Aerospace Science and Technology
Mohammad Hossein Khalesi
Abstract
Unmanned Aerial Vehicles (UAVs) have numerous applications in military, commercial and hobby fields. Among these vehicles, drones with vertical take-off and landing (VTOL) capability have attracted more attention due to their specific capabilities such as better maneuverability and hover flight. In recent ...
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Unmanned Aerial Vehicles (UAVs) have numerous applications in military, commercial and hobby fields. Among these vehicles, drones with vertical take-off and landing (VTOL) capability have attracted more attention due to their specific capabilities such as better maneuverability and hover flight. In recent years, numerous concepts emerged which trying to propose new configurations to enhance UAVs performance. In this paper, we propose a novel concept which integrates single main rotor helicopter and quadrotor structure to overcome some difficulties exist in those applications. This suggested configuration, include a variable pitch main rotor equipped with four smaller counterrotating rotors to overcome its opposite torque (instead of a tail rotor in helicopters) and also sustain a portion of the UAV weight which make it possible to use a smaller main rotor. This design preserves maneuverability of helicopters, while eliminates tail rotor power loss and its asymmetric lateral force and also enhances the flight stability and maneuverability by properly using other four rotors’ thrusts. Preliminary dynamic modeling and control system design are presented in the text and the results show that this idea can be investigated further. The next steps are planned to be studied in next researches.
Aerospace Science and Technology
Hossein Shadmehr; Sajad Ghasemloo; Hamid Parhizkar
Abstract
In this article, the idea of building a supersonic wind tunnel has been provided that uses a high-pressure steam flow of a combined cycle power plant. This has been investigated by CFD method. Using the plant's output steam as a high-pressure source can be used in the ejector to create supersonic airflow ...
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In this article, the idea of building a supersonic wind tunnel has been provided that uses a high-pressure steam flow of a combined cycle power plant. This has been investigated by CFD method. Using the plant's output steam as a high-pressure source can be used in the ejector to create supersonic airflow in the test chamber. For this purpose, first, the numerical model has been validated in comparison with the previous numerical and experimental results. The numerical model used is the viscous compressible flow, which is performed by the k-ω-SST turbulent modeling of the turbulence model. All calculations are performed in ANSYS-FLUENT software. After validating the numerical process, various geometries have been proposed to achieve the ultrasonic secondary flow and each structure is examined numerically separately in a range of functional conditions. Through trial and error method and looking at the achievements of previous research, in a very long process and by testing several different structures, a suitable structure has been obtained to achieve the supersonic testing chamber. This structure has been studied parametrically under different functional conditions. It has been shown that the proposed structure can generate an ultrasonic flow in an acceptable range of power plant steam flow and pressure. This structure has been proposed for the first time in the literature in this field, and in no previous research has such a structure been proposed. Access to the ultrasonic secondary flow is also a major innovation of this research.
Seid H. Dr. Pourtakdoust; A.B. Novinzadeh
Volume 2, Issue 4 , December 2005, , Pages 27-36
Aerospace Science and Technology
Mahdi Fakoor; Seyed Mohammad Navid Ghoreishi; Mohamad Aminjafari
Volume 12, Issue 1 , March 2019, , Pages 27-37
Abstract
In this paper, a combination method has been developed by coupling Multi-Objective Genetic Algorithms (MOGA) and Finite Element Method (FEM). This method has been applied for determination of the optimal stacking sequence of laminated composite plate against buckling. The most important parameters in ...
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In this paper, a combination method has been developed by coupling Multi-Objective Genetic Algorithms (MOGA) and Finite Element Method (FEM). This method has been applied for determination of the optimal stacking sequence of laminated composite plate against buckling. The most important parameters in optimization of a laminated composite plate such as, angle, thickness, number, and material of each layer are considered in the proposed method. These optimization processes have done for 3 types of compressive loads and optimal stacking sequences and Pareto front for each kind of compressive loads are determined. Unlike estimation methods like response surface and simple analytic methods, in the proposed optimization algorithm, objective functions are calculated directly by FEM software which leads to precise results. The results of proposed algorithm are validated against existing data in literature. The effects of different boundary conditions and aspect ratio of plate on Pareto front in buckling of a laminated composite plate are also studied.
