فصلنامه مکانیک هوافضا
سال شانزدهم شماره 1 (پیاپی 59، بهار 1399)

The free and forced vibration of rotating FGM beam with piezoelectric layer using first order shear deformation theory and fixed-free boundary condition have been studied in this article. Rayleigh-Ritz method with Chebyshev series are applied to find the natural frequencies. The results showed the natural frequencies are increased as a result of increasing angular velocity or adding piezoelectric layer. More increasing the natural frequencies are caused by applying the voltage on piezoelectric layer or by increasing hub radius. Moreover, the dynamic response of the beam cause by initial conditions is studied. The frequency of the dynamic response was very near to the first natural frequency of the beam. The results had a good agreement with known reference and Abaqus software results. Also, the influence of harmonic, step and impulse force on forced vibration of the beam has been studied. Decreasing the vibration amplitude of the beam is caused by applying angular velocity and piezoelectric voltage.

In this paper, the attitude of high-speed projectiles has been estimated usingdata fusion of magnetometer and Micro Electro Mechanical Systems (MEMS) gyroscope. MEMS gyroscopes have the high error for high speed. Also, magnetometers have low accuracy due to the presence of Non-Earth magnetic fields. For this reason, data fusion of magnetometer and MEMS gyroscope have been suggested. Due to the nonlinearity of the system equations and observation, a nonlinear estimator must be used. The developed Kalman filter inserts an error by ignoring the high order sentences of Taylor's expansion, which cannot be ignored in fast nonlinear systems. Unlike the Kalman filter, the particle filter has good results for nonlinear systems. The biggest weakness of this filter is its high computational time, which limits its applicability. To reduce the computational time of particle filter, a particle swarm optimization algorithm has been used. The simulation results were evaluated using 100 samples of the test, which illustrates the desirable performance of the combined particle filter with the particle swarm optimization algorithm in the data fusion of gyroscope and magnetometer information in the estimation of angles.

In this paper, a navigation guidance law is designed based on a sliding mode control and harmony search algorithm to track a maneuvering target in three-dimensional space. Despite the high efficiency of classical guidance laws in target tracking without any maneuvering, in the presence of uncertainty, disturbance, the nonlinearity of dynamic systems and target maneuvering, robust navigation guidance is required. Hence, a sliding mode control method is used for designing three-dimensional robust navigation guidance laws. Besides, parameters of sliding mode control are determined by minimizing multi-objective fitness function, which is the summation of the relative distance between missile-target and yaw angle of the line of sight. To show the effectiveness of the optimal sliding mode method, the simulation results are compared with some other techniques such as Proportional Navigation Guidance (PNG) and Augmented Proportional Navigation Guidance (APNG). It is proved that both the performance and efficiency of the proposed regulated-sliding-mode-based guidance scheme have significantly improved in comparison with these methods.

This study aims to predict pressure oscillation in a full scale solid rocket motor from the measured data of a subscale one. Therefore, the oscillatory pressure in a subscale solid engine was measured using accurate and high resolution sensors and data acquisition system. The importance of this study is due to the roll of pressure fluctuations into the motor on generating vibrations in structure of the motor and its payload. The frequency of pressure oscillation in a solid rocket motor changes around the acoustic mode frequency which has inverse relation with the length of the motor combustor. Therefore, in the short-length motors the high frequency oscillations occur. In other words, a data acquisition equipment for a subscale solid rocket motor must be have high accuracy and resolution. In the present work, a piezoelectric pressure transducer and an accurate data acquisition system have been used. The frequency of pressure oscillation of the subscale motor was measured around 10 kHz that indicating coincidence of the acoustic mode frequency of vortex shedding and shows a good agreement with calculation using the existing analytical relation. In the end, the analysis of data was performed using proper signal processing tools such as FFT of oscillatory signals

