Showing papers on "Transient (oscillation) published in 1996"

A theoretical and experimental study

Abstract: A Iheoreticat and experimental model which describes the transient behaviour of a matrix solar air heater is presented. The transient behaviour of the heater results from sudden changes in the intensity of the incident solar radiation and the inlet fluid temperature. The temperature distributions in both the fluid and the solid matrix domains are given exactly, and experiments are conducted to verify the validity of the theoretical model. There was good agreement between the measured and predicted values.

Transient growth in compressible boundary layer flow

Abstract: The potential for transient growth in compressible boundary layers is studied. Transient amplification is mathematically associated with a non‐orthogonal eigenvector basis, and can amplify disturbances although the spectrum of the linearized evolution operator is entirely confined to the stable half‐plane. Compressible boundary layer flow shows a large amount of transient growth over a wide range of parameter values. The disturbance size is here measured by a positive definite energy like quantity that has been derived such that pressure‐related transfer terms in its evolution equation mutually cancel. The maximum of the transient growth is found for structures which are independent of the streamwise direction and is found to scale with R2. This suggests that the transient growth originates from the same lift‐up mechanism found to give large growth in incompressible shear flows. The maximum growth is also found to increase with Mach number. In compressible flow, disturbances that experience optimal transi...

Computer analysis of transient voltages in large grounding systems

Abstract: A computer model for transient analysis of a network of buried and above ground conductors is presented The model is based on the electromagnetic field theory approach and the modified image theory Validation of the model is achieved by comparison with field measurements The model is applied for computation of transient voltages to remote ground of large grounding grid conductors Also computation of longitudinal and leakage currents, transient impedance, electromagnetic fields, and transient induced voltages is possible This model is aimed to help in EMC and lightning protection studies that involve electrical and electronic systems connected to grounding systems

Envelop transient analysis: a new method for the transient and steady state analysis of microwave communication circuits and systems

Abstract: The two popular and general purpose simulation techniques, Time Domain Integration and Harmonic Balance, do not fulfil the requirement for analysis of microwave communication systems with arbitrary modulated carrier frequency. A new technique is presented, which overcomes this default. A dramatic saving in computer memory space and computation time is obtained with respect to the previous methods.

A gate-level simulation environment for alpha-particle-induced transient faults

Abstract: Mixed analog and digital mode simulators have been available for accurate /spl alpha/-particle-induced transient fault simulation. However, they are not fast enough to simulate a large number of transient faults on a relatively large circuit in a reasonable amount of time. In this paper, we describe a gate-level transient fault simulation environment which has been developed based on realistic fault models. Although the environment was developed for /spl alpha/-particle-induced transient faults, the methodology can be used for any transient fault which can be modeled as a transient pulse of some width. The simulation environment uses a gate level timing fault simulator as well as a zero-delay parallel fault simulator. The timing fault simulator uses logic level models of the actual transient fault phenomenon and latch operation to accurately propagate the fault effects to the latch outputs, after which point the zero-delay parallel fault simulator is used to speed up the simulation without any loss in accuracy. The environment is demonstrated on a set of ISCAS-89 sequential benchmark circuits.

Increased ductility in high velocity electromagnetic ring expansion

Abstract: Thin rings have been rapidly expanded using large, transient magnetic fields to study the effect of deformation velocity on strains to failure of ductile metals. A classical electrodynamics analysis similar to one developed previously by Gourdin was employed to estimate sample velocities. Within expansion velocities studied (50 to 300 m/s), the experimental results show that ductility of Al 6061 and OFHC Cu increases monotonically with increasing velocity. In each case, sample strain at failure is almost twice as great at 300 m/s as in the static condition. Comparison to a one-dimensional rigid-viscoplastic dynamic finite element method analysis suggests that inertial effects are mainly responsible for enhanced ductility over a wide range of velocity.

