• 대한전자공학회논문지SP
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• 제44권2호
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• pp.144-152
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• 2007

본 논문에서는 멀티 레이저 라인 조사 방법을 이용한 능동적 비젼(Active Vision)의 방법으로 비등속 이동물체의 표면을 효율적으로 모델링 하는 방법을 제안한다. 레이저 라인을 물체에 조사하고 레이저가 조사된 방향과 각도를 달리한 방향에서 이를 관찰하면 레이저 라인이 표면의 굴곡에 따라 휘어지는 현상을 관찰할 수 있다. 이를 삼각기법(triangulation method)을 이용하여 분석하면 물체의 표면 3차원 정보 획득이 가능하다. 기존에 대표적 구조화 조명기법인 단일 라인(single stripe) 기법과 단일 프레임(single frame) 기법의 장단점과 제안하는 멀티 라인 기법의 장점을 설명하고 정밀도를 높이기 위한 레이저 라인의 효율적 배치에 대하여 설명한다. 강인한 레이저 라인의 추출을 위하여, 레이저 라인 피크 검출기법과 색 분석을 통해 얻은 레이저 반응도를 함께 이용하는 방법을 소개하였고, 효과적인 레이저 라인의 라벨링 기법을 새로 제안하였다. 개별 3차원 복원 표면을 전체영상으로 표현하기 위하여 동기화 정보 획득에 영상 간 특징점 매칭을 활용한 영상 정합 기법을 접목하였다. 3차원 표면 모델링 기술을 최종적으로 컨테이너 표면 데미지 검사에 활용하여 제안 3D 모델링 기술의 우수성을 확인하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.402-406
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• 1995

The shadow moire is one the optical techniques which able to give contour lines of an object with respect to a master grating plane. The moire patterns are issued from the superposition of a grating and its shadow projected on the surface of an object. But in the conventional shadow moire method the reference grating and deformed grating are mutually dependent, it is impossible to obtain uniform phase shifts on the whole field by moving the reference grating. Here we propose ane trial to apply phase shifting to conventional shadow moire. When, in the conventional arrangement, Phase-shifting that is sctually constant regardless of fringe orders is achieved by moving the grating and the light source. Finally we obtained a better result by using this procedure and applied the phase shifting shadow moire to three dimensional measurement.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1867-1870
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• 1997

A Laser Doppler Vibrometer (LDV) based on the heterodyne method was developed using He-Ne laser as a light source. The heterodyne method was employed to eliminate the ambiguity in the direction of the motion. The frequency shifted object beam (40 MHz) by a Bragg cell was focused on the surface of the moving target and the Doppler shifted reflected beam was combined at the fast photodetector to produce frequency modulated signal centered at 40 MHz. The signal from the detector was amplified, filtered and downconverted to intermediate frequency centered at 5 MHz. The voltage output that was proportional to the velocity of the moving surface was obtained using PLL. This LDV can be used to measure the resonant frequency of the electric equipments such as circuit breakers and bushings, of which resonant frequencies are changed when they are damaged.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.818-821
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• 2004

With a rapid development in the area of micro and ultra precision technology, the micro surface machining of small size parts are explosively increased. Especially, to improve efficiency of various beams in lens and reflector, non-rotational symmetric form and several mm level heights changeable surface can be machined at a time. These geometric complex 3D surface cannot be machined by general short stroke FTS. The long stroke FTS if firmly needed to move directly several mm and have nm level positioning accuracy for the complex surface form. The long stroke FTS used linear motors to drive moving unit long and fine, aero static bearings to decrease friction and moving errors in guide way, optical linear scale with nm level resolution to measure position of FTS. Furthermore, to increase the performance of acceleration of FTS, the light material, such as AL is used for the structure and the high stiffness box type structure is selected. In this paper, the genetic algorithm approach is described to determine a set of design parameters for auto tuning. The authors have attempted to model the design problem with the objective of minimizing the error, such as variable pattern change. This method can give the better alternative than existing other method.

• Nuclear Engineering and Technology
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• 제48권4호
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• pp.915-924
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• 2016

After a severe accident to the nuclear reactor, the in-vessel retention strategy is a key way to prevent the leakage of radioactive material. Nanofluid is a steady suspension used to improve heat-transfer characteristics of working fluids, formed by adding solid particles with diameters below 100nm to the base fluids, and its thermal physical properties and heat-transfer characteristics are much different from the conventional working fluids. Thus, nanofluids with appropriate nanoparticle type and volume concentration can enhance the heat-transfer process. In this study, the moving particle semi-implicit method-meshless advection using flow-directional local grid method is used to simulate the bubble growth, departure, and sliding on the downward-facing heating surface in pure water and nanofluid (1.0 vol.% $Al_2O_3/H_2O$) flow boiling processes; additionally, the bubble critical departure angle and sliding characteristics and their influence are also investigated. The results indicate that the bubble in nanofluid departs from the heating surface more easily and the critical departure inclined angle of nanofluid is greater than that of pure water. In addition, the influence of nanofluid on bubble sliding is not significant compared with pure water.

