• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.3
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• pp.168-173
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• 2013

In this paper, we tried different two approach to improve the performance of the IGBT. The first approach is that adding N+ region beside P-base in the conventional IGBT. It can make the conventional IGBT to get faster turn-off time and lower conduction loss. The second approach is that adding P+ region on right side under gate to improve latching current of conventional IGBT. The device simulation results show improved on-state, latch-up and switching characteristics in each structure. The first one was presented lower voltage drop(3.08V) and faster turn-off time(3.4us) than that of conventional one(3.66V/3.65us). Also, second structure has higher latching current(369A/?? ) that of conventional structure. Finally, we present a novel IGBT combined the first approach with second one for improved trade-off characteristic between conduction and turn-off losses. The proposed device has better performance than conventional IGBT.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.3
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• pp.153-159
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• 2018

Many researches have been carried out on carbonation, a representative deterioration in underground structure. The carbonation of RC (Reinforced Concrete) structure can cause steel corrosion through pH drop in concrete pore water. However extension of service life in RC structures can be obtained through simple surface protection. Unlike the conventional deterministic maintenance technique, probabilistic technique can consider a variation of service life but it deals with only normal distributions. In the work, life time-probability distributions considering not only normal but also log distributions are induced, and repair cost estimation technique is proposed based on the induced model. The proposed technique can evaluate the repair cost through probabilistic manner regardless of normal or log distribution from initial service life and extended service life with repair. When the extended service life through repair has log distribution, repair cost is effectively reduced. The more reasonable maintenance strategy can be set up though actual determination of life-probability distribution based on long term tests and field investigations.

• Korean journal of applied entomology
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• v.8
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• pp.25-28
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• 1969

In order to find out the effect of contactor to form appressorial structure of Glomerella glycines, this experiment was carried out by using several contactors such as cover glass. cellophane, vinyl and oil paper respectively. In the case of cover glass placed on a drop of conidial suspension of the fungus which is incubated on water agar for 12 hours, 67.7 percent of appressoria were resulted, whereas no appressorial structure was found in the control. Vinyl was known best physical contactor and cellophane, cover glass and oil paper were fairly good in that order. Effects of temperature, time and relative humidity on the formation of appressoria of G. glycines were similar to each of optimum growth range of temperature and relative humidity $25^{\circ}-30^{\circ}C$ and 70-100 Percent, respectively. In addition, maximum appressorial formation was resulted in the conidial suspension incubated on soybean leaves for 36 hours. No appressorium was found at above $35^{\circ}C$, below R.H. 70 percent and 5 hours incubation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.18-31
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• 2018

Rotorcrafts have more severe crashworthiness conditions than fixed wing aircraft owing to VTOL and hovering. Recently, with the increasing demand for highly efficient transportation system, application of composite materials to aircraft structures is increasing. However, due to the characteristics of composite materials that are susceptible to impact and crash, demand to prove the crashworthiness of composite structures is also increasing. The purpose of present study is to derive the structural concept of composite subfloor for rotorcrafts and verify it. In order to design a crashworthy composite subfloor, the conceptual design of the testbed helicopter for the demonstration and the derivation of energy absorbing requirement were carried out, and the composite energy absorber was designed and verified. Finally, the testbed for the demonstration of a crashworthy composite structure was fabricated, and performed free drop test. It was confirmed that the test results meet the criteria for ensuring occupant survivability.

• Journal of the Korean Chemical Society
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• v.53 no.2
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• pp.175-188
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• 2009

In this study, we developed an experimental method of the Charles' law applicable to school. Science textbooks and literatures on this principle were analyzed to extract factors utilized in organizing the experimental setup and method. A combined structure such as with a vial and a glass tube, the former of which is for deciding the total volume and the latter of which is for easy measurement of volume, was better in measurement of volume with temperature rather than a simple structure such as syringe. Use of graduated cylinder as a water bath to control the temperature showed advantage in cooling time than using other bath of larger volume such as a beaker. A liquid drop was used as a plug in the glass tube. This plug has little resistance with the glass wall when the gas volume changes. Water as a liquid drop in the glass tube had a significant effect in volume change of gas due to evaporation, especially in the beginning of the measurement. Glycerol showing negligible effect in volume change was used. This method took about one hour and produced a good linear relationship between the temperature and volume of gas with $R^2$ = 0.999 and absolute zero temperature = $-216.7\;{^{\circ}C}$. The Charles' law experiment developed in this study can be performed with appropriate adjustment of procedure considering the purpose of the curriculum of science and chemistry subject at each school level.

