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Shiv Nadar University

Coupling nonlinear dynamical systems can lead to a host of phenomena, one of which leads to the complete cessation of their oscillations. This phenomenon is referred to as amplitude death (AD) in the dynamical systems literature. Recently, there is a growing interest to mitigate oscillatory or dynamic instabilities in a variety of engineering systems using AD. Deriving impetus from the same, we investigate the possibility of cessation of oscillatory instabilities in aeroelastic systems using the concept of AD. In specific, the suppression of flutter instability that arises in aeroelastic systems due to highly nonlinear fluid–structure interactions is investigated from the purview of AD. To that end, we consider two identical airfoils that are exposed to input fluid forces along the axial directions. The airfoils, via translational and rotational springs, are allowed to oscillate in plunge and pitch degrees of freedom. To augment the findings to in-field scenarios, we consider the individual cases of the input flow to be either uniform (deterministic) or possess randomly time varying components, respectively. To promote coupled interactions, the airfoils are coupled using a linear torsional spring. The coupled interaction of the airfoils at the flutter regime are then studied by obtaining the pitch and plunge responses. Further, the strength of the coupling and the time delay between the airfoils are systematically varied to investigate its effect on the regime of AD. The ability of AD to suppress flutter instability and thereby serve as a possible flutter suppression mechanism in both deterministic and stochastic input flow cases is then demonstrated. Finally, the phase delay values between the airfoils is computed to heuristically present a relationship between the coupling parameters and the post coupling signatures. © 2020 Elsevier Ltd

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Mechanical Engineering

International Journal of Non-Linear Mechanics

Investigating amplitude death in a coupled nonlinear aeroelastic system

In this work, a new simulation approach of transient analysis on single cavity dielectric-modulated (DM) p-type of tunnel field-effect transistor (TFET) is examined for biosensing applications. The device operation and performance are investigated using the 2D device simulator and results are well-calibrated with experimental data. In this work, we have examined DC transfer characteristics, the transient response of drain current, drain current sensitivity (S), and selectivity (Δ S). Focussing more on the transient results, we have obtained maximum sensitivity of orders greater than 108 for APTES biomolecule with respect to air and a significant selectivity value in orders of 103 for APTES with respect to Biotin biomolecule. The performance of the device in terms of selectivity can be further improved (104) by optimizing the back-gate bias, and therefore, the impact of back-gate bias has been analysed. The results for charged biomolecules and partially filled cavity are further investigated highlighted. The DM p-TFET biosensor shows a significant improvement in the results with the transient response for biosensing applications with the feasibility of operating at low voltages (gate voltage of-2.0 V, drain voltage of-0.5 V and back gate voltage 0 to 0.5 V). © 2001-2012 IEEE.

Electrical Engineering

IEEE Sensors Journal

A New Simulation Approach of Transient Response to Enhance the Selectivity and Sensitivity in Tunneling Field Effect Transistor-Based Biosensor

The paper deals with Nonlinear Energy Sinks (NES), utilizing piezoelectric transduction mechanism, focusing on the degree of effect the auxiliary nonlinear stiffness has on the performance of the NES and the performance of NES with the primary system subjected to random excitation. Hence, a parametric sweep of the auxiliary nonlinear stiffness over a broad range of values has been done and the variations in primary vibration suppression and voltage generation by the NES have been observed for its corresponding values. It has been conducted with the NES attached to a linear primary system and then an essentially nonlinear one. Comparison of results and validation of the performance of NES for both the cases have been performed. Following that, performance of the NES has been investigated when a linear primary system is subjected to random excitation. Two separate cases have been utilized to randomize the excitation. Results regarding vibration control and voltage generated have been derived for both and compared to those obtained for deterministic excitation. By and large, it is found that NES is successful in protecting a primary system and broadening the operation bandwidth, while satisfyingly generating voltage, irrespective of the type of excitation on the primary system. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Investigations into Nonlinear Energy Sinks for a Stochastic Dynamical Oscillator

The cost of decompressing (decoding) data can be prohibitive for certain real-time applications. In many scenarios, it is acceptable to sacrifice (to some extent) on compression in the interest of fast decoding. We study anovel problem of finding a prefix tree having the best decode time under the constraint that the code length does not exceed a certain threshold for a natural class of memory access cost functions that use blocking (also referred to as lookup tables). We present exact and approximation algorithms for this problem that are based on dynamic programming and capitalize on interesting structures of the optimal solutions. The full version of this paper is available at [1] © 2021 IEEE.

Data Compression Conference Proceedings

Efficient algorithms for decode efficient prefix codes

To solve the increasing power demand of the growing population without increasing carbon footprint, energy efficiency for renewable sources needs to be improved. This paper focuses on the performance improvement of Savonius vertical axis wind turbine, commonly utilized to harness low wind speed potentials. Such turbines can find excellent use in places where the wind speed is not sufficient for introducing traditional horizontal axis wind turbines. To develop a better aerodynamic design that can reduce drag, dimples introduced on the blade profile. The effect of endplate also studied for improving the performance of the turbine. The design and comparative analysis performed with an endplate and dimpled blade profile. Computational fluid dynamics simulations carried out for understanding the performance of the turbine with dimples and endplates when subjected to low incoming wind velocity. Comparative analysis performed between the proposed design with the baseline design, i.e. with endplates, without endplates and with dimples on blades to show how it affects the efficiency of the turbine. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021.

