• 소성∙가공
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• 제28권4호
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• pp.212-218
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• 2019

In this study, the first drawing die for the production of coil wedge is redesigned in order to enhance properties such as dimensional accuracy, dimensional uniformity, non-magnetism, and residual stress. The equivalent strain distribution is observed to be asymmetric at certain corners of the product and un-filling of material is also observed at the same location, based on the results of FEM simulation for the current drawing process. Additionally, a relatively huge amount of deformation is concentrated on the surface of the reference product leading to an increase in magnetic component and surface residual stress. After re-designing the cross-section of the first drawing step process conformed to relatively higher amount of reduction ratio, reduction of both surface residual stress and the volume fraction of magnetic component could be achieved for the finally-drawn coil wedge product.

• Child Health Nursing Research
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• 제25권1호
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• pp.38-47
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• 2019

Purpose: The purpose of this study was to investigate the influence of perceptions of death, end-of-life (EOL) care stress, and emotional intelligence on attitudes toward EOL care among nurses in the neonatal intensive care unit (NICU). Methods: The participants were 111 nurses working in a NICU who had experienced EOL care at least once. Data were analyzed using the t-test, Pearson correlation coefficient, and stepwise multiple regression analysis in SPSS for Windows. Results: The mean score for perceptions of death was 3.16 out of 5, the mean score for EOL care stress was 3.61 out of 5, the mean emotional intelligence score was 4.66 out of 7, and the average score for EOL care attitudes was 2.77 out of 4. The factors affecting attitudes towards EOL care were academic degree, anxiety regarding death, negativity towards death, experiences of patient death, and emotional intelligence. The explanatory power of these variables for attitudes towards EOL care was 24.7%. Conclusion: The results of this study are expected to serve as a basic reference for the development of nursing education programs and EOL care protocols to improve attitudes toward EOL care among NICU nurses.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.241-248
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• 2021

High cycle fatigue life for the cables with two different types of clamps is estimated comparatively through acceleration testing. The high cycle fatigue fracture of overhead lines is caused mainly by the aeolian vibration which is induced by vortex shedding. It is necessary to manage the integrity of cables continuedly considering that the aeolian vibration is unavoidable since it occurs in steady and relatively low wind velocity. Two types of clamps which are largely used for overhead lines of the distribution grids are selected and failure data are obtained by step stress testing with a electrodynamic shaker with them. The inverse power law is assumed to describe the stress-life relationship and the fatigue limit at any specified life is supposed to follow Weibull distribution. The life of the cable is defined as the number of cycles to the time that one of strands is completely broken. Finally, the fatigue limits of the cables with two clamp types are estimated at the reference life of 500 Mcycles and compared each other based on a bending vibration amplitude.

• 한국기계가공학회지
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• 제21권1호
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• pp.66-72
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• 2022

The Mooney-Rivlin second order optimal strain energy function derived through uniaxial tensile test and analysis was applied to a gasket to confirm the internal stress and surface pressure generated during compression. The Taguchi method, a statistical technique, was used to design the optimum shape of the gasket, and through characteristic evaluation, the optimum shape of the gasket was obtained when the reference plane (T: 0.15 mm), contact surface (W: 1.00 mm), and curvature (R: 0.30 mm) were used. It was determined that the optimum shape yields a von Mises stress of 4.83 MPa, and the contact pressure stress is 20.14 MPa, which satisfies breakage and sealing requirements. In the future, we plan to manufacture a jig that can measure surface pressure to conduct comparative verification studies between the test results and analysis results.

• Composites Research
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• 제32권5호
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• pp.216-221
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• 2019

Piecewise Integrated Composite (PIC) 보는 하중 유형에 따라 구간을 나누어, 각 구간마다 하중 유형에 강한 복합재료의 적층 순서를 배열한 보이다. 본 연구에서는 보의 거동을 고려하여 PIC 보의 구간을 머신 러닝을 통해 나누어 기존에 제시되었던 PIC 보에 비해 우수한 굽힘 특성을 갖게 하는 것이 목적이다. FE 모델의 240개 요소가 참조점으로 선택되었다. 선행 유한요소해석은 머신 러닝의 학습데이터 생성을 위하여 규칙적으로 분포된 참조점에서 3축 특성 값(Triaxiality)으로 나타냈다. 3축 특성 값은 인장, 압축 그리고 전단의 하중유형을 나타낸다. 머신 러닝 모델은 하이퍼파라미터(Hyperparameter)와 학습데이터로 구성되었으며, 하이퍼파라미터 튜닝을 통해 적절한 하중 충실도를 도출하였지만, 거동이 큰 보의 옆면에서는 적절하지 않은 하중 충실도가 도출되었다. 이를 해결하기 위하여 고르게 배치한 참조점을 보의 거동에 따라 배치하여 학습 데이터를 얻었고, 머신 러닝 모델이 생성되었다. 앞서 생성된 머신 러닝 모델을 통하여 보가 매핑 되었고, PIC 보에 대하여 유한요소 해석을 진행한 결과, 기존에 제시되었던 PIC 보에 비해 최대하중과 흡수 에너지가 커지는 특성이 나타났다.

