986): 17–25. http://dx.doi.org/10.1115/1.3268046.
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The flapping motion of a single wind turbine rotor blade has been analyzed and equations describing the flapping motion have been developed. The analysis was constrained to allow only flapping motions for a cantilevered blade, and the equations of motion are linearized. A computer code, called FLAP (Force and Loads Analysis Program), to solve the equations of motion and compute the blade loads, has been completed and compared to measured loads for a 3-bladed downwind turbine with stiff blades. The results of the program are presented in tabulated form for equidistant points along the blade and equal azimuth angles around the rotor disk. The blade deflection, slope and velocity, flapwise shear and moment, edgewise shear and moment, blade tension, and blade torsion are given. The deterministic excitations considered in the analysis include wind shear, tower shadow, gravity, and a prescribed yaw motion.
2
Stanisławski, Jarosław. "Simulation of Boundary States of Helicopter Flight". Journal of KONES 26, nr 2 (1.06.2019): 137–44. http://dx.doi.org/10.2478/kones-2019-0042.
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Abstract Results of simulation of main rotor blade loads and deformations, which can be generated during boundary states of helicopter flight, are presented. Concerned cases of flight envelope include hover at maximum height, level flight at high velocity, pull-up manoeuvres applying cyclic pitch and mixed collective and cyclic control. The simulation calculations were executed for data of light helicopter with three-bladed articulated rotor. For analysis, the real blades are treated as elastic axes with distributed masses of blade segments. The model of deformable blade allows for out-of-plane bending, in plane bending, and torsion. For assumed flight state of helicopter, the equations of rotor blades motion are solved applying Runge-Kutta method. According to Galerkin method, for each concerned azimuthal position of blade the parameters of its motions are assumed as a combination of considered bending and torsion eigen modes of the blade. The loads of rotor blades generated during flight depend due to velocity of flight, helicopter mass, position of rotor axis in air and deflections of swashplate that correspond to collective and cyclic pitch angle applied to rotor blades. The results of simulations presenting rotor loads and blade deformations are shown in form of time-runs and as plots of rotor-disk distributions. The simulations of helicopter flight states may be useful for prediction the conditions of flight-tests without exceeding safety boundaries or may help to define limitations for manoeuvre and control of helicopter.
3
Christensen, René H., i Ilmar F. Santos. "Modal Controllability and Observability of Bladed Disks and their Dependency on the Angular Velocity". Journal of Vibration and Control 11, nr 6 (czerwiec 2005): 801–28. http://dx.doi.org/10.1177/1077546305054596.
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Rotating bladed disks are characterized by time-variant mathematical models presenting vibration coupling among rotor lateral motion and blade flexible motion. Moreover, they present parametric vibration modes and the blade natural frequencies may change depending on the angular velocity due to centrifugal stiffening. Consequently, the degree of controllability and observability of bladed disks also becomes time-varying, dependent on angular velocity, and a difficult task to analyze. In this paper we present a methodology for analyzing the modal controllability and observability of a bladed disk, based on time-variant modal analysis. The method takes into account time-variant parametric vibration mode shapes, and quantitative measures of modal controllability and observability are calculated. Numerical results show that, in order to control blade and shaft vibrations of a tuned bladed disk, by means of active control, blade-based as well as shaft-based sensing and actuation are required to monitor and control all vibration levels. If rotor blades are properly mistuned, the results show that disk as well as blade vibrations are monitorable and controllable by using only shaft-based sensing and actuation. The analysis shows why the mistuned disk becomes theoretically controllable and observable, via the presence of parametric mode shape components. Finally, the results show that the levels of controllability and observability depend significantly on the angular velocity, no matter the number of applied sensors and actuators used or their positioning.
4
He, Shangwen, Kunli Si, Bingbing He, Zhaorui Yang i Ying Wang. "Rub-Impact Dynamics of Shrouded Blades under Bending-Torsion Coupling Vibration". Symmetry 13, nr 6 (16.06.2021): 1073. http://dx.doi.org/10.3390/sym13061073.
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Shroud devices which are typical cyclic symmetric structures are widely used to reduce the vibration of turbine blades in aero engines. Asymmetric rub-impact of adjacent shrouds or aerodynamic excitation forces can excite the bending-torsion coupling vibration of shrouded blades, which will lead to complex contact motions. The aim of this paper is to study the rub-impact dynamic characteristics of bending-torsion coupling vibration of shrouded blades using a numerical method. The contact-separation transition mechanism under complex motions is studied, the corresponding boundary conditions are set up, and the influence of moments of contact forces and aerodynamic excitation forces on the motion of the blade is considered. A three-degree-of-freedom mass-spring model including two mass blocks with the same size and shape is established to simulate the bending-torsion coupling vibration, and the dynamic equations of shrouded blades under different contact conditions are derived. An algorithm based on the fourth-order Runge–Kutta method is presented for simulations. Variation laws of the forced response characteristics of shrouded blades under different parameters are studied, on the basis of which the method to evaluate the vibration reduction characteristics of the shrouded blade system when the motion of the blade is chaotic is discussed. Then, the vibration reduction law of shrouded blades under bending-torsion coupling vibration is obtained.
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Beresnevich, Vitaly, Marina Cerpinska, Janis Viba i Martins Irbe. "Dynamics analysis and structural synthesis of wind energy production device with closed loop conveyor". Vibroengineering PROCEDIA 44 (25.08.2022): 156–62. http://dx.doi.org/10.21595/vp.2022.22867.
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This paper deals with a dual design device for wind energy production, in which the movement of the blade consists of several stages, that is, two stages of rotation about two fixed axes and two stages of the blades straight translation movement. The proposed design offers a closed-shaped flattened conveyor equipped with several identical flat-shaped blades. The blades are mounted on a conveyor belt and have an opportunity to move together with the belt in one straight line direction. Therefore, air flow kinetic energy is transformed into translation motion of flat blades. The conveyor system has a built-in energy generator. To analyse blade interaction with air flow, a superposition principle is applied, in which the fast chaotic motion of air particles (Brownian motion) is separated from the slow flow motion with the given average velocity. On the base of such separation, a differential equation of motion for the entire conveyor system with one degree of freedom is obtained. Dynamics of the system due to the action of air flow is simulated with computer program Mathcad. Optimization of system parameters is performed, using a generated power as criterion. In addition, motion control at changeable airflow is optimized by selecting the blade orientation and corresponding adjustment of generator.
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Stanislawski, Jaroslaw. "A simulation investigation of helicopter ground resonance phenomenon". Aircraft Engineering and Aerospace Technology 91, nr 3 (4.03.2019): 484–97. http://dx.doi.org/10.1108/aeat-11-2017-0256.
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Purpose The purpose of this paper is to present a simulation method applied for investigation of helicopter ground resonance phenomenon. Design/methodology/approach The considered physical model of helicopter standing on ground with rotating rotor consists of fuselage and main transmission gear treated as stiff bodies connected by elastic elements. The fuselage is supported on landing gear modeled by spring-damper units. The main rotor blades are treated as set of elastic axes with lumped masses distributed along blade radius. Due to Galerkin method, parameters of blades motion are assumed as a combination of bending and torsion eigen modes. A Runge–Kutta method is applied to solve equations of motions of rotor blades and helicopter fuselage. Findings The presented simulation method may be applied in preliminary stage of helicopter design to avoid ground resonance by proper selection of landing gear units and blade damper characteristics. Practical implications Ground resonance may occur in form of violently increasing mutual oscillations of helicopter fuselage and lead-lag motion of rotor blades. According to changes of stiffness and damping characteristics, simulations show stable behavior or arising oscillations of helicopter. The effects of different blade balance or defect of blade damper are predicted. Originality/value The simulation method may help to determine the envelope of safe operation of helicopter in phase of take-off or landing. The effects of additional disturbances as results of blades pitch control as swashplate deflection are introduced.