• Journal of Korea Water Resources Association
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• v.52 no.4
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• pp.235-243
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• 2019

Recently, urban inundation was frequently occurred due to the intensive rainfall exceeding marginal capacity of the flood control facility. Furthermore, needs for the underground storage facilities to mitigate urban flood are increasing according to rapidly accelerating urbanization. Thus, in this study, drainage efficiency in drain tunnel connecting to underground storage was investigated from the air-core measurements in the drop shaft against two types of inlet structure. In case of the spiral inlet, the multi-stage structure is introduced at the bottom of the inlet to improve the vortex induction effect at low inflow discharge (multi-stage spiral inlet). The average cross-sectional area of the air-core in the multi-stage spiral inlet is 10% larger than the tangential inlet, and show the highly air emission effect and the highly inflow efficiency at the high inflow discharge. In case of the tangential inlets, the air emission effect decreased after exceeding the maximum inflow discharge, which is required to maintain the inherent performance of the tangential inlet. From the measurements, the empirical formula for the cross-sectional area of the air-core according to locations inside the drop shaft was proposed in order to provide the experimental data available for the inlet model used in experiments.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.167-174
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• 2001

Reflection method using ultrasonic source has been attempted to obtain the information about tunnel lining structures composed of lining, shotcrete, water barrier and voids at the back of lining. In this work, two different types of sources, i.e. single-pulse source and sweep source, can be used. Single-pulse source with short time duration has the frequency content whose amplitudes tend to be concentrated around the dominant frequency, whereas sweep source with long time duration denotes a flat distribution of relatively larger amplitude over a broad frequency band, although the peak to peak amplitude of single-pulse source wavelet is equivalent to that of sweep source one. In traditional seismic application, a single-pulse source(weight drop, dynamite) is typically used. However, to investigate the fine structure, as it is the case in the tunnel lining structure, the sweep wavelet can be also a desirable source waveform primarily due to the higher energy over a broad frequency band. For the investigation purposes of sweep source, a physical modeling is a useful tool, especially to study problems of wave propagation in the fine layered media. The main purpose of this work was using a physical modeling technique to explore the applicability of sweep source to the delineation of inner layer boundaries. To this end, a two-dimensional physical model analogous to the lining structure was built and a special ultrasonic sweep source was devised. The measurements were carried out in the sweep frequency range 10 ∼ 60 KHz, as peformed in the regular reflection survey(e.g. roll-along technique). The measured data were further rearranged with a proper software (cross-correlation). The resulting seismograms(raw data) showed quitely similar features to those from a single-pulse source, in which high frequency content of reflection events could be considerably emphasized, as expected. The data were further processed by using a regular data processing system "FOCUS" and the results(stack section) were well associated with the known model structure. In this context, it is worthy to note that in view of measuring condition the sweep source would be applied to benefit the penetration of high frequency energy into the media and to enhance the resolution of reflection events.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.159-164
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• 2009

Cooled EGR system is an effective method for the reduction of $NO_x$ emission and PM emission from a diesel engine. Proper choice of wavy cooling fins and gas tubes is a key factor of cooled EGR system. As a part of solutions for energy crisis and environmental problems, hybrid vehicles mounted with diesel engines are under development globally. This study investigates the cooled EGR systems for hybrid diesel engine with the specifications of both optimized wavy cooling fins and improved shape of structure to verify the heat exchange efficiency, outlet temperature and gas pressure drop of cooler by means of numerical analyses and rig performance tests. The output of this study will be applied to a 2.0L hybrid diesel engine which is being developed for domestic and overseas market.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.4
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• pp.281-286
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• 2012

Single frame structures with notches were fractured by applying drop impact loadings at room temperature and low temperature. Johnson-Cook shear failure model has been employed to simulate the fractured single frame structures. Through several numerical analyses, material constants for Johnson-Cook shear failure model have been found producing the cracks resulted from experiments. Fracture strain-stress triaxiality curves at both room temperature and low temperature are presented based on the extracted material constants. It is expected that the fracture strain-stress triaxiality curves can offer objective fracture criteria for the assessment of structural fractures of polar class vessel structures fabricated from DH36 steels. The fracture experiments of single frame structures revealed that the structure on low temperature condition fractures at much lower strain than that on room temperature condition despite the same stress states at both temperatures. In conclusion, the material properties on low temperature condition are essential to estimate the fracture characteristics of steel structures operated in the Northern Sea Route.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.89-94
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• 2011

The EGR system is one of important components in diesel engine. The regulation on NOx emission has been tightened up. Therefore, it is a significant issue to develop and commercialize the high efficient EGR cooler system that reduces NOx emission in DI diesel engine. Key performance factor of the EGR cooler system is how to properly design both wavy cooling fins and gas tubes. This paper proposes a high efficient EGR cooler that has been upgraded with both the optimized wavy cooling fins and the improved shape of structure. The evaluation of the heat exchange efficiency, outlet temperature, and gas pressure drop of the EGR cooler is performed with the prototype of the proposed EGR cooler. The result shows a good solution and will be implemented to the model of a clean diesel engine being developed for both domestic and overseas market.