Monopropellant thrusters are very popular in satellite propulsion systems due to their simplicity and reliability. A monopropellant thruster commonly consists of three major components: injector, decomposition chamber and nozzle. Fuel is injected over catalyst bed through an injector and decomposed there instantaneously. The resulting hot gases are expanded through the nozzle section and produce thrust. In this study a Hydrazine monopropellant thruster with Iridium based catalyst bed is analyzed numerically. To this end, one dimensional heat and mass transfer equations are simulated numerically inside the catalyst bed. Since, decomposed gases are not in thermal and chemical equilibrium with catalyst solid particles, two sets of equations are solved for solid and fluid phases (based on the Shankar et al. research). Additionally, a zero-dimension analysis is performed for convergence-divergence nozzle to compute thrust and specific impulse. Using this method, effects of particles size and decomposition chamber length on thruster performance are investigated. The related results indicate that, decreasing the catalyst particles, decreases optimum decomposition chamber length and increases specific impulse.

One-dimensional modeling of aircraft piston engines is one of the methods for studying their behavior and performance in different environmental conditions. In this research, the Rotax 914, an aerial Spark Ignition (SI) turbocharged engine, was modeled one-dimensionally to predict its behavior at different altitudes. To address this issue, the one-dimensional model of all engine components including air filter, carburetor, air manifold, inlet and outlet valves, cylinder and piston along with crankshaft, exhaust manifold and turbocharger were created in GT-Power software.Then by validating the model with the data provided by the manufacturer and ensuring the accuracy, the significant performance parameters of engine and turbocharger performance curves were evaluated for different flight conditions up to 30,000 feet. According to the results, the turbocharger prevented a dramatic decline in engine performance parameters up to 18,000 feet. However above that altitude, due to the compressor reaching the choking region, it is not possible to charge the required air and avoid severe engine performance loss. It was also observed, by studying the effect of ambient temperature changes on engine performance, an increase of 40 °C in the ambient temperature caused a 10% reduction in the braking horse power, and consequently, performance loss during climb period. The effect of changes in ambient temperature and altitude on engine performance varies so that, until the engine reaches the compressor's choking region, the impact of the ambient temperature variations is more perceptible, after that, the height factor will have a greater influence on the engine performance.

Differential wheeled mobile robot is constructed from two independent active wheels and a spherical passive wheel. This robot as a result of pure rolling and nonslip conditions of wheels is a nonlinear system subjected to nonholonomic constraints. In addition, this system is classified as an underactuated system. Trajectory tracking we have concentrated on is one of the most complicated problems in control of wheeled mobile robots. In the first step a kinematic model in which linear and angular velocity are supposed as system inputs has been presented. Then using a feasible reference trajectory for the first time a novel full state backstepping controller has been designed and unlike previous approaches the stability has been provided fully stated and globally. Next, a sliding mode controller which is based on input-output control theory has been suggested. The proof of stability of this controller has been presented as well. Then a feedback linearization controller as an efficient approach has been proposed with the aim of comparing the performance of the controllers. Finally, integrity and robustness of designed controllers against disturbances have been approved using MATLAB simulation and the obtained results are discussed.

This paper investigates a kind of non-diaphragm shock tube equipped with an innovative and new design valve that is capable of generating well-formed shock waves within a driven tube. Diaphragm shock tubes have the advantage of easy building and instantaneous opening. However, some limitations of this kind of shock tube such as the lack of repeatability without opening, the inability to adjust pressure ratio at a specified interval and the inability to automate the shock tube, caused a development on an automated shock tube. In the non-diaphragm shock tubes, the most important factor is the opening time of the shock tube inlet, which directly influence on the formation and uniformity of the shock wave formed in the driven. In this study, an innovative mechanism to achieve high-speed opening valve with an opening time of eight milliseconds (8ms) is proposed. Absence of any disturbances caused by a change in direction or rotation of gas and the opening from the center to the sides are two unique features of this automated non-diaphragm shock tube. Finally, in this investigation, the functional parameters of this non-diaphragm valve are calculated theoretically and compared with measured experimental data.