Department of Mechanical Engineering

&ldquo;IIT Jodhpur is committed to impart quality education to facilitate the creation of qualified, competent and responsible human resources to meet the emerging technological challenges of the world. It is working towards creating an equitable learning platform that is positive, accessible and effective in the face of the modern societal and scientific advancements.

Flexibility in curriculum, in all its academic programs, encompassing elements of teaching, research, creativity, innovation and entrepreneurship is the most unique feature of IIT Jodhpur. The Department of Science and Technology (DST), under the National Mission on Cyber Physical Systems, has identified IIT Jodhpur as a Technology &amp; Innovation Hub in the area of Augmented Reality and Virtual Reality. The institute has also been nominated as the coordinator for the Jodhpur City and Knowledge Cluster by the Office of Principal Scientific Adviser, Government of India.

The sprawling 852-acre IIT Jodhpur campus is a majestic tribute to the deep-rooted diverse cultural heritage of the region. The campus is an architectural masterpiece, which is slated to become an international exemplar of sustainability with net-zero energy, and advanced water and waste management strategies.&rdquo;

IIT Jodhpur

Stability and optimality are the two foremost re-quirements for robotic systems that are deployed in critical operations and are to work for long hours or under limited energy resources. To address these, in this work we present a novel Lyapunov stability based discrete-time optimal kinematic control of a robot manipulator using actor-critic (AC) framework. The robot is actuated using optimal joint-space velocity control input to track a time-varying end-effector trajectory in its task space. In comparison to the existing near-optimal kinematic control solutions for robot manipulator under AC framework, proposed controller exhibits guaranteed analytical stability. We derive a novel critic weight update law based on Lyapunov stability, thus ensuring that the weights are updated along the negative gradient of Lyapunov function. This eventually ensures closed-loop system stability and convergence to the optimal control in discrete-time. Extensive simulations are performed on a 3D model of 6-DoF Universal Robot (UR) 10 in Gazebo, followed by implementation on real UR 10 robot manipulator to show the efficacy of the proposed scheme. © 2020 IEEE.

World University root node

Proceedings of the International Joint Conference on Neural Networks

Discrete-Time Lyapunov based Kinematic Control of Robot Manipulator using Actor-Critic Framework

The objective of the present work is to study two phase flow pressure drop in a helically coiled once through steam generator under sub-atmospheric conditions. Literature survey on two-phase flow pressure drop in a helical coil reveals that most of the research articles correspond to studies under high pressure and only few data are available for sub-atmospheric pressure conditions. In this study, an experimental investigation is carried out for a helically coiled tube of tube diameter 9.5 mm, coil diameter 282.7 mm and tube length 5330 mm. System is operated at sub-atmospheric pressure of 150 mbar and atmospheric pressure, respectively. Water and/or steam mass flow rate through the steam generator are taken at 36 kg/h, 54 kg/h and 72 kg/h. A 50 kW capacity DC power supply is used to supply required heat for steam generation. Experiment is carried out for power input ranging from 10 kW to 30 kW. The steam quality at helical coil exit is kept near to 0.5 and hence the power input is decided by amount of heat required to convert liquid water at inlet temperature to saturated vapour-liquid mixture with vapour quality of 0.5. The liquid to steam density ratio ranges from 7500 to 16000. In this study it is observed that the pressure drop at sub-atmospheric pressure is high as compared to atmospheric pressure. © 2019 Elsevier Ltd.

Materials Today: Proceedings

Experimental study on effect of system pressure on two-phase flow pressure drop at sub-atmospheric conditions

This paper presents a novel CFD-driven machine learning framework to develop Reynolds-averaged Navier-Stokes (RANS) models. The CFD-driven training is an extension of the gene expression programming method Weatheritt and Sandberg (2016) [8], but crucially the fitness of candidate models is now evaluated by running RANS calculations in an integrated way, rather than using an algebraic function. Unlike other data-driven methods that fit the Reynolds stresses of trained models to high-fidelity data, the cost function for the CFD-driven training can be defined based on any flow feature from the CFD results. This extends the applicability of the method especially when the training data is limited. Furthermore, the resulting model, which is the one providing the most accurate CFD results at the end of the training, inherently shows good performance in RANS calculations. To demonstrate the potential of this new method, the CFD-driven machine learning approach is applied to model development for wake mixing in turbomachines. A new model is trained based on a high-pressure turbine case and then tested for three additional cases, all representative of modern turbine nozzles. Despite the geometric configurations and operating conditions being different among the cases, the predicted wake mixing profiles are significantly improved in all of these a posteriori tests. Moreover, the model equation is explicitly given and available for analysis, thus it could be deduced that the enhanced wake prediction is predominantly due to the extra diffusion introduced by the CFD-driven model. © 2020 Elsevier Inc.

