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  • Release : 1937
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  • Pages : pages

Download or read book written by and published by . This book was released on 1937 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: O trabalho constitui repositorio de elementos basicos para o planejamento hidrico, calcado em dados reais e fidedignos, sem o qual nao se podem elaborar projetos de utilizacao racional de recursos de agua da bacia do Sao Francisco. Reune estudos hidrologicos de analise dos dados fluviometricos dos principais postos no rio Sao Francisco, a jusante de Tres Marias. Os dados origianis de campo, resultados de 39 anos de observacoes hidrologicas ao longo do grande rio, foram submetidos a uma analise de consistencia, levada a efeito por meio de correlacoes de cotas medias, diarias e mensais, entre cada posto e o posto mais proximo.

Book Higher Harmonic Blade Pitch Control

Download or read book Higher Harmonic Blade Pitch Control written by John Shaw and published by . This book was released on 1980 with total page 1010 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Smart Helicopter Rotors

Download or read book Smart Helicopter Rotors written by Ranjan Ganguli and published by Springer. This book was released on 2015-12-16 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exploiting the properties of piezoelectric materials to minimize vibration in rotor-blade actuators, this book demonstrates the potential of smart helicopter rotors to achieve the smoothness of ride associated with jet-engined, fixed-wing aircraft. Vibration control is effected using the concepts of trailing-edge flaps and active-twist. The authors’ optimization-based approach shows the advantage of multiple trailing-edge flaps and algorithms for full-authority control of dual trailing-edge-flap actuators are presented. Hysteresis nonlinearity in piezoelectric stack actuators is highlighted and compensated by use of another algorithm. The idea of response surfaces provides for optimal placement of trailing-edge flaps. The concept of active twist involves the employment of piezoelectrically induced shear actuation in rotating beams. Shear is then demonstrated for a thin-walled aerofoil-section rotor blade under feedback-control vibration minimization. Active twist is shown to be significant in reducing vibration caused by dynamic stall. The exposition of ideas, materials and algorithms in this monograph is supported by extensive reporting of results from numerical simulations of smart helicopter rotors. This monograph will be a valuable source of reference for researchers and engineers with backgrounds in aerospace, mechanical and electrical engineering interested in smart materials and vibration control. Advances in Industrial Control aims to report and encourage the transfer of technology in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. The series offers an opportunity for researchers to present an extended exposition of new work in all aspects of industrial control.

Book On the Use of Active Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction

Download or read book On the Use of Active Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction written by Charles E. Hammond and published by . This book was released on 1980 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vibration levels have been a problem in helicopters since their inception. The reason for this lies in the method whereby the helicopter generates its lift, namely, the rotor system. As the rotor blades rotate they encounter a continuously changing aerodynamic environment which results in a continuously changing environment which results in a continuously changing aerodynamic loading on the blades. This changing environment is repeated on each revolution of the rotor. Hence, the rotor develops aerodynamic loads which are oscillatory in nature. These oscillatory loads are transferred directly to the helicopter airframe through the mechanical connection of the rotor to the airframe, i.e., the rotor-shaft/transmission attachment. Oscillatory loads are also transmitted to the airframe by impingement of the rotor wake on the upper portion of the airframe, but the mechanically transferred loads are in most cases much more significant than the aerodynamically transferred loads. (Author).

Book Application of Higher Harmonic Blade Feathering for Helicopter Vibration Reduction

Download or read book Application of Higher Harmonic Blade Feathering for Helicopter Vibration Reduction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-22 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Higher harmonic blade feathering for helicopter vibration reduction is considered. Recent wind tunnel tests confirmed the effectiveness of higher harmonic control in reducing articulated rotor vibratory hub loads. Several predictive analyses developed in support of the NASA program were shown to be capable of calculating single harmonic control inputs required to minimize a single 4P hub response. In addition, a multiple-input, multiple-output harmonic control predictive analysis was developed. All techniques developed thus far obtain a solution by extracting empirical transfer functions from sampled data. Algorithm data sampling and processing requirements are minimal to encourage adaptive control system application of such techniques in a flight environment. Powers, R. W. Unspecified Center NASA-CR-158985 NAS1-14552...

Book Journal of the American Helicopter Society

Download or read book Journal of the American Helicopter Society written by American Helicopter Society and published by . This book was released on 2003 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Inherent Vibration Damping of Helicopter Blades

Download or read book Inherent Vibration Damping of Helicopter Blades written by Wilfred E. Baker and published by . This book was released on 1969 with total page 51 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results are presented of extensive experiments on damping of vibrations in helicopter main rotor blades and compare these results with theoretical and semiempirical methods of predicting blade damping. The feasibility of numerical solution of blade vibration equations which include complex damping effects is demonstrated. Air damping is shown to be relatively unimportant for all but the fundamental bending vibration mode. Structural damping is essentially independent of amplitude but varies significantly with frequency. For much of the experimental data, internal damping of the blade material is the primary source of damping. (Author).

