• Advances in Computational Design
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• 제9권1호
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• pp.39-52
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• 2024

If the governing differential equation arising from engineering problems is treated as an analytic, continuous and derivable function, it can be expanded by one point as a series of finite numbers. For the function to be zero for each value of its domain, the coefficients of each term of the same power must be zero. This results in a recursive relationship which, after applying the natural conditions or the boundary conditions, makes it possible to obtain the values of the derivatives of the function with acceptable accuracy. The elastoplastic analysis of an inhomogeneous thick sphere of metallic materials with linear variation of the modulus of elasticity, yield stress and Poisson's ratio as a function of radius subjected to internal pressure is presented. The Beltrami-Michell equation is established by combining equilibrium, compatibility and constitutive equations. Assuming axisymmetric conditions, the spherical coordinate parameters can be used as principal stress axes. Since there is no analytical solution, the natural boundary conditions are applied and the governing equations are solved using a proposed new method. The maximum effective stress of the von Mises yield criterion occurs at the inner surface; therefore, the negative sign of the linear yield stress gradation parameter should be considered to calculate the optimal yield pressure. The numerical examples are performed and the plots of the numerical results are presented. The validation of the numerical results is observed by modeling the elastoplastic heterogeneous thick sphere as a pressurized multilayer composite reservoir in Abaqus software. The subroutine USDFLD was additionally written to model the continuous gradation of the material.

• 대한전자공학회논문지SP
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• 제40권4호
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• pp.266-274
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• 2003

전방 관측 적외선 영상에서 가려짐이 없는 표적과 부분적으로 가려진 표적을 식별하기 위해 국부적 표적 경계선에 대한 거리함수의 푸리에기술자와 다중의 다층 퍼셉트론을 사용한 특징정보 융합 방법을 제안한다. 표적을 배경으로부터 분리한 후에 표적 경계선의 중심을 기준으로 푸리에 기술자를 구해 전역적 특징으로 사용한다. 국부적인 형상 특징을 찾기 위해 표적 경계선을 분할하여 4개의 국부적 경계선을 만들고, 각 국부적 경계선에서 두 개의 극단점이 이루는 직선과 경계선 픽셀로부터 거리함수를 정의한다. 거리함수에 대한 푸리에 기술자를 국부적 형상특징으로 사용한다. 1개의 광역적 특징 백터와 4개의 국부적 특징 백터를 정의하고 다중의 다층 퍼셉트론을 사용하여 특징정보들을 융합함으로써 최종 표적식별 결과를 얻는다. 실험을 통해 기존의 특징벡터들에 의한 표적식별 방법과 비교하여 제안한 방법의 우수성을 입증한다.

• 한국의류산업학회지
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• 제17권1호
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• pp.11-21
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• 2015

This study analyzed the expressive phenomenon of a blurred boundary in fashion jewelry focused on the relationship between fashion jewelry and costume or fashion jewelry and body. The method of this study was to analyze recent documentaries about jewelry theories in regards to 607 cases of fashion jewelry design in fashion books, fashion magazines, fashion internet sites from 2000 to 2014. The results were: First, phenomenon of blurred boundary between fashion jewelry and costume was expressed in a see-through wear form made of luxury material (gold and diamond) or paste material, a similar form (like fashion accessories made of crystal, bids, and gold chain), an integration of fashion accessories and jewelry, and an attached jewelry on fashion accessories. It reflected a rearrangement of conventional relationships, a blurred relation of function and meaning, dissolution of jewelry form stereotypes, jewelry styling, a harmony of function and decoration, and an alteration to the central role of a fashion image. Second, the phenomenon of a blurred boundary between fashion jewelry and body was expressed in a body organ wrapping, body surface adhesion and sculptural jewelry based on body pose. It reflected a separation from conventional space of jewelry expression, a realization of mystery and fantastic, an expression of new body surface and a blurred boundaries of fashion jewelry and body art. Aesthetic characteristics were analyzed into metaphor and integration by separation from the conventional relationship of fashion jewelry and costume or fashion jewelry and body.

• 대한수학회보
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• 제30권2호
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• pp.229-238
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• 1993

Let M be an n-dimensional compact Riemannian manifold with boundary .part.M. We consider the Neumann eigenvalue problem on M of the equation (Fig.) where .upsilon. is the unit outward normal vector to the boundary .part.M. due to the importance of Poincare inequality for analysis on manifolds, one wishes to obtain the lower bound of the first non-zero eigenvalue .eta.$_{1}$ of (1.1). For the purpose of applications, it is important to relax the dependency of the lower bound on the geometric quantities. For general compact manifolds with convex boundary, Li-Yau [3] obtained the lower bound of .eta.$_{1}$. Recently, Roger Chen [1] investigated the lower bound of the first Neumann eigenvalue .eta.$_{1}$ on compact manifold M with nonconvex boundary. We investigate the lower bound .eta.$_{1}$ with the same conditions as those of Roger chen. But, using the different auxiliary function, we have the following theorem.

