MFBD 해석 기법을 이용한 프론트 엔드 로더의 구조해석 및 취약부 예측

김동현 ( Dong-hyeon Gim ),남주석 ( Ju-seok Nam ),박영준 ( Young-jun Park ) 한국농업기계학회 2023 한국농업기계학회 학술발표논문집 Vol.28 No.1

본 연구는 30마력급 트랙터용 프론트 엔드 로더의 피로수명평가를 위한 취약부 분석을 목적으로 수행되었다. 로더를 사용한 다양한 농작업 부하특성을 반영하기 위하여 해석 및 시험 조건을 Quick drop, Pulling, Crash impact, Off-road(MGR), Digging, Dumping, Leveling으로 분류하였다. 로더의 응력 및 변형률은 상용 다물체 동역학 해석 소프트웨어 RecurDyn V9R5를 사용하여 분석하였다. 동역학 모델은 각 시험 조건을 모사하여 개발되었다. 로더 모델은 작동 메커니즘을 고려하여 8개의 파트로 구분하였고 실린더는 엔진 최대 회전수에서의 유량 기준으로 작동되도록 구성하였다. 트랙터 모델은 모든 부품의 재료 물성을 반영하여 중량 및 관성 모멘트가 실차와 최대한 유사하게 반영될 수 있도록 하였고 타이어 특성이 변동 부하에 미치는 영향을 고려하기 위하여 타이어 모델(UA-Tire)을 사용하였다. 구조 해석 대상은 상대적으로 파손률이 높은 Boom, Post, Mount, Rear frame 으로 선정하였다. 각 해석 대상을 유연체로 구성하고 모드 중첩법(CMS) 기반의 해석 방법을 사용하여 조건별로 시뮬레이션을 수행하였다. 조건별 해석 결과로부터 Principal stress 집중부 20개소를 선정하였고 Principal strain vector 방향을 분석하였다. 각 조건별 부하 특성을 분석하여 응력 집중부 및 주변형 방향의 타당성을 검토하였다. 본 연구 결과로부터 시험 검증을 위한 스트레인게이지 부착위치와 방향을 제시하였다.

Practicable Synthesis of 1-(1-Phenylethyl)-1H-pyrido[2,3-b][1,4]oxazine

Gim, Gyeong-Hyeon,Lijuan, Meng,Hua, Zuo,Ghate, Manjunath,Ahn, Chul-Jin,Won, Tae-Jin,Kim, Tae-Hyun,Reddy, Ch. Raji,Chandrasekhar, S.,Shin, Dong-Soo Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.12

한국 청소년정책의 진단과 발전 방안

이현동(Lee, Hyeon-Dong),김영찬(Gim, Young-Chan) 전북대학교 교육문제연구소 2019 교육문제연구 Vol.25 No.1

이 연구는 한국의 청소년정책이 1960년대 초부터 시작된 이래 지금까지 제대로 자리를 잡고 있지 못하다는 문제의식에서 출발한다. 이에 본 연구에서 청소년정책의 발전과정을 정책수립의 초기단계, 청소년정책 주체자로 참여, 청소년정책의 질적 향상, 글로벌시대 청소년역량강화, 수요자 중심의 맞춤형 청소년정책, 제4차 산업혁명 시대의 청소년정책 등으로 청소년정책기본계획을 분류하여 분석, 진단하였다. 특히, 청소년문제를 기반으로 한 정책, 규제중심의 청소년 관련법 문제, 청소년정책 수립 주체의 혼선, 청소년 사업의 창의성 및 다양화 부족 등은 청소년정책을 충실히 수행하는데 있어 많은 한계가 있었다. 향후 청소년정책을 수립하기 위한 과제로는 다음과 같이 제시하였다. 첫째, 청소 년정책의 발전은 최우선적으로 청소년에 대한 관심을 정책으로 연결시키는 것이다. 둘째, 청소년정책 주체로서의 청소년참여 확대이다. 셋째, 청소년정책과 교육정책이 통합하고 행정부처가 하나가 되어야 한다. 넷째, 청소년정책의 전달체계에 있어 청소년 행정네트워크와 지역사회중심의 포괄적인 체제가 구축되어야 한다. This study starts from the a critical mind that the youth policy in Korea has not been in place since the beginning of the 1960s. This study classified, analyzed and diagnosed the development process of youth policy in the early stage of policy formulation, participation as youth policy subject, quality improvement of youth policy, enhancement of youth capacity in global age, consumer-oriented customized youth policy, youth policy in the Age of the Fourth Industrial Revolution based on the classification of the basic plan of youth policy. Especially, there are many limitations in the implementation of youth policy, such as policies based on youth problems, problems related to youth law centered to regulation, confusion among youth policy makers, lack of creativity and diversification of youth business. In this study, the tasks for establishing youth policy in the future are as follows. First, the development of youth policy is to connect youth s interest to policy as a top priority. Second, it is the expansion of youth participation as a youth policy subject. Third, youth policy and education policy should be integrated and administrative ministries should be one. Fourth, comprehensive system of youth administrative network and community center should be established in youth policy delivery system.

