Department of Mechanical Engineering

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In this paper, the problem of path planning through tight spaces, for the task of spatial payload transportation, using a formation of mobile manipulators is addressed. Due to the high dimensional configuration space of the system, efficient and geometrically stable path planning through tight spaces is challenging. We resolve this by planning the path for the system in two phases. First, an obstacle-free trajectory in {R}{3} for the payload being transported is determined using RRT. Next, near-energy optimal and quasi-statically stable paths are planned for the formation of robots along this trajectory using non-linear multi-objective optimization. We validate the proposed approach in simulation experiments and compare different multi-objective optimization algorithms to find energy optimal and geometrically stable robot path plans. © 2019 IEEE.

World University root node

2019 28th IEEE International Conference on Robot and Human Interactive Communication, RO-MAN 2019

Path Planning through Tight Spaces for Payload Transportation using Multiple Mobile Manipulators

High strength low alloy steels are extensively used in different applications like oil and gas transmission line pipes, pressure vessels and offshore oil drilling platforms. Submerged arc welding (SAW) is mainly used to weld high thickness steel plates. Flux composition and welding parameters play an important role in determining the adequate quality and mechanical properties of the weld. Agglomerated fluxes were formulated based on TiO2-SiO2-MgO and SiO2-MgO-Al2O3 flux system using constrained mixture design and extreme vertices design approach. The chemical compositions of the bead on a plate have been studied using formulated fluxes. Twenty-one beads on plates were applied using submerged arc welding process keeping the parameters: current, voltage, and welding speed constant. Regression models were developed for bead on plate content in terms of individual, binary, and ternary mixture flux constituents for submerged arc multipass bead on plate deposition for pipeline steel (API 5 L X70). In the present study, chemical composition, grain size, and microhardness properties of the multipass bead on a plate (for API 5 L X70 grade pipeline) were optimized using multi-objective optimization approach. Copyright © 2019 by ASME.

Journal of Pressure Vessel Technology, Transactions of the ASME

Design of TiO2-SiO2-MgO and SiO2-MgO-Al2O3-Based Submerged Arc Fluxes for Multipass Bead on Plate Pipeline Steel Welds

Submerged arc welding is mainly used to weld high thickness steel plates in various applications such as offshore oil drilling platforms, bridges, building construction, and pressure vessels. Suitable flux composition and welding parameters play an important role in determining the good bead quality, which further affects the mechanical properties of welded joint. Agglomerated fluxes were formulated based on CaO-SiO2-CaF2 and CaO-SiO2-Al2O3 flux system using constrained mixture design and extreme vertices design approach. The chemical compositions of the bead on plate have been studied using formulated fluxes. Twenty one beads on plate experiments were conducted at constant current, voltage, and welding speed using submerged arc welding process. In the present study, chemical composition, grain size, and microhardness properties of series of bead on plate weld deposits (for API 5 L X70 grade pipe line) were optimized by using multiobjective optimization approach. © 2019 ASME.

Design of CaO-SiO2-CaF2 and CaO-SiO2-Al2O3 Based Submerged Arc Fluxes for Series of Bead on Plate Pipeline Steel Welds - Effect on Carbon and Manganese Content, Grain Size and Microhardness

Submerged arc welding is widely used for manufacturing of pipelines. In the present study physicochemical and thermophysical properties of TiO2-SiO2-MgO and SiO2-MgO-Al2O3 based rutile acidic SAW fluxes were studied. Twenty one flux formulations were designed based on the extreme vertices design methodology. Fluxes were analyzed using x-ray fluorescence (XRF), TGA, DSC, Hot-disc and XRD techniques. Bond length behavior of different fluxes were analyzed using Fourier transform infrared spectroscopy. For finding the thermal stability and enthalpy change of fluxes TGA and DSC was performed in the range 25–900 °C. Hot disc technique was used to estimate the thermophysical behavior such as specific heat, thermal diffusivity and thermal conductivity of each flux. Density and grain fineness number of flux was investigated at room temperature. Multi response optimization was carried out to derive the optimized flux combinations. © 2018 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Investigating the physicochemical and thermophysical properties of submerged arc welding fluxes designed using TiO2-SiO2-MgO and SiO2-MgO-Al2O3 flux systems for linepipe steels