Transient terahertz reflection spectroscopy of undoped InSb from 0.1 to 1.1 THz

Abstract: Using transient terahertz reflection spectroscopy, the far‐infrared (0.1–1.1 THz) reflection amplitude and associated phase change upon reflection from undoped InSb was measured between 80 and 260 K. Using the Drude model, the transient terahertz data were fit by adjusting the values for the electron mobility and carrier concentration. The close agreement between the data and model validates using the Drude model to describe the electronic and optical properties of InSb below 1 THz. These results suggest a possible application of transient terahertz reflection spectroscopy for measuring semiconductor properties of thick samples without surface contact.

Voltage stability analysis in transient and mid-term time scales

Abstract: This paper reviews the general methodology of analysing voltage stability in the mid-term and in the transient time scale. It shows how a simplified simulation of the mid-term dynamics can only be combined with the analysis of "snapshots" using a linearised model for the transient dynamics. Finally it points out how the stability of mid-term dynamics can be predicted using constant power loads in a transient time scale modelling.

Transient electromagnetic fields near large earthing systems

Abstract: Electromagnetic compatibility studies require knowledge of transient voltages that may be developed near earthing systems during lightning discharge, since such voltages may be coupled to sensitive electronic circuits. For such purpose, accurate evaluation of the transient electric field near to and/or at the surface of the grounding conductors is necessary. In this paper, a procedure for computation of transient fields near large earthing systems, as a response to a typical lightning current impulse, based on computational methodology developed in the field of antennas, is presented. Computed results are favorably compared with published measurement results. The model is applied to check the common assumption that the soil ionization can be neglected in case of large earthing systems. Presented results show that the soil ionization threshold is met and exceeded during typical lightning discharge in a large earthing system.

Development of transient stability control system (TSC system) based on on-line stability calculation

Abstract: This paper describes a new transient stability control system named the TSC system developed for application to the trunk power system of Chubu Electric Power Co. (CEPCO). The TSC system prevents wide-area power system blackout by shedding optimal generators when a serious fault occurs. This system has the following features: (1) the TSC system performs detailed stability calculations based on online information telemetered from the actual network, and it periodically evaluates the stability of the power system against contingencies with a high degree of accuracy. The system selects the optimum generators to be shed; (2) if a contingency actually occurs, the generators to be shed that were determined in advance are shed about 150 ms after fault occurrence to maintain the stability of the power system; and (3) the system can be applied to any power system configuration of CEPCO, such as a loop network, radial network, etc. The TSC system will be put into regular service in June 1995. It will be the world's first real-time stability control system that performs detailed transient stability calculations on a large power system online.

Harmonic analysis of transient currents during sympathetic interaction

Abstract: The phenomenon of sympathetic interaction between transformers, which is very likely to occur when a transformer is energised onto a system to which there are other transformers already connected, changes significantly the duration and the magnitude of the transient magnetising currents in the transformers involved. This phenomenon is discussed in the paper, with the harmonic content of the transient currents and its associated overvoltages being analysed. It is shown that the importance of taking into consideration the saturation characteristics of the transformers already in operation when studying transformer transient inrush.

Calculation of machine winding electrical parameters at high frequencies for switching transient studies

Abstract: This paper describes a multiconductor transmission line approach for calculating the machine winding electrical parameters for switching transient studies. The technique is based upon the solution of the one dimension diffusion equation in the slot of electrical machines. The coil electrical parameters are calculated considering both the magnetic flux in the iron and in the air. Several practical formulations for calculating the winding electrical parameter are proposed which take into account the machine winding design characteristics. The computer models are validated by a comparison of measured and calculated results in two high voltage induction motors.

