Department of Mechanical Engineering

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This paper describes a step forward in calculating the nonlinear frequencies and resultant dynamic behavior of high speed rotor bearing system with mass unbalance. Nonlinear strongly coupled equations of motion has been formulated based on strain energy and kinetic energy equations for shaft, disk and unbalance mass with shaft undergoing large bending deformations. Here gyroscopic effects of disk as well as mass unbalance are also considered while vibration effect along the shaft axis is ignored. Time history and FFT analysis for finding the fundamental frequencies for the rotating are portrayed under variation of shaft diameter, frequency of the shaft speed, geometric nonlinearity and disk location. The present research shows an interesting development that the initial conditions are playing an important role in finding the nonlinear frequencies and this variation is strongly due to the presence of nonlinear geometric coupling. In addition, response analysis of the system has been developed due to mass unbalanced using time history. This paper enables an understanding and realization of operating zones of rotational speed of the shaft by which the excessive vibration can easily be avoided due to the resonant conditions occurred as the natural frequencies come closer to the frequency of the rotational speed. © 2016 The Authors.

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Procedia Engineering

Nonlinear Frequencies and Unbalanced Response Analysis of High Speed Rotor-Bearing Systems

An experimental study has been carried out to investigate the nature of transients in vacuum ejector flows during start-up and the dynamics in flow characteristics. The results show that the secondary stream induction progresses with non-uniform rates with the ramping primary jet pressure during start-up. The initial evacuation period is subjected to gradual and highly perturbed secondary fluid entrainment. In this phase, the secondary stream induction by the shear layer is asymmetric leading to an un-even vacuum generation in the secondary chamber. In the second phase, the secondary pressure fluctuations are found to be ceased for a critical primary jet pressure followed by a rapid induction of the secondary fluid till the primary jet expands to the diffuser wall. The transition from the first phase to the second phase is caused by the secondary stream flow choking in the diffuser. Following the second phase, a stable stage exists in the third phase in which the vacuum pressure decreases only marginally. Any further attempt to increase the secondary chamber vacuum level beyond the third phase, by increasing the primary jet total pressure, results in flow reversal into the secondary chamber, spoiling the already achieved vacuum level. In the fourth phase of start-up, a complicated shock interaction transformation from a Mach reflection (MR) to regular reflection (RR) occurs within the diffuser. It is also observed that the primary jet pressures for the minimum secondary chamber pressure, the minimum secondary pressure, and the primary pressure for MR-RR transformation decrease initially with increase in diffuser length and then increase. It is found that the decreasing and increasing trends are caused by the pressure recovery and Fanno effects, respectively.

Physics of Fluids

Flow transients in un-started and started modes of vacuum ejector operation

With the ever-increasing concern for reducing environmental pollution and waste minimization, “green manufacturing” has been successful to draw sufficient amount of attention towards it. Minimum Quantity Lubrication (MQL) is one such technique that has revolutionized the manufacturing industry by not only reducing the amount of working fluid dramatically but also enhancing cutting tool life and reducing material costs. Past studies have reported the use of experiments in MQL based manufacturing but limited computational modeling for optimizing the process parameters Based on the past experimental procedure of machining process (micro-drilling), a computational framework such as Adaptive Neuro Fuzzy Inference System (ANFIS) and Genetic Programming (GP) in quantification of three response characteristics (torque, thrust forces and material removal rate (MRR) is proposed. The performance analysis based on the cross-validation, error metrics, curve fitting and hypothesis tests reveals that among the two models, the GP models have performed better. 2-D and 3-D surface analysis were performed to validate the robustness of the models. Among the three response characteristics, It was found that the nanofluid concentration influences torque the most, which is an important aspect for power consumption. At nanofluid concentration values of 1.4 and 4, the minimum values of torque and thrust forces is achieved respectively. When drill diameter is minimum and the spindle speed is maximum, the values of torque, thrust forces and MRR is the lowest. Thus, the feed rate, nanofluid concentration and drill diameter are most critical for obtaining higher MRR and lower values of torque and thrust force, thus enabling cleaner production and environment. © 2016 Elsevier Ltd

Journal of Cleaner Production

Study of effect of nanofluid concentration on response characteristics of machining process for cleaner production

Thin film gauges (TFGs) are a promising candidate for measuring transient heat fluxes in the applications involving very short duration of heating environment. They are basically resistance temperature detectors (RTDs) having the capability of responding in the range of few microseconds. In the present study, a silver thin film gauge (STFG) is fabricated and calibrated in-house with a view to assess the performance of STFGs in dynamic environment. Convective heat load is supplied by a hot-air gun where the heated air jet strikes the gauge and its response is obtained through voltage signal. Subsequently, the surface heat fluxes are estimated by using one dimensional heat conduction modeling. The similar experimental environment is studied to obtain the flow behavior of hot-air jet emanating into atmosphere by using numerical simulations. The self-similar velocities are plotted as well as the interference of outer domain into the experiment parameters has been studied. Ultimately, the surface heat fluxes obtained from various methods are compared to analyse the performance of this hand-made STFG. This study reveals the ability of STFGs to be used in practical short duration transient situations. © 2016, Indian Academy of Sciences.

