• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.1070-1077
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• 2022

The International Maritime Organization has recently strengthened its marine environment regulations. The energy efficiency index has long been an important indicator of ship design, and now, energy efficiency is being enforced for existing ships as well as new ships. To increase the energy efficiency of existing ships, methods such as retrofitting the bow bulb, selecting an optimized trim during ship operation, and installing an energy saving device have been applied. In this study, the ship resistance was numerically simulated using computational fluid dynamics (CFD) under various bow and stern trim conditions. In addition, the bulb was redesigned to further improve the resistance performance under the selected trim conditions. When the improved bulb was applied, the effective horse power increased by approximately 5%. It is, however, necessary to verify whether the redesigned bulb can reduce ship resistance in waves.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.4
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• pp.115-125
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• 2012

The comparison between the spatial and temporal variability of aridity index, precipitation effectiveness and runoff during El-Nino and La-Nina periods and that of the normal period was conducted to evaluate the regional impacts of El-Nino, La-Nina in hydrologic variables. Aridity index and precipitation effectiveness were estimated using 59 nationwide weather stations data and runoff data of WAMIS were used. The ratio of the difference between El-Nino, La-Nina year value and that of normal year was analyzed. Temporal variation demonstrated that aridity index, precipitation effectiveness and run-off discharge increase in March, April, August, November, December and decrease in February, June, September, October according to El-Nino effect. Aridity index, precipitation effectiveness and run-off discharge increase in March, May, September and decrease in June, August, November, December according to La-Nina effect. The spatial variation of those variables analyzed for different basins showed that impacts in the Han river basin relatively higher than that of other basins.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.5
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• pp.208-215
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• 2016

This study was conducted to improve the performance of low-temperature vacuum dryer by applying desiccant to cold trap. Performance evaluation was carried out using several desiccants. The amounts of absorption and diffusivity were measured based on analytic model. Results of desiccant performance evaluation revealed that silica-gel had the most excellent performance for conditions of low-temperature vacuum drying process. Silica-gel was applied to cold trap for evaluating the drying performance. The experiment results showed that the drying time was extended as the thickness of sample was increased due to increased heat and mass transfer resistance of drying sample. In addition, as heating plate temperature was increased, drying time was decreased due to increased evaporation pressure of drying sample. Furthermore, drying time with desiccant was decreased approximately 20% than that without desiccant.

• Geotechnical Engineering
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• v.11 no.1
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• pp.23-40
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• 1995

In order to investigate the characteristics of the lateral earth pressure at rest under hysteretic Ko -loading l unloading conditions. Seven types of multicyclic models have been studied experimentally using dry sand. For this study a new type of Ko -oedometer appal attn is developed, and horizontal pressure is accurately measured. The multi cyclic models consist of largely 3 cases : (i) Ko-test under the same loading/unloading condition, (ii) multi-cyclic loading /unloading Ko -test exceeding the maximum prevertical stress, and (iii) multi-cyclic loading l unloading Ko -test within the mazimium prevertical stress. As a result, the multi -cyclic model showed that single-cyclic model could be extended as well, in which the exponents for unloading condition(a and a') and the reloading coefficients(m, and m*) were mainily dependent upon type of stress model, number of cycles and relati ve density.

• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.75-84
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• 2010

According to the available study and experimental data about the long term behavior of CFT(Concrete Filled Tube) columns, the creep and of concrete in CFT columns are smaller than those of RC columns because of the confinement effect of outer steel columns. In this study, the uncertainties associated with assumed values for concrete properties such as strength, creep coefficients, and service load have been considered and analyzed for the prediction of time-dependent column shortening of CFT column. The CFT column shortening analysis using Monte Carlo method is proposed and an of a 37 story tall building with CFT columns is studied for illustration. According to the results obtained by the probability analysis with multi parameters, the effect of variation coefficient for 3 parameters is investigated considering confidence interval.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.12
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• pp.645-651
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• 2015

This paper presents an experimental study on the freeze drying process for poly ${\gamma}$ glutamic acid. The physical properties of poly ${\gamma}$ glutamic acid are measured during the freeze-drying process. The moisture contents of poly ${\gamma}$ glutamic acid according to the glass transient temperature are obtained by DSC (Differential Scanning Calorimetry) analysis. The end point of primary drying for the poly ${\gamma}$ glutamic acid with a thickness of 3 mm is obtained by measuring the thickness of the dried layer, the amount of moisture evaporation, the moisture content, and the pressure in the drying vacuum chamber during the freeze-drying process. By considering the variation in the glass transient temperature with respect to the moisture content of the material, a control schedule for the heating plate temperature is suggested during the secondary drying process.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.95-95
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• 2021