A global model for steady-state and transient s.i. engine heat transfer studies

Abstract: A global, systems-level model which characterizes the thermal behavior of internal combustion engines is described in this paper Based on resistor-capacitor thermal networks, either steady-state or transient thermal simulations can be performed A two-zone, quasi-dimensional spark-ignition engine simulation is used to determine in-cylinder gas temperature and convection coefficients Engine heat fluxes and component temperatures can subsequently be predicted from specification of general engine dimensions, materials, and operating conditions Emphasis has been placed on minimizing the number of model inputs and keeping them as simple as possible to make the model practical and useful as an early design tool The success of the global model depends on properly scaling the general engine inputs to accurately model engine heat flow paths across families of engine designs The development and validation of suitable, scalable submodels is described in detail in this paper Simulation sub-models and overall system predictions are validated with data from two spark ignition engines Several sensitivity studies are performed to determine the most significant heat transfer paths within the engine and exhaust system Overall, it has been shown that the model is a powerful tool in predicting steady-state heat rejection and component temperatures, as well as transient component temperatures

Gate-control strategies for snubberless operation of series connected IGBTs

Abstract: Increasing the operation voltage and hence the switching power by series connection of IGBT-modules causes transient and static voltage imbalances. To achieve snubberless operation, novel gate-control strategies have been developed. Active gate-controlled voltage balancing and gate-side di/dt-control as well as dv/dt-control are presented in theory and with measurement results.

A stability model for the advanced series compensator (ASC)

Abstract: This paper develops an accurate and general stability model for the ASC (thyristor controlled reactor). The model is valid for both the capacitive and inductive regions of the ASC operation. It is accurate in that the instantaneous voltage and current waveforms and also the fundamental component of the capacitor voltage (needed for stability) are determined every half-cycle by solving the differential equations of the ASC circuit. The model is capable of incorporating any control algorithms. The validity of the model is demonstrated by comparing the model with the Electromagnetic Transient Program (EMTP) digital simulations using step time of 10 /spl mu/s.

Probabilistic transient stability studies using the method of bisection [power systems]

Abstract: In this paper, a method of bisection is introduced as a tool to considerably reduce the amount of computation time required in the stochastic evaluation of power system transient stability. This method proves to be very helpful in predicting the number of stability runs required to calculate the probabilistic transient stability indices for a given system location, a certain transmission line or for the overall power system. The developed method is examined utilizing a hypothetical test system and the effect of load forecast uncertainty is illustrated. The effect of modeling and employing high-speed simultaneous or adaptive reclosing is also presented and discussed.

Overmodulation strategy for high performance torque control

Abstract: In the overmodulation region, the operation of the electrical drive system with a current controller is characterized by a rapid deterioration of motor torque and speed. It is desirable to use the overmodulation strategy, which guarantees the fast response even in transient state and satisfies the overall closed-loop control performance. In this paper, in order to improve the dynamic characteristics of the electrical drive, a new overmodulation technique is proposed. Considering the current transition characteristics, an efficient overmodulation strategy is introduced to achieve better transient performance through an adequate voltage selection. With the help of a new overmodulation strategy, required electrical torque can be directly produced as quickly as possible, and stable drive characteristics can be achieved in the transient condition. The proposed method has been implemented on an actual inverter system and thoroughly tested on a 900-W interior permanent magnet synchronous machine (IPMSM) to confirm its feasibility.

Analysis of the conductance transient in thick-film tin oxide gas sensors

Abstract: In this paper, we analyse the conductance transient of a Taguchi TGS-822 sensor under a step change in the vapour concentration. A diffusion-limited range in the conductance transient is observed. Adjustments between the theoretical calculations based on a non-linear diffusion-reaction model and the experimental results alloy a constant, τ′, to be estimated, which is independent of the final conductance value and depends, among other parameters, on the effective diffusion coefficients of vapours in the porous tin oxide sensor. From transient measurements of organic solvents (benzene and o-xylene) we have obtained τ′ values that are independent of concentration and characteristic for each vapour. This new parameter can give useful information for gas/vapour recognition.

System and method for locating faults in electric power cables

Abstract: There is provided a system and method for locating faults in power distribution systems with complex topology, such as multi-phase urban networks (6), utilizing reliable time-delay techniques as well as a transponder (22) at a monitoring point to sense the arrival of the transient fault pulse and for transmitting a timing pulse a known time delay after sensing the arrival of the transient fault pulse and a calibration pulse a known time delay after transmitting the timing pulse. Installed along the power distribution system at key locations are receiver stations (4, 4a, 4b) capable of sensing the arrival of the transient fault pulse, timing pulse and calibration pulse and measuring the time intervals occurring between each. The location of the fault is then determined based on these timing intervals, known time delays and the known propagation velocity of the electric power cables in the power distribution system. Fault location accuracy is further enhanced by factoring rise-time effects of the sensed pulses into the time interval measurements.

