# مقالههای Aghil Yousefi–Koma

**توجه:**محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.

##### ۱Active Control of a Smart Fin with Piezoelectric Actuators: Simulation and EXperiment

اطلاعات انتشار:
سیزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۴

تعداد صفحات:
۷

An active control system for vibration suppression of a representative dynamic model of a typical fighter vertical tail was designed and implemented in simulation and experiment in this paper. Piezoelectric patches were employed as actuators in the model. The Frequency Response Function (FRF) of the smart fin was obtained from a Finite Element (FE) model. The corresponding transfer function was derived from the µ synthesis and an active control system was then designed to suppress the vibration of the fin model. Implementation of the control system in practice demonstrated significant vibration reduction of the smart fin.<\div>

##### ۲MODELLING OF A FLAPPING–WING MICRO AERIAL VEHICLE

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۸

This paper explores flapping flight as an effective form of locomotion for unmanned micro aerial vehicles (MAVs). In this paper a dynamic model of a flapping MAV is developed. We focus on a MAV with very limited wing kinematics and simple input control schemes. In particular, we parameterize wing trajectory based on biomimetic principles, i.e. principles that are directly inspired by observation of real insect flight. Flapping flight is analyzed from three different perspectives: biological, technological and control perspectives. Three specific aerodynamic effects are shown as the cause of a lift gain at low Re (Reynold’s number): the circulation generated by the rotation of the wing at the end of a stroke, the delayed stall due to the instationnarity of the movement, and finally the wake capture, as the wing re–enters the flow it has previously disturbed.<\div>

##### ۳NUMERICAL SIMULATION OF TARGET THICKNESS EFFECT ON THE PENETRATION OF STEEL PLATES

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۶

This paper presents a research work on rapid dynamics analysis where the main objective is the application of the finite element method to solve ballistic penetration problems using LS–DYNA. To achieve a reliable methodology in LS–DYNA code, several runs are performed and their results are compared with the experimental data. The main problem addressed here is the penetration of hardened tool–steel rod in steel plates with various thicknesses. In this paper the effects of target plate thickness in the ballistic limit and failure mode is also investigated.<\div>

##### ۴Robust Control of a Smart beam with Piezoelectric Actuators

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۸

In this paper, a robust control system is developed for a flexible beam with piezoelectric actuators (called Smart Beam). The active control system of smart beam satisfied desired properties for all admissible measurement and plant noises, disturbances and model uncertainties. Thus it is the best candidate for sensitive industrial, medical and etc. robot arms and bases a new concept in the use of smart structures in robotics. The Frequency Response Function (FRF) of the smart beam was obtained from a Finite Element (FE) model. The corresponding transfer function was derived from the Mu synthesis and several control schemes were then designed to suppress the vibration. Results showed the effectiveness of the control system in noise and disturbance rejection. Also, the control system performance in presence of plant uncertainties is studied. A comparative study showed significant advantages of the robust controller over conventional controllers.<\div>

##### ۵A NOVEL DESIGN OF MICRO UNDERWATER VEHICLES

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۶

Systems and mechanisms of motion and stability applied in underwater vehicles although various but almost all rely on a conventional structure and frame work. In this paper in pursue of presenting a new mechanism in term of moveability and performance, mainly biomimeticly inspired from fishes flapping and their movement principles particularly flatfish, a new idea is dealt with. In modelling phase using ADAMS we considered dynamic performance of the mechanism. On the other hand in order to take the flexibility of the fins into account, we used ANSYS as a meshing tool. Linking these two software packages the modelling stages are completed.<\div>

##### ۶ANALYTICAL AND NUMERICAL SYSTEM IDENTIFICATION OF A SMART STRUCTURE

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۷

This paper deals with analytical and numerical system identification (system ID) techniques of flexible structures with piezoelectric actuators (i.e. smart structures). Numerical system ID methods developed here are beneficial in optimization of location and size of actuators and sensors of the smart structure as well as control design and implementation. Accuracy verification of the numerical methods is performed using analytical system ID, which derives the dynamic model of the structure from differential equations. In the first numerical system ID technique, Finite Element Method (FEM) is employed to model the dynamic system and to obtain the Frequency Response Function (FRF). Then the µ synthesis technique is used to match a transfer function to the FRF plot. The other numerical method is developed by reducing the order of the FEM model, defining master nodes. The analytical FRF matches well with numerical simulations using FEM.<\div>

##### ۷Active Control of Smart Structures Using Neural Networks

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۹

A neural network based control system was designed and implemented for vibration suppression of a flexible fin with piezoelectric actuators. A new approach in choosing the number of tapped delays of neural networks is introduced. Smart fin vibration was monitored through tip acceleration, and piezoactuators were employed to suppress the vibration. The controller was examined against four cases of disturbances: dwell at the first and second modes, sine sweep, and random excitation. Results indicated that the flexural vibrations were suppressed for both dynamic modes.<\div>

