S. Mohamadnejad
Volume 9, Issue 1 , March 2012
Abstract
To solve crack problems, some coupled methods have been developed in recent years. Most of these methods have some shortcomings such as the need for a transition region. The finite element and enriched element free Galerkin methods are widely used for this class of problems. In order to take the advantages ...
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To solve crack problems, some coupled methods have been developed in recent years. Most of these methods have some shortcomings such as the need for a transition region. The finite element and enriched element free Galerkin methods are widely used for this class of problems. In order to take the advantages of these methods while avoiding the disadvantages, it is essential to follow solution approaches based on a combination of them. Prompted by this idea, in this article, the authors mainly aim at finding a simple way to solve the problem of a cracked plate by using a novel coupled finite element-element free Galerkin (FE-EFG) method. In this procedure, the usage of transition region is bypassed by employing the concept of andldquo;virtual particlesandrdquo;. The enriched element free Galerkin method is applied to approximate regions near a crack tip and the finite element method is put to use in the areas far from the crack tip. Static analysis of two-dimensional crack problems, according to the plane stress condition under mode-I loading, has been done. The results from the present method are indicated to be in excellent agreement with those from the existing analytical solutions.
M. saraf; M.R. Mosavi; K. Mohammadi
Volume 9, Issue 2 , September 2012
Abstract
In this study, two novel learning algorithms have been applied on Radial Basis Function Neural Network (RBFNN) to approximate the functions with high non-linear order. The Probabilistic Evolutionary (PE) and Gaussian Mixture Model (GMM) techniques are proposed to significantly minimize the error functions. ...
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In this study, two novel learning algorithms have been applied on Radial Basis Function Neural Network (RBFNN) to approximate the functions with high non-linear order. The Probabilistic Evolutionary (PE) and Gaussian Mixture Model (GMM) techniques are proposed to significantly minimize the error functions. The main idea is concerning the various strategies to optimize the procedure of Gradient Descent (GD) in terms of the input feature vectors. The probability density of all feature vectors can help to optimize the learning rates of RBFNN by applying GMM. Another possibility is to utilize the Evolutionary Algorithms (EAs) to find the optimum solution. However, EAs often behave randomly which canandrsquo;t be mathematically controlled. So, a combined RBFNN based on novel PE algorithm has been proposed which has a soft behavior through the learning of non-linear function. The PE algorithm defines the occurrence probability of local minima in the space of extracted features as a Gaussian distribution correspondence to each chromosome. Then, it estimates the entire probabilities of local minima in an iterative procedure. These techniques have been utilized in the application of robust satellites subset selection. Geometric Dilution of Precision (GDOP) is the main factor to estimate the strength of goodness of each satellites subset. Then, the subset with the lowest value has been selected for improving the positioning performance, but it is so non-linear and has computational burden to navigation systems. These techniques have been implemented and the results on measured GPS data demonstrate that it significantly track the non-linearity of GPS GDOP comparison with the other conventional approaches.
Aerospace Science and Technology
Majid Bakhtiari; Amirhossein Panahyazdan; Siavash Sabzy
Abstract
The Earth Orientation parameters (EOPs), such as polar motion, universal time, and length of day, play a prominent role in procedures such as monitoring the Earth's rotation, weather modeling, and disaster prevention. This paper estimates the EOPs series based on a combined series approach proposed ...
