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
Nemat Allah Ghahremani; Hassan Majed Alhassan
Abstract
This paper presents a new Modified Predictive Kalman Filter (MPKF). To solve the problem of a strap-down inertial navigation system (SINS) self-alignment process that the standard Kalman filters cannot give the optimal solution when the system model and stochastic information are unknown accurately. ...
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This paper presents a new Modified Predictive Kalman Filter (MPKF). To solve the problem of a strap-down inertial navigation system (SINS) self-alignment process that the standard Kalman filters cannot give the optimal solution when the system model and stochastic information are unknown accurately. The proposed algorithm is applied to SINS in the initial alignment process with a large misalignment heading angle. The filter is based on the idea of an accurate predictive filter applies n-steps ahead prediction of the SINS model errors to effectively enhance the corrections of the current information residual error on the system. Firstly, the formulations of a novel predictive filter and a fine alignment algorithm for SINS are presented. Secondly, the vehicle results demonstrate the superior performance of the proposed method, in which the MPKF algorithm is less sensitive to uncertainty. It performs faster and more accurate estimation of SINS' initial orientation angles compared with the conventional EKF method.
Aerospace Science and Technology
Amir reza Kosari; Alireza Akbar Attar; Peyman Nikpey
Abstract
In this study, the performance requirements influencing the orbital and attitude control system of a geostationary satellite in the station-keeping flight mode considering the coupling effect of both attitude and orbital motion is determined. Controlling and keeping the satellite in its orbital window ...
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In this study, the performance requirements influencing the orbital and attitude control system of a geostationary satellite in the station-keeping flight mode considering the coupling effect of both attitude and orbital motion is determined. Controlling and keeping the satellite in its orbital window have been done using a set of four thrusters located on one side of the satellite body, with considering the coupling effect of the attitude motion on orbital motion. The satellite’s orbital motion could be disturbed by the attitude motion in the allowable orbital window. The main factors conducting this behavior are derived utilizing the satellite attitude and orbital dynamic equations of motion. In the mathematical analysis of this study, the effects of environmental perturbations originating from the oblateness of Earth, third mass gravity like sun and moon, and solar radiation pressure on the satellite dynamic behavior are also considered. Afterward, the condition of using four installed thrusters on one side of the satellite and the reaction wheels in order to control the satellite orbital and attitude motion is investigated. To reduce the satellite attitude’s error, a proportional-derivative controller is employed to activate the reaction wheels properly. The satellite positions in north-south and east-west directions are controlled by a specific array of thrusters in order to maintain in its predefined orbital window. The required amount of velocity variations for a duration of one year via some simulation may demonstrate the effectiveness of the proposed approach in enhancing the orbital maintenance procedure of the satellite.
Aerospace Science and Technology
Omid Habibi; Reza Ebrahimi; Hassan Karimi Mazraeh Shahi
Volume 14, Issue 2 , October 2021, , Pages 141-151
Abstract
The nozzle, an end-element of the propulsive process Cycle, represents a critical part of any aerospace vehicle. The task of accelerating and efficiently exhausting combusted and reactive gases according to the delivered thrust represents the main objective of the propulsion system design. Flow separation ...
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The nozzle, an end-element of the propulsive process Cycle, represents a critical part of any aerospace vehicle. The task of accelerating and efficiently exhausting combusted and reactive gases according to the delivered thrust represents the main objective of the propulsion system design. Flow separation in supersonic convergent–divergent nozzles has been the subject of several experimental and numerical studies in the past. Now, with the renewed interest in supersonic flights and space vehicles, the subject has become increasingly important, especially for aerospace applications (rockets, missiles, supersonic aircrafts, etc). Flow separation in supersonic nozzles is a basic fluid dynamics phenomenon that occurs at a certain pressure ratio of chamber to ambient pressure, resulting in shock formation and shock/turbulent-boundary layer interaction inside the nozzle. From purely gas-dynamics point of view, this problem involves basic structure of shock interactions with separation shock, which consists of incident shock, Mach reflections, reflected shock, triple point and slip lines. In this article A Review on Flow Separation Phenomenon for Supersonic Convergent–Divergent Nozzles has been investigated.
Aerospace Science and Technology
Sahar Noori; Mohamad Saleh Afshar; Nima Karimi
Abstract
Airships usually have low cruising speed due to their large volume and high drag level. This makes the aerodynamic design of the vehicle, including the surfaces shape, the length-to-diameter ratio and the position of the fins, all very important. Furthermore, an important parameter in the vehicle aerodynamic ...