Aerospace Science and Technology
Ehsan Abbasali; Amir reza Kosari; Majid Bakhteiari
Abstract
In this paper, the effect of perturbations of oblate primaries in the Circular Restricted Three-Body Problem is studied, and the equations of satellite orbital motion in the Circular Restricted Three-Body Problem are developed by employing Lagrangian mechanics. Since the equations have no closed-form ...
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In this paper, the effect of perturbations of oblate primaries in the Circular Restricted Three-Body Problem is studied, and the equations of satellite orbital motion in the Circular Restricted Three-Body Problem are developed by employing Lagrangian mechanics. Since the equations have no closed-form solution and numerical methods must be applied, the problem can have different periodic or quasi-periodic solutions depending on the equation's initial conditions of orbital state parameters. For this purpose, an algorithm named “orbital correction algorithm” is proposed to correct the initial conditions of orbital state parameters. The limited number of periodic orbits in the study environment indicates the algorithm’s need for suitable initial guesses as input. In the present paper, suitable initial guesses for orbital state parameters are selected from the third-order approximation of the Unperturbed Circular Restricted Three-Body Problem’s periodic solutions, increasing the chance of obtaining desired periodic solutions. The obtained perturbed and unperturbed periodic orbits are compared in order to understand the effect of perturbations. Adding the perturbations brings the study environment closer to the real environment and helps understand satellites' natural motion.
Aerospace Science and Technology
Ali Davar; Mahdi Mehrabani; MohammadReza Zamani; Mohsen Heydari Bani; Jafar Eskandari Jam
Abstract
The composite lattice cylindrical shells are analyzed in this research while they are subjected to transient dynamic loading. The equilibrium equations for the composite cylindrical shell are expressed in terms of classical shell theory. Additionally, due to the discontinuous distribution of stiffness ...
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The composite lattice cylindrical shells are analyzed in this research while they are subjected to transient dynamic loading. The equilibrium equations for the composite cylindrical shell are expressed in terms of classical shell theory. Additionally, due to the discontinuous distribution of stiffness and shell mass between reinforcing ribs and their proximity to one another (empty or filled with filler material), this issue has been expressed using an appropriate distribution function. On the basis of Lowe's first approximation theory, the strain-displacement and curvature-displacement relationships are considered. The Galerkin method is used to calculate the natural frequencies and shapes of structural modes for the boundary conditions, as well as the transient dynamic response of the composite cylindrical lattice shell to lateral impulsive loading applied extensively and uniformly on a specific rectangular surface. The convolution and a method for summing the effects of the modes are also obtained, and the obtained results are validated using references and ABAQUS finite element software. The effects of various parameters on free and forced vibrations are investigated, including geometric ratios, material properties, cross-sectional dimensions and distances, and lattice configuration. Finally, the effect of strengthening the cylindrical shell with lattice structures is investigated.
Aerospace Science and Technology
Jafar Jafari; Hamid Parhizkar; Sajad Ghasemlooy
Abstract
This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve ...
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This research investigates the effect of optimization of blade cross-section on the performance of the Darrieus wind turbine. The fluid flow around a Darrieus wind turbine is simulated by URANS (Unsteady Reynolds Averaged Navier Stokes) method. And blade cross-section was modeled by the Bezier curve and optimized to increase the average torque of the wind turbine. We used a novel, simple way for remeshing new design points in the optimization process. The Nelder-Mead simplex method was used for optimization, which enhanced the Turbine's performance by 33.7 percent. Results show that optimization of the blade cross-section is effective for increasing the performance of a VAWT (Vertical Axis Wind Turbine), and Nelder-Mead simplex is a proper and fast optimization method to be used in this case. Finally, the optimized airfoil was analyzed and compared with the initial one to understand optimization effects. It was concluded that optimization was more effective in azimuth positions of 90 to 160 degrees. And it decreased the performance in some regions according to changing nature of flow around each blade because of rotational motion. Analyzes show that optimization increased the Turbine's performance by increasing lift force of airfoil in some positions or affecting interaction flow -even accompanied by decreasing lift force of airfoil- in other positions, and it decreased performance in some other azimuth points.
