Abstract: The composite materials are well known by their excellent combination of high structural stiffness and low weight. The main feature of these anisotropic materials is their ability to be tailored for specific applications by optimizing design parameters such as stacking sequence, ply orientation and performance targets. Finding free torsional vibrations characteristics of laminated composite beams is one of the bases for designing and modeling of industrial products. With these requirements, this work considers the free torsional vibrations for laminated composite beams of doubly symmetrical cross sections. The torsional vibrations of the laminated beams are analyzed analytically based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes due to fiber orientation of the laminated beams are neglected. Also, the torsional vibrations of the laminated beams analyzed by shear deformation theory in which the shear deformation effects are considered. Numerical analysis has been carried out using finite element method (FEM). The finite element software package ANSYS 10.0 is used to perform the numerical analyses using an eight-node layered shell element to describe the torsional vibration of the laminated beams. The rotary inertia and shear deformation effects of the element are taken. The influence of fiber directions and stacking sequences of laminates on torsional natural frequencies were investigated. Also, the effects of boundary conditions are demonstrated. Numerical results, obtained by the ANSYS 10.0, classical lamination theory, and shear deformation theory are presented to highlight the effects of fibers orientation and layers stacking sequence on torsional frequencies of the beams. The results obtained by ANSYS are compared against the classical lamination theory, as well as shear deformation theory.

Abstract: Vibration analysis of most critical equipment is considered as one of the most challenging activities in preventive maintenance. Utilities are heart of the process in big industrial plants like petrochemical zones. Vibration analysis methods and condition monitoring systems of these kind of equipment are developed too much in recent years. On the other hand, there are too much operation factors like inlet and outlet pressures and temperatures that should be monitored. In this paper some of the most effective concepts and techniques related to gas turbine vibration analysis are discussed. In addition, a gas turbine SIEMENS 162MW- V94.2 vibration case history related to Iran power industry in Fars province is explained. Vibration monitoring system and machinery technical specification are introduced. Besides, absolute and relative vibration trends, turbine and compressor orbits, fast Fourier transform (FFT) in absolute vibrations, vibration modal analysis, turbine and compressor start up and shut down conditions, bode diagrams for relative vibrations, Nyquist diagrams and waterfall or three-dimensional FFT diagrams in startup and trip conditions are discussed with relative graphs. Furthermore, Split Resonance in gas turbines discussed in details. Moreover, some updated vibration monitoring system, blade manufacturing technique and modern damping mechanism are discussed in this paper.

Abstract: The present paper emphasizes on the estimation of natural frequencies and mode shapes of a shaft supported by more than three bearings. In advent of this, a counter shaft of already developed experimental setup has been considered. The natural frequencies and mode shapes of counter shaft are deteremined analytically by adopting Holzer's method and the results obtained are then compared with the results of software based approach. By adopting the same method, Stresses in the shaft and amplitudes of rotors are also estimated. Based on the obtained data the generallised mathematical models have been formulated for the prediction of stresses in shaft and amplitudes of rotors. Significant independent variables which influence the phenomenon i.e. development of stresses and amplitudes of rotor have been accounted in terms of a group of pie terms. These group of pi terms are accoplished with the help of dimensional analysis technique and they are used to formulate the mathematical models. In this paper the qualitative and quantitative analyses of the established mathematical models are also carried out.

Abstract: This paper presents active amplitude control methodology of a turbocharger rotor using the electromagnetic actuator design. Vibrations in such high-speed engine rotors are inevitable especially while crossing the critical operating speeds. From durability considerations, the rolling element and journal bearings are now-a-days replaced by compliant gas bearings. In present work, the rotor is discretized as a finite element model comprising three Timoshenko beam elements with consideration of gyroscopic effects. Unbalance and gravity are considered as the external forces. Dynamics response of the rotor is obtained by solving resultant dynamic equations using implicit time-integration scheme. An in-house program developed first computes critical operating states and with the help of existing theory of electromagnetic actuators, the vibration amplitudes of system are minimized by providing calculated additional external forces. Control led vibration amplitudes at a disk node is illustrated.

Abstract: Dam-break flows can be described as the flow caused by the sudden release of a contained portion of fluid. Many environmental flows can be modeled as dam-break flows. In this study, the unsteady 2D dam break problem is solved by weakly compressible SPH with water as a Newtonian fluid and a thixotropic gel as a non-Newtonian fluid. In this method, the flow domain is replaced by several representative particles and the mass and momentum conservation equations are solved in a Lagrangian frame work for each representative particle. First, the Newtonian case is verified with previous numerical and experimental published results. Then the thixotropic gel is modeled by Moore rheological model and several simulations are performed to investigate the effects of the model constants. Furthermore, the differences of Newtonian and thixotropic fluid flow including free surface shape and leading edge position are mentioned.