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Airships usually have low cruising speed due to their large volume and high drag level. This makes the aerodynamic design of the vehicle, including the surfaces shape, the length-to-diameter ratio and the position of the fins, all very important. Furthermore, an important parameter in the vehicle aerodynamic drag is determining the flow separation area at the rear of the air vehicle. The flow separation plays an essential role in the amount of drag and lift force, so the location of the fins and the design of the rear of the airship will be very important. By using both analytical and numerical methods, this study examines the aerodynamic efficiency of an airship in three different configurations, focusing on the location, type, and angle of attack of the fin, and compares analytical and numerical results. According to studies conducted among the types of fins, the cross-type will have the best performance among the fins in terms of lift-drag ratio. Also, moving the fins forward and distancing them from the rear of the vehicle disrupts the flow pattern at the rear of the vehicle and delays separation. This will improve aerodynamic efficiency and improve the lift-drag ratio of the vehicle.
Aerospace Science and Technology
Jafar Roshanian; Ehsan Rahimzade
Abstract
In this research, new adaptation law for updating parameters of the model reference adaptive control and the model reference adaptive control with feedback integrators for a specific class of nonlinear systems with additive parametric uncertainty are presented. The innovation presented in this paper ...
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In this research, new adaptation law for updating parameters of the model reference adaptive control and the model reference adaptive control with feedback integrators for a specific class of nonlinear systems with additive parametric uncertainty are presented. The innovation presented in this paper is the consideration of a new form for Lyapunov functions candidate to prove the stability of the closed-loop system. In general, Lyapunov functions candidate, which is used to prove stability and to derive rules for updating control parameters, include two sets of quadratic expressions. The first quadratic expression contains the trajectory tracking error and the second category includes the error of estimating the controller parameters. In this research, it is proved that by selecting quadratic expressions including the variable of trajectory tracking error in the form of power series, a new adaptation law is obtained that includes quadratic expressions in terms of the variable of tracking error in the form of power series. This type of adaptation law can be considered as an adaptation law derived from quadratic Lyapunov functions, except that the gain adaptation matrix parameters vary with time. It has been shown that by using an adaptive controller with a feedback integrator, the tracking error tends to zero faster and the flying object roll angle tracks the reference trajectory after a shorter time. In order to evaluate the control performance of the designed controllers, the system of one degree of freedom of the Wing Rock phenomenon has been used.
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
Amin Sarabchi; Mojtaba Heydarian Shahri; Ali Madadi
Abstract
Compared to the enormous costs of laboratory experiments, numerical approaches to improving the performance of turbomachines are less costly and more practical. In the present study, by using the Taguchi method and orthogonal arrays while doing a limited number of simulations (according to the Taguchi ...
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Compared to the enormous costs of laboratory experiments, numerical approaches to improving the performance of turbomachines are less costly and more practical. In the present study, by using the Taguchi method and orthogonal arrays while doing a limited number of simulations (according to the Taguchi method), the sensitivity level of objective functions have been investigated to optimization variables in a fan of a high-bypass ratio turbofan engine (JT9D-7 Engine). a mathematical parameterized algorithm coupled to a computational fluid dynamic solution is employed to modify the geometry and calculate the objective functions. 15 optimization variables are defined by varying:The radial distribution of the chord length from the hub to the tip of the blade and alsoeach profile's lean and sweep in five control points compared to hub profile.The lean, sweep and chord length are parameterized by a spline algorithm. The objective functions included the pressure ratio, isentropic efficiency and mass flow rate of the fan in the design point. The results showed that the lean angle affects the isentropic efficiency, and the sweep angle affects the mass flow rate of the fan. The pressure ratio was sensitive to both variables. Concerning the design variables, 2-level L16 and L32 arrays of the Taguchi method were used for running the sensitivity analysis. Assuming a fixed number of blades, a fixed angle of incidence, and a fixed camber angle, distributing the chord length did not significantly affect the objective functions compared to the lean and sweep distribution.
Aerospace Science and Technology
Pooya Yousefi Khiabani; Ali Nouri; Enayatullah Hosseinian
Abstract
In this paper, a semi-analytical solution for three-dimensional transient analysis of an annular plate with piezoelectric layers is investigated. The core is a functionally graded material with an exponential distribution. This method, which is a combination of the state space method, Laplace transform ...
