JOURNAL OF AERONAUTICAL ENGINEERING (JOAE)
Year:2011 | Volume:13 | Issue:1|Papers Count:7

The optimization of attitude control system is studied for a special flying vehicle. The vehicle is launched vertically and after a moment, it is rotated to the desired attitude by a reaction jet control system. In the first section of this article, the design process of the attitude control system that includes design of system details as well as the control loops is studied. In a new approach, the design parameters of the subsystems are divided into three sets of parameters, including predefined parameters, design (independent) parameters and dependent parameters. The dependency between the parameters causes some dependent parameters of a subsystem to be input (predefined) parameters of the other(s). So, it is necessary to extract the arrangement of subsystems calculations. Since the attitude control phase is the prerequisite of the guidance phase, it is necessary to attain the minimum rotation time from the vertical to the desired attitude. But, there are some constraints, such as the dynamics and saturation of actuators that causes some difficulties in reaching this goal. On the other hand, one must compromise between the desired mission and the system constraints. For this purpose, the multi-objective optimization approach is utilized to simultaneously reach all goals and satisfy all constraints. In this paper, the reaction jet control system design is defined as an optimization problem with 13 unknown design parameters and 13 system constraints. This problem is solved using the new-developed multi-objective Adaptive Real-coded Memetic Algorithm to simultaneously minimize rise time, overshoot and the actuator bandwidth. The design optimization is performed based on the non-linear 6DOF flight simulation results and considering all constraints such as the saturation of the control signals. Finally, the optimal design is compared with the classic design, obtained based on the trial and error approach.

In this paper, initially the six degrees of freedom aircraft nonlinear equations of motion as well as the navigation relations are derived for a specified air vehicle in state space format. Subsequently through optimal formulation of the problem utilizing linear quadratic regulator (LQR) approach, optimal controls are determined for finite horizons in order to guide the vehicle on a pre-specified trajectory. In the proposed strategy the finite horizon forces and moments are taken as the six controls to be optimally determined using (LQR) and the receding horizon control (RHC) algorithm. These optimal forces and moments could be generated through the conventional existing vehicle mechanisms, namely the engines and the control surfaces. In essence, the engine commands and control surface deflections need to be determined in a fashion that would in turn produces these required optimal forces and moments, that are initially computed. To this end, the mushy state simulated annealing (MSSA) approach is utilized as a novel idea to perform the above-mentioned task that also shows the potential of this intelligent search engine for a practical aerospace problem of flight mechanics. With this idea, the optimal control commands are derived for consecutive time steps through inverted dynamics using algebraic equations in a closed loop fashion. Each time step resulting commands are applied to the vehicle through its nonlinear equations of motion in order to obtain the next updated states of the system. The loop iterates forward while the aircraft tries to track the desired path. It is shown that the proposed integrated closed loop scheme has good robustness properties against disturbances and thus could be potentially used for complex nonlinear control systems.

In this research, thin wings unsteady aerodynamics has been investigated using boundary integral equations. The purpose is to develop a proper basis for the extension of boundary element method applicability to some novel lifting configurations with negligible thickness e.g. membrane wings, flapping and morphing wings. For this purpose, conventional aerodynamic boundary element method that can treat only thick bodies has been formulated and modified so it can be used for thin wings too. Moreover, as boundary element system of equations is expressible in eigenvalue problem form, eigenanalysis of unsteady flow over thin wings has been performed and reduced order aerodynamic models have been constructed based on flow eigenmodes. The proposed boundary element method and BEM-based reduced order models have been used for time domain aerodynamic analysis of various airfoils/wings undergoing different unsteady motions and obtained results are in line with analytical relations, experimental data and verified numerical results.

In this research, the film cooling through multiple squired cross section cold jets inclined normally into a hot cross flow are computationally simulated. The turbulence effects are modeled using the RANS approach applying the `v2¦-kw, Standard k-w and the SST turbulence models and the obtained results are compared. The governing equations of the mass conservation, momentum and energy are discreted and solved using the finite volume method and the SIMPLE algorithm over a structured, non-uniform multi-block grid. The jet into cross flow velocity ratio and the jet Reynolds number are 0.5 and 4700 respectively. The results show that the `v2¦-kw model predicts the complicated structures of the flow more accurately, in comparison with the k-w and the SST models.

The purpose of this research is to present a new way to design and calculate the thermo hydraulic of stator blade of cooled Turbine to examine the effectiveness of cooling system. One of the methods of analyzing the cooling system of the blades is based on using Dynamic fluid calculation (CFD). Another way is hydraulic network in order to distribute the coolant airflow in the internal surface of the turbine blade. The advantage of this method is to reduce the time duration for calculation and its usage in complex geometric figures. Along with determination of the coolant air distribution we will be able to calculate the convection heat transfer coefficient in the internal surface of the blades. The calculation of the hydraulic network is based on graph theory. In this way first, the hydraulic network with coolant blade is created. Next, this network is simulated with an electrical network, and then the hydraulic network flow in the cooling canals systems along with computer codes is calculated by Kirishov rules and finally, in order to prove the validity of the given method, we can use a blade which the distribution of its cooling air into the input and output canals are seen and then the last result should be compared.

Sheet metals, due to their broad applications in aerospace industries, are one of the most important issues in metal forming researches. One of the useful methods in identifying forming limit and preventing sheets from tearing is the use of FLC curve. In addition to the forming limit, this curve presents a boundary for allowable strain. This paper relies mainly on the accuracy and broad application of this method. After reviewing the history of formability limit curves specially the theory suggested by Marciniak and Kuczynski known as M-K, a new model, taking in to account the shortcomings of the above-mentioned theory, is presented which is in line with the results of that theory. In this theory, like M-K theory, a thin plate with non-homogeneity is selected as a decrease in gradient thickness with a sinusoidal function and is under a 2D stress. By analytical study, finally, a differential equation is achieved and the result in the range of positive strains (stretched zone) is the same as the result of M-K theory, and in the range of negative strains (tension zone) completes the FLC curve. The results of applying this equation on two alloys with the hardening exponents of 0.4 and 0.24 show the accuracy of this equation.

Simulated annealing is one the most popular methods that provides a means for optimization of problems with both continuous and discrete variables. The method is basically a Monte-Carlo random search technique in which movement from a local extremum is heuristically possible. In this paper, an approach to the design of laminates based on a modified discrete-variables parallel simulated annealing method is presented. The eight effective elastic moduli and the weight of the laminate are used to develop a cost function that its minimization gives a proper lay-up to be compatible with the required elastic effective moduli and a minimum weight. A parallel simulated annealing procedure in conjunction with a novel adaptive cooling schedule is introduced to speed up the algorithm. Studies show that the introduced modifications are also statistically effective in increasing the solution quality.