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Experimental and numerical investigation of flow instability in a transient pipe flow
No full textThis paper describes the study of instability in a transient pipe flow of decaying nature, considering variation of the base flow with time. Linear stability analysis on the decaying base flow is carried out and the effect of wavenumber on the perturbation energy growth is studied. Non-modal optimal-mode analysis, with time integration, utilising adjoint equations, is found to be suitable for the study of instability in such transient flows. The range of wavenumbers, sensitive to perturbation in providing maximum perturbation energy growth, and the magnitude of the order of growth supports the conjecture that the transient growth of the optimal perturbation is responsible for the observed instability. The findings regarding stability mechanism are substantiated by an experimental investigation accompanied by a numerical study. In an unsteady experiment, where a piston with trapezoidal velocity variation drives the flow, an impulsively blocked duct flow is emulated. Particle image velocimetry (PIV) measurement provides the velocity data; the analytical velocity profiles are obtained using a series solution available in the literature, with a trapezoidal flow-rate-variation approximation. The analytical profiles capture the centreline velocities, various time scales and the reverse-flow regions, which the experiment fails to resolve. Observation of the vorticity fields confirms the appearance of instability waves close to the reverse-flow boundary layer near the wall, and the growth and transformation of the instability waves into fully grown vortices. The coherent wave structures and their associated wavenumbers are extracted quantitatively through spatial dynamic mode decomposition (DMD) analysis. This comprehensive analysis recognises the dynamics of the flow-field development, which suggests that the loss of mean-flow energy and the perturbation energy growth compensate each other, with the remaining energy losses accounted for by viscous dissipation
Multi-objective Optimization Approach for Low RCS Aerodynamic Design of Aerospace Structures
No full textThis paper presents a multidisciplinary, multi-objective optimization approach towards low Radar Cross section (RCS) aerodynamic design of aerospace structures. As a typical example, design and analysis of aircraft intake duct for stealth behavior by integrating computational fluid dynamics (CFD) and computational Electromagnetics (CEM) has been demonstrated. The design constraints (inlet area, throat area, exit area, and diameter) are calculated based on the RAE M2129 diffuser and subsonic flow condition with Mach number 0.8 is considered at the Indian standard atmospheric conditions (ISA_SL + 15). Inlet shaping parameters for intake are modified based on super ellipse equation by retaining the area as constant. Shaping parameter samples have been generated by limiting major axis to maximum length and minor axis to minimum length using MATLAB code. Based on each curvature parameter, three geometries were opted and CAD models are generated from sample space. For these geometries, CFD and CEM analysis has been performed and corresponding pressure recovery and RCS at 10 GHz (X-band) has been estimated. The CFD-CEM performance analysis has been presented for the optimized intake duct geometry. Particle swarm optimization (PSO) in-conjunction with CFD solver and CEM developed indigenous RCS solver has been used for optimization of the designed duct towards stealth characteristics
Raman Fingerprint of Pressure-Induced Phase Transition in SnO2Nanoparticles: Grüneisen Parameter and Thermal Expansion.
No full textPressure-induced phase transition studies in nanomaterials are important to comprehend thermodynamics at the nanoscale. Raman spectroscopic studies at high pressure in a diamond anvil cell were performed up to 40 GPa on rutile tetragonal phase of SnO2 nanoparticles (NPs) of sizes ∼2, 4, and 25 nm to investigate their phase stability and phonon anharmonicity. In 25 nm NPs, evidence of phase transitions was observed at ∼11 and ∼24 GPa, 4 nm NPs indicated a cubic phase transition ∼21 GPa, and the 2.4 nm quasi-nanocrystals were found to stable up to 30 GPa. Raman spectra down to 90 K indicated that phonons of 2.4 nm NPs were more anharmonic. The analysis of total Raman intensity with increasing pressure suggested propagation of disorder from the surface to the central core of the NPs under pressure. Pressure-induced effects on 25, 4, and 2.4 nm NPs reduced their average diameters to 6.4 ± 2.6, 4.04 ± 1.36, and 3.85 ± 0.9 nm, respectively. Using Raman mode Grüneisen parameters γj, the thermal expansion coefficient α of the 25, 4, and 2.4 nm SnO2 NPs at 300 K was estimated as 1.674 × 10–6, 1.178 × 10–6, and 1.690 × 10–6 K–1, respectively
ECG Abnormality Classification and Analysis with SVM Classifier
No full textElectrocardiogram (ECG) is a primary non-invasive tool for monitoring cardiac conditions. Computer-assisted tools are the cutting edge technology to identify minute
changes in ECG waveform. This paper presents an ECG
classification model to detect seven types of arrhythmia using the MIT-BIH arrhythmia database. The proposed method incorporates time-domain statistical feature and wavelet-based feature extraction separately for classification using a support vector machine. The lassifier considers various combinations of ECG time-domain and wavelet features to obtain higher accuracy of classification. Achieved classification accuracy is 97.7 percent within a short computation time. The proposed
classifier model has been validated using Monte Carlo
Simulation. The variance reduction in accuracy is achieved with the Monte Carlo technique for various ECG input
features
Robust Flutter Prediction of an Airfoil Including Uncertainties
No full textThis work presents the robust stability analysis of 2DoF airfoil by including various uncertainties. These uncertainties arise due to several factors such as modeling and manufacturing errors as well as disturbances in the flight conditions. The approach adopted to study the uncertain aeroelastic system is based on the structured singular value (µ-method). In this approach, the aeroelastic system is formulated in a robust stability framework by parameterizing around dynamic pressure and introducing uncertainties in the system parameters to account for errors and disturbances. This results in the perturbed aeroelastic system which is then represented using Linear Fractional Transformation (LFT). Then, the nominal and robust stability analysis of the perturbed aeroelastic system is carried out using µ method. In this work, first the validation of µ method is done for 2DoF airfoil with quasi-steady aerodynamics having uncertainties in the structural and aerodynamic properties. Further, the robust flutter boundary of 2DoF airfoil with Theodorsen’s unsteady aerodynamics is studied using µ method in the presence of stiffness, damping, and aerodynamic uncertainties
