(SoE) School of Engineering

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Shiv Nadar University

Wind tunnel experiments carried out on a pitch-plunge aeroelastic system in the presence of fluctuating flows reveal that flutter instability is presaged by a regime of intermittency. It is observed that as the flow speed gradually increases towards the flutter speed, there appears intermittent bursts of periodic oscillations which become more frequent as the wind speed increases and eventually the dynamics transition into fully developed limit cycle oscillations, marking the onset of flutter. The signature from these intermittent oscillations are exploited to develop measures that forewarn a transition to flutter and can serve as precursors. This study investigates a suite of measures that are obtained directly from the time history of measurements and are hence model independent. The dependence of these precursors on the size of the measured data set and the time required for their computation is investigated. These measures can be useful in structural health monitoring of aeroelastic structures. © 2018 Elsevier Ltd

Mechanical Engineering

World University root node

Journal of Sound and Vibration

Investigations on precursor measures for aeroelastic flutter

Structures made of variable stiffness (VS) composites possess a rich design space for bistable configurations that demonstrate different values of curvatures and out-of-plane displacements. In this study, several VS composites are investigated which can yield cylindrical bistable shapes similar to those generated from unsymmetrical cross-plies. Such configurations have been found favorable as a component for certain morphing applications. A semi-analytical model based on the Rayleigh-Ritz approach is presented to calculate the thermally induced multistable shapes as well as the snap-through forces particularly taking into account the curvilinear paths of VS composites. A nonlinear finite element analysis is performed to check the accuracy of the semi-analytical method. Cylindrical shapes generated from VS laminates and the corresponding straight fiber cross-ply laminates are analyzed and compared. The snap-through forces are subsequently calculated and compared for different VS laminates and the straight fiber cross-ply. It is observed that certain VS composites have a significant reduction of snap-through forces but with a marginal difference in out-of-plane displacement as compared to the corresponding straight fiber cross-ply laminate.

Civil Engineering

Lecture Notes in Applied and Computational Mechanics

Multiscale Modeling of Heterogeneous Structures

Estimating scene flow in RGB-D videos is attracting much interest of the computer vision researchers, due to its potential applications in robotics. The state-of-the-art techniques for scene flow estimation typically rely on the knowledge of scene structure of the frame and the correspondence between frames. However, with the availability of large RGB-D data captured from depth sensors, learning representations for estimation of scene flow has become possible. This paper introduces a first effort to apply a deep learning method for direct estimation of scene flow by presenting a fully convolutional neural network with an encoder-decoder (ED) architecture. The proposed network SceneEDNet involves estimation of three dimensional motion vectors of all the scene points from sequence of stereo images. The training for direct estimation of scene flow is done using consecutive pairs of stereo images and corresponding scene flow ground truth. © 2018 IEEE.

Computer Science and Engineering

2018 15th International Conference on Control, Automation, Robotics and Vision, ICARCV 2018

SceneEDNet: A Deep Learning Approach for Scene Flow Estimation

The operation of transistorized Marx-bank circuits (MBCs) is analyzed, and physics-based modeling is used to understand the anomalous switching behavior of the first stage single trigger avalanche transistors of MBCs at high-current-injection conditions. The role of a voltage trigger pulse having variable rise time when applied to the base terminal is investigated to model the underlying physics of the anomalous switching behavior. Experimental observations related to ultrafast anomalous switching mechanisms of trigger transistor, i.e., either primary breakdown or current mode secondary breakdown, for faster and slower base drives are presented. This demonstrates the importance of the dynamic avalanche process and reverse saturation current on the switching mechanism under high-speed base-trigger ramps for different avalanche BJTs from various manufacturers and different lots. The agreement between 2-D TCAD device simulation results and the experimental observations shows the validity of the proposed theory when the base width and mobile carrier recombination rate are used as parameters in the device simulation setup. © 1973-2012 IEEE.

Electrical Engineering

IEEE Transactions on Plasma Science

Fast Ionization-Front-Induced Anomalous Switching Behavior in Trigger Bipolar Transistors of Marx-Bank Circuits under Base-Drive Conditions

Aeroelastic systems with freeplay nonlinearity can exhibit a wide variety of qualitatively different dynamical responses such as limit cycle oscillations and chaos in the pre-flutter regimes. Consequently, the bifurcation scenario in an aeroelastic system with freeplay nonlinearity under uniform flows have received considerable attention in the literature. However, in reality flows are far from deterministic and often possess a small temporal random fluctuations about a mean value. Input flow fluctuations have the potential to alter the stability and give rise to atypical routes to flutter. Indeed, recent studies have shown that under flow fluctuations the aeroelastic systems loses its stability via a regime of oscillations called intermittency. Further, it is observed that the presence of cubic hardening nonlinearity and input flow fluctuations with predominantly long time scales can give rise to "on-off" type intermittency. This dynamical behaviour is attributed to type of nonlinearity and relatively short time scale for the system to stay and exhibit distinct dynamics. Extending the mechanism of intermittency route to flutter in aeroelastic systems with other prominent types of nonlinearities, such as, freeplay have however, received minimal attention in the literature. The present study devotes itself to investigate the response dynamics of an airfoil with freeplay nonlinearity subjected to long time scale input flow fluctuations. © The Authors, published by EDP Sciences, 2018.

