• 대한기계학회논문집A
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• 제40권7호
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• pp.653-658
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• 2016

가스터빈엔진의 고온 부품은 초내열 합금 재료를 이용하며, 냉각설계 적용으로 형상이 복잡하여 정밀 주조 과정을 거치게 된다. 터빈 부품에 주로 적용이 되는 일방향 응고 및 단결정 재료는 제조 과정에서 결정립 성장 방향이 설계와 다르게 섭동을 가지게 되며, 이는 각 방향에 대한 재료 상수의 섭동을 유발하여 응력 분포의 변화와 함께 피로 수명에 큰 산포를 야기하게 된다. 본 연구에서는 일방향 응고 재료 노즐에 대하여 결정립 성장 방향의 섭동에 대한 구조 건전성의 영향을 저주기 피로 수명을 통해 확인하여, 향후 제작 허용값에 대한 제안 및 좀 더 정교한 통계적 접근이 필요함을 확인하고자 한다. 이를 위해 복합 열전달 해석을 통해 금속 온도 분포를 계산하고 이를 근거로 구조 해석 및 저주기 피로 수명을 계산하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.132-139
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• 2008

The blade vibration problem of bladed disk is the most critical subject to consider since it directly affects the stable performance of the engine as well as life of the engine. Especially, due to complicated vibration pattern of the bladed disk, more effort was required for vibration analysis and test. The research of measuring the vibration of the bladed disk, using NSMS(Non-intrusive stress measurement) instead of Aeromechanics testing method requiring slip ring or telemetry system with strain gauge, was successful. These testing can report the actual stresses seen on the blades; detect synchronous resonances that are the source of high cycle fatigue (HCF) in blades; measure individual blade mis-tuning and coupled resonances in bladed disks. In order to minimize the error being created due to heat expansion, the tip timing sensor is installed parallel to the blade trailing edge, yielding optimal result. Also, when working on finite element analysis, the whole bladed disk has gone through three-dimensional analysis, evaluating the family mode. The result of the analysis matched well with the test result.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.871-876
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• 2008

The blade vibration problem of bladed disk is the most critical subject to consider since it directly affects the stable performance of the engine as well as life of the engine. Especially, due to complicated vibration pattern of the bladed disk, more effort was required for vibration analysis and test. The research of measuring the vibration of the bladed disk, using NSMS(Non-intrusive stress measurement) instead of Aeromechanics testing method requiring slip ring or telemetry system with strain gauge, was successful. These testing can report the actual stresses seen on the blades; detect synchronous resonances that are the source of high cycle fatigue(HCF) in blades; measure individual blade mis-tuning and coupled resonances in bladed disks. In order to minimize the error being created due to heat expansion, the tip timing sensor is installed parallel to the blade trailing edge, yielding optimal result. Also, when working on finite element analysis, the whole bladed disk has gone through three-dimensional analysis, evaluating the family mode. The result of the analysis matched well with the test result.

• Earthquakes and Structures
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• 제10권5호
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• pp.1089-1109
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• 2016

Modified two-surface model (M2SM) is one of the steel elasto-plastic hysteretic constitutive models that consider both analysis accuracy and efficiency. However, when M2SM is used for complex strain history, sometimes the results are irrational due to the limitation of stress-strain path judgment. In this paper, the defect of M2SM was re-modified by improving the judgment of stress-strain paths. The accuracy and applicability of the improved method were verified on both material and structural level. Based on this improvement, the nonlinear time-history analysis was carried out for a deck-through steel arch bridge with a 200 m-long span under the ground motions of Chi-Chi earthquake and Niigata earthquake. In the analysis, we compared the results obtained by hysteretic constitutive models of improved two-surface model (I2SM) presented in this paper, M2SM and the bilinear kinematic hardening model (BKHM). Results show that, although the analysis precision of displacement response of different steel hysteretic models differs little from each other, the stress-strain responses of the structure are affected by steel hysteretic models apparently. The difference between the stress-strain responses obtained by I2SM and M2SM cannot be neglected. In significantly damaged areas, BKHM gives smaller stress result and obviously different strain response compared with I2SM and M2SM, and tends to overestimate the effect of hysteretic energy dissipation. Moreover, at some position with severe damage, BKHM may underestimate the size of seismic damaged areas. Different steel hysteretic models also have influences on structural damage evaluation results based on deformation behavior and low cycle fatigue, and may lead to completely different judgment of failure, especially in severely damaged areas.

• 융합정보논문지
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• 제11권5호
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• pp.50-56
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• 2021

본 연구는 임부의 사회적 지지, 임신 스트레스 그리고 불안이 삶의 질에 영향을 미치는 영향요인을 파악하기 위해 시도 되었다. 본 연구는 2개 지역 D 와 S 지역에 거주하는 임부 117명을 대상으로 한 서술적 조사연구이다. 설문 전 연구의 취지와, 목적, 절차에 대하여 설명을 하고 진행하였다. 자료는 SPSS 21.0 을 이용하였고, 빈도분석, 분산분석, t검증, 상관분석, 희귀분석으로 실시하였다. 자료 수집은 2020년 1월부터 2월까지 하였다. 본 연구결과는 일반적 특성에 따른 임부의 삶의 질 차이는 수면시간, 경제수준, 건강상태, 활동량, 임신주기에서 유의미한 차이를 보였다. 삶의 질에 영향을 미치는 변수는 사회적 지지(β= .432, p= .000), 임신 스트레스(β=- .407, p= .000), 불안(β=- .182, p= .010) 순으로 확인되었다. 임부는 임신 스트레스와 불안 등을 경험하는 삶의 질 저하문제로 이어질 수 있어 임부에 대한 건강증진 프로그램 개발을 해야 할 것이며 삶의 질 증진을 위한 적극적인 간호중재 제공에 대한 필요성이 제기된다.

