F. Javidrad
Volume 4, Issue 1 , March 2007, , Pages 25-32
Abstract
This paper studies the application of an inverse methodology for problem solving in fracture mechanics using the finite element analysis. The method was applied to both detection of subsurface cracks and the study of propagating cracks. The procedure for detection of subsurface cracks uses a first order ...
Read More
This paper studies the application of an inverse methodology for problem solving in fracture mechanics using the finite element analysis. The method was applied to both detection of subsurface cracks and the study of propagating cracks. The procedure for detection of subsurface cracks uses a first order optimization analysis coupled with a penalty function to solve for the unknown geometric parameters associated with the internal flaw. The objective function is calculated from normalizing the finite element determined displacements by the prescribed ones at some arbitrary points of the damaged component. The technique was also used for determination of the propagating both 1-D and 2-D planar crack growth directions using the well known maximum strain energy release rate criterion. In all cases studied, a good agreement between the theoretical and/or the experimentally observed crack behavior and the developed technique is achieved.
Meghdad Torabinezhad; Fariborz Saghafi
Abstract
Parafoil-cargo system, as a complex system, is used widely today and has various usages. This system is a polynomial complex whose components, have dynamic interactions and relative movements. The present study deals with the multibody modeling and simulation of nine degrees of freedom flight dynamics ...
Read More
Parafoil-cargo system, as a complex system, is used widely today and has various usages. This system is a polynomial complex whose components, have dynamic interactions and relative movements. The present study deals with the multibody modeling and simulation of nine degrees of freedom flight dynamics of a parafoil-payload system, which includes the three degrees of transfer freedom and the three degrees of the rotational freedom of the parafoil set (the part with the parachute and the ropes attached to it), and the three degrees of relative rotational freedom of the cargo. By kinematic and dynamic analysis of the system components, a nonlinear model with 18 state variables is obtained. This model has three controlling entrances. In addition to symmetric and asymmetric aerodynamic brakes, the shifting of the weight of the cargo with respect to the parafoil is considered, which leads to the rotation and change of the transverse installation angle of the parachute with respect to the parafoil set. The apparent mass and inertia moment of the parafoil parachute, restraining forces, relative movements between objects, longitudinal and transverse installation angles and also the effect of wind are examined. In order to evaluate how the flight dynamics of the system work and the study of the factors affecting it, the nonlinear differential equations of the model are developed. After examining its stability using Lyapanov method, the model undergoes a numerical integration as well as simulation for several flight conditions and under different inputs by the code and program developed in MATLAB software. The simulation results show the flight stability that is achieved after launching from a high altitude and by which the flight dynamic modeling of the system is validated.
Majid Azadi
Volume 2, Issue 2 , June 2005, , Pages 29-35
Volume 2, Issue 3 , September 2005, , Pages 29-43
Abstract
From Wright Brothers 1903 to present day 2003, aeronautical technology has made a profound progress. This paper demonstrates the outcome of this progress in weight, wing area, and engine thrust in three categories of transport aircraft of short to long range, regional jets, and turbo-prop commuter aircraft. ...
Read More
From Wright Brothers 1903 to present day 2003, aeronautical technology has made a profound progress. This paper demonstrates the outcome of this progress in weight, wing area, and engine thrust in three categories of transport aircraft of short to long range, regional jets, and turbo-prop commuter aircraft. Also the paper includes those aircraft with distinct jump in aeronautical technology. Few of the technologies that have contributed to this progress are elaborated too. An average of four to three times progress in aerodynamic sciences, three to four times in weight reduction for material science, and system design, and two to one and half times progress in propulsion of turbo-fan, and turbo-prop engines are concluded.
A. Ebrahimi; Aliakbar Dr. Moosavian
Volume 4, Issue 4 , December 2007, , Pages 29-36
Abstract
A Space Free-Flying Robot (SFFR) includes an actuated base equipped with one or more manipulators to perform on-orbit missions. Distinct from fixed-based manipulators, the spacecraft (base) of a SFFR responds to dynamic reaction forces due to manipulator motions. In order to control such a system, it ...