##### ۸MODELING OF A CARANGIFORM ROBO FISH; SIMULATION AND EXPERIMENT

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۵

A fish–like propulsion system seems to be a helpful and efficient alternative for propelling in micro underwater vehicles (MUV). This paper present a Modeling, biomimetic design and fabrication of a small underwater robot driven by an oscillating foil. In order to get an underwater robot with high performance, the swimming method of some types of fish was studied and the mathematical and hydrodynamical model of a Bonito fish was extracted. It has the biggest ratio of velocity per length along the fish. Employing servomotors, oscillating mechanism, latex shell and plexy tail, a model of fish–robot has been fabricated and tested.<\div>

##### ۹Performance Control of Hybrid dynamical Systems

اطلاعات انتشار:
شانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۷

تعداد صفحات:
۶

Performance control of Hybrid systems through the use of Hybrid Automaton describing the system behavior, are the main focus of this paper. Hybrid dynamical systems are characterized by discrete event and continuous dynamics which have an interconnected structure and can thus represent an extremely wide range of systems of practical interest. A hybrid automaton is a formal model for a mixed discretecontinuous system. In this paper, a modeling framework as well as feedback control strategies and Analytical solution method for performance control

problems are introduced, and its implementation with illustrative application is presented.<\div>

problems are introduced, and its implementation with illustrative application is presented.<\div>

##### ۱۰Structural Modeling of a Flapping Wing Micro Aerial Vehicle

اطلاعات انتشار:
هشتمین همایش انجمن هوافضای ایران،
سال ۱۳۸۸

تعداد صفحات:
۴

The structural modeling of a micro aerial vehicle (MAV) is developed in this paper. The wing flexibility and complexity of its structure make the analytical solution of the mechanism be difficult and even unsolvable. However, the computational simulation is suggested as the alternative method. The ADAMS software was used to model joints and rigid ribs. Other flexible parts such as wings were modeled in ANSYS software at first and then were transferred to ADAMS by ANSYS–ADAMS connection interface. By several simulations and consideration, a simple model of a flapping bird was generated and deformation of its wings was investigated during flapping an approximately optimized by changing the number and position of the carbon ribs.<\div>

##### ۱۱Experimental Aerodynamic Analysis of a Micro Aerial Vehicle on the Testbed

اطلاعات انتشار:
هشتمین همایش انجمن هوافضای ایران،
سال ۱۳۸۸

تعداد صفحات:
۶

An experimental aerodynamic analysis of a micro aerial vehicle using the testbed has been conducted in this study. Following this purpose a testbed were designed and fabricated to simulate the real fight conditions. The testbed is a five degree freedom platform to simulate the actual flight conditions, with good approximation. Conceptual and detailed design of mechanical and electrical components is presented. Actual tests of a MAV flight have been performed using the testbed. Lift and thrust results were measured through various experiments. By using the testbed in different configurations the lift force was obtained based on MAV's velocity and angels of attack. The subtlety in the approach of this research can be narrowd to the way that it has used to measure flight parameters. Indeed the more real situation presented, the ore accurate results are derived. This is what has mainly addressed in this experimental attempt. It also helps the scientific researches to exploit more reliable and even easier results of studying MAVs' aerodynamics. Another achievement proposed as a result, is the capability of using testbed in different–sized spaces and for variety of MAVs in various dimensions. Finally, and aerodynamic analysis was carried out on a MAV and some of its parameters were optimized. To shed further light on this topic, changing the parameters of MAV like angle of attack and repeating tests, lift can be optimized or can made better. These results can be taken into account for flight controls and also for future designs.<\div>

##### ۱۲Attitude Control of MAVs using L1 Adaptive Algorithm

اطلاعات انتشار:
نوزدهمین همایش سالانه مهندسی مکانیک،
سال ۱۳۹۰

تعداد صفحات:
۴

PID controllers offer high performance for Micro Air Vehicles (MAVs), but they have to be tuned for each MAV and even for each flight test. Moreover, MAV dynamics changes by time and consequently, PID controller performance decreases. Thus, an adaptive control system that compensates these changes is developed in this research. On the other hand, the size of the autopilot system is an important factor. Many adaptive control algorithms suffer from the time consuming computation and need for high memory. In this paper an L1 adaptive controller is developed that self tunes to each MAV and compensates changes in the MAV during its flight. The proposed controller is both simple and efficient. This autopilot system controls the pitch angle through the elevator commands. The simulation results show the efficiency of the proposed control system.<\div>

##### ۱۳Development and Convergence Approve of a Robust Nonlinear Sliding Mode Observer for General Form of Nonlinear Systems

اطلاعات انتشار:
نوزدهمین همایش سالانه مهندسی مکانیک،
سال ۱۳۹۰

تعداد صفحات:
۴

Accurate measurement of state variables of a dynamic system is often not possible due to the high cost of sensors, the space limitation, sensor damages due to contact or hostile environments. In this research a modified robust sliding mode observer is designed to accurately estimate the state variables of nonlinear systems in the presence of disturbances and model uncertainties. The observer has simple structure but efficient observation in the state estimation of dynamical systems. Stability of the developed observer and its convergence is proven. It is shown that the estimated states converge to the actual state in a finite time. The performance of the nonlinear observer is investigated by examining its capability in predicting the motion of a single link flexible manipulator. The link is driven by an electric motor mounted in the joint. Simulation results demonstrate the ability of the observer in accurately estimating the state variables of the system in the presence of structured uncertainties and different initial conditions between the observer and the plant, with various inputs.<\div>