Aerospace Science and Technology
Sayed Hossein Moravej Barzani; Mahdi Mortazavi; Hossein Shahverdi
Abstract
In this paper, the effects caused by the combination of folding angles simultaneously with changing the stiffness ratio of different parts of a folding wing are investigated. The geometrically exact fully intrinsic equations are employed to simulated the wing nonlinear dynamic behavior. The important ...
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In this paper, the effects caused by the combination of folding angles simultaneously with changing the stiffness ratio of different parts of a folding wing are investigated. The geometrically exact fully intrinsic equations are employed to simulated the wing nonlinear dynamic behavior. The important advantages of these geometrically exact equations can be seen as complete modeling without simplifying assumptions in large deformations, low-order nonlinearities, and thus less complexity. In this research, folding angles have been used in the geometrically exact fully intrinsic beam equations and the combination of different folding angles is studied. The applied aerodynamic loads in an incompressible flow regime are determined employing Peter’s unsteady aerodynamic model. In order to check the stability of the system, first the resulting non-linear partial differential equations are discretized, and then linearized about the nonlinear steady-state condition. By obtaining the eigenvalues of the linearized system, the stability of the wing is evaluated. Furthermore, investigation of the effects of the stiffness on the flutter speed and frequency of the folding wing for various folding angles, is another achievement of this study. It is observed that the combination of folding angles can significantly delay the flutter speed and improve the performance of the bird.
A. A. Ganjaei; S. Salman Dr. Noor Azar
Volume 5, Issue 2 , June 2008, , Pages 67-79
Abstract
A new approach to calculate the axially symmetric binary gas flow is proposed Dalton’s law for partial pressures contributed by each species of a binary gas mixture (argon and helium) is incorporated into numerical simulation of rarefied axially symmetric flow inside a rotating cylinder using the time ...
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A new approach to calculate the axially symmetric binary gas flow is proposed Dalton’s law for partial pressures contributed by each species of a binary gas mixture (argon and helium) is incorporated into numerical simulation of rarefied axially symmetric flow inside a rotating cylinder using the time relaxed Monte-Carlo (TRMC) scheme and the direct simulation Monte-Carlo (DSMC) method. The results of flow simulations are compared with the analytical solution and results obtained by Bird, 1994. The results of the flow simulations show better agreements than the results obtained by Bird, 1994 in comparison with the analytical solutions. However, the results of the flow simulations using the TRMC scheme show better agreement than those obtained using the DSMC method in comparison with the analytical solutions.
M.A. Sharbafi; A. Mohammadinejad Mohammadinejad; Jafar Dr. Roshanian; Seddigh Khaki
Volume 6, Issue 2 , June 2009, , Pages 71-78
Abstract
Gain scheduling is one of the most popular nonlinear control design approaches which has been widely and successfully applied in fields ranging from aerospace to process control. Despite the wide application of gain scheduling controllers, there is a notable lack of analysis on the stability of these ...
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Gain scheduling is one of the most popular nonlinear control design approaches which has been widely and successfully applied in fields ranging from aerospace to process control. Despite the wide application of gain scheduling controllers, there is a notable lack of analysis on the stability of these controllers. The most common application of these kinds of controllers is in the field of flight control and autopilots. The main goal of this paper is to apply a methodology to prove stability of a gain scheduled controller used in directing Skid-to-Turn missiles. One of the most widespread applications of gain scheduling controller is the main problem of this paper. To design the controller we use pole placement in state feedback controllers and a kind of innovative interpolation to reduce jumping in gains related to changing the flight conditions. Finally we utilize root locus and Kharitonov’s Theorem to prove stability of the linearized plant. The presented approach for stability analysis is distinctive in the literature.