Read More
A Space Free-Flying Robot (SFFR) includes an actuated base equipped with one or more manipulators to perform on-orbit missions. Distinct from fixed-based manipulators, the spacecraft (base) of a SFFR responds to dynamic reaction forces due to manipulator motions. In order to control such a system, it is essential to consider the dynamic coupling between the manipulators and the base. Explicit dynamics modeling of such systems with flexible appendages is developed in this paper. The SFFR is divided into two parts, the manipulator(s), and the main base body (spacecraft) that consists of flexible appendages. The recursive Lagrangian approach is used to describe dynamics model of the flexible base system. For modeling the multi-manipulator system, a Recursive Newton-Euler approach is followed. The obtained dynamics model can be employed either numerically or symbolically. Interacting forces and torques acting between the manipulators and the main body are also modeled that could be used for simulation studies of controller design.
Seyed Hamid Jalali Naini
Volume 8, Issue 1 , March 2011, , Pages 29-36
Abstract
In this paper, a closedloop strategy in the vertical plane is derived in order to determine the thrust direction of a launch vehicle in terms of velocitiestobe gained The two velocities-to-be-gained are utilized, here, for a given altitude and zero vertical speed in a specied nal time The formulation ...
Read More
In this paper, a closedloop strategy in the vertical plane is derived in order to determine the thrust direction of a launch vehicle in terms of velocitiestobe gained The two velocities-to-be-gained are utilized, here, for a given altitude and zero vertical speed in a specied nal time The formulation is obtained for constant gravity assumption, but it works when the velocitiesto-be-gained are obtained for a spherical-Earth model via explicit or implicit relations-
Aerospace Science and Technology
Hadi Hamedani; Ahmad Mamandi
Volume 14, Issue 2 , October 2021, , Pages 30-51
Abstract
In this paper, the effects of different rotational speed functions in the elastic-plastic deformation and stress analysis of a rotating annular thin disk of functionally graded material (FGM) in Reddy model is studied using the analytical and FEM methods. In this regard, differential equations governing ...
Read More
In this paper, the effects of different rotational speed functions in the elastic-plastic deformation and stress analysis of a rotating annular thin disk of functionally graded material (FGM) in Reddy model is studied using the analytical and FEM methods. In this regard, differential equations governing dynamic equilibrium for displacements and stresses in the elastic region of the FGM rotating disk have been derived using the theory of elasticity in plane stress condition and have been solved by the shooting method. Then, the equations governing the distribution of plastic radial and circumferential stresses on the disk have been extracted using the Prandtl-Reuss theory of plasticity and based on the Ludwig hardening law in conjunction with the von Mises yield criterion. Also, by modeling the annular thin disk in the environment of finite element software ANSYS, the results obtained from the elastic analytical solution and the finite element numerical solution have been compared to each other and to the results reported in the literature for specific cases and validated accordingly. The effects of variation of the disk geometric parameters, functionally graded material power index as well as different type of the time-dependent rotational speed functions such as the constant speed, exponential, and accelerated/decelerated linear, quadratic, and square root functions on the elastic behavior of the disk and distribution of radial displacement, and also distribution of radial, circumferential, and shear stresses on the disk have been studied. Moreover, the results of plastic analysis have been presented for distribution of radial and circumferential stresses on the disk.
Robert A. Goehlich
Volume 3, Issue 1 , March 2006, , Pages 31-42
Abstract
The contribution of this paper to the space transportation system field is to select promising Reusable Launch Vehicle (RLV) concepts by using a formal evaluation procedure. The vehicle system is divided into design features. Every design feature can have alternative characteristics. All combinations ...
Read More
The contribution of this paper to the space transportation system field is to select promising Reusable Launch Vehicle (RLV) concepts by using a formal evaluation procedure. The vehicle system is divided into design features. Every design feature can have alternative characteristics. All combinations of design features and characteristics are compared pairwise with each other. The innovation and novelty of this evaluation procedure is to assess these characteristics with respect to relative importance for a feasible vehicle concept as seen from technical, economic and political aspects. This valuation process leads to a ranked list of design features for suborbital and orbital applications. The result is a theoretical optimized suborbital and orbital vehicle each. The method of pairwise comparison allows to determine not only ranking but also assessing the relative weight of each feature compared to others.
Mahdi Saniei Nejad; R. Jamshidi
Volume 7, Issue 1 , March 2010, , Pages 31-40
Abstract
In the following paper, the effects of a choked jet exhausted from the base of a non-lifting body on its total and base drags at sub-sonic and transonic regimes has been numerically investigated. Having surveyed the results of some turbulence models and after comparing with experimental results, an appropriate ...