Book Vibration Reduction of Helicopter Blade Using Variable Dampers

Download or read book Vibration Reduction of Helicopter Blade Using Variable Dampers written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-21 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the report, the investigation of controlling helicopter-blade lead-lag vibration is described. Current practice of adding passive damping may be improved to handle large dynamic range of the blade with several peaks of vibration resonance. To minimize extra-large damping forces that may damage the control system of blade, passive dampers should have relatively small damping coefficients, which in turn limit the effectiveness. By providing variable damping, a much larger damping coefficient to suppress the vibration can be realized. If the damping force reaches the maximum allowed threshold, the damper will be automatically switched into the mode with smaller damping coefficient to maintain near-constant damping force. Furthermore, the proposed control system will also have a fail-safe feature to guarantee the basic performation of a typical passive damper. The proposed control strategy to avoid resonant regions in the frequency domain is to generate variable damping force in combination with the supporting stiffness to manipulate the restoring force and conservative energy of the controlled blade system. Two control algorithms are developed and verified by a prototype variable damper, a digital controller and corresponding algorithms. Primary experiments show good potentials for the proposed variable damper: about 66% and 82% reductions in displacement at 1/3 length and the root of the blade respectively.Lee, George C. and Liang, Zach and Gan, Quan and Niu, TiechengAmes Research CenterHELICOPTERS; ROTORS; VIBRATION DAMPING; ALGORITHMS; RESONANCE; FAIL-SAFE SYSTEMS; VIBRATION

Book Helicopter Noise Reduction by Individual Blade Control IBC Selected Flight Test and Simulation Results

Download or read book Helicopter Noise Reduction by Individual Blade Control IBC Selected Flight Test and Simulation Results written by W. R. Splettstoesser and published by . This book was released on 2001 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: A collaborative flight test programme was conducted to study among other objectives the potential of open- loop Individual Blade Pitch Control (IBC) to reduce the external noise of a helicopter in partial power descent, a flight regime known to generate the highly annoying Blade-Vortex Interaction (BVI) impulsive noise. The blade root control system employing actuators in the rotating frame, was installed on a BO 105 helicopter, which was flown over an extended linear microphone array. The acoustic measurements on the ground were synchronised to the flight track and rotor performance measurements supplemented by limited simultaneously acquired on-board acoustic and blade surface pressure data. Selected test results quantifying the noise reduction potential of the IBC technique, are presented and compared to numerical rotor simulation results calculated by the aeromechanic S4 code and the acoustic AKUROT code of the DLR. A significant noise reduction benefit (exceeding 5 dB) of the maximum A-weighted (BVI) noise level was obtained for the 2/rev IBC mode; further, over a wide range of IBC phase angles simultaneous noise and vibration reductions were observed. The complete data base acquired will contribute to the development and validation of a fast control algorithm for closed-loop IBC applications.

Book Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction a Feasibility Study

Download or read book Higher Harmonic Blade Pitch Control for Helicopter Vibration Reduction a Feasibility Study written by John Shaw (Jr) and published by . This book was released on 1968 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concept of eliminating most helicopter vibration by changing certain rotor harmonic airloads and blade motions with harmonic pitch control is discussed in detail. A simple method of obtaining the required pitch harmonics by periodic tilting of the swashplate is presented. Attention is given to the origin and characteristics of four problems expected in applying the pitch control concept: shed wake reduction of harmonic pitch effectiveness, high blade bending moments, high blade bending moments, high loads in the pitch control linkages, and the need for adjustment of the pitch control as flight condition changes. Numerical results are given to show the effect of third harmonic pitch on the cockpit vibration caused by a three-bladed articulated rotor at moderate forward speed. Several examples are given to illustrate the strong influence of shed wake on the effectiveness of harmonic pitch variations. Finally, the smooth single-minimum character of vibration dependence on pitch harmonic magnitude and phase suggests that inflight adjustment by steepest-descent type search is feasible. (Author).

Book An Analysis of the Flapwise Bending Frequencies and Mode Shapes of Rotor Blades Having Two Flapping Hinges to Reduce Vibration Levels

Download or read book An Analysis of the Flapwise Bending Frequencies and Mode Shapes of Rotor Blades Having Two Flapping Hinges to Reduce Vibration Levels written by George W. Brooks and published by . This book was released on 1960 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book A Variable Hydraulic Damper for Vibration Reduction in Helicopter Blades

Download or read book A Variable Hydraulic Damper for Vibration Reduction in Helicopter Blades written by Quan Gan and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: