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ABSTRACT
This work deals with the Modal analysis of an engine and gearbox. The rectification of field failure of engine and gearbox under static condition and determination of its life time under vibration in the test rig was studied in depth. Externally exerted vibrations are used for analysis. The frequency of the vibrations are analyzed and required damping frequency needed to arrest the unwanted vibrations are calculated.The analysis involves the determination of natural frequency, mode shape and damping of the engine and gearbox at static condition using modal analysis. The geometry of the combined structure of engine and gearbox is measured and the various node points are selected as per need. The frequency of the vibrations is recorded, analyzed and FRF function is used for analysis and a structural graph is plotted for the vibrations. The modal parameters of the engine and gearbox were calculated and it is compared with the standard data prepared by designers and the required damping is proposed.
INTRODUCTION
The study of structural dynamics is essential for understanding and evaluating the performance of any Engineering product. As we are concerned with printed-circuit board bridges, high-speed suspension printer mechanisms, satellite launchers, dynamic response is fundamental to sustained and satisfactory operation.Modal analysis is an efficient tool for describing, understanding and for modeling structural behavior. The study of modal analysis is excellent for attaining a solid understanding of structural dynamics. Modal analysis of the data obtained from structural testing would provide us a definitive description of the response of a structure which can be evaluated against design specifications. It also enablesus to construct a modal model with which we can check how the structure will perform under different operating conditions.
A simpledefinition of modal analysis can be made by comparing it to frequency analysis, in frequency analysis; complex signal is resolved into a set of simple sine waves with individual frequency and amplitude parameters. In modal analysis complex deflection patternof vibration structure is resolved into a set of simple mode shapes with individual frequency and damping parameters. Such analysis is performed on an engine and gear box assembly.
LITERATURE SURVEY
Fabian Duvigneau.et al (2015) numerically stimulated about the perceived quality of engine sounds periodic combustion sounds are synthesized with the help of numerical stimulations and the results are transferred into an interval scaled ranking of the stimuli and they are visualized to allow a simple qualitative analysis of the sound perception. Song Chaosheng. et al (2015) proposed a systematic dynamic modelling approach for evaluating the dynamic characteristics of a marine gearbox with crossed beveloid gears more realistically. Then numerical integrations applying the explicit Runge–Kutta formula and the implicit direct integration were used to solve the nonlinear dynamic model.by analysing the responses in time domain and frequency domain, the experimental results compared well with the theoretical dynamic results. Ashwani Kumar.et al (2014) simulated the relation between dynamic vibrations of transmission and fixed constraint of vehicle frame. Transmission casing is tightly fixed using 37 connecting bolts and the bolts were loosened caused heavy vibration and deformation. FEA based numerical simulation method was used to find the dynamic response of the casing shows that the natural frequency of one bolt unconstraint condition varies from 1637.2 – 2674 Hz. Pravin P Patil.et al (2014) estimated the effect of mechanical properties of materials on natural frequency and mode shapes of heavy vehicle gearbox transmission casing. Free vibration study was performed for the vibration response study of casing. Solid Edge and Pro-E was used for CAD designing of transmission gearbox casing. The simulation results were compared with experiment results.
Michael Feldman (2010) applied Hilbert transform applications to mechanical vibration which is accessible to non-stationary and nonlinear vibration application in the time domain. It thrives on a large number of examples devoted to illustrating key concepts on actual mechanical signals and demonstrating how the Hilbert transform can be taken advantage of in machine diagnostics, identification of mechanical systems and decomposition of signal components. Yann Pasco.et al (2011) experimented Multi-input multi-output feed forward control of multi-harmonic gearbox vibrations using parallel adaptive notch filters in the principal component space and Experimental results obtained with these adaptive notch filters show good control attenuations at targeted gearbox tones, without amplification of other closely located, unreferenced tones. He Zhenpeng.et al (2015) analysed the elasto-hydrodynamic lubrication model with cavitation theory is built to couple with multi-body dynamic theory to analyse the noise and reliability of the engine, the results were compared with nonlinear spring model and hydrodynamic lubrication model based on a typical in-line six cylinder engines, such as load carrying capacity of the bearing, velocity level of the engine surface, noise level of engine surface and stress of the crankshaft.
