• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.301-305
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• 2012

In this work the mechanical behaviors of GaN nanowires are analyzed during tension, compression, and unloading deformations. The thermal conductivity of the nanowires at each deformed state is evaluated using an equilibrium Green-Kubo approach. Under tensile loading, the [0001]-oriented nanowires with hexagonal cross-sections undergo a phase transformation from wurtzite to a tetragonal structure. The phase transformation is not observed under compressive loading. The thermal conductivity decreases on going from compressive strains to tensile strains. The strain dependence of the thermal conductivity results from the relaxation time of phonon. A reverse transformation from the tetragonal structure to the wurtzite structure is observed during unloading. The thermal conductivities in the intermediate states are lower than the conductivity in the wurtzite structure at same strain. Such differences in the thermal conductivity between different atomic structures are mainly due to changes in the group velocity of phonon.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.971-971
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• 2012

4대강 살리기 사업으로 인하여 4대강에 대한 전면적인 투자와 공사가 이루어지고 있다. 4대강 사업이 마치게 되면 전국에 많은 수의 대규모 보가 설치되고 설치되어진 보는 각각의 강의 관리에 많은 영향을 미치게 될 것이다. 그러므로 이 4대강 사업으로 조성되는 13억 톤 수자원을 융 복합기술을 이용하여 감시 및 관리를 해야 할 것이다. 이를 위해서 실시간 수질 감시 및 모니터링 시스템의 개발과 그에 따른 센서들의 개발을 통하여 4대강 보 운영관리를 위한 통합관리 시스템개발(Ubiquitous River Management)이 이루어 져야 할 것이다. 그동안 계산 시간의 제약을 받아 오던 3 차원 수리동역학의 모의가 컴퓨터관련 기술의 발달에 따라 계산에 소요되는 시간이 계속 단축되고 있으며 이를 수질예측에 사용하는 연구가 활발히 진행되고 있다. 그에 따라 실시간으로 얻은 데이터를 이용하여 모델링 기법을 통해 예측을 해봄으로써 보 내부에 존재하는 여러 취수원 관리에 적용을 할 수 있을 것이다. 본 연구에는 3차원 수리동역학 모델과 수질모델을 결합한 시스템이 저수지 내의 수리특성, 유사이동 및 탁수 현상을 모의하는데 사용이 가능한지를 알아보는 것을 주목적으로 하고 있다. 본 팔당댐 모의에서는 취수구에 따른 수질변화를 모의하기 위해 3차원모델의 사용이 필요하다. 따라서 본 모의에서는 미국 환경부에서 WASP에 이용하기 위해 수정한 EFDC1(2009, USEPA에서 입수)을 사용하였다. 본 연구에서는 팔당호의 2009년의 수위, 수온, 유량 및 농도의 실측자료를 이용하여 3차원 수리 모델링을 실시하고, 수위, 유사이동 및 탁도 예측 모델링을 실시하였다. 3차원 수리동역학 모델과 취수원의 적용에 적절한 모델을 구축하기 위하여 적당한 평면격자의 개수를 선택하여 선택되어진 평면격자에서 수직격자의 층수를 조절하여 매 층마다 DYE TEST를 하였다. 이는 각각의 유입 하천에서 오염물질이라 가정하고 농도가 유입되었을 때 수리특성에 의해서 연구지역에서의 농도 변화를 파악하여 미리 예측을 하여서 그에 따라 취수원에서의 취수 관리를 가능하게 할 수 있다. 이를 위해서 평면격자에 따라서 수직 층의 개수를 5층부터 40층까지 모의를 하여서 시간 및 이동변화에 따라 알맞은 모델을 구축하였다. 또한 층수마다 Sediment 모의를 통하여 호 내의 SS의 이동을 모의하였다. 이 역시 취수원의 관리를 가능하게 할 수 있다.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.709-715
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• 2015

Underwater gliders do not typically have separate propellers for forward motion. They generate propulsive forces based on the difference between their buoyancy and gravity. They can control the volume from the buoyancy engine to adjust the propulsive force. In addition, the attitude of the underwater glider is controlled by a rubberless motion controller. The motion controller can change the mass center and moment of inertia of the inner moving mass. Owing to the change in these parameters, the attitude of the underwater glider is changed. In this study, we derive nonlinear, six degree of freedom (DOF) mathematical models for the motion controller and buoyancy engine. Using these equations, we perform dynamic simulations of the proposed underwater glider, and verify the suitability of the design and dynamic performances of the proposed underwater glider. We then perform the motion control simulation for the pitch and roll angle, and analyze the dynamic performance according to the pitch and roll angles.

