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Silica-alumina based sol-gel coating containing cerium oxide nanofibers as a potent alternative to conversion coating for AA2024 alloy
No full textThe current work demonstrates a study on the improved corrosion protection efficiency of a defect-free sol-gel hybrid coating consisting of cerium oxide nanofibers vis-à-vis sol-gel coating containing commercial nanosize ceria particles as corrosion inhibitors. The less researched organically modified silica-alumina (Si-Al) hybrid sol-gel coating containing cerium oxide nanofibers and commercial ceria are synthesized from 3-glycidoxypropyltrimethoxysilane and aluminum-tri-sec-butoxide. The sol-gel matrix containing cerium oxide nanofibers exhibiting Ce mainly in +3 oxidation state exhibits improved corrosion resistance as corroborated by electrochemical impedance spectroscopy. The corrosion property of this sol-gel coating commensurates well with the conventional chromate conversion coating (CCC) as evidenced by the neutral salt spray test. The developed coating exhibits good compatibility with the top primer layer and thus ascertains that the developed Si-Al based sol-gel coating containing cerium oxide nanofibers is a potent alternative to conventional CCC
Gearbox Health Condition Monitoring Using DWT Features
No full textThe gearbox is an accessory drive, used widely for power transmission in industries and vehicles. Since its invention in the twentieth century, it brought major changes in the field of mechanical engineering. At the same time as the gearbox evolution continues, people are focusing on customized operation with less maintenance cost. Instead of the traditional approach (scheduled and unscheduled maintenance), the industry is looking for condition-based preventive maintenance. Therefore, it is important to monitor the health condition of the gearbox. This paper presents three different architectures to diagnose the gearbox vibration signal between healthy and damaged condition. Fifteen wavelet features are extracted from the segmented signal and tested with infinite latent feature selection (ILFS) algorithm to find useful features based on ranking. Feature classification was done using a support vector machine (SVM) algorithm. The ideology of the round-robin technique was implemented in architecture-2. The result shows that, among the three developed architectures, the first architecture with discrete wavelet transform (DWT—1D) followed by the SVM model is providing better classification accuracy than the other two architectures. The results were presented with 100 Monte Carlo runs
Gas Turbine Engine Fan Blade Flutter Detection Using Casing Vibration Signals by Application of Recurrence Plots and Recurrence Quantification Analysis
No full textGas turbine aero engines are a specific class of turbomachinery wherein compression system and turbine are realized as spinning discs on an interconnecting shaft. Fan-bladed disc undergoes an unsteady aeroelastic phenomenon known as flutter during various operational regimes, which might lead to structural failure of blades. Study of this mode of flutter induced structural response by measuring casing vibration is of interest in health monitoring of aero engines. In this paper, authors present a novel application of detecting the rotating blade flutter based on the feature space constructed using statistical parameters, recurrence plots (RP) and recurrence quantification analysis (RQA) of engine casing vibration data. Feature vectors thus obtained are visualised in several 3D vector space plots to cluster the data points which separate flutter mode from the normal mode of operation. Results obtained through the proposed method have been compared with engine flutter test results obtained through dedicated rotating blade strain gauge instrumentation
Radar Cross Section Analysis of Multi-Layered Resistive Material based Planar/Conformal Radar Absorbing Structures
No full textResistive material based radar absorbing structures (RAS) are potential candidates for reducing radar cross-section (RCS) over a broad band of frequencies and wide range of incident angles. The superior performance can be attributed to both dielectric and ohmic losses contributing simultaneously towards power absorption. In this regard, a novel multi-layered resistive material based broadband RAS configuration using commercially available substrates is presented for both planar as well as conformal applications. The monostatic RCS of both planar and conformal RAS has been estimated using full wave simulation software. The computed results clearly indicate that the proposed RAS models provide more than 8dB RCS reduction (RCSR) from 2GHz to 18GHz in comparison with PEC plate of identical dimensions
Properties of Plasma Sprayed Al2O3-13TiO2 and ZrO2 Blended Coatings on Biomedical Alloy
