فصلنامه مکانیک هوافضا
سال دهم شماره 3 (پیاپی 37، پاییز 1393)

Effects of embedded Shape Memory Alloys (SMA) on free vibrations of sandwich-composite panels with a flexible core are investigated. Embedded SMA Wires, according to the characteristics of these alloys, can be effective on frequency and vibration’s behavior of these structures. At this study, the SMA wires (NiTiNol) are symmetrically embedded at mid-plan of top and bottom faces which is composite multilayer. For investigation of the effects of various parameters of this wires on natural frequency and shape mode, at the face plates the first order shear deformation theory (FSDT) and for flexible mid-core the Improved high-order theory of sandwich plates (IHSPT) are used so that inertia effects of middle core and face plates are fully considered. Equations for simple boundary conditions, is obtained analytically using Hamilton's principle. Recovery stresses generated by the excitation of built-in SMA wires, is assumed as the work of external forces. Result partial differential equations (PDE) by applying the Galerkin method simple and dissolved.

In this paper a new approach for control of Drive mode of a MEMS Vibratory gyroscope is developed, which enables estimation of the input rotation rate. Using this algorithm, besides of estimation of the input rotation rate, the spring and damping coefficients of the system will be obtained online. The methodology of the algorithm is very simple, and can be implemented successfully when the noise of the measurements are small. Results of the simulations show effectiveness of the method.

Cavitations phenomenon is one of the sources of inefficiently operation in a centrifugal pump and also cause reduction in capacity of the pump, decrease in head, blade erosion and corrosion, structure vibration and noise. This paper presents a method for cavitation monitoring of pumps using vibration signal analysis of a centrifugal pump. In this study, cavitation phenomena in centrifugal pump have been simulated by an experimental setup. Vibration signals of the pump have been measured during cavity inception and propagation. Finally, the cavitation effects on the parameters extracted from vibration signals using conventional and advanced signal processing methods in time, frequency and time-frequency domain have been investigated. The results indicate sensitive parameters to cavitation in pump which can be used to design a cavitation condition monitoring system based on vibration signals.

Torsional vibrations analysis of the crankshaft at the diesel engine set is accomplished by AVL EXCITE software based on Holzer method. The parameters such as natural frequencies of torsional system, oscillating torsional torques operated on the divers components of crankshaft, angular displacement of crankshaft in free condition from one side, misfiring conditions, heat dissipated power in damper and transitional torque to the flywheel have been investigated in this research. Simulation results of torsional vibrations in the crankshaft of engine are compared with the experimental results. This comparison illustrates a good accuracy in the results of torsional vibrations modelling.

In this paper, dynamic response of the thick cylindrical shell subjected to mechanical moving pressure has been investigated. First, the equations of motion have been derived using the Hamilton’s principle and the first order Mirsky-Hermann theory.The effects of transverse shear deformation and rotatory inertia were included in the governing equations of the dynamic system. Theobtainedpartial differential equationshave been solved using the converted ordinary differential equations. With this method, the problem can be solved for various mechanical moving pressure loads.The Results of the present analytical method have been verified by comparing with finiteelementresults using ABAQUS Software. The Comparison of the results with the finite element method shows that the first order Mirsky-Hermann theory can predict the dynamic response of the thick cylindrical shell successfully. Also, acceptable results were obtained for dynamic response of long thick cylindrical shell in different dynamic loading position.

Almost all the MEMS gyroscopes are vibratory, and work based on Coriolis force. Analysis of MEMS Vibratory Gyroscopes with ring resonator is proposed in this paper. Different gyro resonators are developed in literature such as circle and 8 edge star. Analyzing these structures with ABAQUS, we introduce a novel 16 edge star resonator. Analytical and simulated frequency answers are compared. Through this ring equation instead of ring model with support and connections is validated. Also response of the system to harmonic input force with constant amplitude is determined.

In this paper, linear and nonlinear analysis of an airfoil with two degrees of freedom in incompressible flow is accomplished for experimental test. Respective equations are extracted by Lagrange's method and used Wagner’s theory to solve this equation in time domain. Two-degree-of-freedom flutter is a combination of bending and torsion vibration modes. A flutter mount system with flexure supports has been developed for flutter tests with rigid wings in wind tunnels. This current study is an experimental investigation into the behaviour of a 2DOF wing section with a flexible structural linearity and nonlinearity support in pitch and plunge motion without free-play. This support system must be providing a well-defined 2DOF dynamical system on which rigid wings can encounter flutter. A classical 2DOF flutter can be described as combination of bending and torsion vibration modes. Evaluation of the results of wind tunnel experiments and effective parameters show that increasing frequency ratio cause the speed of flutter to decrease but it reducedes to minimum value at a frequency ratio and then it increase. Furthermore, it is observed that with increasing the distance center of elastic-axis from leading edge flutter speed decreases.

In this paper, at the first time, dynamic response of double curved, single curved, flat and circular cylindrical composite shells with simply supported and clamped boundary conditions subjected to multi- mass impacts were studied based on the first-order shear deformation theory (FSDT). The mechanical strains were used according to Sander’s theory. Using a new linearized two degrees of freedom spring-mass system (linear form of Hertzian contact law) and complete solution model (nonlinear form of Hertzian contact law), the results are derived and compared with together. For additional verification, the results are compaired with the Abaqus finite element software and the latest available literature. The presented formulation is general and capable to analyses the cylindrical composite shells subjected to multi-mass impacts with arbitrary different masses, initial velocities and impact locations. In this investigation, the effect of geometrical and mechanical parameters, such as length to width ratio (a/b), length to radius ratio (L/R) and velocity of the impactor masses on the impacts response from both presented models are studied and compared with together.