• 한국해양공학회지
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• 제30권5호
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• pp.426-430
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• 2016

Recently, many unmanned surface vehicles (USVs) have been developed and researched for various fields such as the military, environment, and robotics. In order to perform purpose specific tasks, common autonomous navigation technologies are needed. Obstacle avoidance is important for safe autonomous navigation. This paper describes a vector field histogram+ (VFH+) based obstacle avoidance method that uses the monocular vision of an unmanned surface vehicle. After creating a polar histogram using VFH+, an open space without the histogram is selected in the moving direction. Instead of distance sensor data, monocular vision data are used for make the polar histogram, which includes obstacle information. An object on the water is recognized as an obstacle because this method is for USV. The results of a simulation with sea images showed that we can verify a change in the moving direction according to the position of objects.

• 대한조선학회논문집
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• 제46권6호
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• pp.688-698
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• 2009

In this paper, the steady lift force acting on a slender body moving beneath regular wave systems of arbitrary wavelengths and directions of propagation is considered. The momentum conservation theorem and the strip method are used to obtain the hydrodynamic forces acting on the body and affecting its motions on the assumption that the body is slender. In order to obtain the vertical steady force acting on it, or the free surface suction force, the second-order hydrodynamic forces caused by mutual interactions between the components of the first-order hydrodynamic forces are averaged over time. The validity of the method is tested by comparison of the calculated results with experimental data and found to be satisfactory. Through some parametric calculations performed for a typical model, some useful results are obtained as to the depth of submergence of the body, wavelengths, directions, etc.

• Structural Engineering and Mechanics
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• 제30권2호
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• pp.165-176
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• 2008

In this paper, a new iterative method for solving vehicle-bridge interaction problems is proposed. Iterative methods have advantages over the non-iterative methods in that it is not necessary to update the system matrix for a given wheel location, and the method can be applied for a new type of car or bridge with few or no modifications. In the proposed method, the necessity of system matrices update is eliminated using the equivalent interaction force acting on the bridge, which is obtained iteratively. Ballast stiffness is included in the interaction forces and the geometric compatibility at the contact points are used as convergence criteria. The bridge is considered as an elastic Bernoulli-Euler beam with surface irregularity and ballast stiffness. The moving vehicle is modeled as a multi-axle mass-spring-damper system having many degrees of freedom depending on the number of axles. The pitching effect, which is the interaction effect between the rear and front wheels when a vehicle begins to enter or leave the bridge, is also considered in the formulation including extended ground boundaries having surface irregularity and ballast stiffness. The applicability of the proposed method is illustrated in the numerical studies.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.11-22
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• 1999

A numerical prediction method has been proposed to predict non-linear free surface oscillation in a three-dimensional container. The fluid motions are numerically predicted with Navier-Stokes equations discretized in a Lagrangian scheme with sufficient numerical accuracy. The profile of a free surface is precisely represented with three-dimensional body-fitted coordinates (BFC), which are regenerated in each computational step on the basis of the arbitrary Lagrangian-Eulerian (ALE) formulation. In order to confirm the reliability of the computational method, it was firstly applied to three-dimensional flows within complicated-shaped rigid boundaries, such as curved pipes and ducts. Than it was applied to benchmark computations related to free surface oscillations. Following these basic verifications, non-linear sloshings in a cylindrical tank and transitions from sloshing to swirling motions were numerically predicted. Throughout these computations, the applicability of the present computational method has been confirmed and some of the predicted free surface motions were visualized as sequential images and animations to understand their dynamic futures.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1538-1551
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• 1997

Kinetic energy conservation for fixed and moving grids is examined in time-accurate finite element computation of fully unsteady inviscid flows. As numerical algorithms, fractional step method (FSM) and modified SIMPLE are used. To simulate the flow in moving grid system, arbitrary Lagrangian-Eulerian (ALE) method is adopted. In the present study, the energy conserving time integration rule for finite element algorithm is proposed and discussed schematically. It is shown that the discretization by Crank-Nicolson in time and Galerkin (central difference) in space must be used to ensure energy conservation. The developed code has been tested for a standing vortex in fixed or moving grid system, sloshing in a tank and propagation of a solitary wave, and has been shown to be a completely energy conserving algorithm.