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

This paper presents, a robust nonlinear proportional-integral-derivative (PID)-like fuzzy control scheme for a task-space trajectory tracking control of an autonomous underwater vehicle-manipulator system (AUVMS) employed for deep-sea intervention tasks. The effectiveness of the proposed control scheme is numerically demonstrated on a planar underwater vehicle manipulator system (consisting of an underwater vehicle and 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 two main parts: first part uses a feed forward term to reinforce the control activity with extravagance from known desired acceleration vector and carries an estimated perturbed term to compensate for the unknown effects namely external disturbances and unmodeled dynamics and the second part uses a PID-like fuzzy logic control as a feedback portion to enhance the overall closed-loop stability of the system. 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 system. To show the effectiveness of the proposed control scheme, comparison is made with linear and nonlinear 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. © 2017 Elsevier Ltd

World University root node

Ocean Engineering

Robust task-space control of an autonomous underwater vehicle-manipulator system by PID-like fuzzy control scheme with disturbance estimator

This paper addresses the dynamic control of a 2PRP-2PPR vertical planar parallel manipulator. This proposed manipulator can be used for the purpose of lower limb rehabilitation applications (in specific sitting/lying type of lower limb rehabilitation applications). The kinematic and dynamic model of the proposed manipulator are derived and discussed. An augmented PID control along with an uncertainty estimator is proposed for the motion control of the manipulator. The proposed system performance along with the motion controller is demonstrated numerically for the application of lower limb rehabilitation therapies using a clinically recorded gait data. The robustness of the controller and its parameter sensitivity are analysed through different operating conditions and their results are presented. Note: P—stands for Prismatic/translation joint and R—stands for Rotary/revolute joint. © Springer International Publishing AG 2017.

Mechanisms and Machine Science

Augmented PID control of a 2PPR-2PRP planar parallel manipulator for lower limb rehabilitation applications

The present work elucidates a comparative analysis to investigate the discrepancies between the incompressible and low Mach number approximations for numerically solving combined natural convection with radiative heat transfer in participating medium. The motivation behind the study is to quantify the physical differences concerning fluid flow and heat transfer characteristics between low Mach number and incompressible approximation and to examine the validity of the later for convective-radiative problems in an enclosure. A series of numerical experiments are performed considering natural convection with radiative heat transfer at large temperature difference in a square enclosure with a heated cylinder at its center using both approaches. The heated cylinder of three different geometric configurations viz circular, square and triangular shapes are considered in the present analysis to study the combined effects of various geometric form and influence of surface to surface along with gas radiation on flow and heat transfer characteristics in the cavity. Significant discrepancies are observed between the results of incompressible and low Mach number approximations, particularly for gas radiation, especially at high optical thickness. The local Nusselt number distribution also highlights the inaccuracies arising from the use of incompressible approximation demonstrating that it remains invalid for such scenarios. The results from the present low Mach number formulation are also found to be in good agreement with the compressible flow results of OpenFoam demonstrating the need for low-Mach number approximation in such scenarios. Entropy generation analysis shows that square geometry is the optimum design among the three geometries of heated cylinder as it has the maximum heat transfer and minimum entropy generation. © 2016 Elsevier Ltd

International Journal of Heat and Mass Transfer

Critical assessment of numerical algorithms for convective-radiative heat transfer in enclosures with different geometries

The workability and the densification behavior of a porous Al–B4C preforms have been carried out in the present investigation. Hot upsetting tests have been carried out on Al–B4C powder metallurgy (P/M) preforms having an initial preform density of 0.9 and having different B4C compositions of 2%, 4% and 6%. The samples were compressed between two flat dies in a hydraulic press of 50 ton capacity under varying deformation temperatures such as 200 °C, 300 °C, 400 °C and 500 °C under the tri–axial stress state condition. The workability and densification behavior of Al–B4C preforms were analyzed till the initiation of cracks on the outer surface of the preform. The experimental results were analyzed for the various deformation parameters such as axial strain, relative density, formability stress index and different stress ratio parameter under the tri–axial stress state condition. The formability and densification behavior were discussed with the axial strain (εz) during the hot upsetting process. The relationships between the various stress ratio parameters (σq/σeff σm/σeff) and formability stress index (βσ) as a function of the relative density under the tri–axial stress state condition were established. © 2017 The Society of Manufacturing Engineers

Journal of Manufacturing Processes

Hot workability and densification behavior of sintered powder metallurgy Al-B4C preforms during upsetting

