Journal of Aerospace Science and Technology
Volume:13 Issue: 1, Winter and Spring 2020

This article examines the fault tolerance control (FTC) system for the Boeing 747. to reach this goal, firstly 6 degrees of freedom equations are simulated and linearized by using dynamic inversion method. Then, the system is controlled by a linear proportional-integral-derivative controller. To control this system, the angular velocity loop (r, q, p) must be closed and use cascade control to achieve this goal. Faults such as actuator and sensor failure are injected into the system, and by adding an integrated gain to the controller, the system resists these faults.  Also, a redundancy system has been used in sensors to prevent sensor faults. Moreover, a linear Kalman filter has been used to eliminate noise in the system. If an actuator is locked in the Boeing 747, the faulty actuator is removed from the control system. Then, a healthy actuator or other remaining actuators will eliminate the effects of this fault.

With the advancement of science and technology, ultra-light drones with electric propulsion hold many applications. In these drones, the electric motor is the primary consumer of energy. Thus, having an accurate model of power consumption of the motor, propeller, and battery set can play an essential role in determining the drone's flight duration. This paper aims to model the behavior of two sets of motor and propeller in the wind tunnel. One motor set has a low speed, and the other has a medium speed. Also, after the above modeling, the models of speed-power, thrust-power, and speed-efficiency are extracted. Then, a lithium polymer battery with a minimal voltage drop for the drone is used. In the operating speed, the flight time of the desired drone is obtained. The power consumption, speed, and thrust models are obtained using interpolation. Finally, the motor that consumes less power and has a longer flight time is selected.

The vacuum test stand simulates the space systems' engines with a high expansion ratio at high altitudes and vacuum pressure for static tests. This article investigates the flow stability in the diffuser to use in a vacuum stand. Several variables are essential in the operation of this system, including the diffuser length, the location of the nozzle relative to the diffuser, the dimensions of the vacuum chamber, and the diffuser length-to-diameter ratio. In this numerical study, the diffuser length-to-diameter ratio is investigated applied at different pressures by the rocket engine to the stand. These results are performed in three length-to-diameter ratios of 6, 8, and 10, and the applied pressure varies from 30 to 50 bar. With an increase in the geometric ratio of diffuser length-to-diameter, stable conditions can be created in the diffuser at lower applied pressures.

Parafoil-cargo system, as a complex system, is used widely today and has various usages. This system is a polynomial complex whose components, have dynamic interactions and relative movements. The present study deals with the multibody modeling and simulation of nine degrees of freedom flight dynamics of a parafoil-payload system, which includes the three degrees of transfer freedom and the three degrees of the rotational freedom of the parafoil set (the part with the parachute and the ropes attached to it), and the three degrees of relative rotational freedom of the cargo. By kinematic and dynamic analysis of the system components, a nonlinear model with 18 state variables is obtained. This model has three controlling entrances. In addition to symmetric and asymmetric aerodynamic brakes, the shifting of the weight of the cargo with respect to the parafoil is considered, which leads to the rotation and change of the transverse installation angle of the parachute with respect to the parafoil set. The apparent mass and inertia moment of the parafoil parachute, restraining forces, relative movements between objects, longitudinal and transverse installation angles and also the effect of wind are examined. In order to evaluate how the flight dynamics of the system work and the study of the factors affecting it, the nonlinear differential equations of the model are developed. After examining its stability using Lyapanov method, the model undergoes a numerical integration as well as simulation for several flight conditions and under different inputs by the code and program developed in MATLAB software. The simulation results show the flight stability that is achieved after launching from a high altitude and by which the flight dynamic modeling of the system is validated.

The present study investigates the flow around two tandem spheres and their aerodynamic optimization. In a systematic view, the downstream sphere is regarded as the projectile and the upstream sphere is the sensor. The aim of this study is to find the most appropriate configuration with lowest drag force. Therefore, the results of the effects of the center-to-center (CC) distance of the spheres, and the reduction of the sensor’s diameter were investigated in 15 different cases. The results show that as the distance between the spheres decreases, the drag force of the spheres decreases too; reduction in the sensor’s diameter would increase the projectile’s drag while decreasing the sensor’s drag. The highest effects on drag reduction were induced by constant distance between spheres and a change in sensor’s diameter. Consequently, in the last stage of the study, the adjoint solution of the FLUENT software was used to reduce the drag of the whole set through optimization of the sensor frontal hemisphere. However, due to systematic limitations, only the shape of the forepart of the sensor can be changed. Since the sphere is a bluff body, efficient options are needed for the adjoint optimization algorithm and it’s worth noting that the optimized shape in each case is different from other cases. The highest drag reduction happened in the case with a CC distance of 2.5 m and sensor diameter of 0.75 m. Furthermore, the case with CC distance of 1m and sensor diameter of 0.25 is the only case after optimization in which simultaneously the drag force of both spheres has been reduced.