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The Earth Orientation parameters (EOPs), such as polar motion, universal time, and length of day, play a prominent role in procedures such as monitoring the Earth's rotation, weather modeling, and disaster prevention. This paper estimates the EOPs series based on a combined series approach proposed by the International Earth Rotation and Reference System Observatory between 1962 and 2023, incorporating data from diverse space geodetic techniques, including DORIS, laser ranging (LLR and SLR), GNSS, and VLBI to create EOPs series. This paper proposes a hybrid deep-learning prediction model, combining a Convolutional Neural Network (CNN) and Gated Recurrent Unit (GRU) with an attention mechanism. The CNN effectively extracts and enhances features, while the GRU facilitates medium- to long-term predictions based on historical time series data. The attention mechanism prioritizes relevant data aspects, enhancing the Model's ability to discern intricate patterns, particularly for Length of Day (LOD) variations, where some covariants affect its pattern and should be considered. One of the most practical applications of these parameters is mapping the points in the terrestrial and celestial reference systems to each other. These predicted EOPs are used to create a high-accuracy coordinate transformation matrix from ECEF to ECI for applications such as high-precision navigation.
Amireh Norbaskhsh
Abstract
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 ...
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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.
Aerospace Science and Technology
Gholamreza Rashed
Abstract
In this paper, using the Abaqus finite element software, the torsional hysteresis of X52, X60, X65 steels under loadings with different torsion values, has been numerically investigated and they are compared to each other. The shear stress, effective stress, residual stress and elastic and plastic ...
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In this paper, using the Abaqus finite element software, the torsional hysteresis of X52, X60, X65 steels under loadings with different torsion values, has been numerically investigated and they are compared to each other. The shear stress, effective stress, residual stress and elastic and plastic shear strain distribution are presented in the numerical results. In this analysis, the “chaboche” kinematic hardening theory has been used to predict the behavior of the material in the plastic region. By comparing the difference percentage graphs of the steels under the same load, it has been concluded that the hysteresis loops in X65 steel will become stable sooner than X60 and in X60 steel they become stable sooner than X52.
Aerospace Science and Technology
Mohammad Reza Salimi; Mohsen Rostami; Amir Hamzeh Farajolahi; Morteza Ghanbari
Abstract
In this paper, flow and heat transfer inside a helicopter shell and tube heat exchanger is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are ...
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In this paper, flow and heat transfer inside a helicopter shell and tube heat exchanger is simulated in three dimensions. This converter consists of a shell with 90 U-shaped tubes inside. For further heat transfer, the tubes were simulated and compared once without fins and again with fins, which are produced longitudinally and integrally with the tube body. The current flowing in the shell is MIL-PRF 23699 oil and the flowing fluid in the tubes is JP-4 fuel. These two fluids flow in opposite directions and exchange heat with each other. Using Aspen software, the design is done in such a way that the heat exchanger has minimum length and weight to have a better and higher effect on the efficiency of the helicopter. To investigate the effect of tube geometry and oil mass flow on the heat transfer between fuel and oil, simulation has been performed in ANSYS Fluent program. In this simulation, a part of the whole heat exchanger is selected as the geometry and the effect of changing the geometry of the tubes, mass flow of fuel and oil on the heat transfer coefficient, Colburn coefficient, coefficient of friction and their ratio, and outlet temperature changes are investigated. The results of this simulation show that the heat transfer rate between fuel and oil for a heat exchanger with finned tubes is about 11% higher than without a fin. Also, reducing the mass flow of oil entering the shell increases the efficiency of the heat exchanger.
Aerospace Science and Technology
Amir reza Kosari; Elahe Khatoonabadi; Vahid Bohlouri
Abstract
In this paper, the control of a three-axis rigid satellite attitude control system with a fractional order proportional-integral-derivative (PID) controller is investigated in the presence of disturbance and parametric uncertainties. The reaction wheel actuator with the first-order dynamic model is used ...
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In this paper, the control of a three-axis rigid satellite attitude control system with a fractional order proportional-integral-derivative (PID) controller is investigated in the presence of disturbance and parametric uncertainties. The reaction wheel actuator with the first-order dynamic model is used to control the attitude of the satellite. Uncertainties are considered on satellite moment inertia, actuator model and amplitude and frequency of external disturbances. External disturbances are modeled with two fixed and periodic parts and uncertainty is also considered on the disturbances model. The integer order controller is also used for the same conditions to compare the results with the fractional order controller. The usual Granwald-Letinkov definition is used to solve integrals and fractional order derivatives. The mean absolute of the pointing error of the satellite pointing maneuver has been selected as an objective function of the optimization problem. The controller gains in integer and fractional order are obtained by particle swarm evolution algorithm (PSO) optimization method. The performance criterion has been studied in terms of the controller time response and also in terms of the standard deviation of the mentioned uncertainties and external disturbance. The results show that the fractional order controller performs more accurate and robustness than the integer order controllers in the face of uncertainty and disturbance.
