TY - GEN
T1 - Linear time-invariant models of rotorcraft flight dynamics, vibrations, and acoustics
AU - Saetti, Umberto
AU - Horn, Joseph F.
AU - Brentner, Kenneth S.
N1 - Publisher Copyright:
Copyright © 2021 by the Vertical Flight Society. All rights reserved.
PY - 2021
Y1 - 2021
N2 - The paper discusses the development of a novel linearization algorithm to obtain high-order linear time-invariant (LTI) models of the coupled rotorcraft flight dynamics, vibrations, and acoustics. To demonstrate the methodology, the study makes use a nonlinear simulation model of a generic utility helicopter (PSU-HeloSim) that is coupled with an aeroacoustic solver based on a marching cubes algorithm. First, a revisited harmonic balance algorithm based on harmonic decomposition is applied to find the periodic equilibrium and approximate high-order LTI dynamics at 80 kts level flight. Next, the proposed output linearization scheme is applied to derive time-invariant, linearized equations of the main rotor forces and moments, and acoustics. Simulations are used to validate the response of the linearized models against that from nonlinear simulations. Additionally, the cost of linearization and potential performance benefits of employing linear models versus nonlinear simulations are assessed. The high-order LTI models thus obtained are shown to provide similar acoustic predictions compared to those of nonlinear simulations for small amplitude maneuvers, but at a fraction of the computational cost. These linear simulations are shown to run in the order of thousands of times faster than real time, and four orders of magnitude faster than nonlinear acoustic predictions based on a marching cubes algorithm.
AB - The paper discusses the development of a novel linearization algorithm to obtain high-order linear time-invariant (LTI) models of the coupled rotorcraft flight dynamics, vibrations, and acoustics. To demonstrate the methodology, the study makes use a nonlinear simulation model of a generic utility helicopter (PSU-HeloSim) that is coupled with an aeroacoustic solver based on a marching cubes algorithm. First, a revisited harmonic balance algorithm based on harmonic decomposition is applied to find the periodic equilibrium and approximate high-order LTI dynamics at 80 kts level flight. Next, the proposed output linearization scheme is applied to derive time-invariant, linearized equations of the main rotor forces and moments, and acoustics. Simulations are used to validate the response of the linearized models against that from nonlinear simulations. Additionally, the cost of linearization and potential performance benefits of employing linear models versus nonlinear simulations are assessed. The high-order LTI models thus obtained are shown to provide similar acoustic predictions compared to those of nonlinear simulations for small amplitude maneuvers, but at a fraction of the computational cost. These linear simulations are shown to run in the order of thousands of times faster than real time, and four orders of magnitude faster than nonlinear acoustic predictions based on a marching cubes algorithm.
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M3 - Conference contribution
AN - SCOPUS:85108954588
T3 - 77th Annual Vertical Flight Society Forum and Technology Display, FORUM 2021: The Future of Vertical Flight
BT - 77th Annual Vertical Flight Society Forum and Technology Display, FORUM 2021
PB - Vertical Flight Society
T2 - 77th Annual Vertical Flight Society Forum and Technology Display: The Future of Vertical Flight, FORUM 2021
Y2 - 10 May 2021 through 14 May 2021
ER -