PURPOSES : Snow-removal performance is performed in this study to assess the feasibility of replacing calcium-chloride solution with sodium chloride solution at the minimum temperature of -5 ℃ during snowfall. METHODS : The atmospheric temperature distribution in Seoul was analyzed. The manufacturing, storage, and indoor melting performance of calcium-chloride and sodium-chloride solutions were evaluated, and on-site snow-removal performance was evaluated based on the solution type. RESULTS : According to the results of the melting performance test at -5°C, the melting capacity of the sodium chloride solution was expressed at a level exceeding 90% of that of the calcium chloride solution, indicating a similar melting performance between the two solutions. Additionally, based on the snow removal performance test using aqueous solutions, the snow removal performance of the sodium chloride solution was found to be approximately 96% compared to that of the calcium chloride solution, indicating minimal differences in snow removal performance due to changes in the type of solution. CONCLUSIONS : Similar snow-removal performance was achieved when the sodium chloride solution was used instead of calciumchloride aqueous solution at temperatures exceeding -5 ℃.

벨로우즈 신축이음관은 구조적 특성으로 인해 큰 변위 용량을 갖으며 과도한 상대변위에 의한 매립 배관 시스템의 손상을 저감시키기 위해 연결부로써 사용된다. 벨로우즈 신축이음관의 내진성능 평가를 위한 연구에서 한계상태는 변형률을 적용하였지만 변형률 기반 한계상태는 벨로우즈 신축이음관의 큰 변위용량을 고려할 수 없다. 또한 벨로우즈 신축이음관의 성능평가와 한계상태 분석을 위한 해석적 및 실험적 연구는 수행된 사례가 극히 적다. 따라서 본 연구는 단조 및 반복하중을 받는 벨로우즈 신축이 음관의 해석적 연구를 통해 벨로우즈 신축이음관의 한계상태를 분석하였다. 결과적으로 단조하중 보다 반복하중을 받는 벨로우즈 신축이음관은 더 낮은 변위에서 누출이 발생하였다. 반복하중으로 인한 피 로 및 라체팅 현상으로 인해 단조하중 보다 낮은 변위의 성능을 갖는 것으로 보여진다. 따라서 반복하 중에서 관측된 변위응답을 기반으로 벨로우즈 신축이음관의 내진성능 평가를 수행하는 것이 보수적일 것으로 판단된다.

국내 건축물에서는 노후한 철근콘크리트 구조물의 안전성이 중요한 문제로 대두되고 있다. 구조물 부분이나 전체의 무너짐으로 인해 경제적 손실을 초래할 수 있으며, 이는 주로 구성 재료의 내구성 결 함으로 인해 발생한다. 여러 노후화 인자 중 동결융해와 부식은 주요한 열화 요인으로 작용한다. 동결 지역의 구조물은 동결융해가 위험 요소로 작용할 수 있으며, 해양 구조물은 해수에 존재하는 염소이온 에 의해 부식될 수 있다. 이러한 문제를 해결하기 위해서는 복합 열화 작용과 철근콘크리트 부재의 성 능 저하 관계를 이해하는 것이 필요하다. 본 연구는 동결융해와 부식의 복합적 피해가 RC 보의 거동 에 미치는 영향을 실험적으로 조사하였다. 7개의 RC 보를 제작하여 각각 다른 수준의 열화 조건을 부여한 후 휨 시험을 실시하였다.

