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In the present work, an experimental investigation of a transverse fatigue crack has been carried out. A mathematical modelling of cracked rotor system along with the measured vibration is used to find crack parameters that not only detect the fault but also quantify it. Many experimental studies on cracks considered the crack as a slit or notch, which remains open. However, such flaws do not mimic a fatigue crack behavior, in which crack front opens and closes (i.e., breathes in a single revolution of the rotor). The fatigue crack in rotors commonly depicts 2x frequency component in the response, as well as higher frequency components, such as 3x, 4x and so on. In rotors, both forward and backward whirling take place due to asymmetry in rotor, and thus the fatigue crack gives the forward and backward whirl for all such harmonics. A rotor test rig was developed with a fatigue crack in it; rotor motions in two orthogonal directions were captured from the rig at discrete rotor angular speeds using proximity probes. The directional-spectrum processing technique has been utilized to the measured displacements to get its forward and backward whirl components. Subsequently, it is executed in a mathematical model-based estimation procedure to obtain the crack forces, residual unbalances, and remaining rotor system unknown variables. Estimation of crack forces during rotation of the shaft gives its characteristics, which can be used further to develop newer crack models.

Purpose The bump-recess configuration with top foil of air foil journal bearing is analyzed using Functionally Graded Material (FGM). The purpose of the study is to examine journal bearing’s limiting load capacity and coefficients of limiting stiffness. Different top foil texture bump patterns are examined. A journal (foil) bearing's limiting load capacity and limiting stiffness coefficients are explored in relation to the extent and height of the top foil texture bump. Methods The methods presented are based on an analytical model for limiting load capacity and limiting stiffness coefficients of the bump-recess configuration on top foil of air foil journal bearing using FGM. A simplified version of the compressible Reynolds equation is considered to estimate the limiting load capacity and limiting stiffness coefficients. These estimates are made for higher bearing numbers coupled with higher speeds for the journal foil bearing. The theoretical model accounts for the bump-recess configuration with FGM and bump foil compliance. The top foil bearing's limiting pressure gradient solution is examined with a texture bump. Results The results of the limiting load capacity and limiting coefficients of stiffness of bump-type journal foil bearings with FGM are compared for different bump-recess heights. A functionally graded (FG) sub-foil with an extended bump texture top foil varies the cross-coupled non-dimensional stiffness coefficients considerably with increasing nondimensional bump texture height. Conclusion Enhanced bump texture on the top foil improves limiting load capacity and coefficients of limiting stiffness properties of bump-type journal foil bearings with FGM.

In Energy Industries reliability of rotating equipment's plays a key role in overall plant reliability and safer operation, in fact maintaining these equipment's in larger scale is a challenging task. The magnitude of vibration in rotating equipment's is high when the rotor excitation force coincides with the natural frequency. This paper deals with the comparison study on existing steel shaft over laminated composite shaft's lateral and torsional critical speed, which aims to optimize the natural frequency. The rotor system model represented here is undamped, without disc and simply supported with bearing for lateral vibration analysis and considering two discs at ends for torsional vibration analysis. The analysis report represents the comparison of both steel and laminated composite shaft, which features with Campbell diagram.

The purpose of this study is to explore the limiting stiffness coefficients of a foil journal bearing with the texture bump profile of top foil. The limiting stiffness coefficients are evaluated based on simplified compressible Reynolds equation for large bearing numbers with high speeds of foil journal bearing. A limiting pressure gradient solution for a texture bump of top foil bearing is analyzed. The analytical model accounts for the top foil texture bump profile and bottom foil bump compliance. Results of linearized nondimensional stiffness coefficients obtained using infinitesimal perturbation method are compared for various top foil texture bump profiles. The influence of top foil texture bump extent and height on the limiting stiffness coefficients of a foil journal bearing are investigated.

Rotors with one or more offset disks and supported on bearings are common in high speed turbomachinery. During start up, these rotors have to cross through several critical speeds before reaching their operating speed. At critical speeds, the spin speed of the rotor matches with one of its natural frequency leading to the condition of resonance and large vibration amplitude. In rotating systems, these natural frequencies depend on the support stiffness. Also, they are a function on the spin speed because of the phenomenon of gyroscopic effect. The gyroscopic effects on critical speeds of a rotor system supported in bearing can be studied by means of a Campbell diagram, which has been used in the design of turbines. In this paper, gyroscopic effects of a rotor with an offset disk and supported on bearing is studied by means of Campbell diagrams. The numerical study is carried out by modelling of the rotor-bearing system using finite element mass, stiffness and gyroscopic matrices. The solution is obtained by solving the assembled equations of motion; following application of geometric boundary conditions and representing the second order differential equations of motion in statespace form. The results of critical speed obtained are compared with those of the results obtained through modal analysis using FE tool (ANSYS). The analysis of the results can be used to extend the study for a multi-disk rotor with different bearing supports.

