Showing papers on "Transient (oscillation) published in 1986"

A Theory of Post-Stall Transients in Axial Compression Systems: Part II—Application

Abstract: Using the theory developed in Part I, calculations have been carried out to show the evolution of the mass flow, pressure rise, and rotating-stall cell amplitude during compression system post-stall transients. In particular, it is shown that the unsteady growth or decay of the stall cell can have a significant effect on the instantaneous compressor pumping characteristic and hence on the overall system behavior. A limited parametric study is carried out to illustrate the impact of different system features on transient behavior. It is shown, for example, that the ultimate mode of system response, surge or stable rotating stall, depends not only on the B parameter, but also on the compressor length-to-radius ratio. Small values of this latter quantity tend to favor the occurrence of surge, as do large values of B. Based on the analytical and numerical results, several specific topics are suggested for future research on post-stall transients.

Tuning of Field-Oriented Induction Motor Controllers for High-Performance Applications

Abstract: A tuning procedure for high-performance (e.g., axis feed type) applications of feedforward field-oriented controllers is developed and demonstrated. The theoretical basis of the procedure is explained via a novel form of dq vector diagram. This diagram displays both steady and transient states simultaneously. This format also provides substantial insight into the expected behavior of mistuned controllers, especially for analyzing transient torque performance. The procedure is unambiguous to implement, and it requires no additional sensors beyond those required for the feedforward controller.

Investigation of deep levels in high-resistivity bulk materials by photo-induced current transient spectroscopy. I. Review and analysis of some basic problems

Abstract: The use of photo-induced current transients as a means for the detection of deep trapping levels in high-resistivity bulk materials and for the determination of their parameters is discussed. In this perspective some experimental and theoretical problems are discussed on the basis of various models. The conditions which must be satisfied by the kinetics or experimentally in order to observe a quasi-exponential time dependence for the decay of the current corresponding to a single trap are pointed out. Special attention is devoted to various possibilities, depending on the model and on experimental conditions, for the parameters related to the trap or to other centres to be involved in exponential decays and how this can affect the evolution of the transient as a function of temperature. The conclusions of this analysis are of practical importance for the implementation of various possible multigate processing methods of computer recorded transient data, which are evaluated in Part II.

Dynamic Security Assessment Utilizing the Transient Energy Function Method

Abstract: This paper presents applications of an efficient computerized technique for power system dynamic system security assessment using the transient energy function (TEF) method. The technique exploits the sensitivities of the unnormalized transient energy margin with respect to operating indices and critical interface flows in order to arrive at the stability limits for various system outage states and operating conditions, that would be required for on-line application. The paper describes the sensitivity technique and demonstrates a practical application to the dynamic security problem in one portion of the Ontario Hydro system including results of the validation and accuracy tests of the technique.

The case of AC stress in the hot-carrier effect

Abstract: During ac hot-carrier stress, the direction of the transient current flow is demonstrated to be important in device degradation as well as the amount of substrate current generated in transient periods.

An Inverse Finite Element Method for the Analysis of Stationary Arc Welding Processes

Abstract: An inverse finite element computer code was developed to facilitate the experimental analysis of two-dimensional stationary arc welding processes. The method uses transient temperature data from thermocouples inbedded in the solid region of the work piece to determine through a Newton-Raphson interpolation procedure the transient position of the solid-liquid interface and the transient temperature distribution in the solid region of the work piece. The accuracy of the method was demonstrated through comparison with results obtained with a direct finite element code and through comparison with experiments.

Transient ride-through AC inverter

Abstract: A transient protection circuit for an inverter has a rectifier capable of supplying direct current from an alternating current power source, where protection is provided against a voltage transient in the AC power source. A DC bus is fed by the rectifier. A bus capacitor is connected across the DC bus. Solid state switches are connected to the DC bus for supplying alternating current to a load. The DC bus voltage is sensed. In response to a transient rise in the DC bus voltage, a resistor is connected across the bus capacitor to provide a discharge path, the solid state switches are disconnected from the DC bus, and after the transient dies away from the DC bus, the solid state switches are reconnected to the bus and the discharge resistor is disconnected from across the bus capacitor.