Vahid Esfahanian; S. Ghader
Volume 3, Issue 2 , June 2006, , Pages 77-85
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.
mohammad Hassan Djavareshkian; A. Esmaeli; A. Parsania
Volume 7, Issue 2 , September 2010, , Pages 93-106
Abstract
The prediction of aerodynamic characteristics and smart flap of airfoil under the ground effect are carried out by the integration of computational fluid dynamics. Considering different types of beams, a parametric bending profile of a smart flap is designed. Cantilever beam with uniformly varying load ...
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The prediction of aerodynamic characteristics and smart flap of airfoil under the ground effect are carried out by the integration of computational fluid dynamics. Considering different types of beams, a parametric bending profile of a smart flap is designed. Cantilever beam with uniformly varying load with roller support at the free end is considered in here. A pressure-based implicit procedure is utilized to solve Navier-Stokes equations and a nonorthogonal mesh with collocated finite volume formulation is used for simulation. The boundedness criteria for this procedure is determined by Normalized Variable diagram (NVD) scheme. The procedure incorporates the eddy-viscosity turbulence model. The SIMPLE algorithm is applied for turbulent aerodynamic flows around the airfoil with smart and conventional flaps. The results of two flaps are compared for different flap length, flap angle and ground clearance. It is found that: 1- The pressure coefficient distribution in smart flap is smoother than conventional flap. 2- Lift-drag ratio in smart flap is higher than conventional flap. 3- The maximum lift-drag ratio is at flap angle 7.5?. 4- The minimum ground clearance has the highest lift-drag ratio. 5- The increasing of flap length leads to the increasing lift-drag ratio.
Mohammad Zaman Kabir; Arash Rojhani
Volume 5, Issue 3 , July 2008, , Pages 115-121
Abstract
Optimum laminate configuration for minimum weight of filament–wound laminated conical shells subject to buckling load constraint is investigated. In the case of a laminated conical shell the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing ...
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Optimum laminate configuration for minimum weight of filament–wound laminated conical shells subject to buckling load constraint is investigated. In the case of a laminated conical shell the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing both the buckling load and its weight. These effects complicate the optimization problem considerably. The first level of complexity is attributed to the correlation between the volume and the buckling load and their dependence on the fiber configuration. The second level of complexity is associated with the high computational cost involved in calculation of the buckling load. Thus, the main objective of this study is to solve the optimization problem as well as to reduce the computational cost associated with it. Based on the characteristic buckling behavior of laminated conical shells the usual penalty function method is used.
Aliakbar Dr. Moosavian
Volume 3, Issue 3 , September 2006, , Pages 135-142
Abstract
In this paper, a minimum and near-minimum time optimal control laws are developed and compared for a rigid space platform with flexible links during an orientating maneuver with large angle of rotation. The control commands are considered as typical bang-bang with multiple symmetrical switches, the time ...
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In this paper, a minimum and near-minimum time optimal control laws are developed and compared for a rigid space platform with flexible links during an orientating maneuver with large angle of rotation. The control commands are considered as typical bang-bang with multiple symmetrical switches, the time optimal control solution for the rigid-body mode is obtained as a bang-bang function and applied to the flexible system after smoothening the control inputs to avoid stimulation of the flexible modes. This will also reflect practical limitations in exerting bang-bang actuator forces/torques, due to delays and non-zero time constants of existing actuation elements. The smoothness of the input command is obtained by reshaping its profile based on consideration of additional derivative constraints. the optimal control problem is converted into parameter optimization problem. The steps of the solution procedure and numerical algorithm to obtain the time optimal control input are discussed next. The developed control law is applied on a given satellite during a slewing maneuver, and the simulation results show that the control input with just few switching times can significantly lessen the vibrating motion of the flexible appendage, which reveals the merits of the developed control law. the modified realistic optimal input compared to the bang-bang solution goes well with the practical limitations and also alleviates the vibrating motion of the flexible appendage, which reveals the merits of the new developed control law.
Saeid Irani; M. Lashgari
Volume 5, Issue 4 , December 2008, , Pages 167-174
Abstract
In this work the equations of motion of a Solid State Wave Gyroscope (SWG) with rotary thin cylindrical shell resonator is analyzed using the shell and plates elasticity theory. The gyroscope conversion factor found in this analytical study corresponds with the experimental results obtained and listed ...
