Department of Mechanical Engineering

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

In this paper, a robust single-input fuzzy logic control Robust Single Input Fuzzy Logic Controller (RSIFLC) scheme is proposed and applied for task-space trajectory control of an autonomous underwater vehicle manipulator system (AUVMS) employed for underwater manipulation tasks. The effectiveness of the proposed control scheme is numerically demonstrated on a planar underwater vehicle manipulator system [consisting of an underwater vehicle and a two link rotary (2R) serial planar manipulator]. The actuator and sensor dynamics of the system are also incorporated in the dynamical model of an AUVMS. The proposed control law consists of a feedforward term to exaggerate the control activity with immoderation from the known desired acceleration vector and an estimated perturbed term to compensate for the unknown effects namely external disturbances and unmodeled dynamics as a first part and a single-input fuzzy logic control as a feedback portion to enhance the overall closed-loop stability of the system as a second part. The primary objective of the proposed control scheme is to track the given end-effector task space trajectory despite of external disturbances, system uncertainties, and internal noises associated with the AUVMS. To show the efficacy of the proposed control scheme, comparison is made with conventional fuzzy logic control (CFLC), sliding mode control (SMC), and proportional-integral-derivative (PID) controllers. Simulation results confirmed that with the proposed control scheme, the AUVMS can successfully track the given desired spatial trajectory and gives better and robust control performance. © 1976-2012 IEEE.

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IEEE Journal of Oceanic Engineering

Task Space Control of an Autonomous Underwater Vehicle Manipulator System by Robust Single-Input Fuzzy Logic Control Scheme

We discuss the development and assessment of a robust numerical algorithm for simulating multiphase flows with complex interfaces and high density ratios on arbitrary polygonal meshes. The algorithm combines the volume-of-fluid method with an incremental projection approach for incompressible multiphase flows in a novel hybrid staggered/non-staggered framework. The key principles that characterise the algorithm are the consistent treatment of discrete mass and momentum transport and the similar discretisation of force terms appearing in the momentum equation. The former is achieved by invoking identical schemes for convective transport of volume fraction and momentum in the respective discrete equations while the latter is realised by representing the gravity and surface tension terms as gradients of suitable scalars which are then discretised in identical fashion resulting in a balanced formulation. The hybrid staggered/non-staggered framework employed herein solves for the scalar normal momentum at the cell faces, while the volume fraction is computed at the cell centroids. This is shown to naturally lead to similar terms for pressure and its correction in the momentum and pressure correction equations respectively, which are again treated discretely in a similar manner. We show that spurious currents that corrupt the solution may arise both from an unbalanced formulation where forces (gravity and surface tension) are discretised in dissimilar manner and from an inconsistent approach where different schemes are used to convect the mass and momentum, with the latter prominent in flows which are convection-dominant with high density ratios. Interestingly, the inconsistent approach is shown to perform as well as the consistent approach even for high density ratio flows in some cases while it exhibits anomalous behaviour for other scenarios, even at low density ratios. Using a plethora of test problems of increasing complexity, we conclusively demonstrate that the consistent transport and balanced force treatment results in a numerically stable solution procedure and physically consistent results. The algorithm proposed in this study qualifies as a robust approach to simulate multiphase flows with high density ratios on unstructured meshes and may be realised in existing flow solvers with relative ease. © 2017 Elsevier Inc.

Journal of Computational Physics

A novel consistent and well-balanced algorithm for simulations of multiphase flows on unstructured grids

The present study describes the effect of thermally assisted machining (TAM) parameters on the cutting force, tool wear and surface integrity characteristics (surface roughness, surface topography, and microhardness) of Inconel 718. An inexpensive flame heating technique using oxy-acetylene flame is used to heat the workpiece material. The TAM parameters such as cutting speed, feed rate, depth of cut, and workpiece temperature were selected as process parameters over cutting force, tool wear and surface integrity characteristics.The experimental results reveal that the cutting forces and surface roughness decrease with increases in cutting speed and workpiece temperature, while the workpiece temperature increases as tool wear decreases. The tool wear mechanisms observed were abrasive, adhesive, diffusion and notch wear. The XRD results of thermally assisted machining reveal that neither phase change nor broadening of the peaks were observed at different machining conditions. © 2017, Springer Science+Business Media Dordrecht.

Silicon

Influence of Thermally Assisted Machining Parameters on the Machinability of Inconel 718 Superalloy

The influence of growth substrate temperature on the development of CuAlNi shape memory alloy (SMA) over Kapton Polyimide sheet and its effect on tuning the thermomechanical behavior has been investigated. The SMA bi-morph was synthesized at varying substrate temperatures ranging from 100 °C–200 °C. Two-way shape memory effect could be demonstrated by the bi-morps without any post-processing and training, due to pre-straining of the flexible substrates. The deposited SMA film was responsible for the forward displacement and the return was achieved because of flexible kapton polyimide substrate. To investigate the life cycle behavior of the as developed SMA bi-morph, an in-house life cycle setup was developed with Joule heating as the actuation source. The cyclic behavior was investigated for 500 cycles, at three varying voltages of 2 V, 2.5 V and 3 V with an actuation frequency of 0.5 Hz. The film deposited with growth substrate temperature of 100 °C and 200 °C showed a maximum displacement of 0.6 mm and 0.9 mm, whereas samples prepared with substrate heating at 150 °C showed a maximum displacement of 2.6 mm with actuation voltage of 3 V. To probe the influence of substrate temperature in tuning the thermomechanical behavior, an analysis on the structural, morphological and thermal properties of the bi-morphs has been investigated in detail.

