• Title/Summary/Keyword: boundary method

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Watermarking Technique using Image Characteristics

  • Jung, Soo-Mok
    • International Journal of Internet, Broadcasting and Communication
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    • v.13 no.1
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    • pp.187-193
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    • 2021
  • In this paper, we propose an image watermarking technique that effectively hides confidential data in the LSB of image pixels by utilizing the characteristics of the image. In the proposed technique, the image is precisely divided into boundary surface and normal region other than the boundary surface and performs different processing. The boundary surface existing in the image is created by meeting different regions and contains important information of the image. One bit of confidential data is concealed in the LSB of the pixel at the boundary surface to preserve the characteristics of the boundary surface. In normal region other than the boundary surface, the pixel values are similar, and the change with the adjacent pixel values is smooth. Based on this property, even if the 2 bits of confidential data are hidden in the lower 2 bits of the pixel in the normal region, the difference cannot be visually distinguished. When confidential data is concealed in an image as described above, the amount of confidential data concealed in an image can be increased while maintaining excellent image quality. Concealing confidential data by applying the proposed method increases the amount of confidential data concealed by up to 84.6% compared to the existing method. The proposed technique can be effectively used for commercial image watermarking that hides copyright information.

Nonlinear primary resonance of functionally graded doubly curved shells under different boundary conditions

  • Jinpeng Song;Yujie He;Gui-Lin She
    • Steel and Composite Structures
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    • v.50 no.2
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    • pp.149-158
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    • 2024
  • Considering that different boundary conditions can have an important impact on structural vibration characteristics. In this paper, the nonlinear forced vibration behavior of functionally graded material (FGM) doubly curved shells with initial geometric imperfections under different boundary conditions is studied. Considering initial geometric imperfections and von Karman geometric nonlinearity, the nonlinear governing equations of FGM doubly curved shells are derived using Reissner's first order shear deformation (FOSD) theory. Three different boundary conditions of four edges simply supported (SSSS), four edges clamped (CCCC), clamped-clamped-simply-simply (CCSS) were studied, and a system of nonlinear ordinary differential equations was obtained with the help of Galerkin principle. The nonlinear forced vibration response of the FGM doubly curved shell is obtained by using the modified Lindstedt Poincare (MLP) method. The accuracy of this method was verified by comparing it with published literature. Finally, the effects of curvature ratio, power law index, void coefficient, prestress, and initial geometric imperfections on the resonance of FGM doubly curved shells under different boundary conditions are fully discussed. The relevant research results can provide certain guidance for the design and application of doubly curved shell.

A Back-Analysis of Tunnels in Multi-Layered Underground Structures (다층구조계내 터널 거동의 역해석)

  • 전병승;이상도;나경웅;김문겸
    • Tunnel and Underground Space
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    • v.4 no.1
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    • pp.17-23
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    • 1994
  • This study consists of two procedures on back analysis and forward analysis which is a basic tool of the former. For a safe and economical construction of underground structures, it is required to identify the structural parameters and analyze the structural behavior as exactly as possible. In this paper, a boundary element method to analyze the behavior of multi-alyered underground structures is studied, in which body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are considered. That is, each layer is discritized into subregions using infinite fundamental solutions, and terms of body forces and initial stresses are transformed into boundary integral where the applied direct integral method is used. And the system of equations containing body forces and initial stresses are composed, then the method to solve unknowns is used with applying compatibility and equilibrium conditions between interfaces. As well, the direct search method is applied in back analysis problems. By Powell's method as a technique to search unknown parameters, assuming displacements calculated from boundary element analysis as in-situ displacements, elastic moduli and initial stresses are presumed. As consequences of this study, the results of boundary element analysis of the behavior of multilayered structure considering body forces and initial stresses are agreed with those of finite element analysis. And results of back analysis of elastic moduli and initial stresses in each layers are agreed with exact values with a little difference. Therefore, it is known that this study can be efficiently applied for analyzing the behavior of underground structures including back analysis problems.

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Numerical Study on Flow over Moving Circular Cylinder Near the Wall Using Immersed Boundary Lattice Boltzmann Method (가상경계 격자볼쯔만법을 이용한 벽면에 근접하여 이동하는 실린더주위의 유동해석)

  • Kim, Hyung-Min
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.12
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    • pp.924-930
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    • 2008
  • Immersed boundary method (IBM) is the most effective method to overcome the disadvantage of LBM (Lattice Boltzmann Method) related to the limitation of the grid shape. IBM also make LBM possible to simulate flow over complex shape of obstacle without any treatment on the curved boundary. In the research, IBLBM was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of IBLBM on the moving obstacle near the wall, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of moving cylinder in the channel using IBLBM. The simulations were performed in a moderate range of Reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag and lift coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical Reynolds number for vortex shedding is Re=50 and the result is the same as the case of fixed cylinder. As the cylinder approaching to a wall (${\gamma}<2.5$), the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. When the cylinder is very closed to the wall, ${\gamma}<0.6$, the cylinder acts like blockage to block the flow between the cylinder and wall so that the vortex developed on the upper cylinder elongated and time averaged lifting and drag coefficients abruptly increase.

Vibration Regulations and Damages Evaluation Method for Human (인체에 대한 진동의 허용 기준 및 피해 산정에 관한 연구)

  • 양형식;전양수;이경운
    • Tunnel and Underground Space
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    • v.7 no.4
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    • pp.310-322
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    • 1997
  • New limits of comfort boundary, psychological damage boundary and exposure limit for building residents by continuous and vibration are suggested. These limits are derived from the ISO 2631 and DIN 4150 regulations. A reasonable method to evaluate damages by vibrations is also suggested using the "total over-exposure of vibration" concept.; concept.

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Stress Analysis of the Thin Intersected Axe Gear By 3-DM Boundary Element Methed. (삼차원 경계요소법에 의한 박육직교축 치차의 응력 해석)

  • 장지연
    • Journal of Advanced Marine Engineering and Technology
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    • v.14 no.1
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    • pp.72-82
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    • 1990
  • It is impossible to directly analyse stress distribution on thin bevel Gear. On this Paper, the author propose a method to analyse the stress of thin bevel gear boundary element method and develope a computer program. The propriety of this program is verified by comparing the numerical calculating results with theoretical results.

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