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LeGrand, Scott A., Bradley J. Hindman, Franklin Dexter, Julie B. Weeks i Michael M. Todd. "Craniocervical Motion during Direct Laryngoscopy and Orotracheal Intubation with the Macintosh and Miller Blades". Anesthesiology 107, nr 6 (1.12.2007): 884–91. http://dx.doi.org/10.1097/01.anes.0000291461.62404.46.
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Background Previous studies have characterized segmental craniocervical motion that occurs during direct laryngoscopy and intubation with a Macintosh laryngoscope blade. Comparable studies with the Miller blade have not been performed. The aim of this study was to compare maximal segmental craniocervical motion occurring during direct laryngoscopy and orotracheal intubation with Macintosh and Miller blades. Methods Eleven anesthetized and pharmacologically paralyzed patients underwent two sequential orotracheal intubations, one with a Macintosh blade and another with a Miller in random order. During each intubation, segmental craniocervical motion from the occiput to the fifth cervical vertebra (C5) was recorded using continuous lateral cinefluoroscopy. Single-frame images corresponding to the point of maximal cervical motion for both blade types were compared with a preintubation image. Using image analysis software, angular change in the sagittal plane at each of five intervertebral segments was compared between the Macintosh and Miller blades. Results Extension at occiput-C1 was greater with the Macintosh blade compared with the Miller (12.1 degrees +/- 4.9 degrees vs. 9.5 degrees +/- 3.8 degrees, respectively; mean difference = 2.7 degrees +/- 3.0 degrees; P = 0.012). Total craniocervical extension (occiput-C5) was also greater with the Macintosh blade compared with the Miller (28.1 degrees +/- 9.5 degrees vs. 23.2 degrees +/- 8.4 degrees, respectively; mean difference = 4.8 degrees +/- 4.4 degrees; P = 0.008). Conclusions Compared with the Macintosh, the Miller blade was associated with a statistically significant, but quantitatively small, decrease in cervical extension. This difference is likely too small to be important in routine practice.
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Person, M. "The Equations of Motion of n-Bladed Propellers with Arbitrarily Positioned Hinges and Their Application to an Experimental One-Bladed Wind Turbine". Proceedings of the Institution of Mechanical Engineers, Part A: Power and Process Engineering 199, nr 4 (listopad 1985): 237–44. http://dx.doi.org/10.1243/pime_proc_1985_199_030_02.
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The equations of motion of n-bladed propellers with arbitrarily positioned hinges are derived out of the equations of a one-bladed propeller, by superposition. Different types of propellers are compared for time variances at the equations. An unbalanced start-up and the stability analyses (Floquet) of an experimental one-bladed propeller illustrate the need to consider the interaction of the motions of nacelle or hub and blade.
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Stanisławski, Jarosław. "A Comparison of Helicopter Main Rotor Features Due to Stiffness of Rotor Blade-Hub Connection". Transactions on Aerospace Research 2018, nr 1 (1.03.2018): 119–36. http://dx.doi.org/10.2478/tar-2018-0008.
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Abstract The paper presents results of simulation calculations concerning an influence of stiffness of blade-hub connection on rotor loads and blades deflections in hover, level flight and pull up maneuver. The three versions of rotor are considered with articulated, elastic and stiff connections of blades and hub. The blades with the same distributions of stiffness, mass and the same aerodynamic characteristics are applied for all rotor cases. The rotor loads are calculated applying Runge-Kutta method to solve the equations of motion of deformable blades. According to the Galerkin method, the parameters of blades motion are treated as combination of considered blade bending and torsion eigen modes. The results of calculations indicate for possibility to generate the greater rotor control moments and to improve helicopter maneuverability in the case of applying the non-changed blade of articulated rotor combined with elastic rotor hub.
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Gribin, Vladimir, Ilya Gavrilov, Aleksandr Tishchenko, Victor Tishchenko, Vitaliy Popov, Sergey Khomyakov i Roman Alexeev. "Features of liquid phase movement in the inter-blade channel of nozzle blade cascade". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 232, nr 5 (13.09.2017): 452–60. http://dx.doi.org/10.1177/0957650917730947.
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The experimental results of wet steam flow in the blade channel of flat nozzle blade cascade have been considered in the paper. The aim of this work is to study the motion of liquid droplets inside the inter-blade channel. Experimental studies were performed on installation circuit of wet steam. In order to obtain velocity fields of droplets in investigated channel, the laser diagnostics system was used. It carries out the cross-correlation method—particle tracking velocimetry. Numerical simulation of wet steam flow in studied channel was performed. According to the obtained data, the main features of the droplets motion in the blade channel have been revealed. Basic droplets streams and the sources of their appearance have been determined. The process of deposition and breakdown of the droplets on the surface of the blades have been studied. It is shown that reflected region of droplets (“fountain”) is formed around the leading edge. The experimental data were compared with the results of numerical simulation of the droplets motion in the flat nozzle blade cascade.
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Douvi, Dimitra, Eleni Douvi i Dionissios P. Margaris. "The Operation of a Three-Bladed Horizontal Axis Wind Turbine under Hailstorm Conditions—A Computational Study Focused on Aerodynamic Performance". Inventions 7, nr 1 (21.12.2021): 2. http://dx.doi.org/10.3390/inventions7010002.
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The aim of this study is the aerodynamic degradation of a three-bladed Horizontal Axis Wind Turbine (HAWT) under the influence of a hailstorm. The importance and originality of this study are that it explores the aerodynamic performance of an optimum wind turbine blade during a hailstorm, when hailstones and raindrops are present. The commercial Computational Fluid Dynamics (CFD) code ANSYS Fluent 16.0 was utilized for the simulation. The first step was the calculation of the optimum blade geometry characteristics for a three-bladed rotor, i.e., twist and chord length along the blade, by a user-friendly application. Afterwards, the three-dimensional blade and the flow field domain were designed and meshed appropriately. The rotary motion of the blades was accomplished by the application of the Moving Reference Frame Model and the simulation of hailstorm conditions by the Discrete Phase Model. The SST k–ω turbulence model was also added. The produced power of the wind turbine, operating in various environmental conditions, was estimated and discussed. Contours of pressure, hailstone and raindrop concentration and erosion rate, on both sides of the blade, are presented. Moreover, contours of velocity at various cross sections parallel to the rotor are demonstrated, to understand the effect of hailstorms on the wake behavior. The results suggest that the aerodynamic performance of a HAWT degrades due to impact and breakup of the particles on the blade.
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Wang, Hao, Junyu Yi, Wei Chen i Zhexin Zhou. "Flutter Analysis of Piezoelectric Material Based Smart Wind Turbine Blade". International Journal of Acoustics and Vibration 26, nr 3 (30.09.2021): 240–47. http://dx.doi.org/10.20855/ijav.2021.26.31787.
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This paper presents a smart wind turbine blade of piezoelectric material. Based on Theodorsen unsteady aerodynamics and the V-g method, the flutter analysis in frequency domain is carried out for the smart wind turbine blade and the ordinary wind turbine blade. The simulation results demonstrate that the flutter critical velocity, that is, the reduced velocity of the smart wind turbine blade, is obviously much higher than that of the ordinary wind turbine blade. The smart wind turbine blade of piezoelectric material can effectively restrain the flutter of the wind turbine blade, especially for the flap motion. For the torsion motion, the smart wind turbine blade is kept away from the critical flutter. Then, to investigate the influences of different parameters on the flutter of the smart wind turbine blade, the influences of the center of gravity, the frequency ratio and the mass ratio of the blades on the flutter critical velocity of the smart wind turbine blade are researched respectively. The increase of the applied external electrical load of the piezoelectric material can increase the flutter critical velocity of the smart wind turbine blade.