Journal of Computational Physics

RANS turbulence model development using CFD-driven machine learning

Evaporation characteristics of a radiatively heated (~1000 W/m2 of incident heat flux) unconventional porous medium consisting of closely packed vertical capillaries have been investigated. Three stages of mass loss from a conventional porous medium, consisting of spheres, are well known; high evaporation rate in stage 1 is sustained by capillary liquid films, which transport liquid from lower regions of a porous medium to its exposed top surface. We show that in a bundle of capillaries, stage 1 is sustained by near-zero radii (NZR) of contacts, formed throughout the contact line of two or more touching capillaries, which can theoretically lead to infinite height rise. Some of the evaporative features of these NZR of contacts were recently (Kumar and Arakeri, 2018b) explored. With closely packed capillaries, along with the existence of the NZR of contacts (as in rods’ case), we get an additional advantage of having inner diameter, which we show act as a reservoir for the nearby NZR of contacts. We report extremely high (time) duration of high rates of evaporation from a bundle of capillaries, which is seemingly impossible to achieve in the conventional systems. In passive systems like loop heat pipes and capillary pumped loops, an additional reservoir is not needed in case a wick consisting of closely packed capillaries are used. © 2019 Elsevier Masson SAS

International Journal of Thermal Sciences

Heat and mass transfer from a system of closely packed capillaries – Possible choice for wicks

The application of location-specific controlled porosity based frustum shaped subsurface porous vessels (SSPV) for irrigation is discussed in this article. For manufacturing of the SSPV, location-specific clay and sawdust were taken in percent by volume, press formed to frustum shapes under a 50-t load, and baked at a temperature of 750-800°C. The SSPV is hybridized with a surrounding layer of animal dung during sub-surface installation. The experiment is set on saline loamy sands of the Thar Desert Region in India for vegetable and fruit productivity. The farmers get their SSPV vessels from the traditional potter in the same village making this irrigation technology economical and sustainable. For this pilot study, cluster beans (Cyamopsis tetragonoloba), cucumber melon (Cucumis callosus), cucumber (Cucumis sativus), and water melon (Citrullus lanatus) were grown on an area of 7.5 m2 during the Kharif season. This controlled porosity based SSPV technology can be viewed as a modified form of pitcher irrigation. The desert soil showcased a steep rise in carbon content with a reduction in salinity after this technological intervention. The production rate of cluster beans, cucumber melon, cucumber, and watermelon for a projected 0.02 ha area was calculated to be 530, 2,010, 940, and 2,110 kg, respectively. The results indicate 80-90% productivity compared to yields from a fertilized flood irrigated field. The implication illustrates a possible scale-up for this low cost, inorganic-fertilizer-free, water, and soil conserving hybridized SSPV irrigation-based farming technology across the Thar Desert and other similar areas around the globe. © 2020 International Society for Horticultural Science. All rights reserved.

Acta Horticulturae

Controlled porosity based sub-surface porous vessel (SSPV) structures for irrigating organic farms of fruits and vegetables

The advancements in the domain of CAD/CAM and CNC machine tools facilitated machining of complex geometric shapes to meet functional requirements and/or aesthetic appearances. These shapes combine several geometric features such as zero curvature (straight), constant curvature (circular) and variable curvature surfaces. The components often contain thin-walled sections having inherently lower stiffness that induces static deflections transforming into surface error and violation of error limits specified by the designer. This paper presents a comparison of deflection induced surface error profile generated during the end milling of zero and constant curvature thin-walled components. The proposed framework incorporates computational model to estimate cutting forces, Finite Element Analysis (FEA) model to compute workpiece deflections, and surface generation mechanism to derive error profile. The paper also investigates the effect of change in the radial engagement area due to workpiece curvature by introducing the concept of 'Equivalent Radial Depth of Cut'. Further, the effect of change in workpiece curvature is investigated on the surface error profile in the paper. The proposed framework has been generalized to accommodate the variation of workpiece geometry, and the results are validated by conducting a set of end milling experiments. © 2020 The Authors. Published by Elsevier B.V.

