• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.66-74
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• 1990

The thermal-hydraulic characteristics of the 17$\times$17 OFA (Optimized Fuel Assembly) used in the KNU 7&8 are analyzed and compared with that of the 17$\times$17 SFA (Standard Fuel Assembly) loaded in the KNU 5&6. The thermal-hydraulic characteristics analyzed are minimum DNBR, fuel centerline temperature and exit void fraction at normal operation and design over power transient. Additionally, local linear rod power, which will cause fuel centerline melting, is calculated. The DNBR sensitivity calculations are performed with respect to the reactor operating parameters. COBRA-IV-I code is used for these calculations. The modified W-3 correltion and the drift-flux model are applied for the critical heat flux calculation and the void fraction calculation, respectively. From the calculated results, it has been found that the possibility of DNB occurrence is higher in the OFA than in the SFA. The other hand, the local linear power resulting in fuel centerline moiling of the OFA is nearly equal to that of the SFA.

• Journal of Korean Association for Spatial Structures
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• v.23 no.4
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• pp.59-69
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• 2023

Recently, the occurrence frequency of earthquake has increased in Korea, and the interests for seismic reinforcement of existing school buildings have been raised. To this end, the seismic performance evaluations for school buildings that did not accomplish the seismic design are required. In particular, this study checks the eigenvalue analysis, pushover curves, maximum base shears, performance points and story drift ratios, and then analyzes the seismic performance characteristics according to bracing configuration of steel frame system reinforcement. Also, this study presents the practical field application methods through the comparison of analysis results for the seismic performance characteristics.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.872-875
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• 2004

In this paper, thermal response analysis of a temperature controlled three-axis accelerometer for high temperature environments with integrated micro-heaters and temperature sensors is investigated with finite element method (FEM) program, ANSYS and infrared thermal measurement systems. And availability to application fields from a viewpoint about short thermal response time is discussed. In this paper, the time of three-axis accelerometer for high temperatures becoming $300^{\circ}C$ by integrated micro-heaters and temperature sensors to reduce thermal drift characteristics was analyzed as a thermal response time of this device. The simulated thermal response time (time until SOI piezoresistors actually becomes $300^{\circ}C$) of three-axis accelerometer for high temperatures with ANSYS is about 0.6s, and measured result with infrared temperature measurement systems is about 0.64s. Experimental results using infrared thermal measurement systems agreed well with these theoretical results.

• Steel and Composite Structures
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• v.21 no.1
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• pp.93-107
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• 2016

Seismic fragility analysis is a probabilistic decision-making framework which is widely implemented for evaluating vulnerability of a building under earthquake loading. It requires ingredient named probabilistic model and commonly developed using statistics requiring collecting data in large quantities. Preparation of such a data-base is often costly and time-consuming. Therefore, in this paper, by developing generic seismic drift demand model for regular-multi-story steel moment resisting frames is tried to present a novel application of the probabilistic decision-making analysis to practical purposes. To this end, a demand model which is a linear function of intensity measure in logarithmic space is developed to predict overall maximum inter-story drift. Next, the model is coupled with a set of regression-based equations which are capable of directly estimating unknown statistical characteristics of the model parameters.To explicitly address uncertainties arise from randomness and lack of knowledge, the Bayesian regression inference is employed, when these relations are developed. The developed demand model is then employed in a Seismic Fragility Analysis (SFA) for two designed building. The accuracy of the results is also assessed by comparison with the results directly obtained from Incremental Dynamic analysis.

• Journal of Ocean Engineering and Technology
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• v.28 no.6
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• pp.508-516
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• 2014

A numerical method to investigate the non-linear motion characteristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodynamic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous drag force acting on the platform and tendons is also considered by using Morison’s drag. The results of the present numerical method are compared with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morison's formula.

• Journal of Industrial Technology
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• v.31 no.B
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• pp.45-50
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• 2011

Recently, machine olfactory systems that have been proposed as an artificial substitute of the human olfactory system are being studied by many researchers because they can scent dangerous gases and identify the type of gases in contamination areas instead of the human. In this paper, we present an effective design method for the gas identification system. The design method adopted the sequential combination between genetic algorithms and TSK fuzzy logic system. First, the proposed method allowed the designed gas identification system effectively performing the pattern analysis because it was able to avoid the curse of dimensionality caused by use of a large number of sensors. Secondly, the method led the gas identification system to good performance because it was able to deal with drift characteristics of the sensor data by using description ability of the fuzzy system for nonlinear data. In simulation, we demonstrated the effectiveness of the designed gas identification system by using the simulation results of five types of gases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.22-23
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• 2008

The conventional IGBT has two problems to make the device taking high performance. The one is high on state voltage drop associated with JFET region, the other is low breakdown voltage associated with concentrating the electric field on the junction of between p base and n drift. This paper is about the structure to effectively improve both the lower on state voltage drop and the higher breakdown voltage than the conventional IGBT. For the fabrication of the circular trench IGBT with the circular trench layer, it is necessary to perform the only one wet oxidation step for the circular trench layer. Analysis on both the on state voltage drop and the Breakdown voltage show the improved values compared to the conventional IGBT structure. Because the circular trench layer disperses electric field from p base and n drift junction to circular trench, the breakdown voltage increase. The on state voltage drop decrease due to reduction of JFET region and direction change of current path which pass through reversed layer channel.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.77-84
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• 2004

This study presents an effective stiffness-based optimal technique to control quantitatively lateral drift for tall frameworks using composit member subject to lateral loads. To this end, displacement sensitivity depending on behavior characteristics of tall frameworks is established and approximation concept that preserves the generality of the mathematical programming and can efficiently solve large scale problems is introduced. Specifically, under the 'constant-shape' assumption, resizing techniqe of composite member is developed. Two types of 50 story frameworks are presented to illustrate the features of the quantitative lateral drift control technique proposed in this study.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.1
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• pp.27-31
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• 2011

In this paper, the electron transport characteristics in $CF_4$ has been analysed over the E/N range 1~300[Td] by a two-term approximation Boltzmann equation method and by a Monte Carlo simulation. The motion has been calculated to give swarm parameters for the electron drift velocity, longitudinal diffusion coefficient, the ratio of the diffusion coefficient to the mobility, electron ionization and attachment coefficients, effective ionization coefficient, mean energy, collision frequency and the electron energy distribution function. The electron energy distribution function has been analysed in $CF_4$ at E/N=5, 10, 100, 200 and 300[Td] for a case of the equilibrium region in the mean electron energy and respective set of electron collision cross sections. The results of Boltzmann equation and Monte Carlo simulation have been compared with experimental data by Y. Nakamura and M. Hayashi. The swarm parameter from the swarm study are expected to serve as a critical test of current theories of low energy electron scattering by atoms and molecules, in particular, as well as crucial information for quantitative simulations of weakly ionized plasmas.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.