Browsing by Author "Kumar, Arvind"

Now showing 1 - 4 of 4
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    Application of spectral and spatial indices for specific class identification in Airborne Prism EXperiment (APEX) imaging spectrometer data for improved land cover classification
    (SPIE, 2016-09) Kallepalli, Akhil; Kumar, Arvind; Khoshelham, K.; James, David B.
    Hyperspectral remote sensing's ability to capture spectral information of targets in very narrow bandwidths gives rise to many intrinsic applications. However, the major limiting disadvantage to its applicability is its dimensionality, known as the Hughes Phenomenon. Traditional classification and image processing approaches fail to process data along many contiguous bands due to inadequate training samples. Another challenge of successful classification is to deal with the real world scenario of mixed pixels i.e. presence of more than one class within a single pixel. An attempt has been made to deal with the problems of dimensionality and mixed pixels, with an objective to improve the accuracy of class identification. In this paper, we discuss the application of indices to cope with the disadvantage of the dimensionality of the Airborne Prism EXperiment (APEX) hyperspectral Open Science Dataset (OSD) and to improve the classification accuracy using the Possibilistic c–Means (PCM) algorithm. This was used for the formulation of spectral and spatial indices to describe the information in the dataset in a lesser dimensionality. This reduced dimensionality is used for classification, attempting to improve the accuracy of determination of specific classes. Spectral indices are compiled from the spectral signatures of the target and spatial indices have been defined using texture analysis over defined neighbourhoods. The classification of 20 classes of varying spatial distributions was considered in order to evaluate the applicability of spectral and spatial indices in the extraction of specific class information. The classification of the dataset was performed in two stages; spectral and a combination of spectral and spatial indices individually as input for the PCM classifier. In addition to the reduction of entropy, while considering a spectral-spatial indices approach, an overall classification accuracy of 80.50% was achieved, against 65% (spectral indices only) and 59.50% (optimally determined principal components
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    Effects of angular injection, and effervescent atomization on high-velocity suspension flame spray process
    (Elsevier, 2016-06-11) Mahrukh, Mahrukh; Kumar, Arvind; Gu, Sai
    This work presents the nanostructured coating formation using suspension thermal spraying through the HVOF torch. The nanostructured coating formation requires nanosize powder particles to be injected inside a thermal spray torch using liquid feedstock. The liquid feedstock needs to be atomized when injected into the high-velocity oxygen fuel (HVOF) torch. This paper presents the effects of angular injection and effervescent atomization of the liquid feedstock on gas and droplet dynamics, vaporization rate, and secondary breakup in the high-velocity suspension flame spray (HVSFS) process. Different angular injections are tested to obtain the optimum value of the angle of injection. Moreover, effervescent atomization technique based on twin-fluid injection has been studied to increase the efficiency of the HVSFS process. Different solid nanoparticle concentrations in suspension droplets are considered. In angular injection the droplets are injected into the core of the combustion zone; this immediately evaporates the droplets, and evaporation is completed within the torch. The value of 10°–15° is selected as the optimal angle of injection to improve the gas and droplet dynamics inside the torch, and to avoid the collision with the torch's wall. The efficiency of the effervescent atomization can be enhanced by using high gas-to-liquid mass flow rate ratio, to increase the spray cone angle for injecting the suspension liquid directly into the combustion flame. It is also found that the increment in the nanoparticle concentration has no considerable effects on the droplet disintegration process. However, the location of evaporation is significantly different for homogeneous and non-homogeneous droplets.
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    Modeling the effects of concentration of solid nanoparticles in liquid feedstock injection on high-velocity suspension flame spray process
    (American Chemical Society, 2016-02-03) Mahrukh, Mahrukh; Kumar, Arvind; Gu, Sai; Kamnis, S.; Gozali, E.
    This paper presents the effects of the concentration of solid nanoparticles in the liquid feedstock injection on the high-velocity suspension flame spray (HVSFS) process. Four different concentrations of solid nanoparticles in suspension droplets with various droplet diameters are used to study gas dynamics, vaporization rate, and secondary breakup. Two types of injections, viz. surface and group, are used. The group-type injection increases the efficiency of droplet disintegration and the evaporation process and reduces the gas cooling. The initiation of the fragmentation process is difficult for small droplets carrying a high concentration of nanoparticles. Also, smaller droplets undergo rapid vaporization, leaving clogs of nanoparticles in the middle of the barrel. For larger droplets, severe fragmentation occurs inside the combustion chamber. For a higher concentration of nanoparticles, droplets exit the gun without complete evaporation. The results suggest that, in coating applications involving a higher concentration of nanoparticles, smaller droplet sizes are preferred.
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    Numerical analysis of the effects of using effervescent atomization on solution precursor thermal spraying process
    (American Chemical Society, 2017-09-09) Mahrukh, Mahrukh; Kumar, Arvind; Nabavi, Seyed Ali; Gu, Sai; Sher, Ilai
    The solution precursor thermal spraying (SPTS) process is used to obtain nano-sized dense coating layers. During the SPTS process, the in situ formation of nanoparticles is mainly dependent on combustion gas-temperature, gas-pressure, gas-velocity, torch design, fuel type, and Oxygen-Fuel (O/F) mixture ratios, precursor injection feeding ratio and flow rates, properties of fuel and precursor and its concentration, and the precursor droplets fragmentation. The focus of the present work is the numerical study of atomization of pure solvent droplets streams into fine droplets spray using an effervescent twin-fluid atomizer. For better droplet disintegration appropriate atomization techniques can be used for injecting the precursor in the CH-2000 high-velocity oxygen fuel (HVOF) torch. The CFD computations of the SPTS process are essentially required because the internal flow physics of HVOF process cannot be examined experimentally. In this research for the first time, an effervescent twin-fluid injection nozzle is designed to inject the solution precursor into the HVOF torch, and the effects on the HVOF flame dynamics are analyzed. The computational fluid dynamics (CFD) modeling is performed using Linearized Instability Sheet Atomization (LISA) model and validated by the measured values of droplets size distribution at varied Gas-to-Liquid flow rate Ratios (GLR). Different nozzle diameters with varied injection parameters are numerically tested, and results are compared to observe the effects on the droplet disintegration and evaporation. It is concluded that the effervescent atomization nozzle used in the CH-2000 HVOF torch can work efficiently even with bigger exit diameters and with higher values of viscosity and surface-tension of the solution. It can generate smaller size precursor droplets (2 µm