Aerospace Science and Technology
Mahshid Soleymani; Maryam Kiani
Abstract
Solar sails use sunlight to propel a vehicle through space by reflecting solar photons off a mirror-like surface made of light reflective material. To be able to work as an interplanetary cargo-ship, the solar sail area should be large enough to receive required acceleration from the sunlight. However, ...
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Solar sails use sunlight to propel a vehicle through space by reflecting solar photons off a mirror-like surface made of light reflective material. To be able to work as an interplanetary cargo-ship, the solar sail area should be large enough to receive required acceleration from the sunlight. However, mechanical deploying mechanisms are not reliable to deploy such a large solar sail. This paper presents formation control of space robots for on-orbit assembly of large solar sails. Contrary to previous works, the dynamic equations of space robots in the formation are derived by considering relative motion of the space robots with respect to the sail hub orbiting the Earth. The uncertainties including external disturbances, unmolded dynamics, and parameter uncertainties, are considered as a single time-varying term in the dynamic model. Then, an adaptive sliding mode controller combined with a second-order observer is expanded to control the on-orbit formation of space robots as well as resisting the disturbances. Finally, the efficacy of the proposed approach is demonstrated by a numerical simulation.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, ...
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Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, impeller and the turbomachine itself. Surge emerges when a pump is operating with a positive slope of head and flow curve. The coincidence of the surge phenomenon with cavitation results in a damaging phenomenon called "auto-oscillation." Thus, predicting a pump's behavior outside the design points is of great importance particularly in low flow rates. In this paper, the characteristic curve of a high-speed centrifugal pump is extracted using CFD analysis to determine the stable operating range of the pump. The studied pump consists of an inducer, impeller and volute. The simulation in the pump was carried out three-dimensionally due to the asymmetry of geometry. The simulations are performed over a wide range of flow rates and the characteristic curve of the pump (head coefficient in terms of mass flow rate coefficient) is extracted. Finally, the range of stable operation of the pump is determined using its characteristic curve.
Aerospace Science and Technology
Ali Cheraqi; Reza Ebrahimi
Abstract
This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation ...
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This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation number was calculated based on the cavitation breakdown characteristic curve. Two-phase flow inside the pump was simulated using the homogenous mixture method and the Rayleigh-Plesset model. The SST turbulence model and MRF rotating model were used to simulate turbulence and rotation of the flow throgh the pump, respecively. The critical cavitation number that was the outcome of numerical analysis results was compared to the experimental data. This comparison implied the necessity of considering the safety factor for determining the critical cavitation number and inlet pressure required to uninterrupted operation of the pump cavitation, using the results of numerical analysis.
Aerospace Science and Technology
Majid Sedghi; Rouhollah Khoshkhoo
Abstract
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 ...
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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.
Aerospace Science and Technology
Seyed mohammad navid Ghoreishi; Bahar Salimi
Abstract
In this study, a comprehensive investigation of the fracture parameters in a grooved rotating disc containing a three-dimensional semi-elliptical crack under different working conditions has been investigated. In this regard, three models of radial, circumferential and inclined crack with an angle of ...