Torsional vibration is a frequent perturb for heavy rotating and high speed machinery. Development of large torsional vibrations produce torsional stresses which leads to increase in bearing loads and results in generation of cracks in the high stress areas of the transmission system and propeller. So, it is important to model and analyze the torsional characteristics of Power transmission system. The information obtained regarding torsion vibration characteristics will be useful to study the system dynamics and prevent premature failure caused due to resonance at critical speeds. In this paper, torsional vibration analysis is carried out for a marine power transmission system. The propulsion system is modeled as a flexible shaft with multiple inertias as lumped masses and shaft sections with torsional stiffness. Holzer method is employed to calculate the torsional resonant frequencies and their corresponding mode shapes. An algorithm for Holzer method is designed and programmed using MATLAB software.

This paper presents the analytical model of a ball bearing with localized defect in the outer race. The outer raceway defect is modelled based on the reduction in the contact force due to localised increase in the clearance. The contact forces are modelled based on Hertzian contact deformation theory. The geometry of the defect is considered as a half sinusoidal wave. The contact between the ball and the outer raceway is modelled using non-linear springs, acted upon rotor mass. The system governing equations of motion are obtained and represented in state space form. Numerical simulations are carried out using MATLAB environment to study the effect of outer race defect on vibration responses. Time and Frequency domain characteristics of the simulated vibration signals are obtained.

In this work study of a rotor supported on ball bearings and containing a fatigue crack is carried out. The primary objective of the work is to obtain the load-distribution of the ball bearings from which the support stiffness in two transverse directions are obtained. The other objective is the rotor-dynamic analysis of a shaftsupported on these bearings. A mathematical model of a rigid rotorsupported on flexible bearings is considered for the purpose. Effects of bearing stiffness, damping and gyroscopic effects are included in the study. The governing equations of motion are obtained. The whirl frequencies of the rotor system are obtainedusing Eigen value formulation of the problem. A Campbell diagram is plotted which is used to obtain the critical speeds of the rotor system. These results are supported with the results from frequency response function plots.

A raising population and to meet the raising needs there is an increasing demand for tall structure both for commercial use and industrial purpose. Wind behaviour is a key design parameter for such structures and need to be assessed accurately in the preliminary and secondary design stages. This study is aimed at prediction and analysis of deflection of hollow structure due to steady wind loads. Hollow structures typically represent chimneys that are used in the coal fired stream power plant. A hollow cylindrical part with base diameter of 6 cm is fabricated and tested in wind tunnel at constant speeds of 10, 15 and 20 m/s. An accelerometer is mounted on top of body to measure the deflection. Next, the deflection of the body is predicted numerically using commercial ANSYS software. Initially Computational Fluid Dynamics (CFD) simulations are performed to predict the flow field and associated wind force acting on the body. The wind load is transferred to the structural solver to predict the deflection of the body. The predicted deflection compared well with the wind tunnel experiments. Further FSI simulations are performed by changing the thickness of the hollow structure. The results are analysed to study the effect of wind speed and thickness on the deflection. A cubic polynomial curve-fit for the deflection, as a function of the wind speed is developed.

The present investigation is aiming to get better squeeze film dampers which are normally used in high speed jet engines to minimize small amplitude large force vibrations. The investigation was started with squeeze film dampers employing conventional lubricating oils. Magneto rheological fluids are then used to enhance the viscosity characteristics of the fluid under the influence of magnetic fields in order to improve the damper performances. It is observed that the dynamic characteristics of the damper with magneto rheological fluids are enhanced. Further to improve the damper performance, few modifications in the damper assembly are carried out in this research work. A good amount of reduction in the amplitude of vibrations is observed in these modified squeeze film dampers coupled with magneto rheological fluids. This research work discusses dual and triple clearance squeeze film dampers and bump foil squeeze film damper, also subjected to variation in temperature. Dynamic characteristics are found to be decreasing as the viscosity of the fluid decreases with rise in temperature of the fluid.