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In this paper, a semi-analytical solution for three-dimensional transient analysis of an annular plate with piezoelectric layers is investigated. The core is a functionally graded material with an exponential distribution. This method, which is a combination of the state space method, Laplace transform and its inversion, and the one-dimensional differential quadrature method, is used to obtain the response of three-dimensional motion equations plate and the stress-displacement relations of the state space equations obtaining an analytical solution in the direction of the thickness and by applying the differential quadrature method to the equations of state space, a semi-analytical solution of the plate is obtained. To obtain a solution in the time domain, the Laplace transform and its numerical inversion are used. Analyzing the convergence of the present method, the obtained numerical results have been compared with the results of articles and with results obtained from using finite element analysis. Various parameters were studied including boundary conditions, piezoelectric properties, voltage applied to the actuator, the ratio of core thickness to layers, the ratio of outer to inner radius, and the functionally graded material variations index.
Aerospace Science and Technology
Asad Saghari; Amirreza Kosari; Masoud Khoshsima
Abstract
This paper deals with the problem of optimal selection of orbital parameters for an Earth observation mission in the absence of the possibility of injection into sun-synchronous orbit by considering the requirements and limitations of the mission and the satellite platform. By modeling the existing relationships ...
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This paper deals with the problem of optimal selection of orbital parameters for an Earth observation mission in the absence of the possibility of injection into sun-synchronous orbit by considering the requirements and limitations of the mission and the satellite platform. By modeling the existing relationships between each of the three areas of orbit, mission and platform, the effects of changes in each of the parameters have been analyzed and tracked. One of the important advantages of the proposed solution is that in the process of optimal selection of relevant parameters, all aspects of the orbit, mission and platform are considered simultaneously. This, in turn, can lead to an implementable and operational option for accomplishing the mission. In evaluation of effects of changing orbital parameters on the mission characteristics and requirements of the satellite platform, a developed computer code has been used.
Aerospace Science and Technology
Bahram Ghorbani Rezaei; Jafar Eskandari Jam
Abstract
While the composite pipes and cylinders manufacture by filament wound system, there are a lot of parameters that influence on the strength and mechanical behavior of them. This various mechanical behavior causes various buckling behavior. One of the most important parameters is winding pattern ...
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While the composite pipes and cylinders manufacture by filament wound system, there are a lot of parameters that influence on the strength and mechanical behavior of them. This various mechanical behavior causes various buckling behavior. One of the most important parameters is winding pattern that have effects on critical buckling loads. So this parameter should be controlled since it effects on mechanical behavior of pipes and cylinders. In the present work the influence of winding patterns on the critical buckling load of filament wound pipes exposed by pure axial loading have been studied. The studied specimens are Glass/Epoxy tubes with [+55,-55]6 lay-up(diameter to thickness ratio d/t of 10 and length of 280mm). Parameters were all considered to be consistent to investigate the effects of winding patterns there is just difference in winding pattern between three the experimental specimens. The lay-up is the result of classical theories. Love model and Galerkin’s method were used to provide buckling equations and solve theoretically the resulted equation respectively. Although the results illustrate that there is a difference, about 2-4 percent, in terms of critical buckling load between disparate winding patterns, 16 unit cells winding pattern bears higher buckling load than other patterns. Also the results show that no evident patterns influence on buckling modes of pipes. Later, the maximum lateral buckling loads of the patterns are verified with experimental data.
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
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
Parisa Ghanooni; Mostafa Kazemi; Mahmoud Mani
Abstract
This study focuses on improving performance of a supercritical wing equipped with winglets at different cant angles. This study aims to experimentally investigate the variation of aerodynamic performance of a supercritical wing of NASA Sc (2)-0410 airfoil at lower Reynolds numbers with winglets at various ...
