• 농업생명과학연구
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• 제52권6호
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• pp.103-109
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• 2018

점적기의 성능은 압력보상 기능에 따른 유량 균등성에 의해 좌우되고, 유량의 균등성은 점적기 내부의 위치에 따른 공급압력이 일정할 때 이루어진다. 점적기의 압력보상은 탄성을 가진 연질의 실리콘과 미로가 동시에 결합된 경우에 가장 큰 효과를 나타낸다. 그러나 경질 미로만으로 구성된 점적기의 경우에는 미로의 길이와 내부구조에 따라 유량이 크게 달라진다. 경질 미로만으로 구성된 점적기의 경우에는 연질의 실리콘을 동시에 결합한 점적기보다 공급 압력에 따른 유량의 오차가 훨씬 크게 나타나므로 간편한 반면에 성능에서는 불리한 조건을 가진다. 경질미로로 구성된 점적호스의 경우 공급 압력과 미로의 길이와 단면에 따른 최적 설계를 통하여 적절한 조건에서 폭넓게 사용할 수 있는 장점이 있으므로 이에 대한 연구는 점적기의 성능을 개선하는데 매우 중요한 역할을 한다. 그러나 이러한 분야의 연구는 거의 이루어지지 않은 실정이다. 따라서 본 연구에서는 경질미로로 구성된 점적호스의 성능평가를 구명하기 위해 원형의 미로를 길이별로 8단계(#1~#8)로 나누어, 공급압력(0.5~3.0bar) 변화에 따른 출구유량을 실험적 방법과 이론적 해석(CFD)으로 구하였다.

• 한국해양공학회지
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• 제33권4호
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• pp.350-357
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• 2019

The development of marine technology is expected to increase the demand for marine plants because of increasing oil prices. Therefore, there is also expected to be an increase in the demand for cylindrical structures such as URF (umbilical, riser, flowline) structures and spars, which are used operating in various seas. However, a cylindrical structure experiences vortex induced motion (VIM) in a current. In particular, for risers and umbilicals, it is important to identify the characteristics of the VIM because interference between structures can occur. In addition, various studies have been conducted to reduce VIM because it is the cause of fatigue damage to structures. The helical strake, which was developed for VIM reduction, has an excellent VIM reduction performance, but is difficult to install on structures and has a negative effect on heave motion. Therefore, the purpose of this study was to supplement the shortcomings of the helical strake and develop a high-performance reduction device. In the reduction device developed in this study, a string is placed around the structure inside the flow, causing vibration. The vibration of this string causes a small turbulence in the flow field, reducing the VIM effect on the structure. Finally, in this study, the 2-DOF motion characteristics of models without a suppression device, models with a helical strake, and models with a string were investigated, and their reduction performances were compared through model tests.

• 항공우주시스템공학회지
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• 제16권5호
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• pp.62-69
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• 2022

EHA(Electro-Hydrostatic Actuator)는 기존의 중앙집중식 유압시스템에 비해 높은 에너지 효율을 가진다. 특히 항공기용 EHA는 고장상황에 대비하여 이중화 설계가 일반적이다. 또한 장착공간의 한계로, 구동기 길이를 최적화 하여야 한다. 따라서 양로드형 실린더와 단로드형 실린더의 직렬 구성이 유리하다. 하지만 피스톤 수압부 면적의 비대칭성으로 인해, 일반적인 제어 기법으로 이중화 구동 시 두 실린더 사이에 Force Fighting 현상이 발생하게 된다. 본 논문에서는 이중화된 EHA의 시뮬레이션을 통해 Force Fighting 현상을 확인하였다. 이를 억제하기 위한 방법으로 Load Compensation 제어기와 힘 제어 기반 위치 제어기를 적용하였고 시뮬레이션을 통해 각각의 성능을 비교 분석하였다.

• 한국해양공학회지
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• 제30권2호
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• pp.91-99
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• 2016

The global demand for oil and natural gas has increased, and resource development is moving to the deep sea. Floating and flexible offshore structures such as semi-submersible, spar, and FPSO structures have been widely used. The major equipment of floating structures is always exposed to waves, currents, and other marine environmental factors, which cause structural damage. Moreover, flexible risers are susceptible to an exciting force due to the motion of the floating body. The inline and transverse responses from the three-dimensional behavior of a floating structure occur because of various forces. Typical risers are made of steel pipe and applied in the oil and gas development field, but flexible materials such as polyethylene are suitable for OTEC risers. Consequently, the optimal design of a flexible offshore plant requires a dynamic behavior analysis of slender bodies made of the different materials commonly used for offshore flexible risers. In this study, a three-dimensional motion measurement device was used to analyze the displacements of riser models induced by external force factors, and forced oscillation of a riser was linked to forced oscillation under a steady flow and regular wave condition.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.206-222
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• 2015