No full textPlasma spray grade Al2O3-13TiO2 and ZrO2 powders were blended physically in different proportions (80 wt% Al2O3-13TiO2 + 20 wt% ZrO2, 20 wt% Al2O3-13TiO2 + 80 wt% ZrO2 and 50 wt% Al2O3-13TiO2 + 50 wt% ZrO2) and plasma sprayed on biomedical Ti-13Nb-13Zr alloy using identical plasma spray parameters. Microstructural and phase analyses of the as-sprayed coatings were carried out using scanning electron microscopy and X-ray diffractometry. Results showed that the 80% Al2O3-13TiO2 + 20% ZrO2 coating had enhanced corrosion and wear resistance compared to the other two compositions and appeared to be a propitious coating for biomedical applicatio
Image-based analysis of interactions between a steady jet and an impulsively started jet
No full textIgnition overpressure (IOP) is a principal dynamic load experienced by a launch vehicle during liftoff. The IOP arises due to the sudden ignition of the solid rocket boosters (SRBs) of a launch vehicle. The present work attempts to simulate the ignition of an SRB with an impulsively started supersonic Md 2.0 jet generated using a quick-open valve. High-speed schlieren flow visualization is used to document the evolution of an impulsively started jet flowfield that included the characteristic precursor shock wave (that simulates the blast wave causing the IOP) and the following vortex ring. The dynamic interactions between the impulsively started supersonic jet and an established steady supersonic jet from another nozzle (Md 2.0) in close proximity are also investigated. Both the precursor shock wave and the vortex ring interact strongly with the established steady-jet column as they proceed downstream from the nozzle exit, thereby introducing new sources of acoustic waves. When a generic jet blast deflector is introduced downstream of the nozzles, the precursor shock wave reflected from it, propagating upstream toward the nozzle exit. The reflected shock wave is recognized as the source of IOP experienced by the launch vehicle. The results show that the quick-open valve presents a unique way to generate impulsively started jets for understanding transients associated with the ignition of the SRB leading to the IOP, without the complexity associated with the use of open-ended shock tubes for carrying out such simulations
Lateral directional aircraft aerodynamic parameter estimation using adaptive stochastic nonlinear filter
No full textThis paper aims to accurately estimate the lateral directional aerodynamic parameters in real time irrespective of the variations in the process and measurement covariance matrices. The proposed algorithm for parameter estimation is based on the integration of adaptive techniques into a stochastic nonlinear filter. The proposed adaptive estimation algorithm is applied to flight test data, and the lateral directional derivatives are estimated in real time. The estimates are compared with those obtained from the Filter Error Method (FEM), an offline parameter estimation method accounting for process noise. The estimation results are observed to be very comparable, and the supremacy of the adaptive filter is illustrated by varying the covariance matrices of both process and measurement noises. The parameters estimated by the adaptive filter are found to converge to their actual values, whereas the estimates of the regular filter are observed to diverge from the actual values when changing the noise covariance matrices. The proposed adaptive algorithm can estimate the lateral directional aerodynamic derivatives more accurately without prior knowledge of either process or measurement noise covariance matrices. Hence, it is of great value in online implementations
Sprayable reduced graphene oxide based high-temperature solar absorber coatings for concentrated solar power applications
No full textReduced graphene oxide (RGO) based composite non‐selective solar absorber coatings (RGO/silicate) were developed using a simple spray technique. RGO powders were prepared using the modified Hummers' method. RGO‐silicate suspensions were obtained by adding an appropriate quantity of RGO in a sodium silicate solution. Transmission electron microscopy studies showed the corrugated morphology of reduced graphene oxide powders. The presence of RGO in the composite absorber coatings was confirmed by X‐ray photoelectron spectroscopy data. In order to study the thermal stability, the coatings were deposited on stainless steel (SS) and Inconel substrates. The composite nonselective coating exhibited an absorptance (α) of 0.96 and emittance (ε) of 0.88 at 82°C on SS and Inconel substrates. The coatings sprayed on SS substrates showed good thermal stability for 428 hours at 500°C in air. The coatings sprayed on Inconel substrates were thermally stable in air at 600°C for 96 hours. The performance evaluation tests revealed that these coatings can be used for concentrated solar power applications. Reduced graphene oxide based absorber coating was developed for solar thermal applications. A simple, and cost effective spray process was used for the deposition. High absorptance of 0.96, and an emittance of 0.88 was obtained for the RGO based absorber coating. The coatings exhibited very high thermal stability in air at 500°C for 428 hours
Asymmetric meander line slot-based X-band leaky wave antenna.
