Pratiher, Barun

The present work primarily deals with the study of the influence of internal moving pulsatile fluid on the dynamic stability of cantilever based single-walled carbon nanotubes considering the modified couple stress elasticity theory and the Timoshenko beam model. The axial fluid speed is characterized as simple harmonic variation about a constant mean speed. The second order method of multiple scales is employed in order to determine the closed-form expressions for the instability regions subjected to parametric resonance condition. The influences of the length scale parameter, Poisson's ratio, aspect ratio of SWCNTs, and the amplitude of static and dynamic components of the flow velocity, on the parametric instability regions are investigated. These results obtained from perturbation analysis are verified by solving the temporal equation using numerical technique.

Thermocells in box and flat cell configurations were demonstrated via simplified design and cost effective materials like activated charcoal and potassium ferri/ferrocyanide solution and MWCNTs respectively. Employing saturated concentrations of potassium ferri/ferrocyanide in aqueous solution as electrolyte in combination with the electrodes resulted in a highly feasible redox-mediated electron transfer. Effects of concentration of potassium ferri/ferrocyanide (0.1 mM, 1 M and 4 M in aqueous medium) on the performance of the devices were analyzed. The electrolyte trapped in agar-agar gel functions as a solid like medium. In the case of box configuration the maximum power density attained being 22.463 W/m² yielding 20-30% of Carnot efficiency and 0.563 W/m² for MWCNT based flat cells reaching 0.5-18% higher than the Carnot efficiency. The efficiency of the thermocells at different ΔT from 30 C to 130 C was reported. The power density increased by 14.92 times for activated charcoal thermocell operating in 1 M K 3[Fe(CN)6]/K4[Fe(CN)6] at ΔT = 60 C in comparison with MWCNT based thermocells at the same ΔT. Other low cost electrode materials like activated charcoal, acetylene black were employed to study the performance of thermocells. Cells were connected in series and parallel to study the feasibility of performance improvement at different ΔT. © 2013 Brazilian Metallurgical, Materials and Mining Association.

Shaft misalignment, rotor unbalance, rubbing, bearing faults and cracks are the commonly observed faults in the rotor-bearing systems. Vibration signature has been considered to be one of the best ways to detect and diagnosis subsequent condition monitoring of rotor-bearing faults. A flexible shaft with a rigid disc supported by flexible bearings at both the ends has been considered for the present critical observations. The bearing is considered as a spring with linear stiffness and damping. Further, Timoshenko beam theory is considered to describe mathematically the model of rotor element. We used finite element analysis to obtain the critical whirling speeds of rotor-bearing system for different modes at various system parameters with the illustration of Campbell diagram and Fourier spectrum. Vibration spectrums in the transverse direction are illustrated for different modes of vibration using successive approaches of Hamilton principle, Galerkin’s method and Newmark’s integral method. Condition monitoring of vibration spectrums considering rotor unbalance and shaft misalignment as well as their identification has been analysed with FFT, time responses, phase portrait and Poincare’s map, numerically and experimentally.

Free and forced vibration analysis of a geometrically rotating shaft supported on ball bearings has been studied using the numerical method and compared with the results obtained experimentally. This study is concerned with vibration analysis of geometrically nonlinear rotating model with a rigid disk. The shaft has been designed under the frame of Euler–Bernoulli beam theory with additional effects such as rotary inertia, gyroscopic effect, higher-order large deformations, and rotor mass unbalance in order to replicate an equivalent practical model of rotor-bearing system. The mathematical expressions have been derived to demonstrate the nonlinear free and forced vibrations of the rotating shaft coupled with rigid disk in two transverse planes. Solutions of the nonlinear equation are being obtained using method of multiple scales as well as numerical methods. Effects of rotor parameters such as bearing stiffness and damping coefficient are examined with help of this nonlinear mathematical model. The obtained results are portrayed for a better understanding free and forced vibration analysis with time response, FFT, phase portrait, and Poincare’s map. The present outcomes enable an understanding on how the system dynamics influenced with the variations in the values of different parameters.

This present work has made a noteworthy attempt to demonstrate brief modeling of N-link manipulator and subsequent modal characterization along with the determination of static deflection of a two-link flexible manipulator with a payload. In addition, investigation of nonlinear phenomena of dynamic responses under 3:1 internal resonance has also been accomplished considering geometric nonlinearities. An appropriate and realistic dynamic modeling of the two-link manipulator taking into account of inertia coupling and geometry compatibility between equations of motion and boundary conditions has been derived using the extended Hamilton’s principle. The effect of parametric variation on system eigenfrequencies is well tabulated, and the corresponding eigenspectrums are illustrated graphically. Further, the nonlinear phenomena of dynamic solutions have been demonstrated by using MMS of second order for its statutory effect onto the system instability for the existence of S-N bifurcations. The effect of nonlinearities and various design parameters on the dynamic responses and subsequent bifurcations for 3:1 internal resonance has also been demonstrated. The outcome of the present work enables new understanding into the design criterion and performance limitation of multi-link flexible robots.