Read More
In the following paper, the effects of a choked jet exhausted from the base of a non-lifting body on its total and base drags at sub-sonic and transonic regimes has been numerically investigated. Having surveyed the results of some turbulence models and after comparing with experimental results, an appropriate turbulence model i.e. SST K-?, has been chosen and this model has been used in the subsequent analysis. The analysis have been conducted in the free stream Mach number range of 0.4
Volume 4, Issue 2 , June 2007, , Pages 33-42
Abstract
This paper qualifies the effect of different convection schemes and center-domains on the simulation of winter precipitation over Iran using RegCM3 numerical climate model. It is compressible, finite difference with hydrostatic equilibrium in sigma coordinate with a semi-implicit algorithm for reduction ...
Read More
This paper qualifies the effect of different convection schemes and center-domains on the simulation of winter precipitation over Iran using RegCM3 numerical climate model. It is compressible, finite difference with hydrostatic equilibrium in sigma coordinate with a semi-implicit algorithm for reduction of horizontal diffusion. Iran experienced two dry and wet periods during winters of 1997 and 2000. In this paper sensitivity of the RegCM3 regional climate model has been analyzed using different convection schemes, including Grell-AS, Grell- FC, Emanuel and Kuo and different center domains including Himalaya, Mediterranean sea, Iran and Indian ocean (near Pakistan southern boundaries). NNRP1 data with 5 degree resolution, GLCC and GTOPO are used as initial and boundary conditions, land use and topography data, respectively. We found that there is an intelligence between model skill and center domain, for example Himalaya center domain gives good results when a Siberian high pressure develops over Iran. The minimum bias and MAE of -0.7mm and 0.6mm are captured by Kuo convection scheme in the modeling of dry year 2000, but Grell convection scheme have minimum error among two wet and dry winter simulation. Precipitation amounts are underestimated for both convection and center domain experiments when compared to observations during winter 2000. The largest difference occurred in Himalaya experiment. We found that CRU reanalysis data can not be considered as a reference data for calibration of RegCM3 over Iran. It is also found that there is an eastward shift in Caspian Sea precipitation pattern in all experiments.
H. Shafiei; A.R. Setoodeh
Volume 11, Issue 2 , October 2017, , Pages 33-41
Abstract
The present work derives the exact analytical solutions for buckling and post-buckling analysis of nano-composite beams reinforced by single-walled carbon nanotubes (SWCNTs) based on the Euler-Bernoulli beam theory and principle of virtual work. The reinforcements are considered to be aligned in the ...
Read More
The present work derives the exact analytical solutions for buckling and post-buckling analysis of nano-composite beams reinforced by single-walled carbon nanotubes (SWCNTs) based on the Euler-Bernoulli beam theory and principle of virtual work. The reinforcements are considered to be aligned in the polymeric matrix either uniformly distributed (UD) or functionally graded (FG) distributed through the thickness direction of the beam. In FG beams, material properties vary gradually along the thickness direction. The effective material properties of the nano-composite beam are predicted based on the extended rule of mixture. Also, by applying von Kármán assumptions, the geometric nonlinearities are taken into consideration. The developed governing equations are solved by utilizing analytical methods and exact closed form solutions for buckling and post-buckling loads of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beam with different boundary conditions are obtained. By comparing the present post-buckling load results with the ones reported in the literature, the accuracy and reliability of the current method are demonstrated. Eventually, the numerical results are provided and the effects of CNTs distribution, CNTs volume fraction, slenderness ratio, maximum deflection of the beam and boundary conditions on the post-buckling characteristics of the CNTRC beam are discussed.
Aerospace Science and Technology
Benyamin Ebrahimi; Jafar Roshanian; Ali Asghar Bataleblu
Abstract
Significant attention has been given to the field of multi-agent systems in recent years due to its potential to solve complex problems that cannot be addressed by a single agent. One such problem is the cooperative search and coverage application, which requires multiple agents to efficiently search ...