• Journal of applied mathematics & informatics
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• 제31권1_2호
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• pp.221-228
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• 2013

The method of upper and lower solutions and the generalized quasilinearization technique is developed for the existence and approximation of solutions to boundary value problems for higher order fractional differential equations of the type $^c\mathcal{D}^qu(t)+f(t,u(t))=0$, $t{\in}(0,1),q{\in}(n-1,n],n{\geq}2$ $u^{\prime}(0)=0,u^{\prime\prime}(0)=0,{\ldots},u^{n-1}(0)=0,u(1)={\xi}u({\eta})$, where ${\xi},{\eta}{\in}(0,1)$, the nonlinear function f is assumed to be continuous and $^c\mathcal{D}^q$ is the fractional derivative in the sense of Caputo. Existence of solution is established via the upper and lower solutions method and approximation of solutions uses the generalized quasilinearization technique.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 봄 학술발표회 논문집
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• pp.137-144
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• 1994

In this study, a new procedure for solving 2-D dynamic problems of semi-infinite medium in time domain by boundary element method (BEM) is presented. Efficient modelling of the far field region, infinite boundary elements are introduced. The shape function of the infinite boundary element is a combination of decay functions and Laguerre functions. Though the present shape functions have been developed for the time domain analysis, they may be also applicable to the frequency domain analysis. Through the response analysis in a 2-D half space under a uniformly distributed dynamic load, it has been found that an excellent accuracy can be achieved compared with the analytical solution

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권1호
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• pp.83-106
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• 2016

This paper reviews and compares three different methods for modeling incompressible and immiscible ternary fluid flows: the immersed boundary, level set, and phase-field methods. The immersed boundary method represents the moving interface by tracking the Lagrangian particles. In the level set method, an interface is defined implicitly by using the signed distance function, and its evolution is governed by a transport equation. In the phase-field method, the advective Cahn-Hilliard equation is used as the evolution equation, and its order parameter also implicitly defines an interface. Each method has its merits and demerits. We perform the several simulations under different conditions to examine the merits and demerits of each method. Based on the results, we determine the most suitable method depending on the specific modeling needs of different situations.

• 제어로봇시스템학회논문지
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• 제7권5호
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• pp.393-398
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• 2001

This paper presents a new method with time-varying boundary layer and input gain, variated by Fuzzy Logic Control(FLC) by means of the system state in Sliding Mode Control (SMC). In addition to the time-varying boundary layer, the time-varying range of the fuzzy membership function has an effect on not only chattering reduction but also fast response characteristics. On the basis of SMC with time-varying boundary and FLC with time-varying input and output range, a computer simulation for inverted pendulum results in elimination of the chattering phenomenon and fast response.

• 한국대기환경학회지
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• 제13권1호
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• pp.65-77
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• 1997

A theoretical and numerical investigation on the boundary-layer flow over a two- or three-dimensional hill is presented. The numerical model is based on the finite volume method with boundary-fitted coordinates. The k-$\varepsilon$ turbulence model with modified wall function and the low-Reynolds-number model are employed. The hypothesis of Reynolds number independency for the atmospheric boundary-layer flow over aerodynamically rough terrain is confirmed by the numerical simulation. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the wind-tunnel experiments on the flow over a hill show good agreement. The linear theory provides generally good prediction of speed-up characteristics for the gentle-sloped hills. The flow separation occurs in the hill slope of 0.5 and the measured reattachment points are compared with the numerical prediction. It is found that the k- $\varepsilon$ turbulence model is reasonably accurate in predicting the attached flow, while the low- Reynolds-number model is more suitable to simulate the separated flows.ows.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1320-1326
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• 2002

In a one-dimensional heat conduction domain with heated and insulated walls, an integral approach is proposed to estimate time-dependent boundary heat flux without internal measurements. It is assumed that the expression of the heat flux is not known a priori. Hence, the present inverse heat conduction problem is classified as a function estimation problem. The spatial temperature distribution is approximated as a third-order polynomial of position, whose four coefficients are determined from the heat fluxes and the temperatures at both ends at each measurement. After integrating the heat conduction equation over spatial and time domain, respectively, a simple and non-iterative recursive equation to estimate the time-dependent boundary heat flux is derived. Several examples are introduced to show the effectiveness of the present approach.