원자력 발전소에서 배관 시스템은 냉각수 및 오염수를 운반하고 생성된 증기를 터빈으로 이동시켜 에너지를 생산하는 중요한 설비이다. 국내에 건설된 원자력 발전소의 가동연수가 증가함에 따라 배관 시스템의 물리적, 기계적 성질의 열화현상은 발생할 수 있으며 이를 경년열화로 정의한다. 배관 시스 템의 경년열화는 재료의 피로, 부식(국부감육), 마모 등과 같은 메커니즘을 통해 발생할 수 있으며 재 료의 강도 및 시스템의 성능 저하와 균열을 야기할 수 있다. 지속적이고 안정적인 에너지 생산을 위해 경제성과 정확도를 고려한 원전 배관 시스템의 손상 감시 기술은 필요하다. 따라서 본 연구는 원전 배 관 시스템의 손상 감시 기술을 개발하기 위한 기초적인 연구로써 배관 시스템의 취약요소로 판단되는 elbow의 국부적인 감육에 따른 거동의 변화를 분석하고자 한다.

현재 농촌은 고령화, 여성화로 인해 기계화가 요구되지만 잡곡류 수확기계의 기계화율은 약 20% 수준으로 확인되어진다. 소요노동력의 절감과 기계화율 제고를 위해 소규모의 경지 조건에 따라 소형 콤바인의 개발이 필요하다. 따라서 본 연구에서는 메밀과 율무를 대상으로 소형 콤바인의 시작기를 제작하여 메밀과 율무 각각의 포장과 수확 작업 시험을 진행하며 작업속도에 따른 각각의 데이터 분석을 진행하였다. 1 m/s 이상의 작업속도에서 메밀의 포장, 수확 시험 결과 전체 손실 비율은 약 21.8%였다. 이 때 가장 높은 비중을 차지한 것은 탈립손실비율이 약 64.1%였고, 다음으로 배진 손실비율이 약 20.9%로 측정되었다. 데이터 분석 결과 탈립손실비율과 배진손실비율에 대해서는 작업속도에 따라 손실율이 높아지는 상관관계 분석 결과가 도출되었고 수집손실비율과 미예취손실비율에 대해서는 작업속도에 따른 각각의 손실율이 감소하는 상관관계를 나타냈다. 메밀의 수확 곡물의 완전립의 비율은 83.2~96.7%로 측정되었으며 작업속도와 상관관계가 없는 것으로 나타났다. 율무의 포장, 수확작업 결과 총곡립손실비율은 전체 작업속도에 대해 평균 약 22.8%가 측정되었다. 작업속도와 손실비율간의 상관관계 분석에서 배진 손실비율을 제외한 다른 손실비율은 양의 상관관계를 나타냈다. 율무의 수확 곡물 품질 분석 결과 완전립의 비율은 작업속도 0.24 ~ 1.05 m/s에서 87.1~95.7%로 측정되었으 며, 손상립과 지경부착립의 비율에서만 양의 상관관계가 있는 것으로 나타났다. 따라서 본 연구에서는 소형 작물을 대상으로한 소형 콤바인 시작기를 제작하였고, 제작된 시작기의 메밀과 율무를 대상으로한 포장, 수확 시험 결과와 이전의 연구들과 비교했을 때 시작기의 성능이 우수한 것을 확인하였 으며 작업속도에 따라 손실에 영향을 끼칠 수 있는 항목을 규명하였다.

The operating parameters considered in this study include evaporating and condensing temperature, degree of subcooling and degree of superheating. in R744-R717 cascade refrigeration system and R744 two-stage compression refrigeration system with the range of low temperature -50℃∼-30℃. The coefficient of performance(COP) of R744-R717 cascade refrigeration system is about 16∼20% greater than that of R744 two-stage compression refrigeration system in the range of evaporation temperature of -50℃∼-30℃. R744 two-stage compression refrigeration system is unstable because its coefficient of performance changes significantly depending on the evaporating temperature and total compression work, and compression efficiency decreases. In this case, not efficient for long-term use. Whereas R744-R717 R744-R717 is a cascade refrigeration system using eco-friendly refrigerants. And this system is a high-efficiency refrigeration system that performs well even under various operating conditions. This is why it can be configured by selecting a refrigerant suitable for the high temperature side and the low temperature side.

