• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.59-59
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• 2017

무인 헬리콥터의 양력을 개선하기 위한 익형 설계 단계로서 두꺼운 익형(V1505A)과 얇고 처진 익형(V2008B)의 기본 두 익형의 특성을 예측하는데 있어 회전하는 블레이드의 현실적 조건을 반영한 3D 모델을 마련하고 성능을 예측하였다. Fluent를 이용한 400 mm 선형모델의 시뮬레이션에서는 V1505A 익형은 높은 받음각에서 안정적인 특성을 보인 반면 V2008B는 비교적 높은 동력효율 특성을 보였으나, 높은 받음각에서는 실속 이후 양력이 급락하는 특성을 나타낸다. 형성된 노드 수는 약 870,000개로 하였다. 시위길이 135 mm인 익형 V2008B의 형상은 ANSYS (Fluent v16.2)를 이용해 반경(길이) 1,502 (1,380) mm 의 로터 블레이드를 구성하였다. 충분하지 않은 유동장이 익형 표면에서의 유동의 영향에 영향을 주지 않도록 직경 20 m의 원방경계(far field)를 형성하였다. 사용된 매쉬의 형태는 정사면체 형태로 로터 표면으로부터의 첫 번째 두께 높이는 0.001 m이고 10개의 층으로 형성하였다. 정지 비행하는 헬리콥터의 상태를 가정하여 회전좌표계를 이용하여 정상상태의 유동을 해석하고 사용된 난류모델은 넓은 영역에서의 유동을 고려하여 Realizable $k-{\varepsilon}$ 모델을 사용하였다. 내측그립 받음각 $6{\sim}22^{\circ}$에 대하여 현실적인 회전속도를 연동하여 600~1000 rpm을 적용하였다. 반복수(iteration)는 2000으로 하여 잔차값(residual)이 충분히 수렴하도록 하였다. 전체적으로 실제 헬리콥터가 발휘하는 양력보다는 낮은 수치로 예측되었으며 모델 및 해석 조건에 대한 검토가 필요해 보인다. 양력 값은 받음각 $10^{\circ}$에서 자중(약 68 kgf)을 극복하였고 받음각 $12^{\circ}$에 유상하중 20 kgf을 발휘하며 888 N의 양력을 보였다, 이어 받음각 $22^{\circ}$에서 실속 현상이 발생하였다. 받음각이 증가함에 따라 항력 역시 증가하였으며 받음각 $12^{\circ}$에서 121 N이었고 실속에 이르며 항력은 갑자기 증가할 것으로 예측된다. 본 연구는 변이 익형 개발의 선행 단계로 기본 익형에 대한 공력특성을 CFD 시뮬레이션을 통하여 예측하였다. 예측 값은 현실적 실험방법을 통하여 검증이 되어야 하며 이후 변이익형에 대한 예측과 설계가 가능하다.

• Journal of Navigation and Port Research
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• v.36 no.10
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• pp.839-844
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• 2012

Anemometer is a meteorological instrument that measures wind direction and wind speed in real time, and is mounted to the cranes that are used at ports, shipbuilding yards, off-shore structure, or construction sites that are influenced by wind, and it is used in conjunction with the safety system. Load cell-type anemometer measures the wind direction through the ratio of load between 4 positions by mounting the thin plate to 4 load cells, and measures wind velocity through the summation of loads. According to previous research, the load ratio between two adjacent windswept with respect to the wind direction has unstable value due to vortex around windswept. This causes the result that increases an error on the wind direction. In this study we compared and analyzed the difference between the load ratio with respect to three type windswept shapes in order to suggest the proper windswept shape to reduce this error. The computational fluid flow analysis is carried out with ANSYS CFX to analyze the load ratio between three windswept shapes. Wind direction was adopted as the design variable, and selected 9 wind direction conditions from $0^{\circ}{\sim}90^{\circ}$ with $11.25^{\circ}$ interval for computational fluid flow analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.22-28
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• 2017