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In this study, a comprehensive investigation of the fracture parameters in a grooved rotating disc containing a three-dimensional semi-elliptical crack under different working conditions has been investigated. In this regard, three models of radial, circumferential and inclined crack with an angle of 45 degree have been considered in the rotating disk, and the fracture parameters under mixed mode loading (I, II, III) have been extracted. The effects of various parameters such as rotational speed, crack location, aspect ratio, material and presence of grooves on SIFs and crack opening displacement have been studied simultaneously. The finite element results indicated that in the crack with a low aspect ratio (0.4 and 0.6) where the shape of the crack is more like a semi-elliptical, the maximum value of the mode I SIF occurs at the central point of the crack front, while the crack with a high aspect ratio (0.8 and 1) where the shape of the crack is more like a semi-circular, the maximum value of the mode I SIF occurs at the free surface of the crack. The mode II SIF for the rotating disk containing an inclined crack before the central point of the crack front, has the highest value for steel, titanium and aluminium rotating disk, respectively. Also, the numerical results indicated that the highest value of the SIF is related to the grooved rotating disk containing a circumferential crack, and the lowest value of the SIF is for the grooved rotating disk containing a radial crack
Aerospace Science and Technology
Gholamhosein Pouryoussefi; Sara Javanmard; MohamadAli Heidari
Abstract
In this study, the performance of a cold atmospheric pressure plasma jet using neutral helium gas was experimentally investigated. Cold atmospheric pressure helium plasma jets have gained popularity in various processing applications due to their stability and enhanced reaction chemistry. The researchers ...
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In this study, the performance of a cold atmospheric pressure plasma jet using neutral helium gas was experimentally investigated. Cold atmospheric pressure helium plasma jets have gained popularity in various processing applications due to their stability and enhanced reaction chemistry. The researchers examined the effect of applied voltage, flow rate, and electrode configurations on the length of the helium plume and analyzed the physical parameters of the plasma plume, including discharge voltage and average gas and discharge gap temperatures. The study revealed the presence of three operational modes: plasma bullets, a chaotic mode, and a continuous mode. Initially, the plasma jet operated in a deterministic chaotic mode after breakdown. Transitioning to the turbulent mode, increasing the gas flow rate resulted in a decrease in the plasma jet length. The flow rate required for laminar-to-turbulent transition increased with the applied voltage. By increasing the electrode separation and flow rate, the continuous mode was observed, where excited species remained within the inter-electrode space throughout the voltage cycle. Additionally, it was observed that the temperature of the discharge gap was close to room temperature. These findings provide valuable insights into plasma jet formation mechanisms and highlight the potential of tailoring plasma jet modes for specific processing applications.
Aerospace Science and Technology
alireza moradi; fathollah ommi; Zoheir Saboohi
Abstract
In the course of all-round advancement of engineering science, space research can be considered as the drivers of this forward movement. In the field of space propulsion, this trend can be seen as a backward trend, not in the sense of regression, but in the sense of optimizing the original designs used ...
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In the course of all-round advancement of engineering science, space research can be considered as the drivers of this forward movement. In the field of space propulsion, this trend can be seen as a backward trend, not in the sense of regression, but in the sense of optimizing the original designs used for space systems, which not only lead to the re-invention of these systems based on the acquisition of specific modern manufacturing technologies, but also strengthened the link between sciences such as Materials science and Mechanics science. In this research, according to the space propulsion system roadmap and also the review of old and reference designs, an attempt has been made to study some of the optimizations made in recent years and to express the weaknesses and challenges ahead. One of the ideas that optimizes, minimizes and increases the reliability of the space propulsion system is the injection of fuel through the porous media. The study of a type of showerhead injector expresses the formation path of the idea of using porous materials in the injection system and then the efficiency of these two types of injections is compared in a design that connects the porous material with the coaxial injector design.
Aerospace Science and Technology
M. Khoshnood; H. Ashoori
Abstract
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 ...
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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.
Aerospace Science and Technology
Farid Shahmiri; Fatemeh Kiani
Abstract
The optimum rotor blade planform of helicopters required to minimize power, maximize rotor thrust, and maximize lift-to-drag ratio in forward flight, using a numerical optimization approach, is investigated. Here, the traditional approach is modified by Central Composite Design Data (CCD) and a flight ...
