Journal of Aerospace Science and Technology
Volume:14 Issue: 2, Summer and Autumn 2021

To keep pace with current trends in the wind industry, this paper aims at the improvement of the annual energy production of a horizontal axis wind turbine by aerodynamic optimization of blades at the wind conditions of the Manjil site. To achieve this goal, the Riso wind turbine, whose characteristics are publicly available, is selected, and its twist angle and chord length distributions along the blades are optimized. The blade element momentum theory with appropriate corrections is used to predict the turbine output power. The genetic algorithm optimization tool, and Weibull probability density function, for wind regime representation, are also utilized in this work. Optimization results show a 9.4% and 11.6% increase in annual energy production, respectively, for the blade with optimal twist angle and the blade with optimal chord length and twist angle distributions. Finally, the superiority of selecting annual energy production as the objective function is assessed in comparison with other objective functions.

The main application of dynamic coefficients is in the flight path simulation and autopilot design of flying objects. This paper reveals a general process for calculating the roll damping coefficient of a typical airship. The process presented in this article has a step-by-step path that can be used to calculate the roll dumping coefficient of all projectiles and flying objects. The method applied in this paper is fully numerical and the dynamic coefficient will be extracted from the Fluent software using the moving reference frame (MRF) techniques. In this process, first, the roll moment coefficient is extracted from the fluent using the moving reference frame technique, and then the roll damping coefficient will be calculated using some relations presented in this paper. At the beginning of the present work, the general process of calculating dynamic coefficients is discussed. This process is then used to calculate the dynamic coefficient of a typical geometry. The results of the present work and the process of calculating this coefficient, which is fully discussed in this article, can be used to calculate this coefficient in other flying objects with similar geometry. In order to validate the present article, the results of the present work are validated with the results of another article. Acceptable agreement of the results of the present work with references, proves the correctness of the process presented in this paper for calculating this dynamic coefficient.

In this study, Adaptive Network-Based Fuzzy Inference System (ANFIS) is presented with sensor data fusion approach to estimate satellite attitude. The active sensors are sun and earth sensors. Satellite attitude dynamic, including attitude quaternion and angular velocities are estimated simultaneously utilizing the measured values by the sensors. The Extended Kalman Filter (EKF) is employed to verify and evaluate the efficiency of the presented method. Additionally, the neural networks with Radial Basis Function (RBF) and Multi-Layer Perceptron (MLP) are also designed to prove the superiority of the proposed ANFIS network among the smart methods of sensor data fusion for satellite attitude estimation. Root Mean Square Error (RMSE) as a numerical criterion and graphical analysis of residues are utilized to evaluate the simulation results. The simulations confirm that the obtained estimations from ANFIS network have more accuracy in modeling of nonlinear complex systems compared to EKF, MLP and RBF networks. In general, using intelligent data fusion, especially ANFIS, reduces attitude estimation error and time in comparison to the classical EKF method.

In the present paper, the effect of different rotational speed functions in the elastic-plastic deformation and stress analysis of a rotating annular disc of functionally graded materials (FGM) in Reddy model is studied using the analytical and FEM methods. In this regard, differential equations governing dynamic equilibrium for displacements and stresses in the elastic region of the FGM rotating disk have been derived using theory of elasticity in plane stress condition and have been solved by shooting method. Then, the equations governing the distribution of plastic radial and circumferential stresses on the disc have been extracted using the Prandtl -Ross theory of plasticity and based on Ludwig hardening law in conjecture with the von-Mises yield criterion. Also, by modeling the annular disc in the environment of finite element software ANSYS, the results obtained from elastic analytical solution and finite element numerical solution have been compared to each other and to the results reported in the literature for specific cases and validated accordingly. The effect of variation of the disk geometric parameters, functionally graded material power index as well as type of the time-dependent rotational speed function such as the constant speed, exponential, and accelerated/decelerated linear, quadratic, and square root functions on the elastic behavior of the disk and distribution of radial displacement, and also distribution of radial, circumferential, and shear stresses in the disk have been studied. Moreover, the results of plastic analysis have been presented for distribution of radial and circumferential stresses in the disk.

