• 한국자동차공학회논문집
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• 제7권8호
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• pp.150-159
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• 1999

Exhaust system is composed of several parts. Among, them , design of muffler system strongly influences on engine efficiency and noise reduction. So , through comprehension of flow characteristics inside muffler is necessary . In this study , three-dimensional steady and unsteady compressible flow analysis was performed to understand the flow characteristics, pressure loss and amplitude variation of pulsating pressure. The computational grid generation was carried out using commercial preprocessor ICEM CFD/CAE. And the three-dimensional fluid motion inside the muffler was analyzed by STAR-CD, the computational fluid dynamics code. RNG k-$\varepsilon$ tubulence model was applied to consider the complexity of the geometry and fluid motion. The steady and unsteady flow field inside muffler such as velocity distribution, pulsating pressure and pressure loss was examined. In case of unsteady state analysis, velocity of inlet region was converted from measured pulsating pressure. Experimental measurement of pressure and temperature was carried out to provide the boundary and initial condition for computational study under three engine operating conditions. As a result of this study, we could identify the flow characteristics inside the muffler and obtain the pressure loss, amplitude variation of pulsating exhaust gas.

• Fibers and Polymers
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• 제2권1호
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• pp.140-143
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• 2001

To better understand the formation of necking in drawing processes of fibers, strain distributions during drawing processes have been analyzed. For simplicity, one-dimensional incompressible steady flow at a constant temperature was assumed and quasi-static model was used. To describe mechanical properties of solid polymers, non-linear visco-plastic material properties were assumed using the power law type hardening and rate-sensitive equation. The effects of various parameters on the neck formation were matematically analyzed. As material property parameters, strain-hardening parameter, visco-elastic coefficient and strain-rate sensitivity were considered and, for process parameters, the drawing ratio and the process length were considered. It was found that rate-insensitive materials do not reach a steady flow state and the rate-sensitivity plays a key role to have a steady flow. Also, the neck formation is mainly affected by material properties, especially for the quasi-static model. If the process length changes, the strain distribution was found to be proportionally re-distributed along the process line by the factor of the total length change.

• 전기의세계
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• 제18권6호
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• pp.9-22
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• 1969

This thesis has suggested a method of applying the Maximum Principle of Pontryagin to the optimal control of distributive electrical networks. In general, electrical networks consist of branches, nodes, sources and loads. The effective values of steady state currents and voltages are independent of time but only expressed as the functions of position. Moreover, most of the node voltages and branch currents are not predetermined, that is, initially unknown, and their inherent loop characteristics satisfy only Kirchhoff's current and voltage laws. The Maximum Principle, however, needs the initial fixed values of all state variables for its standand way of application. In spite of this inconsistency this thesis has undertaken to suggest a new approach to the successful solution of the above mentioned networks by introducing scaling factors and a state variable change technique which transform the boundary-value unknown problem into the boundary-value partially fixed and partially free problem. For the examples of applying the method suggested, the control problems for minimizing copper quantity in a distribution line have been solved with voltage drop constraint imposed on. In the case of uniform load distribution it has been shown that the optimal wire diameter of the distribution line is reciprocally proportional to the root of distance. For the same load pattern as above the wire diameter giving the minimum copper loss in the distribution line has been shown to be reciprocally proportional to distance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.267-269
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• 2004

Recently, due to increasing the application of power electronic equipment, harmonics generated from the non-liner load are fairy produced. Harmonics can cause a distribution problems such as the overheating of distribution transformer, the breakdown of device and communication interference. Interest about power quality decline of distribution system is very increased. In this paper, we are measured the harmonic voltage and current of distribution system to analyze harmonic characteristics, and it is analyzed Total Harmonic Distortion(HTD). Also, we are modeled distribution system using PSCAD/EMTDC. And it is analyzed harmonic voltage and current in steady-state. The study result have been indicated the utility about harmonics analysis and modeling for distribution system.

