• 한국자동차공학회논문집
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• 제1권1호
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• pp.131-139
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• 1993

Low cycle fatigue characteristics of cast aluminum alloy A356 with a yield strength and ultimate strength of 229 and 283 MPa respectively was evaluated using smooth axial specimen under strain controlled condition. Reversals to failure ranged from 16 to 107. The cast aluminum alloy exhibited cyclically strain-gardening behavior. The results of low cycle fatigue tests indicated that the conventional low cycle fatigue tests indicated that the conventional low cycle fatigue life model was not a satisfactory representation of the data. This occurred because the elastic strain-life curve was not-log-log linear and this phenomena caused a nonconservative and unsafe fatigue life prediction at both extremes of long and short lives. A linear log-log total strain-life model and a bilinear log-log elastic strain-life model were proposed in order to improve the representation of data compared to the conventional low cycle fatigue life model. Both proposed fatigue life models were statistically analyzed using F tests and successfully satisfied. However, the low cycle fatigue life model generated by the bilinear log-log elastic strain-life equation yielded a discontinuous curve with nonconservatism in the region of discontinuity. Among the models examined, the linear log-log total strain-life model provided the best representation of the low cycle fatigue data. Low cycle fatigue life prediction method based on the local strain approach could conveniently incorporated both proposed fatigue life models.

• 전산구조공학
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• 제10권3호
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• pp.167-174
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• 1997

계가 혼돈거동을 나타낼 경우에는 변수들의 미소변화에 의해서도 계가 전혀 다른 거동을 나타낼 수 있기 때문에 비선형계의 설계 및 해석시에는 이를 고려해야 한다. 따라서 본 연구에서는 구형 쉘의 중앙에 충격하중이 수직방향으로 작용하는 경우, 쉘의 기하학적 비선형성과 재료적 비선형성으로부터 기인되는 혼돈거동을 해석하였다. 쉘의 탄소성거동을 유한요소법을 이용하여 구한 후 계의 거동을 변위-시간이력, 프앙카레 맵, phase diagram등의 표준적인 방법들을 이용하여 쉘의 혼돈거동을 규명하였다. 해석결과, 계는 혼돈거동을 나타내었으나 탄소성보의 경우와는 달리 초기조건의 미소변화에 대한 극도의 민감도는 나타나지 않았으며 시간에 대한 쉘의 거동특성도 크게 변하지 않았다. 프앙카레 맵은 한정된 영역에 결쳐서 점들이 분포되었기 때문에 계의 거동이 혼돈거동임을 보여 주고 있지만 혼돈계의 프앙카레 맵에서 나타나는 기하학적 구조는 나타나지 않았다. 에너지선도를 이용하여 쉘이 하중의 작용방향 또는 반대방향으로 불규칙적으로 snap-through되는 원인을 규명하였다.

• 보건의료산업학회지
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• 제6권2호
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• pp.211-217
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• 2012

To identify health behavior of Peptic ulcer patients among all employees in Korea and examine relevant factors to present basic data for improving Korean adult employees' health conditions and quality of living, 3,515 employees aged 20 to 69 were sampled from the group that responded to the question concerning the presence of Peptic ulcer in the fourth Korea National Health and Nutrition Examination Survey for the third year (2009). After logistic regression analysis was carried out to see the effects of working conditions, harmful factors, shift work, stress perception, and experience of depression on the presence of Peptic ulcer, it was found that unsafe or unpleasant working conditions led to higher risk of getting Peptic ulcer, that flexible workers were more likely to get Peptic ulcer, and that depression or stress perception exerted almost no effect on Peptic ulcer. With the increase in the number of flexible workers, increasingly more interest is taken in the effects of shift work on health; occupational Peptic ulcer tends to become chronic as compared with the condition in the general population and reappear even after recovery in many cases; therefore, it is necessary to take special management measures by estimating the number of those at a risk of getting Peptic ulcer and by finding out its risk factors.

• 산업융합연구
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• 제16권3호
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• pp.1-7
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• 2018

본 연구는 지역사회 노인의 일반적 특성 및 건강관련 특성을 조사하여, 낙상두려움 요인을 규명하고, 낙상두려움, 낙상태도 및 낙상효능감과의 관계를 파악하기 위한 서술적 조사연구이다. 연구대상자는 D시의 복지관을 이용하는 노인 140명이었다. SPSS 21.0 프로그램을 이용하여 분석하였다. 연구결과 성별, 동거인, 주관적 건강상태, 통증, 불안전한 걸음걸이에서 낙상두려움의 차이가 있었다. 낙상두려움과 낙상태도(r=-.396, p<.001), 낙상두려움과 낙상효능감(r=-.184, p=.030)은 유의한 음의 상관관계를 보였고, 낙상태도와 낙상효능감(r=.411, <,001)은 양의 상관관계를 보였다. 본 연구결과에 기초하여 낙상두려움, 낙상태도 및 낙상효능감을 향상시킬 수 있는 낙상예방프로그램 개발 및 적용이 필요하다.

