Journal of Aerospace Mechanics
Year:2014 | Volume:10 | Issue:1|Papers Count:11

In this paper, dynamical modeling of a gyro stabilized platform in the presence of angular motions of the vehicle is studied. After introducing the computational models, the system is simulated first in an uncontrolled and then in closed loop mode using PID & LQR controllers, separately. Results show that both PID & LQR controllers have good capability to stabilize the gyro stabilized platform and can provide a fast and over damped process for it.

Adaptive cruise control (ACC) and stop-and-go scenarios are example of problems related with longitudinal control. Driver assistant systems currently under development by the most automotive manufactories around the world. This Research describes a vehicle speed & vehicle-to-vehicle distance control algorithm for vehicle cruise control and also vehicle stop-and-go cruise control. So first, a complete dynamic model of car has been simulated that consists of an SI engine, automatic transmission and tire. The vehicle longitudinal control scheme consists of a speed control algorithm and a distance control algorithm and throttle-brake control law. A desired acceleration for the vehicle has been designed using linear quadratic optimal control theory. It has been shown that the two proposed control laws provide good performance.

Dynamic response (transient vibration) of a magnetorheological elastomer (MRE) based simply supported sandwich beam under various transient loads is investigated. The MRE is modeled as a Kelvin-Voigt viscoelastic material. Hamilton’s principle in conjunction with the classical Euler-Bernoulli beam equations and linearized compatibility relations of sandwich beams with transversely flexible cores is used to derive the equations of motion and pertaining boundary conditions. Fourier series and Durbin’s algorithm for the inversion of Laplace transform are used to solve the equations of motion for different transient loads (i.e. impulse, moving load, and uniformly distributed harmonic load) in different magnetic fields. Limiting cases are compared with the data in the classic literature as verification

Nonlinear models of the flow control valves relate the control flows through the valve ports to the valve parameters. An integrated model covers thoroughly the critical-lapped, over-lapped and under-lapped valves. The non-equality of spool lands and incorrect null position of spools can also be simulated using this model. Moreover, the simplified model can be used base on some assumptions for ease of analysis. In this paper, an accuracy analysis is performed to compare a fully nonlinear valve model to the conventional simplified one. According to the second order linear model of a servohydraulic system, a non-dimensional analysis for the fully nonlinear model shows that the accuracy of the model is independent of the specific categories of its parameters. In fact, the model error for a certain amount of hydraulic damping coefficient does not depend on the model parameters, such that a combination of these parameters leads to a constant damping coefficient. Therefore, the accuracy of the model can already be determined using simulation. This point provides a high flexibility to the hydraulic control system designer to put up the possibility of using simplified models without any need to determine the model errors. Because the hydraulic systems are barely driven beyond the scope of the desired frequency, it can be concluded that for some applications, the simplified model of the valves can accurately express the valve dynamic.

A control algorithm for preventing vehicle from spinning and drifting and improving its handling, has been carried out by applying correction angle to the steered wheel, which is based on the optimal and adaptive theory, has been proposed in this paper. The nonlinear 4DOF model is initially developed; then it is simplified to 2DOF model with reasonable assumption to design observer and optimal controllers. Then a simplified model developed for steering system. The numerical simulation has been carried out, using a vehicle parameters for standard maneuvers in dry and wet roads. Simulation results show obviously the effects of nonlinear adaptive optimal controllers also on vehicle handling, moreover a hardware in the loop method has been applied to prove the controller ability in realistic situation.

The paper concerns with the identification of the surface and subsurface defects based on Lamb wave generation and propagation in a structure with piezoelectric wafer active sensor. The piezoelectric wafer acts as an actuator at the initial instant for Lamb wave generation and then as sensor to monitor Lamb waves reflected from different surfaces of the structure. A finite element model is developed to analyze the response of the structure and piezoelectric wafer subjected to initial activation signal. The model simulates the generation of Lamb waves which are divided into symmetric and anti-symmetric waves propagating with different velocities. The reflection of Lamb waves from exterior surfaces of the structure or the surfaces of the defects are identified using the present model. The performance of the damage identification procedure is evaluated for a plate structure with single or multiple transverse grooves whose dimensions are very small compared to structural dimensions in order to simulate the transverse cracks in the structure. The results have shown that Lamb waves are very sensitive to transverse grooves and determine the location of transverse damages with a reasonable accuracy.

In the present paper, the transverse vibrations of Euler - Bernoulli beam along with the poor dry friction at the boundary conditions has been investigated. With special attention to the force of friction on the boundary conditions which plays a role as one non-linear factor and brings out nonlinear response, Natural frequencies also change despite the linear systems and these natural frequencies become a function of the force of friction and the force of friction in substrates also is a function of other parameters. The Calculation of the beam frequencies and the proper modeling of boundary conditions have been interesting for the researchers and scientists. Under present study, the force of friction at substrates is investigated through the friction force modeling by using nonlinear elastic - plastic Valanis model and also by the Classical Model of Coulomb friction. The assumed modes method for solving was used and the resulting equations by using Fourth Runge-Kutta numerical method have been solved. These two models have been compared and the results of modal testing were used for the validation. Finally, according to Valanis parameters, it was shown that this model has a positive relation with findings. Due to the weak of force of friction on the substrate, the softening effect of the frequency response-curves was observed.

In this paper, a new guidance law for yaw channel of homing interceptors is designed. Because of using the sliding mode theory, the nonlinear equations of motion are used and the target acceleration is considered as an uncertainty. Therefore, the precise measuring or estimating of target acceleration is not required and only the upper bound of target maneuvers is used. A sliding surface is defined using the angle rate of the interceptor-target line of sight. For producing a smooth control signal and removing the chattering of the guidance commands, the discontinuous term of guidance law has been approximated with a continuous function. Adjusting the parameter of sliding term leads to decreasing the missile control effort, the time of flight and velocity loses. Simulation results in the presence of a real control system dynamics of a homing interceptor show the effectiveness and robustness of the designed guidance law against maneuvering target in comparison with the proportional navigation algorithm.