This work uses different finite element approaches to the free vibration analysis of reinforced shell structures, and a simplified model of a typical launcher with two boosters is used as an example. The results obtained using a refined one-dimensional (1D) beam model are compared to those obtained with commercial finite element software. The 1D models that are used in the present work are based on the Carrera Unified Formulation (CUF), which assumes a variable kinematic displacement field over the cross-sections of the beam. Two different sets of polynomials that correspond to Taylor (TE) or Lagrange (LE) expansions were used. The analyses focused on three reinforced structures: a stiffened panel, a reinforced cylinder and the complete structure of the launcher. The frequencies and natural modes obtained using one-dimensional models are compared to those obtained from classical finite element analysis. The classical FE models were built using a beam-shell or solid elements, and the results indicate that the refined beam models can in fact be used to investigate the behavior of very complex reinforced structures. These models can predict the shell-like modes that are typical of thin-walled structures that cannot be detected using classical beam models. The refined 1D models used in the present work provide results that are as accurate as those from solid FE models, but the 1D models have a much lower computational cost.

• Radiation Oncology Journal
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• 제33권3호
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• pp.226-232
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• 2015

Purpose: Toxicity of mucosa is one of the major concerns of radiotherapy (RT), when a target tumor is located near a mucosal lined organ. Energy of photon RT is transferred primarily by secondary electrons. If these secondary electrons could be removed in an internal cavity of mucosal lined organ, the mucosa will be spared without compromising the target tumor dose. The purpose of this study was to present a RT dose reduction in near target inner-surface (NTIS) of internal cavity, using Lorentz force of magnetic field. Materials and Methods: Tissue equivalent phantoms, composed with a cylinder shaped internal cavity, and adjacent a target tumor part, were developed. The phantoms were irradiated using 6 MV photon beam, with or without 0.3 T of perpendicular magnetic field. Two experimental models were developed: single beam model (SBM) to analyze central axis dose distributions and multiple beam model (MBM) to simulate a clinical case of prostate cancer with rectum. RT dose of NTIS of internal cavity and target tumor area (TTA) were measured. Results: With magnetic field applied, bending effect of dose distribution was visualized. The depth dose distribution of SBM showed 28.1% dose reduction of NTIS and little difference in dose of TTA with magnetic field. In MBM, cross-sectional dose of NTIS was reduced by 33.1% with magnetic field, while TTA dose were the same, irrespective of magnetic field. Conclusion: RT dose of mucosal lined organ, located near treatment target, could be modulated by perpendicular magnetic field.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2008년도 학술대회 1부
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• pp.210-214
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• 2008

로봇이 실제 가정환경에 존재하는 모든 물체를 사전에 모델화하여 데이터베이스에 보존하는 것은 현실적으로 불가능하다. 따라서 본 논문은 이러한 문제를 해결하기 위하여 가정 내에서 흔히 볼 수 있으며 로봇에게도 조작이 용이한 컵, 병, 캔 등의 실린더 형 물체를 우선적 모델링 대상으로 선정하고, 이 물체들의 공통된 범주적 특성을 정의한 보편적 모델(Generic Model)을 사용하여 부분적 데이터로부터 전체 형상을 추정하는, 로봇 자가 모델링에 활용 가능한 새로운 물체 모델링 기법을 제안한다. 구체적으로 3D 센서로부터 얻은 3D 영상으로부터 우리가 모델링 하기를 원하는 실린더 형의 물체를 분리해낸 후 물체 표면상의 점의 좌표와 법선벡터를 이용해서 실린더의 초기 중심축을 구하는 방법, 오차를 가지고 있는 중심축을 교정해주는 방법, 최종적으로 실린더 단면의 중심축과 반지름을 이용하여 전체 실린더 형 물체를 모델링하는 방법 등을 제안하고 또한 실험을 통해서 우리가 제시하는 모델링 기법이 노이즈가 존재하는 실제 환경에서도 얼마 만큼의 정확성을 갖는지를 평가하였다.

