Journal of Aerospace Mechanics
Year:2017 | Volume:13 | Issue:2 (48)|Papers Count:11

In this paper the behavior of a sensitive box to vibration, which connected to the vehicle by means of four undamped passive vibration isolator mounts, is studied using a ten DOF model to the road excitation. First, the governing differential equations are obtained using the Lagrange method, and the power spectral density (PSD) of the road profile is determined based on the ISO. The natural frequencies and mode shapes are extracted using modal analysis, and the response to the random base excitation is calculated based on random vibration theory. The root of mean square (RMS) is calculated by integration of PSD curve. The RMS of vertical acceleration of the box is plotted vs. the RMS of its relative vertical displacement by varying the stiffness of isolators in a real interval and the optimal stiffness is selected as the minimum point on the curve. The results indicate that the optimum isolator can be selected gardless of wheels and suspension system and the natural frequencies of isolator are between the natural frequencies of wheels and of suspension system. The RMS of acceleration the box has low sensitivity to the variation of the isolator stiffness around the optimum point.

In this paper, a mobile robot path planning method in unknown dynamic environment is presented. Obstacles are moving with variable velocities and their paths are not predefined The unknown motion data of the obstacles are detected when they come to range of robot sensors. In this method, position of goal point and it’s relative position and velocity vectors between robot and obstacles are used to navigate the robot such that the difference between robot and the goal position connected line to be minimized. The procedure continuously repeated to avoid obstacles and reach the goal. For calculation and simulation, The maximum speed of the obstacles are assumed lower than the maximum speed of the robot. Theoretical analysis and simulation in the MATLAB software show that the presented method is effective to avoid collisions with moving obstacles in a dynamic environment.

In this paper, at the first time, dynamic response of the curved sandwich shells with simply supported and clamped boundary conditions subjected to low velocity multi- mass impacts was studied based on an improved higher order sandwich panel theory. Using a new linearized two degrees of freedom spring-mass system and complete solution model, the results are derived and compared with each other. The presented formulation is general and capable to analyses the curved sandwich panel subjected to multi-mass impacts with arbitrary different masses, initial velocities and impact locations. In this investigation, the effect of geometrical parameters, such as length to width ratio (a/b) and thickness of the core to thickness of the shell ratio (hc/h), on the impacts response from both presented models are studied and compared together.

A homogenous plate with a high length to width ratio (2D model) and simply supported boundary conditions is assumed. The effect of panel curvature is considered and a non-linear deformation via Von Karman’s strains is taken into account. A frequency and flutter analysis of flat and curved plate under in-plane loads and thermal effects for the structure with temperature dependent properties has been performed. The first order piston theory is deployed to model supersonic aerodynamic loading. The system of non-linear PDE equations has been derived using the Hamilton principle and transformed into a set of non-linear ODE equations via the Galerkin method. By transforming the equations into the state space form and defining the proposed Jacobian matrix, eigenvalue analysis has been performed. The frequency and flutter analyses of a curved plate show that the effects of different environmental loadings are noticeable and have been carried out for the first time. The results show that the plate’s curvature has a profound effect on the instability boundary of the plate under supersonic aerodynamic loading. Also, Thermal property effected flutter domain.

In this study, dynamic response of an articulated vehicle carrying liquid in a circular cylindrical tank at steady state and transient maneuvers has been investigated. A sixteen degree-of-freedom nonlinear dynamic model of an articulated vehicle was initially developed, then it was validated using TRUCKSIM software for standard maneuver. Dynamic interaction between the vehicle and the liquid is studied using potential function method. In potential function method, the liquid free surface gradient subjected to roll angle and lateral acceleration of the semi-trailer can be determined with assumptions of non-viscous fluid flow and calculation the pressure gradient. The simulation results show the interaction between the vehicle dynamic and liquid. Further research shows that roll stability of the articulated vehicle carrying liquid is intensely affected by sloshing of the liquid and lower rollover stability limit is observed for this vehicle than the same vehicle carrying rigid cargo, especially under lane change maneuver.