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The optimum rotor blade planform of helicopters required to minimize power, maximize rotor thrust, and maximize lift-to-drag ratio in forward flight, using a numerical optimization approach, is investigated. Here, the traditional approach is modified by Central Composite Design Data (CCD) and a flight dynamic simulation program coupled with a desirability optimization technique implemented in the process of blade optimization. The optimum blade planform parameters (i.e, root chord, taper ratio, taper offset, two-per revolution (2/rev) harmonic control, and 2/rev blade dynamic twist) for different gross weights and flight speeds are therefore obtained by this modified procedure. In addition, the main effects and the interaction of all parameters on helicopter performance are assessed. The results of optimization in case 1 confirm that the appropriate 2/rev harmonic control and twist of the partially tapered blades improve the helicopter power required by 2.6% and lift-to-drag ratio up to about 20% at a baseline gross weight. In case 2 of optimization, tapering the blade to 60% from 0.9R with an appropriately phased 1/rev and 2/ rev twist and 2/rev harmonic control increases the rotor thrust coefficient by 23%, and the lift-to-drag-ratio by about 15%. The helicopter gross weight is declared influence on the thrust increment achieved by the 2/rev twist and 2/rev harmonic control. Overall, 2/rev harmonic control can be incorporated into existing helicopters by a modification of the swashplate and control inputs can be transmitted to the rotor using a fixed outer member with a track linked to a conventional swashplate.
Aerospace Science and Technology
Hamed Arhami; Mohammad Mazidi Sharfabadi
Abstract
In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. ...
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In this research, combustion modeling inside the combustion chamber of a typical turboprop engine has been investigated. The complex geometry of this combustion liner was modeled according to the technical drawings and the turbulent flow and internal combustion were simulated numerically and three-dimensionally. The non-premixed combustion model is used to simulate combustion and the K-ω method is used to simulate turbulent flow. This study investigated how the combustion phenomenon occurs, the internal temperature distribution, the outlet, and the wall of the combustion tube, for which comprehensive three-dimensional data were not previously available. These simulations have identified the weaknesses of the combustion tube and by eliminating these weaknesses, the problem of reducing the efficiency of several gas turbine engines has been solved. Comparison of the results of the present study with a similar numerical analysis showed that the results of this study are more in line with laboratory results. The results of the simulation of combustion pipe defects show that the combustion liner that had a welding line near the outlet had a 25% higher pressure drop than a typical combustion liner and the effective cross-sectional area of the fluid flow was reduced by 11%. The output of a repaired combustion tube is different from a typical type.
Aerospace Science and Technology
Hossein Faveadi; Ali R. Davari; Farshad Pazooki; Majid Pouladian
Abstract
Flight simulation is a powerful and usefull instrument in design, testing, evaluation and validation of aircrafts; The results of aerolastic simulation along with rigid simulation can be used in the many areas of designs, such as modification or optimization, stability analysis and evaluating field test ...
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Flight simulation is a powerful and usefull instrument in design, testing, evaluation and validation of aircrafts; The results of aerolastic simulation along with rigid simulation can be used in the many areas of designs, such as modification or optimization, stability analysis and evaluating field test data; It can be said that the use of simulation in the fields of design and optimization, especially during the initial and detailed design, should be considered more than other fields; In this research, by use of simulation, the effect of some design parameters such as slenderless ratio, maneuvering acceleration, propulsion curve, natural frequency of the structure, aerodynamic load distribution , etc. On issues such as flight and tracking behavior, stability and collision accuracy, has been examined; In cases such as: evaluating the initial error or veviation of the thurst vector or its curve, rolling speed, tracking of control commands, etc. aerolastic simulation gives a more realistic output compared to rigid simulation; Further more in cases such as investigating the effect of aerodynamic load distribution or stiffness ans and mass distribution, only aerolastic simulation is able to respond. Accordingly, the main orientation of this research is to develop an approach with acceptable accuracy and speed in order to simulate elastic projectiles in order to achieve some of the mentioned goals; However, due to the wide range of effective parameters and their interaction, in this study, only the role of thrust and body rigidity has been examined.
