• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.252-256
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• 2018

호우 시 산지하천 유역에서 빈발하는 토석류에 따라 하천 흐름에 들어온 전석과 같이 상대적으로 큰 물체는 하류로 이송되거나 하상에 퇴적하여 기존 흐름과 하상을 변화시키는 교란요인이 된다. 따라서 산지하천 흐름에서 전석의 영향을 예측하는 것이 필요하나 이는 유속, 전석의 크기와 형상, 유입조건, 부유사 농도 등 수 많은 변수들에 영향을 받기 때문에 그 경로를 정확히 예측하기 어렵다. 이 연구는 유리와 철로 된 구형물체가 개수로 흐름에서 이동하는 경로를 조사한 것이며 흐름의 수심, 물체의 크기와 초기침강조건을 고려하여 수리실험을 실시하고 물체의 이동경로와 유하거리를 분석하였다. 개수로 흐름에 유입한 구형 물체는 침강에 의한 항력과 유수에 의한 항력을 동시에 받는다. 이 힘은 물체의 형상, 유수의 점성, 난류, 물체와 물의 밀도차가 복합적으로 작용한 결과이며 구체의 이동경로와 시간을 좌우한다. 실험결과 개수로 흐름에서 낙하중인 구형물체는 하상에 가까워질수록 흐름방향 이동거리가 증가하였다. 물체의 수중무게가 작을수록 유수 중에서 체류하는 시간이 길고 이동거리가 더 크며, 구체에 작용하는 초기항력에 따라 초기 낙하각도와 이동거리가가 증가하는 것을 확인하였다.

• Journal of Power System Engineering
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• v.9 no.3
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• pp.71-78
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• 2005

A high-pressure hose includes rebar layers of the synthetic fiber such as nylon or a steel wire to control internal pressure. The hose assembly is manufactured through the swaging process to clamp the hose into the metal fittings. Usually, the hose behavior is affected by the resultant of the longitudinal and circumferential forces produced by the internal pressure. The rebar layers can appear the most ideal rebar effect when they are arranged to the same direction as the resultant force. The braid angle applied in the rebar layers is an important factor in determining ultimate burst pressure and overall hose life. Failure can occur on the contacted parts of a hose with the metal fittings under severe operating conditions such as high pressure and temperature of the inner fluid. In this paper, the mechanical behavior between the hose and the metal fittings during the swaging process and the stress variation characteristics of a high-pressure hose under a constant applied pressure are analyzed with respect to the braid angle of steel wire using the finite element method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.310-316
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• 2016

We propose a novel contact-free transportation system in which an axial electrodynamic wheel is applied as an actuator. When the electrodynamic wheel is partially overlapped by a fixed conductive plate and rotates over it, three-axis magnetic forces are generated on the wheel. Among these forces, those in the gravitational direction and the lateral direction are inherently stable. Therefore, only the force in the longitudinal direction needs to be controlled to guarantee spatial stability of the wheel. The electrodynamic wheel consists of permanent magnets that are repeated and polarized periodically along the circumferential direction. The basic geometric configuration and the pole number of the wheel influence the stability margin of a transportation system, which would include several wheels. The overlap region between the wheel and the conductive plate is a dominant factor affecting the stiffness in the lateral direction. Therefore, sensitivity analysis for the major parameters of the wheel mechanism was performed using a finite element tool. The system was manufactured based on the obtained design values, and the passive stability of a moving object with the wheels was verified experimentally.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.72-72
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• 2017

국내 농업에서 토양의 반전, 쇄토, 배토, 가능한 복합작업기인 무동력 디스크해로우 방식의 경운과 배토 고효율 복합작업기의 수요가 증가 하고 있다. 경운작업에서 일련의 과정은 작물의 생육과 관리차원에서 큰 의미를 지니며 작물재배의 첫 단계로 중요시 다루어져야할 과정이다. 이러한 작업기의 성능 시험에서 포장시험을 통해 복합기의 신뢰도와 실제 필드에서 발생하는 문제들을 포괄적으로 해결 할 수 있는 방안이 필요하다. 토양 경작을 위한 농업기기의 작업 저항은 식물 생산에서 유용성을 평가하는 가장 중요한 지표중 하나이다. 작업 저항(수평, 수직 방향의 힘)은 트랙터의 힘에 의해 생성된 동작을 방해하므로 토양 경운 시 에너지 소비를 결정하고 설계 매개 변수 측면에서 최적의 작업 조건을 결정하는 데 중요한 영향을 미친다. 따라서 본 연구에서는 경상대학교 내 위치한 실험동에서 Soil-bin에 이송장치를 설치한 후, 이송장치에 디스크 해로우 (Multidisc Vario, Tulip Agri., Netherlands)를 부착하여 실험을 진행하였다. 디스크 해로우의 원주 평면과 수직 평면 사이의 각 a(토양 표면에 수직)와 디스크의 해로우의 원주 평면과 작업 방향 사이의 각 b의 값을 독립 변수로 두고 a, b를 변화 시키면서 발생하는 이송장치의 견인력을 측정하여 농가 및 효율적인 경운작업 시 기초자료로 활용하고자 한다.

• Transactions of Materials Processing
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• v.4 no.1
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• pp.17-27
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• 1995

The tact switch is widely used in electric and electronic products. The dome type tact spring is produced by stamping. Stamping of the tact spring and operation of the tact switch have been simulated by the elasto-plastic finite element method. The operating characteristics of the switch may be given by the relation between the operating force and stroke. For a given material, this is affected by two main factors. One is the geometry of dome spring which is determined by the geometry of stamping dies and the stamping pressure, and another one is the dimension of switch. From the calculation, it was possible to obtain the stamping conditions and switch dimension for a predetermined force-stroki relation And, the hoop stresses and effective strains distributions due to the stamping and during the operation of the switch indicate a possibility of cracking in the center and rim of dome spring.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.648-655
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• 2020

The firing pin of modern automatic rifles detonates the primer of loaded ammunition via a hammer. During this process, the firing pin receives an impact load and repetitive force throughout the life of the rifle. An endurance test of a rifle showed that the firing pin breaks prematurely at 96.26% of life. Accordingly, a case study was conducted through cause analysis and a reconstruction test. Optical microscopy and scanning electron microscopy of the broken surface of the firing pin showed that a crack began in the circumferential direction of the surface, resulting in a fatigue crack to the core after repeated impact. Crack growth and fatigue destruction occurred at the end due to the repetitive impact and was estimated using a notch. For verification, a sample that produced a 0.03mm circumferential notch was broken at 64.25% of life in the reconstruction test. A test of breakage according to the notch types showed that a 0.3mm and a 0.5mm one-side notch were broken at 66.53% and 50.76%, respectively, and a 0.03mm six-point notch was broken at 85.65%. The endurance life of a sample firing pin with a rough surface and tool mark was examined, but an approximately 381 ㎛ internal crack formed. Through this study, failure for each notch type was considered. These results show that quality control of the notch and surface roughness is essential for ensuring the reliability of a component subjected to repeated impact.