Correction : Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

Kim Seung-Jun,Gim Dong-Hyeon,장문경,황석준,김정훈,양윤정,남주석 한국농업기계학회 2024 바이오시스템공학 Vol.49 No.1

Continuous bundles of aligned electrospun PAN nano-fiber using electrostatic spiral collector and converging coil

Lee, Jung Hun,Shin, Dong Wook,Nam, Ki Bong,Gim, Yeong Hyeon,Ko, Han Seo,Seo, Dong Kyun,Hui lee, Geon,Kim, Yong Hyup,Kim, Sang Woo,Oh, Tae Sik,Yoo, Ji Beom Elsevier 2016 Polymer Vol.84 No.-

<P><B>Abstract</B></P> <P>We develop an advanced electrospinning process that uses an electrostatic spiral collecting coil and a converging coil to produce a polyacrylonitrile (PAN) polymer fiber with a nanometer-sized diameter. The electrostatic spiral collecting coil was used as a collector on which to deposit a continuous and aligned PAN polymer fiber, and the converging coil was used to adjust the collecting area of the fibers. The fiber bundles were continuously withdrawn from the spiral collector, and to estimate the behavior of the fibers, equipotential lines were calculated for the electrospinning system by using a 3D simulation program. A high-speed camera and a magnifying camera were used to observe the actual behavior of the fibers. In this study, the interval distance of the spiral collecting coil was adjusted to obtain bundles of with various diameters for use in various applications. The average diameter of the fibers is of about 250 nm, and the range of the average diameter of the bundles is between 30 μm and 120 μm. Among the fiber bundles, around 90 μm of the bundle was best well-aligned and its fracture force and strain strength were of around 80 mN and 12.6 MPa before the stabilization process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Continuously aligned nano-fiber bundle was produced. </LI> <LI> Without change the fiber thickness, the diameter of fibers bundles were controlled. </LI> <LI> The mechanism of how diameter of the bundles were controlled. </LI> <LI> Roll to roll process for electrospinning nanofiber. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Development of Regression Model for Predicting the Maximum Static Friction Force of Tractors with a Front-End Loader

Kim Seung-Jun,Gim Dong-Hyeon,Jang Moon-Kyeong,황석준,Kim Jeong-Hun,양윤정,남주석 한국농업기계학회 2023 바이오시스템공학 Vol.48 No.3

Purpose In this study, regression models that can predict the maximum static friction force of tractors with a front-end loader were developed. Methods For the development of the regression models, the maximum static friction force of a tractor was measured under various load and soil conditions. Tests were then conducted on pavement and off-roads while varying the payload of the front-end loader and rear ballast weight. The maximum static friction force measured in the regression analysis was set as a dependent variable, and independent variables were set by combining the tractor weight, payload of the front-end loader, and vertical reaction forces of the front and rear axles. The accuracy of the multiple regression models developed through regression analysis was evaluated based on the coefficient of determination (R2), root mean squared error (RMSE), and mean absolute error (MAE). Results In the analysis results, the regression model constructed based on the vertical reaction forces of the front and rear axles exhibited the highest accuracy with R2, RMSE, and MAE values of 0.37, 0.69 kN, and 0.59 kN, respectively, followed by the regression model constructed based on the total weight. Conclusion The utilization of the regression model constructed based on the vertical reaction force of the front and rear axles achieved the highest accuracy. But separate calculations were needed according to the load conditions. Therefore, the consideration of the regression model constructed based on the total weight is determined to be more efficient in predicting the maximum static friction force.

A resistivity anomaly at 380 K in reproduced LK-99

Sangjin Kim,Kwang-Tak Kim,Jeonghun Kang,Dong-Hyeon Gim,Yoon Han Lee,Kee Hoon Kim 한국초전도저온학회 2023 한국초전도저온공학회논문지 Vol.25 No.4

To confirm the room-temperature superconductivity at ambient pressure as claimed in recent arXiv preprints by Lee et al., we followed the original authors’ systematic solid-state synthesis recipe to reproduce Cu-doped Pb-apatite, known as LK-99. Using X-ray diffraction and Raman spectroscopy, we identified inclusion of various impurities alongside the apatite phase in our sample. While the sample exhibited an overall semiconducting behavior in electrical transport, an intriguing resistivity anomaly at 380 K was observed, possibly originating from a structural phase transition of the Cu2-δS impurity. Based on the transport and magnetization measurements, we conclud that the sample is a non-magnetic semiconductor, with absence of superconductivity.