Aerospace Science and Technology
Fatemeh Amozegary; Amir reza Kosari; Mahdi Fakoor
Abstract
The ever increasing demand for placing satellites in the geostationary orbit has caused the revision and change of the conventional mechanism of allocating orbital slots. Therefore, collocation approaches and station keeping of several satellites with a common position have been developed to improve ...
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The ever increasing demand for placing satellites in the geostationary orbit has caused the revision and change of the conventional mechanism of allocating orbital slots. Therefore, collocation approaches and station keeping of several satellites with a common position have been developed to improve the utilization of the capacity of the geostationary orbit. This, in turn, leads to an increase in the complexity and sensitivity of the modeling, guidance, and control processes. However, new restrictions are added to the problem of maintaining a common location, such as maintaining the minimum separation distance between satellites to prevent possible interference. Employing a collocation strategy is essential, especially for effective control of high-demand orbital regions that will lead to space congestion.Controlling the relative motion of satellites by maintaining a safe distance between them is the main rule in collocation. This article investigates the problem of the relative motion of satellites corresponding to collocation strategies. Then, the results are implemented and compared using a solution based on geometrical modeling of relative orbit and the concepts of spherical geometry. In this regard, the relative orbital elements of the two satellites are calculated using the presented relative motion modeling. Also, the relative position of the satellites is obtained. The case studies and evaluations confirmed that the inclination and eccentricity separation strategies are suitable options for meeting the fuel consumption requirements and providing more space for collocated satellites than other strategies.
Aerospace Science and Technology
Bahareh Mojarrad; Saeed Oveisi; Mostafa Kazemi; Mahmoud Mani
Abstract
The primary objective of this study was to demonstrate how plasma actuators could be used to discharge a perpendicular dielectric barrier as a virtual Gurney flap. This study utilized wind tunnel experiments on a flat plate airfoil. Each experiment is conducted at two different free flow velocities of ...
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The primary objective of this study was to demonstrate how plasma actuators could be used to discharge a perpendicular dielectric barrier as a virtual Gurney flap. This study utilized wind tunnel experiments on a flat plate airfoil. Each experiment is conducted at two different free flow velocities of ten and twenty meters per second. To study and extract the aerodynamic phenomena generated by plasma actuators and to compare them to the Gurney phenomena of a physical flap, velocity profiles in the model sequence were measured using a hot wire flow meter in two different longitudinal positions relative to the model. All experiments were conducted from five distinct vantage points, 0, 2, 4, 6, and 8, and plasma actuators were activated in two distinct settings to extract concepts under a variety of conditions. Wind tunnel experiments indicate that downward sequence transfer occurs when plasma actuators are used. Additionally, there are two distinct types of vortex shedding on the model's back: one that resembles Karman vortex shedding and another that occurs below the model. The observation of velocity profiles demonstrates that the deformation of the sequence caused by the use of plasma actuators is very similar to that caused by an airfoil sequence equipped with a physical Gurney flap.
Aerospace Science and Technology
Amirali Nikkhah; Hoseyn Mojarrab; Fatemeh Mojarrab; Reza Zardashti
Abstract
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. The system independent of 3 dimensional maps, works by using a forward looking ...
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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. The system independent of 3 dimensional maps, works by using a forward looking camera. In addition, the obstacle is analyzed by digital image processing techniques. An optimal flight control system based on discrete-time linear quadratic tracker is designed, to fly over or pass obstacles like mountains automatically.
