• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.119-125
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• 1994

Transient power level of the fuel rod is one of the key parameters for the transient fuel behavior. Through the analysis of the fuel performance data bases and sensitivity analyses of such parameters as rod power history, fast neutron flux, fuel enrichment and cycle length, which can affect the transient fuel behavior, a methodology generally applicable to find the allowable transient power level during the ANS Conditions I and II below which the mechanical integrity of the fuel rod is maintained was derived, and allowable transient power levels for the 17$\times$17 KOFA fuel rod have been determined as a function of the burnup. With the introduction of this methodology, design analysis of the transient fuel behavior currently being calculated every cycle can be replaced by the simple check of the peak transient power level achievable during the cycle, and an operational flexibility of the reactor can be obtained by allowing higher transient power level up to 689.5 w/cm at low burnup range than current maximum allowable transient power level, 591 w/cm for the 17$\times$17 KOFA fuel.

• Proceedings of the KIPE Conference
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• 1998.11a
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• pp.64-67
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• 1998

This paper proposes the hybrid PWM scheme that can obtain less harmonic characteristics in GTO inverters. By employing the variable of the dc-link voltage Vdc, the hybrid PWM pattern can ideally compensate the dc input fluctuation together with selected harmonics elimination. The transient behavior, which the magnetic flux and torque are altered and the large current flows instantly, may be produced when the mode change. To reduce such an undesirable transient behavior, it is also presented the technique for the gear changing of inverter operated with the hybrid PWM. The results are verified by simulations and experiments.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.88-93
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• 1996

The initial condition should be consistent with real reactor core state for the simulation of the core transient. The initial xenon distribution, which cad not be measured in the core, has a significant effect on the transient with xenon dynamics of PWR. In the simulation of the transient stating from non-equilibrium xenon state, the accurate initialization of the non-equilibrium xenon distribution is essential to predict the core transient behavior. In this study, the xenon initialization method to predict the core transient more accurately was developed through the first-order perturbation theory of the relationship between simulated power and measured power distribution and verified by the application of the simulation for a startup test of Yonggwang Unit 3.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.2
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• pp.54-61
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• 2013

This paper presents transient response behavior and frequency-dependent ground impedance of a single carbon ground electrode. The ground impedance of the carbon ground electrode was measured as a function of frequency of injected currents and simulated by using the distributed parameter circuit model with due regard to the frequency-dependent soil parameters, and the transient response behavior of the carbon ground electrode against impulse currents were investigated. As a consequence, the frequency-dependent ground impedance of the carbon ground electrode showed the capacitive behavior, that is, the ground impedance decreases with increasing the frequency of injected currents and lowers at the fast front time of impulse current. It was found that the carbon ground electrode is effective in grounding system for lightning protection. The ground impedance simulated with due regard to the frequency-dependent soil parameters was in good agreement with the measured data. The adequacy of the simulation technique and the distributed parameter circuit model for the carbon ground electrode was verified. It is expected that the simulation methodology, which analyzes the frequency-dependent ground impedance of the carbon ground electrode proposed in this work, can be used in the design of a grounding system for protection against lightning.

• Journal of ILASS-Korea
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• v.15 no.2
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• pp.74-82
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• 2010

In order to understand the behavior of transient gaseous injection used in an LPG (Liquefied Petroleum Gas) engine, turbulent incompressible transient jets with butane and propane were measured and analyzed at pressures of 1.5 bar and 2.0 bar with injector diameters of 3 mm and 5 mm. Mie-scattering method with a tracer was used, and images were processed to investigate the behavior of butane and propane jets. Distances from the nozzle to transition region were measured as $L_e/d_{inj}$=4.35~19.4, where $L_e$ and $d_{inj}$ indicate respectively a distance from nozzle to transition point and nozzle diameter. Slits and tubes around jet at near-field were introduced to measure the effect of entrainment and the diameter of jet, which revealed that the entrainment of surrounding air is significant for developing jet diameter. When the entrainment is restricted, the behavior of jet became deviating from the baseline. It was found that the virtual origin located outside of a nozzle towards jet tip within the conditions of this work, and its location was estimated as $x_o/d_{inj}$=0.56~7.25, where $x_o$ is a distance from nozzle to virtual origin.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.231-235
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• 1999

An integrated finite element-based model is presented for the prediction of the three dimensional, transient thermo-mechanical behavior of the work roll in hot strip rolling. The model is comprised of basic finite element models which are incorporated into an iterative solution procedure to deal with the interdependence between the thermo-mechanical behavior of the strip and that of work roll, which arises from roll-strip contact, as well as with the interdependence between the thermal and mechanical behavior. Demonstrated is the capability of the model to reveal the detailed aspects of the thermo-mechanical behavior and to reflect the effect of various process parameters.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.234-238
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• 2007

Magnesium alloy sheets in room temperature have unusual mechanical properties such as high in-plane anisotropy/asymmetry of yield stress and hardening behavior. In this paper, the continuum plasticity models considering the plastic behavior of AZ31B Mg alloy sheet were derived. A new hardening law based on modified two-surface model was developed to consider the general stress-strain response of metals including Bauschinger effect, transient behavior and the unusual asymmetry. Three deformation modes observed during the continuous tension/compression tests were mathematically formulated with simplified relations between the state of deformation and their histories. To include the anisotropy and asymmetry of the initial yield stress, the Drucker-Prager's pressure dependent yield surface was modified by adding anisotropic constants.

• Advances in materials Research
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• v.6 no.1
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• pp.27-43
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• 2017

The transient thermo-mechanical behavior of a simply-supported beam made of a functionally graded material (FGM) under the effect of a moving heat source is investigated. The FGM consists of a ceramic part (on the top), which is the hot side of the beam as the heat source motion takes place along this side, and a metal part (in the bottom), which is considered the cold side. Grading is in the transverse direction, with the properties being temperature-dependent. The main steps of the thermo-elastic modeling included deriving the partial differential equations for the temperatures and deflections in time and space, transforming them into ordinary differential equations using Laplace transformation, and finally using the inverse Laplace transformation to find the solutions. The effects of different parameters on the thermo-mechanical behavior of the beam are investigated, such as the convection coefficient and the heat source intensity and speed. The results show that temperatures, and hence the deflections and stresses increase with less heat convection from the beam surface, higher heat source intensity and low speeds.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.122-128
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• 2002

In this paper dynamic responses of an engine, which is supported by hydraulic mount, to throttle tip-in/Tip out are analyzed. Because the hydraulic mounts have non-linearity that the characteristics of stiffness and damping vary with frequencies, it is difficult to analyze the dynamic behavior of an engine using general integral algorithms. Convolution integral and relationship between unit impulse response functions and frequency response functions are therefore used to simulate the transient behaviors of an engine indirectly. In time domain, impulse response functions are calculated by two-side discrete inverse courier transform of frequency response function achieved by laplace transform of equations of motion. Considering the fact that the shapes of behavior of an engine simulated by the proposed method are in good agreement with test results, it is confirmed that the proposed method is very effective for the analysis of transient response to throttle tip-in/out of an engine with hydraulic mounts.