Sharif Digital Repository

A series of experiments were carried out to study the unsteady wakes behind an oscillating airfoil. The airfoil is a section of a wind turbine blade oscillating in pitch about the quarter chord axis at various reduced frequencies, oscillation amplitude and mean angles of attack. Real time velocity profiles were obtained using total and static pressure at 35 vertically aligned points behind the airfoil via two similar rakes. The rakes were located at a distance of 1.5 chord length behind the model. The results show great influence of oscillation amplitude and reduced frequency on the wake velocity profiles. Copyright © 2007 by ASME  

The laser powder deposition (LPD) process is an advanced material processing technique with many applications. Despite this fact, reliable and accurate control schemes have not yet been fully developed for the process. In this paper, identification of the LPD process is examined to find a more accurate model to predict and control the height of clad in real time. The model is adaptive single inputsingle output (SISO) and its structure is very similar to the Hammerstein model when the effective power (a function of laser power and velocity) is selected as the input and the clad height as the output. Weighted extended recursive least square (WERLS) is adopted to simultaneously estimate the... 

Nowadays the size and dimension of mobile manipulators have been decreased for being usable in various regions. This leads several problems such as danger of instability. Therefore, many researches have been done to overcome the problem of overturning of a mobile manipulator. In this paper, an algorithm for increasing the stability of a mobile manipulator is presented based on the optimization of a performance index. The path of vehicle and the desired task of the end-effector are predefined. In order to apply the optimal stability criterion, it is more convenient that the manipulator be of a redundant. Considering the interaction between the vehicle and the manipulator and using the genetic... 

Knowing the exact position and rotation is a crucial necessity for the navigation of autonomous robots. Even in outdoor environments GPS signals are not always accessible for estimating online rotation and position of robots. Also inertial aided navigation methods have their own defects such as the drift of gyroscope or inaccuracy of accelerometer in agile motions and environmental sensitivity of compass. In this article, we have introduced a novel online visual gyroscope that can estimate the rotation of a moving car with analyzing the images of a monocular camera installed on it. Our real time visual gyroscope utilizes an efficient method of rotation estimation between each pair of camera... 

The aim of this article is design, fabricate, and control a conceptual prototype of a flexible wearable robot to increase fingers’ force using a novel cable mechanism. In this robot, force and position are controlled in separate phases by a fuzzy system equipped with emotional learning. A Flexible structure has been chosen for this robot, because flexible gloves are lighter and much more suitable for use in daily tasks compared to rigid structures. Since this system is supposed to be substituted for weak or damaged limb, it should have a behavior similar to the body organs as much as possible. Therefore, a novel mechanism, inspired by the natural movement mechanism of the human hand, has... 

This paper presents a new approach based on Artificial Potential Fields (APF) method which provides simple and effective motion planners for practical path planning in fully dynamic environments. We have exploited the fuzzy modeling to define Fuzzy Artificial Potential Fields (FAPF) which provides a real-time and flexible path planning, in contrast with classical approaches which make use of analytic harmonic functions to solve the navigation problem. It is shown that FAPF paves a way to merge both global and local path planning strategies. In this particular application, the proposed fuzzy system is used to obtain the gradient of the harmonic functions via weighting the membership functions... 

In some systems with hysteresis behavior like Shape Memory Alloy (SMA) actuators and Piezo actuators, we essentially need an accurate modeling of hysteresis either for controller design or performance evaluation. One of the most interesting Hysteresis non-linearity identification methods is Preisach model in which hysteresis is modeled by linear combination of elemental operators. Despite good ability of Preisach modeling to extract main features of system with hysteresis behavior, cause of tough numerical nature of Preisach, it is not convenient to use in real-time control applications. In this paper we present a novel method based on Artificial Neural Network. For evaluation of proposed... 

In this paper, a new nonlinear heuristic filter based on the hybridization of an extended Kalman filter and an ant colony estimator is proposed to estimate the states of a nonlinear system. In this filter, a group of virtual ants searches the state space stochastically and dynamically to find and track the best state estimation while the position of each ant is updated at the measurement time using the extended Kalman filter. The performance of the proposed filter is compared with well-known heuristic filters using a nonlinear benchmark problem. The statistical results show that this algorithm is able to provide promising and competitive results. Then, the new filter is tested on a nonlinear... 

In this paper, a new nonlinear heuristic filter based on the hybridization of an extended Kalman filter and an ant colony estimator is proposed to estimate the states of a nonlinear system. In this filter, a group of virtual ants searches the state space stochastically and dynamically to find and track the best state estimation while the position of each ant is updated at the measurement time using the extended Kalman filter. The performance of the proposed filter is compared with well-known heuristic filters using a nonlinear benchmark problem. The statistical results show that this algorithm is able to provide promising and competitive results. Then, the new filter is tested on a nonlinear... 

In this study, a new heuristic multiple model filter, called Multiple Model Extended Continuous Ant Colony Filter, is proposed to solve a nonlinear multiple model state estimation problem. In this filter, a bank of extended continuous ant colony filters are run in parallel to solve the multiple model estimation problem. The probability of each model is continually updated and consequently both the true model and the states of the nonlinear system are updated based on the weighted sum of the filters. The new multiple model filter is tested on an engineering problem. The problem is to estimate simultaneously the states of a fixed-wing unmanned aerial vehicle as well as the wind model, applied... 

Main objective of this article is to present the implementation and simulation of a Conjugate Structure Algebraic Code Excited Linear Prediction speech coder (CSACELP) based upon ITU-T's G.729 recommendation and to optimize it for real-time implementation on an FPGA. The suggested architecture is characterized by pipelining and parallel operation of functional units; using fixed point two's complement representation for integers. The design was functionally verified by utilizing the ModelSim software package from Mentor Graphics Corporation Company and then synthesized by Xilinx Integrated Software Environment (ISE) 6.1 software. Preliminary results show that the overall system delay is less... 

Harmonic pollution minimisation in voltage-source programmed pulse-width modulation (PPWM) inverters is defined as a time-limited optimisation problem in real-time applications with variable DC sources. In order to obtain minimum total harmonic distortion (THD) as the objective function, shuffled-frog-leaping algorithm (SFLA) is modified and employed to calculate the switching angles and compared with non-linear programming as a traditional optimisation method. In addition, particle swarm optimisation and three of its modified versions as popular evolutionary optimisation algorithms are employed to ensure the capability of the proposed optimisation method. Moreover, modified sinusoidal PWM... 

In systems with hysteresis behavior like Shape Memory Alloy (SMA) actuators and Piezo actuators, an accurate modeling of hysteresis behavior either for performance evaluation and identification or controller design is essentially needed. One of the most interesting hysteresis none-linearity identification methods is Preisach model which the hysteresis is modeled by linear combination of hysteresis operators. In spite of good ability of the Preisach model to extract the main features of system with hysteresis behavior, due to its numerical nature, it is not convenient to use in real time control applications. In this paper a novel artificial neural network (ANN) approach based on the Preisach...