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This study focuses on improving performance of a supercritical wing equipped with winglets at different cant angles. This study aims to experimentally investigate the variation of aerodynamic performance of a supercritical wing of NASA Sc (2)-0410 airfoil at lower Reynolds numbers with winglets at various cant angles. The tests were performed by measuring the lift and drag force using a three-component balance within a broad range of angle of attack from -4 to 20 degrees and at three different subsonic flow velocities. Results include changes in lift, drag, and aerodynamic performance for each winglet cant angle compared to the baseline wing. The results show that winglets generally increase the lift force and decrease the drag force by decreasing the size and strength of the wingtip vortices. Moreover, the optimal winglet for each case is extracted based on the aerodynamic performance provided by each winglet. In order to better and more accurately compare the effect of different mounting angles of the winglet on the aerodynamic performance of the base wing, the impact of each winglet is shown separately. Accordingly, it is observed that the winglets with angles of 0o and 15 o, namely W0 and W15, have shown good performance in increasing the lift coefficient. Also, the winglet with 90 degrees has shown good performance in creating the least drag force.
Aerospace Science and Technology
Ali Motamedi; Abolghasem Naghash
Abstract
The purpose of this paper is to present a Multi-Input Multi-Output (MIMO) linear controller based on the eigenstructure assignment method for a fixed-wing Unmanned Aerial Vehicle (UAV) in longitudinal and lateral-directional channels. To this end, a six degree-of-freedom model of the aerial vehicle is ...
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The purpose of this paper is to present a Multi-Input Multi-Output (MIMO) linear controller based on the eigenstructure assignment method for a fixed-wing Unmanned Aerial Vehicle (UAV) in longitudinal and lateral-directional channels. To this end, a six degree-of-freedom model of the aerial vehicle is considered, where dynamic modes of the system in each channel are analyzed, and the effect of each dynamic mode on state and output variables of the system is investigated. Then, the eigenvalue and eigenvector parameters of the designed controller are appropriately assigned for the system dynamic modes in each channel. In addition, the system requirements of each dynamic mode are satisfied with the proposed controller, and the adverse interaction between the system state variables is minimized. The capability and effectiveness of the designed controller in a desired maneuver are demonstrated with a nonlinear model simulation of a fixed-wing UAV. In this regard, the results in longitudinal and lateral-directional channels are presented.
Aerospace Science and Technology
ali Vahedi; Mohammad Homayoun Sadr; Saied Shakhesi
Abstract
Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their ...
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Epoxy is among the most important polymers, which is extensively employed in various technologies and applications. Nevertheless, epoxy polymers present low thermal conductivities and thus the enhancement of their thermal conductivity is an important research topic. Carbon nanotubes (CNTs) owing to their excellent thermal conductivities have been widely considered for the enhancement of the thermal conduction of epoxy polymers. In this work, we developed a combined molecular dynamics finite element multiscale modelling to investigate the heat transfer along CNT/epoxy nanocomposites. To this aim, the heat transfer between the CNT and epoxy atoms at the nanoscale was explored using the atomistic classical molecular dynamics simulations. In this case, we particularly evaluated the interfacial thermal conductance between the polymer and fillers. We finally constructed the continuum models of polymer nanocomposites representative volume elements using the finite element method in order to evaluate the effective thermal conductivity. The developed multiscale modelling enabled us to systematically analyze the effects of CNT fillers geometry (aspect ratio), diameter and volume fraction on the effective thermal conductivity of nanocomposites. Our results suggest that the interfacial thermal conductance between the CNT additives and epoxy polymer dominate the heat transfer mechanism at the nanoscale.The obtained findings in this study provide good vision regarding the enhancement of thermal conductivityof polymeric materials using highly conductive nanofillers.
Aerospace Science and Technology
Ali Ansari; Jafar Eskandari Jam; Ali Alizadeh; Mohsen Heydari Beni; Majid Eskandari Shahraki
Abstract
This study was designed to investigate the ballistic behavior of ceramic-reinforced aluminum composite plates numerically and experimentally and to present an optimal sample design. The parameters studied were ceramic reinforcement percentage and type of matrix alloy. This study used the matrix alloys ...
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This study was designed to investigate the ballistic behavior of ceramic-reinforced aluminum composite plates numerically and experimentally and to present an optimal sample design. The parameters studied were ceramic reinforcement percentage and type of matrix alloy. This study used the matrix alloys 6061, 7075, and 5083. The percentage of ceramics used in this study is 15, 30, and 45% by weight. The samples are in three thicknesses of 20, 25, and 30 mm. 27 simulated samples were numerically analyzed with Abaqus finite element software in this study based on existing ballistic protection criteria, one then determines the optimal numerical sample. Using the squeeze casting method, a laboratory sample has been made and experimentally tested to evaluate the numerical results. Lastly, the numerical analysis and the experimental test were compared and the optimal sample was determined.
