• Structural Engineering and Mechanics
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• 제59권5호
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• pp.901-920
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• 2016

MeshFree methods have become popular owing to the ease with which high stress gradients can be identified and node density distribution can be reformulated to accomplish faster convergence. This paper presents a strategy for nodal density refinement with strain energy as basis in Element-Free Galerkin MeshFree technique. Two popular flat plate problems are considered for the demonstration of the proposed strategies. Issue of integration errors introduced during nodal density refinement have been addressed by suggesting integration cell refinement. High stress effects around two symmetrical semi-circular notches under in-plane axial load have been addressed in the first problem. The second considers crack propagation under mode I and mode II fracture loading by the way of introducing high stress intensity through line crack. The computational efficacy of the adaptive refinement strategies proposed has been highlighted.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.135-145
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• 2023

This study presents the free vibrational responses of bi-directional axially graded cylindrical shell panels using 3D graded finite element approximation under a temperature field. The cylindrical shell panel is graded in two directions and made of metal-ceramic materials. To extract material properties, the Voigt model is combined with a Power-law material distribution. Convergence and validation studies are performed on the developed computational model to ensure its accuracy and effectiveness. Furthermore, a parametric study is performed to evaluate the developed model, which demonstrates that geometrical parameters, imperfect materials (porosity), support conditions, and surface temperature all have a significant impact on the free vibration responses of a bi-directional axially graded cylindrical shell panel in a thermal environment.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1458-1465
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• 2003

An eigenvalue analysis of the circular Mindlin plates with free boundary conditions is presented. The analysis is based on the Chebyshev-Fourier pseudospectral method. Even though the eigenvalues of lower vibration modes tend to convergence more slowly than those of higher vibration modes, the eigenvalues converge for sufficiently fine pseudospectral grid resolutions. The eigenvalues of the axisymmetric modes are computed separately. Numerical results are provided for different grid resolutions and for different thickness-to-radius ratios.

• Journal of applied mathematics & informatics
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• 제16권1_2호
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• pp.165-181
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• 2004

Based on Landau-type transformation, a Stefan problem with non-linear free boundary condition is transformed into a system consisting of parabolic equation and the ordinary differential equations. Semidiscrete approximations are constructed. Optimal orders of convergence of semidiscrete approximation in $L_2$, $H^1$ and $H^2$ normed spaces are derived.

• 한국융합학회논문지
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• 제11권5호
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• pp.209-217
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• 2020

본 연구의 배경은 드론 시장이 거대해짐에 따라 정부는 '드론 촬영 자유구역 지정'을 논의하고 있으나 법 제도 및 절차, 관련 환경요건들이 상충되거나 명확하지 않아 선행되어야 할 요건들을 정립할 필요성이 제기되었다. 연구목적은 촬영 불가지역 범위를 설정하고 자유구역 지정 및 절차에 관한 선결조건을 제시하는 것이다. 연구방법은 문헌연구를 통해 설문서 구성, 인터뷰를 통해 항목 구체화, 전문가 선택 및 참여자 토의를 통해 조건을 제시한다. 연구결과는 항공안전법 등 개정 2개, 자유구역 지정 기준 및 절차 8개, 안내소 운용 등 4개를 도출하였다. 기대효과는 첫째, 드론 촬영을 항공안전법에 포함으로 자유구역 지정에 관하여 국토부와 협의체 구성이 가능하다. 둘째, 촬영금지 영역을 공중까지 확대하여 입체적인 드론 보안이 가능하다. 셋째, 자유구역 지정을 쉽게 적용할 수 있도록 '용인지역 표준모델'을 제시하였다. 향후 연구방향은 드론 촬영 관련 항공안전법 우선 개정과 국가정보원과 연계한 33개 관할지역의 자유구역지정 절차를 준용하여 추진이 필요하다.

• 대한수학회논문집
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• 제12권2호
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• pp.467-478
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• 1997

A nonlinear Galerkin method for the Burgers equation is considered. Due to the lack of the divergence free condition, the nonlinear term is treated differently compared to that of the Navier-Stokes equations. Strong convergence results are proved for the nonlinear Galerkin method.

• ETRI Journal
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• 제29권6호
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• pp.835-837
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• 2007

A multi-bit sigma-delta modulator architecture is described for low-distortion performance and a high-speed operation. The proposed architecture uses both a delayed code and a delayed differential code of analog-to-digital converter in the feedback path, thereby suppressing signal components in the integrators and relaxing the timing requirement of the analog-to-digital converter and the scrambler logic. Implemented by a 0.13 ${\mu}m$ CMOS process, the sigma-delta modulator achieves high linearity. The measured spurious-free dynamic range is 89.1 dB for -6 dBFS input signal.

• 한국전산유체공학회지
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• 제19권4호
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• pp.20-28
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• 2014

An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.

• 한국초등과학교육학회지:초등과학교육
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• 제39권2호
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• pp.243-254
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• 2020

This study analyzed the characteristics of "free inquiry" products for scientifically-gifted elementary school students. To do this, 5~6 graders (n=99) at a gifted science education institutes in Seoul were selected. The products (n=82) of "free inquiry" submitted by the students in 2018 and 2019 were analyzed according to their contents and method types. The analysis of the results showed that the free inquiry outputs of scientifically-gifted students tended to not include the scientific knowledge of the upper grades than the corresponding students. In the outputs, the scientific knowledge in different grades were often not linked. There were relatively many cases of convergence of knowledge in various science and/or non-science subjects and knowledge of 'physics', whereas knowledge of 'earth science' were the least. The outputs were more often aimed at "finding scientific facts" than "development and invention" and tended to target non-living things rather than living things. The scientifically-gifted students tended to conduct free inquiry using 'experimental-centered inquiry' by themselves rather than by group. They were also most likely to conduct experiments only once, and did not clearly write down the period of their inquiry. Educational implications of these findings are discussed.

• Ocean Systems Engineering
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• 제6권4호
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• pp.363-375
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• 2016

Large numbers of submarine pipelines are laid as the world now is attaching great importance to offshore oil exploitation. Free spanning of submarine pipelines may be caused by seabed unevenness, change of topology, artificial supports, etc. By combining Iwan's wake oscillator model with the differential equation which describes the vibration behavior of free-span submarine pipelines, the pipe-fluid coupling equation is developed and solved in order to study the effect of both internal and external fluid on the vibration behavior of free-span submarine pipelines. Through generalized integral transform technique (GITT), the governing equation describing the transverse displacement is transformed into a system of second-order ordinary differential equations (ODEs) in temporal variable, eliminating the spatial variable. The MATHEMATICA built-in function NDSolve is then used to numerically solve the transformed ODE system. The good convergence of the eigenfunction expansions proved that this method is applicable for predicting the dynamic response of free-span pipelines subjected to both internal flow and external current.