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Kuang, J. H., i B. W. Huang. "Mode Localization of a Cracked Blade Disk". Journal of Engineering for Gas Turbines and Power 121, nr 2 (1.04.1999): 335–41. http://dx.doi.org/10.1115/1.2817125.
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In this paper, the effect of blade crack on the mode localization of a rotating blade disk is studied. Pretwisted taper beams are used to simulate blades of a blade disk. The crack on the blade can be regarded as a local disorder of this periodically coupled blades system. An application of Hamilton’s principle and Galerkin’s method is used to formulate the equations of motion of the mistuned system. Effects of pretwisted angle, rotating speed, and crack depth of the blade on the in-plane and off-plane mode localizations of a rotating system are investigated. Numerical results indicate that the increase of rotating speed, pretwisted angle, and crack depth could enhance the localization phenomenon significantly.
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Afagh, F. F., F. Nitzsche i N. Morozova. "Dynamic modelling and stability of hingeless helicopter blades with a smart spring". Aeronautical Journal 108, nr 1085 (lipiec 2004): 369–77. http://dx.doi.org/10.1017/s0001924000005182.
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AbstractThe aeroelastic stability of a uniform, untwisted hingeless ‘smart’ helicopter rotor blade in hover has been analysed. The concept of a ‘smart’ blade is achieved by implementing a piezoelectric stack at an appropriate location along a host blade such that upon actuation it enters the load path becoming an integral part of the host structure. Thus, the stiffness characteristics of the rotor are altered causing modal damping augmentation of the blade. The perturbation equations of motion for the ‘smart’ blade that describe the unsteady blade motion about the equilibrium operating condition are obtained using Galerkin’s method. These differential equations with periodic time coefficients are analysed for stability utilising the Floquet method. Six different regimes of actuation are investigated, and a parametric study is carried out by considering six different design cases. It is shown that, compared to a ‘host’ blade the stability characteristics of the ‘smart’ blade are not affected adversely. In fact, a judicious design and actuation of the ‘smart’ spring has the potential of improving the stability boundaries of individual blades.
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Savov, V., i M. Raikov. "Autorotating rotor with ornithopter-like flapping blades". Aeronautical Journal 106, nr 1061 (lipiec 2002): 399–409. http://dx.doi.org/10.1017/s0001924000092162.
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AbstractClassification of the winged aircraft according to the character of wing (blade) motion in horizontal and vertical plane is presented. Design of a rotor, the blades of which are driven into rotation via flapping motion similar to the movement of an ornithopter's wing is proposed and the principle of operation is considered. Mathematical model of the aerodynamics of the autorotating rotor with flapping blades in hover is made on the base of the helicopter rotor blade-element theory. Geometric and kinematic parameters influence on the rotor lift and efficiency is analysed. It is shown that in hover the efficiency of an autorotating rotor with flapping blades is approximately equal to the one of a helicopter rotor.
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Yao, Minghui, Li Ma i Wei Zhang. "Nonlinear Dynamics of the High-Speed Rotating Plate". International Journal of Aerospace Engineering 2018 (2018): 1–23. http://dx.doi.org/10.1155/2018/5610915.
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High speed rotating blades are crucial components of modern large aircraft engines. The rotating blades under working condition frequently suffer from the aerodynamic, elastic and inertia loads, which may lead to large amplitude nonlinear oscillations. This paper investigates nonlinear dynamic responses of the blade with varying rotating speed in supersonic airflow. The blade is simplified as a pre-twist and presetting cantilever composite plate. Warping effect of the rectangular cross-section of the plate is considered. Based on the first-order shear deformation theory and von-Karman nonlinear geometric relationship, nonlinear partial differential dynamic equations of motion for the plate are derived by using Hamilton’s principle. Galerkin approach is applied to discretize the partial differential governing equations of motion to ordinary differential equations. Asymptotic perturbation method is exploited to derive four-degree-of-freedom averaged equation for the case of 1 : 3 internal resonance-1/2 sub-harmonic resonance. Based on the averaged equation, numerical simulation is used to analyze the influence of the perturbation rotating speed on nonlinear dynamic responses of the blade. Bifurcation diagram, phase portraits, waveforms and power spectrum prove that periodic motion and chaotic motion exist in nonlinear vibration of the rotating cantilever composite plate.
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Qin, Xiaoyu, Bin Deng i Hongqiang Wang. "Micro-Doppler Feature Extraction of Rotating Structures of Aircraft Targets with Terahertz Radar". Remote Sensing 14, nr 16 (9.08.2022): 3856. http://dx.doi.org/10.3390/rs14163856.
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The micro-Doppler features formed by the micro-motion of rotating blades of rotors and turbines are of great significance for aircraft target detection and recognition. Mastering the micro-motion features is the premise of radar target identification. The blades’ length and rotation rate are vital parameters for classifying aircraft targets. One can instantly judge the type and state of the targets by extracting micro-Doppler features. To extract the micro-Doppler features of rotating blades of the turbine target, we utilized microwave-band and terahertz-band radar to simulate the target and extract the Doppler frequency-shift information. For a turbine model with an obvious blade tip structure, we propose an algorithm based on wavelet coefficient enhancement and inverse Radon transform, integrating the time–frequency analysis with image processing. Under low SNR, this method allows for a high-accuracy parameter estimate. For a two-bladed rotor model without an obvious blade tip structure, we conducted an actual measurement experiment on the model utilizing a 120 GHz radar, and we propose a parameter estimation algorithm based on the fitting of the time–frequency distribution. By fitting the data of the time–frequency diagram, the micro-motion characteristic parameters of the rotor target were obtained. The simulation and experimental results demonstrate the benefits of terahertz radar in target detection, and indicate that the proposed algorithms have the characteristics of high extraction precision and insensitivity to noise.
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Kim i Kwon. "Effect of Platform Motion on Aerodynamic Performance and Aeroelastic Behavior of Floating Offshore Wind Turbine Blades". Energies 12, nr 13 (30.06.2019): 2519. http://dx.doi.org/10.3390/en12132519.
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In the present study, a numerical framework for predicting the aerodynamic performance and the aeroelastic behavior of floating offshore wind turbine rotor blades involving platform motion was developed. For this purpose, the aerodynamic and structural analyses were conducted simultaneously in a tightly coupled manner by exchanging the information about the aerodynamic loads and the elastic blade deformations at every time step. The elastic behavior of the turbine rotor blades was described by adopting a structural model based on the Euler-Bernoulli beam. The aerodynamic loads by the rotor blades were evaluated by adopting a blade element momentum theory. The numerical simulations were conducted when the platform of the wind turbine independently moves in each of the six degrees-of-freedom directions consisting of heave, sway, surge, roll, pitch, and yaw. It was observed that flexible blades exhibit complicated vibratory behaviors when they are excited by the aerodynamic, inertia, and gravitational forces simultaneously. It was found that the load variation caused by the platform surge or pitch motion has a significant influence on the flapwise and torsional deformations of the rotor blades. The torsional deformation mainly occurs in the nose-down direction, and results in a reduction of the aerodynamic loads. It was also found that the flapwise root bending moment is mainly influenced by the platform surge and pitch motions. On the other hand, the edgewise bending moment is mostly dictated by the gravitational force, but is not affected much by the platform motion.
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Dalli, Uğbreve;ur, i Şcedilefaatdin Yüksel. "Identification of Flap Motion Parameters for Vibration Reduction in Helicopter Rotors with Multiple Active Trailing Edge Flaps". Shock and Vibration 18, nr 5 (2011): 727–45. http://dx.doi.org/10.1155/2011/675791.