##### ۱۴Experimental System Identification of a Small Unmanned Aerial Vehicle

اطلاعات انتشار:
نوزدهمین همایش سالانه مهندسی مکانیک،
سال ۱۳۹۰

تعداد صفحات:
۴

In the synthesis of automatic controllers of an unmanned aerial vehicle (UAV) as for other dynamic moving vehicles, a mathematical model of motion should be used. Advanced utilization of the vehicle dynamics is only possible if a control system is designed considering as exact as possible characteristics of the vehicle. This paper aims to conduct a consequence of the systematic approach to identify a model identification of a small unmanned aerial vehicle in loitering flight, based on the input–output data collected from flight tests on a 1–m–sized model aircraft. A miniature system, which consists of the onboard Processing unit and sensory section, is equipped with a multichannel data logger associated with the data acquisition and estimation software. Because of the complex coupled, multivariable and nonlinear dynamics of the aircraft in general, the test flight is confined to loitering condition to develop linear SISO structures for both the lateral and longitudinal models. Using time domain system identification techniques, two fourth–order ARX (Auto Regressive with eXogenous input) models are successfully identified, and the performance analysis is carried out based on the flight test data. The validity of the identified model is verified by both time domain model prediction and frequency–domain response analysis.<\div>

##### ۱۵Analytical analysis of an electro statically actuated nano beam based on coupled stress theory

اطلاعات انتشار:
دومین کنفرانس بین المللی آکوستیک و ارتعاشات،
سال ۱۳۹۱

تعداد صفحات:
۷

When the size of the structural elements such as beams, plates, and membranes (used as components in micro or nano electro mechanical system) becomes small, both the experimental and atomistic modelling methods show a considerable size effect in mechanical properties of these structures. On the other hand, the classical continuum theories cannot predict this size dependent behaviour of micro and nano structures. This paper aims to find an analyticalresponse of an electro statically actuated micro beam using recently developed nonclassical methods named, the modified couple stress. Taylor expansion is used to expandelectro–statically force and the equation of beam is solved using Modified Variation Iteration(MVI) method analytically. Consequently, the response of the system under different DC voltages and the effect of number of Taylor expansion terms are analysed in the end of the paper<\div>

##### ۱۶Damage Detection in Bounded Fluid Loaded Plates UsingPiezoelectric Fiber Composite Generated LambWaves

اطلاعات انتشار:
سومین کنفرانس بین المللی آکوستیک و ارتعاشات،
سال ۱۳۹۲

تعداد صفحات:
۹

This paper focuses on damage detection in a bounded plate while damage reflection andboundary reflections arrive at the sensor simultaneously. The plate is assumed to be fluidloaded, so a proper Lamb mode, excited and received by piezoelectric fiber composite (PFC)transducers, is selected such that it is not affected by fluid loading. A dispersion and wavestructure study is done in order to select the Lamb mode, which is S1 at f.d=3.8 MHz.mm,with zero out of plane displacement. Having selected the proper mode, an experimental setupwhich is a 6.25 mm thick steel plate is prepared and equipped with a four element PFC transducer.It is experimentally shown that the excited S1 mode is not affected by fluid loadingwhile other excited modes are affected and attenuated. Two notches are placed on the platesuch that wave reflections from notches interfere with boundary reflection, thus a suitablesignal processing method is needed. It is shown that a correlation followed by signal differencecalculation can be used for detecting the notch reflection from boundary reflection.Moreover, Continuous Wavelet Transform (CWT) based signal processing can clarify the damage reflection from transducer response peaks in experiments, successfully.<\div>

##### ۱۷Comparison of the Performance of Helical and Normal Pin Fins

اطلاعات انتشار:
دومین کنفرانس بین المللی پژوهش در علوم و تکنولوژی،
سال ۱۳۹۴

تعداد صفحات:
۶

In many engineering applications, fin arrays are used as a method to increase heat transfer rate from a surface. The amount of heat transfer depends on film coefficient of the coolant fluid (e.g. air) which is a function of the flow regime. More turbulence in air flow results in higher amounts of heat transfer. Therefore, causing turbulence in air flow is desirable in many cases. A practical way to cause turbulence in air flow which is passing through an array of fins, is using helical fins instead of straight normal fins. In this paper, the performance of helical and normal fins, which are attached to a surface with a high temperature, is evaluated using numerical simulation. It should be noticed that the pitch length of helical fins must be in an appropriate range in order to obtain better functionality. We have done CFD analysis on several models of helical pin fin arrays with different pitch lengths, the optimum amount of pitch length is found. The results show that helical pin fins with specific optimum pitch length could be used to increase the amount of heat transfer significantly<\div>

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