Multiprocessing transient event detector for use in a nonintrusive electrical load monitoring system

Abstract: A multi-processing transient event detector for use in a nonintrusive electrical load monitoring system has been provided. Templates of transient pattern data associated with each electrical load which may be monitored are stored. Such templates are then used to match and correlate with the actual monitored transient pattern data at the load site. The decomposition in which time scales are changed is accomplished in parallel along with one or more parallel event detection processing modules for each decomposition.

Quench levels and transient beam losses in LHC magnets

Abstract: The last evaluation of quench levels related to transient beam losses was done in 1987 [1]. The subject is reevaluated with a more detailed approach of the thermodynamics of the superconducting cables in response to a transient heat load associated to beam losses. CERN{SL Division CERN{LHC Division Formerly CERN{SL Division, now at Siemens-Matsushita OHG, Deutschlandsberg,Austria jbj@mail.cern.ch Administrative Secretariat LHC Division CERN CH-1211 Geneva 23 Switzerland Geneva, 29 July 1996

Analysis of floating body induced transient behaviors in partially depleted thin film SOI devices

Abstract: Emphasis toward manufacturability of thin film SOI devices has prompted more attention on partially depleted devices. In this paper, drain current transients in partially depleted SOI devices due to floating-body effects are investigated quantitatively. A one-dimensional analytical model is developed to predict the transient effect and MEDICI simulation is performed to confirm the model. With the model, the amount of the turn-on current enhancement and the turn-off current suppression are calculated. The transient characteristics can be used in investigating the quality of the SOI materials by determining the carrier lifetime. The impact of the transient effect on the device parameter extraction is described.

Hyperbolic damped-wave models for transient light-pulse propagation in scattering media

Abstract: Transient optical transport in highly scattering media such as tissues is usually modeled as a diffusion process in which the energy flux is assumed proportional to the fluence (intensity averaged over all solid angles) gradients. Such models exhibit an infinite speed of propagation of the optical signal, and finite transmission values are predicted even at times smaller than those associated with the propagation of light. If the hyperbolic, or wave, nature of the complete transient radiative transfer equation is retained, the resulting models do not exhibit such drawbacks. Additionally, the hyperbolic equations converge to the solution at a faster rate, which makes them very attractive for numerical applications in time-resolved optical tomography.

Improvement of settling response of disk drive head positioning servo using mode switching control with initial value compensation

Abstract: A Mode Switching Control (MSG) design method for disk drive head positioning servo is proposed. The MSC includes several controllers and switches from one to the other to achieve both precise positioning and short seek time requirements. The issue is "settling", the transient state after switching. This paper proposes the initial value compensation (IVC) method to improve transient characteristics after switching. Under the IVC method, certain values are placed in the state variables of the controller or an additional input is added at switching. From experimental data, we have proved that IVC reduces overshoot and slow transient response after switching. Also this IVC method does not affect any closed loop characteristics such as stability.

Low-voltage transient bipolar effect induced by dynamic floating-body charging in scaled PD/SOI MOSFETs

Abstract: An increased significance of the parasitic bipolar transistor (BJT) in scaled floating-body partially depleted SOI MOSFETs under transient conditions is described. The transient parasitic BJT effect is analyzed using both simulations and high-speed pulse measurements of pass transistors in a sub-0.25 /spl mu/m SOI technology. The transient BJT current can be significant even at low drain-source voltages, well below the device breakdown voltage, and does not scale with technology. Our analysis shows that it can be problematic in digital circuit operation, possibly causing write disturbs in SRAMs and decreased retention times for DRAMs. Proper device/circuit design, suggested by our analysis, can however control the problems.