The performance of lithium ion batteries used in electric vehicles (EV) varies greatly depending on the battery temperature. In this paper, the finite difference method was used to evaluate the temperature change, state of charge (SOC), internal resistance, and voltage change of the battery due to heat generation in the battery. The simulation model was linked with AMESim to calculate the driving range of an EV traveling in New European Driving Cycle (NEDC) mode. As the temperature dropped below $25^{\circ}C$, the internal resistance of the battery increased, which increased the amount of heat generated and decreased the driving range of EV. At battery temperatures above $25^{\circ}C$, the driving range was also decreased due to reduced SOC that deteriorated the battery performance. The battery showed optimal performance and the driving range was maximized at $25^{\circ}C$. When battery temperatures of $-20^{\circ}C$ and $45^{\circ}C$, the driving range of EV decreased by 33% and 1.8%, respectively. Maintaining the optimum battery temperature requires heating the battery at low temperature and cooling it down at high temperature through efficient battery thermal management. Approximately 500 W of heat should be supplied to the battery when the ambient temperature is $-20^{\circ}C$, while 250 W of heat should be removed for the battery to be maintained at $25^{\circ}C$.

• Journal of Bio-Environment Control
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• v.4 no.1
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• pp.17-24
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• 1995

This study was carried out to make fundamental data for structural safety test of pipe- houses. Experiment on the stress distribution of pipe- houses was conducted to find suitable structural analysis model by examination of end support conditions of pipe. Besides, the loading test and the pile driving test were done to find pull-out capacity and bearing capacity of pipe on the assumption that pipe is pile foundation. For single span pipe - house, the theoretical results assuming the end support condition of pipe is fixed under ground agreed closely with the experimental results of stress distribution. On the other hand for double span pipe -house, the end support conditions of pipe were fixed support when vertical load is applied, and hinged one when horizontal load is applied. The pull - out capacity and allowable bearing capacity of the pipe portion that was buried in the grounds that were soft soil of paddy field and medium or hard soils of dry field derived from experimental results.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.41-46
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• 2018

The wireless sensor network system has the advantage of confirming the behavior of the entire facility by improving the disadvantages of conventional monitoring system. As a result, it is widely proposed as safety diagnosis and measurement of structures, water management systems, and management systems for dam structures. However, there is a lack of research that can evaluate the condition of facilities such as safety at the same time as monitoring. In this study, it is proposed a wireless sensor network system which can evaluate the behavior characteristics of facilities and evaluate the safety status for improving the technical disadvantages on conventional monitoring system. The geotechnical risk factors for the reservoir dam facility were evaluated and the limit values for the risk factors causing the failure of the facility were set. In other words, the system was set up so that the risk factors can be measured and the limit status can be evaluated immediately for each factor. In this study, numerical analysis is carried out for seepage and slope stability analysis using the typical cross section for reservoir dams. The stress-porewater coupling finite difference numerical analysis is performed for establishing the limit displacement for reservoir dam structures. It is developed a system that can estimate the time to reach the critical value by regression analysis using the measured datas.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.381-381
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• 2019

