Articles written in Sadhana

    • Experimental identification of shaft misalignment in a turbo-generator system


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      Precise and authentic estimation of the dynamic features of rotating machines and prevention of failure requires accurate experimental characterisation of their critical components, for example, bearings and couplings. These are difficult to model theoretically, and they often suffer from uncertain parameters in their model. Especially, when there is a misalignment in the rotor system, dynamic characterisation of bearings and couplings changes drastically. In the present study, multiple fault parameters (MFPs) of critical components of turbo-generator, that is, bearing and coupling together with residual unbalances (RUs), are evaluated experimentally using model-based methodology. A test rig was developed and used for experimentation in which different levels of misalignment was introduced. After estimating the MFPs, then the accuracy was checkedthrough an impact test on the rotor test rig. The effect of different levels of misalignments on estimated parameters was studied.

    • Multi-objective optimization in geometric design of tapered roller bearings based on fatigue, wear and thermal considerations through genetic algorithms


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      To improve the fatigue, wear and thermal based failures of Tapered Roller Bearings (TRBs) a multi-objective optimization technique has been proposed. Objective functions considered are: the dynamic capacity (Cd) that is related to fatigue life, the elasto-hydrodynamic minimum film thickness (hmin) that isassociated to the wear life, and the maximum bearing temperature (Tmax) that is related to the lubricant life. This paper presents a non-linear constrained optimization problem of three objectives with eleven design variables and twenty-eight constraints. The said objectives have been optimized individually (i.e., the single-objective optimization) and concurrently (i.e., the multi-objective optimization) through a multi-objective evolutionary procedure, titled as the Elitist Non-dominated Sorting Genetic Algorithm. A set of standard TRBs have beenselected for the optimization. Pareto-optimal fronts (POFs) and Pareto-optimal surfaces (POSs) are obtained for one representative standard TRB. Out of many solutions on the POFs/POSs only the knee-point solution hasbeen shown in a tabular form. Life comparison factors have been calculated based on both the optimized and standard TRBs, and results indicate that the optimized TRBs got enhanced lives than standard bearings. To get the graphical impression of optimized TRBs, a skeleton of radial dimensions of all seven optimized bearings based on various combinations of objectives has been shown for one of the representative standard TRB. In few cases the multi-objective optimization has better convergence as compared to single objective optimization due to its inherent diversity by the principle of dominance. The sensitivity investigation has also been conducted to observe the sensitivity of three objectives with design variables. From the sensitivity analysis data, toleranceshave been provided for design variables. These tolerances could be used by the manufacturing industry while producing TRBs

    • On-line field balancing technique using virtual trial unbalances in rotor-bearing system incorporated with active magnetic bearing


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      A practical online balancing methodology is proposed for a rotor system supported on conventional bearings, utilizing an Active Magnetic Bearing (AMB). It does not require mechanical trial masses to be kept at different balancing planes to estimate system parameters and residual unbalances. An Improved Influence Coefficient Method (IICM) is utilized to estimate the residual unbalances at the limited balancing plane locations in the rotor system having residual unbalances. The virtual trial unbalances utilized in the IICM aregenerated by the AMB as magnetic forces. The residual unbalances are estimated on the experimental test rig designed for rotor balancing incorporated with AMB. With corrected residual unbalances, the rotor system is rotated, both inclusive and exclusive of AMB, to observe the suppression of the vibration responses. It is seen that without application of the AMB also, the balanced system rotates with very less amplitude of vibration, which is useful in case the AMB system fails to suppress the vibration.

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