1,720,969 research outputs found
Low-order models and numerical techniques for the analysis of rotorcraft flight mechanics
Full text linkThe dissertation describes (i) a mathematically rigorous approach for the derivation and validation of low-order helicopter mathematical models from first principles and (ii) the development or improvement of a set of numerical techniques that provide computationally efficient and reliable tools for the analysis of rotorcraft flight mechanics, and in particular evaluation of maximum performance and assessment of handling qualities. Simplified models are expected to provide results at a fraction of the computational cost required for performing the same analysis on the basis of higher order models, but, at the same time, the reliability of these results needs to be carefully assessed, which is one of the objectives of the present work. The techniques developed are tested on various single main rotor rotorcraft configurations, with a focus on articulated, teetering, and two-bladed-gimballed rotor
Multibody Analysis of Terminal Phase for a Reentry Vehicle: A Comparative Study
No full textThe multibody analysis of the system formed by an entry vehicle and a parachute is the subject of the present paper. In particular, two different models of the system made of bridles (connecting the vehicle to the suspension point) and riser (connecting the suspension point to the suspension lines of the parachute) are considered. This allows one to highlight if and how the simplifying assumptions at the basis of many techniques adopted for sizing the suspension system are reasonable and if they affect the most important factors that characterize the final phase of an entry trajectory, such as peak load and maximum deceleration at parachute inflation and landing site dispersion footprint. A Monte Carlo analysis is performed to account for uncertainties on initial conditions and system parameter
Assessment of helicopter model accuracy through inverse simulation
No full textThe paper deals with the assessment of the reliability of simplified rotorcraft models in the evaluation of maneuvering potential using inverse simulation. Inverse solutions obtained for the same maneuver from models of different complexity and fidelity are compared with the objective of identifying the most appropriate model for a consistent evaluation of vehicle handling qualities at the minimum computational cost. Inverse solutions are obtained by means of an integration method for hurdle-hop, slalom, and lateral repositioning maneuvers. Once the maneuvers are solved for the baseline rotorcraft model, the uncertainty associated with the command law identified by means of simpler models is determined. The quantitative evaluation of model reliability from a set of simulation tests is further analyzed on a pop-up-pop-down maneuver and a 180 deg fast turn for validating the approach. The results show that uncertainty intervals are correctly identified, although with some degree of conservativeness when less demanding maneuvers are dealt with
Model predictive control scheme for rotorcraft inverse simulation
Full text linkA novel inverse simulation scheme is proposed for application to rotorcraft dynamic
models. The algorithm is based on a model predictive control scheme that allows for a
faster solution of the inverse simulation step, working on a lower{order, simplified helicopter
model. The control action is then propagated forward in time on a more complete model.
The algorithm compensates for discrepancies between the models by means of a simple
guidance scheme.
The proposed approach allows for the assessment of handling quality potential on the
basis of the most sophisticated model, adopted for the forward simulation, while keeping
model complexity to a minimum level for the computationally more demanding inverse
simulation algorithm. This allows for a faster solution of the inverse problem, if compared
with the computational time necessary for solving the same problem on the basis of the
full{order, more complex model. At the same time, the results are not a�ected by modeling
approximations at the basis of the simpli�ed one. The reported results, for an articulated
blade, single main rotor helicopter model demonstrate the validity of the approach
Assessment of Helicopter Model Fidelity through Inverse Simulation
No full textThe paper presents a technique for assessing the reliability of a set of helicopter models in predicting the required control action when executing a given (set of) manoeuvre task(s). An inverse simulation algorithm based on the integration method is used in order to derive the time-history of control commands necessary for following a prescribed ight path. A quantitative comparison between the control laws thus obtained is performed in order to assess the reliability of lower order models with respect to the baseline, most complete one, adopted as a reference for the analysis. Two metrics are developed, one for evaluating a global error level in the definition of the required control law, and a second one for the identification of the uncertainty in the control action when adopting a lower order model. A total of 9 main rotor dynamic models, 3 main rotor inow models and 3 fuselage aerodynamic databases are combined in order to obtain as many as 13 difierent helicopter simulation models, analyzed in 3 manoeuvres: a hurdle-hop, a slalom and a lateral repositioning. The evaluation of the uncertainty associated with the command law identified by means of simpler models is thus performed in terms of the considered metrics, the validity of which is then tested on two more manoeuvres: a pop-up-pop-down manoeuvre and a 180 deg fast turn. The results show that most of the times uncertainty intervals are correctly identified, although with some degree of conservativeness, when less demanding manoeuvres are dealt with. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved
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