Read More
Significant attention has been given to the field of multi-agent systems in recent years due to its potential to solve complex problems that cannot be addressed by a single agent. One such problem is the cooperative search and coverage application, which requires multiple agents to efficiently search and cover a given area. However, the effectiveness of such systems is dependent on various factors, including mission definition parameters and the approach used to achieve mission performance optimality. In this paper, an optimal strategy for segregating multi-agent missions for search and coverage applications is proposed. The proposed strategy involves dividing a single mission into several simultaneous missions based on the optimal division of the environment that ensures system performance optimality while achieving a common goal. The mission area is divided into sub-areas, and each sub-area is assigned to specific agents to improve overall system performance. The effectiveness of the proposed strategy is demonstrated through simulations and relevant comparisons.
Ava Shahrokhi; Alireza Jahangirian
Volume 5, Issue 1 , March 2008, , Pages 35-43
Abstract
The effect of airfoil shape parameterization on optimum design and its influence on the convergence of the evolutionary optimization process is presented. Three popular airfoil parametric methods including PARSEC, Sobieczky and B-Spline (Bezier curve) are studied and their efficiency and results are ...
Read More
The effect of airfoil shape parameterization on optimum design and its influence on the convergence of the evolutionary optimization process is presented. Three popular airfoil parametric methods including PARSEC, Sobieczky and B-Spline (Bezier curve) are studied and their efficiency and results are compared with those of a new method. The new method takes into consideration the characteristics of viscous transonic flows particularly around the trailing edge. The methods are applied to airfoil shape optimization at high Reynolds number turbulent flow conditions using Genetic Algorithm. An unstructured grid Navier-Stokes flow solver with a two-equation K-e turbulence model is used to evaluate the objective function. The original mesh movement strategy (Spring analogy) is modified particularly inside the boundary layer in order to maintain the quality of cells in this area. The aerodynamic characteristics of the optimum airfoil obtained from the proposed parametric method are compared with those from alternative methods. It is concluded that the new method is capable of finding efficient and optimum airfoils in fewer number of evaluations.
P. Heydari; H. Khaloozadeh; A.P. Heydari
Volume 6, Issue 1 , March 2009, , Pages 35-44
Abstract
In this paper statistical and time series models are used for determining the random drift of a dynamically Tuned Gyroscope (DTG). This drift is compensated with optimal predictive transfer function. Also nonlinear neural-network and fuzzy-neural models are investigated for prediction and compensation ...
Read More
In this paper statistical and time series models are used for determining the random drift of a dynamically Tuned Gyroscope (DTG). This drift is compensated with optimal predictive transfer function. Also nonlinear neural-network and fuzzy-neural models are investigated for prediction and compensation of the random drift. Finally the different models are compared together and their advantages are discussed
Aerospace Science and Technology
Alireza Pourmoayed; keramat Malekzadeh fard
Volume 12, Issue 2 , October 2019, , Pages 35-48
Abstract
In this article, the vibrational behavior of a spinning cylindrical thick shell carrying spring- mass systems and conveying viscos fluid flow under various temperature distributions is investigated. This structure rotates about axial direction and the formulations include the coriolis and centrifugal ...
Read More
In this article, the vibrational behavior of a spinning cylindrical thick shell carrying spring- mass systems and conveying viscos fluid flow under various temperature distributions is investigated. This structure rotates about axial direction and the formulations include the coriolis and centrifugal effects. In addition, this system is conveying viscous fluid, and the related force is calculated by modified Navier–Stokes relation considering slip boundary condition and Knudsen number. The modeled cylindrical thick shell, its equations of motion, and boundary conditions are derived by the principle of minimum total potential energy and based on a new three-dimensional refined higher-order theory (RHOST). For the first time in the present study, attached mass-spring systems has been considered in the rotating cylindrical thick shells conveying viscous fluid flow. The accuracy of the presented model is verified with previous studies. The novelty of the current study is consideration of the rotation, various temperature distributions, mass-spring systems and conveying viscous fluid flow implemented on proposed model using RHOST. Generalized differential quadrature method (GDQM) is presented to discretize the model and to approximate the governing equations. In this study the simply supported conditions has been applied to edges and cantilever boundary conditions has been studied in x=0, L. Finally, the effects of the velocity of viscous fluid flow, angular velocity, temperature changes and spring-mass systems on the critical speed, critical velocity, critical temperature and natural frequency of the structure are investigated.
Aerospace Science and Technology
Sarallah Abbasi; MohammadAmin Daraei
Abstract
In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, ...
