Steady-state Analysis Techniques Research Articles

Controlled Photoinduced Generation of "Visual" Partially and Fully Charge Separated States in Viologen Analogues.

Charge-separated states with a lifetime scale of seconds or longer not only favor studies using various steady-state analysis techniques but are important for light-energy conversion and other applications. Through a steric-hindrance-induced method, unprecedented photoinduced generation of a partially charge separated (PCS) state with a lifetime of days has been detected in the "visual" mode during the decay of excited states to a commonly observed fully charge separated (FCS) state for viologen analogues. One pale yellow 4,4'-bipyridine-based metalloviologen compound, with an interannular dihedral angle of 1.84° in 4,4'-bipyridine, directly decays to the purple FCS state after photoexcitation. The other pale yellow compound, with a similar coordination framework but a larger interannular dihedral angle (33.74°), changes first to a yellow PCS state and then relaxes slowly (in the dark in Ar, ca. 2 days; 70 °C in Ar, ca. 1 h) to the purple FCS state. The two-step coloration phenomenon is unprecedented for viologen compounds and their analogues and also rather rare for other photochromic species. EPR and Raman data reveal that photoinduced charge separation first generates univalent zinc and radicals and then the received electron in Zn(I) slowly distributes further to 4,4'-bipyridine. Reduction of π-conjugation and a direct to indirect change in band gap account for the prolongation of the relaxation process and the capture of the PCS state. These findings help to understand and control decay processes of excited states and provide a potential design strategy for multicolor photochromism, light-energy conversion with high efficiency, or other applications.

Real-Time Diagnostics of Gas Lift Systems: A Case Study

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 124926, ’Real-Time Diagnostics of Gas Lift Systems Using Intelligent Agents: A Case Study,’ by G. Stephenson, SPE, Occidental Petroleum; R. Molotkov, SPE, Weatherford; and N. De Guzman, SPE, and L. Lafferty, SPE, Intelligent Agents Corporation, prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October; revised for publication. The paper has been peer reviewed. Published: February 2010 SPE Production & Operations, page 111. One problem related to the operation of gas lift wells is the ability to identify underperforming wells and to address the underlying issues appropriately and in a timely manner. This problem is compounded by a trend toward leaner operations and relative scarcity of application-specific domain knowledge. A method is presented that leverages real-time data, gas lift domain expertise, and proven steady-state analysis techniques in a desktop software application. Introduction For cases in which these resources are limited or unavailable, automation technology could be a solution. To assist production engineers in the well-by-well optimization of gas lift systems, a system was developed that uses intelligent software agents that leverage both real-time data and gas lift domain knowledge to assist engineers in these well-by-well optimization tasks. Challenges With Historical Approach One of the most fundamental challenges is that the historical approach tends to be both reactive and episodic in nature, resulting in missed opportunities for production enhancement. Much of this work requires individuals with specialized artificial-lift-domain expertise, which is increasingly scarce as the demographics of the industry change. The ability to detect and address the numerous opportunities in a field is limited by the labor-intensive nature of the work and the volume of competing priorities. It is common for problems in gas lifted wells to go undetected for months or even years because gas lift is such a forgiving artificial-lift method. Even those gas lifted wells that have a serious performance problem and are not producing optimally will often continue to produce fluids. With other forms of lift, failures tend to be catastrophic in nature and are identified and addressed much more quickly. Addressing the Need A system was developed to provide real-time diagnostics of continuous gas lift wells. The system enables decisions that optimize wells. The system provides engineers with the status of all gas lifted wells under their control. Software agents monitor the wells’ situation by collecting and filtering data, assessing the meaning of those data, recommending actions for correcting problems and responding to threats, and explaining their assessment results and recommendations. Agents can detect the initial symptoms of a problem and prompt for corrective action before well performance degrades seriously. The performance of these key functions enables surveillance engineers to optimize many more wells on a continuous basis. The agents integrate continuous data, such as pressure readings, with well-test data and predictions from commercially available systems-analysis tools, and use diagnostic principles stored in a knowledge base to determine each well’s condition and recommend corrective action. The agent reviews all gas lifted wells in the field and prioritizes recommended actions in accordance with pre-established criteria that include increased production potential and possible cost efficiencies.

