• 대한기계학회논문집A
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• 제37권11호
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• pp.1315-1321
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• 2013

볼 베어링의 손상 상태를 예측하기 위한 방법을 본 논문에서 제시하였다. 손상 진전율을 추정하기 위해 확률적 베어링 피로 결함 진전 모델을 적용하고 잡음이 포함된 가속도 신호의 RMS 데이터를 이용하여 손상 상태와 고장 시간을 계산하였다. 확률적 결함 진전 모델의 파라미터는 볼 베어링에 대한 일련의 Run-to-Failure 시험을 수행하여 결정하였다. 가속도 RMS값으로부터 손상 진전율과 손상 상태를 추정하기 위해 규칙화된 파티클 필터 추정 방법을 적용하였다. 미래 시점에서의 손상 상태는 최근 측정된 데이터와 직전에 추정된 상태값을 이용하여 예측하였다. 예측된 손상 상태와 시험 데이터와 비교하여 개발된 방법의 적절성을 확인하였다.

• Nuclear Engineering and Technology
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• 제50권5호
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• pp.673-682
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• 2018

One of the most widely used methods to estimate core damage during a nuclear power plant accident is containment radiation measurement. The evolution of severe accidents is extremely complex, leading to uncertainty in the containment dose rate (CDR). Therefore, it is difficult to accurately determine core damage. This study proposes to conduct uncertainty analysis of CDR for core damage assessment. First, based on source term estimation, the Monte Carlo (MC) and point-kernel integration methods were used to estimate the probability density function of the CDR under different extents of core damage in accident scenarios with late containment failure. Second, the results were verified by comparing the results of both methods. The point-kernel integration method results were more dispersed than the MC results, and the MC method was used for both quantitative and qualitative analyses. Quantitative analysis indicated a linear relationship, rather than the expected proportional relationship, between the CDR and core damage fraction. The CDR distribution obeyed a logarithmic normal distribution in accidents with a small break in containment, but not in accidents with a large break in containment. A possible application of our analysis is a real-time core damage estimation program based on the CDR.

• 한국기계가공학회지
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• 제17권2호
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• pp.103-108
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• 2018

In interrupted cutting, the workpiece has a groove that impacts both the cutting tool and the workpiece. Therefore, cutting tool damage occurs rapidly. In this study, I performed interrupted cutting of carbon steel for machine structures (SM20C) using an uncoated carbide tool (SNMG120404, P20), and observed tool damage, cutting chip shape, and the workpiece surface. Results: Under the specific cutting conditions of feed rate = 0.066 mm/rev, cutting speed = 120 m/min, and depth of cut = 0.1 mm; and feed rate = 0.105 mm/rev, cutting speed = 120 m/min, and depth of cut = 0.2 mm, the observed tool damage was small. Similar chip shape was observed (Expt. No. 1, 3, 7). Workpiece damage was observed (Expt. No. 3, 5, 7, 9).

• 한국표면공학회지
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• 제51권5호
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• pp.291-296
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• 2018

In this study, we carried out an ultrasonic-chemical decontamination process with immersion type, reproduced in the laboratory. The corrosion damage characteristics, depending on kind of materials and ultrasonic process time, were investigated. Inconel 600, which showed lower corrosion potential and higher corrosion current density than that of STS 316, revealed severer corrosion damage and higher weight-loss rate than STS 316. Weight-loss rate of Inconel 600 increased with increasing ultrasonic process time. On the other hands, STS 316 presented a negligibly small corrosion damage, which was almost indistinguishable from visual observation. There was no effect of ultrasonic process time on the weight-loss rate of STS 316.