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An active control method utilizing the multiple trailing edge flap configuration for rotorcraft vibration suppression and blade loads control is presented. A comprehensive model for rotor blade with active trailing edge flaps is used to calculate the vibration characteristics, natural frequencies and mode shapes of any complex composite helicopter rotor blade. A computer program is developed to calculate the system response, rotor blade root forces and moments under aerodynamic forcing conditions. Rotor blade system response is calculated using the proposed solution method and the developed program depending on any structural and aerodynamic properties of rotor blades, structural properties of trailing edge flaps and properties of trailing edge flap actuator inputs. Rotor blade loads are determined first on a nominal rotor blade without multiple active trailing edge flaps and then the effects of the active flap motions on the existing rotor blade loads are investigated. Multiple active trailing edge flaps are controlled by using open loop controllers to identify the effects of the actuator signal output properties such as frequency, amplitude and phase on the system response. Effects of using multiple trailing edge flaps on controlling rotor blade vibrations are investigated and some design criteria are determined for the design of trailing edge flap controller that will provide actuator signal outputs to minimize the rotor blade root loads. It is calculated that using the developed active trailing edge rotor blade model, helicopter rotor blade vibrations can be reduced up to 36% of the nominal rotor blade vibrations.
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de Andrade, Donizeti, i David A. Peters. "Coupling of a State-Space Inflow to Nonlinear Blade Equations and Extraction of Generalized Aerodynamic Force Mode Shapes". Applied Mechanics Reviews 46, nr 11S (1.11.1993): S295—S304. http://dx.doi.org/10.1115/1.3122648.
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The aeroelastic stability of helicopter rotors in hovering flight has been investigated by a set of generalized dynamic wake equations and hybrid equations of motion for an elastic blade cantilevered in bending and having a torsional root spring to model pitch-link flexibility. The generalized dynamic wake model employed is based on an induced flow distribution expanded in a set of harmonic and radial shape functions, including undetermined time dependent coefficients as aerodynamic states. The flow is described by a system of first-order, ordinary differential equations in time, for which the pressure distribution at the rotor disk is expressed as a summation of the discrete loadings on each blade, accounting simultaneously for a finite number of blades and overall rotor effects. The present methodology leads to a standard eigenanalysis for the associated dynamics, for which the partitioned coefficient matrices depend on the numerical solution of the blade equilibrium and inflow steady-state equations. Numerical results for a two-bladed, stiff-inplane hingeless rotor with torsionally soft blades show the importance of unsteady, three-dimensional aerodynamics in predicting associated generalized aerodynamic force mode shapes.
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Uchiyama, T. "Numerical study on the propulsive performance of a wiggling blade in bubbly flow". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 216, nr 12 (1.12.2002): 1187–96. http://dx.doi.org/10.1243/095440602321029427.
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In order to search for an efficient propulsion mechanism in an air-water bubbly flow, the propulsive performance of a blade wiggling in the bubbly flow is analysed by a two-dimensional numerical method. The blade, whose geometry is similar to an NACA65–010 hydrofoil, is set in a straight conduit, in which the bubbly mixture flows. The wiggling motion is expressed by a progressive wave with reference to the swimming motions of fish. The bubbly flow is calculated by an incompressible two-fluid model in conjunction with the finite element method proposed by the author in an earlier paper. The calculations reveal the effects of a progressive waveform and volumetric fraction of air upstream of the blade on the propulsive performance of the blade. The time variations of the flow properties around the blade are also discussed in relation to the blade motion and propulsive performance.
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Brunner, C. E., J. Kiefer i M. Hultmark. "Comparison of dynamic stall on an airfoil undergoing sinusoidal and VAWT-shaped pitch motions". Journal of Physics: Conference Series 2265, nr 3 (1.05.2022): 032006. http://dx.doi.org/10.1088/1742-6596/2265/3/032006.
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Abstract The aerodynamics of vertical axis wind turbines (VAWTs) are inherently unsteady because the blades experience large angle of attack variations throughout a full turbine revolution. At low tip speed ratios, this can lead to a phenomenon known as dynamic stall. To better characterise the unsteady aerodynamics and represent them in models and simulations, data from studies of individual static or pitching airfoils are often applied to VAWT blades. However, these studies often involve sinusoidally pitching airfoils, whereas the pitching motions experienced by VAWTs are more complex. Here, the pressures and forces on an airfoil undergoing VAWT-shaped pitch motions corresponding to various tip speed ratios are compared to those of a sinusoidally pitching airfoil in order to assess whether a sinusoidal motion represents a reasonable approximation of the motions of a VAWT blade. While the lift development induced by the sinusoidal motion yields good agreement with that induced by the VAWT-shaped motion at the higher tip speed ratios, notable discrepancies exist at the lower tip speed ratios, where the VAWT motion itself deviates more from the sinusoid. Comparison with sinusoidal motions at reduced frequencies corresponding to the upstroke or downstroke of the VAWT-shaped motion yield better agreement in terms of the angle of stall onset.
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Wall, A. S., R. G. Langlois i F. F. Afagh. "Modeling Helicopter Blade Sailing: Dynamic Formulation in the Planar Case". Journal of Applied Mechanics 74, nr 6 (4.01.2007): 1104–13. http://dx.doi.org/10.1115/1.2722766.
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As part of a research project aimed at simulating rotor dynamic response during shipboard rotor startup and shutdown operations, a dynamic model of the ship–helicopter–rotor system that is appropriate for use in predicting rotor elastic response was developed. This planar model consists of a series of rigid bodies connected by rotational stiffness and damping elements that allow motion in the flapwise direction. The rotors were partitioned into an arbitrary number of rigid beam segments having the inertial and geometrical properties of a typical rotor. Helicopter suspension flexibility and damping were also modeled, although the helicopter was otherwise considered as a rigid body. Lagrange’s equation was used to derive the governing dynamic equations for the helicopter–rotor model. The effect of ship motion on blade deflection was also considered. The ship motion supplied as input to the model included representative frigate flight deck motion in three dimensions corresponding to an actual sea spectrum, ship particulars and ship operating conditions. This paper is intended to detail the dynamic approach adopted for this blade sailing study, and its conceptual validation in the planar case. The methodologies that have been developed lend themselves to easy expansion into three dimensions, and into torsion and lead/lag modeling. The amount of blade motion induced by ship motion on nonrotating helicopter blades is included. Although aerodynamic loads are a major contributor to blade sailing, this paper focuses on the dynamics aspect of the problem, and thus does not include aerodynamic effects.
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Arnold, Paul M., Ivan Cheng, Jonathan A. Harris, Mir M. Hussain, Chengmin Zhang, Brian Karamian i Brandon S. Bucklen. "Single-Level In Vitro Kinematic Comparison of Novel Inline Cervical Interbody Devices With Intervertebral Screw, Anchor, or Blade". Global Spine Journal 9, nr 7 (28.02.2019): 697–707. http://dx.doi.org/10.1177/2192568219833055.
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Study Design: In vitro cadaveric biomechanical study. Objective: To compare the biomechanics of integrated anchor and blade versus traditional screw fixation techniques for interbody fusion. Methods: Fifteen cadaveric cervical spines were divided into 3 equal groups (n = 5). Each spine was tested: intact, after discectomy (simulating an injury model), interbody spacer alone (S), integrated interbody spacer (iSA), and integrated spacer with lateral mass screw and rod fixation (LMS+iS). Each treatment group included integrated spacers with either screw, anchor, or blade integrated spacers. Constructs were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) under pure moments (±1.5 N m). Results: Across all 3 planes, the following range of motion trend was observed: Injured > Intact > S > iSA > LMS+iS. In FE and LB, integrated anchor and blade significantly decreased motion compared with intact and injured conditions, before and after supplemental posterior fixation ( P < .05). Comparing tested devices revealed biomechanical equivalence between screw, anchor, and blade fixation methods in all loading modes ( P > .05). Conclusion: All integrated interbody devices reduced intact and injured motion; lateral mass screws and rods further stabilized the single motion segment. Comparing screw, anchor, or bladed integrated anterior cervical discectomy and fusion spacers revealed no significant differences.