Optimization of electrode structure to control liquid crystal director nearby domain boundary in a Z-shape patterned vertical alignment mode

Woo-Il Kim,Dae Hyun Kim,Dong Won Kwon,Hye Young Gim,이승희,Yeon Hak Jeong,Jae Jin Ryu,Kyeong Hyeon Kim 한국물리학회 2011 Current Applied Physics Vol.11 No.3

Various pixel structures have been proposed in the patterned vertical alignment (PVA) mode to improve transmittance and response time because collisions of the liquid crystal directors are inevitable near domain boundary region. One of them is well known as Z-shape structure, which shows multi-domain characteristic but low transmittance due to forming disclination lines at the domain boundary. This characteristic comes from the LC director that cannot tilt down to 45° with respect to the transmissive axis of crossed polarizers. In order to overcome this problem, we proposed a new pixel structure which improves transmittance while keeping the number of masks same as before. Consequently, the proposed structure improved transmittance up to 18% compared with conventional Z-shape structure.

논문 : 노외기계시스템공학 ; 차축의 중량 분포와 타이어의 공기압이 트랙터 작업의 연료 효율에 미치는 영향

이진웅 ( Jin Woong Lee ),김경욱 ( Kyeong Uk Kim ),김동현 ( Dong Hyeon Gim ),최규정 ( Kyu Jeong Choi ) 한국농업기계학회 2011 바이오시스템공학 Vol.36 No.5

This study was conducted to investigate the effects of axle weight distribution and inflation pressure of tire on the fuel economy of tractors as well as operational range of tractor engine in terms of engine speed and power when a 4WD tractor of 38.2 kW rated power at 2500 rpm is used for plowing and flooded-field rotavating in paddy fields. (1) Plowing operation required an average engine power of 9.6~13.5 kW which equals 25~35% of rated PTO power. Engine speed ranged from 1,320.4 to 1,737.4 rpm, work velocity from 3.4 to 4.8 km/h, and fuel consumption from 3.2 to 4.2 L/h, respectively. (2) Flooded-field rotavating required an average engine power of 11.5~18.5 kW which equals 30~48.4% of rated PTO power. Out of this 6.2~12.2 kW was used for PTO power. Engine speed ranged from 1,557 to 2,067 rpm, work velocity from 2.5~5.4 km/h and fuel consumption from 3.2~5.5 L/h, respectively. (3) Axle weight distribution, inflation pressure of tire and moisture content of soil did not affect significantly the specific volumetric fuel consumption but affected significantly the fuel consumption per unit area of operation. Fuel savings amounted to 65% in plowing operation and 20% in flooded-field rotavating when the axle weight distribution and inflation pressure of tire were optimally adjusted. (4) Optimal adjustment of axle weight distribution and inflation pressure of tire are expected to save fuel consumption by 10~65% per unit area of operation in plowing and 10~20% in flooded-field rotavating.

회귀분석을 통한 로더 부착 트랙터의 정지 마찰력 예측식 개발

김승준 ( Seung-jun Kim ),남주석 ( Ju-seok Nam ),김규봉 ( Kyu-bong Kim ),김동현 ( Dong-hyeon Gim ) 한국농업기계학회 2023 한국농업기계학회 학술발표논문집 Vol.28 No.1

트랙터의 정지 마찰력은 차체 하중, 토양 조건 등의 변수에 영향 받으며 일부 예측식 개발 연구가 수행되었으나 로더를 부착한 트랙터를 대상으로 한 연구는 거의 없다. 본 연구에서는 회귀분석을 통해 로더가 부착된 트랙터의 정지 마찰력 예측식을 도출하였다. 시험 방법은 트랙터의 전후차축 중량 분포에 따라 트랙터가 견인될 때 최대 정지 마찰력이 작용하는 순간의 견인하중을 로드셀로 계측하였다. 전후차축 중량은 시험 대상 트랙터의 후방 밸러스트와 로더 탑재중량을 조정하여 다양하게 설정하였다. 다양한 하중 및 토양 조건에서의 정지 마찰력 계측 결과를 회귀분석하여 예측식을 도출하였다. 예측식은 트랙터와 로더의 자중을 합한 트랙터 중량 및 로더의 탑재 하중을 활용하여 1차식 또는 제곱근의 수식으로 도출되었다. 예측식과 실제 계측된 정지 마찰력의 평균 오차율은 최대 8% 미만으로 나타났으며, 트랙터 중량과 로더 탑재중량을 개별 변수로 한 예측식보다 두 중량을 합하여 하나의 변수로 처리한 예측식의 정확도가 더 높았다. 향후 다양한 조건에서의 추가 실험을 통해 개발된 예측식을 검증할 필요가 있다.