(SoE) School of Engineering

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Electrochemical noise measurements were taken in a 7.5 cm diameter, 10 m long multiphase oil/water/gas flow system. Full pipe flow studies were conducted for liquid velocities of 0.8, 1.0 and 1.5 m/s and slug flow for Froude numbers 4, 6, 9 and 12, using two phase (ASTM standard saltwater and carbon dioxide gas) and three phase (oil of 2cP viscosity, saltwater and gas) flow. The pressure was maintained at 134 KPa and temperature at 40 C. Noise data was measured with a Zero Resistance Ammeter and analyzed using software provided with the instrument. The noise fluctuations show trends which can be related to the type of How. Full pipe flow studies show random fluctuations around the mean for both potential and current noise.This implies the occurrence of uniform corrosion. The Fast Fourier Transform (FFT) shows roll-off greater than -40 dB/decade in magnitude, characteristic of uniform or general corrosion. In slug flow the potential noise fluctuations take the form of characteristic transients. The frequency of these transients correspond to the observed frequency of slugs. The FFT of this data shows roll-off slopes less than -20 dB/decade shown to be characteristic of pitting corrosion. A second slope of magnitude greater than -30 dB/decade is observed at higher frequencies and this might signify the presence of a second time constant controlling the corrosion reaction. This is due to the unique mechanisms associated with the mixing zone of slugs. Peaks in the Fast Fourier Transform (FFT) are also seen at particular frequencies. One of these corresponds to the slugging frequency. An increase in the percent change in standard deviation of current with Froude number implies enhanced corrosion activity on the surface of the electrode. The electrochemical noise technique is extremely useful for studying corrosion mechanisms and flow parameters in multiphase flow pipelines. Its ability to isolate dynamic incidents and study them both in the time and frequency domain makes it a powerful tool for gaining an insight into mechanistic information on corrosion in multiphase pipelines. © 1996 by NACE International.

World University root node

Electrical Engineering

NACE - International Corrosion Conference Series

Use of electrochemical noise to monitor multiphase flow and corrosion

We describe a very simple deterministic parallel algorithm for linear programming in fixed dimension d that takes poly(log log n) time in the common CRCW PRAM model and does optimal O(n) work. Our algorithm is based on multidimensional search and an effective use of approximation algorithms to speed-up the basic search in the CRCW model. Our method also yields very fast poly(log log n) algorithm for smallest enclosing sphere and approximate ham-sandwich cuts as well as an O(log n) time work-optimal algorithm for exact ham-sandwich cuts of separable point sets. For all these problems, particularly for the fixed-dimensional linear programming, o(log n) time efficient deterministic PRAM algorithms were not known until very recently.

Annual ACM Symposium on Parallel Algorithms and Architectures

Parallel multidimensional search using approximation algorithms: With applications to linear-programming and related problems

In this paper we focus on the problem of designing very fast parallel algorithms for the convex hull problem in two and three dimensions in the arbitrary CRCW model whose running times are output-size sensitive. We present a fast randomized algorithm for planar hulls that runs in expected time O(log H · log log n) and does optimal O(n log H) work where n and H are the input and output sizes respectively. For log H = Ω(log log n), we can achieve the optimal running time of O(log H) for planar hulls while simultaneously keeping the work optimal. In three dimensions, our algorithm runs in expected time O(log log2 n·log H) with optimal O(n log H) work for all H. Hence, for O(logO(1) n) size outputs, our algorithms in two and three dimensions achieve poly(log log n) running time and optimal O(n log log n) work. The previously known output-sensitive work-optimal algorithms for convex hulls have running times Ω(log n) (expected) and Ω(log3 n) in two and three dimensions respectively. Our algorithms assume no input distribution and the running times hold with high probability. We also describe a very simple O(log n log H) time optimal deterministic algorithm for planar hulls which is an improvement for small outputs. For larger output-sizes, a running time of O(log n log log n)) can be achieved.

Proceedings of the Annual Symposium on Computational Geometry

Faster output-sensitive parallel convex hulls for d ≤ 3: optimal sublogarithmic algorithms for small outputs

In the present paper a comparative performance of the SVS auxiliary controllers for the dynamic performance enhancement of long transmission lines with and without series compensation has been evaluated. A new controller, namely, combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of the transmission line. The proposed SVS auxiliary controllers, considerably, enhances the system damping and the unstable system modes are stablized. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the performance of the proposed controller.

Journal of the Institution of Engineers (India): Electrical Engineering Division

SVS Auxiliary Controllers to Improve the Dynamic Performance of Long Transmission Lines with and without Series Compensation

In this paper a novel concept of a static var system (SVS) auxiliary controller application for damping subsynchronous resonance in power systems has been proposed and demonstrated. An SVS controller, known as the combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of a series compensated long transmission line. The studies are conducted on a system having a similar spread of the torsional modes as the first IEEE benchmark model. The proposed SVS auxiliary controller stabilizes all the torsional modes over a wide operating range. A digital computer simulation study has been performed, using a nonlinear system model, to illustrate the effectiveness of the proposed SVS auxiliary controller.

Electric Power Systems Research

Application of an auxiliary controlled static var system for damping subsynchronous resonance in power systems

In this letter we demonstrate that a photothermal microscopy experiment can be used to determine the electronic diffusivity (or carrier mobility) in the same way it is now widely used to measure locally thermal diffusivity of various nonsemiconductor materials. The main difficulty lies in the fact that in order to separate thermal and carrier diffusion, the experiment must be performed for a relatively large distance between the pump and probe beams. Photothermal signals are therefore rather weak and great experimental care must be taken. We present and discuss experimental results on Si. © 1996 American Institute of Physics.

Fulltext

Applied Physics Letters

Electronic diffusivity measurement in silicon by photothermal microscopy

A novel ultrasonic flow metering system been developed that has the capability of measuring liquid film thicknesses of the order of 0.1 mm and mist contents in gas flow of 4-5%. The principle of this nonintrusive technique is based on recording the transit time and attenuation of ultrasonic signals in both axial and radial directions using sets of upto eight transducers flush-mounted on the outside pipe wall at intervals around the pipe circumference and at two locations along the pipeline. The data from the meter is then used in existing multiphase flow models developed at the Corrosion in Multiphase Systems Center, to predict the quality of the gas and flow rate of the individual phases as a function of time.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

Development of a novel non-intrusive, ultrasonic flow meter for wet gas pipelines

This paper presents a novel synchronous dc link voltage notching circuit topology for zero voltage switching (ZVS) of PWM inverters. The link voltage will fall to zero almost immediately after the controlled switch is turned on. Thus, the synchronous operation of the link voltage with any PWM pattern is facilitated. Analysis and simulation have demonstrated the successful operation of the new topology. The feasibility of the proposed scheme is experimentally verified on a laboratory prototype.

Proceedings of the IEEE International Conference on Power Electronics, Drives & Energy Systems for Industrial Growth, PEDES

Novel synchronised resonant DC-link PWM inverter with minimum voltage stress across the switches

In this paper the coordinated application of the controlled series compensation (CSC) and the SVS auxiliary controllers has been demonstrated for the dynamic and transient performance enhancement of a series compensated long transmission line. An SVS controller, known as the combined reactive power and frequency (C.R.P.F.) auxiliary controller, has been developed and incorporated in the SVS control system located at the middle of the transmission line. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the comparative effectiveness of the CSC and the SVS auxiliary controllers developed.

Auxiliary controlled SVS and controlled series compensation for flexible AC transmission systems

The paper presents a comparative performance evaluation of SVS auxiliary controllers for transient stability enhancement of long transmission lines over a wide operating range. The SVS has been considered located at the middle of the transmission line. The application of the auxiliary controllers considerably enhances the system damping and unstable system modes are stabilized. A new controller, namely Combined Reactive Power and Frequency (C.R.P.F.) auxiliary controller, has been developed for the SVS located at the middle of the transmission line. To illustrate the comparative effectiveness of the auxiliary controllers under disturbance condition, a digital computer simulation study has been performed. © 1996 Taylor & Francis.