Abstract: Chatter is a issue of uncertainty in the metal reducing procedure. The trend is characterized by aggressive oscillations, noisy sound and low quality of surface finish. Chatter causes a reduction of the life of the device and affects the efficiency by disrupting the regular functioning of the machining procedure. This paper presents a coupled model of high-speed end-mill spindle system by considering the dynamics of angular contact ball bearings and cutting forces. Initially, the spindle device is examined by considering the gyroscopic and centrifugal terms using Timoshenko beam theory. Hertz bearing contact forces considered at front and rear side ends of the spindle. Frequency response functions at the tool-tip are obtained from the dynamic spindle model. In the second phase, solid model of the system is developed and its dynamic response is obtained from three dimensional finite element analysis. After, verification of the outcomes with beam theory concept, the stability lobes are plotted from the tool-tip frequency response (FRF). Later parametric analysis are conducted for different tool-overhang measures, bearing span values and helix angle of the cutting tool conditions to effectively plot the stability lobes for the spindle system.

Abstract: One of the most promising materials for nanotechnology is annular Boron Nitride sheets (ABNSs). In this study, however, differential quadrature method (DQM) and nonlocal piezoelasticity theory are used to investigate the nonlinear vibration response of embedded single layered annular Boron Nitride sheets (SLABNSs). The interactions between the SLABNSs and its surrounding elastic medium are simulated by nonlinear Pasternak foundation. A detailed parametric study is conducted to elucidate the influences of the nonlocal parameter, elastic medium, temperature change and maximum amplitude on the nonlinear frequency of the SLABNSs. The results are in good agreement with the previous researches.

Abstract: Accurate prediction of critical speeds in rotating machinery is of great importance to designer and many attempts have been made to calculate it exactly. At the design stage it is necessary to predict accurately the dynamic behavior of rotating system of rotating parts of Wankelengine in order to avoid resonant conditions at operating speeds. Critical speed of a rotating shaft differs from its non-rotating natural frequency. The main reason for this difference is known to be the gyroscopic momentum. So it is quite great important to determine the natural frequency of the eccentric shaft in non-rotating condition (free-free condition) i.e. degrees of freedom are not restricted. In this study the natural frequency and mode shapes are predicted for the eccentric shaft in free-free condition (non-rotating) by using the commercial software package (ANSYS) in its modal analysis option. And results obtained from it are compared with experimental modal analysis (FFT analyzer). The verified results leads to the prediction of the dynamic behavior of the eccentric shaft viz. design calculations, natural frequencies, mode shapes.

Abstract: In this research, numerical and experimental static and low velocity impact behaviors of sandwich structures with composite skins and Nomex™ honeycomb core is presented. By using ABAQUS/Explicit, a three-dimensional finite element model of sandwich panels with glass/epoxy skins and a Nomex™ honeycomb core have been obtained. By doing quasi static and dynamic experiments, indentation forces, applied to the structures and also the vertical displacements, resulted due to the applied forces, are measured. Finally, the results validation and also the parametric studies will be done to study the effects of different parameter variations. The comparison has not only been based on a load–displacement curve, but has been further exemplified by detailed photographical images, throughout the whole loading process of the local behavior of the cells crushing.

Abstract: In manufacturing an engine, it is needed to evaluate the engine performance. This is performed in test cell. During the test, a significant portion of fuel energy is wasted. In this work, an Organic Rankine Cycle (ORC) is used to produce electrical power from the waste heat of the engine test cell. To achieve the best results, different working fluids are examined in ORC and performance of the system is determined for each case from the energy and exergy viewpoints. Finally a parametric study is done to reveal the effects of some decision variables on the performance of the system. The results show that selection of different working fluids in ORC has considerable effect on energy and exergy performance of the system. It is concluded that, the system with R123 as a working fluid for the organic rankine cycle, has the highest work produced, among considered working fluids, whereas R11 results the highest energy and exergy efficiency for heat recovery process. Also, the results of parametric study reveal that, increasing evaporator temperature increases produced work and exergy efficiency while increasing condenser temperature, pinch point temperature difference in the evaporator and degree of superheat at ORC turbine inlet decreases produced work and exergy efficiency.