Aerospace Science and Technology
Ali Mirzaee kahagh; Alireza Sekhavat Benis
Abstract
The current research was conducted with the aim of identifying the role of unmanned aerial vehicles in future smart cities. The current research was conducted in terms of mixed statistical methods (qualitative-quantitative). The participants of the qualitative part, which was implemented based on the ...
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The current research was conducted with the aim of identifying the role of unmanned aerial vehicles in future smart cities. The current research was conducted in terms of mixed statistical methods (qualitative-quantitative). The participants of the qualitative part, which was implemented based on the method of thematic analysis, were 14 knowledgeable experts, including specialized and experienced managers in the fields of urban security, transportation, road, and urban development, aviation organization and aviation industry, and The Information and Communication Technology Organization of Greater Tehran cities until reaching theoretical saturation and in the quantitative part, all the expert experts of the relevant devices were 134 people, and using Cochran's formula and targeted sampling method, the number of 99 people was were selected as sample members. The reliability coefficient of the qualitative part was recorded by the method of two coders with the final result (83%) and the reliability of the quantitative part was recorded with Cronbach's alpha coefficient with the final result (0.91). MAXQDA software was used for qualitative data analysis and SPSS software was used for quantitative data analysis. The findings showed that in the process of explaining the role of unmanned aerial vehicles in future smart cities; There are 5 comprehensive themes, 16 organizing themes, and 58 basic themes. The results showed that unmanned aerial vehicles can play a significant role in creating future smart cities through 1- intelligent air transportation, 2- agile monitoring and inspection, 3- smart agriculture, 4- smart urban and citizen services, and 5- smart law enforcement.
R.Ali Abbaspour; A.A. Heidari
Abstract
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 ...
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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.
Aerospace Science and Technology
Mahyar Naderi; Liang Guozhu; Hassan Karimi; Sara Pourdaraei
Abstract
In order to reduce cost and time along with enhancing the safety issues, numerical computer modelling and simulations are widely used for analyzing complex systems such as launch vehicle or spacecraft propulsion system. The objective of this research is to obtain an algorithm for simulation of ...
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In order to reduce cost and time along with enhancing the safety issues, numerical computer modelling and simulations are widely used for analyzing complex systems such as launch vehicle or spacecraft propulsion system. The objective of this research is to obtain an algorithm for simulation of staged combustion cycle liquid propellant engines. For this purpose the space shuttle main engine (SSME), as one of the world’s most complicated engines, is selected as a case study. A total of 34 elements is taken into account and using more than 100 linear/non-linear equations, the engine’s steady state system model has been established in MATLAB SIMULINK software. The simulation method uses eleven nested loops for iteration. The algorithm is based on the known parameters at the inlet of engine main feed lines namely mass flow rate and pressure, similar to the known conditions during hot test of engine on test stand. The simulation is capable of predicting the engine’s operation in wide range of thrust throttling levels from 69 percent to 109 percent of the nominal thrust. In order to validate the suggested method, SSME main component parameters, operating at 109 percent of rated thrust is presented. Simulation result mean error is less than 5 percent.
Aerospace Science and Technology
Mahdi Karami Khorramabadi; Ali Reza Nezamabadi
Abstract
In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and ...
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In this paper, the buckling behavior of functionally graded simply supported nanocomposite beams reinforced by nano clay is studied. The specimens were prepared and the experimental tensile and buckling tests are carried out. The elastic modulus of epoxy/clay nanocomposite for functionally graded and uniformly distributed of nanoclay are estimated through a model based on the genetic algorithm approach. The results show that GA can be considered as an acceptable optimization research technique to identify Young’s modulus of nanocomposites with maximum accuracy. For simply supported beam, the first order shear deformation beam theory is applied for displacement field and the governing equations are derived by using Hamilton principle. The influence of nanoparticles for functionally graded and uniform distribution on the buckling load of a beam is presented. Comparison study is conducted to assess efficacy and accuracy of the present analysis. A comparison for theoretical analysis with the experimental results demonstrated the high accuracy.
