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IIT Hyderabad

Department of Mechanical and Aerospace Engineering

In this paper, we developed two dimensional and three dimensional boundary element method (BEM) to compute hydrodynamic forces due to the oscillation of non-uniform beam (NUB) in a quiescent incompressible fluid with linear and quartic varying widths. To model the fluid flow under small amplitude oscillation of thin NUB in its first mode, the linearized unsteady Stokes equation is solved using BEM. After finding the converged structural and fluid nodes in all the cases, we compute real and imaginary components of hydrodynamic function. Subsequently, damping ratio or quality factor is found from energy dissipation due to drag forces mainly because of stress jumps across the thin beam thickness. Similarly, the frequency shift is found due to virtual added mass obtained from the mean hydrodynamic thrust force. The results are validated with existing literature and further analysis is done in terms of tapering parameter and index of non-uniform beam, and the corresponding aspect ratio and frequency parameters. Based on the analysis presented, it is found that quartic converging beam provides better quality factor and least added mass effect and it can be explored to design a cantilever based resonator operating in fluid with improved performance such as AFM probes. Thus, the new model developed for non-uniform beam can be useful to drag forces in other types of 2D and 3D beams. © 2022 Elsevier Ltd

World University root node

International Journal of Mechanical Sciences

Hydrodynamic forces in non-uniform cantilever beam resonator

The Eastern Uttar Pradesh region of India is known for its endemicity of acute encephalitis syndrome (AES). Decades of research have established that Orientia tsutsugamushi, a causative of scrub typhus, is a substantial contributor (>60%) for the AES cases besides other aetiology, but additional factors in the remaining proportion are still unidentified. Rickettsial infections are challenging to diagnose in clinical settings due to overlapping clinical symptoms, the absence of definitive indicators, a low index of suspicion, and the lack of low-cost, rapid diagnostic tools. Hence, the present study was designed to determine the load of rickettsial infections among AES cases. Furthermore, we aim to find out the prevalent rickettsial species in AES cases as well as in the vector population at this location. The study included the whole blood/cerebrospinal fluid of AES patients and arthropod specimens from rodents. The molecular identification was performed using the 23S-5S intergenic spacer region and ompB gene with genomic DNA obtained from studied specimens. We detected 5.34% (62/1160) of rickettsial infection in AES cases. Among these, phylogenetic analysis confirmed the presence of 54.8% Rickettsia conorii (n = 34) and 16.1% of Rickettsia felis (n = 10), while the rest proportion of the isolates was unidentified at the species level. Furthermore, R. felis was identified in one CSF sample from AES patients and three flea samples from Xenopsylla cheopis. Rickettsia spp. was also confirmed in one Ornithonyssus bacoti mite sample. The results of this investigation concluded the presence of spotted fever group Rickettsia spp. among AES identified cases as well as in the mite and flea vectors that infest rodents. © 2023 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.

Zoonoses and Public Health

Molecular detection of spotted fever group of Rickettsiae in acute encephalitis syndrome cases from eastern Uttar Pradesh region of India

In typical split-Hopkinson pressure bar set-ups, the striker bar is propelled in a barrel of larger diameter. Teflon/brass sabots are used to concentrically-align the striker inside the barrel. The influence of the area mismatch between barrel and striker, length of the sabots and interface condition between sabot and striker are analyzed in detail using finite element simulations. We show that for a given geometry of the sabot, a frictionless interface does not alter the incident signals. In the presence of friction, the incident signals deviate from the classical trapezoidal shape. The magnitude of the deviation depends on the geometry of the sabot. As an alternative to the shrink/press fitted sabot, a stepped striker is used to eliminate some issues faced during the usage of the shrink/press-fitted sabot. The stepped striker has a non-uniform diameter such that at two locations its diameter is that of the barrel, and at other locations it has the same diameter as the incident bar. The influence of the geometry of the stepped striker on the distortion of the incident signal is investigated in detail using the method of characteristics. A parametric study is used to quantify this distortion for various geometric configurations of the stepped striker. Three striker geometries are chosen from these configurations to validate the parametric study using experiments. High strain rate characterization of SS304 is also carried using these strikers to illustrate the effect of the geometry of the stepped striker on the stress versus strain and strain rate versus strain response. © 2023 Elsevier Ltd

