Airton Nabarrete

On Nonlinear Dynamics and Flight Control at High Angles of Attack With Uncertain Aerodynamics

In this paper we consider the flight dynamics of fighter aircraft at high angles of attack with uncertain aerodynamic coefficients. Stochastic parametric uncertainty is dealt with by employing spectral decomposition of the random variables by means of the generalized polynomial chaos expansion. We propose an optimal linear feedback strategy for the automatic pilot system to recover the aircraft from stall and provide acceptable dynamic response. Optimality of the proposed control law is proved by solving the Hamilton-Jacobi-Bellman equation and asymptotically stability of the controlled nonlinear aircraft model is guaranteed in the Lyapunov sense. Numerical results are verified with Monte-Carlo simulations.Copyright

Chaotic Behavior in the Double Pendulum Under Parametric Resonance

In literature, the classic parametrically excited pendulum is vastly studied. It consists of a pendulum vertically displaced with a harmonic motion in the support while it oscillates. The chaos in this mechanism may appear depending on the frequency and amplitude of excitation in superharmonic and subharmonic resonance. The double pendulum is also well analyzed in literature, but not under parametric excitation. Therefore, this is the novelty in the present paper. The present analysis considers a double pendulum under a harmonic excitation following the same idea performed previously for a single pendulum. The results are obtained based on methods, such as, phase portraits, Poincare sections and bifurcation diagrams. The 0–1 tests analyze the presence of chaos while the parameters are varied. The dimensionless parameters take into account the excitation frequency and amplitude as mentioned for the classic parametric pendulum. In this case, we have the particular characteristic that the two pendulums have the same length, the same mass and the same friction coefficient in the joints. The types of motion observed include fixed points, oscillations, rotations and chaos. Results also demonstrated that there was a self-synchronization between these pendulums in ideal excitation.Copyright

Results of the GVT of the Unmodified GARTEUR SM-AG19 Testbed in South America

This work presents the results of the modal analysis performed during the ground vibration testing of a testbed originally designed by the Group for Aeronautical Research and Technology in Europe (GARTEUR). The model testing brought challenges in determining modes with very close frequency values, which were detected independently of the excitation signal. A modal validation process was carried out in order to identify these close-spaced modes as well as their dynamic characteristics. The reliability of the experimental modal model was verified by modal assurance criterion calculations between the experimental data and validated by comparison with a finite element model.

Study on the Soft Suspension Behavior for Aircraft Ground Vibration Test Set-Up

The influence of the aircraft boundary conditions when setting a Ground Vibration test is always an issue. As aircrafts designs are becoming bigger is size and weight, the challenge in developing test set-ups for a successful GVT also increases. These challenges include not only the mechanical design of test devices, but also the goal to have the test performed in a shorter time, and with limited budget. Embraer decided years ago to have reliable device, which could duplicate the aircraft boundary condition, allowing at the same time fast test set-up and fast dismount. Even though, that design was modified and some opportunities had to be evaluated. This paper shows the conclusions of some variations on actual aircraft GVT set-ups, as well as studies performed in a small aircraft- like structure.

SDRE Control Applied to the Wheel Speed of a Compressed Air Engine with Crank-Connecting-Rod Mechanism

Renewable energy sources for vehicles have been the motivation of many researches around the world. The reduction of fossil fuels deposits and increase of the pollution in cities bring the need of more efficient and cleaner energy sources. In this way, this work will present the application of a compressed air engine applied to a bicycle. The engine is composed of two pneumatic cylinders connected to the bicycle wheel through a crank-connecting-rod mechanism. In order to control the velocity of the bicycle, a strategy of control composed of two controls was implemented: a feedback and a feedforward control. For feedback control, the State-Dependent Riccati Equation (SDRE) control and also a proportional-derivative (PD) control are considered, considering three cases for velocity bicycle variation: 10 km/h, 20 km/h, and 30 km/h. The equations of motion of the system were obtained through the Lagrangian energy method. Numerical simulations were performed in order to analyze the dynamics of the system and the efficiency of the controllers.

Optimal Control for Robot Manipulators with Three-Degress-of-Freedom

This work presents the modeling and simulation of a manipulator robot with three degrees of freedom and considering its structures with rigid behavior. The concepts of kinematics for the mathematical deduction and the Lagrangian mechanics were used to obtain the dynamic models of the manipulator and the DC actuators with permanent magnet. Due to nonlinearity and dynamics characteristics, both the states observer and the control used were based on State Dependet Ricatti Equation (SDRE). The simulations made for constant performance parameters demonstrated the effectiveness of the optimal control applied to the manipulator and to the chosen DC actuator models. The applications of trajectories to the manipulator enrich the applicability of the project and the results obtained with the techniques chosen show his efficiency.

Nonlinear Identification Using Polynomial NARMAX Model and a Stability Analysis of an Aeroelastic System

This work describes the nonlinear identification applied to an aeroelastic pitch-plunge system using polynomial NARMAX model and a stability analysis. The apparatus is available and consists of a wing typical section with pitch and plunge degrees of freedom. The identification procedure aims to obtain the parameters for the mathematical model including the torsional stiffness as a quadratic polynomial function. The candidate structure to the polynomial model is obtained from discretization of a continuous-time state-space model and the predictions are obtained via the identification procedure using simulated data. The simulation is performed considering the aerodynamics with free stream velocity increased within an established velocity range which includes the flutter phenomenon. In future work, a data acquisition from the experimental apparatus will be performed. The NARMAX model indicates a polynomial function of fourth order for the nonlinearity and a stability analysis, discussed in this work, mapping the nonlinear regions.