동남아시아의 급격한 도시인구 증가는 도시화로 파생되는 제반문제를 유발하고 있으며 특히 집중호우와 홍수배제 시설의 부족 및 유관시설의 정보관리체계 부재는 홍수 피해규모를 가중시키고 있다. 인도네시아의 경우 물 재해 관리기관 간의 정보공유체계 부재로, 홍수로 인한 문제해결에 대하여 효과적인 대응이 어려운 실정이다. 주요 물 관리 기관인 유역관리청(BBWS)의 경우 조기홍수경보시스템을 보유하고 있으나 단순 수문현황 모니터링에 국한되어 운영되고 있다. 이에 본 연구에서는 홍수피해를 최소화 할 수 있는 동남아시아 맞춤형 물 재해 관리 클라우드 플랫폼을 개발하여 비구조적 홍수 문제해결의 매개체로 활용하고자 한다. 기본적인 유역 수문현황 모니터링과 함께 댐, 보, 배수문 및 펌프장 등 홍수방어시설물의 운영현황 정보, 홍수상황분석, 홍수위험지도 등 종합적인 물 재해 정보를 제공하고 사전에 홍수위험 지역을 분석하여 유관기관과 공유할 수 있는 물 재해 관리 의사결정지원시스템을 개발하고자 한다. 기본적인 정보관리 체계화를 위하여 인도네시아의 다양한 물 재해 관련기관에서 보유하고 있는 자료들의 통합 클라우드 DB관리 시스템을 구축하였다. 연구대상지역은 인도네시아 수도인 자카르타의 Pesanggrahan유역과 인근 Batam섬 Baloi유역을 선정하였으며 대상 유역의 수문, 기상자료 및 GIS 정보수집은 공동연구기관인 인도네시아 공공사업부 수자원청(MPWH)과 주요 물 관리기관인 유역관리청(BBWS)의 협조를 통하여 진행하였다. 수집된 자료들은 관계형 데이터베이스 관리시스템인 MySQL을 사용하여 통합 물 재해 정보 데이터베이스를 구축하였으며 완성된 데이터베이스의 정보제공 및 공유시스템은 웹기반 인터페이스를 통해 관리되도록 설계하였다. 홍수유출 해석을 위한 분석 엔진은 K-water의 홍수분석 시스템인 FAS를 이용하였다. FAS의 홍수분석모형인 COSFIM과 수리모형인 Fldwav를 연계하는 데이터 분석 플랫폼을 완성하였으며 인도네시아 현지 조건에 부합하는 홍수분석 시스템으로 Customizing과정을 수행하였다. 또한 FAS의 PC기반 시뮬레이션 형식을 DB 연계형 웹서비스 방식으로 연동되도록 개량하였으며 추후 SaaS형 물 재해 분석시스템으로 전환할 수 있는 개발환경을 확보하였다. 개발된 물 재해 분석 플랫폼(WRMP)을 활용하여 인도네시아 공동연구기관과의 협의를 통해 물 재해 관리 시나리오를 수립하고 그 대안을 제시하였으며, 적용 시나리오별 홍수피해 저감 효과를 분석하였다. 또한 향후 방재시설물까지 연계하여 운영효과를 분석할 수 있도록 구조화하였다. 개발된 물 재해 관리 시스템은 개선된 정보처리 및 분석시스템을 활용하여 종합적인 물 재해정보를 제공하고, 사전에 홍수위험 지역을 분석하여 유관기관과 공유할 수 있는 물 재해 관리 의사결정 지원시스템으로써 유용하게 활용될 수 있을 것이다.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.542-549
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• 2023

Since the growing interest in surrogate modeling, there has been continuous research aimed at simulating nonlinear chemical processes using data-driven machine learning. However, the opaque nature of machine learning models, which limits their interpretability, poses a challenge for their practical application in industry. Therefore, this study aims to analyze chemical processes using Explainable Artificial Intelligence (XAI), a concept that improves interpretability while ensuring model accuracy. While conventional sensitivity analysis of chemical processes has been limited to calculating and ranking the sensitivity indices of variables, we propose a methodology that utilizes XAI to not only perform global and local sensitivity analysis, but also examine the interactions among variables to gain physical insights from the data. For the ammonia synthesis process, which is the target process of the case study, we set the temperature of the preheater leading to the first reactor and the split ratio of the cold shot to the three reactors as process variables. By integrating Matlab and Aspen Plus, we obtained data on ammonia production and the maximum temperatures of the three reactors while systematically varying the process variables. We then trained tree-based models and performed sensitivity analysis using the SHAP technique, one of the XAI methods, on the most accurate model. The global sensitivity analysis showed that the preheater temperature had the greatest effect, and the local sensitivity analysis provided insights for defining the ranges of process variables to improve productivity and prevent overheating. By constructing alternative models for chemical processes and using XAI for sensitivity analysis, this work contributes to providing both quantitative and qualitative feedback for process optimization.

• 기호학연구
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• no.57
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• pp.211-255
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• 2018