Numerical analysis of savonius vertical axis wind turbine with dimpled blades

In this study, the authors fabricated a hierarchically structured aluminum surface through facile hot-water treatment and abrasive machining. The developed surfaces were composed of nanoflakes exhibiting extreme wetting states, superhydrophilicity (θ s less than 5°) and superhydrophobicity (θ s greater than 150°) following salinization. The engendered surface morphologies composed of different length scales showed a significant influence on the wetting and durability characteristics. The stability of the observed Cassie state showed a direct correlation with the geometric parameters, particularly the interspatial distance. The critical surface tension for the transition from the Cassie to the Wenzel state increased with the interspatial distance. The surfaces structured with a smaller interspatial distance also exhibited high wetting resilience under dynamic conditions involving single-droplet impacts corresponding to We = 585 owing to a high negative capillary pressure. Further, the fine-structured hierarchical surfaces also exhibited appreciable antifogging and anticorrosion characteristics. Under simulated rain testing, the fine-structured hierarchical surfaces showed better durability than the coarser counterpart, enduring low contact angle hysteresis (CAH) (<10°) even after multiple cycles. Further, weathering tests performed on these samples showed an insignificant influence on their de-wettability. The present study highlights the fabrication of durable metallic surfaces through facile and sustainable fabrication method for multifunctional applications. © 2022 ICE Publishing: All rights reserved.

Surface Innovations

Facile approach for modulating wetting of hierarchically structured metallic surface

Thermal spraying is a scalable surface engineering technique used to add or to restore functionality of a solid surface by applying a coating. Examples of this include protection against wear, erosion, abrasion, and heat. In a specific sense, thermal spraying is particularly used to deposit thermal barrier coatings (TBCs) which finds use in transportation, power generation and automotive sector. As being a surface technique, thermal spraying much like other surface coating techniques can avoid the use of excessive bulk materials and in turn offers longevity to the life of the component, so it already contributes to the reduction of global warming by virtue of avoiding the use of excessive scarce materials and improving fuel efficiency. In terms of its contribution to the cause of global warming, thermal spraying stands in sharp contrast to the energy-intensive processes such as melting, casting, extrusion and welding. With the rise of additive manufacturing, it is possible to use thermal spray to complement that process in many ways and “cold spray additive manufacturing” (CSAM) is already gaining popularity. The thermal spraying technique relies on using selective types of gases—hydrogen being one of them and few types of metals/alloys which are now classed as critical raw materials due to them being on the supply risk register. Efforts to consider recycling and reuse and to find alternatives to these are very timely to continue drawing the advantage of thermal spraying being a relatively green technique. In particular, the green energy initiatives and the drive to develop energy storage and battery technologies could challenge the supply of raw materials such as hydrogen gas and rare earth elements. This underlines the research and development need for alternate materials and processes to address the issue of climate change which is the major focal point of the COP 26 Summit at Glasgow in 2021. The combination of digital technologies and thermal spray coatings will reduce gas, powder and power consumption, which will make this manufacturing process even greener. © 2021, The Author(s).

Fulltext

Emergent Materials

Role of thermal spray in combating climate change

This work considers the 5G new radio (5G-NR) frame structure through the 3GPP channel model in Rural-Macro (RMa) scenario. A graph-based channel-coding scheme to ensure data-security to the intended user/destination in a MIMO-cooperative communication network in presence of an external passive eavesdropper is proposed. For this purpose, two graphs: mathcal{G} {M}( mathrm{V} {M}, mathcal{E} {M}, mathrm{W} {M}) , mathcal{G} {E}( mathrm{V} {E}, mathcal{E} {E}, mathrm{W} {E}) corresponding to the source-relay-destination, source-relay-eavesdropper are considered in MIMO-channels environment respectively. The channel coding scheme, based on the inverse graph Fourier transformation (IGFT) of the mathcal{G} {M} , is proposed to create increased bit/symbol errors at the eavesdropper along with the MIMO-diversity gain at the main user. The GFT of mathcal{G} {M} based postcoder is used at the destination to detect the transmitted symbols whereas GFT of mathcal{G} {E} with/without postcoder at the eavesdropper is used to estimates the signal. Physical layer security (PLS) scheme based on the difference of BERs between destination and the eavesdropper is proposed. © 2021 IEEE.

Proceedings of the 2021 IEEE 18th India Council International Conference, INDICON 2021

Graph-Based Channel-Aware Secure-Coding for Cooperative Communication

Thermal analysis of Silicon Carbide (SiC) power semiconductor packages is a crucial design step to ensure highly reliable device performance at elevated temperatures. The square-root-t extrapolation method is widely adopted to approximate the temperature development within the SiC die for short time transients when device temperature measurements cannot be performed. The reduced thermal resistance of the SiC die leads to smaller thermal time constants. Therefore, the approximation of the heat propagation in SiC devices also has to include the die attach. This paper analyzes the thermal behavior of SiC power semiconductor packages by means of comprehensive FEM simulations, allowing to more precisely determine the error of the temperature estimation based on the square-root-t approximation for SiC power devices. © 2021 IEEE.

IEEE International Reliability Physics Symposium Proceedings

Accuracy of Thermal Analysis for SiC Power Devices

The Visual Question Answering (VQA) task combines challenges for processing data with both Visual and Linguistic processing, to answer basic ‘common sense’ questions about given images. Given an image and a question in natural language, the VQA system tries to find the correct answer to it using visual elements of the image and inference gathered from textual questions. In this survey, we cover and discuss the recent datasets released in the VQA domain dealing with various types of question-formats and robustness of the machine-learning models. Next, we discuss about new deep learning models that have shown promising results over the VQA datasets. At the end, we present and discuss some of the results computed by us over the vanilla VQA model, Stacked Attention Network and the VQA Challenge 2017 winner model. We also provide the detailed analysis along with the challenges and future research directions. © 2021, Springer Nature Singapore Pte Ltd.