• Advances in concrete construction
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• 제16권3호
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• pp.141-153
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• 2023

In order to develop and take full advantage of pasture fiber and waste concrete, this article studied how different amounts of pasture fiber influenced the toughness and pore structure of concrete with different replacement rates of recycled fine aggregate. Pasture fiber recycled concrete constitutive equations were established under idealized stiffness and toughness damage rate, based on fracture energy and damage mechanics theories. The relationship between pore structure and toughness was studied utilizing nuclear magnetic resonance and fractal theory. The toughness of text groups (0% (JZ), 10% (ZS10), 20% (ZS20)) first increased and then decreased with increasing amounts of pasture fiber, based on the damage rate of toughness. The toughness of concrete samples with recycled fine aggregate and pasture fiber is negatively correlated to the fractal dimension of small and medium-sized pores with a pore size of 0-500 nm. At a replacement rate of 10% of the recycled fine aggregate, the fractal dimension of the air voids (r: 500-9000 nm, i.e., Lg(r) ∈ [2.7, 3.9]) shows a gradual decrease with the increase of grass fiber dosage, indicating that with such a replacement rate of the recycled fine aggregate, the increase of pasture fiber can reduce the complexity of the pore structure of the air voids (500-9000 nm).

• 산업경영시스템학회지
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• 제20권44호
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• pp.263-271
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• 1997

This paper presents a preventive maintenance model for determining the preventive replacement period of a system in which a failure rate is affected by the cumulative damage of fault and inspection. Especially, the failure rate function is considered to be a function of the cumulative damage of the fault and inspection time. Types of replacement considered are preventive replacement and failure replacement. Failure rate and expected cost function between replacement are derived. An optimal policy is obtained that minimizes the average cost per unit time for preventive replacement, failure replacement, inspection and repair.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.290-298
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• 2014

Purpose: To ascertain the increase of the farm income that predominantly relies on human resources by mechanizing Welsh onion harvesting, a tractor-mounted Welsh onion harvester was developed in this study. Method: An experiment for evaluating harvesting performance was performed for the developed Welsh onion harvester in an actual Welsh onion farm. The harvest performance was evaluated at the tractor running speeds of 5.0 cm/s, 11.4 cm/s and 15.8 cm/s, by comparing the operating efficiency, harvest rate, and damage rate of the Welsh onion harvester. Results: The performance of the harvester was rated as very good, with a 100% harvest rate, regardless of tractor running speed. Furthermore, it is shown that work efficiency of the harvester is expected to increase as the running speed increases. Nonetheless, the damage rate of the harvested Welsh onions at running speeds 5.0 cm/s, 11.4 cm/s, and 15.8 cm/s, increased correspondingly and proportionally to speeds from 4.55% to 6.53% and to 11.29%. The residual amount of soil on the harvested Welsh onions was about 0.24% of their weight showing excellent soil-removal performance of the harvester. Conclusion: The developed Welsh onion harvester is believed to improve the labor productivity and cultivation environment of Welsh onion farmhouses by the mechanization of the harvesting process that is currently associated with the largest amount of labor hours.

• 한국표면공학회지
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• 제49권4호
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• pp.349-356
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• 2016

In this study, electrochemical damage behaviors with flow rate were investigated for anodized 5083 aluminum alloy in seawater. As the results of anodic polarization experiments and potentiostatic experiments at +1.0 V (vs. SSCE), the non-flow condition presented largely damaged surface resulting from a tendency of local pitting damage. Under various flow rate conditions, however, less surface damages under the application of anodic potential was obtained which is attributed to no accumulation of $H^+$ and $Cl^-$ ions on the surface. On the other hand, the results of the potentiostatic experiments at -1.0 V (vs. SSCE) with flow rate showed that anodized 5083 aluminum alloys could achieve the effective cathodic protection by low cathodic protection current density less than $2.61{\times}10^{-7}A/cm^2$ even under high flow rate of 1 m/s.