Read More
In this research, the thermodynamic analysis of a three-spool mixed-flow turbofan engine has been studied by examining parameters such as flight altitude, flight Mach number, fan pressure ratio, high and Intermediate-pressure compressor pressure ratios, bypass ratio and burner exit temperature. First, the effect of these parameters on the thrust, thrust specific fuel consumption (TSFC) and engine efficiency was investigated and then in the exergy analysis, it was found that the lowest exergy efficiency with a value of 85.45% belongs to the combustion chamber; Therefore, a parametric study was conducted to improve the performance and exergy efficiency of the burner; For example, in the case of bypass ratio of 2.2 and fan pressure ratio of 2, the exergy efficiency of the burner is increased by 12.23% compared to the base case. In addition, the results of sensitivity analysis show that the burner exit temperature and the HPC pressure ratio with 21.81 and 2.2%, respectively, have the most and the least effect on the engine net thrust; Also, the burner exit temperature and the flight altitude with 4.57% and 0.11%, respectively, have the most and the least effect on the TSFC.
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 ...
Read More
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.
Aliakbar Dr. Moosavian
Volume 2, Issue 4 , December 2005, , Pages 37-43
Abstract
In this paper, slewing maneuver of a flexible spacecraft with large angle of rotation is considered and assuming structural frequency uncertainties a robust minimum-time optimal control law is developed. Considering typical bang-bang control commands with multiple symmetrical switches, a parameter optimization ...
Read More
In this paper, slewing maneuver of a flexible spacecraft with large angle of rotation is considered and assuming structural frequency uncertainties a robust minimum-time optimal control law is developed. Considering typical bang-bang control commands with multiple symmetrical switches, a parameter optimization procedure is introduced to find the control forces/torques. The constrained minimization problem is augmented with the robustness constraints, which in turn increases the number of switches in the bang-bang control input to match the total number of the constraint equations. The steps of the solution 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 robust control input with just few switching times can significantly lessen the vibrating motion of the flexible appendage in the presence of structural frequency uncertainties, which reveals the merits of the developed control law.
Roohollah Talebitooti; Kamran Daneshjoo
Volume 4, Issue 3 , September 2007, , Pages 37-43
Abstract
In this paper, classical thin shell theory is used to analyze vibration and critical speed of simply supported rotating orthotropic cylindrical shell. The effects of centrifugal and Coriolis forces due to the rotation are considered in the present formulation.. In addition, axial load is applied on ...
Read More
In this paper, classical thin shell theory is used to analyze vibration and critical speed of simply supported rotating orthotropic cylindrical shell. The effects of centrifugal and Coriolis forces due to the rotation are considered in the present formulation.. In addition, axial load is applied on cylinder as a ratio of critical buckling load. Finally the effects of orthotropic ratio, material and geometry of the shell as well as axial loads on bifurcation of natural frequency are investigated.
Aerospace Science and Technology
Mahdi Amani Estalkhkuhi; Jafar Roshanian
Abstract
In this paper, a multi-input/multi-output sliding controller is proposed and analyzed for a quad tilt-wing unmanned aerial vehicle (QTW-UAV). The vehicle is equipped to do take-off and landing in vertical flight mode and is capable of flight over long distances in horizontal flight mode. The full dynamic ...
Read More
In this paper, a multi-input/multi-output sliding controller is proposed and analyzed for a quad tilt-wing unmanned aerial vehicle (QTW-UAV). The vehicle is equipped to do take-off and landing in vertical flight mode and is capable of flight over long distances in horizontal flight mode. The full dynamic model of the vehicle is originated from the Newton-Euler formulation. For developing the controller, a set of integral type sliding surfaces is selected and it is necessary to mention that in this approach, there isn't any linearization during controller design. Simulation has been conducted for a nonlinear, multivariable model that includes uncertain parameters and in the presence of pitch angle measurement noise and pitch moment disturbance. For verification, the proposed controller is compared with linear based controller design simulation. Results exhibit that the proposed controller is robust in the face of uncertainties, noise and disturbance and meets performance demands with control inputs of low amplitude.
Aerospace Science and Technology
Mohammad Yavari; Nemat Allah Ghahremani; Reza Zardashti; Jalal Karimi
Abstract
In this paper a new mid-course guidance algorithm for intercepting high altitude target is proposed. A part of target flight path is outside the atmosphere. The maximum acceleration command is designed as a variable constraint that varies with altitude. This physical limitation is happened for the aerodynamically ...