The present study is an attempt to observe the hot corrosion behavior of P91 boiler steel when exposed to different molten salt environments at higher temperature. The hot corrosion behavior was observed for temperature range 550–850 °C under the application of air, 40% Na2SO4 + 60% V2O5 (salt 1), 40% K2SO4 + 60% NaCl (salt 2), 50% Na2SO4 + 50% NaCl (salt 3), 40% Na2SO4 + 40% K2SO4 + 10% NaCl + 10% KCl (salt 4). Thermogravimetric study results in parabolic oxidation kinetics when the specimen was exposed to temperature 550 °C and 650 °C, whereas multistage oxidation kinetics was observed at temperatures above 650 °C. An acceleration in the oxidation process was observed with the increase in the exposure temperature, also causing an increase in the oxide scale thickness. Specimen exposed to salt mixtures containing more Na2SO4 and NaCl (salt 2 and salt 3) experienced severe corrosion attack at 750 °C and 850 °C. Thick, non-adherent, and porous magnetite and hematite layers were observed on the outer scale of the specimen which resulted in higher weight gain of the alloy. The corrosion rate of P91 alloy exposed to different salt mixtures was in the order: salt 3 &gt; salt 2 &gt; salt 1 &gt; salt 4 &gt; air. © 2019, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Hot Corrosion Study of 9Cr–1Mo Boiler Steel Exposed to Different Molten Salt Mixtures

The present paper deals with the theoretical studies to determine the modal parameters and investigate the dynamic instability of a harmonically driven planar two-link manipulator with flexible joints. An appropriate dynamic model incorporating both link and joint flexibilities subjected to a harmonic motion has been developed while joint flexibility has been modeled as a combination of torsional spring-inertia elements. Modal parameters for various modes of vibration have been evaluated and graphically demonstrated. Then, method of multiple scales has been employed to further analyze the vibration attributes of steady state responses and their stability under resonance condition. The comparative mode shapes and bifurcation diagrams those describe the vibrating system have been illustrated to demonstrate the dynamics of the flexible manipulator. The effect of geometric and inertial coupling existing between the flexible arms on bifurcation states and stability of the obtained solutions has been thoroughly investigated. Analytically obtained results have been verified numerically and found to be in good agreement. The present theoretical results deliver a useful insight into the attributes of vibration characteristics along with the nonlinear dynamic behavior and operational stability of two-link flexible manipulator under joint motion. © 2018 Elsevier Ltd

Mechanism and Machine Theory

Nonlinear modeling and vibration analysis of a two-link flexible manipulator coupled with harmonically driven flexible joints

Precise quantification of surface heat fluxes in highly transient environment is of paramount importance from the design point of view of several engineering equipment like thermal protection or cooling systems. Such environments are simulated in experimental facilities by exposing the surface with transient heat loads typically step/impulsive in nature. The surface heating rates are then determined from highly transient temperature history captured by efficient surface temperature sensors. The classical approach is to use thin film gauges (TFGs) in which temperature variations are acquired within milliseconds, thereby allowing calculation of surface heat flux, based on the theory of one-dimensional heat conduction on a semi-infinite body. With recent developments in the soft computing methods, the present study is an attempt for the application of intelligent system technique, called adaptive neuro fuzzy inference system (ANFIS) to recover surface heat fluxes from a given temperature history recorded by TFGs without having the need to solve lengthy analytical equations. Experiments have been carried out by applying known quantity of ‘impulse heat load’ through laser beam on TFGs. The corresponding voltage signals have been acquired and surface heat fluxes are estimated through classical analytical approach. These signals are then used to ‘train’ the ANFIS model, which later predicts output for ‘test’ values. Results from both methods have been compared and these surface heat fluxes are used to predict the non-linear relationship between thermal and electrical properties of the gauges that are exceedingly pertinent to the design of efficient TFGs. Further, surface plots have been created to give an insight about dimensionality effect of the non-linear dependence of thermal/electrical parameters on each other. Later, it is observed that a properly optimized ANFIS model can predict the impulsive heat profiles with significant accuracy. This paper thus shows the appropriateness of soft computing technique as a practically constructive replacement for tedious analytical formulation and henceforth, effectively quantifies the modeling of TFGs. © 2018, The Institution of Engineers (India).