• 한국해양학회지
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• v.26 no.2
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• pp.133-143
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• 1991

A new internal tide model for solving flow fields and wave generations is presented here which seems to be simple to apply, converges fast and yields accurate results. The new method employs a representation of vertical structure using dynamic basis functions which depend on the stratifications. The present method has been applied to the East Sea. For a constant Brunt-Vaisala case, weak baroclinic currents are generated over the entire continertal slop: however, results using a more realistic stratification can be described using only the lowest modes and exhibit much more realistic behavior. Baroclinic tide generation is confined to the upper slope. Model results for the East sea show the semi-diurnal baroclinic modes contain almost all the energy transferred from the barotropic mode.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1382-1387
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• 2004

From the viewpoint of a macro state, there is no thermal boundary resistance (TBR) at an interface if both surfaces at an interface are perfectly contacted. However, recent molecular dynamics (MD) studies reported that there still exists the TDR at the interface in an ideal epitaxial superlttice. Our previous studies suggested the model to predict the TBR not only quantitatively also qualitatively in superlattices. The suggested model was based on the classical theory of a wave reflection, and provided highly satisfactory results for an engineering purpose. However, it was not the complete model because our previous model was derived by considering only the effects from a mass ratio and a potential ratio of two species. The interaction of two species presented by the Lennard-Jones (L-J) potential is governed by the mutual ratio of the masses, the potential well depths, and the diameters. In this study, we performed the preliminary simulations to investigate the effect resulting from the diameter ratio of two species for the completion of our model and confirmed that it was also a ruling factor to the TBR at an interface in superlattices.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.155-161
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• 2023

Ion concentration polarization (ICP) is one of the essential important mechanisms for biomolecule preconcentration devices as well as a fundamental transport phenomenon found in electrodialysis, electrochemical cell, etc. The ICP triggered by externally applied voltage enables the biomolecular analyte to be preconcentrated at an arbitrary position by a locally amplified electric field inside the microchannel. Conventional preconcentration methodologies using the ICP have two limitations: uncertain equilibrium position and hydrodynamic instability of preconcentration plug. In this work, a new preconcentration method in the dead-end microchannel around cation exchange membrane was numerically studied to resolve the limitations. As a result, the numerical model showed that the analyte was concentrated at a shock front developed in a geometrically confined dead-end channel. Furthermore, the electrokinetic behaviors for preconcentration dynamics were analyzed by changing microchannel's applied voltage and volumetric charge concentration of microchannel as key parameters to describe the dynamics. This work would provide an effective means for a point-of-care platform that requires ultra-fast preconcentration method.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.648-657
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• 2014

This paper is about the study on a newly developed small waterproofed 4-axis robot arm and the analysis of its kinematics and dynamics. The structure of robot arm is designed to have Pitch-Pitch-Pitch-Yaw joint motion for inspection using a camera on itself and the joint actuator driving capacity are selected and the joint actuators are designed and test for 10m waterproofness. The closed-form solution for the robot arm is derived through the forward and inverse kinematics analysis. Also, the dynamics model equation including the damping force due to the mechanical seal for waterproofness is derived using Newton-Euler method. Using derived dynamics equation, a sliding mode controller is designed to track the desired path of the developed robot arm, and its performance is verified through a simulation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.126-131
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• 2017

Numerical analysis using commercial CFD code was carried out to develop the drag force type vertical axis hydraulic turbine for the improvement of the production efficiency of small hydro energy at low flow velocity condition. Blade pressure changes and internal flows were analyzed according to the presence or absence of the hydraulic turbine blade holes at flow velocity of less than 1.0~3.0 m/s. According to the numerical results, the pressure and flow velocity is severly affected by the flow velocity in turbine blade with no holes, while the influence of flow velocity is comparatively decreased in turbine blade with holes. It is also found that the pressure and flow velocity on the blade surface with holes are evenly distributed with no singular location and it is believed that forming a hole in the blade may be helpful in terms of structural safety.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.8
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• pp.1251-1258
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• 2003

This paper presents a nonlinear robust approach to the slip control problem for a torque converter bypass clutch in a passenger car. The proposed nonlinear robust controller builds upon only the measurements avail-able from inexpensive sensors that are already installed in passenger cars for control. The issue of torque estimation problems for the implementation of the proposed controller is addressed. The stability of the internal dynamics is investigated, upon which a nonlinear robust controller is designed using input-output feedback linearization and Lyapunov redesign technique. The performance of the designed controller is validated by simulation studies.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10b
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• pp.550-552
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• 2000

최근에는 디지털 박물관을 비롯하여, 미술품이나 역사적 유물들을 디지털 형태로 재현하려는 시도들이 활발해지고 있다. 디지털 형태로의 재현은 시공간의 제약을 받지 않으면서 컴퓨터 상에서 해당 미술품이나 유물을 감상할 수 있는 기회를 제공한다. 반면에, 고전적인 기계식 시계들 중의 하나인 테리 시계(Terry's clock)와 같은, 움직이는 유물은 내부의 기계 장치와 그에 따른 동적인 움직임 때문에 컴퓨터 상에서 재현하기가 까다롭다. 특히, 시계를 비롯한 비교적 오래된 기계 장치들은 기어나 진자와 같은 각각의 부품들을 재현한 후, 그 움직임을 동역학 기법들을 비롯한, 물리 법칙에 기반한 기술들로 재현하여야 한다. 본 논문에서는 기존의 운동학 방법들을 이용하여 각 부품의 움직임을 재현함으로써, 테리 시계를 컴퓨터 상에서 복원하였다. 본 논문에서 사용된 방법들은 다른 기계 장치들의 재현에도 응용 가능하다.