Aerospace Science and Technology
Ahmad Sharafi
Volume 14, Issue 2 , October 2021, , Pages 52-65
Abstract
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 ...
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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.
M. Fakoor; P. Mohammadzade; E. Jafari
Volume 11, Issue 2 , October 2017, , Pages 43-51
Abstract
Composite stiffened cylindrical shells are widely used as primary elements in aerospace structures. In the recent years, there has been a growing research interest in optimum design of composite stiffened cylindrical shell structures for stability under buckling load. This paper focuses upon the ...
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Composite stiffened cylindrical shells are widely used as primary elements in aerospace structures. In the recent years, there has been a growing research interest in optimum design of composite stiffened cylindrical shell structures for stability under buckling load. This paper focuses upon the development of an efficient optimization of ring-stringer stiffened cylindrical shell. The optimization problem used in this study involves weight minimization of ring-stringer stiffened composite cylindrical shell with buckling load and stress, which are considered as design constraints. The proposed methodology is based on Particle Swarm Optimization (PSO) algorithm. The material of shell is composite, but the material of stiffeners is considered to be isotropic. The approach adopted in modeling utilizes the Rayleigh-Ritz energy method and the stiffeners are treated as discrete members. In addition, a 3-D Finite Element (FEM) model of the ring-stringer stiffened cylindrical shell is developed that takes into consideration the exact geometric configuration. The results obtained using the Rayleigh-Ritz energy method are compared with those using 3-D FE model. The proposed methodology is implemented on the ring-stringer stiffened cylindrical shell using the PSO algorithm. The obtained results show a 13% reduction in the weight of the ring-stringer stiffened cylindrical shell whilst all the design constraints are satisfied. In addition, the results show that the proposed methodology provides an effective way of solving composite stiffened cylindrical shell design problems.
A. nouri; S. Astaraki
Volume 11, Issue 2 , October 2017, , Pages 53-63
Abstract
In this paper, optimization of the sound transmission loss of finite rectangular anisotropic laminated composite plate with simply supported boundary conditions has been developed to maximize transmission loss. Appropriate constraints were imposed to prevent the occurrence of softening effect due to ...
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In this paper, optimization of the sound transmission loss of finite rectangular anisotropic laminated composite plate with simply supported boundary conditions has been developed to maximize transmission loss. Appropriate constraints were imposed to prevent the occurrence of softening effect due to optimization. For this purpose, optimization process was incorporated into comprehensive finite element software. The transmission loss (TL) obtained from the numerical solution was compared with those of other authors indicated good agreement. The discrete frequencies have been chosen based upon the sound transmission class with A-weighting constant. Several traditional composite materials have been studied and the results have shown that in the mass control region, the optimization of stacking sequence and optimal thickness has not been an effective contribution to improve the transmission loss. The results also show that, the lamina thickness optimization has an important effect on improving the transmission loss, but the advantage of low weight composite material is compromised by optimization.
S.Hamid Jalali -Naini; Sh. Ahmadi Darani
Volume 11, Issue 1 , June 2017
Abstract
In this paper, the preferred region of design parameters for quasi-normalized equations of single-axis attitude control of rigid spacecraft using pulse-width pulse-frequency modulator (PWPFM) is presented for rest-to-rest maneuvers. Using the quasi-normalized equations for attitude control reduces the ...
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In this paper, the preferred region of design parameters for quasi-normalized equations of single-axis attitude control of rigid spacecraft using pulse-width pulse-frequency modulator (PWPFM) is presented for rest-to-rest maneuvers. Using the quasi-normalized equations for attitude control reduces the system parameters, that is, the moment of inertia, the filter gain, and the maximum torque of modulator are merged to other parameters and the total number of parameters is reduced. Therefore, the computational burden is decreased and moreover, the results are usable for grouped parameters, regardless of the value of each parameter separately. The optimization is carried out by grid search method with the performance index of fuel consumption or number of thruster firings for a range of inputs. Finally, the suggested upper and lower bounds of parameters are obtained based on the optimization results.