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
Rahman Amiri; Ali Madadi; Abolghasem Mesgarpour Tousi
Abstract
Designing and manufacturing turbine engines have many complexities and challenges that need time and cost. Therefore, reputable companies producing gas turbines have always sought to shorten the design and construction processes, one of which is to use the core of aerial gas turbines in industrial gas ...
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Designing and manufacturing turbine engines have many complexities and challenges that need time and cost. Therefore, reputable companies producing gas turbines have always sought to shorten the design and construction processes, one of which is to use the core of aerial gas turbines in industrial gas turbines. This category of industrial gas turbines is called aero-derivative gas turbines. Aerial gas turbines can be used as industrial gas turbines due to their particular characteristics such as lightweight, relatively small dimensional size, high efficiency, and performance. These characteristics can shorten the design and manufacturing process. In the present work, ALF 502 aero gas turbine has been studied to convert its application to the derived industrial gas turbine. GasTurb software has been used to model this gas turbine for industrial applications. In this study, six different scenarios have been studied for converting aero engines to industrial engines, and results have been discussed. Finally, three scenarios were selected to be implemented on this engine among the studied scenarios.
Aerospace Science and Technology
Sina Jahandari; Ahmad Kalhor; Babak Nadjar Araabi
Abstract
This paper presents a novel approach to modeling of jet transport aircraft. Initially, basic mathematical models of jet transport are derived. Afterwards by focusing on the bank angle system of the jet transport, considering the aileron as the input, adverse methods of identification are utilized to ...
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This paper presents a novel approach to modeling of jet transport aircraft. Initially, basic mathematical models of jet transport are derived. Afterwards by focusing on the bank angle system of the jet transport, considering the aileron as the input, adverse methods of identification are utilized to estimate parameters of the system in an online manner. Then, effects of different types of noise on identification process are analyzed. Eventually, effects of time varying parameters are discussed. Recursive least squares method and its extended version, covariance resetting and forgetting factor methods were the fundamental tools in the system identification process of jet transport. Comprehensive simulations are presented and cast some light on effectiveness and disadvantages of different approaches.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
One of the most effective ways of high-speed motion in water is the motion in the supercavitation regime. This way provides the possibility to avoid considerable viscose resistance of boundary layer and consequently reach to very small drag coefficient which can be several times smaller than, that ...
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One of the most effective ways of high-speed motion in water is the motion in the supercavitation regime. This way provides the possibility to avoid considerable viscose resistance of boundary layer and consequently reach to very small drag coefficient which can be several times smaller than, that of the continuous flow. In this study the numerical simulation of developed and supercavitating flow is performed. The CFX code which served as a platform for the present work is a three-dimensional code that solves the Reynolds-Averaged Navier-Stokes equations with a finite volume method. The cavitation model is implemented based on the use of Rayleigh-Plesset equation to estimate the rate of vapor production. A high Reynolds number form ĸ-ε model is implemented to provide turbulence closure. For steady state flows and poor mesh resolution near the wall (using log-law wall functions), there is a priori no difference between the two equations formulations. For the different case studies, multi-block structured meshes were generated and the numerical simulation is performed in a wide range of cavitation numbers. Results are presented for steady state flows with natural cavitation about various bodies. Comparisons are made with available measurement of surface pressure distribution, cavitation bubble geometry (cavity length and cavity width) and drag coefficient. The simulated results are in a good agreement with the experimental data. Finally, the three-dimensional results are presented for a submerged body running at several angles of attack.
Aerospace Science and Technology
Sina Jahandari; Ahmad Kalhor; Babak nadjar Araabi
Abstract
This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived ...
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This paper addresses the adaptive control problem of an aircraft and focuses on the task that the pitch angle of the aircraft is required to follow the desired path. Considering the elevator deflection angle as the input and the pitch angle as the output, a mathematical model of the aircraft is derived to specify the structure of the system. Three diverse deterministic self-tuning regulators are designed using direct and indirect methods. Assuming that the system is unknown, recursive least squares method is applied to estimate parameters of the system or that of the controller’s. Diophantine equation and minimum degree pole-placement methods are utilized to calculate the control law. Not only do simulation results clearly demonstrate the privilege and effectiveness of the proposed approaches, but also comprehensive discussion is presented to distinguish advantages and disadvantages of them.
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
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
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.
