• 한국철도학회논문집
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• 제17권4호
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• pp.233-244
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• 2014

이 연구에서는 자기부상열차-가이드웨이 상호작용 해석기법을 현장에서 계측된 자료를 활용하여 검증한다. 자기부상열차의 차체와 대차는 병진운동과 회전운동을 하는 강체 질량으로 모사한다. 대차의 부상전자석에서 발생하는 부상력은 능동 제어 알고리즘에 의해 제어된다. 가이드웨이는 Euler-Bernoulli beam을 사용하여 수치 모형을 구성한다. 대차의 회전 운동으로 인한 부상공극의 변화와 가이드웨이에 작용하는 위치의 변화를 엄밀히 고려하여 자기부상열차-가이드웨이 상호작용계의 동적거동 해석을 수행한다. 인천공항 자기부상철도 노선에서 계측된 실측 자료를 이용하여 해석기법을 검증한다. 해석 결과와 현장 계측 결과의 비교를 통해 해석 기법의 정확성을 검증하고, 대상 구조물이 설계 기준을 만족하도록 안전하게 설계되고 시공되었음을 확인한다.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1161-1170
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• 2011

이 논문은 촉매 담체에서 열유동 및 구조해석의 실동경계조건에 대한 역문제 해법을 나타낸다. 촉매 담체의 배기가스 정화효율은 열유동 매개변수와 촉매 성분 등에 영향을 받고 열유동 균일도에 의해 평가된다. 역문제의 정식화-열유동 매개변수(입구 온도, 속도, 반응열, 대류열전달계수)를 얻고-와 직접 문제-주어진 출구 온도 분포로부터 평가-를 설명하였다. 실험계획법과 반응표면 최적화 기법은 제안된 역문제 해결을 위해 이용하였다. 촉매 담체의 온도 분포는 예측된 열유동 매개변수에 대한 열유동해석에 의해 얻었다. 열응력과 내구성 평가는 이 온도 분포에 기반해서 수행하였다. 역문제 접근 방법의 유효성과 정확성은 반응표면모델과 측정된 실차 시험과 좋은 일치를 달성함으로써 설명하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.45-51
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• 2002

An acoustic finite element model of a bridge is developed to evaluate the noise generated by the traffic-induced vibration of the bridge. The dynamic response of a multi-girder bridge, modeled by a 3-dimensional frame element model, is analyzed with a 3-axle 8 DOFs truck model and a 5-axle 13 DOFs semi-trailer. The flat plate element is used to analyze the acoustic pressure due to the fluid-structure interactions between the vibrating surface and contiguous acoustic fluid medium. The radiation fields of noise with a specified distribution of vibrating velocity and pressure on the structural surface are also computed using the Kirchhoff-Helmholtz integral. Although the noise produced by the bridge vibration is not serious in itself, which is below the audible frequency range, it should be considered as an interaction problem between vehicle noise and bridge vibration noise in order to evaluate the traffic noise around the bridge.

• 한국항공우주학회지
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• 제49권3호
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• pp.185-195
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• 2021

본 연구의 날갯짓 초소형 비행체는 실제 생명체의 날개를 모방하여, 매우 유연한 재질의 캠버날개를 활용한다. 캠버 날개는 생명체와 유사하게 앞전, 시맥, 박막과 같이 특성이 서로 다른 세가지 재질로 구성되어 있고 다양한 방식으로 구속되어 있다. 날개의 유연성을 활용한 수동 회전(passive rotation) 방식은 앞전과 시맥의 재질이 날갯짓 궤적에 매우 큰 영향을 미치는 요소이기 때문에 적절한 유연성을 갖는 재질의 선정이 필수적이다. 이러한 날개의 재질들과 복잡한 형상을 사실적으로 모델링하여 정밀하게 해석할 수 있는 유체-구조 연성해석 프로그램을 개발하고, 날개의 앞전과 시맥의 탄성 계수의 변화에 따른 공력탄성학 효과를 정밀하게 분석하였다. 결과적으로 재료의 탄성 계수 변화만으로도 날개의 비틀림각 궤적을 적절히 발생시킴으로써 날갯짓 비행체의 추력 및 효율을 크게 증가시킬 수 있음을 보였다.

• 한국철도학회논문집
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• 제20권1호
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• pp.111-119
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• 2017

이 연구에서는 자기부상열차-가이드웨이 상호작용을 고려하여 자기부상철도 가이드웨이 구조물의 진동사용성을 고려한 처짐한계를 제안한다. 간략화된 자기부상철도 시스템의 운동방정식을 유도하고, 자기부상력 제어를 위한 되먹임 상수가 부상공극의 변동량이 최소가 되도록 최적화한다. 이 시스템에 대하여 자기부상열차의 운행속도, 가이드웨이 경간장, 2차 현가장치의 고유진동수와 감쇠비를 변화시켜 가며, 부상공극의 크기와 차체의 연직가속도에 대한 사용성 기준을 만족하는 가이드웨이의 처짐한계를 조사한다. 해석 결과로부터 자기부상열차의 2차 현가장치에 대한 요구 조건과 가이드웨이 구조물이 만족시켜야 하는 처짐한계를 제안한다.