• 치위생과학회지
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• 제11권6호
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• pp.553-562
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• 2011

치과위생사의 직무스트레스 수준과 관련된 직무요인을 파악하기 위하여 부산 경남지역의 500명 중 부적절하게 조사된 184명을 제외한 316명을 연구대상으로 한국인 직무스트레스 측정도구 기본형(KOSS-43)을 활용하여 자기기입식 설문조사를 시행한 결과는 다음과 같다. 1. 치과위생사의 전체 직무스트레스는 $52.42{\pm}4.95$로 나타났으며, 세부항목별로는 관계갈등이 $64.56{\pm}12.17$로 가장 높게 나타났고, 물리환경 $59.85{\pm}13.59$, 조직체계 $54.60{\pm}13.51$, 직무요구 $52.37{\pm}11.47$, 보상부적절 $51.71{\pm}10.58$, 직무자율성 결여 $48.14{\pm}12.97$, 직무불안정 $46.68{\pm}9.25$, 직장문화 $41.46{\pm}15.98$의 순으로 나타났다. 2. 치과위생사의 직무스트레스와 관련된 요인으로는 일반적 특성 중 운동, 직무관련 특성 중 신체적 부담감과 반복 작업시간 등 이었다. 이상의 연구결과 치과위생사의 직무스트레스는 한국인 근로자의 직무스트레스 수준과 비교하여 평균이상의 높은 수준을 나타내었고, 직무스트레스의 예방을 위하여 적절한 직무부담과 작업시간 조절을 통한 신체적 부담을 줄일 수 있는 방법과 치과위생사의 직무특성을 고려한 적절한 작업량 조절방안 등이 필요할 것이다.

• 대한인간공학회지
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• 제32권1호
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• pp.125-137
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• 2013

Objective: The aim of this study was to comprehend major concepts and flows that penetrate international guides or standards for developing a quantitative possibility measure of human errors that can be committed or omitted in nuclear power plants. Background: For a few past decades, lots of researchers have studied the effect of stress and/or fatigue which can result in human errors. Thus, this study was carried out on the assumption that much of them were summarized as an international guidelines or manuals, if any, for human error prevention. Method: A literal survey was conducted with materials and documentation published by international organizations related with safety and standardization, such as ISO, OSHA, NIOSH, NASA, and so on with special reference to human error prevention through management of work stress and fatigue as major Performance Shaping Factors. Results: International guides or management manuals on stress or fatigue management for human error prevention hardly were found, and most researches seemed to concentrate on one of them individually. Conclusion: There was few vestige of research that studied both concurrently. However, it was verified that not a few researches have been tried to develop quantitative measures to estimate probability or job characteristics for human error prevention and/or performance downgrading. Application: The results of this study would help to develop a causal model of human errors due to work stress and fatigue that can result in unexpected accidents in nuclear power plant.

• 대한기계학회논문집A
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• 제37권5호
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• pp.631-640
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• 2013

본 논문에서는 R6 코드와 RCC-MR A16 코드에서 원주방향 균열 배관에 대해 제시하는 1,2 차 복합 하중하에서 J-적분 계산법에 대한 정량적인 비교를 하였다. 균열의 형상, 균열의 깊이, 2 차 하중의 크기 변수에 대한 유한요소 해석을 수행 하였고 유한요소 해석 결과를 이용해 각 코드의 J-적분 평가법에 대한 정량적인 비교를 하였다. R6 코드는 $L_r=1$ 부근에서 보수적으로 평가 되었으며 RCC-MR A16 코드의 경우 기계하중이 작은 영역에서 보수적으로 평가되었다. 이와 같은 결과를 토대로 본 논문에서는 원주방향 균열이 있는 배관에 대하여 각 코드의 J-적분 계산을 보완할 수 있는 방법을 제시하였다. 그 결과로 보완된 J-적분 계산이 유한요소해석 결과와 잘 일치하는 것을 확인 하였다.

• Nuclear Engineering and Technology
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• 제27권1호
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• pp.45-52
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• 1995

수평 유로를 통과하는 이상류 내에서 기체상의 난류 응력이 이상류 시스템의 전반적 거동 특성에 미치는 영향을 연구하였다. 이를 위하여 이미 오랜 연구 노력으로 입증된 평균 이상류 거동 방정식을 채택하여 수평관에서 흔히 발생하는 성층류형 이상류에 대하여 적절히 모델하였다. 모델의 고유치를 계산하고 그의 특성 방정식으로부터 이상류 시스템의 well-posedness 및 다른 이상 유동 영역으로의 천이 경계를 새로이 결정하였다. 그 결과로 지금까지 무시해 왔던 기체상의 난류웅력이 이상류 시스템의 안정성에 커다란 영향을 주는 것이 발견되었다. 본 연구에서는 그 영향이 정량화 되었으며 그외의 효과도 정량화 하는 방법을 정립하였다. 본 연구는 원자로 시스템 해석 코드에 쓰이고 있는 열수력 모델 중 불확실성이 많은 모델인 수평관에서의 이상유동 영역 천이 조건식을 개선함으써 시스템 해석 결과의 신뢰도를 높이는 데 이용할 수 있다.

• 한국해양공학회지
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• 제30권6호
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• pp.474-483
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• 2016

Accidental events such as collisions, groundings, and hydrocarbon explosions in marine structures can cause catastrophic damage. Thus, it is extremely important to predict the extent of such damage, which determines the total amount of oil spills and the residual hull girder strength. Punching fracture tests were conducted by Choung (2009b), where various sizes of indenters and circular unstiffened steel plates with different thicknesses were used to quasi-statically realize damage extents. A three-dimensional fracture strain surface was developed based on a reference (Choung et al., 2015b), where the average stress triaxiality and average normalized Lode angle were used as the parameters governing the fracture of ductile steels. In this study, new numerical analyses were performed using very fine axisymmetric elements in combination with an Abaqus user-subroutine to implement the three-dimensional fracture strain surface. Conventional numerical analyses were also conducted for the tests to identify the best fit fracture strain values by changing the fracture strains. Based on the phenomenon of the average normalized Lode angle starting out positive and then becoming slightly negative, it was inferred that the shear stress primarily dominates in determining the fractures locations, with a partial contribution from the compressive stress. It should be stated that the three-dimensional fracture surface effectively predicted at least the shear stress-dominant fracture behavior of a mild steel.