Hekmat Alighanbari

Particle Swarm Optimization Applied to Spacecraft Reentry Trajectory

THE numerical solution of optimal control problems that are nonlinear and, therefore, generally without analytical solutions, can be categorized into different classes with their own advantages and characteristics. In the direct approach, the model equations of the considered system are discretized, and the control trajectories are parametrized to obtain a finite-dimensional parameter optimization problem [1]. Among these direct methods, global optimization methods (also known as evolutionary algorithms), have become of interest in recent years and various research has been done in this area [1–4]. Some well-known methods in this category are genetic algorithms (GAs), which model the evolution of species based on Darwin’s principle of survival of the fittest; simulated annealing (SA), which mimics the equilibrium of large numbers of atoms during an annealing process; and ant-colony optimization, which is inspired by the behavior of the ants. Among all global optimization techniques, the swarm intelligence (SI)-based methods are becoming more popular due to their speed and accuracy qualities. They are inspired by natural phenomena such as the behavior of groups of birds, ant colonies, herds of animals, and even social connections between human beings [3]. The idea of particle swarm optimization (PSO) that is addressed in this Note was first introduced in 1995 by Eberhart and Kennedy [5] and was then followed and modified by other researchers [6]. The most important factor that stands out in SI methods is that because they use the whole experience of the group of individuals, rather than only the experience of each individual particle (i.e., one potential solution), their convergence speed is faster than other methods. The scope of this Note is to present a new method for solving an optimal control problem using a PSO method and avoiding the calculations needed in the common analytical approaches. This is accomplished by using an existing solution for a specific problem and then trying to find other possible trajectories for other objectives of interest. This Note is organized as follows: in Sec. II, the system of equations ofmotion for a reentry spacecraft is presented based on [7]. In Sec. III the PSO optimization method and mapping procedure are described. In Sec. IV the results are presented for two different objective functions. The first objective is for validating the proposed method in terms of accuracy and the other objective isminimizing the integral of the heat applied to the spacecraft.

Analysis of Nonlinear Aeroelastic Signals

The objective of this investigation is to present proper signal processing techniques to analyze nonlinear aeroelastic time series where limit cycle oscillations and chaotic motions may occur. A powerful method to study nonlinear aeroelastic behavior of aircraft structures is the phase-space reconstruction technique. In the reconstruction process, the mutual information function and the percentage of false neighbors methods are used to estimate the time-delay and the dimension of the attractor, respectively. The dynamics of the system is then determined from the Lyapunov exponents. A method of estimating frequency and damping values of the aeroelastic system from the reconstructed phase-space is also presented. Examples are given for a two-dimensiona l airfoil oscillating in pitch and plunge with either a bilinear or a cubic spring nonlinearity in one of the degrees of freedom.

Controller design for rotary inverted pendulum system using particle swarm optimization algorithm

This paper presents particle swarm optimization approach for designing Rotary Inverted Pendulum (RIP) controller. The goal is to balance the pendulum in the inverted position. The intuition of this work is using state-feedback controller as the stabilizer component of the system whereas in other existing systems, only Proportional-Integral-Derivative (PID) is used for that purpose. Simulation results demonstrate effectiveness of the proposed controller design method and can be considered as promising ways for control of various similar nonlinear systems.

Enhanced adaptive unscented Kalman filter for reaction wheels

This paper presents a methodology for improving the fault detection scheme of reaction wheels as actuators onboard satellites. An enhanced adaptive unscented Kalman filter (AUKF) is used, based on a generic adaptive Kalman filter combined with a particle swarm optimization for fault detection. Results show superior performance compared with a generic AUKF.

Numerical modelling of a low Reynolds number plunging airfoil flow field characteristics

Complex viscous mechanisms such as leading edge vortices play a dominant role in the generation of instantaneous force and moment in low Reynolds number flows. The dependence of the corresponding fluid flow characteristics on the governing flow and system parameters in unsteady motions, e.g. plunging, adds to the inherent complexity of the problem. The respective fluid dynamics of such a flow is investigated here via computational fluid dynamics based on a finite volume method. The governing equations are the unsteady, incompressible two-dimensional Navier–Stokes equations. The flow field and vortical patterns around a thin ellipsoidal plunging airfoil are examined in detail with and without freestream velocity, and the effects of Reynolds and Strouhal numbers on the flow characteristics are explored. It is shown that both Reynolds and Strouhal numbers increase the aerodynamic performance in nonzero freestream velocity simulations. Increasing Reynolds and Strouhal numbers causes the airfoil to generate thrust for some time intervals of the plunging period. This thrust generation is penalized with higher peaks of drag coefficient when Strouhal number increases. However, the same penalty in the Reynolds number effect simulations is negligible compared to that of the Strouhal number effects. Increasing Strouhal number causes the airfoil to experience negative pitching moment with higher peak values for longer time intervals, but Reynolds number does not change the time at which negative pitching moment is exerted on the airfoil, but the peaks of pitching moment depend on the governing Reynolds number. The lift coefficient changes noticeably versus Strouhal number, where there is significant lead/lag at the peak lift coefficient for zero-freestream velocity simulations. Reynolds number effects on the lift coefficients mostly occur around the time at which the peak lift coefficient is obtained for both zero and nonzero freestream velocity cases. All of these effects are caused by the complex vortical patterns around the airfoil, described throughout the present article.