전 세계 담수 자원의 예측 및 관리에 있어서 유출량 변화의 예측은 중요하다. 하지만 강수량 대비 유출량의 비율인 유출율이 수자원 시스템에 중요한 영향을 미치는지에 대한 여부는 여전히 불분명하다. 본 연구에서는 전 세계의 1,636개 관측소에서 관측된 유출량과 강수량 자료를 이용하여 최근 60년 (1956-2015) 동안 유출량, 강수량, 증발산량의 관계에 있어서 유출율의 역할에 관해 연구하였다. 수문 기후학적으로 습한 지역과 건조한 지역을 구분할 수 있는 임계값으로 유출율을 사용할 수 있다는 점을 Budyko 공간에서 적용하여 건조 지수와의 비교를 통해 발견할 수 있었다. 유출량 변화에 대한 상세한 분석을 위해 강수량 및 증발산량 변화율에 따라 6가지의 범주를 설정하였고 그 결과 대부분의 관측소에서는 강수량의 변화와 일관된 방향으로 유출량이 변화하는 것으로 밝혀져 유출량의 변화는 강수 변화에 더 민감하다는 결론을 얻었으며 모든 범주에 있어서 유출율은 강수량과 증발산량의 변화에 의한 유출량 변화의 크기에 상당한 영향이 있음이 밝혀졌다. 본 연구의 결과들을 통해 우리는 기후 변화에 따른 유출량 변화에 대한 예측성 향상에 있어서 유출율에 대한 물리적인 이해가 잠재적인 주요한 요소라고 제안한다. 토지 피복 및 토지 이용과 같은 인위적 영향은 유출율을 직접 감소 또는 증가시켜 유출량의 민감도를 변화시킬 수 있다. 본 연구에서 제안된 수치적인 접근 방식은 수자원 가용성에 대한 기후 변화 및 인위적 영향을 완화하기 위해 실행 가능한 정보를 제공할 것으로 보인다.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.3
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• pp.95-100
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• 2009

Fine fuel moisture code (FFMC), a main component of forest fire weather index(FWI) in the Canadian forest fire danger rating system(CFFDRS), indicated a probability of ignition through expecting a dryness of fine fuels. According to this code, a rising of temperature and wind velocity, a decreasing of precipitation and decline of humidity in a weather condition showed a rising of a danger rate for the forest fire. In this study, we analyzed a weather condition during 5 years in Kangwon province, calculated a FFMC and examined an application of FFMC. Very low humidity and little precipitation was a characteristic during spring and fall fire season in Kangwon province. 75% of forest fires during 5 years occurred in this season and especially 90% of forest fire during fire season occurred in spring. For developing of the prediction model for a forest fire occurrence probability, we used a logistic regression function with forest fire occurrence data and classified mean FFMC during 10 days. Accuracy of a developed model was 63.6%. To improve this model, we need to deal with more meteorological data during overall seasons and to associate a meteorological condition with a forest fire occurrence with more research results.

• Journal of the Korean Association of Geographic Information Studies
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• v.25 no.4
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• pp.1-18
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• 2022

Currently, the Korea Meteorological Administration evaluates the meteorological drought by region using SPI6(standardized precipitation index 6), which is a 6-month cumulative precipitation standard. However, SPI is an index calculated only in consideration of precipitation at 69 weather stations, and the drought phenomenon that appears for complex reasons cannot be accurately determined. Therefore, the purpose of this study is to calculate and compare SPI considering only precipitation and SDCI (Scaled Drought Condition Index) considering precipitation, vegetation index, and temperature in Gyeonggi. In addition, the advantages and disadvantages of the station data-based drought index and the satellite image-based drought index were identified by using results calculated through the comparison of SPI and SDCI. MODIS(MODerate resolution Imaging Spectroradiometer) satellite image data, ASOS(Automated Synoptic Observing System) data, and kriging were used to calculate SDCI. For the duration of precipitation, SDCI1, SDCI3, and SDCI6 were calculated by applying 1-month, 3-month, and 6-month respectively to the 8 points in 2014. As a result of calculating the SDCI, unlike the SPI, drought patterns began to appear about 2-month ago, and drought by city and county in Gyeonggi was well revealed. Through this, it was found that the combination of satellite image data and station data increased efficiency in the pattern of drought index change, and increased the possibility of drought prediction in wet areas along with existing dry areas.

• Geotechnical Engineering
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• v.11 no.4
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• pp.63-74
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• 1995

Much of Taegu and Kyungpook areas are composed of sedimentary rocks. This paper is concerned with the engineering characteristi os of weathered shale soils and mudstone soils. In this study, the engineering characteristics of weathered shale soils and mudstone soils are investigated by performing tests such as compaction, gradation, CBR permeability and crushability according to compaction energy and water content. The experiments were carried out to obtain the relationships of the ratio of surface area(Sw'/Sw) and the indez of crushing(IC) The results are found as follows : (1) Weathered shale soils are larger than weathered mudstone soils in maximun dry den sixty, but weathered shale soils are smaller than weathered mudstone soils in OMC. (2) Minimum permeability is found in OMC's 1~2% wet side, and the more compaction energy is high, the more the change's range of permeability becomes narrow. (3) There is linear correlation between the ratio of surface area and the indez of crushing. IC : 14.286sw'/Sw -8.429(r=0.9937) (4) Soaked CBR value becomes maximum in OMC's dry side, and it decreases as the water content increases. Whereas the more compaction energy is high the more unsoaked and soaked CBR values are high in OMC's dry side, unsoaked and soaked CBR values are opposed to that in OMC's wet side.