Read More
In this paper a new mid-course guidance algorithm for intercepting high altitude target is proposed. A part of target flight path is outside the atmosphere. The maximum acceleration command is designed as a variable constraint that varies with altitude. This physical limitation is happened for the aerodynamically control interceptors at high altitudes because of decreasing air density. Based on generalized incremental predictive control approach, a new formulation for parallel navigation guidance law is proposed. Using the nonlinear kinematic equations of target-interceptor, the commands of the new guidance method are computed by optimization of a cost function involved the velocity perpendicular to the line of sight errors and guidance commands. An important feature of the proposed method is the minimization of the line- of - sight angular rate in a finite period of time. The various simulation results of the proposed guidance law shows the higher effectiveness of the designed guidance law in comparison with proportional navigation and sliding mode guidance.
Aerospace Science and Technology
Hamidreza Jafari; Farid Shahmiri
Volume 12, Issue 1 , March 2019, , Pages 39-51
Abstract
In this paper, the particular solution technique for inverse simulation applied to the quadrotor maneuvering flight is investigated. The trust-region dogleg (DL) technique which is proposed alleviates the weakness of Newton’s method used for numerical differentiation of system states in the ...
Read More
In this paper, the particular solution technique for inverse simulation applied to the quadrotor maneuvering flight is investigated. The trust-region dogleg (DL) technique which is proposed alleviates the weakness of Newton’s method used for numerical differentiation of system states in the solution process. The proposed technique emphasizes global convergence solution to the inverse simulation problem. This algorithm is evaluated by calculating the control inputs necessary to enable the quadrotor to follow a specified trajectory including climb-hover and cruise-hover maneuvers. The trajectory is generated by the direct simulation using a linear optimal control developed for the quadrotor. The model of rotors for the quadrotor is a nonlinear model developed based on blade element theory (BET), linear aerodynamics, and non uniform inflow over the rotor disc. The results show that the control inputs obtained from the inverse simulation are in good agreement with control inputs estimated by direct simulation. The results also confirm that the maximum difference between the prescribed trajectory and the trajectory generated by the direct simulation is less than 0.02%, and thus the potential application of the inverse simulation with the trust-region dogleg optimization is evident.
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 ...
Read More
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
Seyedeh sepideh Madani; mohammad ali shahi ashtiyani
Abstract
Nowadays, operational usage of the unmanned aerial vehicles (UAVs) in various missions is on the increase considering their capabilities. Provided that there is coordination between the UAV, navigation and control system, operational capability of the UAVs increases. Since there is no pilot in UAVs, ...
Read More
Nowadays, operational usage of the unmanned aerial vehicles (UAVs) in various missions is on the increase considering their capabilities. Provided that there is coordination between the UAV, navigation and control system, operational capability of the UAVs increases. Since there is no pilot in UAVs, the task of guidance and control of the UAV for carrying out the mission depends on the ability of the autopilot and guidance system. This paper regards the control and the guidance as two separate entities in way point tracking problem. To do so, backstepping controller design for inner loop to track the commands is generated by the outer loop. The outer loop is designed based upon fuzzy logic. The proposed system uses standard Mamdani fuzzy controllers that provide speed, heading, and flight path angle references for the autopilots. Nonlinear six-degree-of-freedom equations of motion are used to model the vehicle dynamics. Simulations were carried out to verify the performance of the system. The results indicate the ability of way point tracking system to track the desired set of waypoints.
I. Shafieenejad; Alireza Novinzadeh
Volume 6, Issue 2 , June 2009, , Pages 79-85
Abstract
A new guidance scheme for the problem of Low-thrust transfer between inclined orbits is developed within the framework of optimal control theory. The objective of the guidance scheme is to provide the appropriate thrust steering program that will transfer the vehicle from an inclined low earth orbits ...
Read More
A new guidance scheme for the problem of Low-thrust transfer between inclined orbits is developed within the framework of optimal control theory. The objective of the guidance scheme is to provide the appropriate thrust steering program that will transfer the vehicle from an inclined low earth orbits to the high earth orbits. The presented guidance scheme is determined using Pontryagin’s principle such that three desired performance measures are minimized and boundary conditions for this unspecified final time problem are satisfied. One of the novelties of this work is changing independent variable from time to thrust angle and considering properties of autonomous system equations to reduce to one where exact analytical solution is obtained.