Influence of Unsteady Parameters on the Aerodynamics of a Low Reynolds Number Pitching Airfoil

The objective of the present study is to investigate low Reynolds number aerodynamics of a harmonically pitching NACA0012 airfoil. To this mean, the influence of some unsteady parameters; amplitude of oscillation, d, reduced frequency, k, and Reynolds number, Re, on the aerodynamic performance of the airfoil is investigated. Computational Fluid Dynamics (CFD) is utilized to solve Navier-Stokes equations discretized based on Finite Volume Method (FVM). The instantaneous lift coefficients are obtained and compared with analytical data from Theodorsen’s equations. The simulation results reveal that d, k, and Re are of great importance in the aerodynamic performance. They affect the maximum lift coefficients, hysteresis loops, strength and number of generated vortices within the harmonic motion, and the extent of the figure-eight phenomenon region. Thus, the optimum aerodynamic performance demands a careful selection of these parameters.Copyright

Unsteady Low Reynolds Number Computational Study of an Airfoil Undergoing a Novel Figure-Eight Kinematics

The objective of the present study is to simulate the low Reynolds number (LRN) fluid dynamics of a two-dimensional (2-D) elliptic airfoil performing a novel figure-eight-like motion. To this end, the influence of Reynolds number (Re) and amplitude of pitching motion on the fluid flow is investigated. Navier-Stokes (N-S) equations are solved using a Finite Volume Method (FVM), and the instantaneous lift and drag coefficients and the corresponding vortical structures are analyzed. The results show that both Re and the amplitude of pitching oscillations have great influence on the fluid dynamics characteristics of the flapping airfoil.

Effects of tilting rate variations on the aerodynamics of the tilting ducted fans mounted at the wing tips of a vertical take-off and landing unmanned aerial vehicle

Tilting ducted fans mounted at the wing tips of vertical take-off and landing unmanned aerial vehicles define new applications for these types of aerial vehicles. This new configuration gives vertical take-off and landing unmanned aerial vehicles the ability to hover like helicopters and fly forward like airplanes, which results in using any arbitrary location for take-off and landing combined with increasing range and speed. Furthermore, generating additional lift by using asymmetrical shape for the external body of the ducted fans can lead to reducing the wing area and related overall drag, which results in saving more energy. The transition between cruise mode and hovering can be done by choosing different tilting rates, which can produce instabilities in the aerodynamics of the tilting ducted fans mounted at the wing tips of the vertical take-off and landing unmanned aerial vehicles. This research provides the computational fluid dynamics simulations to investigate these instabilities and compare them for two different ducted fans. “Actuator disk model” combined with the assumption of “constant delivered power” to the propeller were used successfully to calculate the induced velocity to the rotor plane of the ducted fan in the computational fluid dynamics simulations. The effects of the flow separation on the aerodynamic coefficients were discussed and compared for both symmetrical and asymmetrical ducted fans in different tilting rates.

Simulation and analysis of flow around tilting asymmetric ducted fans mounted at the wing tips of a vertical take-off and landing unmanned aerial vehicle

Tilting ducted fans attached to the wing tips of vertical take-off and landing unmanned aerial vehicles define new applications for these types of aerial vehicles. This new configuration gives vertical take-off and landing unmanned aerial vehicles the ability to hover like helicopters and fly forward like airplanes, which results in using any arbitrary location for take-off and landing combined with increasing range and speed. Furthermore, generating additional lift using asymmetrical shape for the external body of the ducted fans can lead to reducing the wing area and related overall drag, which results in saving more energy. This research provides experimental results from wind tunnel tests in addition to computational fluid dynamics simulations to investigate the advantages of using an asymmetrical tilting ducted fan instead of a symmetrical one. “actuator disk model” combined with the assumption of “constant delivered power” to the propeller were used successfully to calculate the induced velocity to the rotor plane of the ducted fan in the computational fluid dynamics simulations. The effects of the stall and flow separation on the aerodynamic coefficients were also studied and compared for the symmetrical and asymmetrical ducted fans. Both computational fluid dynamics and experimental results showed noticeable improvement in the lift coefficient using an asymmetrical shape for the external body of the tilting ducted fans.

On the force signatures of a pair of multi-plunging airfoils

The unsteady aerodynamics of a pair of multi-plunging airfoils is studied using computational fluid dynamics based on a finite volume method and dynamic layering mesh motion algorithm. The two-dimensional unsteady, incompressible Navier–Stokes equations are used as the governing equations while the thin ellipsoidal airfoils, commonly used in micro aerial vehicles, perform harmonic plunging motion. The instantaneous lift and drag coefficients are examined in detail and the effects of Reynolds number, frequency and amplitude of oscillations, and the airfoils’ centre-to-centre spacing on the force coefficients are investigated. It is shown that the force coefficients of each of the plunging airfoils differ noticeably from those of a single plunging airfoil both quantitatively and qualitatively, showing the significance of the airfoil–airfoil interaction. It is also observed that the investigated parameters affect the magnitude and characteristics of the real-time lift and drag coefficients. There is an optimum frequency of oscillations, resulting in the highest thrust generation between the investigated frequencies. The amplitude of oscillations increases the aerodynamic performance by increasing the mean lift coefficient but decreasing the mean drag coefficient at the same time. Re effects on the lift coefficient are negligible; however, it is shown that increasing Re causes the airfoils to generate more thrust compared to the lower Re investigated here.