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 article investigates a new robust nonlinear proportional integral derivative (PID) position tracking control applied on a serial underwater spatial manipulator with three degrees of freedom. The proposed controller integrates the known approximated inverse dynamic model output as a model-base portion of the controller. It uses a feed forward term to enhance the control activity with indulgence from known desired acceleration vector. The proposed control scheme carries an estimated perturbed term to compensate for the unknown effects namely external disturbances and unmodelled dynamics. Finally, it has a decoupled nonlinear PID controller as a feedback portion to enhance closed-loop stability and account for the estimation error of uncertainties. The usefulness and competency of the proposed approach are demonstrated with the help of numerical simulations. © 2015 IEEE.

World University root node

IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM

Robust PID control for position tracking of an underwater manipulator

We compute the drag on a circular and liquid microdomain diffusing in a two-dimensional fluid lipid bilayer membrane surrounded by a fluid above and below. Under the assumptions that the liquids are incompressible and the flow is of low Reynolds number, Stokes' equations describe the flow in the two-dimensional membrane as well as in the surrounding three-dimensional fluid. The expression for the drag force on the liquid domain involves Fredholm integral equations of the second kind, which we numerically solve using discrete collocation method based on Chebyshev polynomials. We observe that when the domain is more viscous than the surrounding membrane (including the rigid domain case), the drag force is almost independent of the viscosity contrast between the domain and the surrounding membrane, as also observed earlier in experiments by other researchers. The mobility also varies logarithmically with Boussinesq number β for large β. On the other hand, for a less viscous domain the dimensionless drag force reduces with increasing viscosity contrast, and a significant change in the drag force, from that when there is no viscosity contrast or when the domain is rigid, has been observed. Further, the logarithmic behaviour of the mobility no longer holds for less viscous domains. Our method of computing the drag force and diffusion coefficient is valid for arbitrary viscosity contrast between the domain and membrane and any domain size (subject to β ≥ 5). © 2015 Cambridge University Press.

Journal of Fluid Mechanics

Drag force on a liquid domain moving inside a membrane sheet surrounded by aqueous medium

Studies on binary drop collisions have been performed in literature to understand the physical phenomena which occur during the process. They also have applications of interest in modelling engines for example, where collision and coalescence are likely to be prevalent due to the dense nature of the sprays and the low droplet-droplet distance. In the present study, the collision behavior of two immiscible liquid drops namely a water drop and an n-Heptane drop of varying drop size ratios has been investigated experimentally. Experiments were performed at an atmospheric environment of 298 K and 101.325 kPa. Two mono-disperse droplet streams generated by piezoelectric droplet stream generators were used for the collision study. Collision outcomes were studied for size ratio of 1, at different Weber-numbers for non-dimensional impact-parameter B.The results from the experiments describe the boundaries of collision outcomes namely encapsulation and separation as a function of the impact parameter B and relative velocity Ur © 2015 International Conference on Liquid Atomization and Spray Systems. All rights reserved.

ICLASS 2015 - 13th International Conference on Liquid Atomization and Spray Systems

Encapsulation and separation in collision between immiscible liquid drops

The present trend in the manufacturing industry is to make machining processes more environment friendly by adopting topractices such as dry machining, minimum usage of cutting fluid, and usage of non-reactivegas based coolants etc., The concept of Minimum Quantity Lubrication (MQL)has been suggested by several researchers long time back as a cause for addressing the environmental, healthand economic issues related with conventional bulk cooling processes. The MQL technique consists of atomizing a very small quantity of cutting fluid into fine droplets. In other words, the effectiveness of MQL system depends on the quality of these droplets. This paper presents the combination of microscopy and image processing techniques to ascertain the quality of droplets,by spraying the MQL fluidonto an acrylic sheet. The raw droplet features arecaptured with stereo zoom microscopeandanalyzed by measuring the average droplets size and number of droplets per unit area. Reliable MQL application is achieved when the MQL parameters like the distribution of the droplets,the applied carrier gas air pressure, fluid flow rate, nozzle tip to machining zone distance, and the angle at which the nozzle keptis optimal.The optimal MQL conditions as obtained from theseresults have been usedto improve the grindability of Ti-6Al-4V.

An Effective Method to Determine the Optimum Parameters for Minimum Quantity Lubrication(MQL) Grinding

Mixed mode analysis of obliquely oriented edge cracked semicircular disk under compression

Blade failure is a common problem of a steam turbine and it's failure in-service results in safety risks, repair cost and non operational revenue losses. Thus, the reliability of these blades is very important for the successful operation of a steam turbine. Dynamic analysis of a steam turbine blade in computational environment is carried out in the present work. In order to gain physical insight into the flexural dynamics of such turbine blades with the inclusion of the rotor dynamic effect, the turbine blade was approximated as a twisted cantilever beam with an asymmetric aerofoil cross-section fixed on a rigid rotor disk. Methods to validate the computational procedures for cantilever beam were established. Similar computational procedures were leveraged for the turbine blade. Critical speeds were obtained for different excitations.

INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control

Vibration analysis of a steam turbine blade

This paper describes the problems concerning turbine rotor blade vibration that seriously impact the structural integrity of a developmental aero gas turbine. Experimental determination of vibration characteristics of rotor blades in an engine is very important from fatigue failure considerations. The blades under investigation are fabricated from nickel base super alloy through directionally solidified investment casting process. The blade surfaces are coated with platinum aluminide for oxidation protection. A three dimensional finite element modal analysis on a bladed disk was performed to know the likely blade resonances for a particular design in the speed range of operation. Experiments were conducted to assess vibration characteristics of bladed disk rotor during engine tests. Rotor blade vibrations were measured using non-intrusive stress measurement system, an indirect method of blade vibration measurement utilizing blade tip timing technique. Abnormalities observed in the vibration characteristics of the blade tip timing data measured during engine tests were used to detect the blade damage. Upon disassembly of the engine and subsequent fluorescent penetrant inspection, it was observed that three blades of the rotor assembly were identified to have damaged. These are the blades that exhibited vibration abnormalities as a result of large resonant vibration response while engine tests. Further, fractographic analysis performed on the blades revealed the mechanism of blade failures as fatigue related. The root cause of blade failure is established to be high cycle fatigue from the engine run data history although the blades were put into service for just 6 h of engine operation. © 2014 Elsevier Ltd.

Engineering Failure Analysis

Vibration based damage detection of rotor blades in a gas turbine engine

In a rotor bearing system operating with constant angular acceleration, after passing through the critical speed, typical beat characteristics are observed because the transverse vibration response contains both excited and natural motion, and shortly after passing resonance, vibrations with close frequencies appear. The present study explains a method for estimating damping of rotor bearing systems from transient beat vibration signals observed during run up stage. A mathematical derivation to prove that a part of run-up vibration of the rotor system consists of beat phenomenon when the system crosses critical speed. It is also observed from the mathematical model that the beat vibrations depend on the damping in the system. This beat response is considered for Hilbert analysis and the damping is estimated. Increase in angular acceleration of the rotor will increase the damping. This paper investigates how the damping varies with respect to different angular acceleration values of the rotor bearing system. Experimental validation of the beat phenomenon and damping estimation are done for the rotor system. The proposed method is validated by using half-power band width method applied to run-up response. © 2014, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Journal of Mechanical Science and Technology

Damping identification in rotors from run-up beat responses using Hilbert transforms

Many types of rotating components commonly operate above the first or second critical speed and they are subjected to run-ups and shutdowns frequently. The present study focuses on developing FRF of rotor bearing systems for damping estimation from swept-sine excitation. The principle of active vibration control states that with increase in angular acceleration, the amplitude of vibration due to unbalance will reduce and the FRF envelope will shift towards the right (or higher frequency). The frequency response function (FRF) estimated by tracking filters or Co-Quad analyzers was proved to induce an error into the FRF estimate. Using Fast Fourier Transform (FFT) algorithm and stationary wavelet transform (SWT) decomposition FRF distortion can be reduced. To obtain a theoretical clarity, the shifting of FRF envelope phenomenon is incorporated into conventional FRF expressions and validation is performed with the FRF estimated using the Fourier Transform approach. The half-power bandwidth method is employed to extract damping ratios from the FRF estimates. While deriving half-power points for both types of responses (acceleration and displacement), damping ratio (ζ) is estimated with different approximations like classical definition (neglecting damping ratio of order higher than 2), third order (neglecting damping ratios with order higher than 4) and exact (no assumptions on damping ratio). The use of stationary wavelet transform to denoise the noise corrupted FRF data is explained. Finally, experiments are performed on a test rotor excited with different sweep rates to estimate the damping ratio. © 2013 Elsevier Ltd.

Journal of Sound and Vibration

Swept sine testing of rotor-bearing system for damping estimation

This paper addresses the issue of developing a robust and efficient controller for a manipulator for underwater applications by proposing a terminal sliding mode control scheme along with a disturbance observer and incorporating the same for 3-RRR serial spatial manipulator to ensure finite time convergence as asymptotic convergence in undesirable in underwater tasks like positioning and tracking of a trajectory. The performance of the proposed scheme is studied using extensive numerical simulations depicting practical circumstances with external disturbances and parameter uncertainties within the system. The capability of the control scheme to overcome hydrodynamic forces and moments including added mass effects, damping effects are extensively studied and validated for the control scheme. The dynamic modelling is done using the Euler-Lagrangian approach involving the energy associated with the system. The results are presented after analyzing the trajectory tracking capabilities of the manipulator in the presence of external disturbances and model uncertainties. © 2014 IEEE.