Journal of Aerospace Mechanics
Year:2019 | Volume:14 | Issue:4 (54) |Papers Count:8

In this paper, at the first time, free vibration and buckling analysis of the cylindrical sandwich panels whit flexible cores and Magneto-Rheological Fluid Layers for simply supported boundary conditions are studied based on an improved higher order sandwich panel theory. In order to validate the results, the obtained results were compared with those obtained using finite element ABAQUS software. In this investigation, the effects of magnetic field, geometrical parameters such as the length to radius ratio, the core thickness to panel thickness ratio, MR layer thickness to panel thickness ratio and Fiber angle on the natural Frequency, buckling Load and loss factors of sandwich structure were investigated. The results suggest that the natural frequencies, critical buckling loads (eigen values) and the modal transverse displacements (eigen vectors) of the cylindrical sandwich panels whit flexible cores and Magneto-Rheological Fluid Layers in the face sheets are strongly influenced by the intensity of the applied magnetic field.

The main purpose of this study is to determine the initial configuration of suborbital manned spacecraft in the conceptual design phase. During the suborbital flight path, stability of capsule is very important factor for the success of the mission. For this purpose, in this study using conventional manned spacecraft geometries which are generally blunt-cone shape, 5 configurations of space capsule are proposed. The configurations are numerically investigated during reentry phase at altitude of the 25 km from earth surface with Mach number 3.15 for different angles of attack. In order to determine longitudinal static stability characteristics of configurations during re-entry phase, the pitching moment coefficients of configurations are studied and compared to each other. Finally, the optimal configuration of the space capsule considering system requirements and base on the suitable static stability and volumetric efficiency is proposed.

Traditionally, contribution of the motion system in motion cueing algorithm is carried out by a simplistic representation of a set of operational space related state variables. Neglecting the nonlinear inverse kinematics of the motion system as the fundamental part of motion cueing system is an unrealistic simplification with undisclosed consequences. In this paper, the complete motion cueing (MC) potential of the simulator in a more realistic manner is investigated by directly penalizing the general nonlinear inverse kinematics of the motion system. The developed real time model predictive control (MPC) motion cueing strategy enables the faithful reproduction of the perception of motion along with effectively constricting the motions within the limited workspace of the motion system. The partially linearized inverse kinematic model of the motion system specifically developed for the purpose of this study along with the constant coefficient inverse kinematics model at particular so-called neutral state value are employed to examine the performance of the motion cueing based on general nonlinear kinematical model. The results of conducted comparative simulations reveal that nonlinear MPC-based motion cueing algorithm enables more effectively handling the platform workspace while faithfully reproducing the realistic perception of motion with no complicated computational burden.

Graphene sheets have gained much popularity and strong potential applications in design of nano-sized structural elements. Because of production process and constrains conditions, circular graphene sheet may be opposed to structural defect. These defects can be inverted to greater holes as amorphous construction when the graphene sheet is working in room temperature. Some of the defects and pin holes on a circular graphene sheet can be considered as multiple eccentric hole on the sheet. Hence, analyzing behavior of circular graphene sheet with multiple holes is important. According to high surface to volume ratio in single layer graphene sheet, surface effect is not negligible, should be considered. Free vibration of an annular graphene sheet, as the basis of any dynamical analysis, is analytically studied. Multipole Trefftz method as well as the translational addition theorem are employed to consider effects of circular defects on behavior of freely vibrating circular graphene sheet. Kirchhoff plate theory is used to solve the problem. Effects of surface effect parameter are investigated on the natural frequencies. These frequencies are derived by minimum singular value decomposition (SVD) method.

In this paper, the effect of van der Waals force and size-dependent on dynamic stability is studied for single degree of freedom model of torsional electrostatic micro/nano mirror. First, the equation of motion of system is derived and applying state space method, dynamic equations are solved and desired results are obtained. The pull-in parameters including tilting angel and voltage are considered and their dependency on van der Waals force and size effect is investigated. As well as results show that eqilibrium points of dynamic system include center points, stable focus points and unstable saddle points. The phase portraits related to these equilibrium points created periodic orbits, heteroclinic orbits, and homoclinic orbits. Furthermore, in present study, using modified couple stress thoery the influence of size effect on amplitude and frequency of system is considered. Obtained results show that the model presented in this paper is very good agreement with experimental results.

Inertial Navigation Systems are one of the most important systems used to determine position, velocity and attitude ofmoving vehicles such as ships, airplanes, missiles, and so on. The base of this science is Newton’s laws. In these systems, three accelerometers and three gyroscopes are used to measure linear accelerations and angular velocities of vehicles, respectively. By using of output of these sensors and special inertial algorithms in different frames, parameters of vehicle such as position, velocity and attitude are calculated. In this paper, firstly, different frames such as body, inertial, ECEF and NED coordinate system are introduced. Then algorithms of inertial navigation in these frames are proposed and diagrams of navigation in any coordinate system will be presented in suitable method. In the following, simulations of INS in inertial, ECEF and NED frame are carried out by Simulink software. For this purpose, three different motion scenarios in two and three-dimensional coordinates are investigated and their simulation results will be brought. The results of simulation show that the algorithms of inertial navigation in different frames have good performance and suitable accuracy in navigation. Also for simulation of any other motion scenarios, navigation of vehicle is done by outputs of accelerometers and gyroscopes and presented simulator profile. At the end of this paper, performance evaluation of inertial navigation systems, general model of inertial sensors and integration between INS and GPS using Kalman filter will be noted.

One of the main concerns in flight performance is to determine the highest level of capabilities for flying vehicles to perform the assigned missions. The objective of the current research is to utilize the maximum aerodynamic and propulsive capabilities of a flying robot. In this regard, the problem of optimal performance during all phases of a mission profile is proposed. By integrating a multi objective heuristic optimization algorithm with constrained optimization approaches, all phases of a typical mission profile have been optimized. The major advantage of the proposed approach is that it provides the optimal time history for all state variables as well as the optimal flight path and the amount of required fuel.

Bearings are the most important and most used components in different industries. Early bearing fault diagnosis can prevent human and financial losses. One of the best methods for fault diagnosis of these elements is via vibration analysis. In this paper Empirical Mode Decomposition (EMD) which is a fairly new signal processing method of nonlinear and nonstationary signals is used for analyzing vibration signals extracted from bearings. This method was proposed by Huang in 1998. In this research, extracted signal from healthy and faulty bearings are decomposed in to empirical modes. By analyzing different empirical modes from 8 derived empirical modes for healthy and faulty bearings under different load conditions from zero to three horsepower, the first mode has the most information to classify bearing condition. From the first empirical mode six features in time domain were calculated for healthy bearing, bearing with inner race fault, bearing with outer race fault and bearing with ball fault. These eight features were used as input vector to a designed ANFIS network for bearing condition classification. The ANFIS network was able to detect different condition of bearing with 100% precession.