• 대한기계학회논문집A
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• 제33권7호
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• pp.664-672
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• 2009

Nozzle in nuclear power plant is connected to pipe using safe end. Dissimilar metal weld between nozzle and safe end is followed by similar metal weld between safe end and pipe. And thus residual stress in dissimilar metal weld can be affected by similar metal weld. Similar metal weld impose bending stress on dissimilar metal weld, which is according to the length of safe end. In this study, simple nozzle model which covers various radius to thickness ratios was proposed to quantify residual stress in dissimilar metal weld based on finite element analyses. As a result, short length of safe end was proved to be more effective to mitigate residual stress in dissimilar metal weld and critical effective length of safe end is provided according to the radius to thickness ratio.

• 대한기계학회논문집A
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• 제32권8호
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• pp.668-677
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• 2008

In nuclear power plants, ferritic low alloy steel nozzle was connected with austenitic stainless steel piping system through alloy 82/182 butt weld. Accurate estimation of residual stress for weldment is important in the sense that alloy 82/182 is susceptible to stress corrosion cracking. There are many results which predict residual stress distribution for alloy 82/182 weld between nozzle and pipe. However, nozzle and piping system usually connected through safe end which has short length. In this paper, residual stress distribution for pressurizer nozzle of Kori nuclear power plant was predicted using FE analysis, which consideded safe end. As a result, existing residual stress profile was redistributed and residual stress of inner surface was decreased specially. It means that safe end should be considered to reduce conservatism when estimating the piping system.

• 대한기계학회논문집A
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• 제39권10호
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• pp.979-984
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• 2015

본 논문에서는 국내 가동 중인 원자력발전소의 안전주입노즐을 대상으로 안전단의 길이와 동종금속용접부의 두께가 이종금속용접부의 응력분포에 미치는 영향을 평가하였다. 이를 위해 4가지의 서로 다른 안전단 길이와 4가지의 서로 다른 동종금속용접부 두께를 고려한 상세 2차원 유한요소 열해석 및 응력해석을 수행하였다. 유한요소해석 결과 동종금속용접부의 두께는 안전단의 길이가 짧은 경우 축방향 응력에 어느 정도 영향을 미쳤으나 원주방향 응력에는 거의 영향을 미치지 않았다. 안전단의 길이는 길이가 증가함에 따라 내면에서의 축방향 및 원주방향 응력값이 증가하는 것으로 나타났으나 특정 안전단 길이를 기준으로 응력분포가 구분되는 경향을 나타냈다.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.1145-1151
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• 2022

A hybrid cutting using both plasma and end mill was developed for safe and efficient dismantling of nuclear facilities. In this cutting method, a moving arc plasma heats up the workpiece before milling. Thermally softened part of the workpiece is then removed quickly and deeply with an end mill. For the cutting experiments, a three-axis numerical control (NC) milling machine was combined with a commercialized arc plasma torch and used to cut 25 mm thick stainless steel plates. Experimental results revealed that pre-heating by arc plasmas can improve the cutting volume per unit time higher than 40% by reducing the cutting load and increasing the cuttable depth when using an end mill without cutting fluids. These advantages of a hybrid cutting process are expected to contribute to quick and safe segmentations of metal structures with radioactively contaminated inner surfaces.

• Journal of Korean Neurosurgical Society
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• 제61권4호
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• pp.503-508
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• 2018

Objective : Anterior odontoid screw fixation is a safe and effective method for the treatment of odontoid fractures. The surgical technique is recommended for perforation of the apical cortex of the dens by the lag screw. However, overpenetration of the apical cortex may lead to potentially serious complications such as damages of adjacent vascular and neural structures. The purpose of this study was to assess the role of three-dimensional computed tomography (CT) scan to evaluate the safe margin beyond dens tip to ventral dura for anterior odontoid screw fixation. Methods : We retrospectively analyzed the three-dimensional CT scans of the cervical spines in 55 consecutive patients at our trauma center. The patients included 38 males and 17 females aged between 22 and 73 years (mean age${\pm}$standard deviation, $45.8{\pm}14.2years$). Using sagittal images of 3-dimensional CT scan, the safe margins beyond dens tip to ventral dura as well as the appropriate screw length were measured. Results : The mean width of the apical dens tip was $9.6{\pm}1.1mm$. The mean lengths from the screw entry point to the apical dens tip and posterior end of dens tip were $39.2{\pm}2.6mm$ and $36.6{\pm}2.4mm$. The safe margin beyond apical dens tip to ventral dura was $7.7{\pm}1.7mm$. However, the safe margin beyond the posterior end of dens tip to ventral dura was decreased to $2.1{\pm}3.2mm$, which was statistically significant (p<0.01). There were no significant differences of safe margins beyond dens tip to ventral dura with patient gender and age. Conclusion : Extension by several millimeters beyond the dens tip is safe, if the trajectory of anterior odontoid screw is targeted at the apical dens tip. However, if the trajectory of the screw is targeted to the posterior end of dens tip, extension beyond dens tip may lead to damage immediately adjacent to the vental dura mater.

