Nematollah Ghahramani; Abolqasem Naghash; Farzad Towhidkhah
Volume 5, Issue 3 , July 2008, Pages 99-105
Abstract
In this paper, a new incremental predictive guidance method based on implicit form of velocity to be gained algorithm is proposed. In this approach, the generalized incremental predictive control (GIPC) approach is applied to the linearized model for compensating the guidance error. Instead of using ...
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In this paper, a new incremental predictive guidance method based on implicit form of velocity to be gained algorithm is proposed. In this approach, the generalized incremental predictive control (GIPC) approach is applied to the linearized model for compensating the guidance error. Instead of using the present state in popular model based predictive controller (MPC), in the new method both previous and present states are utilized. GIPC approach introduces a feedback action including the weighted difference of the process states and the summation of the control action increments. To evaluate the robustness and performance of the proposed approach, the parameter uncertainties of the guidance and control are considered and a comparison with standard GPC is performed by extensive computer simulations. The results show a significant improvement in the robustness as well as tracking performance for the perturbed initial value of velocity to be gained or the reference signal.
Mohammad J. Sadigh; Ali Salehi
Volume 5, Issue 3 , July 2008, Pages 107-113
Abstract
Many space applications require robotic manipulators which have large workspace and are capable of precise motion. Micro-macro manipulators are considered as the best solution to this demand. Such systems consist of a long flexible arm and a short rigid arm. Kinematic redundancy and presence of unactuated ...
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Many space applications require robotic manipulators which have large workspace and are capable of precise motion. Micro-macro manipulators are considered as the best solution to this demand. Such systems consist of a long flexible arm and a short rigid arm. Kinematic redundancy and presence of unactuated flexible degrees of freedom, makes it difficult to control micro-macro manipulators. This paper presents a closed-loop control based on artificial constrained motion which helps to keep the end-effector on the prescribed trajectory, while the flexible arm can freely vibrate. The robustness of algorithm is checked against uncertainties of the system, which shows good performance except in the presence of gravity. A gravity compensating term is added to eliminate the drift due to gravity.
Mohammad Zaman Kabir; Arash Rojhani
Volume 5, Issue 3 , July 2008, Pages 115-121
Abstract
Optimum laminate configuration for minimum weight of filament–wound laminated conical shells subject to buckling load constraint is investigated. In the case of a laminated conical shell the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing ...
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Optimum laminate configuration for minimum weight of filament–wound laminated conical shells subject to buckling load constraint is investigated. In the case of a laminated conical shell the thickness and the ply orientation (the design variables) are functions of the shell coordinates, influencing both the buckling load and its weight. These effects complicate the optimization problem considerably. The first level of complexity is attributed to the correlation between the volume and the buckling load and their dependence on the fiber configuration. The second level of complexity is associated with the high computational cost involved in calculation of the buckling load. Thus, the main objective of this study is to solve the optimization problem as well as to reduce the computational cost associated with it. Based on the characteristic buckling behavior of laminated conical shells the usual penalty function method is used.
fariborz saghafi; Seyed Mohammad Khansari Zadeh
Volume 5, Issue 3 , July 2008, Pages 123-128
Abstract
In the present paper, an efficient method for three dimensional aircraft pattern recognition is introduced. In this method, a set of simple area based features extracted from silhouette of aerial vehicles are used to recognize an aircraft type from its optical or infrared images taken by a CCD camera ...
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In the present paper, an efficient method for three dimensional aircraft pattern recognition is introduced. In this method, a set of simple area based features extracted from silhouette of aerial vehicles are used to recognize an aircraft type from its optical or infrared images taken by a CCD camera or a FLIR sensor. These images can be taken from any direction and distance relative to the flying aircraft. A multilayer perceptron neural network has been used for the purpose of aircraft classification. The network training has been carried out using a library of images generated by a 3D model of each aircraft. The neural network is successfully trained and used to recognize and classify arbitrary real aircraft images. The results show more than 90% accuracy in ideal conditions and very good robustness in the presence of noise.
reza ansari; M. Darvizeh; Milad Hemmatnezhad
Volume 5, Issue 3 , July 2008, Pages 129-138
Abstract
In this paper, a unified analytical approach is proposed to investigate vibrational behavior of functionally graded shells. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives ...
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In this paper, a unified analytical approach is proposed to investigate vibrational behavior of functionally graded shells. Theoretical formulation is established based on Sanders’ thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stokes transformation. Material properties are assumed to be graded in the thickness direction according to different volume fraction functions such as power-law, sigmoid, double-layered and exponential distributions. A FGM cylinderical shell made up of a mixture of ceramic and metal is considered. The Influence of some commonly used boundary conditions, the effect of changes in shell geometrical parameters and variations of volume fraction functions on the vibration characteristics are studied by comparing the results from the present theory with those from the First order Shear Deformation Theory (FSDT). Furthermore, the results obtained for a number of particular cases show good agreement with those available in the open literature. The simplicity and the capability of the present method are also discussed.
hasan Abedi; M. Sohrabian
Volume 5, Issue 3 , July 2008, Pages 139-144
Abstract
In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. ...
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In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. One of the main factors in reducing the precision and producing instabilities is nutation vibration. This fluctuating motion, which is a dynamical inherent property of the system, is related to the gyro lateral moment of inertia, the length of gyro and its rotating speed. In order to investigate the capabilities of nutation damper and removing the wobble motion of a freely precessing body, this paper analyzes a ring damper partially filled with viscous liquid with taking into account the behavior of the damper and its subsystems. The equations of motion for the dynamical motion of gyro, are obtained using Lagrangian approach, taking into account the friction of dampers and interaction of the liquid with the system equations of motion.