Journal of Engineering and Thermal Sciences
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Investigation of vibro-acoustic properties of modern lathe collet chuck
Get PDFManufacturing industry has been attempting to attain the required cutting performance in order to achieve high precision, fast productivity and lower maintenance costs. Vibrations generated during machining can be a serious problem degrading component quality, precision, tool service life, lathe performance and cutting rates. This paper is concerned with analysis of cutting process by using modal testing. Static and dynamic deformations of lathe collet chuck have a significant impact on cutting process stability, which affects workpiece quality and production output. Modal analysis was applied to develop a mathematical model of chucks dynamics, which consist of a number of mode shapes each with natural frequency and modal damping. Modal analysis and experimental measurements were performed on a collet chuck of CNC lathe installed in metal working company UAB “Stevila”
Frequency analysis of chatter vibrations in tandem rolling mills
Get PDFChatter in high speed tandem mills affects the quality of the product and the production rate of the rolling mill. It may also cause damage to mill components and strip rupture. To monitor chatter generation within the rolling mill, it is highly recommended to use online chatter detecting systems. This paper presents a set of guidelines to optimal control and prevention of chatter in rolling mills. Investigation is based on experimental results of the third octave chatter in a two-stand tandem rolling mill. Online vibration monitoring system that was used has provided different acceleration signals from various components of the rolling stand. Acceleration signals have been analyzed by a vibration analysis toolbox. Frequency analysis and signal processing techniques were used for examining the vibration data. From frequency spectrum analysis it is found that the prominent frequency in the vibration spectrum of the upper backup roll is the most significant one. It is demonstrated that the upper backup roll and top housing are more sensitive to chatter than the work rolls and they are suitable locations for installing the permanent acceleration sensors for chatter warning system
Free flexural vibrations of a piezoelectric bimorph plate with periodic edge conditions
Get PDFThis work analyzes the vibrations of a fully-electroded annular piezoelectric bimorph plate with a free inner edge and an outer edge that is built-in with a periodicity. To this end, a variational formulation with the extensive use of Lagrange multipliers for a bimorph plate with polar orthorhombic symmetry is performed first. The mechanical displacement and the electric potential that must satisfy constraint conditions at the electrodes are expanded as the sums of powers in the thickness coordinate. The resulting piezoelectric bimorph plate equations are used along with the introduction of appropriate Lagrange multipliers to analyze the polar orthorhombic annular sectorial plates with free radial and inner circumferential edges, and an entirely built-in or free outer edge. The results are then combined to obtain the solutions for the mixed boundary value problem. The extended Hamilton’s principle with the method of Lagrange multipliers is employed, followed by a Frobenius-type series expansion for solution functions. The eigensolutions are calculated from the resulting transcendental equation and compared with those obtained from an FEA to ensure the validity of the procedure
Introduction to synthesis of the torsional vibrating discrete-continuous mechatronic systems by means of the hypergraphs and structural numbers method
Get PDFIn this paper the modeling by a different category graphs and an analysis of vibrating clamped – free mechatronic system by the approximate method called Galerkin's method has been presented. The frequency - modal analysis and assignment of amplitude -frequency characteristics of the mechatronic system is considered. The aim was to nominate the relevance or irrelevance between the characteristics obtained by exact - only for shaft - and approximate method. Such formulation especially concerns the relevance of the natural frequencies - poles of characteristics both of mechanical subsystem and the discrete – continuous clamped – free vibrating mechatronic system. This approach is a fact, that approximate solutions fulfill all conditions for vibrating mechanical and/or mechatronic systems and can be an introduction to synthesis of these systems modeled by different category graphs. Using the hypergraph methods of modeling and synthesis methods of torsionally vibrating bars to the synthesis of discrete-continuous mechatronic systems is originality of such formulation of problems
Characterization of mechanical properties by inverse technique for composite reinforced by knitted fabric. Part 2. Experimental evaluation of mechanical properties by frequency eigenvalues method
