• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.9
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• pp.431-437
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• 2001

Since the eddy current problem usually depends on the geometry of the moving conductive sheet and the shape of the pole projection area, there is no general method to find out its analytical solution. The analysis of the eddy current in a rotating disk is performed in the case of time-invariant field to find its analytical solution. As a method to solve the eddy current problem, the concept of the Coulomb charge and image method are proposed with the consideration of the boundary condition. Firstly, the line charge is obtained from the volume charge generated in the rotating disk and Coulomb's law is applied. Secondly, the finite disk radius is considered by introducing an imaginary eddy current to satisfy the boundary condition that the radial component of the eddy current is zero at the edge of the relating disk. Thirdly, the braking torque is calculated by applying Lorentz force law. Finally, the computed braking torque is compared with the measured one As a result, it can be said that the proposed model presents fairly accurate results in a low angular velocity range although a large error is observed as the angular velocity of the disk increases.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.66-74
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• 1992

A panel method in the spirit of Hess & Smith(1962), and also of Dawson(1977) was developed to compute the wave resistance of a submerged, or a surface piercing, body moving in the water of finite depth. As a boundary condition on the free surface what is called the Poisson equation is used, while Yasukawa(1989) chose the Dawson equation for which the double-body flow is regarded as the basic one. In order to satisfy the boundary condition on the bottom surface automatically, the sum of a Rankine source and its image with respect to the bottom surface is chosen as the Green function, and hence the singularity is distributed only on the body and on the free surface thereby decreasing the required number of panels dramatically, compared to that of Yasukawa, without the consequential loss of accuracy. Calculations were done for a submerged sphere and for the Wigley hull, and the results are compared with other existing analytical and numerical data.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.4
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• pp.224-230
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• 2015

This manuscript presents a real-time solution for 3D human body reconstruction with multiple RGB-D cameras. The proposed system uses four consumer RGB/Depth (RGB-D) cameras, each located at approximately $90^{\circ}$ from the next camera around a freely moving human body. A single mesh is constructed from the captured point clouds by iteratively removing the estimated overlapping regions from the boundary. A cell-based mesh construction algorithm is developed, recovering the 3D shape from various conditions, considering the direction of the camera and the mesh boundary. The proposed algorithm also allows problematic holes and/or occluded regions to be recovered from another view. Finally, calibrated RGB data is merged with the constructed mesh so it can be viewed from an arbitrary direction. The proposed algorithm is implemented with general-purpose computation on graphics processing unit (GPGPU) for real-time processing owing to its suitability for parallel processing.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.3
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• pp.58-71
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• 2022

Analytical solutions for two-dimensional velocities of regular waves generated by bottom wave makers in a flume were derived in this study. Triangular and rectangular bottom wave makers were adopted. The velocity potential was derived based on the linear wave theory with the bottom moving boundary condition, kinematic and dynamic free surface boundary conditions. Then, analytical solutions of two-dimensional particle velocities were derived from the velocity potential. The velocity potential and two-dimensional particle velocities which were derived as complex integral equations were numerically calculated. The solutions showed physically valid results as velocities of regular waves generated by bottom wave makers in a flume.

• Smart Structures and Systems
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• v.31 no.1
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• pp.29-43
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• 2023

This study investigates the possibility of damage detection of a real bridge by means of a modal parameter-based finite element (FE) model update. Field moving vehicle experiments were conducted on an actual steel plate girder bridge. In the damage experiment, cracks were applied to the bridge to simulate damage states. A fast Bayesian FFT method was employed to identify and quantify uncertainties of the modal parameters then these modal parameters were used in the Bayesian model update. Material properties and boundary conditions are taken as uncertainties and updated in the model update process. Observations showed that although some differences existed in the results obtained from different model classes, the discrepancy between modal parameters of the FE model and those experimentally obtained was reduced after the model update process, and the updated parameters in the numerical model were indeed affected by the damage. The importance of boundary conditions in the model updating process is also observed. The capability of the MCMC model update method for application to the actual bridge structure is assessed, and the limitation of FE model update in damage detection of bridges using only modal parameters is observed.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.24-33
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• 2023

