Journal of Aerospace Mechanics
Year:2016 | Volume:11 | Issue:4 (42) (DYNAMICS, VIBRATIONS AND CONTROL)|Papers Count:9

In this paper, free vibration of a functionally graded rectangular plate reinforced by carbon nanotubes have been investigated. The material properties of the composite plate have been calculated by the Mori-Tanaka model and the governing differential equations of problem have been derived using 3-D elasticity. For solving the differential equations of motion we used the generalized differential quadrature (GDQ) technique by regarding the appropriate grid points. Finally, by solving the numerical example for a simply supported plate, the frequency vibration of plate by assuming the variation of problem parameters (distribution of carbon nanotubes-properties of plate-geometrical features of problem) has been calculated. Also, the convergence of the method is demonstrated and to validate the results, comparisons are made with the available references.

Airbags are very important in reducing the impact on the aircrafts. Their main function is reducing the velocity to zero with the least impact on the vehicle. The aim of current study is two-fold. Firstly, using drop test, dynamical properties (stiffness and damping) of airbags are experimentally found. Secondly, with the suitable measurements, shock response spectrum is plotted to determine the severity of the applied shock in the dropping process. This is an appropriate means in analysis and design of airbags and it is carried out for the first time in the present paper. A drop test apparatus was used for carrying out the experiments, and the airbag in the drop process is modelled as a single degree of freedom model. To determine the shock response spectrum, numerical simulation is applied to solve the differential equation of motion. Using an empirical criterion and shock response spectrum data, critical region of the applied shock is obtained. This study shows that the drop test is an important technique in determining dynamical properties of airbags, and can be useful especially in aero, vehicle and many other industrial activities.

Interactions of the translational motion of a gyrostat satellite on its attitude dynamics is considered in this paper. The mathematical model is first derived using the Hamiltonian method for the rotation-Translation motion of the gyrostat satellite followed by the reduction of the coupled equations of motion using the extended Deprit canonical transformation. The analytical Melnikov method along with the numerical Lyapunov exponent criterion, Poincare' section, trajectories of phase portrait, and the time history responses are used to study the heteroclinic bifurcation and chaos phenomena on the reduced model. On the basis of the results obtained from Melnikov integral, the parameters of the gyrostat satellite can be designed to prevent chaos in the system in the absence of a control system.

In this paper a novel optimal and robust guidance law for three dimensional flying-object system is proposed based on the extended kalman filter. New guidance law consists of sliding mode and backstepping guidance laws. In this guidance law there are some coefficients that must be adjusted. These coefficients are adjusted using Genetic Algorithm (GA). Also system states are estimated by using of Continues Extended Kalman Filter (CEKF). Finally, proposed guidance law is compared with Augmented Proportional Navigation Guidance (APNG) law. Simulation results show that proposed guidance law is better than APNG law.

This paper is concerned with the design of an attitude control system for a suborbital module based on the pulse width and pulse width-pulse frequency modulators. The control algorithm is designed based on the quaternion error vector and performance of the two modulators is compared. Numerical simulation shows if parameters of PWPF modulator is tuned proper then the control effort decreases. Therefore this method proposed to implement in suborbital module.

In this paper, effect of order of the thruster transfer function is investigated for a single-axis attitude control of a rigid satellite using two sets of opposing thrusters. The thruster dynamics is modeled by a pure delay in series with an arbitrary-order transfer function (TF) consisting of similar first-order lags. For this purpose, bang-bang controllers, bang-bang with dead zone, Schmitt-trigger and PWPF modulator are used in the analysis. The thruster dynamics order is selected using existing empirical thruster profiles. Considering the empirical profiles, usually a TF’s order lower than 2 is not recommended. Simulation results show that the TF’s order may be considered as an uncertainty applied to the attitude control problem and its sensitivity analysis.

In this paper, behavior of the aircraft with flexible wing in dealing with atmospheric disturbances has been modeled and analyzed. In this research, material of wing is metal and wing has been modeled as a thin-walled (wing box), as well as wing mass distribution, shape modes and frequency is calculated by lumped mass and assumed mode shape method. For analyzing the effect of aircraft mass on the vehicle behavior, four models with different mass are simulated until critical condition is determined. Atmospheric disturbance is a undesirable input to aircraft dynamic where decrease flight safety therefore, the effect of this phenomena are analyzed as a random input on aircraft behavior. The using model for atmospheric disturbance is Monte Carlo model where the method of modeling is submitted. The effect of this disturbance has been simulated in two conditions. In the first simulation, intensity of turbulence is 100 ft/sec and intensity of the second simulation is 400 ft/sec until the turbulence that makes instability is assigned.

Earthquake is one of the natural disasters with the potential of catastrophic damages. One of the best reinforcement solutions in building is the usage of vibration controller that reduces the vibration and its displacement magnitude significantly. Controller could be an active or passive system that which is used in multi degree of freedom structures subjected to earthquake in order to control and reduce the vibrations. To investigate the behavior of the structure, a PD controller designed for a passive control. Also fuzzy and optimal controllers are designed for an active control device. The advantage of the optimal controller approach is its robustness and ability to handle the non-linear behavior of the system. The results showed that the optimal controller has better performance in comparison with fuzzy and PD controllers.

In this research is prepared the optimum design muffler code for maximum silence in perforated muffler to use in APU exhaust. According to far Annex 16 the power of sound (SPL) must be less than 90 dB on ground from aircraft. One of the sources of noise on ground is the exhaust noise of APU. The APU is used for product pressurize air for main engine start and air condition and for produce electric energy. So the muffler must be use in APU exhaust. In this paper was studied the method of calculation and effective parameters on transmission loss. After that, a code was produced for design muffler with respect to limitation of dimension and designer requirement. For verification of design code, the result of this code was compared with test result. By this code the muffler was designed for respective aircraft by attention to limitation of situation.