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In this work the equations of motion of a Solid State Wave Gyroscope (SWG) with rotary thin cylindrical shell resonator is analyzed using the shell and plates elasticity theory. The gyroscope conversion factor found in this analytical study corresponds with the experimental results obtained and listed in the References. The function of the SWG to measure the angular velocity or the rotating angle depends on the type of resonator’s excitation. This paper analyzes two types of excitations, a positional and a parametric excitation. The former has a rate gyroscope whereas the latter has a rate integrating gyroscope. The equations of motion are solved using Bobnov-Galerkin method, where the forces produced from excitation electrodes are assumed to be the external non-conservative forces. Finally, the relationship between the input and output of the gyroscope are derived to demonstrate that the type of the excitation, determines the type of gyroscope.
Naghdali Choupani
Volume 3, Issue 4 , December 2006, , Pages 185-193
Abstract
Failures in composite materials occur mainly due to interlaminar fracture, also called delamination, between laminates. This indicates that characterizing interlaminar fracture toughness is the most effective factor in the fracture of composite materials. This study reports investigation on mixed-mode ...
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Failures in composite materials occur mainly due to interlaminar fracture, also called delamination, between laminates. This indicates that characterizing interlaminar fracture toughness is the most effective factor in the fracture of composite materials. This study reports investigation on mixed-mode interlaminar fracture behaviour in woven carbon fibre/polyetherimide (CF/PEI) thermoplastic composite material based on experimental and numerical analyses. Experiments were conducted using the special test loading device. By varying the loading angle,? from 0? to 90?, pure mode-I, pure mode-II and a wide range of mixed-mode data were obtained experimentally. Using the finite-element results, geometrical factors were applied to the specimen. Based on experimentally measured critical loads, mixed-mode interlaminar fracture toughness for the composite under consideration determined. The fracture surfaces were examined by scanning electron microscopy to gain insight into the failure responses.
Labid Hassan; M.B. Malaek
Volume 9, Issue 1 , March 2012
Abstract
Based on the idea of Continuous Fuzzy Guidance Law (CFGL), a andldquo;three-phase fuzzy guidanceandrdquo; (TFG) law is proposed for the class of surface to air homing missiles. The current approach enables the guidance law to track a maneuvering target from the beginning of the launch phase up to the ...
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Based on the idea of Continuous Fuzzy Guidance Law (CFGL), a andldquo;three-phase fuzzy guidanceandrdquo; (TFG) law is proposed for the class of surface to air homing missiles. The current approach enables the guidance law to track a maneuvering target from the beginning of the launch phase up to the terminal one while itdynamically attempts to keep miss-distance, flight time and control effort at a minimum acceptable level. The guidance law developed heredepends on four factors:line-of-sight (LOS) angle, LOS rate, LOS angular acceleration, and relative distance to the target. To show the relative superiority of the approach, the performance of the new guidance law has been compared with that of proportional navigation guidance. The results confirm the validity of the idea; as for a TFG,we get quite comparable results. The current approach also shows a relatively good robustness for a wide variety of flight conditions.
S.H. Jalali Naini
Volume 9, Issue 2 , September 2012
Abstract
In this paper, an approximate solution of sensitivity matrix of required velocity with final velocity constraint is derived using a piecewise linear gravity assumption. The total flight time is also fixed for the problem. Simulation results show the accuracy of the method. Increasing the midway points ...
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In this paper, an approximate solution of sensitivity matrix of required velocity with final velocity constraint is derived using a piecewise linear gravity assumption. The total flight time is also fixed for the problem. Simulation results show the accuracy of the method. Increasing the midway points for linearization, increases the accuracy of the solution, which this, in turn, depends on the total flight time.
امیرعلی نیکخواه
Volume 10, Issue 1 , March 2013
Abstract
In this paper, with the aim of estimating internal dynamics matrix of a gimbaled Inertial Navigation system (as a discrete Linear system), the discretetime Hamilton-Jacobi-Bellman (HJB) equation for optimal control has been extracted. Heuristic Dynamic Programming algorithm (HDP) for solving equation ...
