Rotor/fuselage vibration isolation studies by a Floquet-harmonic iteration technique
01 Jan 1990-Journal of Aircraft (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 27, Iss: 1, pp 81-89
TL;DR: In this article, the equations of motion for the coupled rotor/isolator/fuselage dynamical system were formulated for the prediction of vibrations in helicopters during forward flight using a combined Floquet theory/frequency-response technique.
Abstract: The equations of motion for the coupled rotor/isolator/fuselage dynamical system are formulated for the prediction of vibrations in helicopters during forward flight. Using a combined Floquet theory/frequency-response technique, the equations are solved to predict the vibratory loads at the various locations of the helicopter. In addition, the influence of the isolator on the hub and blade loads is established.
Citations
More filters
01 Dec 1968
TL;DR: In this paper, it was shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution.
Abstract: Abstract : It is shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution. This gives an explicit condition for applying Galerkin's procedure and reveals the wide applicability of Galerkin's procedure to general nonlinear periodic differential systems. The proof of this result is based on existence theorems which are derived from idea contained in Newton's iterative method. The relationship of Galerkin's procedure to the method of averaging is also discussed. Finally the paper exemplifies Galerkin's procedure with a certain nonlinear equation. (Author)
252 citations
TL;DR: In this article, the authors address the problem of the formulation and solution of an active vibration control scheme for helicopters, based on the concept of active control of structural response, which is a challenging problem to the helicopter designer.
Abstract: Vibration control has always been a challenging problem to the helicopter designer. This paper addresses the problem of the formulation and solution of an active vibration control scheme for helicopters, based on the concept of active control of structural response. First, using a mathematical procedure employing the Fisher information matrix, optimum sensor locations have been identified in a threedimensional model of a flexible fuselage structure. The reference parameters used in the selection process are the elements of a vector defined as the effective independence distribution vector and the condition number of the Fisher information matrix. It is observed that, irrespective of the excitation frequency, these optimally selected sensor locations experience relatively high levels of vibration. Then, using the measurement from these optimal sensor locations, a multi-input/mu lti-output control problem has been formulated and solved to obtain the active control forces required for vibration minimization in the helicopter fuselage. It is observed that sensor locations have a significant influence on the level of vibration reduction in a fuselage structure.
9 citations
Dissertation•
03 May 1996
TL;DR: Results for the generalized system show that the filtered-X LMS algorithm does converge for time-periodic disturbance inputs and can produce very small errors, and for the helicopter rotor blade system the algorithm is shown to produce verysmall errors.
Abstract: Extensive disturbance rejection methods have been established for time-invariant systems. However, the development of these techniques has not focused on application to time-periodic systems in particular until recently. The filtered-X LMS algorithm is regarded as the best disturbance rejection technique for aperiodic systems by many, as has been proven in the acoustics industry for rejecting unwanted noise. Since this is essentially a feedforward approach, we might expect its performance to be good with respect to time-periodic systems in which the disturbance frequency is already known. The work presented in this thesis is an investigation of the performance of the filtered-X LMS algorithm for disturbance rejection in time-periodic systems. Two cases are examined: a generalized linear, time-periodic system and the helicopter rotor blade in forward flight. Results for the generalized system show that the filtered-X LMS algorithm does converge for time-periodic disturbance inputs and can produce very small errors. For the helicopter rotor blade system the algorithm is shown to produce very small errors, with a 96%, or 14 dB, reduction in error from the open-loop system. The filtered-X LMS disturbance rejection technique is shown to provide a successful means of rejecting time-periodic disturbances for time-periodic systems. iii Acknowledgments I would like to thank those people who helped me through this project. I would like to first thank Dr. Harry Robertshaw for his encouragement, support and brainstorming sessions. Dan Cole gets a big thank-you; his guidance and advice were invaluable. Thanks to Dr. William Saunders for the brainstorming sessions and advice. I would also like to thank my other committee member, Dr. Harley Cudney for his help and support. Lastly I would like to thank my fiancé, Christian Fowler, for his neverending support and understanding. Thanks for putting up with my busy schedule and stressful semester.