Journal of Alloys and Compounds

Parametric investigations to enhance the thermomechanical properties of CuAlNi shape memory alloy Bi-morph

In this paper, we study the variation of natural frequencies for thin walled circular cylindrical shells subject to external radial load (uniform and hydrostatic pressure). The study has been performed for four different types of boundary conditions viz. pinned-pinned, pinned-free, clamped-free and one end is pinned and other end axially constrained. Towards this, we have used approximate shape functions and Galerkin projections of the PDEs governing the shell motion, linearized about a steady state solution due to the applied mean radial pressure. Our results have very good agreement with the experimental and theoretical results available in literature. They have also been verified against finite element analysis (FEA) using ABAQUS. We have found that with increasing magnitude of inward radial load, the natural frequency decreases, however, the circumferential wavenumber corresponding to the lowest natural frequency increases. For outward radial load the opposite happens. Furthermore, the circumferential wavenumbers corresponding to lowest natural frequency and first buckling mode are different for short cylinders with the difference decreasing with increasing length of the cylinder. We have also found an interesting result for the beam mode vibration of cylindrical shells. For short cylinders, the natural frequency of the beam mode increases (decreases) with internal (external) pressure, which is consistent with other circumferential modes. Subsequently, we obtain a critical length at which the applied radial pressure has no effect on the natural frequency. For cylinders longer than the critical length, the effect of the radial load is opposite of that observed for the short cylinders, and this is contrary to the behavior of the other circumferential modes. As a result, buckling of the beam mode happens for an outward radial (internal) pressure. © 2017 Elsevier Ltd

International Journal of Mechanical Sciences

Effect of radial loads on the natural frequencies of thin-walled circular cylindrical shells

Selective Catalytic Reduction (SCR) using Urea-Water Solution (UWS) as an ammonia precursor is considered as one of the best choices to meet the current stringent emission norms for reduction of NOx in diesel engines. UWS sprayed in the engine exhaust line forms ammonia, and this ammonia reduces NOx into nitrogen. The NOx reduction efficiency depends on the mixing and evaporation behavior of the UWS spray in the hot exhaust gas. Spray characteristics decide the evaporation rate and hence the NOx reduction efficiency. The spray structure is closely related to the breakup point and breakup mode of the jet. Hence, in this study, breakup length and breakup mode were investigated by injecting UWS (32.5 \% by weight) through a nozzle in a hot air cross flow. A CCD camera and pulsed Nd:Yag laser were used for capturing the images. Experiments were conducted with varying nozzle size (150, 250 and 400 micron), injection pressure (0.5 to 3 bar), temperature (32 degrees C,150 degrees C and 200 degrees C) and air flow rate. The effect of operating parameters (nozzle size, injection pressure, air temperature and velocity) in terms of dimensionless numbers (Weber number and momentum flux ratio) on jet breakup mode and jet breakup length was studied. It was observed that the breakup length for UWS was close to that of water. The jet breakup length increases with momentum flux ratio since a jet having a higher momentum is able to penetrate a larger distance in the cross flow. Increasing the air temperature increases the velocity of the cross flow and hence reduces the breakup length. A correlation for jet breakup length was developed. The effect of inclusion of Weber number in the breakup length correlation, in addition to the momentum flux ratio, was studied. Visual observation shows that droplet sizes obtained from the plain orifice injector without preheating is large. Preheating the UWS before injection is recommended to reduce the droplet size.

Breakup Length of Urea Water Solution Jet in a Hot Cross Flow

Visualization of work surface topography through simulations is very challenging task in grinding process due to the complexity of wheel-work interactions with a very high number of cutting points (grits). Kinematic mapping of abrasive grits on a three-dimensional wheel topography enables the evaluation of ground surface topography through simulations. In this paper, a method for generating the ground surface topography based on wheel specifications is presented. Abrasive grits size, abrasives volume percentage and their nature of distribution on the wheel surface are considered in the modeling and visualization of wheel topography. The simulation results of ground surface topographies prove the feasibility of the developed method.

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Applied Mechanics and Materials

A Method to Predict and Visualize the Wheel and Work Surface Topography in Surface Grinding

Performance improvement in grinding of Ti-6Al-4V alloy and modeling of surface roughness

Estimation of nonlinear damping in rotor bearing systems using continuous wavelet transform based approach is proposed. Krylov-Bogobliubov method is used to obtain the approximate analytical solution for the nonlinear equation of motion of the rotor-bearing system. The envelope of the free vibration signal is extracted using the wavelet based approach to identify the nonlinearities in damping. Two different nonlinear damping models are studied using the proposed approach. Two examples are illustrated as coupled and uncoupled versions of equation of motion of a rotor-bearing system including nonlinear viscous external and internal damping. The performance of the method is tested on signals acquired from experiments and found successful. © 2016 Elsevier Ltd.

Mechanism and Machine Theory

Nonlinear damping identification in rotors using wavelet transform

The rotordynamic characteristics of gas turbine seals have been investigated in numerous previous studies. However, the effects of centrifugal growth were often ignored; and no extensive studies have been reported. To this end, the present work examines numerically the influence of centrifugal growth on the rotordynamic characteristics of a typical rotating labyrinth gas turbine seal. A computational framework developed based on combined 3D FE/CFD methodology along with an appropriate rotordynamic model has been employed. For a given seal clearance and eccentricity, various flow and operating conditions are investigated covering a range of pressure ratios and rotational speeds. A substantial variation in both the cross-coupled stiffness and direct damping is noticed and the influence increases with rotational speed. The stability characteristics reveal that centrifugal growth of the seal has a detrimental effect at relatively low pressure ratio and high rotational speed combinations. The computational approach is validated against a typical labyrinth seal results reported in the literature. © 2016 Elsevier Ltd. All rights reserved.