Air-fuel ratio control device for internal combustion engine

Abstract: PURPOSE: To improve learning precision and to improve transient response, by a method wherein a learning value during steady running is computed by means of a target air-fuel ratio, an actual air-fuel ratio, and a feedback correction amount, which serve as a parameter, and a learning value during transient running is computed by a fundamental injection amount and a transient correction amount, which serve as a parameter. CONSTITUTION: Detecting values from a throttle valve opening sensor 25, a crank angle sensor 32, a water temperature 33, an oxygen sensor 34 and the like are inputted to a control unit 35, and from the opening of a throttle valve and the number of revolutions, an intake air amount is determined to compute a fundamental injection amount. Feedback control is made on the fundamental fuel injection amount based on a detecting value from the oxygen sensor 34, and during deceleration, feedback control is applied thereon by means of a transient correction amount responding to a fuel delay due to a change in an amount of fuel adhered. Further, a learning correction factor during steady running is renewed is renewed by means of a target air-fuel ratio, an actual air-fuel ratio, and a feedback correction factor, which serve as a parameter, and a learning correction factor during a transient state is renewed by means of the target-air-fuel ratio factor, the actual air-fuel ratio, and the feedback correct ion factor, which serve as a fundamental fuel injection pulse width and a transient correction amount. COPYRIGHT: (C)1988,JPO&Japio

Zine oxide surge arresters

Abstract: Zinc oxide surge arresters are used to replace capacitive elements for voltages below the pick-up voltage of the surge arrester. Advantageously, the surge arresters may be provided in an alternating current network to provide a high degree of protection against transient disturbances without increasing cost.

Transient temperature distribution of a multilayer composite wall with effects of internal thermal radiation and conduction

Abstract: The transient temperature distribution in a multilayer composite, semitransparent or transparent, absorbing and emitting medium that is suddenly exposed to a thermal radiative flux is investigated. Effects of both thermal radiation and conduction within each layer and convection on both exterior surfaces of the composite wall are considered. The internal heal generation from an electrically conductive thin-film heater is also considered. An analytic relation for obtaining the radiative flux in the multilayer stack is presented. Transient temperature solutions are obtained by a hybrid numerical algorithm. Illustrative solutions are presented for the transient surface temperature of a multilayer transparent medium after exposure to a very high radiative flux. Various surface reflectivities are examined.

Analysis of the periodic transient state of a static Kramer drive

Abstract: The performance of a static Kramer drive is substantially affected by the DC voltage waveform of the thyristor recovery bridge and the inductance of the DC link smoothing reactor. The paper describes a novel method of analysis of the periodic transient performance of such a drive, in which full account is taken of these practical aspects of the recovery system. The analytical model obtained has been verified by comparison of calculated and measured performance for four different types of recovery bridge. The computed results have allowed a more comprehensive examination of drive performance than is possible from the results of practical tests.

Calculation of Generation-Shedding Requirements of the B. C. Hydro System Using Transient Energy Functions

Abstract: The Transient Energy Function method is applied to assess the transient stability of a power network at the end of a complex disturbance sequence. Following this assessment, a method is devised for estimating the amount of generation-shedding required, early in the disturbance sequence, to prevent loss of synchronism. The technique developed for the above assessment is applied to a reduced model of the B. C. Hydro system.

Transient Analysis of Single and Coupled Lines with Capacitively-Loaded Junctions

Abstract: Transient processes are studied for a single line or a pair of coupled lines consisting of line sections with different characteristic admittances and with capacitances loaded at the junctions of line sections. Equations for the Laplace transform of the reflection and transmission coefficients of single and coupled lines are derived for the general case. When the capacitances are loaded at regular intervals, the corresponding expressions of the transient response waveforms at different terminal ports of these lines for both a step and a ramp input are developed. Based on the theoretical analysis, we illustrate the transient responses to ramp signals on some simplified computer signal lines, such as parallel-plate lines with transverse ridges, and parallel striplines with perpendicular crossing strips sandwiched between common upper and lower ground planes. The numerical results suggest that signals with a rise time of t/sub r/<50 ps will cause too much distortion, and should not be used when the length of the line is longer than 2 cm.

A Nonequilibrium Three-Region Model for Transient Analysis of Pressurized Water Reactor Pressurizer

Abstract: A nonequilibrium three-region model is developed for the accurate prediction of the pressure in the pressurizer under both transient and accident conditions.The mathematical model derived from the ...

Electromagnetic Sensors and Measurement Techniques

Abstract: This paper reviews a subject which has developed over the past two decades: the optimal design of sensors for transient (or broadband) electromagnetic measurements and proper installation of the sensors involving concepts from topology and symmetry.