7 citations
18 Apr 2005
TL;DR: In this article, the authors present the vibration control of a highly simplified two degree of freedom model of a helicopter using both active and passive vibration control schemes, where the active control is achieved using a combination of piezo stack sensor and actuator mechanism.
Abstract: This paper presents the vibration control of a highly simplied two degree of freedom model of a helicopter. The vibration control study has been performed using both active and passive vibration control schemes. In the case of active vibration control, the feedback mechanism affects the stiffness of the system; whereas in passive vibration control, the absorber mass affects the inertia of the system. The active control is achieved using a combination of piezo stack sensor and actuator mechanism. A nite element model for the piezo stack mechanism has been developed to obtain a relation between deformation, applied/induced potential and externally applied mechanical load. The results of this study indicate that inclusion of sensor and actuator units increases the natural frequency of the system due to increase in stiffness of the system. It is observed that in the case of active vibration control, the frequency response of acceleration of the system is highly sensitive to small variations in the magnitude of gain around its optimum value and insensitive to changes in excitation frequency; whereas in passive vibration control, the frequency response does not exhibit any signicant change in the characteristics with respect to the variation in the absorber mass, while it is highly sensitive to changes in operating frequency.
3 citations
05 May 1995
TL;DR: In this paper, three control strategies are investigated: LQR method of feedback control, feedforward control, and hybrid control (a combination of feedback and feed forward control) for rotor blade vibration reduction based on individual blade control.
Abstract: Various control methods of rotor blade vibration reduction based on individual blade control are presented and compared. The benchmark model used is based on a four-bladed helicopter at hover conditions. In this paper, three control strategies are investigated: LQR method of feedback control, feedforward control, and hybrid control (a combination of feedback and feedforward control). It was found that the LQR method provided substantial improvements in the system and very low gains. Feedforward control was found to be somewhat less effective and the hybrid control method, which combines both feedforward and LQR feedback methods, was proven to be the most effective method.
1 citations
References
More filters
TL;DR: In this paper, it was shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution.
Abstract: : It is shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution. This gives an explicit condition for applying Galerkin's procedure and reveals the wide applicability of Galerkin's procedure to general nonlinear periodic differential systems. The proof of this result is based on existence theorems which are derived from idea contained in Newton's iterative method. The relationship of Galerkin's procedure to the method of averaging is also discussed. Finally the paper exemplifies Galerkin's procedure with a certain nonlinear equation. (Author)
288 citations
Additional excerpts
...2) Using the blade flap equilibrium equations [Eqs. (1012)], the blade flapping coefficients /30, /3ic> and &\s are evaluated....
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01 Dec 1968
TL;DR: In this paper, it was shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution.
Abstract: Abstract : It is shown that Galerkin's procedure is always available for twice continuously differentiable periodic differential systems if a periodic solution is restricted to an isolated periodic solution. This gives an explicit condition for applying Galerkin's procedure and reveals the wide applicability of Galerkin's procedure to general nonlinear periodic differential systems. The proof of this result is based on existence theorems which are derived from idea contained in Newton's iterative method. The relationship of Galerkin's procedure to the method of averaging is also discussed. Finally the paper exemplifies Galerkin's procedure with a certain nonlinear equation. (Author)
252 citations
141 citations
108 citations
TL;DR: In this article, an explicit expression for the steady-state periodic response of a linear dynamical system subjected to combined parametric and forcing excitations of periodic nature is given in terms of the fundamental matrix of the homogeneous system.
Abstract: A linear dynamical system subjected to combined parametric and forcing excitations of periodic nature is governed by a system of inhomogeneous differential equations with periodic coefficients. Presented here is an explicit expression for the steady-state periodic response of such a system, given in terms of the fundamental matrix of the homogeneous system. Based upon this expression, specific analytic formulas of the steady-state response can be derived for some physical systems. For a general system where such an analytical determination is not feasible, the derived expression allows us to devise a straightforward numerical procedure which is particularly suited for computer evaluation and which is equally suited for high-order systems.
60 citations