• 품질경영학회지
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• 제49권3호
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• pp.327-340
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• 2021

Purpose: The purpose of this study is to propose a system predicting whether an electricity distribution system is abnormal by analyzing the temperature of the deteriorated system. Traditional electricity distribution system abnormality diagnosis was mainly limited to post-inspection. This research presents a remote monitoring system for detecting thermal images of the deteriorated electricity distribution system efficiently hereby providing safe and efficient abnormal diagnosis to electricians. Methods: In this study, an object detection algorithm (YOLOv5) is performed using 16,866 thermal images of electricity distribution systems provided by KEPCO(Korea Electric Power Corporation). Abnormality/Normality of the extracted system images from the algorithm are classified via the limit temperature. Each classification model, Random Forest, Support Vector Machine, XGBOOST is performed to explore 463,053 temperature datasets. The process capability index is employed to indicate the quality of the electricity distribution system. Results: This research performs case study with transformers representing the electricity distribution systems. The case study shows the following states: accuracy 100%, precision 100%, recall 100%, F1-score 100%. Also the case study shows the process capability index of the transformers with the following states: steady state 99.47%, caution state 0.16%, and risk state 0.37%. Conclusion: The sum of caution and risk state is 0.53%, which is higher than the actual failure rate. Also most transformer abnormalities can be detected through this monitoring system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.205-207
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• 2005

In this paper, the Point of Common Coupling (PCC) is selected to analyze harmonic characteristic of distribution system by IEC 61000 - 3 - 6 in Electromagnetic Compatibility(EMC). Harmonic voltage and current were measured at the PCC of real distribution system. Harmonic distribution, nonlinear load component and Total Harmonic Distortion(THD) were verified by measurement. The effective and accurate modelling of real distribution system were proved through a analysis of harmonic impedance, voltage and current in steady-state. Harmonic transfer characteristic in distribution system were summarized and investigated through a analysis of harmonic voltage and harmonic current in harmonic current source.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2038-2043
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• 2007

Analysis of the internal state of the blast furnace is needed to predict and control the operating condition. Especially, it is important to develop modeling of blast furnace for predicting cohesive zone because shape of cohesive zone influences on overall operating condition of blast furnace such as gas flow, temperature distribution and chemical reactions. Because many previous blast furnace models assumed cohesive zone to be fixed, they can't evaluate change of cohesive zone shape by operation condition such as PCR, blast condition and production rate. In this study, an axi-symmetric 2-dimensional steady state model is proposed to simulate blast furnace process using the general purpose-simulation code. And Porous media is assumed for the gas flow and the potential flow for the solid flow. Velocity, pressure and temperature distribution for gas and solid are displayed as the simulation results. The cohesive zones are figured in 3 different operating conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2528-2533
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• 2007

Thermoforming is one of the most versatile and economical processes available for the manufacturing polymer products. The drawback of thermoforming is difficult to get uniform thickness of final products. For the distribution of thickness strongly depends on the temperature distribution of sheet, the adjustment of heater power is very important In this paper, an optimization study for getting uniform temperature distribution was carried out using dual optimization steps. At first, the steady state optimal distribution of heater power is searched by numerical optimization to get uniform temperature of sheet surface. In the second step, time-dependent optimal heater inputs have been found out to decrease the temperature difference through the direction of thickness using Rseponse Surface Method and D-optimal method. The optimization results show that the time-dependent optimal heater power distribution gives acceptable uniform sheet temperature in the field of forming temperature..

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1178-1183
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• 2004

Temperature distribution and heating characteristic of the panel heater for infrared heating have been investigated. The temperature variation with time is firstly measured with the thermocouple to figure out the response time of the heater to the power input. The heater reaches faster to the steady state in comparison to the ceramic heater. The infrared thermal imaging system is utilized to investigate the temperature distribution over the heater surface. The measured thermal images show that the thermal boundary layer induced by the free convection near the heater surface affects the temperature distribution on the surface. The images also show the fairly good uniformity of the temperature distribution in the core region of the surface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.262-267
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• 2001

In this study, the Reliability of degraded steam turbine blade was evaluated using the limited fatigue data. The statistical estimation of limited fatigue data implies that some unknown uncertainties which may be involved in fatigue reliability analysis. Therefore, an appropriate distribution in the fatigue strength was determined by the characteristic distribution - linear correlation coefficient, fatigue physics, error parameter. 3-parameter Weibull distribution is the most appropriate distribution to assume for infinite region. The load applied on the blade is mainly tensile. The maximum Von-Mises stress is 219.4 MPa at the steady state service condition. The failure probability($F_p$) derived from the strength-stress interference model using Monte carlo simulation under variable service condition is 0.25% at the 99.99% confidence level.