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Ekaterinaris, J. A., N. N. So̸rensen i F. Rasmussen. "Numerical Investigation of Airfoil Dynamic Stall in Simultaneous Harmonic Oscillatory and Translatory Motion". Journal of Solar Energy Engineering 120, nr 1 (1.02.1998): 75–83. http://dx.doi.org/10.1115/1.2888050.
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Wind turbine blades are subject to complex flow conditions. For operation in yaw and turbulent inflow, the blade sections appear to execute a motion more complex than a harmonic blade oscillation, which causes dynamic stall. Predictions of dynamic stall caused by simple harmonic oscillation are crucial to efforts in understanding and improving wind turbine performance. Investigation of dynamic stall development caused by a combined oscillatory and translatory motion contributes to better understand blade loading under complex flow conditions. In this paper, numerical predictions of light and deep stall caused by simple oscillatory motion are obtained first. The ability of the numerical solution to predict dynamic stall loads caused by a combined motion is further investigated. The numerical solution is obtained with a factorized, upwind-biased numerical scheme. The turbulent flow region is computed with a one-equation turbulence model. A transition model is used to simulate the transitional flow effects, which play an important role to the overall unsteady flowfield development. The computed results are compared with available experimental data.
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Vershkov, V. A., B. S. Kritsky i R. M. Mirgazov. "FEATURES OF MODELING THE FLOW AROUND THE HELICOPTER MAIN ROTOR TAKING INTO ACCOUNT ARBITRARY BLADES MOTION". Civil Aviation High TECHNOLOGIES 22, nr 3 (29.06.2019): 25–34. http://dx.doi.org/10.26467/2079-0619-2019-22-3-25-34.
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The article considers the problem of the flow around the helicopter main rotor taking into account blades flapping in the plane of rotation and in the plane of thrust as well as the elastic blades deformation. The rotor rotation is modeled by the method of converting Navier-Stokes equations from a fixed coordinate system associated with the incoming flow into a rotating system associated with the rotor hub. For axial flow problems, this makes it possible to formulate the problem as stationary at a constant rotational speed of rotor. For a mode of skewed flow around the rotor in the terms of incident flow in this system it is necessary to solve the non-stationary problem. To solve the problem, the method of deformable grids is used, in which the equations are copied taking into account the grid nodes motion determined in accordance with the spatial blades motion, and SST turbulence model is used for closure. The results of the test calculations of the main rotor aerodynamic characteristics with and without blade flapping are presented in this paper. The coefficients of the main rotor thrust cT and the blades hinge moments mh are compared. The calculations were carried out in the CFD software ANSYS CFX (TsAGI License No. 501024). The flow around a four-bladed main rotor of a radius of 2.5 meters is modeled in the regime of skewed flow. The speed of the incoming flow came to 85 m/s under normal atmospheric conditions. The rotor was at an angle of attack of −10˚. To calculate the rotor motion without taking into account the flapping movements, we used the nonstationary system of Navier-Stokes equations with the closure with SST turbulence model. The calculation was being carried out until the change in the maximum value of the rotor thrust during one revolution became less than 1%. For modeling flapping blade movements, the control laws and equations describing the angle of blade flapping as a function from its azimuth angle obtained from the experiment were used. The procedure for reconstructing the grid according to a given law was conducted using standard grid deformation methods presented in the ANSYS CFX software. When solving the nonstationary Navier-Stokes equations, a dual time step was used. The obtained results show that accounting of the effect of flapping movements and cyclic control of the blades has an impact on the character of changing the main rotor thrust coefficient during one revolution and significantly changes the shape of the graph of the hinge moment coefficient of each blade.
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Arnold, James. "Mini-Blades and a Mini-Blade Handle for Hair Transplantation". American Journal of Cosmetic Surgery 14, nr 2 (czerwiec 1997): 195–200. http://dx.doi.org/10.1177/074880689701400217.
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Mini-blades are particularly useful in creating incisional pockets as recipient sites for hair transplants. With the aid of a special mini-blade handle, the length and depth of each incision can be accurately controlled. Surgeons can rapidly produce multiple uniform incisions with the technique described. Mini-blades are thicker than other blades and partially dilate each incision. Graft insertion is simplified by the partial dilation. More substantial dilation of the larger miniblade incisions can be produced with a twisting motion imparted to the mini-blade during the incisional process.
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Crawley, E. F., E. H. Ducharme i D. R. Mokadam. "Analytical and Experimental Investigation of the Coupled Bladed Disk/Shaft Whirl of a Cantilevered Turbofan". Journal of Engineering for Gas Turbines and Power 108, nr 4 (1.10.1986): 567–75. http://dx.doi.org/10.1115/1.3239948.
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The structural dynamics of a rotating flexible blade-rigid disk-flexible cantilevered shaft system is analytically and experimentally investigated. A simple analytical model yields the equations of motion expressed in the rotating frame, which show that the blade one nodal diameter modes dynamically couple to the rigid body whirling motion of the shaft-disk system. The blade modes higher than one nodal diameter are uncoupled from the shaft-disk dynamics. Nondimensionalization of the coupled equations of motion yield the criteria for the propensity and magnitude of the interaction between the bladed disk and shaft-disk modes. The analytical model was then correlated with the results of a structural dynamic experiment performed on the MIT Aeroelastic Rotor, a fan similar in design to a modern high bypass ratio shroudless turbofan. A special whirl excitation apparatus was used to excite both forward and backward asynchronous whirl, in order to determine the natural frequencies of the system. The agreement between the predicted and experimental natural frequencies is good and indicates the possibility of significant interaction of the one nodal diameter blade modes with the shaft-disk modes.
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Yao, Xue Shi. "Vibration Analysis of Shaft-Bladed System Undergoing both Global Motion and Elastic Deformation". Applied Mechanics and Materials 602-605 (sierpień 2014): 299–302. http://dx.doi.org/10.4028/www.scientific.net/amm.602-605.299.
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The vibration model of on a shaft-bladed system is built undergoing both global motion and elastic deformation by finite element method (FEM).The blade’s dynamic equation in rotating reference frame is established.The various effects are analysed such as Coriolis force,centrifugal force,spin softening,acceleration ect,which have influence to a blade vibtation frequencies in varying degrees.The shaft’s dynamic equation in stationary reference frame is deduced by setting gyroscopic matrix and inertia effects.The beam element model in the shaft-bladed system was set and the critical speeds were calculated.Calculation shows that the effects of the prestress and spin softening have great influence on shaft-bladed system vibration frequencies.The blade’s frequencies decreases slightly because the blade stiffness reduced in the system relatively.The work lays a basic foundation for improving the dynamic stability of the rotor system.
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Zu, Li, Lei Zhang i Hua Kun Wang. "Optimization Design of the Lawn Mowing Vehicle's Blade Based on Aerodynamics". Advanced Materials Research 199-200 (luty 2011): 173–81. http://dx.doi.org/10.4028/www.scientific.net/amr.199-200.173.
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In this paper, air movement states within the cutter deck caused by high-speed rotating blades are studied, impacts on the mowing blade by the air movement are analyzed with the consideration of the cutter structure. It will provide important references for the blade optimal design. By Computational Fluid Dynamics (shortened as CFD) method, the high relative speed motion model between the blade and air flow is established, the flow field through the blade tip section are simulated, and the instantaneous movement of air flow around the blade can be known. By the analysis of the aerodynamic influence, the optimized design of the mowing blade can be achieved. The lawn mowing vehicle with the optimized blade can have a good and stable flow conditions when cutting the grass, the performance and the value of the vehicle thereby are enhanced.
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Srinivasan, V., i R. J. Goldstein. "Effect of Endwall Motion on Blade Tip Heat Transfer". Journal of Turbomachinery 125, nr 2 (1.04.2003): 267–73. http://dx.doi.org/10.1115/1.1554411.