Mehmet Bozca (2010) proposed the optimization of gearbox geometric design parameters to reduce rattle noise in an automotive transmission based on a torsional vibration model during the optimization, a four-degree-of-freedom torsional vibration model of the pinion gear–wheel gear system is obtained and the minimum singular value of the transfer matrix is considered as the objective functions. It is concluded that the optimized geometric design parameters lower the rattle noise by 10% compared to the calculated rattle noise for sample gearbox. G. Kouroussis.et al (2014) presented an effective formulation to model an automatic transmission for evaluating the vehicle performance in the early development stage of a powertrain design. The equations are obtained with the help of the virtual power principle, involving all rotating parts of the gearbox. The acceleration of the vehicle is calculated by including the gearbox model in the equations and the developed model reveals itself as a valuable tool for simulating the implementation of different control laws governing the gear shifts.
Diego J. Pedregal.et al (2008) developed a forecasting system in condition monitoring based on vibration signals in order to improve the diagnosis of certain critical equipment at an industrial plant. The system is thoroughly tested on the equipment available, showing its correctness with the data in a statistical sense and its capability of producing sensible results for the condition monitoring programme. Ali El Hafidi.et al (2010) composed his research as three parts The first part describes an indirect semi- experimental method which is used to reconstruct the excitation force of an operating diesel engine from the acceleration data measured at the mounting points.The second part deals with prevention of low frequency vibration of the powertrain from spreading to the rest of the vehicle. Three uncoupling techniques are used to minimize these vibrations. In the third part, numerical and experimental results were discussed. JacekDybala (2012) presented a new pattern recognition approach to the condition monitoring of technical objects working under time varying load.In the presented pattern recognition approach, relations between spectral components of the gearbox vibration signal were investigated in the full range of gearbox operating conditions.which enabled to perform error-free recognition of the gearbox condition including the cases of no load or small load.
MODAL ANALYSIS
Most practical noise and vibration problems are related to response phenomena, where the operational forces excite one or more of the modes of vibration. Modes of vibration which within frequency range of the operational dynamic forces always represent potential problems. An important property of modes is that any forced or free dynamic response of a structure can be reduced to a discrete set of modes. The modal parameters areModal frequency, Modal damping and Mode shape. The modal parameters of all modes, within the frequency range of interest, constitute a complete dynamic description of the structure. Here the modes of vibration represent the inherent dynamic properties of a free structure that is a structure on which there are no forces acting.
Modal analysis is the process of determining all the modal parameters, which are then sufficient for formulating a mathematical dynamic model. Modal analysis may be accomplished either through analytical or experimental technique.In an engine and gearbox arrangement dynamic vibration is measured using accelerometer by giving a force through an impact hammer. Accelerometer is installed at fifteen points in the engine and gearbox arrangement. By giving a force through the impact hammer vibration at each point is observed throughout the setup. The corresponding values of observed vibrations at each point were recorded by the accelerometer.Then for reducing the vibrations damping is suggested. By using simulation software the amount of damping to be given is calculated so that the vibration can be minimized.
RESULT AND DISCUSSION
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The damped frequency and the complexity were compared and the values were plotted between the readings from accelerometer and iteration values. The Modal Analysis is done by using Geometry and nodes of the combined section of engine and gearbox and using the simulation softwares.
CONCLUSION
From the analysis it is clear that, by modal analysis we can find the natural frequency, mode shape and damping of the engine and gearbox using simulation software. The obtained mode shapes and data helped to identify the weak spots in the engine and gear box.From the study we suggest that by increasing the stiffness in the weak spots thefailure can be avoid.