Sadhana - Academy Proceedings in Engineering Sciences

Calibration of a silver thin film gauge for short duration convective step heat load

The filtered-x least mean square algorithm (FxLMS) is a widely used technique in active noise control. In a conventional FxLMS algorithm, the value of convergence coefficient is kept constant which may not yield optimum performance if frequency of the primary noise changes. For some frequencies, this may result into a slower convergence and for some other frequencies, it may lead to instability. To deal with this situation, a normalized FxLMS algorithm, in which the convergence coefficient is normalized with the power of the filtered reference signal, is proposed. In the eigenvalue equalization method, the magnitude of secondary path transfer function is equalized such that the power of filtered reference signal remains equal at all the frequencies. The method proposed in this paper attempts to optimally adapt the convergence coefficient of the FxLMS algorithm for continuously varying noise. It is based on estimating how frequency of noise is varying using fast Fourier transforms of the reference signal and then, using this information to optimally adapt the convergence coefficient. The optimum value of the convergence coefficient is decided based upon the power and delay of the filtered reference signal and sampling frequency. A numerical study in a 3D acoustic cavity is presented to test the effectiveness of the proposed method and the results are also compared with the conventional FxLMS and the frequency-domain FxLMS algorithm. It is found that the proposed method leads to a faster convergence which results in higher noise reduction especially when the frequency of noise varies continuously. Simulation results show that the noise reduction obtained depends upon the rate at which the frequency of the primary noise varies. The higher the rate of variation and the duration for which the variation exist, the better the performance of the proposed method is over the conventional FxLMS algorithm in terms of noise reduction. The frequency-domain FxLMS algorithm is not found to be effective if the frequency of primary noise varies continuously. © 2016 Institute of Noise Control Engineering.

Noise Control Engineering Journal

A variable step-size filtered-x least mean square algorithm for continuously varying noise

42nd European Rotorcraft Forum 2016

Damage assessment of composite main rotor blade by finite element simulation and experiment

Helicopter main rotor blade made of fibre reinforced composites experience complex load spectrum during its service life. These aeroelastic loads tend to cause various type of damages in the rotor blade such as fibre failure, matrix failure, interlaminar delamination. These defects not only initiates from aeroelastic loads but also sometimes from process variations or raw material variations such as resin richness or starvation. In the present study, finite element simulation is carried out on main rotor blade root to study the fibre and matrix damage using Hashin damage criteria for assessment of damage region, delamination using cohesive elements at ply-by-ply level using submodeling and virtual crack closure technique. The virtual crack closure technique is used to obtain the energy release for modes of fracture during the progression of delamination based on predetermined crack length. Experimental results obtained are compared with finite element results. Copyright © 2016 by the American Helicopter Society International, Inc. All rights reserved.

5th Asian-Australian Rotorcraft Forum, ARF 2016

Delamination studies of composite rotor blade using VCCT in finite element simulation and experiment

Recent advances in the field of nanotechnology have led to a considerable progress in the domain of engineered molecular interactions which has resulted in the emergence of nano-biodevices. Various methods to modify surfaces suitably for realizing bioactive surfaces have emerged due to combined research in nanotechnology and molecular biology areas. This article presents a summary of the several technological achievements in the area of nano-biodevices and provides an overview of the various surface modification strategies carried out. The different strategies related to covalent and non-covalent immobilization of biomolecules have also been addressed to understand the efficacy of a substrate surface used in nano-biodevices. © 2016 Scrivener Publishing LLC.

Reviews of Adhesion and Adhesives

Surface modification strategies for fabrication of nano-biodevices: A critical review

Frequency spectra obtained from the measurements of light intensity and angle of arrival (AOA) of parallel laser light propagating through the axially homogeneous, axisymmetric buoyancy-driven turbulent flow at high Rayleigh numbers in a long (length-to-diameter ratio of about 10) vertical tube are reported. The flow is driven by an unstable density difference created across the tube ends using brine and fresh water. The highest Rayleigh number is about 8 ? 109 . The aim of the present work is to find whether the conventional Obukhov-Corrsin scaling or Bolgiano-Obukhov (BO) scaling is obtained for the intensity and AOA spectra in the case of light propagation in a buoyancy-driven turbulent medium. Theoretical relations for the frequency spectra of log amplitude and AOA fluctuations developed for homogeneous isotropic turbulent media are modified for the buoyancy-driven flow in the present case to obtain the asymptotic scalings for the high and low frequency ranges. For low frequencies, the spectra of intensity and vertical AOA fluctuations obtained from measurements follow BO scaling, while scaling for the spectra of horizontal AOA fluctuations shows a small departure from BO scaling. © 2016 Optical Society of America.

Applied Optics

Intensity and angle-of-arrival spectra of laser light propagating through axially homogeneous buoyancy-driven turbulence

From experiments of axially homogeneous turbulent convection in a vertical tube using heat (Prandtl number Pr≃6) and brine (Pr≃600) we show that at sufficiently high Rayleigh numbers (Rag), the Nusselt number Nug∼(RagPr)1/2, which corresponds to the so-called ultimate regime scaling. In heat experiments below certain Rag, however, there is transition to a new regime, Nug∼(RagPr)0.3. This transition also seems to exist in earlier reported data for Pr=1 and Pr≃600, at different Rag. However, the transition occurs at a single Grashof number, Grgc≃1.6×105, and unified flux scalings for Pr≥1, Nug/Pr∼Grg0.3, and Nug/Pr∼Grg1/2 can be given for the two regimes. © 2016 American Physical Society.