Journal of The Institution of Engineers (India): Series C

Prediction of Experimental Surface Heat Flux of Thin Film Gauges using ANFIS

Thin film materials along with nanotechnology can be a useful tool to efficiently estimate the surface heat flux. The advancement of soft computing methods can also be used for automated estimation of thermal performances of various heat gauges. Thus, in this study, thin film gauges (TFG) made from Ag, Au, CNT/Ag nano-composite topped on insulating substrate have been tested experimentally under impulsive heat loads from laser. The fabrication of TFGs was done using paint method and physical vapor deposition. The fabricated TFGs were calibrated first and then surface heat fluxes were calculated analytically from temperature history by utilizing one-dimensional heat conduction theory applied on semi-infinite solids. The advanced soft computing methods viz. Adaptive Neuro Fuzzy Inference System (ANFIS) and Genetic Programming (GP) were used to estimate heat fluxes for these three TFGs. The statistical evaluation of GP with ANFIS models on the heat flux experimental database reveals that the ANFIS models have performed better in predicting the peak heat fluxes whereas the GP models have performed better in capturing the trend of heat fluxes. This combined approach paved a way to automated estimation of heat fluxes for industrial applications. © 2018 Elsevier Ltd

Applied Thermal Engineering

Thermal performance of thin film heat gauges of gold, silver and nano-composite

In the present study, dissimilar weld joint was prepared using the P91 and P92 steel plate of 8-mm thickness, using the multi-pass gas tungsten arc (GTA) welding with filler (weld 1) and autogenous tungsten inert gas welding (A-TIG) process (weld 2). Evolution of δ-ferrite patches was studied in weld zone and heat affected zone (HAZ) for both weld 1 and weld 2. Effect of varying post weld heat treatment (PWHT) duration was also studied on δ-ferrite patches and mechanical properties of the dissimilar weld joint. PWHT was carried out at 760°C. For weld 2, weld zone showed poor impact toughness and higher peak hardness as compared to weld 1. After the PWHT, a considerable reduction in hardness was obtained for both weld 1 and weld 2,while impact toughness of weld zone showed a continuous increment with PWHT duration. For weldments characterisation, optical microscope, scanning electron microscope (SEM) and microhardness tester were utilised. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

Materials at High Temperatures

Characterisation of dissimilar P91 and P92 steel welds joint

The Modal FxLMS algorithm is recently proposed for reduction of global level of noise in vibro-acoustic cavities. The algorithm minimizes acoustic potential energy expressed in modal domain which allows a choice of acoustic modes whose modal amplitudes are desired to be minimized. The working of the algorithm and its effectiveness has been demonstrated previously through a numerical study and an experimental study is required to test the effectiveness of the algorithm in practice. To meet this objective this paper presents an experimental study of this algorithm for global active noise control in a rectangular box cavity. The algorithm utilizes modal filtered reference signals and modal amplitudes of the selected acoustic modes of the cavity. To identify modal filtered reference signals, modal secondary paths are utilized. In the present study, modal secondary paths are identified using experimentally identified physical secondary paths and acoustic mode shapes. Modal amplitudes of the acoustic modes are identified on the basis of acoustic pressure measurements from eight microphones suitably placed throughout the cavity. The performance of the algorithm is studied under the presence of acoustic and structural disturbances using one or two control loudspeakers. The active control is carried out at harmonic frequencies coinciding with cavity-controlled resonances and panel-controlled resonances. It is found from the experimental results that the Modal FxLMS algorithm is successful in reducing modal amplitudes of the selected acoustic modes. When all the significantly contributing acoustic modes are chosen, a reduction in global level of noise is observed at cavity as well as panel controlled resonances. © 2019 Elsevier Ltd