International Journal of Impact Engineering

Revisiting the effect of sabot on the incident signals of split-Hopkinson pressure bar

The objective of this study is to experimentally characterize the performance of four different composite/composite single lap joint configurations at various loading rates. The four joint configurations are single bolted joint, simply bonded joint, single bolted hybrid joint (a single bolt is used along the lap length of a simply bonded joint) and multiple micro bolted hybrid joint (four micro-bolts are used along the lap length of a simply bonded joint). The lap joints are tested at various loading rates using tensile split-Hopkinson bar and fatigue testing machine. Experiments reveal that, for a given joint configuration, the peak load, initial stiffness, and energy absorbed generally increased with the loading rates, whereas the plateau load is relatively insensitive to the loading rates. Finite element analysis (FEA) using the commercial software Abaqus/Explicit solver for all the configurations is also performed to simulate experimental loading conditions. It has revealed that by accounting for rate dependency of adhesive one can qualitatively explain the experimental observations. © 2023 Elsevier Ltd

Composites Part A: Applied Science and Manufacturing

Experimental characterization of CFRP single lap joints under tension at various loading rates

Cyclones are among the most hazardous extreme weather events on Earth. In certain scenarios, two co-rotating cyclones in close proximity to one another can drift closer and completely merge into a single cyclonic system. Identifying the dynamic transitions during such an interaction period of binary cyclones and predicting the complete merger (CM) event are challenging for weather forecasters. In this work, we suggest an innovative approach to understand the evolving vortical interactions between the cyclones during two such CM events (Noru-Kulap and Seroja-Odette) using time-evolving induced velocity-based unweighted directed networks. We find that network-based indicators, namely, in-degree and out-degree, quantify the changes in the interaction between the two cyclones and are excellent candidates to classify the interaction stages before a CM. The network indicators also help to identify the dominant cyclone during the period of interaction and quantify the variation of the strength of the dominating and merged cyclones. Finally, we show that the network measures also provide an early indication of the CM event well before its occurrence. © 2023 Author(s).

Chaos

Study of interaction and complete merging of binary cyclones using complex networks

TWAM (twin-wire welding additive manufacturing) is a new additive manufacturing (AM) technology that uses gas metal arc welding (GMAW) to create metallic objects. Apart from greater deposition rates, twin-wire welding also allows for the creation of gradient objects with variable mechanical characteristics by using dissimilar filler wires. One of the most challenging problems to address is how to control thermal stresses while depositing many layers on the substrate plate. This research investigates residual stresses and distortion developed during weld bead deposition using finite element simulations (FES) and experimental approaches. Two additive beads with 32% lateral overlap were modeled in FEA software (ABAQUS) using the element birth technique. A passive coupled thermo-mechanical model was used to calculate the temperature gradient-driven residual stresses and distortion created during and after material deposition. Weld deposition was carried out with a twin-wire GMAW setup with online thermal monitoring using a thermocouple. The development of residual strains during weld bead deposition is influenced by temperature distribution. Residual stresses and distortion were quantified with X-ray diffraction (XRD) and a coordinate measuring machine (CMM). Experimental residual stresses and distortion have a good agreement with those found in FE simulations; this proves the numerical model to be accurate. © 2022, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Experimental and Numerical Investigation of Double Pass Overlapping Beads by Twin-Wire Welding Additive Manufacturing Process

This study explored the discrete element method to model the Inconel powder flow through the laser head nozzles. The laser head was modeled with four nozzles. Bi-particulate powder flow simulations were carried out using discrete element modeling through LIGGGHTS open-source software. Then, the temperature distribution on the powder particles on the base plate was captured using finite element simulations using COMSOL. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Modeling of Inconel Powder Flow and Thermal Distribution During the Direct Energy Deposition Process