In this article, we analyze the existing de-orbiting mechanisms in the world and analyze different types of these mechanisms for Nano satellites, also known as CubeSats. Moreover, a new passive and efficient design of the de-orbiting mechanism for the CubeSats have been proposed. Utilizing de-orbiting mechanisms are important in Nano satellites or CubeSats to prevent production of space debris in LEO (low-earth orbit), and in NASIR-1 CubeSat, Sail Drag method was used to do so. In this method, the satellite is deorbited using passive two-sided de-orbiting approach in 1.7 years on average, or less than a maximum of 2 years. Software analysis is used to calculate membrane size and the required boom mechanisms in LEO, 600 km from the earth’s surface. Drag sail is designed using software and the prototype as well as the final version for engineering model are made and tested. The passive two-sided sail drag design of NASIR-1 is a more efficient mechanism compared to active, four-sided models in terms of volume, weight and the required electrical power and it offers a larger available externa surface on CubeSat’s surfaces.

In the present study, the aerodynamic performance of the ducted fan is investigated using the surface vorticity method and the lifting line theory. In previous research, to consider the effects of the duct, most of the parameters derived from empirical tests or computational fluid dynamics. Our goal is to present a new method for considering the effects of the duct on the fan enclosed in a duct. In this method, the lift and drag coefficients are only input parameters. The present method requires considerably less computational time than CFD methods. Also, the aerodynamic optimization of fan blades geometry has been carried out using particle swarm optimization method (PSO) to achieve the optimum blade geometry and the maximum output power. The results of this method are in excellent agreement with experimental data in references. By optimizing the geometry of the blade, the output power of ducted fan increased 10 percentage in comparison to ducted fan with old blade geometry.

In this paper, the nonlinear thermal buckling of moderately thick functionally graded cylindrical panels is analyzed based on the first-order shear deformation theory (FSDT) and large deflection von Kármán equations. The highly coupled nonlinear governing equations are solved using the combination of dynamic relaxation approach with the finite-difference discretization method at various boundary conditions. The material properties of the constituent components of the FG shell are considered to vary continuously along the thickness direction based on simple power-law and Mori-Tanaka distribution methods, separately. The critical thermal buckling load is considered based on the thermal load-displacement curve derived by solving the incremental form of nonlinear equilibrium equations. In order to consider the accuracy of the present results, a comparison study has been carried out. The effects of the boundary conditions, rule of mixture, grading index, radius-to-thickness ratio, length-to-radius ratio and panel angle are studied on the thermal buckling loads. It is observed from the results that in high values of radius-to-thickness ratios, there is no difference between the values of critical buckling temperature differences for linear and nonlinear distributions.

This research aims to numerically investigate the efficiency of the plasma actuator in a small wind turbine. The studies were conducted on a domestic wind turbine with a diameter of 1.93 m and the Suzen-Huang model was employed to simulate the DBD plasma actuator. In this research, first, a wind turbine without the plasma actuator was simulated at different tip speed ratios. Then, the DBD plasma actuator was activated at a tip speed ratio of 4.35, and changes in the power output, torque distribution, and surface streamlines were studied. The results indicate with an increase in the power of the plasma actuator, the separation point moved away from the leading edge, the span-wise flows were reduced, and the turbine power output increased. The performance of the plasma actuator is varied along the wind turbine blade length. For the radii r/R=0.4-0.95, a difference in the generated torque can be observed for active and inactive plasma modes, and the plasma actuator did not significantly affect the power output in other sections. The maximum increase in torque due to the plasma actuator has occurred at the radii r/R=0.5-0.7. In these regions, the distance between the separation point and the plasma actuator location is about 0.2 times the chord length of the airfoil.

The design of a ground collision avoidance system for an airplane based on optimal control theory is presented in this paper. A control system is designed by linear quadratic tracker to track desired Euler angles of airplane. Two different systems are designed here. 1- A system independent of 3 dimensional maps, called Digital Terrain Database(DTD), by using a forward looking camera; 2- A system using DTD. Also the obstacle is analyses by digital image processing techniques. An optimal flight control system based on discrete-time linear quadratic tracker is designed, to fly over/ side of obstacles like mountains automatically. Two distinctive systems are designed. First system uses forward-looking camera (as a backup system, when three-dimensional maps are not available); and the second system as the main system, which uses digital terrain models of terrain. Therefore, by generating desired state variables in guidance system, and using these outputs of the guidance system as the inputs of the optimal controller (LQT), the airplane would hopefully no more crash into terrain. In addition, the optimal controls, the angle of attack, and load factor, are within the allowable ranges, and are acceptable. The angular velocities and Controls became zero at the end of the maneuvers.

This paper presents a new Modified Predictive Kalman Filter (MPKF). To solve the problem of a strap-down inertial navigation system (SINS) self-alignment process that the standard Kalman filters cannot give the optimal solution when the system model and stochastic information are unknown accurately. The proposed algorithm is applied to SINS in the initial alignment process with a large misalignment heading angle. The filter is based on the idea of an accurate predictive filter applies n-steps ahead prediction of the SINS model errors to effectively enhance the corrections of the current information residual error on the system. Firstly, the formulations of a novel predictive filter and a fine alignment algorithm for SINS are presented. Secondly, the vehicle results demonstrate the superior performance of the proposed method, in which the MPKF algorithm is less sensitive to uncertainty. It performs faster and more accurate estimation of SINS' initial orientation angles compared with the conventional EKF method.

In this study, the performance requirements influencing the orbital and attitude control system of a geostationary satellite in the station-keeping flight mode considering the coupling effect of both attitude and orbital motion is determined. Controlling and keeping the satellite in its orbital window have been done using a set of four thrusters located on one side of the satellite body, with considering the coupling effect of the attitude motion on orbital motion. The satellite’s orbital motion could be disturbed by the attitude motion in the allowable orbital window. The main factors conducting this behavior are derived utilizing the satellite attitude and orbital dynamic equations of motion. In the mathematical analysis of this study, the effects of environmental perturbations originating from the oblateness of Earth, third mass gravity like sun and moon, and solar radiation pressure on the satellite dynamic behavior are also considered. Afterward, the condition of using four installed thrusters on one side of the satellite and the reaction wheels in order to control the satellite orbital and attitude motion is investigated. To reduce the satellite attitude’s error, a proportional-derivative controller is employed to activate the reaction wheels properly. The satellite positions in north-south and east-west directions are controlled by a specific array of thrusters in order to maintain in its predefined orbital window. The required amount of velocity variations for a duration of one year via some simulation may demonstrate the effectiveness of the proposed approach in enhancing the orbital maintenance procedure of the satellite.

The nozzle, an end-element of the propulsive process Cycle, represents a critical part of any aerospace vehicle. The task of accelerating and efficiently exhausting combusted and reactive gases according to the delivered thrust represents the main objective of the propulsion system design. Flow separation in supersonic convergent–divergent nozzles has been the subject of several experimental and numerical studies in the past. Now, with the renewed interest in supersonic flights and space vehicles, the subject has become increasingly important, especially for aerospace applications (rockets, missiles, supersonic aircrafts, etc). Flow separation in supersonic nozzles is a basic fluid dynamics phenomenon that occurs at a certain pressure ratio of chamber to ambient pressure, resulting in shock formation and shock/turbulent-boundary layer interaction inside the nozzle. From purely gas-dynamics point of view, this problem involves basic structure of shock interactions with separation shock, which consists of incident shock, Mach reflections, reflected shock, triple point and slip lines. In this article A Review on Flow Separation Phenomenon for Supersonic Convergent–Divergent Nozzles has been investigated.