Real-Time Diagnostics of Gas Lift Systems Using Intelligent Agents: A Case Study

Summary This paper describes a new method to continuously monitor and diagnose the condition of wells producing through continuous gas lift. The paper describes the application of this system in a mature onshore gas lift field in the western United States and the results obtained. A central problem related to the operation of gas lift wells is the ability to identify underperforming wells and to address the underlying issues appropriately and in a timely manner. This problem is compounded by the trend toward leaner operations and relative scarcity of application-specific domain knowledge. The purpose of this method is to address these issues by leveraging real-time data, gas lift domain expertise, and proven steady-state analysis techniques in a desktop software application. This system performs four key functions: Monitoring the wells' condition by collecting data, assessing the meaning of these data, recommending actions for correcting problems and responding to threats, and explaining recommendations. The performance of the system has met initial expectations and has provided additional unforeseen benefits. This paper cites specific cases that compare agent predictions to expert diagnoses and quantify the benefits of taking the recommended actions. What was found was that while the correct diagnoses of well performance issues was beneficial, the real benefit was in allowing production engineers to analyze a greater number of wells in far less time. To that end, the paper will discuss the role of this system as it relates to the overall production management workflow. The success of this project has demonstrated that intelligent agents can effectively perform functions historically performed by a handful of experts. The paper will discuss key system-design features that enable this level of functionality as well as other potential areas in which the technology can be extended in the future.

STEADY-STATE ANALYSIS OF NONLINEARLY COUPLED CHUA'S CIRCUITS WITH PERIODIC INPUT

In this paper, nonlinearly coupled identical Chua's circuits, when driven by sinusoidal signal have been analyzed in the time-domain by using the steady-state analysis techniques of piecewise-linear dynamic systems. With such techniques, it has become possible to obtain analytical expressions for the transfer functions in terms of the circuit parameters. The proposed system under consideration has also been studied by analog simulations of the overall system on a hardware realization using off-the-shelf components as well as by a time-domain analysis of the synchronization error.

Graphical phasor analysis of three-phase PWM converters

A graphical steady-state analysis technique based on the complex 0-sequence, forward-rotating, and backward-rotating (0fb) phasors is described for balanced three-phase PWM inverters, rectifiers and cycloconverters. The technique avoids the cumbersome algebra of the 0fb transformation, and the coupling between the subcircuits resulting from the real direct-axis/quadrature-axis (dq) transformation. Using symmetric and de-coupled subcircuits that are time-invariant under steady state, the graphical method makes the analysis of three-phase converters straightforward and insightful. In the paper, time-invariant transient models with respect to an arbitrary reference node are first derived for all three-phase converter components. Application of the component models to steady-state analysis is demonstrated for the buck-boost inverter. The steady-state equivalent circuits for the popular buck and boost inverters, rectifiers, and cycloconverters are given along with the steady-state values for their capacitor voltages and inductor currents.

A useful relationship between time‐dependent and steady state solutions of the Boltzmann equation

A simple proof shows that, under certain conditions, a solution of the time‐dependent Boltzmann equation integrated over the lifetime of a finite event equals the steady state solution. This is true regardless of the shape of the particle injection function. A key restriction is that the transport parameters remain constant in time on the flux tube or set of flux tubes where the measurements are made, a condition most likely to be satisfied in short‐duration events. The theorem has important practical benefits: it means that steady state analysis techniques can be applied with rigor to certain solar particle events, and at the same time it permits improved statistical accuracy by summing measurements over the whole event.

An efficient method of simulating the detailed electromechanical response of industrial power systems

A new method is presented for simulating the large-disturbance, electromechanical response of mine and other industrial power systems. With this method, detailed waveforms that include the transient components of machine currents and bus voltages can be obtained rapidly. This approach may be a useful supplement to traditional steady-state analysis techniques when considering circuit breaker requirements in light of a variety of system transients including the following: starting of large motors or groups of motors, reclosure of motors following temporary isolation or during bus transfers, and rapid changes in the mechanical loading of motors. The short simulation times associated with this method are achieved by modeling the power system with line charging capacitance neglected. This eliminates high frequency modes, which often lead to long computation times in other detailed simulations, but retains the machine stator transients that affect significantly the instantaneous currents and voltages throughout the system. With shunt capacitance neglected, however, the system model is represented by a set of differential-algebraic equations (DAEs). The crux of the new method is a systematic procedure for establishing a readily simulated state-space model from these DAEs.

Optimization of forced nonlinear periodic circuits

An algorithm for the optimization of nonlinear circuits which are operating in periodic steady state is discussed. This algorithm makes use of an efficient steady-state analysis technique to find a network's periodic response. Suggestions are also given for reducing the computational cost of the algorithm.