We analyzed the performance of hubless rim propellers based on the number of blades, maintaining a fixed pitch ratio and expanded area ratio, using computational fluid dynamics (CFD). Thrust coefficient, torque coefficient and efficiency according to the number of blades were analyzed. In addition, the pressure distribution on the discharge and suction sides of the blade was analyzed. As the advance ratio increases, the thrust coefficient decreases. The highest thrust was shown when the advance ratio was lowest. For the three, four, five and six-blades, the torque coefficient tended to decrease as the advance ratio increased. In the case of seven and eight-blades, the torque coefficient tended to increase as the advance ratio increased. The maximum efficiency was found when the advance ratio was 0.8. When the three-blade, it showed high efficiency at all advance ratios. A high pressure distribution was observed at the leading edge of the discharge blade, and a low pressure distribution was observed at the trailing edge. Applying a hubless rim-driven thruster with the three-blade can generate higher thrust and increase work efficiency.

Water utilities are making various efforts to reduce water losses from water networks, and an essential part of them is to recognize the moment when a pipe burst occurs during operation quickly. Several physics-based methods and data-driven analysis are applied using real-time flow and pressure data measured through a SCADA system or smart meters, and methodologies based on machining learning are currently widely studied. Water utilities should apply various approaches together to increase pipe burst detection. The most intuitive and explainable water balance method and its procedure were presented in this study, and the applicability and detection performance were evaluated by applying this approach to water supply pipelines. Based on these results, water utilities can establish a mass balance-based pipe burst detection system, give a guideline for installing new flow meters, and set the detection parameters with expected performance. The performance of the water balance analysis method is affected by the water network operation conditions, the characteristics of the installed flow meter, and event data, so there is a limit to the general use of the results in all sites. Therefore, water utilities should accumulate experience by applying the water balance method in more fields.

PURPOSES : The purpose of this study is to provide basic data to improve the service life of asphalt pavement using basalt aggregate in Jeju Island by evaluating the performance of asphalt pavement through analysis of material and structural aspects. METHODS : To evaluate the performance of Jeju Island's asphalt pavement, cracks, permanent deformation, and longitudinal roughness were analyzed for the Aejo-ro road, which has high traffic and frequent premature damage. Cores were collected from Aejo-ro sections in good condition and damaged condition, and the physical properties of each layer were compared and analyzed. In addition, plate cores were collected from two sections with severe damage and the cause of pavement damage was analyzed in detail. RESULTS : About 45% of the collected cores suffered damage such as layer separation and damage to the lower layer. The asphalt content of surface layer in the damaged section was found to be 1.1% lower on average than that in the good condition section, and the mix gradations generally satisfied the standards. The density difference between the cores of each layer was found to be quite large, and the air voids was found to be at a high level. CONCLUSIONS : Test results on the cores showed that, considering the high absorption ratio of basalt aggregate, the asphalt content was generally low, and the high air voids of the pavement was believed to have had a significant impact on damage. High air voids in asphalt pavement can be caused by poor mixture itself, poor construction management, or a combination of the two factors. Additionally, the separation of each layer is believed to be the cause of premature failure of asphalt pavement.

Recently, there has been an increasing attempt to replace defect detection inspections in the manufacturing industry using deep learning techniques. However, obtaining substantial high-quality labeled data to enhance the performance of deep learning models entails economic and temporal constraints. As a solution for this problem, semi-supervised learning, using a limited amount of labeled data, has been gaining traction. This study assesses the effectiveness of semi-supervised learning in the defect detection process of manufacturing using the MixMatch algorithm. The MixMatch algorithm incorporates three dominant paradigms in the semi-supervised field: Consistency regularization, Entropy minimization, and Generic regularization. The performance of semi-supervised learning based on the MixMatch algorithm was compared with that of supervised learning using defect image data from the metal casting process. For the experiments, the ratio of labeled data was adjusted to 5%, 10%, 25%, and 50% of the total data. At a labeled data ratio of 5%, semi-supervised learning achieved a classification accuracy of 90.19%, outperforming supervised learning by approximately 22%p. At a 10% ratio, it surpassed supervised learning by around 8%p, achieving a 92.89% accuracy. These results demonstrate that semi-supervised learning can achieve significant outcomes even with a very limited amount of labeled data, suggesting its invaluable application in real-world research and industrial settings where labeled data is limited.