Get PDFThis paper is the second part of the research work dedicated to evaluation of mechanical properties of polymer composites reinforced by knitted fabric. Three different approaches were applied for the task. Two of them: a) FEM analysis using Solid Works combined with structural modeling based on experimentally-determined mechanical and geometrical properties of the reinforcement and matrix, and b) direct measurement of mechanical properties (described in Part 1). Present investigation (Part 2) is based on application of vibrational analysis. Modal testing in combination with the mathematical optimization procedure were used for evaluation of elastic properties of a layered material. It is worth mentioning that the application of this approach for materials with high damping ability (laminated composites reinforced by knitted fabric) is still poorly investigated. The inverse technique exploited in this work is based on the direct orthotropic plate free vibration measurements and subsequent mathematical optimization procedure (the planning of experiments or response surface technique), which is based on minimization of error functional. Finally, elastic constants established by the inverse technique were discussed and compared with the results obtained in Part 1
An adaptive method for inertia force identification in in cantilever under moving mass
Get PDFThe present study is concerned with the adaptive method based on wavelet transform to identify the inertia force between moving mass and cantilever. The basic model of cantilever is described and a classical identification method is introduced. Then the approximate equations about the model of cantilever can be obtained by the identification method. However, the order of modal adapted in the identification methods is usually constant which may make the identification results unsatisfied. As is known, the frequency of the highest order of modal is usually higher than the frequency of the input force in forward calculation methods. Therefore, wavelet transform is applied to decompose the data of deflection. The proportion of the low frequency component is chosen as the parameter of a binary function to decide the order of modal. The calculation results show that the adaptive method adapted in this paper is efficient to improve the accuracy of the inertia force between the moving mass and cantilever, and also the relationship between the proportion of low frequency component and the order of modal is indicated
Improved aerodynamic optimization for the design of wind turbine blades
Get PDFA wind turbine rotor converts the kinetic energy of wind to drive a generator which in turn yields electricity. The aerodynamic analysis and the optimization of design parameters for the wind turbine blades are key techniques in the early stage of the development of wind turbine blades. In this study a computational procedure using artificial neural network and numerical optimization techniques was developed for three-dimensional blades design of a wind turbine. The procedure was applied for improving a previously studied wind turbine rotor design. Results showed that the aerodynamic performance of the new blade has remarkable improvement after optimization
Vibration analysis of geared rotor system under time varying mesh stiffness effects
Get PDFThe present work contributes to the analysis of the interactions between gears, shafts and journal bearings in a geared rotor-bearing system. Although there are analyses for both of the gear and rotor-bearing system dynamics, the coupling effect of the nonlinear variable pressure angle and geared rotor-bearing system is deficient. In contrast to the majority of the models in the literature, the variable mesh stiffness and pressure angle are introduced in this paper while they were considered as constant in previous models. The equations of motion for the geared rotor- bearing system are obtained by applying Lagrange’s equation, and the Runge-Kutta numerical method is used to solve the equations of motion. Numerical results of this study indicated that the proposed model provides realistic dynamic response of a geared rotor-bearing system
Investigation of eigenvalue problem of water tower construction interacting with fluid
Get PDFThe paper concerns problems, in which both the structural and fluid responses of a complex construction to mechanical actions are strongly coupled. Particularly, there are treated problems, in which the structural dynamic response to actions is significantly affected by the presence of the fluid in the structure. The work presents the evolution of the way of solving that problem of the complex solution of the generalized problem of the structure using multiphysical ANSYS program package. The formulation of fluid finite elements is discussed, considering both pressure (Euler) with/without sloshing and displacement (Lagrange) approaches. The solution is demonstrated on thin-walled steel water tower structure
Research of dynamics of lifting equipment
Get PDFIn the recent years, girder bridge cranes are replaced by double-beam overhead cranes with beams of rectangular cross-section. In addition, new materials are used for their fabrication, characterized by different values of allowable loads and deformations. In the paper, two overhead cranes from JSC "Vilniaus kranai" are considered. A mathematical model is proposed that enables assessment of the impact of the hydraulic damper built in the cargo suspension system upon the dynamic features of the crane in the beginning of the lifting process. It was determined that in such a way the period of vibration damping is reduced. However, the impact of the damper upon the dynamics of the metal structure of the crane is limited because of high mobility of the rope as compared to the mobility of the total structure