• 한국융합학회논문지
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• 제12권11호
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• pp.391-401
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• 2021

본 연구는 코로나19 시기 인터넷 중독이 2030세대의 자아존중감에 미치는 영향에서 스트레스 대처방식의 조절효과를 검증하는 데 목적이 있다. 온라인 설문조사를 통하여 최종 762명의 유효 표본을 선정하고 수집된 자료는 SPSS WIN26.0 프로그램을 활용하여 빈도분석, 상관분석, 위계적 회귀분석을 실시하였다. 분석결과, 인터넷 중독은 자아존중감에 부정적인 영향을 미쳤고, 스트레스 대처방식의 조절효과는 사회적지지 추구 대처방식만이 조절변수로서 작용하였다. 즉 인터넷중독이 높을수록 자아존중감은 낮아지며, 인터넷중독이 자아존중감에 미치는 영향은 사회적 지지 추구 대처 수준에 따라 변화됨을 알 수 있었다. 연구결과에 따른 제언으로 연구대상의 확장과 학제 간 융합연구, 스트레스 대처관리 프로그램 제공, 지역사회 차원에서의 커뮤니티 구축, 2030세대의 역할과 과업달성에 중요한 영향을 미치는 자아존중감의 부정적 역할을 상쇄시키는 변수 발굴 등을 제시하였다.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1410-1417
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• 1999

A thorough understanding of the transient behavior during start-up is essential in the design and operation of the heat recovery steam generator(HRSG). During this period of time, material that is exposed to high temperature and experiences a large temperature variation is subject to high thermal stress. In this work, a transient formulation of the HRSG is constructed including the estimation of the thermal stress and fatigue of the drum wall. Start-up behavior of a single-pressure HRSG is analyzed and the effect of bypassing part of the gas turbine exhaust flow on the thermal stress evolution is examined. It is found that the modulation of the gas flow rate using a bypass damper is very useful in view of reducing the thermal stress of the drum and ensuring the fatigue lifetime.

• 한국기계가공학회지
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• 제6권1호
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• pp.50-56
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• 2007

Exhaust manifold is generally subjected to thermal cycle loadings ; at hot condition, large compressive plastic deformations are generated, and at cold condition, tensile stresses are remained in highly deformed critical zones. These phenomena originate from the fact that thermal expansions of the runners are restricted by inlet flange clamped to the cylinder head, because the former is less stiff than the latter and, the temperature of the inlet flange is lower than that of the runners. Since the failure of an exhaust manifold is mainly caused by geometric constraints between the cylinder head and the manifold, the thermal stress can be controlled by geometric factors. The generic geometric factors include the inter distance (2R), the distance from the head to the outlet (L), the tube diameter(d) and the tube thickness (t). This criteria based on elastic analysis up to onset of yield apparently indicate that the pre-stress also reduces the factor; however, high temperature relaxation may reduce this effect at later operation stage.

• 대한토목학회논문집
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• 제14권4호
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• pp.703-710
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• 1994

극저사이클 하중하에서 강구조부재의 비선형 유한요소해석을 실험과 더불어 수행하였다. 본 해석은 강진과 같은 반복하중하에서 강구조부재의 균열발생전까지를 유한요소법으로 추적한 것이다. 해석과 실험결과로부터 얻어진 히스테러틱 거동을 비교한 후, 큰 반복변형을 받는 응력집중부에 있어서 국소변형율의 이력을 수치해석에 의해 시뮬레이션하였다. 이 국소변형율의 이력과 극저사이클 파괴설험시의 균열발생 현상과의 관계를 정량적으로 분석하였다. 실험과 수치해석 결과를 바탕으로 강구조부재의 내전안전성 평가를 위한 새로운 방법이 본 논문에서 제시되었다.

• 한국안전학회지
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• 제29권6호
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• pp.144-150
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• 2014

A man is a component of a large system how complex it may be so that human performance which can influence on the system safety should be included in system safety assessment. Meanwhile, human performance can vary over time due to lots of factors. Among them, stress is an indirect factor that may cause human error which can result in industrial accidents. To assess stress level of human workers, not a few assessment tools have been developed. However, it can be questionable to utilize them for human performance anticipation because they were mainly developed with the viewpoint of mental health, though stress assessment can be also required in the safety aspect. Therefore, this study aimed to survey the possibility of their application with safety purpose. About 10 kinds of work stress tools were collected and analyzed with reference to assessment items, assessment and analysis methods, and follow-up measures. The results showed that most tools focused their weights on Demands, Supports, and Relationships, in sequence. However, they, except only one tool developed by the Japanese researchers, merely advised to set up counterplans in PDCA cycle or risk management activities. In consequence, application of stress assessment tools mainly developed for mental health seemed impractical for safety purpose with respect to human performance anticipation so that it was concluded that development of a new assessment tools aimed to human performance variation and accident prevention would be inevitable.