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.

In this study, numerical analysis was performed for the purpose of analyzing the flow characteristics and performance according to the change in the inflow hydrogen temperature and differential pressure of the receptacle of the hydrogen charging system. The pressure distribution and turbulent kinetic energy in the filter area were analyzed by changing the outlet pressure condition under the inlet hydrogen temperature condition, and the flow velocity change at the outlet was compared and analyzed. As a result of the analysis, as the differential pressure decreased, the flow rate at the outlet of the receptacle decreased by up to about 70% at the 2.86 MPa condition compared to the 1.86 MPa condition, and the mass flow rate decreased by about 56.5% at the maximum. It was found that the standard CV performance was not satisfied when the differential pressure at the inlet and outlet was 1.12 MPa or less under the 363K temperature condition.

Recently, the International Maritime Organization is strengthening regulations for ships operating in polar regions. Hence, insulated multi-core tubes as components for vessels operating in extreme cold need to be investigated in various aspects. Furthermore, the demand for research on electric propulsion vessels is also increasingly growing. Thus, to utilize a 4-core insulated multi-core tube with glass wool as insulation, which was previously developed for ships operating in polar regions, as a water-cooled electrical cable, this study conducted an experiment on the temperature change when water at normal temperature 25℃ was supplied as a coolant under the overcurrent varied from 10A to 25A. As a result, the temperature increase of the core in 10A condition was 3.3℃, but it increased to 13.05℃ in the 25A condition. This showed that a temperature difference of approximately 9.75℃ occurred according to the overcurrent load. However, the coolant inlet and outlet temperatures were relatively uniform around 1℃ in all conditions. This suggests that increasing the residence time by proper control of the coolant flow in the future could achieve a higher cooling effect.

PURPOSES : This study aims to analyze and summarize test results related to permeable blocks used for sidewalks and roadways as an alternative to conventional urban road pavement technology, specifically focusing on low-impact development (LID) techniques. Furthermore, it aims to provide reference data on the feasibility of current policy implementation and future policy directions through a longterm analysis of the performance and durability of permeable blocks in sidewalk and roadway construction. METHODS : The research methodology involves (1) conducting a survey on the status and actual conditions of permeability sustainability tests based on the results of permeability persistence tests conducted in Seoul over nine years, from 2013 to 2021; (2) analyzing the differences between the permeability block rating system of Seoul City and that employed by the Ministry of Environment; (3) analyzing the permeability of graded pavement sections in permeable blocks for sidewalks after three years of public use and deriving a regression analysis formula to estimate the maintenance period; (4) analyzing the permeability of pavement sections in permeable blocks for roadways after five years of public use and deriving a regression analysis formula to estimate the maintenance period. RESULTS : This study revealed significant improvements in the performance and quality control of permeable blocks since the implementation of the permeability sustainability test in Seoul in 2013. An analysis of the differences in the permeability coefficient and distribution based on the rating systems of Seoul City and the Ministry of Environment showed that rating system of Seoul City has approximately twice the permeability coefficient quality standard compared to that of the Ministry of Environment. Regression analysis indicated that the firstgrade permeable block was predicted to maintain its permeability for approximately 5.1 years, whereas the third-grade permeable block was predicted to maintain its permeability for approximately 3.1 years. In roadway-permeable block pavements, the first-grade sections maintained excellent quality conditions even after five years, and regression analysis predicted a permeability maintenance period ranging from eight to 17 years. CONCLUSIONS : The correlation analysis of the permeability coefficients based on the common usage period of permeable blocks for sidewalks and roadways presented in this study can provide more accurate estimations of commonality. However, further research under various environmental conditions is required to supplement these findings. Considering the lack of studies on permeable block commonality analysis in Korea, this study highlights the significance of conducting long-term experimental follow-up research to establish commonality prediction formulas for different usage scenarios.