The nonlinear behavior of a rotating system with large elastic deformation subjected to harmonically varying ground disturbance has been investigated numerically. The Euler-Bernoulli beam theorem has been adopted in order to derive the partial differential equation governing the dynamics characteristics of the rotating system using extended Hamilton’s principle. Method of multiple scales has been selected in approximately finding the nonlinear dynamic characteristics of the system for possible resonance conditions. The effect of nonlinearities and other variations in the values of different parameters like amplitude of external excitation, position of disk along the span, and mass of the disk on the system performance has been investigated. The outcome from the present work will furnish a proper guidance to the designers in the vicinity of the limitation and safe range of operational speed of rotor shaft under the variation of other control parameters.

This article presents the dynamic modeling and nonlinear analysis of two-link flexible manipulator with generic payload whose center of gravity is different than the point of attachment with the link. The manipulator is driven by harmonic joint motions and subjected to a constraint force at the terminal end due to its interaction with working environment. Hamilton’s approach is adopted to dynamically model the multi-link manipulator for longitudinal and transverse vibrations incorporating the nonlinearities associated with axial stretching. The resulting set of eigenfrequency equations are solved numerically with subsequent generation of eigenspectrums. Further, this paper investigates the resonant behavior of manipulator links for the subharmonic and primary resonance conditions due to end follower force and revolute joint motions, respectively. The resonant responses show the jump phenomenon and existence of multi-valued solutions at pitchfork and saddle-node bifurcation points. The numerical and graphical results thus obtained, clearly indicate the significant influence of variation of system configurations and generic payload on eigencharacteristics and nonlinear responses, and hence must be given consideration during dynamic modeling of a manipulator in order to attenuate undesirable vibrations.

In the current study, CFD simulations and static structural analysis were carried out to estimate the wind loads for up and downstream wind directions on ground mounted arrayed solar panels. The goal of simulations is to estimate the loads (i.e. drag and lift forces and also moment coefficients) and wind pressure that act upon their surface. Static structural analysis coupled with CFD simulation is done to determine the total deformation due to wind loads on each panel. The motive of the study is to protect the integrity of the solar panels in a situation like cyclone and typhoon so that energy production is not hindered throughout their service life. Simulations were carried out on arrayed nine panels with changing various parameters (i.e. clearance height, inter row spacing between panels and panel inclination) that effect wind loading on the panels

The effect of all-inclusive generic offset payload characteristics on the modes of vibration and nonlinear characteristics of a rotating flexible manipulator with a revolute pair has been accomplished in the present article. A brief dynamic modelling and free vibration analysis to obtain the eigenspectrums of the system, whereafter nonlinear analysis of a manipulator with a general offset payload undergoing overall motion has been accomplished. Dynamic equation of motion and associated boundary conditions have been developed where the payload is considered as a mass whose center of gravity doesn’t coincide with the point of attachment with the manipulator. The effect of various system parameters such as offset mass, offset inertia, offset length, hub mass, actuated inertia and hub stiffness on eigenfrequency is well tabulated and the same effect on eigenspectrums is presented graphically. Further, MMS is employed to investigate the effect of parametric variation on the nonlinear behaviour and associated bifurcation of the rotating single-link flexible manipulator being harmonically driven at the joint under primary resonance considering the centrifugal forces acting on the link and payload as well. The present analysis indicated the pronounced effect of system mass, inertia, stiffness and rotating speed on the eigencharacteristics and bifurcations of a flexible manipulator with a rotating joint.

The assessment of nonlinear phenomena with a focus on investigating the bifurcations and chaotic behaviour of an elastically induced flexible rotor-bearing system subjected to a harmonic ground motion has been studied. The higher-order Euler–Bernoulli deformation theorem has been adopted that governs the nonlinear dynamic characteristics of the rotating system. Nonlinear vibration analysis has been carried out to determine the critical speeds, i.e., Campbell diagram followed by demonstrating the inherent nonlinear signatures through the illustration of time history, Fourier spectrum and Poincare’s map upon varying the system design variables. The perturbation technique has been used to obtain the approximate nonlinear solutions from a set of polynomial algebraic equations under steady-state condition in various resonance cases. Further, stability analysis along with successive bifurcations of the solutions has been investigated. The present nonlinear model formulated based on Euler theory has been found to be capable enough to predict the correct value of critical speeds and dynamic responses in comparison with that of model developed based on Timoshenko theory. The present outcomes can offer immense practical importance for any application of the flexible rotor-bearing system when it performs high-speed operation.