• 한국농공학회논문집
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• 제66권1호
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• pp.39-48
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• 2024

Plastic greenhouses are simple structures consisting of lightweight materials such as steel pipes and polyvinyl chloride. However, serious damage occurs due to heavy winds and typhoon every year. To prevent a collapse of structural members, the Ministry of Agriculture and Rural Development has distributed plans and specifications for disaster-resistant standards. Despite these efforts, more than 50% of greenhouses still do not satisfy the disaster-resistant standards. Among the greenhouses that do not meet these standards, 85% are single-span greenhouses proposed 20 years ago. Consequently, there is a need to evaluate the safety of wind loads for the single-span greenhouse. Unfortunately, there are no design specifications for the greenhouses under wind loads. Therefore, a Korean design standard (KDS) has been utilized. KDS is defined with reference to wind speeds occurring once every 500 years, raising concerns about potential overdesign when considering the durability of plastic greenhouses. To address this, the modified wind load, considering the durability of the plastic greenhouse, was calculated, and a safety evaluation was conducted for sigle G-type plastic greenhouse. It was observed that the moment acting on the windward surface was substantial, and there was a risk of the foundation being pulled out if the basic wind speed exceeded 32 m/s. In terms of the combination strength ratio, it was less than 1.0 only on the leeward side when the basic wind speed was 24 m/s and 26 m/s. However, in all other cases, it exceeded 1.0, indicating an unsafe condition and highlighting the necessity for reinforcement.

• Smart Structures and Systems
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• 제20권5호
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• pp.549-562
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• 2017

The US railroad network carries 40% of the nation's total freight. Railroad bridges are the most critical part of the network infrastructure and, therefore, must be properly maintained for the operational safety. Railroad managers inspect bridges by measuring displacements under train crossing events to assess their structural condition and prioritize bridge management and safety decisions accordingly. The displacement of a railroad bridge under train crossings is one parameter of interest to railroad bridge owners, as it quantifies a bridge's ability to perform safely and addresses its serviceability. Railroad bridges with poor track conditions will have amplified displacements under heavy loads due to impacts between the wheels and rail joints. Under these circumstances, vehicle-track-bridge interactions could cause excessive bridge displacements, and hence, unsafe train crossings. If displacements during train crossings could be measured objectively, owners could repair or replace less safe bridges first. However, data on bridge displacements is difficult to collect in the field as a fixed point of reference is required for measurement. Accelerations can be used to estimate dynamic displacements, but to date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate total transverse displacements of a railroad bridge under live train loads using acceleration and tilt data at the top of the exterior pile bent of a standard timber trestle, where train derailment due to excessive lateral movement is the main concern. Researchers used real bridge transverse displacement data under train traffic from varying bridge serviceability levels. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic using a shake table for the input of train crossing data collected from the field into a laboratory model of a standard timber railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. Various readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. An average peak error of 10% and a root mean square error average of 5% resulted, concluding that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference.

• 지능정보연구
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• 제7권2호
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• pp.117-127
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• 2001

본 연구에서 대상으로 하고 있는 LG정유 광양항 제품부두는 7선석(Berth)에 재화중량(DWT) 300톤에서 48000톤의 선박까지 다양한 선박이 이용하고 있으며, 해상의 기상상태에 따른 선박 입출항 통제 지침 설정이 어렵고, 현재 사용하고 있는 지침의 근거가 명확하지 않아 현재의 부두 운영이 비효율적이거나 안정성이 결여되어 있다고 할 수 있다. 따라서 이를 개선하기 위한 합리적인 부두운영 제한조건 개발이 절실히 요구되었다. 본 논문에서는 대상 부두의 특성, 대상 선박의 특성, 하중상태, 선박 운항자의 특성 등을 고려하여 해상/기상 상황(바람, 조류 및 파랑)에 따른 부두 입출항 가능 여부를 정량적으로 판단하고, 안전성 향상 방안을 제시할 수 있는 의사결정 시스템을 개발하고 5번, 7번 선석을 대상으로 이를 검증하였다. 여기서는 입출항 여부를 정량적으로 판단하여 결과를 제시하기 위해서 유전적 프로그램이(Genetic Programming)을 이용한 기계학습 방법을 이용하였으며, GP의 방대한 계산량을 줄이기 위한 가중 선형 연상 기억(Weighted Linear Associative Memory:WLAM) 방법의 도입 및 전역 최적점을 쉽게 찾기 위한 Group of Additive Genetic Programming Trees(GAGPT)를 도입함으로써 학습 성능을 개선하였다.