It is very important to measure and analyze various driving performance in the vehicle development stage. Particularly in racing vehicles, analysis of driving characteristics on various courses is very important, and data measurement and analysis technology using actual measurement equipment are widely used in racing strategies. In this paper, we present an analytical approach using vehicle acceleration, which is relatively easy to measure among various factors. Measured acceleration data is used to analyze optimal driving performance.

목적 : 미국의 EYENETRA 회사가 개발한 모바일 앱 기반 이동형 자동굴절력계(NR)는 피검사자가 직접 기기 를 작동하여 굴절이상도를 측정하는 기기로, 그 임상성능을 확인하기 위해, 고정형 자동굴절력계(HRK-8000)와 자각적 굴절검사(subjective refraction, SR) 측정값을 비교 분석하고자 하였다. 방법 : 경기도 소재 M 안경원의 고객 중, 치료 중인 전신질환 및 안질환이 없고, 안과 수술을 받은 적이 없는 근시 또는 근시성 난시 124명(248안)을 대상으로 하였다. 굴절이상도 측정값을 얻기 위하여 NR, HRK-8000과 SR 순서로 검사를 진행하였다. 통계처리는 SPSS program(version 26)을 사용하였고, p<0.050인 경우를 통계 적으로 유의한 것으로 판단하였다. 결과 : 구면, 원주, 등가구면 굴절력은 NR 측정값의 근시도가 가장 높게 측정되었고(p<0.010), SR에 대한 NR 의 평균값은 HRK-8000보다 차이가 크게 나타나 표준편차 범위를 벗어났다. SR에 대한 난시축 일치도는 ±5° 범위에서 NR이 41.4% 일치하였고, HRK-8000은 90.8% 일치하여 NR의 난치축 일치도가 낮게 나타났다. SR에 대한 NR과 HRK-8000의 정확도를 확인하기 위해 95% 일치 한계(LOA)를 비교한 결과 구면, 원주굴절력과 SE 성분의 NR 범위는 각각 +2.01∼-2.72, +1.69∼-2.20와 +1.89∼-2.81 D로 나타났고, HRK-8000 범위는 각 각 +0.84∼-0.96, +0.42∼-0.73와 +0.81∼-1.09 D로 나타났으며, 모든 변수에서 NR의 범위가 넓어 정확도 가 낮은 것으로 확인되었다. 결론 : 이상의 결과를 종합하면, 기존의 자동굴절력계를 대체하기는 어려울 것으로 판단되었고, 임상에서 예비 검사로 활용되기 위해서는 정확도가 개선될 필요가 있다고 사료된다.

In the case of a school building, even though it is a regular structure in terms of plan shape, if the masonry infill wall acts as a lateral load resisting element, it can be determined as a torsionally irregular building. As a result, the strength and ductility of the structure are reduced, which may cause additional earthquake damage to the structure. Therefore, in this study, a structure similar to a school building with torsional irregularity was selected as an example structure and the damping performance of the PC-BRB was analyzed by adjusting the eccentricity according to the amount of masonry infilled wall. As a result of nonlinear dynamic analysis after seismic reinforcement, the torsional irregularity of each floor was reduced compared to before reinforcement, and the beams and column members of the collapse level satisfied the performance level due to the reduction of shear force and the reinforcement of stiffness. The energy dissipation of PC-BRB was similar in the REC-10 ~ REC-20 analytical models with an eccentricity of 20% or less. REC-25 with an eccentricity of 25% was the largest, and it is judged that it is effective to combine and apply PC-BRB when it has an eccentricity of 25% or more to control the torsional behavior.