This work is to observe the wake flow generated behind a ramp. We have conducted a large eddy simulation with two ramp models having different heights with two different inflow conditions. Reynolds number based on the height of the large ramp (LR) and small ramp (SR) are Re_h = 2.8×10⁴ and 1.4×10⁴ respectively. The wake flow visualization shows the formation of streamwise counter-rotating vortices pairs at the downstream of the obstacle. These primary vortices are stretched and lifted up when moving downstream. In order to observe the effect of the inflow condition on the wake transition, two different inlet flow conditions are given on the inlet section as an inlet boundary condition. Induced counter-rotating vortices pairs due to sharp-edged triangular ramp obstacles are developed and propagated downstream. In the result, the large ramp shows a more complicated wake structure of the boundary layer than the small ramp.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8C
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• pp.1175-1183
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• 2004

This paper propose a method to trace a moving object based on the information directly obtained from MPEG-2 compressed video stream without decoding process. In the proposed method, the motion flow is constructed from the motion vectors involved in compressed video and then we calculate the amount of pan, tilt, zoom associated with camera operations using generalized Hough transform. The local object motion can be extracted from the motion flow after the compensation with the parameters related to the global camera motion. The moving object is designated initially by a user via bounding box. After then automatic tracking is performed based on the mean-shift algorithm of the motion flows of the object. The proposed method can improve the computation speed because the information is directly obtained from the MPEG-2 compressed video, but the object boundary is limited by blocks rather than pixels.

• The KIPS Transactions:PartB
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• v.16B no.5
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• pp.367-376
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• 2009

In this paper, we propose a flame detection method using Haar wavelet and moving averages in outdoor infrared video sequences. Our proposed method is composed of three steps which are Haar wavelet decomposition, flame candidates detection, and their tracking and flame classification. In Haar wavelet decomposition, each frame is decomposed into 4 sub- images(LL, LH, HL, HH), and also computed high frequency energy components using LH, HL, and HH. In flame candidates detection, we compute a binary image by thresholding in LL sub-image and apply morphology operations to the binary image to remove noises. After finding initial boundaries, final candidate regions are extracted using expanding initial boundary regions to their neighborhoods. In tracking and flame classification, features of region size and high frequency energy are calculated from candidate regions and tracked using queues, and we classify whether the tracked regions are flames by temporal changes of moving averages.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.493-499
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• 2007

The Taylor expansion expresses a differentiable function and its coefficients provide good approximations for the given function and its derivatives. In this study, m-th order Taylor Polynomial is constructed and the coefficients are computed by the Moving Least Squares method. The coefficients are applied to the governing partial differential equation for solid problems including crack problems. The discrete system of difference equations are set up based on the concept of point collocation. The developed method effectively overcomes the shortcomings of the finite difference method which is dependent of the grid structure and has no approximation function, and the Galerkin-based meshfree method which involves time-consuming integration of weak form and differentiation of the shape function and cumbersome treatment of essential boundary.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.2
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• pp.195-203
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• 2018

Among the techniques of reducing the drag to increase the speed of underwater moving bodies, we studied on the drag reduction method by gas injection. Researches on gas injection method have been paid much attention to reduce the drag of vessels or pipe inner walls. In this study, we used a sintered metal mesh that can uniformly distribute fine bubbles by gas injection method, and applied it to a cylindrical underwater moving body. Using the KRISO medium-sized cavitation tunnel, we measured both the bubble size on the surface of the sintered mesh and the bubble distribution in the boundary layer. Then, drag reduction tests were performed on the cylinder type underwater moving models with cylindrical or round type tail shape. Experiments were carried out based on the presence or absence of tail jet injection. In the experiments, we changed the gas injection amount using the sintered mesh gas injector, and changed flow rate accordingly. As a result of the test, we observed increased bubbles around the body and confirmed the drag reduction as air injection flow rate increased.