No full textThis article presents broadband, high gain, and highly efficient, leaky wave antenna for X-band applications. The proposed leaky wave antenna consists of periodic unit cells created by a combination of modified asymmetric meander line slots and an array of metallic via. The proposed unit cell configuration work as a composite left hand-right hand leaky wave transmission line and it is characterized using dispersion analysis. The simulated and measurement results indicate that the proposed antenna offers a wide bandwidth of 52.94% (*with stop band of 2.1%) and a large beam scanning range from −59° to 70° with a maximum measured gain of 13.1 dBi
Effect of homologue impurity phases on thermoelectric transport properties of heavily doped ZnO
No full textA comprehensive study of polycrystalline samples of dual-doped Zn1-xAlx/2Inx/2O (x = 0.02, 0.04 and 0.06), Zn1-xGax/2Inx/2O (x = 0.02, 0.04 and 0.06) and triple-doped Zn1-xAlx/3Gax/3Inx/3O (x = 0.03, 0.06 and 0.09) systems synthesized through the solid-state reaction is presented in the light of structure-property correlations. Rietveld refinement of powder XRD data confirmed the presence of impurity phases on highly doped compositions (x ≥ 0.4) for Zn1-xAlx/2Inx/2O and Zn1-xAlx/3Gax/3Inx/3O systems and scanning electron microscopy microstructural analyses showed the presence of elongated morphological feature in all the compositions associated with ZnO homologue systems. Raman studies confirmed presence of both impurity phase and ZnO homologue phase. No visible traces of the presence of impurity phase in Zn1−xGax/2Inx/2O causes relatively low electrical resistivity (ρ ~ 4–5 mΩ cm) in this composition. On the other hand, Zn1−xAlx/2Inx/2O and Zn1-xAlx/3Gax/3Inx/3O systems had electrical resistivity in the range of 10–20 mΩ cm that is one order of magnitude higher than Zn1−xGax/2Inx/2O system. This is arising from the presence of the insulating secondary phases in Zn1−xAlx/2Inx/2O and Zn1−xAlx/3Gax/3Inx/3O systems. Contrary to electrical resistivity, thermal conductivity of Zn1−xAlx/2Inx/2O and Zn1-xAlx/3Gax/3Inx/3O (6–8 Wm−1K−1) systems is one order of magnitude lesser than Zn1-xGax/2Inx/2O (12 Wm−1K−1) systems. The impurity phase present causes phonon–phonon and phonon-interface scattering in Zn1−xAlx/2Inx/2O and Zn1-xAlx/3Gax/3Inx/3O systems which in turn stands beneficial in reducing the total thermal conductivities of the system. Therefore, chemical doping acts as an important parameter for controlling the interdependent electrical and thermal transport properties in ZnO system resulting in relatively superior thermoelectric (TE) performance in Zn0.94Ga0.03In0.03O system. Further, lowering of electrical resistivity and thermal conductivity through doping in Zn0.94Ga0.03In0.03O system causes four times improvement of TE performance in comparison with un-doped ZnO