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Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7×105 based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and ‘blocking the flow,’ leading to reduced tip gap velocities and hence lower mass transfer.
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Guo, Haonan, Yongmin Yang, Fengjiao Guan, Haifeng Hu, Guoji Shen, Zifang Bian i Guangrong Teng. "A Blade Dynamic Strain Inversion Method for Rotating Blades Based on Blade Tip Timing". Journal of Physics: Conference Series 2029, nr 1 (1.09.2021): 012073. http://dx.doi.org/10.1088/1742-6596/2029/1/012073.
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Abstract Based on the vibration response transfer ratio and Natural Neighbor Interpolation (NNI), the research on the noncontact inversion method of dynamic strain of high-speed rotating blades is carried out. The high-speed rotating blade is analyzed through the motion equation, and the correction method of the transfer ratio is proposed through NNI. The three-dimensional model of the rotating blade is established, and the Finite Element Analysis (FEA) considering stress stiffening is carried out to obtain the transfer ratio between the blade tip displacement and the blade strain at a certain speed. The vibration experiment of the high-speed rotating blade is carried out, and the blade tip displacement and the dynamic strain of the key points of the blade are obtained based on Blade Tip Timing (BTT) and strain gauges. The experimental data are processed to obtain the actual transfer ratio of the key points of the blade, and the theoretical transfer ratio is corrected based on NNI. The results show that when the 1st-order resonance of the rotating blade occurs at the rotating speed of 7960RPM, the strain inversion error of the test point can be reduced to less than 5%, which verifies the proposed correction method. Therefore, the blade dynamic strain can be inverted more accurately based on BTT.
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Yang, B. D., J. J. Chen i C. H. Menq. "Prediction of Resonant Response of Shrouded Blades With Three-Dimensional Shroud Constraint". Journal of Engineering for Gas Turbines and Power 121, nr 3 (1.07.1999): 523–29. http://dx.doi.org/10.1115/1.2818504.
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In this paper, the three-dimensional shroud contact kinematics of a shrouded blade system is studied. The assumed blade motion has three components, namely axial, tangential, and radial components, which result in a three dimensional relative motion across the shroud interface. The resulting relative motion can be decomposed into two components. The first one is on the contact plane and can induce stick-slip friction. The other component is perpendicular to the contact plane and can cause variation of the contact normal load and, in extreme circumstances, separation of the two contacting surfaces. In order to estimate the equivalent stiffness and damping of the shroud contact an approach is proposed. In this approach, the in-plane slip motion is assumed to be elliptical and is decomposed into two linear motions along the principal major and minor axes of the ellipse. A variable normal load friction force model (Yang and Menq, 1996) is then applied separately to each individual linear motion, and the equivalent stiffness and damping of the shroud contact can be approximately estimated. With the estimated stiffness and damping, the developed shroud contact model is applied to the prediction of the resonant response of a shrouded blade system. The effects of two different shroud constraint conditions, namely two-dimensional constraint and three-dimensional constraint, on the resonant response of a shrouded blade system are compared and the results are discussed.
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Hoyniak, D., i S. Fleeter. "Forced Response Analysis of an Aerodynamically Detuned Supersonic Turbomachine Rotor". Journal of Vibration and Acoustics 108, nr 2 (1.04.1986): 117–24. http://dx.doi.org/10.1115/1.3269311.
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High-performance aircraft engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this paper, an analysis is developed to predict the flow-induced forced response behavior of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, due to the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is then utilized to investigate the effect of aerodynamic detuning on the forced response characteristics of a 12-bladed rotor, with Verdon’s Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that for forward traveling wave gust excitations, aerodynamic detuning is generally very beneficial, resulting in significantly decreased maximum amplitude blade responses for many interblade phase angles.
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Zheng, Jian Xin, i Jia Wen Xu. "Basic Experimental Research on the NC-Contour Evolution Ultrasonic Assisted Grinding Ceramic Blade Surface". Key Engineering Materials 359-360 (listopad 2007): 369–273. http://dx.doi.org/10.4028/www.scientific.net/kem.359-360.369.
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Ultrasonic machining is a practical process for advanced ceramic machining. Usually, ceramics with complex surfaces are machined with two common ultrasonic assisted contour machining methods, which may be classified as surface/point contact machining mode. While these methods are not suitable to machine some complex surfaces such as blade surface, so an ultrasonic assisted contour machining method using a simple shaped diamond grinding wheel to machine ceramic blade surface is presented, which is named as Numerical Control-Contour Evolution Ultrasonic Assisted Grinding (NC-CEUAG) method. In the NC-CEUAG process, the contour evolution motion of the grinding wheel is controlled by the NC system and the blade surface is the enveloping surface formed by the grinding wheel’ cutting edges when they cut into the ceramic specimen. In this paper, the relative motion between the grinding wheel and the specimen in the process of NC-CEUAG ceramic blade surface is analyzed. The mathematical models of ruled surfaces are constructed. The ceramic blades with ruled surface are machined with selected machining parameters on the retrofitting NC-CEUAG machine tool.
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Nielsen, Mikkel Schou, Ivan Nikolov, Emil Krog Kruse, Jørgen Garnæs i Claus Brøndgaard Madsen. "High-Resolution Structure-from-Motion for Quantitative Measurement of Leading-Edge Roughness". Energies 13, nr 15 (31.07.2020): 3916. http://dx.doi.org/10.3390/en13153916.
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Over time, erosion of the leading edge of wind turbine blades increases the leading-edge roughness (LER). This may reduce the aerodynamic performance of the blade and hence the annual energy production of the wind turbine. As early detection is key for cost-effective maintenance, inspection methods are needed to quantify the LER of the blade. The aim of this proof-of-principle study is to determine whether high-resolution Structure-from-Motion (SfM) has the sufficient resolution and accuracy for quantitative inspection of LER. SfM provides 3D reconstruction of an object geometry using overlapping images of the object acquired with an RGB camera. Using information of the camera positions and orientations, absolute scale of the reconstruction can be achieved. Combined with a UAV platform, SfM has the potential for remote blade inspections with a reduced downtime. The tip of a decommissioned blade with an artificially enhanced erosion was used for the measurements. For validation, replica molding was used to transfer areas-of-interest to the lab for reference measurements using confocal microscopy. The SfM reconstruction resulted in a spatial resolution of 1 mm as well as a sub-mm accuracy in both the RMS surface roughness and the size of topographic features. In conclusion, high-resolution SfM demonstrated a successful quantitative reconstruction of LER.
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Zhao, Tiantian, i Haitao Sun. "Research on dynamic aerodynamic performance of wind turbine airfoil under large blade deformation". Journal of Physics: Conference Series 2230, nr 1 (1.03.2022): 012001. http://dx.doi.org/10.1088/1742-6596/2230/1/012001.
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Abstract 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.
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Ma, Jiaobin, Zhufeng Liu, Di Zhang i Yonghui Xie. "Numerical Study on Vibration Response of Compressor Stator Blade Considering Contact Friction of Holding Ring". Applied Sciences 13, nr 11 (23.05.2023): 6380. http://dx.doi.org/10.3390/app13116380.
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There are many kinds of assembly structures in heavy-duty gas turbine compressor stator blades which have significant influence on the complex damping vibration characteristics. At present, compressor design is becoming more and more compact, so it is very meaningful to accurately obtain stator blade vibration characteristics of structures with contact damping. Firstly, a fretting slip friction dynamic model was introduced, and then a vibration analysis model of the compressor stator blade with outer ring structure was established based on the slip friction theory. Then, the vibration response of the compressor stator blade was obtained according to various working conditions, and the main factors affecting the vibration characteristics of the stator blade were revealed. Finally, the vibration response of the blade under a particular exciting force condition was simulated. The results show that the damping vibration characteristics of the compressor stator blades were affected by the excitation force and the normal load of the contact surface. The vibration response curve of the stator blade and the equivalent stiffness coefficient of the contact surface were analyzed, and the friction motion of the contact surface changed with the change of the working condition. The model can simulate the nonlinear vibration characteristics of stator blades. This method provides a reference for the vibration safety analysis of compressor stator blades.