• 대한기계학회논문집B
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• 제41권3호
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• pp.171-181
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• 2017

2상 횡 유동은 응축기, 증발기와 원자력의 증기 발생기와 같은 열교환기의 튜브와 셀 사이에 존재한다. 공기/물의 2상 유동에 놓인 관군에 작용하는 항력을 실험적으로 평가하였다. 2상 유동에 놓인 관군은 정사각형 배열이다. 피치 직경 비는 1.35이었고, 실린더의 직경은 18 mm이다. 관군에 유동방향으로 작용하는 항력을 측정하여 항력계수와 2상 유동 감쇠비를 계산하였다. 2상 유동 감쇠비는 균질 2상 유동의 이론식을 사용하여 구하여 실험의 결과와 비교하였다. 압력과 항력의 상관계수를 실험결과를 고려하여 평가하였다. 상관계수는 이론적으로 항력을 계산할 때에 사용된다. 질량유량을 증가할수록 측정된 항력으로부터 구한 항력계수와 감쇠비가 균질 유동의 이론적 결과와 잘 일치함을 보이고 있다. 결과적으로 충분히 큰 질량 유량의 기포 유동인 경우에는 감쇠비를 균질 유동에 근거한 이론식으로 계산할 수 있다.

• 한국패류학회지
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• 제27권4호
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• pp.377-386
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• 2011

The ultrastructures of germ cells during spermatogenesis and sperm morphology in male Mya arenaria oonogai, which was collected on the coastal waters of Samcheonpo, south coast of Korea, were investigated by transmission electron microscopic observations. In the early stage of the spermatid during spermiogenesis, a few granules and a proacrosomal granule, which is formed by the Golgi complex, appear on the spermatid nucleus, and then it becomes a proacrosomal vesicle. Consequently, it becomes an acrosome by way of the process of acrosome formation. The morphologies of the sperm nucleus type and the acrosome of this species have a curved cylindrical type and cone shape, respectively. The spermatozoon is approximately $48-50{\mu}m$ in length including a curved cylinderical sperm nucleus (about $2.65{\mu}m$ long), an acrosome (about $0.64{\mu}m$ in length) and tail flagellum ($40-45{\mu}m$ long). As some ultrastructural characteristics of the acrosomal vesicle, the peripheral parts of two basal rings show electron opaque part (region), while the apex part of the acrosome shows electron lucent part (region). These charateristics of the sperm belong to the family Myidae or some species of Veneridae in the subclass Heterodonta, unlike a characteristic of the subclass Pteriomorphia showing all part of the acrosome being composed of electron opaque part (region). Therefore, it is easy to distinguish the families or the subclasses by the acrosome structures. Exceptionally, In particular, a cylinder-like nucleus of the sperm is curved (the angle of the nucleus is about $20^{\circ}$), as seen in some species of Veneridae (range from $0^{\circ}-80^{\circ}$). The number of mitochondria in the midpiece of the sperm of this species are four, as one of common characteristics appeared in most species except for a few species in Veneridae in the subclass Heterodonta. Cross-sectioned axoneme of the sperm tail flagellum shows a 9+2 structure: the axoneme of the sperm tail flagellum consists of nine pairs of peripheral microtubules at the periphery and a pair of central doublets at the center.

• 한국패류학회지
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• 제30권3호
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• pp.211-218
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• 2014

Spermatid differentiations during spermiogenesis and sperm ultrastructures in male Mercenaria stimpsoni were investigated by transmission electron microscopic observations. In the early stage of the spermatid during spermiogenesis, a few granules and a proacrosomal granule, which is formed by the Golgi complex, become a proacrosomal vesicle. Consequently, it becomes an acrosome by way of the process of acrosome formation. The morphologies of the sperm nucleus type and the acrosome of this species have a curved cylindrical type and cap shape, respectively. The spermatozoon is approximately $48-51{\mu}m$ in length including a curved cylinderical sperm nucleus (about $4.18{\mu}m$ long), an acrosome (about $0.52{\mu}m$ in length) and tail flagellum ($42-45{\mu}m$ long). As some ultrastructural characteristics of the acrosomal vesicle, the peripheral parts of two basal rings show electron opaque part (region), while the apex part of the acrosome shows electron lucent part (region). These charateristics of the sperm belong to the family Veneridae in the subclass Heterodonta, unlike a characteristic of the subclass Pteriomorphia showing all part of the acrosome being composed of electron opaque part (region). Therefore, it is easy to distinguish the families or the subclasses by the acrosome structures. Exceptionally, In particular, a cylinder-like nucleus of the sperm is curved (the angle of the nucleus is about $80^{\circ}$), as seen in some species of Veneridae (range from $0^{\circ}$ to $80^{\circ}$). The number of mitochondria in the midpiece of the sperm of this species are four, as one of common characteristics appeared in most species except for a few species in Veneridae in the subclass Heterodonta. Cross-sectioned axoneme of the sperm tail flagellum shows a 9+2 structure.