Butterfly valves as control valves are used when a small pressure drop is required in the valve. The results of numerical studies of solving the incompressible flow equations around the butterfly valve in three dimensions are presented in this paper. ANSYS CFX commercial software is used to solve the flow equations. The ε-k turbulence model is used to simulate flow disturbances. Velocity, pressure distribution, kinetic energy, and turbulence intensity profiles are the factors that provide flow characteristics. The position of the disk at the opening angles of 0˚, 15˚, 30˚, 45˚, 60˚, and 75˚ as well as the inlet velocities of 1, 2, and 3 m/s have been investigated. Torque and valve performance factors such as flow coefficient and Hydrodynamics torque coefficient have been calculated for these different opening angles. The results of this simulation have been compared with the available experimental results for validation. The results show that the pressure drop across the valve, the flow coefficient, and the hydrodynamic torque coefficient depend on the opening angle. As the opening angle increases, the flow coefficient and the hydrodynamic torque coefficient decrease, and the torque and pressure drop increase across the valve. Flow separation has also been investigated at the mentioned opening angles.

In the last decade, nonlinear normal modes have attracted the attention of many researchers, and many methods and algorithms have been proposed to calculate them. Among the proposed methods, the combination of the shooting method and the continuation of the periodic solution is the strongest methods. However, the computational cost of the method has still limited its application. In this paper, an updated formula is used to reduce the computational costs of the method. Using this updated formula significantly reduced the computation time so that the computational speed of nonlinear normal modes increased tenfold. Also, as the power of nonlinear terms increases in the system, the efficiency of the updated formula increases. In order to evaluate the accuracy of the proposed method, a system with two degrees of freedom was studied, and it was observed that the results obtained are consistent with the results in other works.

In this paper, growth and collapse of a cavitation bubble inside a rigid cylinder with a compliant coating (a model of human’s vessels) are studied using Boundary Integral Equation and Finite Difference Methods. The fluid flow is treated as a potential flow and Boundary Integral Equation Method is used to solve Laplace’s equation for velocity potential. The compliant coating is modeled as a membrane with a spring foundation. At the interface between the fluid and the membrane, the pressure and normal velocity in the flow are matched to the pressure and normal velocity of the membrane using linearized condition. The effects of the parameters describing the flow (the fluid density, the initial cavity size and its position) and the parameter describing the compliant coating (membrane tension) on the interaction between the fluid and the cylindrical compliant coating are shown throughout the numerical results. It is shown that the bubble life time slightly decreases by increasing membrane tension.

In this paper, a neural network backstepping controller is designed for the control of a  reentry vehicle. The backstepping control system is applied to the nonlinear six degree of freedom dynamics of the reentry vehicle for tracking the desired input. The neural network is used for estimation of nonlinear parts of backstepping controller during entry to atmosphere and to estimate the nonlinear terms as well as the external disturbances. Numerical simulations have been performed to verify the performance of the proposed control  method.

This article addresses a new approach to 3D path planning of UCAVs. To solve this NP-hard problem, imperialist competitive algorithm (ICA) was extended for path planning problem. This research is related to finding optimal trajectories before UCAV missions. Developed planner provides 3D optimal paths for UCAV flight with real DTM of Tehran environment. In UCAV mission, final computed paths should be smooth that made the path planning problems constrained. This planner can offer flyable 3D paths based on mission requirements. It’s a comprehensive study for efficiency evaluation of EA planners, and then novel approach will be proposed and compared to ICA, GA, ABC and PSO algorithms. Then path planning task of UCAV is performed. Simulations show advantage of proposed methodology.

This study focuses on using rotor blade turbine winglets for the purpose of controlling the wingtip vortex in airplanes. The aim of the study is to investigate the effective geometric properties of the rotor blades that are used as winglets, as well as experimental evaluation of their effects on drag, lift coefficient and the aerodynamic efficiency ratio of the airplane. Seven different types of rotor blades were chosen in regard of their span length, number of blades, and the shape of the blades and experimented in a wind tunnel. The drag and lift force were directly measured via a 3-axis external balance. The position and place of installment of the rotor blades were selected through the studies mentioned in the literature and their geometric properties were further investigated. A finite wing with a NACA641412 cross-sectional airfoil, two similar rotor blades with different span length, two similar rotor blades with different blade count, and three rotor blades with different aerodynamic shapes in terms of installation and twist angle were used as models in this study. All the experiments were conducted at a Reynolds Number of 100,000 and angles of attack ranging from negative 4 to positive 20. The results showed the existence of turbine winglets has increased the lift coefficient and results in a reduction in the drag coefficient. Rotor blades with larger span lengths have increased the aerodynamic efficiency, although they have increased the drag coefficient as well. The number of the blades has had different effect in different angles of attack. The results indicate that rotor blades with acceptable aerodynamic properties can increase the value of aerodynamic efficiency almost twice its base value and delay the wing stall up to the  attack angles above 20 degrees.

In this paper, a new method for optimal guidance in the atmospheric return phase is proposed. This guidance method is based on instantaneous and online trajectory optimization in which optimal guidance commands are obtained from sequential solving of optimal control problems. In order to solve optimal control problems quickly and online, a combined approach including the concepts of differential flatness, B-spline curves, direct collocation, and non-linear programming is used. By performing the trajectory optimization process in the form of closed-loop control and implementing the receding horizon control, the open-loop responses of optimal control can be dependent on the instantaneous conditions of the object and the target. In this case, guidance commands can be generated based on various objective functions and constraints, and model uncertainties can be considered by entering the vehicle conditions into the trajectory optimizer. In order to show the capabilities of the proposed guidance method, a numerical example of the guidance of a reentry vehicle in the presence of model uncertainties is presented.