مقالات رزومه ولی الله غفاری

Usually, constrained lateral acceleration would have undesirable effects on the stability and performance of a guidance system. The composite nonlinear feedback (CNF) can be effectively used to improve the transient response of the closed-loop system in the presence of the constrained input. In this way, guidance law consists of an extra nonlinear term besides the conventional linear one. As a result, such a term adjusts the qualitative characteristics of the transient response. Meanwhile, the nonlinear term is a function of the rate of line-of-sight (LOS) angle which is not activated at origin and infinity. Thus it would be effective only in a specified region. In this paper, proportional navigation is employed for the linear term of the CNF-based guidance law. Therefore, a guidance algorithm is developed for tracking problems using the CNF idea. Applying the proposed guidance method, the closed-loop stability is analytically proved via the well-known Lyapunov stability theory. The suggested approach is simulated in a numerical example. Then the results are compared with an existing technique. As expected, guaranteeing closed-loop stability, in contrast to a similar method, the addressing scheme considerably improves the performance and transient response of the guidance system in the presence of lateral acceleration limitations.

In the guidance algorithms based on the line-of-sight (LOS) rate, the lateral acceleration commands are computed in such a way that the LOS rate is nullified. So, keeping constant the LOS angle, the condition in which the vehicle speed is greater than the target speed, the vehicle reaches the target position asymptotically. In this paper, a new guidance algorithm, based on the LOS angle, is presented for a typical guidance system. To this aim, considering the governed guidance equations and using the corresponding trigonometric relations, the proposed guidance law is transformed into an algebraic equation. Although the utilized guidance procedure is independent of the rate of LOS angle, the rate of LOS angle would equal zero instantly via applying the proposed method. Then, to illustrate the effectiveness of the idea, the derived mechanism is evaluated in a two-dimensional guidance problem. The advantages of the approach are shown in comparison with similar methods.

In this paper, a robust model predictive control (MPC) algorithm is designed for nonlinear uncertain systems in presence of the control input constraint. To achieve this goal, first, the additive and polytopic uncertainties are formulated in the nonlinear uncertain system. Then, the control policy is chosen as a state feedback control law in order to minimize a given cost function at each known sample-time. Finally, the robust MPC problem is transformed into another optimization problem subject to some linear matrix inequality (LMI) constraints. The controller gains are determined via the online solution of the proposed minimization problem in real-time. The suggested method is simulated for a second order nonlinear uncertain system. The closed-loop performance is compared to other control techniques. The simulation results show the effectiveness of the proposed algorithm compared to some existing control methods.

This paper concerns on guidance law design by considering of the actuator effect. For achieving this goal, the proportional guidance (PN) method would be modified via the back-stepping approach such that the closed-loop stability is guaranteed in the presence of the actuator dynamic. Thus, it is interested to improve the guidance system performance (for example the transient response characteristic and miss-distance error) by the proposed guidance algorithm. Hence, the PN guidance law would be corrected such that the closed-loop system is asymptotically stabilized. The suggested algorithm is numerically simulated in a typical guidance problem. The simulation results verify the effectiveness of the redesigned guidance technique in comparison with the PN method.

A proportional-derivative sliding-mode control (PD-SMC) scheme is addressed for tracking problem of a two-degree of freedom robot manipulator. The sliding-mode control (SMC) may be a robust method in presence of parameters change and system uncertainties. In a typical control problem, the proportional-derivative (PD) control law provides a fast response while the stability of the closed loop system is increased. Hence a two degree of freedom robot manuplator is considered. Then the asymptotic stability of closed loop system with the PD-SMC policy would be shown by using of the well-known Lyapunov stability theory. As a result of this paper, the asymptotic stability criteria would be checked in term of some simple matrix inequalities. Having satisfaction of such matrix inequalities in the tracking problem of the robot manipulator, the tracking error and its derivative would be converged to zero. In order to compare the results with the other control approaches, the controller parameters are firstly tuned in an optimization way via the genetic algorithm (GA) method. Then some numerical examples are provided to show the effectiveness and robustness of the PD-SMC in comparing with the existing methods.

In this paper, an ANFIS+PID hybrid control policy has been addressed to control a 6-degree-of freedom (6-DOF) robotic manipulator. Then its error convergence has been also evaluated. The ability to formulate and estimate the system uncertainties and disturbances along with system dynamics and rejecting the disturbances effect are some advantages of the proposed method in   comparing with the conventional ANFIS structures. The error convergence could not be proved in the ordinary ANFIS structures. But in the proposed method, the error convergence of the robot manipulator can be established under considering some mathematical conditions. The proposed control law is realized via parallel combination of ordinary ANFIS network and PID controller. The suggested method has been successfully applied in a 6-DOF robot manipulator system. Furthermore, in presence of uncertainties and  external  disturbances  error  convergence  would  be  justified  using  the Lyapunov-like  theorem and Barbalat lemma.

In this paper, an LMI based guidance algorithm is mainly addressed to design a model predictive guidance law in presence of the input acceleration constraint. For achieving this purpose, firstly, the model predictive guidance problem is mathematically formulated in a two-dimensional problem. In the proposed algorithm, the future behavior of the guidance problem can be predicted by using a dynamical model. At each certain time, the commanded acclamation would be determined while a typical cost function is minimized. In this study, an acceleration command proportional to the line of sight (LOS) rate is considered as the predictive guidance policy with unknown variable gain. Then the model predictive guidance problem would be translated into another minimization problem subject to some linear matrix inequalities (LMI). Hence such an optimization problem can be numerically solved at each known time in the real-time applications. Then the gain of the proposed guidance algorithm can be automatically updated. The proposed method will be used in a typical two-dimensional guidance problem. The simulation results will show the effectiveness of the suggested method in comparing with the existing guidance algorithms.

This paper is mainly concentrated on performance improvement and miss-distance reduction in a typical guidance system. These goals would be achieved by adding some attitude control motors (ACM) to the existing guidance algorithm. The ACM system usually contains some disposable thrusters, which are installed on lateral body of a vehicle. An extra force would be applied to the vehicle body through each thruster activation. Hence, it may cause a torque about the center of gravity. Then the induced rotation can be used to the attitude control. For increasing the agility and supplying the lateral acceleration in the end game phase, the lateral thrusters may be added to the guidance system. The yaw and pitch components of the line of sight (LOS) rates would be used to guide the vehicle with multiple actuators. For this purpose, a six degree of freedom vehicle model would be generated, considering the physical information, engineering assumptions, and adaptations images. The vehicle model would be firstly obtained by the DATCOM software. Then, the guidance system is numerically simulated in the MATLAB environment. The effectiveness of the proposed guidance method is shown compared with the existing algorithm.

The design of ship maneuvers in the early stages of ship design and operation is of great importance. Having a precise model of vessel maneuvers along with the coefficients in the maneuvering equations of ships, is essential for research on maneuverability of vessels, the design of a ship motion control system, and the development of ship maneuvers simulators. Over the past few years, there have been various models of maneuvering ships that can explain ship maneuvers with an appropriate approximation. The design of ship maneuvers in the early stages of ship design and operation is of great importance. Having a precise model of vessel maneuvers along with the coefficients in the maneuvering equations of ships, is essential for research on maneuverability of vessels, the design of a ship motion control system, and the development of ship maneuvers simulators. Over the past few years, there have been various models of maneuvering ships that can explain ship maneuvers with an appropriate approximation.