Fulltext

Effect of workpiece curvature on axial surface error profile in flat end-milling of thin-walled components

The static deflections of cutting tool and workpiece are the primary source for the deviation of machined components from the design specifications during end milling of thin-walled geometries. The deviations are expressed as per the Geometric Dimensioning and Tolerancing (GD&T) principles using size, form, and orientation of the features. This paper proposes a computational framework to estimate cutting force induced cylindricity error during end milling of thin-walled circular components. The framework combines computational elements such as Mechanistic force model, Finite Element Analysis (FEA) based workpiece deflection model, Cantilever beam formulation based tool deflection model, and Particle Swarm Optimization (PSO) based cylindricity estimation algorithm. It has been observed that the static deflections of a cutting tool and thin-walled component influence the cylindricity error considerably. The inevitable aspects associated with the end milling of thin-walled circular components such as concave-convex side machining and workpiece rigidity are investigated subsequently. It was observed that the cylindricity error during concave side machining is considerably smaller due to geometric configuration imparting adequate stiffness to thin-walled components. The study also demonstrated that an appropriate combination of productive cutting conditions and the component thickness could reduce cylindricity error considerably. The outcomes of the present study are substantiated by conducting a set of computational simulations and end milling experiments over a wide range of cutting conditions. The computational framework proposed in the present study can assist process planners in selecting appropriate cutting conditions to manufacture thin-walled circular components within tolerance limits specified by the designer. © 2020 Elsevier Inc.

Precision Engineering

Predictive framework for cutting force induced cylindricity error estimation in end milling of thin-walled components

Graphene, a two-dimensional material consisting of carbon sheets with exceptionally superior mechanical, electrical and thermal properties, presents itself as an effective second phase reinforcement option for composites and functionally graded materials. Although polymer matrix composites reinforced with graphene have been explored extensively, metal/graphene composite is a comparatively new field of research. This perspective article reviews electrochemical deposition as a strategy to fabricate well-dispersed metal/graphene composites for their potential to enhance mechanical and physical characteristics. The recent state of the art research works has been discussed along with the challenges that are being encountered and their possible solutions.

JOURNAL OF THE ELECTROCHEMICAL SOCIETY

Perspective-Electrodeposition of Graphene Reinforced Metal Matrix Composites for Enhanced Mechanical and Physical Properties: A Review

To establish the relationship between wettability and structure with the change in SAW flux composition, the contact angle measurement study was performed at 1700 K. For MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system the wetting behaviour was studied by evaluating the contact angle as well as surface tension properties. Sessile drop method was used to determine the wetting properties of SAW fluxes. Twenty-one SAW fluxes were designed &amp; developed by applying mixture design approach of design of experiments. Chemical, phase and structural properties of SAW fluxes were measured using modern techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD) &amp; Fourier Transform Infra-red spectroscopy (FTIR). As per the calculated contact angle value, different surface tension values for MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system was calculated using Young's &amp; Boni's equations. Using Dupre's equation the adhesion energy for twenty-one basic fluxes was also calculated. Measured contact angle value increased with increase in the TiO2/MgO &amp; TiO2/Al2O3 flux ratio. Lower contact angle gives higher wettability between the flux and the heating substrate. With increase of TiO2/SiO2 ratio up to 1.5 to 2.0 the calculated surface tension value is decreasing while after that it is increased with increase in TiO2/SiO2 ratio. © 2019 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Experimental investigation on high temperature wettability and structural behaviour of SAW fluxes using MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system

In the present paper, investigation on wettability and contact angle measurement of twenty-one SAW fluxes for CaO-SiO2-TiO2 & Al2O3-CaO-SiO2 welding flux system at a temperature of 1300 °C was studied. Wettability observed by measuring the contact angle properties of twenty-one SAW fluxes. The purity of flux constituents determined by the XRF technique. Si-O-Si and Al-O-Al symmetric bond behaviour and various crystalline phases observed using FTIR and XRD techniques. Lower contact angle gives higher wetting and spreading properties. The contact angle increased with the increase of TiO2/SiO2 ratio. For the composition range 1.5 to 2.0, there is a higher value of contact angle observed. A maximum increase of contact angle noticed for the composition range 1.5 to 2.0. There is a constant rise in the amount of contact angle for the composition that varies from 1.0 to 1.2. © 2020, Springer Nature B.V.