• International Journal of Aeronautical and Space Sciences
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• 제18권4호
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• pp.807-815
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• 2017

For liquid rocket engine(LRE)-based space launch vehicles, longitudinal instability, often referred to as the pogo phenomenon in the literature is predicted. In the building block of system-level task, accurate dynamic modeling of a fluid-filled tank is an essential. This paper attempts to apply the virtual mass method that accounts for the interaction of the vehicle structure and the enclosed liquid oxygen to LOX-filled tanks. The virtual mass method is applied in a modal analysis considering the hydroelastic effect of the launch vehicle tank. This method involves an analysis of the fluid in the tank in the form of mass matrix. To verify the accuracy of this method, the experimental modal data of a small hemispherical tank is used. Finally, the virtual mass method is applied to a 1/8-scale space shuttle external tank. In addition, the LOX tank bottom pressure in the external tank model is estimated. The LOX tank bottom pressure is the factor required for the coupling of the LOX tank with the propulsion system. The small hemispherical tank analysis provides relatively accurate results, and the 1/8-scale space shuttle external tank provides reasonable results. The LOX tank bottom pressure is also similar to that in the numerical results of a previous analysis.

• Reproductive and Developmental Biology
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• 제35권2호
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• pp.159-165
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• 2011

To explore the role of histone deactylase (HDAC) activation in an in vivo model of hypertrophy, we studied the effects of Trichostatin A (TSA). TSA subjected to thoracic aortic banding (TAB)-induced pressure stress in mice. In histological observations, TAB in treated mice showed a significant hypertrophic response, whereas the sham operation remained nearly normal structure with partially blunted hypertrophy. TSA treatment had no effect (measured as HW/BW) on sham-operated animals. TAB animals treated with vehicle manifested a robust ~50% hypertrophic response (p<0.05 vs sham). TAB mice treated with 2 mg/kg/day TSA manifested a blunted growth responses, which was significantly diminished (p<0.05) compared with vehicle-treated TAB mice. TAB mice treated with a lower dose of TSA (0.5 mg/kg/day) manifested a similar blunting of hypertrophic growth (~25% increase in heart mass). Furthermore, to determine activity duration of TSA in vitro, 1 nM TSA was added to H9c2 cells. Histone acetylation was initiated at 4 hr after treatment, and it was peak up to 18 hr, then followed by significantly reduced to 30 hr. We also analyzed the expression of p53 following TSA treatment, wherein p53 expression was elevated at 4 hr, and it was maintained to 24 hr after treatment. ERK was activated at 8 hr, and maintained till 30 hr after treatment suggesting an intracellular signaling interaction between TSA and p53 expression Taken together, it is suggested that HDAC activation is required for pressure-overload growth of the heart. Eventually, these data suggest that histone acetylation may be a novel target for therapeutic intervention in pressure-overloaded cardiac hypertrophy.

• 한국해양공학회지
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• 제33권6호
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• pp.620-626
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• 2019

With the development of robot technology, the expectation of autonomous mission operations has increased, and the research on robot control architectures and mission planners has continued. A scalable and robust control architecture is required for unmanned surface vehicles (USVs) to perform a variety of tasks, such as surveillance, reconnaissance, and search and rescue operations, in unstructured and time-varying maritime environments. In this paper, we propose a robot control architecture along with a new utility function that can be extended to various applications for USVs. Also, an additional structure is proposed to reflect the operator's command and improve the performance of the autonomous mission. The proposed architecture was developed using a robot operating system (ROS), and the performance and feasibility of the architecture were verified through simulations.

• 한국정밀공학회지
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• 제27권9호
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• pp.58-66
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• 2010

This study examines thermal safety on three-way catalyst that dominates 70 % among whole exhaust gas purification device in 2003. Three-way catalyst durability in the Korea requires 5 years/80,000 km in 1988 but require 10 years/120,000 km after 2002. Three-way catalyst durability in the USA requires 7 years/120,000 km but require 10 years/160,000 km after 2004. Three-way catalyst maintains high temperature in interior domain but maintains low temperature on outside surface. Therefore this device shows tensile stress on outside surface. Temperature distribution of three-way catalyst was acquired by thermal flow analysis for predicted thermal flow parameter. Thermal stress analysis for three-way catalysis was performed based on this temperature distribution. Thermal safety of three-way catalyst was estimated by power law dynamic fatigue life estimation and strength reduction methods for thermal stress.

• 한국분말재료학회지
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• 제25권4호
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• pp.336-339
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• 2018

A unique porous material with controlled pore characteristics can be fabricated by the freeze-drying process, which uses the slurry of organic material as the sublimable vehicle mixed with powders. The essential feature in this process is that during the solidification of the slurry, the dendrites of the organic material should repel the dispersed particles into the interdendritic region. In the present work, a model experiment is attempted using some transparent organic materials mixed with glass powders, which enable in-situ observation. The organic materials used are camphor-naphthalene mixture (hypo- and hypereutectic composition), salol, camphene, and pivalic acid. Among these materials, the constituent phases in camphor-naphthalene system, i.e. naphthalene plate, camphor dendrite, and camphor-naphthalene eutectic exclusively repel the glass powders. This result suggests that the control of organic material composition in the binary system is useful for producing a porous body with the required pore structure.