Polymer-graphene composites as anticorrosive materials
No full textCorrosion of structural metals is a universal problem that causes economic and environmental damage every year due to the gradual failure of conventional protective coatings over time. In the past, graphene has emerged as a promising anticorrosive material owing to its unique properties such as chemical inertness, impermeability, and high conductivity, although scalability is still a big issue. This chapter outlines the utility and recent advances in graphene and graphene-derived materials containing polymer-based anticorrosive coatings. Additionally, an overview of pure graphene corrosion protective coating is also given. The potential applications of various polymer-graphene composites in the field of metal corrosion protection and their viability and challenges in near-future applications are also discussed
Mahalanobis-ANOVA criterion for optimum feature subset selection in multi-class planetary gear fault diagnosis
No full textThe empirical analysis of a typical gear fault diagnosis of five different classes has been studied in this article. The analysis was used to develop novel feature selection criteria that provide an optimum feature subset over feature ranking genetic algorithms for improving the planetary gear fault classification accuracy. We have considered traditional approach in the fault diagnosis, where the raw vibration signal was divided into fixed-length epochs, and statistical time-domain features have been extracted from the segmented signal to represent the data in a compact discriminative form. Scale-invariant Mahalanobis distance–based feature selection using ANOVA statistic test was used as a feature selection criterion to find out the optimum feature subset. The Support Vector Machine Multi-Class machine learning algorithm was used as a classification technique to diagnose the gear faults. It has been observed that the highest gear fault classification accuracy of 99.89% (load case) was achieved by using the proposed Mahalanobis-ANOVA Criterion for optimum feature subset selection followed by Support Vector Machine Multi-Class algorithm. It is also noted that the developed feature selection criterion is a data-driven model which will contemplate all the nonlinearity in a signal. The fault diagnosis consistency of the proposed Support Vector Machine Multi-Class learning algorithm was ensured through 100 Monte Carlo runs, and the diagnostic ability of the classifier has been represented using confusion matrix and receiver operating characteristics
Lignin addition to polyacrylonitrile copolymer solution and its effect on the properties of carbon fiber precursor
No full textPolyacrylonitrile copolymer (PAN) fiber and PAN/lignin (PL) fiber were wet spun from the PAN copolymer solution and PAN/Lignin blend solution using dimethyl sulphoxide (DMSO) solvent. A blend of 90% by weight (wt %) PAN terpolymer and 10wt% lignin dissolved in DMSO was used in wet spinning of PL fiber. Viscoelastic properties of PAN solution and PAN/lignin solution in DMSO were determined by rheometer. The properties of precursor fiber with and without lignin were evaluated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mechanical testing. The diffusion of lignin out of coagulated filament was observed during wet spinning of PL solution and was quantitatively estimated by UV–Vis studies. DSC results showed that blending lignin with PAN copolymers can improve the thermal oxidation performance of the precursor fiber and accelerate the thermal stabilization process. A schematic illustration has been deduced for the decrease in tensile strength of PL fiber compared to that of PAN fiber
A comparison of damage tolerance behaviour of two different nickel base super alloys under a turbine standard spectrum loads
No full textIn this investigation, the damage tolerance behavior of two different aero-engine materials i.e., GTM718 and GTM720 nickel base super alloys subjected to a turbine standard spectrum loads was experimentally determined and compared. Compact tension (CT) specimens as per ASTM test standard specifications were cut and prepared from the forged discs of these materials. Fatigue crack growth (FCG) tests were conducted using CT specimens in a 100 kN servo-hydraulic universal test machine at ambient temperature and lab air atmosphere. Constant amplitude cyclic fatigue loads were applied on CT specimen to initiate a pre-crack of about 2.0 mm in length from the notch root. Further, the fatigue crack was propagated under standard cold-TURBISTAN spectrum load sequence. The crack length was measured by compliance method as well as by using optical traveling microscope at regular intervals of completion of load blocks. Loading waveform employed during the test was triangular with a frequency of 2 Hz i.e., four reversals per second. The average fatigue crack growth life under turbine standard spectrum loads observed was observed to be lower in GTM718 when compared to GTM 720 material. The measured crack growth life was about 48 blocks and 38 blocks in GTM 720 and GTM 718 respectively. It was clear from these experiments that GTM720 is more damage tolerant than GTM718 material
Synthesis of lanthanum titanate (La2Ti2O7) for high temperature sensor applications
No full textLanthanum titanate (La2Ti2O7) with perovskite-like layered structure is a candidate material for high temperature sensor application due to its high curie temperature (Tc = 1461 °C) and linearity of temperature vs. electrical resistance. La2Ti2O7 (LTO) was synthesized by solid state reaction using constituent powders at 1250 °C for 2 h. The LTO samples prepared in the form of circular pellets were sintered in temperature ranges (1350 to 1400 °C for 2 h). The sintered density was found highest at 1400 °C for LTO samples (> 97.24% Th.). Moreover, the sintered LTO samples were characterized for their ferroelectric properties as well as DC electrical resistivity (ρ) measured in the temperature range of 100 to 900 °C. The electrical resistivity was decreased from 1013 to 106 Ω cm linearly with the increase in temperature from 100 to 900 °C. Hence, LTO is a promising sensor material for high temperature applications