The flow in the atmospheric boundary layer behind an abrupt transition in the surface roughness is studied using large eddy simulations (LES). A key ingredient of the LES is the ‘wall model’ that prescribes the instantaneous shear stress at the bottom surface as a function of the velocity field at the lower-most computational grid point. Two previously-developed wall models are evaluated; the first (BZ) is based on filtering the velocity field and the second (APA) is based on a blending function. The axial evolution of the wall shear stress, and vertical profiles of several quantities such as the stream-wise velocity, turbulence intensity and the total shear stress are evaluated. The APA model is found to predict the shear stress at the surface more accurately than the BZ model when compared with previous experimental results. Not all statistics are found to be equally sensitive to the wall models. We also employ the LES to evaluate an empirical relation for the height of the internal boundary-layer (IBL), which is commonly used to derive analytical models for the mean velocity profiles and wall shear stresses. The empirical relation is found to be reasonably accurate when the IBL height is calculated based on the shear stress but not when it is calculated based on the streamwise velocity variance. These results suggest that the wall model in LES of heterogeneously rough surfaces plays a key role and should be selected carefully in view of the quantity of interest. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Sensitivity of Atmospheric Boundary Layer Statistics to LES Wall Shear Stress Models Behind a Surface Roughness Jump

We investigate the morphology and size distribution of satellite droplets resulting from the interaction of a freely falling water droplet with a swirling airstream of different strengths by employing shadowgraphy and deep-learning-based digital in-line holography techniques. We found that the droplet exhibits vibrational, retracting bag and normal breakup phenomena for the no swirl, low and high swirl strengths for the same aerodynamic field. In the high-swirl scenario, the disintegrations of the nodes, rim and bag-film contribute to the number mean diameter, resulting in smaller satellite droplets. In contrast, in the low-swirl case, the breakup of the rim and nodes only contributes to the size distribution, resulting in larger droplets. The temporal variation of the Sauter mean diameter reveals that for a given aerodynamic force, a high swirl strength produces more surface area and surface energy than a low swirl strength. The theoretical prediction of the number-mean probability density of tiny satellite droplets under swirl conditions agrees with experimental data. However, for the low swirl, the predictions differ from the experimental results, particularly due to the presence of large satellite droplets. Our results reveal that the volume-weighted droplet size distribution exhibits two (bi-modal) and three (multi-model) peaks for low and high swirl strengths, respectively. The analytical model that takes into account various mechanisms, such as the nodes, rim and bag breakups, accurately predicts the shape and characteristic sizes of each mode for the case of high swirl strength. © The Author(s), 2023. Published by Cambridge University Press.

Department of Chemical Engineering

Fulltext

Journal of Fluid Mechanics

Droplet size distribution in a swirl airstream using in-line holography technique

The size distribution of child droplets resulting from a dual-bag fragmentation of a water drop is investigated using shadowgraphy and digital in-line holography techniques. It is observed that parent drop fragmentation contributes to the atomisation of tiny child droplets, whereas core drop disintegration predominantly results in larger fragments. Despite the complexity associated with dual-bag fragmentation, we demonstrate that it exhibits a bi-modal size distribution. In contrast, the single-bag breakup undergoes a tri-modal size distribution. We employ the analytical model developed by Jackiw &amp; Ashgriz (J. Fluid Mech., vol. 940, 2022, A17) for dual-bag fragmentation that convincingly predicts the experimentally observed droplet volume probability density. We also estimate the temporal evolution of child droplet production in order to quantitatively illustrate the decomposition into initial and core breakups. Furthermore, we confirm that the analytical model adequately predicts the droplet size distribution for a range of Weber numbers. © Indian Institute of Technology Hyderabad, India, 2023. Published by Cambridge University Press.