Methods and apparatus for dynamic systems control

Abstract: Methods and apparatus for the control of dynamic systems, more particularly complex dynamic systems and especially those systems exhibiting minimum phase behavior. The method utilizes observer theory to estimate the state variables of the system. Based in part upon the estimated values of the state variables, a pseudo or compensated output for the system is generated. This compensated output represents the steady state asymptote of the actual system output without the unstable or transient system responses. The actual outputs are then controlled by controlling the compensated output.

Charge-control analysis of the COMFET turn-off transient

Abstract: A quasi-static charge-control analysis of the unique transient turn-off characteristic of the COMFET is developed. The analysis describes the transient behavior in terms of steady ON-state current components that flow in the constituent MOSFET and BJT in the basic COMFET structure. The effects of the expanding depletion region at the cathode and of minority-carrier injection into the anode are properly accounted for. Consequently, the physics underlying the turnoff time is clarified, and device design criteria for shortening it, without considerably degrading the ON-state current conduction capability, are suggested.

The effect of feedback on pathway transient response.

Abstract: The effect of variation of the rate of input of material on the transient behaviour of metabolic pathways is examined. This reveals the existence of three transient times which make up the overall pathway transient. Two of these have been described previously and represent the times required for the accumulation of the free intermediate pool and the pool of enzyme-bound intermediate. They are state functions and as such are independent of the way in which the steady state was reached. The third is attributable to the variation in the rate of input of material to the pathway. It is dependent on three further factors. These are (a) the time required for the initial enzyme to reach its own steady state, (b) substrate depletion and (c) feedback. The description of the transient is: (Formula: see text) where V0 represents the rate of input and Vss represents the steady-state flux. The transient time associated with the transition between steady-states is shown to be a simple function of the transients for the establishment of each steady state from rest and may be expressed as: tau = tau b-Va/Vb . tau a where Va and Vb refer to the fluxes in the two steady states and tau a and tau b represent the transient times for the establishment of each of the steady-states from rest. The total pathway transient may now be completely defined as: (formula: see text) where summation over all intermediates, I, is implied. The significance of this to the analysis of pathway behaviour is discussed with more general examples of pathway transient analysis.

Transient overvoltages on power systems

Abstract: Power systems are subjected to many forms of transient phenomena brought about essentially by sudden changes in the steady state values of voltages or currents. Such changes may be the result of a lightning stroke, some malfunction of the system or be brought about by the switching of a circuit either to clear a fault or as a normal operational procedure. To be practical the scope of the review has had to be restricted. Nevertheless it has been found possible to cover a wide range of transient voltages from those which pose problems in transmission systems operating at the highest levels of system voltage down to those which can appear in the domestic situation. Apart from mentioning nonlinear elements in systems, the review is, in the main, restricted to phenomena which are essentially linear in nature and no attempt has been made to include the more complicated phenomena associated with ferroresonance or the production and propagation of harmonic voltages and currents. The review does not claim to be exhaustive but it is hoped that the major causes of transient overvoltages have been considered. In addition to dealing with the causes of transient overvoltages, the review indicates the range of analytical methods that are now available for their analysis and assessment.

A Taylor-Galerkin finite element algorithm for transient nonlinear thermal-structural analysis

Abstract: A Taylor-Galerkin finite element method for solving large, nonlinear thermal-structural problems is presented. The algorithm is formulated for coupled transient and uncoupled quasistatic thermal-structural problems. Vectorizing strategies ensure computational efficiency. Two applications demonstrate the validity of the approach for analyzing transient and quasistatic thermal-structural problems.

Ultrasonic system for the detection of transient liquid/gas interfaces using the pulse‐echo technique

Abstract: An ultrasonic method has been chosen to examine liquid/gas interfacial areas in closed systems. Although commercial equipment was used for the transducer and ultrasonic analyzer, commercial transient memory devices were inadequate. Consequently, a real‐time data analysis and transient memory (DATM) unit was designed and constructed. A series of flight times for a succession of 1024 signals are calculated and recorded in the transient memory. The system clock operates at 10 MHz and increments a 12‐bit binary counter. The counter is capable of measuring return signal times as long as 212 μs (4.096 ms) with a 1‐μs resolution. The data are available as analog voltages for display on an oscilloscope or the digital data may be directly transferred to a microcomputer for analysis, display, or archival storage. The DATM device was successfully applied, collecting data for the analysis of rising bubbles in metallurgical systems and two‐phase flow in horizontal tubes.