• 한국조경학회지
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• 제37권3호
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• pp.113-124
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• 2009

본 연구는 교보생명빌딩 그린하우스를 대상으로 광조건에 따른 수목피해 및 생육상태 영향을 조사 분석하여 실내식물의 적절한 생육환경을 유지할 수 있는 적정 조도기준 도출을 목적으로 하였다. 광조건에 따른 조도현황과 고사목 교체주수, 수목피해율을 분석하여 생육조건에 따른 문제점을 파악하고 적정 조도기준을 도출하였다. 조도조사 결과 남측 음지와 양지에서 각각 531lux, 602lux로 가장 낮은 차이를 보인 반면에, 중앙 음지와 양지에서 210lux, 782lux로 약 500lux의 가장 높은 차이가 발생하였다. $1990{\sim}2004$년간 수목고사 조사결과 식재된 수목 중 아왜나무가 161주로 교체율이 가장 높았으며, 대나무 69주, 동백나무 40주, 후피향나무 40주 등의 순으로 조사되었다. 수목피해도 결과는 수종에 관계없이 채광이 양호한 양지구역에서는 평균 수목피해율이 $4.4{\sim}6.4%$로 경미하였으며, 음지구역에서는 수목피해율이 $21.9{\sim}48.8%$로 심각한 피해현상이 나타났다. 조도를 독립변수로, 수목피해도를 종속변수로 상관분석과 회귀분석을 각각 실시한 결과, 조도가 낮아질수록 수목피해율은 증가하였다. 조도가 $500{\sim}600lux$ 사이에서 피해율이 급격히 감소하였으며, 700lux 수준에서 피해율이 최소화되었다. 따라서 실내식물의 광조건에 의한 피해율을 줄이기 위해서는 최소 700lux이상의 조도가 필요한 것으로 판단되었다.

• 대한핵의학회지
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• 제5권2호
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• pp.19-40
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• 1971

Since the iron balance is maintained by regulated intestinal absorption rather than regulated excretion, there have been many reports concerning the factors which may influence the intestinal iron absorption. As the liver is the largest iron storage organ of the body, any hepatocellular damage may result in disturbances in iron metabolism, e,g., frequent co-existence of hemochromatosis and liver cirrhosis, or elevated serum iron level and increased iron absorption rate in patients with infectious hepatitis or cirrhosis. In one effort to demonstrate the influence of hepatocellular damage on intestinal iron absortion, the iron absorption rate was measured in the rabbits whose livers were injured by a single subcutaneous injection of carbon tetrachloride (doses ranging from 0.15 to 0.5cc per kg of body weight) or by a single irradiation of 2,000 to 16,000 rads with $^{60}Co$ on the liver locally. A single oral dose of $1{\mu}Ci\;of\;^{59}Fe$-citrate with 0.5mg of ferrous citrate was fed in the fasting state, 24 hours after hepatic damage had been induced, without any reducing or chelating agents, and stool was collected for one week thereafter. Serum iron levels, together with conventional liver function tests, were measured at 24, 48, 72, 120 and 168 hours after liver damage had been induced. All animals were sacrificed upon the completing of the one week's test period and tissue specimens were prepared for H-E and Gomori's iron stain. Following are the results. 1. Normal iron absorption rate of the rabbit was $41.72{\pm}3.61%$ when 0.5mg of iron was given in the fasting state, as measured by subtracting the amount recovered in stool collected for 7 days from the amount given. The test period of 7 days is adequate, for only 1% of the iron given was excreted thereafter. 2. The intestinal iron absorption rate and serum iron level were significantly increased when the animal was poisoned by a single subcutaneous injection of 0.15cc. per kg. of body weight of carbon tetrachloride or more, or the liver was irradiated with a single dose of 12,000 rads or more. The results of liver function tests which were done simultaneously remained within normal limit except SGOT and SGPT which were somewhat increased. 3. In each case, there has been good correlation between the extent of liver cell damage and degree of increased iron absorption rate or serum iron level. 4. The method of liver damage appeared to make no obvious difference in the pattern of iron deposit in liver. This may be partly due to the fact that tissue specimens were obtained too late, for by this time the elevated serum iron level had returned within normal range and the pathological changes were almost healed. 5. The possible factors and relationship between intestinal iron absorption and hepatic parenchymal cell damage has been discussed.