In this paper, the propagation of the waves in the laminated composite plates which is subjected to low velocity impact is investigated using the finite element method. Considering a finite element model the governing equations of the problem are discretized and the mass, stiffness and force matrix are obtained. The governing equations of the plate and the projectile are solved in the time domain using the Newmark and Nicolson numerical integration method. The contact force is modeled using the modified Hertz contact law. The propagation of the waves in the plate with different sets of edge boundary conditions are studied in the numerical results. The node dependency of the results is investigated and the effects of boundary conditions of the plate on the maximum impact load are studied. Various results for the propagation of the wave in the time domain are presented and the time history of the contact force, impact time duration and second impacts are studies in the numerical results. The analysis of results indicates that the wave propagation depends on the boundary conditions of the plate and the layer stacking of the composite plate.

Identification and analysis of geographic and climatic conditions for scientific researches and strategic studies is one of the main issues in countries. Nowadays, the use of Unmanned Aerial Vehicle because of its safety and high performance has been widely used in many countries. Exact action of this system leads to obtain accurate data and thereby achieve critical information. Therefore, an appropriate control system and perfect control of the drone is important. In this paper, an intelligent control using Fuzzy- Genetic Algorithm is presented on longitudinal flight dynamics of an Unmanned Aerial Vehicle. In this approach, all the membership functions and fuzzy rules are extracted from genetic algorithm method to minimize the over shoot and the steady-state error of the system. Finally, an example is illustrated to compare the proposed method with the classical PID controller.

Electrical Generator has a vital and important role in vehicles, especially the vehicles with Multiplex data transfer system. Developing electric malfunctions can cause catastrophic damages to other electric and electronic systems. Therefore alternator fault detection and monitoring has a significant role to avoid developing faults in other systems. In this research alternator fault detection and monitoring has been done with data extracted from vibration signals using Adaptive Neuro Fuzzy Inference System (ANFIS). To accomplish this task, certain faults are made on the alternator deliberately. Then vibrations from each specific fault are gathered and stored for subsequent analysis. The faults consist of: one phase disconnection, disconnection of positive voltage of regulator, burning of one and two diodes of rectifier set. The vibration signals of healthy alternator as well as different faulty states are gathered from two piezoelectric sensors mounted on alternator body for 30 seconds and 1000, 1500, and 2000 motor RPM. For analyzing vibration signals wavelet packet decomposition in level one was used. The mother wavelet with maximum energy to Shannon entropy was selected as the best choice. First and second energy bands were computed and used as the feature vector to the designed ANFIS. Results shows the proposed ANFIS model was effective and it could predict different faults with perfect match.

In this study, using kinetic energy, strain energy and non-conservative forces work of the wing and flutter the governing equations of motion were derived through Lagrange’s method. The wing preforms as a Cantilever Euler-Bernoulli beam and unsteady aerodynamic lift and moment are considered in terms of Theodorsen’s function. The effects of rotor and its location, thrust force, blades angular velocity and air stream velocity on the wing flutter and dynamic stability of wing have been investigated. Numerical simulations are indicated that increasing the distance of the rotor location from tip of the wing, the amplitude of oscillations is increased and with dramatic reduction of flutter speed the instability can be observed in the system. The increasing of thrust force also results the increase of flutter speed and instability of the system. Furthermore, where the speed of air stream reaches higher than the flutter speed, instability occurs in the system.

Because of production process and constrains conditions, circular graphene sheet may be opposed to structural defect and pin hole, respectively. Some of the defects and pin hole on a circular graphene sheet can be considered as an eccentric hole on the sheet. Hence, analyzing behavior of circular graphene sheet with an eccentric hole is important. Free vibration of an eccentric annular graphene sheet, as the basis of any dynamical analysis, is studied. Nonlocal theory of plate is used to solve the problem and Trefftz method is used to model the free vibration of graphene with an eccentric hole. Effects of nonlocality and eccentricity are investigated on the natural frequencies. These frequencies are derived by singular value decomposition (SVD) method.