When a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture. The shape of the deformed area nevertheless remains circular, its radius first increases with the depth from the surface of the stack and then decreases. In contrast, here we show that the symmetry of the deformed area breaks down when instead of a smooth elastomeric layer, one with topographical patterns is used in the stack. The metallic foil deforms through a polygonal area. The size and shape of the polygonal area vary with the flexibility of foil, geometry and dimension of the patterns and the intensity of the impact. For example, for one elastomeric layer decorated with pillars arranged in a square array, the damaged area turns rectangular to hexagonal and then to octagonal with increasing severity of impact, very much similar to polygonal wetting and spreading by a liquid on a patterned substrate. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Journal of Adhesion Science and Technology

Polygonal deformation of a metallic foil subjected to impact by an axisymmetric indenter

This paper presents the end-effector pose error modeling and motion accuracy analysis of a planar 2PRP-PPR parallel manipulator with an unsymmetrical (U-shape) fixed base. The error model is established based on the screw theory with considerations of both configuration (geometrical) errors and joint clearances. It also proposes a robust cascaded control scheme for the end-effector pose (task-space) error correction in trajectory-tracking of the manipulator due to mechanical inaccuracies. The proposed control scheme uses redundant sensor feedback, i.e., individual active joint displacements and velocities and, end-effector positions and orientation are obtained as feedback signals using appropriate sensors. To demonstrate the efficacy and show complete performance of the proposed controller, real-time experiments are accomplished on an in-house fabricated planar 2PRP-PPR parallel manipulator. © 2017 Elsevier Ltd

Mechatronics

Error analysis and control scheme for the error correction in trajectory-tracking of a planar 2PRP-PPR parallel manipulator

This paper presents a comprehensive analytical solution to the forward kinematic problem of a newly introduced spatial parallel manipulator, namely, the 3-RPRS. The manipulator has three legs with two actuators in each, which connect a moving triangular platformto a fixed base. Loop-closure equations are formed to find the unknown passive rotary joint angle in each leg. These equations are subsequently reduced to a single univariate polynomial equation of degree 16. The coefficients of this equation are obtained as closed-form functions of the architecture parameters of the manipulator and the input joint angles, and therefore the analysis covers all possible architectures and configurations. Furthermore, it is found that the polynomial has only the even powers, therefore leading to 8 pairs of solutions, each pair being mirrored at the base platform. The theoretical developments are illustrated via a numerical example. The results obtained are validated by checking the residues of the original loop-closure equations, thereby establishing the correctness of the formulation as well as the results. © Springer International Publishing Switzerland 2017.

Forward kinematic analysis of the 3-RPRS parallel manipulator

We propose an unified formulation for thermobuoyant flows an arbitrary mesh topologies. Unlike incompressible flow, the pressure correction equation is derived from the energy equation. The resulting Poisson’s equation reduces to continuity constraint ∇ · u = 0, only in absence of thermal gradient and compressibility effects. Investigations are carried out for flows with small and large temperature differences in a differentially heated square enclosure. Studies using Cartesian and triangular grids show that the proposed approach can successfully simulate non-Boussinesq convection with extreme density variation. © Springer India 2017.

Lecture Notes in Mechanical Engineering

Unified solver for thermobuoyant flows on unstructured meshes

Variable density flows are basically those in which density variations cannot be neglected and hence the density is treated as a variable. This formidable change in density may be caused by either of three variables of the ideal gas equation (when dealing with gases) namely pressure, temperature and molar-mass. When pressure causes considerable change in density, the flow is no longer incompressible and they are dealt separately under compressible flows. But when density variation is caused by the other two aforementioned variables then the flow is still incompressible but the density will vary. Presence of varying density in governing equations poses a formidable challenge for numerical simulation as there is a very strong coupling between momentum and scalar transport equations. This work involves the development of three-dimensional Navier-Stokes solver to compute variable density incompressible flows on hybrid unstructured grids. The density variation due to temperature and species concentration has been considered. © Springer India 2017.

Computation of variable density flows on hybrid unstructured grids

This paper presents the complete dynamic model of a new six degrees of freedom (DOF) spatial 3-RPRS parallel manipulator. The geometry parameters of the manipulator are optimized for a given constant orientation workspace. Further, a robust task-space trajectory tracking control is also designed for the manipulator along with a nonlinear disturbance observer. To demonstrate the efficacy and show the complete performance of the proposed controller, virtual prototype experiments are executed using one of the multibody dynamics software namely MSC Adams. The computer-based virtual prototype experiment results show that the manipulator tracking performance is satisfactory with the proposed control scheme. In addition, the controller parameter sensitivity and robustness analyses are also accomplished. © Author(s) 2017.