Arun Mulpur

Two-stage electrical array reconfiguration controller for PV-powered water pump

Abstract This paper presents a technique to improve the performance of photovoltaic—powered (PV) water pumps. The method uses a solid state, two-stage electrical array reconfiguration controller (EARC), which senses the radiation as high or low. The limit of each stage can be changed. Accordingly, the controller chooses one favorable set of V-I characteristics for starting and another favorable set of V-I characteristics for steady-state operation. This is done by switching the solar panels, depending upon the starting current requirements and the insolation level, from a predominantly parallel connection to a predominantly series connection. The switching occurs at the end of the start-up of the motor. This produces a sufficient starting torque which considerably improves the pumps performance, particularly in the early morning, late evening, and on cloudy days, providing valuable extra pumping hours for the user. The performance of a direct coupled system, and a system equipped with a two-stage EARC, is presented and compared.

Transition to chaos in acoustically driven flows

In this paper, a model describing the process of transition to chaotic fluid motion in an acoustically driven fluid is presented. The nonlinear interaction between the Stokes boundary layer and linearly unstable three‐dimensional vortical disturbances is examined. Special consideration is given to the amplitude range above which these disturbances bifurcate from linear stability. It is found that oscillatory modulation present in the basic‐flow results in successive period‐doubling bifurcations of the three‐dimensional vortical disturbances. It is shown that these bifurcations result in the disturbance amplitude becoming chaotic.

Modal diameter control of linear isothermal optical fibers

In this paper, a simulation-based investigation of a strategy to control optical fiber diameter variations is reported. The proposed control scheme is based on the principles of modal control. A model of the fiber manufacture is presented and its sensitivity to the fiber draw speed is demonstrated. A control methodology, utilizing the basic concepts of modal control approach, is attempted on the linear isothermal optical fiber model, and this approach is shown to yield satisfactory results. The proposed approach can be modified and extended for nonlinear control of the fiber diameter.<<ETX>>

Fluid Dynamic Instabilities in Drawn Fibers

The nonlinear stability analysis of viscoelastic fibers is presented. The molten fiber is modeled as a Maxwellian viscoelastic fluid and the zeroth order equations governing its behavior given. Linear stability analysis is performed to determine the influence of winder speed and impedance as well as viscosity and elasticity. The results of numerical solution of the nonlinear equations are given.

Nonlinear control of optical fiber diameter variations

This paper presents a simulation based investigation of nonlinear control of optical fiber diameter variations. A nonlinear model of the fiber drawing process is presented and a control scheme based on this dynamic model is formulated. Simulation results indicate that the developed control scheme allows fiber manufacture process speed to be increased. The control methodology is shown to be robust in the presence of significant model uncertainties errors and external disturbances.

Chaotic motion in an oscillatory boundary layer

The chaotic time oscillations in an incompressible fluid driven into motion by a harmonic time-varying pressure gradient is examined. Special attention is given to centrifugal destabilization of the viscous boundary layer. The basic flow is shown to be linearly unstable. For increasing modulation amplitude, the flow exhibits chaotic oscillations. The energy exchange between subharmonics and superharmonics of the least-stable spanwise wave number is considered. The presence of subharmonic Fourier modes are shown to accelerate the transition to temporally chaotic motion. (c) 1996 American Institute of Physics.

Acoustic radiation from a chaotic viscous layer

The Stokes boundary layer has been shown to exhibit linear instability with increasing amplitude of acoustic excitation. Special consideration is given to the amplitude range above which these disturbances bifurcate from linear stability. It is found that oscillatory modulation present in the basic‐state results in successive period‐doubling bifurcations for three‐dimensional vortical disturbances. The acoustic radiation from these unstable vortical disturbances will be addressed.

Theoretical Study Of Streaming Due To An Oscillating Surface

An analysis of acoustic streaming driven by the oscillatory displacement of rl piston is presented. Strwming in a broiichial tube with a bifurcation aids in gas exchange with the environment. and is a mtjor factor 111 irihalcd acrosol motion [I] . A thcw-d 1(.d 11i0clc~l describing the streaming mot ion in tlw fluid IS given. The dynamics of thr fluid motion is characterized by the values of thrw parameters; the oscillatory Reynolds niini1)c~r. St rouhal riiimber and a gcomctry paramc3tc.r.

Instability and chaos in acoustically driven flows

A number of inquiries into the mechanisms responsible for the instabilities observed in time‐periodic fluid motion have been made. However, only recently has it been theoretically shown that a fluid, driven by a time‐periodic acoustic wave, can bifurcate from stability at a fixed acoustic particle velocity amplitude. This departure from stability is the result of the action of the gradient of the Reynolds stress. Hence, the parametric interaction of acoustically driven vorticity with external disturbances is important. This basic result will serve as the foundation material. Sensitivity of the acoustic instability mechanism to temporal and spatial modulations generated by harmonics resulting from shock formation will be examined. A theoretical model will be presented to describe the nonlinear evolution of unstable disturbances, such as burst‐associated, Reynolds stress pulses near a rigid boundary wall. The relationship between unstable vortical disturbances and self‐modulation to experimentally observed ...