M. H. Djavareshkian; A. Esmaeili
Volume 10, Issue 2 , September 2013
Abstract
Optimization of the sectional wing in ground effect (WIG) has been studied using ahigh order numerical procedure and response surface method (RSM). Initially, the effects of the ground clearance, angle of attack, thickness, and camber of wing have been investigated by a high-resolutionscheme, which is ...
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Optimization of the sectional wing in ground effect (WIG) has been studied using ahigh order numerical procedure and response surface method (RSM). Initially, the effects of the ground clearance, angle of attack, thickness, and camber of wing have been investigated by a high-resolutionscheme, which is highlystrong and accurate. In the numerical simulation, Normalized Variable Diagram (NVD) scheme is applied to the boundedness criteria. In the optimization process, lift to drag ratio (L/D) is considered as an objective function and static conditions and shape parameters are noticeable to be considered as design variables;.Ths is because the main factor in the design of WIG vehicles is moving near the ground and the distance to the ground draws attention to the significance of it.Therefore, the static conditions strenuously defend this view that they are irrefutable parameters in the aerodynamic optimization of WIG vehicles. Adaptive Neuro-Fuzzy Interface System (ANFIS) is employed to generate the surface response, because the objective function and constraints are particularlynoisy. Sensitivity analysis is also done and the sensitivity amount of the objective function from design variables is explored
Alireza Mohamadifard; Abolqasem Naghash
Volume 8, Issue 2 , September 2011, , Pages 87-95
Abstract
A near-optimal midcourse trajectory shaping guidance algorithm is proposed for both air and ballistic target engagement mission attributes for generic long range interceptor missile. This guidance methodology is based on the maximum final velocity as the objective function and maximum permissible flight ...
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A near-optimal midcourse trajectory shaping guidance algorithm is proposed for both air and ballistic target engagement mission attributes for generic long range interceptor missile. This guidance methodology is based on the maximum final velocity as the objective function and maximum permissible flight altitude as the in-flight state constraint as well as the head-on orientation as the terminal state constraint for anti-ballistic trajectory. Guidance algorithm utilizes the combination of the Generalized Vector Explicit Guidance or GENEX guidance with the Bezier curve-generating functions. Nominal Bezier curves are fitted by choosing control points intuitively. Waypoints are then selected on the curve to divide it to suitable portions according to the curve’s length and curvature. These waypoints are then fed into the GENEX guidance law. To avoid acceleration command jumps, an algorithm is designed to switch to the next waypoint at a distance from the current currently-approaching waypoint. To provide near-optimality and meet the in-flight and terminal constraints, all the guidance algorithm parameters including Bezier control points, waypoints, switching distances and the GENEX law gain are optimized using Genetic Algorithm by setting the mentioned cost function and constraints. Simulation results show better performance compared to nominal trajectories while ensuring the flight altitude constraint for air target and head-on orientation for ballistic target.
A. Abedian
Volume 3, Issue 4 , December 2006, , Pages 167-176
Abstract
Several traditional stopping criteria in Genetic Algorithms (GAs) are applied to the optimization process of a typical laminated composite plate. The results show that neither of the criteria of the type of statistical parameters, nor those of the kinds of theoretical models performs satisfactorily in ...
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Several traditional stopping criteria in Genetic Algorithms (GAs) are applied to the optimization process of a typical laminated composite plate. The results show that neither of the criteria of the type of statistical parameters, nor those of the kinds of theoretical models performs satisfactorily in determining the interruption point for the GA process. Here, considering the configuration of the history curve of the maximum objective or fitness value with generation number, a Logarithmic Performance Criterion (LPC) is introduced as a stopping criterion for optimization of composite plates. The results highlight the advantages of LPC in performing sufficiently smooth (no noise), requiring reasonable number of generations, less parameter dependency, lower need for conservative assumption, on-line controllability, wide scope applicability, and reasonably easy application in engineering decision-making problems.