• 한국산학기술학회논문지
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• 제18권1호
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• pp.210-215
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• 2017

로터리 제진기의 rake에 대한 설계 및 구조강도 해석을 수행하였다. 수중부의 경우 물에 의해 발생되는 수중 마찰력 및 협착물에 발생되는 수중 마찰력 등을 계산하여 하중조건을 주었고, 수상부는 rake의 자중 $239kg_f$를 분포 하중으로 설정한 후 협착물의 위치에 따라 협착물 하중 $261kg_f$을 좌측, 중앙, 우측 집중하중으로 나누어서 해석하였다. 3가지 하중조건의 해석결과는 최대 등가응력이 모두 86MPa 이하이므로 3가지 하중조건 모두 소성변형이 발생하지 않고, 안전성이 있다고 판단되었다. 협착물의 무게와 물에 의한 마찰력에 따라 발생할 수 있는 하중에 대해 $1,000kg_f$, $1,300kg_f$, $1,500kg_f$ 3가지 하중으로 나누어서 해석하였다. $1,000kg_f$, $1,300kg_f$의 해석 결과의 경우 각각 143.6MPa, 186.6MPa의 등가응력이 발생하였고 소성변형이 발생하지 않아 안전성이 있는 반면에, $1,500kg_f$의 경우는 215.41MPa의 등가응력이 발생하였고 소성변형이 발생하고 안전성이 없다고 해석되었다. ANSYS를 활용한 로터리 제진기의 rake에 가해지는 하중에 대한 구조강도 해석의 결과는 기본설계의 지침이 될 수 있었으며, 이 시제품의 기능 및 성능시험을 통하여 유한요소해석의 결과를 신뢰할 수 있었다.

• 한국농촌건축학회논문집
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• 제13권2호
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• pp.1-8
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• 2011

Due to rapid decrease in population of farming and fishing villages and drain of young rural manpower to the cities, aging is being intensified, and the conditions of housing and welfare of elderly households are inadequate. Currently, group home is being discussed as part of specialized housing and welfare support policy for the people in the vulnerable class with poor self-supporting abilities such as the aged living alone in farming and fishing villages, and aged farming and fishing households. So the purpose of this research is to present the basic data for proposing the policy of supplying group home through examining the realities of housing and welfare of the people in the vulnerable class in farming and fishing villages. Survey was conducted on the 4 regions -Cheonan-si, Gongju-si, Yesan-gun, and Seosan-si - whose apartments were all occupied by the residents among the group homes for the elderly living alone in Chungcheongnam-do and the following results were derived from the analysis on the data collected from the survey. First, great effects can be attained at small costs by reorganizing and utilizing the public facilities that are unused or little used and the existing houses that are exposed to risks due to improper maintenance. Second, it can be pointed out that the residential environment of the vulnerable members of society was improved without impairing the existing village landscape. Third, housing welfare was enhanced without investing a large sum of money and the system to promptly cope with negligent accidents and emergency can be built and operated. Fourth, the cases promoted to solve the problems of the poor, unhygienic, and unsafe housing of the elderly and the vulnerable members of society were very positive and well worthy of being presented as planning direction of future group homes in farming and fishing villages. Finally, if they are operated entirely for free, it will cause the lack of the sense of ownership and the problems in securing the budget, so the ways of paying minimum individual housing expenses should be examined. The alternatives of housing welfare for the vulnerable members of farming and fishing villages are needed and the ways of constructive planning and researches should be continuously made. Also, the government's support policy should be actively promoted.

• 유기물자원화
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• 제24권3호
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• pp.5-13
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• 2016

본 연구는 바이오가스화 처리 유 무에 따라 하수슬러지 처리방법별, 즉 소각, 탄화, 건조, 고형화 등에 대한 환경성 및 경제성 분석을 실시하였다. 환경성 분석에 대하여, 소각 및 탄화로부터의 대기오염물질은 기준치의 1-34 % 수준으로 배출되고 있었다. 건조 및 고형화는 악취 기준치의 30 % 정도 배출되고 있었다. 나머지 오염물질들은 검출되지 않거나 기준치 이하에서 관리되고 있었다. 고형화에서 부산물은 매립지 복토재로서 사용될 때, 일축강도가 기준치보다 못미쳐서 차량 통해서 불완전하고 토양유실의 가능성이 있다. 또한 고형화는 빈번한 공정 막힘과 운전 중단 등의 어려움이 많은 것으로 조사되었다. 결과적으로, 환경성 및 경제성을 고려할 때 혐기소화 이후 후처리로 소각 또는 건조하는 경우가 가장 타당한 것으로 분석되었으며, 후처리로 탄화처리하는 경우가 가장 타당성이 적은 것으로 분석되었다. 고형화 처리는 가장 경제적이었으나 환경적 및 운전성이 부족하여 타당성이 부족한 것으로 분석되었다.