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Chen, Ziwen, Xiaodong Wang i Shun Kang. "Effect of the Coupled Pitch–Yaw Motion on the Unsteady Aerodynamic Performance and Structural Response of a Floating Offshore Wind Turbine". Processes 9, nr 2 (3.02.2021): 290. http://dx.doi.org/10.3390/pr9020290.
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The floating offshore wind turbines (FOWTs) have many more advantages than the onshore wind turbines, but they also have more complicated aerodynamic characteristics due to complex platform motions. The research objective of this paper is to investigate unsteady aerodynamic characteristics of a FOWT under the pitch, yaw, and coupled pitch–yaw platform motions using the computational fluid dynamics (CFD) method in the Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. The pitch, yaw, and coupled pitch–yaw motions are studied separately to analyze the platform motions’ effects on the rotor blade. The accuracy of the numerical simulation method is verified, and the overall performances, including power and thrust, are discussed. In addition, the comparison of total aerodynamic performance, force coefficients at different spans and structural dynamic response is provided. The numerical simulation results show that the platform pitching is the main influencing factor of power fluctuation, and the average thrust values of the pitch, yaw, and coupled motions are consistent regardless of the frequency value. The angle of attack (AOA) of airfoils is much more sensitive to the yaw motion, while the blade normal and tangential forces are mainly affected by pitch motion. As for the structural response, the results suggest that the aerodynamic loads of the wind turbine are more sensitive to the pitch motion, which is confirmed by the thrust force and torque of each blade during the platform motions.
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Tin, Trinh Van. "The motion equation of turbine blade by the finite element method". Vietnam Journal of Mechanics 15, nr 4 (31.12.1997): 42–48. http://dx.doi.org/10.15625/0866-7136/10219.
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In this paper, the finite element method has been applied to deriving the motion equation of turbine blade in coupled bending - bending - torsion vibrations. These equations permit us to develop straightforwardly digital computer programs for studying vibration problems of turbine blades in turbo machinery as well as in other structural dynamic applications.
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Reinhardt, A. K., J. R. Kadambi i R. D. Quinn. "Laser Vibrometry Measurements of Rotating Blade Vibrations". Journal of Engineering for Gas Turbines and Power 117, nr 3 (1.07.1995): 484–88. http://dx.doi.org/10.1115/1.2814121.
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One of the most important design factors in modern turbomachinery is the vibration of turbomachinery blading. There is a need for developing an in-service, noncontacting, noninterfering method for the measurement and monitoring of gas turbine, jet engine, and steam turbine blade vibrations and stresses. Such a technique would also be useful for monitoring rotating helicopter blades. In the power generation industry, blade failures can result in millions of dollars of downtime. The measurement of blade vibrations and dynamic stresses is an important guide for preventive maintenance, which can be a major contributor to the availability of steam turbine, gas turbine, and helicopter operations. An experiment is designed to verify the feasibility of such a vibration monitoring system using the reference beam on-axis laser-Doppler technique. The experimental setup consists of two flat, cantilever blades mounted on a hub attached to the shaft of a dc motor. The motor rests on a linear bearing permitting motion only in the direction of the motor shaft. The motor and blade assembly is then excited via an electrodynamic shaker at the first natural frequency of the blades. The resulting blade vibration is then detected using a laser vibrometer. The vibration frequencies and amplitudes of the two rotating blades are successfully measured.
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Choi, Kyu Sung, Young Hun Choi, Jung-Eun Cheon, Woo Sun Kim i In One Kim. "Application of T1-weighted BLADE sequence to abdominal magnetic resonance imaging of young children: a comparison with turbo spin echo sequence". Acta Radiologica 61, nr 10 (24.01.2020): 1406–13. http://dx.doi.org/10.1177/0284185120901512.
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Background The image quality of abdominal magnetic resonance imaging (MRI) in children who cannot hold their breath has been severely impaired by motion artifacts. Purpose To evaluate the usefulness of T1-weighted (T1W) BLADE MRI for axial abdominal imaging in children who cannot hold their breath. Material and Methods Two different BLADE sequences, with and without an inversion recovery (IR-BLADE), were compared to conventional turbo-spin echo (TSE) with a high number of excitations in 18 consecutive patients who cannot hold their breath. Overall image quality, motion artifact, radial artifact, hepatic vessel sharpness, renal corticomedullary differentiation, and lesion conspicuity were retrospectively assessed by two radiologists, using 4- or 5-point scoring systems. Signal variations of each sequence were measured for a quantitative comparison. The acquisition times of the three sequences were compared. Results IR-BLADE and BLADE showed significantly improved overall image quality and reduced motion artifact compared with TSE. IR-BLADE showed significantly better hepatic vessel sharpness and corticomedullary differentiation compared to both BLADE and TSE. Radial artifacts were only observed on IR-BLADE and BLADE. In nine patients with lesions, there were no significant differences in lesion conspicuity among three sequences. Compared to TSE, both IR-BLADE and BLADE showed decreased signal variations in the liver and muscle, and an increased signal variation through air. The mean acquisition times for IR-BLADE, BLADE, and TSE were comparable. Conclusion Compared to the TSE sequence, T1W IR-BLADE for pediatric abdominal MRI resulted in improved image quality, tissue contrast with a diminished respiratory motion artifact, and a comparable acquisition time.
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Liao, Gaohua, Ying Zhao, Zhimin Hong, Zhiyi Zhang i Haoyu Zeng. "Closed-loop Control of Biaxial Fatigue Loading of Wind Turbine Blades Based on Visual Inspection". Journal of Physics: Conference Series 2503, nr 1 (1.05.2023): 012088. http://dx.doi.org/10.1088/1742-6596/2503/1/012088.
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Abstract Based on the inertial vibration excitation device, a biaxial fatigue loading system for wind turbine blades is established by using visual inspection technology and virtual spindle decoupling to control the vibration excitation motion of wind turbine blades. The image feature point tracking method is used to detect the blade vibration state. Considering the system vibration frequency characteristics, the phase difference between the exciting force and the vibration displacement is detected based on the phase detector, and the system resonance frequency is adaptively tracked to achieve accurate control of the double-free amplitude of the blade. The fatigue test shows that the control system can maintain the amplitude error of the blade, the adaptive tracking control method is reliable and effective, and the accuracy and reliability of the fatigue test are improved.
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Cao, Dengqing, Xiaochun Gong, Dong Wei, Shiming Chu i Ligang Wang. "Nonlinear Vibration Characteristics of a Flexible Blade with Friction Damping due to Tip-Rub". Shock and Vibration 18, nr 1-2 (2011): 105–14. http://dx.doi.org/10.1155/2011/425039.
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An approximate approach is proposed in this paper for analyzing the two-dimensional friction contact problem so as to compute the dynamic response of a structure constrained by friction interfaces due to tip-rub. The dynamical equation of motion for a rotational cantilever blade in a centrifugal force field is established. Flow-induced distributed periodic forces and the internal material damping in the blade are accounted for in the governing equation of motion. The Galerkin method is employed to obtain a three-degree-of-freedom oscillator with friction damping due to tip-rub. The combined motion of impact and friction due to tip-rub produced a piecewise linear vibration which is actually nonlinear. Thus, a complete vibration cycle is divided into successive intervals. The system possesses linear vibration characteristic during each of these intervals, which can be determined using analytical solution forms. Numerical simulation shows that the parameters such as gap of the tip and the rotational speed of the blades have significant effects on the dynamical responses of the system. Finally, the nonlinear vibration characteristics of the blade are investigated in terms of the Poincare graph, and the frequency spectrum of the responses and the amplitude-frequency curves.