Fulltext

MATEC Web of Conferences

Investigating the route to flutter in a pitch-plunge airfoil with freeplay nonlinearity subjected to input flow fluctuations

Cavitation erosion and corrosion of structural materials are serious concerns for marine and offshore industries. Durability and performance of marine components are severely impaired due to degradation from erosion and corrosion. Utilization of advanced structural materials can play a vital role in limiting such degradation. High entropy alloys (HEAs) are a relatively new class of advanced structural materials with exceptional properties. In the present work, we report on the cavitation erosion behavior of Al0.1CoCrFeNi HEA in two different media: distilled water with and without 3.5 wt\% NaCl. For comparison, conventionally used stainless steel SS316L was also evaluated in identical test conditions. Despite lower hardness and yield strength, the HEA showed significantly longer incubation period and lower erosion-corrosion rate (nearly 1/4th) compared to SS316L steel. Enhanced erosion resistance of HEA was attributed to its high work-hardening behavior and stable passivation film on the surface. The Al0.1CoCrFeNi HEA showed lower corrosion current density, high pitting resistance and protection potential compared to SS316L steel. Further, HEA showed no evidence of intergranular corrosion likely due to the absence of secondary precipitates. Although, the degradation mechanisms (formation of pits and fatigue cracks) were similar for both the materials, the damage severity was found to be much higher for SS316L steel compared to HEA. © 2017 Elsevier B.V.

Ultrasonics Sonochemistry

Exceptionally high cavitation erosion and corrosion resistance of a high entropy alloy

It is generally believed that the existence of all organisms present on this earth has their point of convergence in a common gene pool. The current species passed through an evolutionary process which is still underway. The theoretical assumptions relating to the common descent of all organisms are based on four simple facts: first, they had wide geographical dispersal; second, the different life forms were not remarkably unique and did not possess mutually exclusive characteristics; third, some of their attributes which apparently served no purpose had an uncanny similarity with some of their lost functional traits; and last, based on their common attributes these organisms can be put together into a well-defined, hierarchical and coherent group, like a family tree. Phylogenetic networks are the main tools that can be used to represent biological relationship between different species. Biologists, mathematicians, statisticians, computer scientists and others have designed various models for the reconstruction of evolutionary networks and developed numerous algorithms for efficient predictions and analysis. Even though these problems have been studied for a very long time, but the computational model built to solve the biological problems fail to give accurate results while working on real biological data, which could be due to the premises on which the model is based. The objective of this paper is to test and analyse the transmission of commonly occurring diseases to fit into more realistic models. The problems are not only important because we need to know how they came into existence and how they migrated, but also helpful for the treatment of such diseases and drug discovery. © 2018, Springer Nature Singapore Pte Ltd.

Advances in Intelligent Systems and Computing

Analysing the genetic diversity of commonly occurring diseases

This paper presents a compact triple band antenna for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) application. The proposed antenna has a rectangular patch with rectangular ring slot and a small rectangular shape slot in a partial ground plane. The dimensions of the patch, the ground and the two slots are optimized to obtain resonance at 1.6 GHz, 2.4 GHz and 5.2GHz frequencies. © 2018 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Triple band antenna for WLAN/WiMAX applications

There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, where numerous desirable attributes are achieved simultaneously from multiple elements in equimolar (or near equimolar) proportions. While there are several review articles on alloy development, microstructure, mechanical behavior, and other bulk properties of these alloys, then there is a pressing need for an overview that is focused on their surface properties and surface degradation mechanisms. In this paper, we present a comprehensive view on corrosion, erosion and wear behavior of complex concentrated alloys. The effect of alloying elements, microstructure, and processing methods on the surface degradation behavior are analyzed and discussed in detail. We identify critical knowledge gaps in individual reports and highlight the underlying mechanisms and synergy between the different degradation routes. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

Metals

Corrosion, erosion andwear behavior of complex concentrated alloys: A review

Three-phase segmented gas-liquid-liquid (G/L/L) flows in minichannels are important to several chemical process applications involving gas-liquid-liquid reactions. In the present work, we have investigated segmented G/L/L flows in a double T-junction minichannel, with cross-section of 0.95 mm × 1 mm, through high-speed imaging experiments and Volume-of-Fluid (VOF) simulations. The dynamics of bubble/slug formation at the 1st T-junction and importantly that of water drop/slug formation at the 2nd T-junction was simulated under different flow conditions (Caoil=2.63×10-3-1.101; Weair=4.24×10-4-2.62×10-3; Wewater=0.0431-7.14) and different surfactant concentrations (0.3 and 2 wt/wt.\%) in aqueous phase. The predicted formation mechanisms, three-phase flow regimes, and drop/bubble/slug lengths were compared quantitatively with the measurements. Different mechanisms of bubble/slug formation observed for the aforementioned range of the Caoil and Weair, and bubble/slug lengths were predicted in a satisfactory agreement with the measurements. The complex formation mechanism of water drops/slugs that was governed by viscous force exerted by continuous oil phase, inertial force exerted by water phase, interfacial tension force acting on the oil-water interface and also by incoming air bubbles/slugs; could be predicted in a satisfactory agreement with those observed in the experiments. Different three-phase flow regimes, e.g., drop-bubble, drop-slug and slug-slug, observed for different oil, air and water flow rates; and for different values of oil-water interfacial tensions are also predicted in satisfactory agreement with the measurements. The results reported in the present work help to understand the hydrodynamics of complex three-phase gas-liquid-liquid flows in minichannels, which in turn is crucial to device microreactor systems for process applications involving G/L/L flows. © 2018 Elsevier B.V.