• International Journal of Aeronautical and Space Sciences
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• 제6권1호
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• pp.77-88
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• 2005

KOMPSAT-2 is the second Korean earth observation satellite after KOMPSAT-l: the 1 meter GSD cartographic capability and planning to launch at the end of 2005 by ROKOT launch vehicle. The dedicated AOCS operational modes are designed for KOMPSAT-2 based on KOMPSAT-l experience All of AOCS operational modes requires gyro information. To compensate this drawback, Power Safe Mode is designed and implemented. Successfully AOCS on-board software is developed and extensively verified through a nonlinear simulation process. The simulation results of Power Safe Mode and Science Fine Submode are provided to demonstrate its functionality as well as its performance.

• Safe Food
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• 제8권2호
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• pp.24-30
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• 2013

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1323-1326
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• 2004

A bogie frame of welded type have some problems. Some end beam has cracked. The cracks have profound influence on the safe freight service. The bogie consists of a frame, suspensions, brakes and wheel sets. Various analyses including a numerical simulation using a finite element method, a static load test, a fatigue test, and running test should be carried out to design the bogie. However cracks have been found at some end beams of the bogies mounted on the freight cars running with the high speed. The cracks of the end beam results in deterioration of the brake performance and the running safety. Numerical simulations and dynamic tests are carried out to figure out the causes of cracks in the existing bogie, and the vibrational characteristics of the improved bogie are compared with those of the conventional one. In this reports, the vibration characteristics were dealed with the most pressing matters for the solution of the end beam crack.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.361-364
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• 2005

Some bogie frames manufactured in 1999, 2000 year have the fatal problem. Three or four years later, the cracked end beam among them have discovered in 2002, 2003 year. The crack situation of the end beam have a bad effect on brake system. In that case, the cars would be in danger of derailment. To improve the end beam, a research of covering the whole field of welded type bogie frame was started. Main line real tests were performed at Young-Dong line. The stress of main positions for bogie frame was measured. Also up-down direction and left-right direction vibration acceleration of the bogie frame were measured. At this time the tests were performed for the three types bogie. The test result concludes that the crack cause of the end beam is not brake load but vibration at running mainly. It is estimated that the life of the improved car which end beam reinforced is safe within the car permitted life(25 years). The improvement methods of the end beam are presented by construction modification, parts modification. The integrity evaluation is inspected by analysis the real line test results, the improvement methods of the end beam.

• 스마트미디어저널
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• 제11권9호
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• pp.9-20
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• 2022

심층강화학습은 자율주행 도메인에서 널리 사용되는 end-to-end 데이터 기반 제어 방법이다. 그러나 기존의 강화학습 접근 방식은 자율주행 과제에 적용하기에는 비효율성, 불안정성, 불확실성 등의 문제로 어려움이 존재한다. 이러한 문제들은 자율주행 도메인에서 중요하게 작용한다. 최근의 연구들은 이런 문제를 해결하고자 많은 시도가 이루어지고 있지만 계산 비용이 많고 특별한 가정에 의존한다. 본 논문에서는 자율주행 도메인에 불확실성 순차 모델링이라는 방법을 도입하여 비효율성, 불안정성, 불확실성을 모두 고려한 새로운 알고리즘 MCDT를 제안한다. 강화학습을 높은 보상을 얻기 위한 의사 결정 생성 문제로 바라보는 순차 모델링 방식은 기존 연구의 단점을 회피하고 효율성과 안정성을 보장하며, 여기에 불확실성 추정 기법을 융합해 안전성까지 고려한다. 제안 방법은 OpenAI Gym CarRacing 환경을 통해 실험하였고 실험 결과는 MCDT 알고리즘이 기존의 강화학습 방법에 비해 효율적이고 안정적이며 안전한 성능을 내는 것을 보인다.