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In this paper, with the aim of estimating internal dynamics matrix of a gimbaled Inertial Navigation system (as a discrete Linear system), the discretetime Hamilton-Jacobi-Bellman (HJB) equation for optimal control has been extracted. Heuristic Dynamic Programming algorithm (HDP) for solving equation has been presented and then a neural network approximation for cost function and control input has been extracted to simplify the sloution of HJB. Design process of the optimal controller shows that we do not need to know the system matrix. This important isuue and convergence of the HDP algorithm to the optimal control policy makes possible the estimation of the internal dynamics matrix.
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
A. R. Jahangirian; M. Ebrahimi
Volume 11, Issue 1 , June 2017
Abstract
An efficient method for scattering Genetic Algorithm (GA) individuals in the design space is proposed to accelerate airfoil shape optimization. The method used here is based on the variation of the mutation rate for each gene of the chromosomes by taking feedback from the current population. An adaptive ...
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An efficient method for scattering Genetic Algorithm (GA) individuals in the design space is proposed to accelerate airfoil shape optimization. The method used here is based on the variation of the mutation rate for each gene of the chromosomes by taking feedback from the current population. An adaptive method for airfoil shape parameterization is also applied and its impact on the optimum design and convergence of the optimization process isinvestigated. In order to demonstrate the efficiency of the proposed method, a geometric inverse design using Genetic Algorithm is carried out and the capability of the method for producing airfoil shapes is assessed. The performance of the method is further evaluated by an aerodynamic shape optimization. Results indicate the merits of the method in increasing the maximum objective value about7percent as well as decreasing the total computational time up to28 percent.
Aerospace Science and Technology
Mohammad Reza Hashemi; Seyyed Majid Malek Jafarian; Mojtaba Dehghan Manshadi
Abstract
In this research, the effects of canard flow on a diamond wing equipped with LEX, same as new-generation fighters, have been investigated, using a closed-circuit wind tunnel. All tests were performed at a speed of 12.5 meters per second, which is equivalent to Reynolds number 214000 based on model length. ...
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In this research, the effects of canard flow on a diamond wing equipped with LEX, same as new-generation fighters, have been investigated, using a closed-circuit wind tunnel. All tests were performed at a speed of 12.5 meters per second, which is equivalent to Reynolds number 214000 based on model length. The pressure measurement is conducted by the five-hole probe, which is normalized by the dynamic pressure of the free stream velocity in four cross-sections over the wing. The results showed that at a low angle of attack, a strong vortex is produced at the leading-edge of the wing, called the leading-edge vortex. As the leading-edge vortex moves downstream, the diameter of its core and distance from the wing surface increases. At higher angles of attack, LEX, canard and body vortices are also present, which combine with the leading-edge vortex and cover a large cross-flow area over the wing. At these angles of attack, the movement of the vortical flow downstream leads to an increase in the pressure coefficient of the vortex core, which indicates the beginning of instability and vortex breakdown. The results showed that the pressure increase in the vortex core was not sudden and this results in that the breakdown phenomenon in the diamond wing equipped with LEX and canard occurs slowly.
Jafar Eskanadari Jam; Neda Garshasbi Nia
Volume 2, Issue 1 , March 2005, , Pages 21-27
Kamran Daneshjou; Aria Alasty; Shahram Rezaei
Volume 1, Issue 1 , October 2004, , Pages 23-29
Abstract
A satellite, in its orbit, is affected by perturbing forces, such as atmospheric drag, solar radiation pressure, Earth oblateness, and gravity of the celestial masses (other than the Earth). In this paper, the effects of these forces on the trajectories of different types of LEO satellites and a sample ...
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A satellite, in its orbit, is affected by perturbing forces, such as atmospheric drag, solar radiation pressure, Earth oblateness, and gravity of the celestial masses (other than the Earth). In this paper, the effects of these forces on the trajectories of different types of LEO satellites and a sample satellite (Z-SAT) are discussed. A few analyses are done on these orbits and the relevant results are categorized as substantial logics of perturbation influences on Keplerian parameters of the orbits. The Variation of Parameters Method is used for analyses.