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Beresnevich, Vitaly, Marina Cerpinska, Martins Irbe i Janis Viba. "CONVEYOR-TYPE SMALL HYDROPOWER PLANT FOR SHALLOW RIVER WATERS". ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference 3 (13.06.2023): 46–49. http://dx.doi.org/10.17770/etr2023vol3.7229.
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This paper deals with the development of a small conveyor-type hydropower plant intended for operation in shallow river waters without construction of a dam. The proposed design offers a closed-shaped flattened conveyor equipped with flat-shaped blades. The conveyor is oriented perpendicular to the fluid flow. Several identical flat blades interacting with fluid flow are mounted on conveyor belt and move together with the belt in one straight line direction. Then after turning in the reversing mechanism, blades move in the opposite direction. The conveyor system has a built-in energy generator which drive shaft is connected with one of the reversing ends of the plant. Conveyor belt system dynamics analysis is performed on the base of equivalent model with one degree of freedom. The interaction of a moving conveyor flat blade in translation motion with fluid flow is studied by computer simulation with program Mathcad using a superposition principle. In accordance with this approach, a fast-chaotic motion of fluid particles (Brownian motion) is separated from the slow-directed flow motion, with the given average velocity. Optimization of system parameters (blade orientation angle to fluid flow, interaction constants of the braking generator) is performed, using a generated power as criterion. Simulation results confirm the serviceability and operational efficiency of the proposed hydropower plant in shallow river waters.
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Ferreira, Carlos, Wei Yu, Arianna Sala i Axelle Viré. "Dynamic inflow model for a floating horizontal axis wind turbine in surge motion". Wind Energy Science 7, nr 2 (8.03.2022): 469–85. http://dx.doi.org/10.5194/wes-7-469-2022.
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Abstract. Floating offshore wind turbines may experience large surge motions, which can cause blade–vortex interaction if they are similar to or faster than the local wind speed. Previous research hypothesized that this blade–vortex interaction phenomenon represented a turbulent wake state or even a vortex ring state, rendering the actuator disc momentum theory and the blade element momentum theory invalid. This hypothesis is challenged, and we show that the actuator disc momentum theory is valid and accurate in predicting the induction at the actuator in surge, even for large and fast motions. To accomplish this, we develop a dynamic inflow model that simulates the vorticity–velocity system and the effect of motion. The model's predictions are compared to other authors' results, a semi-free-wake vortex ring model, other dynamic inflow models, and CFD simulations of an actuator disc in surge. The results show that surge motion and rotor–wake interaction do not result in a turbulent wake or vortex ring state and that the application of actuator disc momentum theory and blade element momentum theory is valid and accurate when applied correctly in an inertial reference frame. In all cases, the results show excellent agreement with the higher-fidelity simulations. The proposed dynamic inflow model includes a modified Glauert correction for highly loaded streamtubes and is accurate and simple enough to be easily implemented in most blade element momentum models.
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Yang, B. D., i C. H. Menq. "Characterization of Contact Kinematics and Application to the Design of Wedge Dampers in Turbomachinery Blading: Part 1—Stick-Slip Contact Kinematics". Journal of Engineering for Gas Turbines and Power 120, nr 2 (1.04.1998): 410–17. http://dx.doi.org/10.1115/1.2818138.
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Friction dampers are often used in turbine design to attenuate blade vibration to acceptable levels so as to prolong blades’ service life. A wedge damper, also called a self-centering, blade-to-blade damper, can provide more design flexibility to meet various needs in different operating conditions when compared with conventional platform dampers. However, direct coupling of the two inclined friction interfaces of the wedge damper often leads to very complex contact kinematics. In Part I of this two-part paper, a dual-interface friction force model is proposed to investigate the coupling contact kinematics. The key issue of the model formulation is to derive analytical criteria for the stick-slip transitions that can be used to precisely simulate the complex stick-slip motion and, thus, the induced friction force as well. When considering cyclic loading, the induced periodic friction forces can be obtained to determine the effective stiffness and damping of the interfaces over a cycle of motion. In Part II of this paper, the estimated stiffness and damping are then incorporated with the harmonic balance method to predict the forced response of a blade constrained by wedge dampers.
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Wang, L. T., F. Zhang, W. M. Qian, Y. Y. Ji i Y. Li. "The Study on the Key Technology of Turbine Blade CNC Belt Grinding Machine". Key Engineering Materials 392-394 (październik 2008): 283–88. http://dx.doi.org/10.4028/www.scientific.net/kem.392-394.283.
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According to the structure features of turbine blade, the analysis of the grinding motion has been done and, based on the restriction conditions, the structural configuration of belt grinding machine has been described. Then the configuration of the control axis of belt grinding motion and the machine tool structure has been determined. The kinematics model of the blade grinding has been built by the motion control chain of the machine tool. The tool path algorithm of belt grinding has been proposed with STL 3D data model of blade surface. Based on IPC and Programmable Multi-Axis Controller PMAC, the CNC system of turbine blade belt grinding machine has been designed. Finally, the prototype of Turbine Blade CNC Belt Grinding Machine has been made.
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SEPAHI, O., M. R. FOROUZAN i P. MALEKZADEH. "FREE VIBRATION ANALYSIS OF TRIPLY COUPLED PRE-TWISTED ROTOR BLADES BY THE DIFFERENTIAL QUADRATURE METHOD". International Journal of Structural Stability and Dynamics 11, nr 01 (luty 2011): 127–47. http://dx.doi.org/10.1142/s0219455411004014.
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Key parameters on the dynamic characteristics of triply coupled pretwisted rotor blades are investigated. The issues of concern include the combined flap-wise bending, chord-wise bending, and torsion vibrations of the pretwisted rotor blade, considering the centrifugal force and Coriolis effects. The governing differential equations of motion presented by Houbolt and Brooks for the rotor blade are used as the basis of study, which contain many factors previously ignored. The differential quadrature method is adopted as the method of solution for its ease in implementation, accuracy, and fast convergence. The dynamic responses of the rotor blade are obtained for different cases of coupling and geometries, which agree well with existing results. The dynamic responses of the rotor blades are plotted against parameters such as angular velocity, pretwisting angle, and hub radius in proper curves and discussed in details.
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Hansen, Morten Hartvig. "Modal dynamics of structures with bladed isotropic rotors and its complexity for two-bladed rotors". Wind Energy Science 1, nr 2 (30.11.2016): 271–96. http://dx.doi.org/10.5194/wes-1-271-2016.
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Abstract. The modal dynamics of structures with bladed isotropic rotors is analyzed using Hill's method. First, analytical derivation of the periodic system matrix shows that isotropic rotors with more than two blades can be represented by an exact Fourier series with 3/rev (three per rotor revolution) as the highest order. For two-bladed rotors, the inverse mass matrix has an infinite Fourier series with harmonic components of decreasing norm; thus, the system matrix can be approximated by a truncated Fourier series of predictable accuracy. Second, a novel method for automatically identifying the principal solutions of Hill's eigenvalue problem is introduced. The corresponding periodic eigenvectors can be used to compute symmetric and antisymmetric components of the two-bladed rotor motion, as well as the additional forward and backward whirling components for rotors with more than two blades. To illustrate the use of these generic methods, a simple wind turbine model is set up with three degrees of freedom for each blade and seven degrees of freedom for the nacelle and drivetrain. First, the model parameters are tuned such that the low-order modal dynamics of a three-bladed 10 MW turbine from previous studies is recaptured. Second, one blade is removed, leading to larger and higher harmonic terms in the system matrix. These harmonic terms lead to modal couplings for the two-bladed turbine that do not exist for the three-bladed turbine. A single mode of a two-bladed turbine will also have several resonance frequencies in both the ground-fixed and rotating frames of reference, which complicates the interpretation of simulated or measured turbine responses.