This paper attempts to "re-read" the webtoon Misaeng, which was once an important issue in the field of public discourse on "labor". Our hypothesis was that the dual actactial structure of Misaeng's hero Jang Geurae gave a dual structure to the entire text, which leads to the discovery of text meaning that was not mentioned in the existing discourse. This is based on the concept of 'meta-story character', which Hiroki Azuma talked in his postmodern literary theory. To verify this hypothesis we analyzed the text by applying the Parisian semiotics, more specifically J. Fontanille's theory. Jang Geurae is observed to be a actant of dual structure divided into 'character' of the enunciated level and 'player' of the enunciation level. Considering this characteristic of the hero, Misaeng can be interpreted as a metafiction that shows the 'shifting' between the subject of the enunciated level and the subject of the enunciation level. On the level of 'character' Jang's existence mode turns out to be "Deficiency (actualized)", but on the level of 'player' Jang 's existence mode turns out to be "Inanity(potentiallized)." His somatic responses also show a duality, which is represented by Fontanille's corps-actant model, where on the level of 'character' the somatic actant of Jang consists of 'Moi-chair(ego-flesh)' and 'Soi-idem(self-idem)', and on the level of 'player' it consists of 'Moi-chair(ego-flesh)' and 'Soi-ipse(self-ipse)'. The former mainly acts as a 'role' and takes charge of exteroceptive perception, while the latter mainly acts as 'attitude' and takes charge of interoceptive perception. Because of this dissociative nature of actant, Jang's two 'self' draw the re-adjustment of values without serious conflict between the collective norms and the individual identity. This is in sharp contrast with other characters who struggle with the conflict between the environment and "self". It becomes customary to adopt norms that are suspected to ineffective, but if you raise questions, the normative system can be updated. On one axis of Misaeng there are characters who have lost themselves in customs. On the other axis, there is Jang who can not help dismantling the existing ineffective norms and updating the normative system. Jang's existence mode seems to be one of many possible modes generated by this era where people share no longer solid community values, His actantial structure also communicates with readers of these days who put themselves more in subject of enunciation level than of enunciated level.

• Korean Journal of Remote Sensing
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• v.33 no.5_3
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• pp.855-866
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• 2017

Several research cases using remote sensing methods to analyze changes of storage and dynamics of groundwater aquifer were reviewed in this paper. The status of groundwater storage, in an area with regional scale, could be qualitatively inferred from geological feature, surface water altimetry and topography, distribution of vegetation, and difference between precipitation and evapotranspiration. These qualitative indicators could be measured by geological lineament analysis, airborne magnetic survey, DEM analysis, LAI and NDVI calculation, and surface energy balance modeling. It is certain that GRACE and InSAR have received remarkable attentions as direct utilization from satellite data for quantification of groundwater storage and dynamics. GRACE, composed of twin satellites having acceleration sensors, could detect global or regional microgravity changes and transform them into mass changes of water on surface and inside of the Earth. Numerous studies in terms of groundwater storage using GRACE sensor data were performed with several merits such that (1) there is no requirement of sensor data, (2) auxiliary data for quantification of groundwater can be entirely obtained from another satellite sensors, and (3) algorithms for processing measured data have continuously progressed from designated data management center. The limitations of GRACE for groundwater storage measurement could be defined as follows: (1) In an area with small scale, mass change quantification of groundwater might be inaccurate due to detection limit of the acceleration sensor, and (2) the results would be overestimated in case of combination between sensor and field survey data. InSAR can quantify the dynamic characteristics of aquifer by measuring vertical micro displacement, using linear proportional relation between groundwater head and vertical surface movement. However, InSAR data might now constrain their application to arid or semi-arid area whose land cover appear to be simple, and are hard to apply to the area with the anticipation of loss of coherence with surface. Development of GRACE and InSAR sensor data preprocessing algorithms optimized to topography, geology, and natural conditions of Korea should be prioritized to regionally quantify the mass change and dynamics of the groundwater resources of Korea.

• Journal of Broadcast Engineering
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• v.8 no.4
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• pp.325-338
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• 2003

Video adaptation in response to dynamic resource conditions and user preferences is required as a key technology to enable universal multimedia access (UMA) through heterogeneous networks by a multitude of devices In a seamless way. Although many adaptation techniques exist, selections of appropriate adaptations among multiple choices that would satisfy given constraints are often ad hoc. To provide a systematic solution, we present a general conceptual framework to model video entity, adaptation, resource, utility, and relations among them. It allows for formulation of various adaptation problems as resource-constrained utility maximization. We apply the framework to a practical case of dynamic bit rate adaptation of MPEG-4 video streams by employing combination of frame dropping and DCT coefficient dropping. Furthermore, we present a descriptor, which has been accepted as a part of MPEG-21 Digital Item Adaptation (DIA), for supporting terminal and network quality of service (QoS) in an interoperable manner. Experiments are presented to demonstrate the feasibility of the presented framework using the descriptor.