• Nonlinear Functional Analysis and Applications
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• 제29권1호
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• pp.225-258
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• 2024

In this paper, we study the problem of finding a common solution to a fixed point problem involving a finite family of ρ-demimetric operators and a split monotone inclusion problem with monotone and Lipschitz continuous operator in real Hilbert spaces. Motivated by the inertial technique and the Tseng method, a new and efficient iterative method for solving the aforementioned problem is introduced and studied. Also, we establish a strong convergence result of the proposed method under standard and mild conditions.

• International Journal of Concrete Structures and Materials
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• 제2권2호
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• pp.123-136
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• 2008

A new plastic-damage constitutive model applicable to lightweight concrete (LWC) and normal weight concrete (NWC) is proposed in this paper based on both continuum damage mechanics and plasticity theories. Two damage variables are used to represent tensile and compressive damage independently. The effective stress is computed in the Drucker-Prager multi-surface plasticity framework. The stress is then computed by multiplication of the damaged part and the effective part. The proposed model is coded as a user material subroutine and incorporated in a finite element analysis software. The constitutive integration algorithm is implemented by adopting the operator split involving elastic predictor, plastic corrector and damage corrector. The numerical study shows that the algorithm is efficient and robust in the finite element analysis. Experimental investigation is conducted to verify the proposed model involving both static and dynamic tests. The very good agreement between the numerical results and experimental results demonstrates the capability of the proposed model to capture the behaviors of LWC and NWC structures for static and impact loading.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.885-892
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• 2009

This manuscript will discuss a numerical method where the six equations of two-phase flow, the solid heat conduction equations, and the two equations that describe neutron diffusion and precursor concentration are solved together in a tightly coupled, nonlinear fashion for a simplified model of a nuclear reactor core. This approach has two important advantages. The first advantage is a higher level of accuracy. Because the equations are solved together in a single nonlinear system, the solution is more accurate than the traditional "operator split" approach where the two-phase flow equations are solved first, the heat conduction is solved second and the neutron diffusion is solved third, limiting the temporal accuracy to $1^{st}$ order because the nonlinear coupling between the physics is handled explicitly. The second advantage of the method described in this manuscript is that the time step control in the fully implicit system can be based on the timescale of the solution rather than a stability-based time step restriction like the material Courant limit required of operator-split methods. In this work, a pilot code was used which employs this tightly coupled, fully implicit method to simulate a reactor core. Results are presented from a simulated control rod movement which show $2^{nd}$ order accuracy in time. Also described in this paper is a simulated rod ejection demonstrating how the fastest timescale of the problem can change between the state variables of neutronics, conduction and two-phase flow during the course of a transient.

• Nonlinear Functional Analysis and Applications
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• 제26권3호
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• pp.451-474
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• 2021

In this paper, we investigate a hybrid algorithm for finding zeros of the sum of maximal monotone operators and Lipschitz continuous monotone operators which is also a common fixed point problem for finite family of relatively quasi-nonexpansive mappings and split feasibility problem in uniformly convex real Banach spaces which are also uniformly smooth. The iterative algorithm employed in this paper is design in such a way that it does not require prior knowledge of operator norm. We prove a strong convergence result for approximating the solutions of the aforementioned problems and give applications of our main result to minimization problem and convexly constrained linear inverse problem.

• Coupled systems mechanics
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• 제5권2호
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• pp.145-156
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• 2016

An efficient and general numerical strategy for fluid-structure interaction problems is presented where either the fluid or the structure part are represented by nonlinear models. This partitioned strategy is implemented under the form of code coupling that allows to (re)-use previous made developments in a more general multi-physics context. This strategy and its numerical implementation is verified on classical fluid-structure interaction benchmarks, and then applied to the impact of tsunamis waves on submerged structures.

• 대한수학회지
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• 제34권1호
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• pp.87-118
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• 1997

This paper is concerned with a mixed Lagrangian formulation of the wiscous, stationary, incompressible Navier-Stokes equations $$ (1.1) -\nu\Delta u + (u \cdot \nabla)u + \nabla_p = f in \Omega $$ and $$ (1.2) \nubla \cdot u = 0 in \Omega $$ along with inhomogeneous Dirichlet boundary conditions on a portion of the boundary $$ (1.3) u = ^{0 on \Gamma_0 _{g on \Gamma_g, $$ where $\Omega$ is a bounded open domain in $R^d, d = 2 or 3$, or with a boundary $\Gamma = \partial\Omega$, which is composed of two disjoint parts $\Gamma_0$ and $\Gamma_g$.

• 한국컴퓨터정보학회논문지
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• 제17권7호
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• pp.67-76
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• 2012

본 논문에서는 보행자에 장착된 카메라로부터 입력된 자연영상에서 외부 환경 변화에 강인한 적응적인 보도 경계선 검출 기법을 제안한다. 제안하는 방법은 두 단계로 구성되어 안정적으로 보도 영역을 분할한다. 첫 번째 단계에서는 복잡한 외부 환경에 강인하도록 적응적인 임계치를 이용하는 에지 검출 방법을 통해 소실선과 소실점을 추출한다. 두 번째 단계에서는 소실점에 기반하는 VRay를 이용한 방사형 영역 분할법을 통해 보도의 경계선을 검출한다. 성능평가를 위해서는제안된 에지 검출 방법과 케니 에지 검출기와의 비교를통해 제안된 방법이 외부 환경의 조명조건 변화에 강건함을 확인하였으며, VRay의 가상 광선의 길이 변화에 따른 영역분할 결과를 비교하여 방사형 영역 분할법의 타당성을 입증하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권1호
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• pp.27-41
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• 2014

In this paper, we present an efficient numerical method for multiphase image segmentation using a multiphase-field model. The method combines the vector-valued Allen-Cahn phase-field equation with initial data fitting terms containing prescribed interface width and fidelity constants. An efficient numerical solution is achieved using the recently developed hybrid operator splitting method for the vector-valued Allen-Cahn phase-field equation. We split the modified vector-valued Allen-Cahn equation into a nonlinear equation and a linear diffusion equation with a source term. The linear diffusion equation is discretized using an implicit scheme and the resulting implicit discrete system of equations is solved by a multigrid method. The nonlinear equation is solved semi-analytically using a closed-form solution. And by treating the source term of the linear diffusion equation explicitly, we solve the modified vector-valued Allen-Cahn equation in a decoupled way. By decoupling the governing equation, we can speed up the segmentation process with multiple phases. We perform some characteristic numerical experiments for multiphase image segmentation.

• 대한교통학회지
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• 제27권6호
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• pp.157-166
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• 2009

교통망설계문제(network design problem, NDP)는 교통체계(transportation system)을 최적화시키는 설계변수(design parameter, design variable)를 구하는 문제이다. 본 연구에서는 교통망설계문제를 조금 변환시킨 목표지향 교통망설계문제(target-oriented network design problem, target-oriented NDP)를 제시하고 이를 풀기 위한 기법도 제시한다. 목표지향 교통망설계는 교통운영자(traffic operator) 또는 관리자(travel manager)가 특정 교통정책 목표(target)를 미리 설정하고 이를 달성하기 위한 최적 설계변수를 찾는 문제이다. 즉, 일반적인 교통망설계문제(general NDP)는 총통행비용이나 순편익 등 특정목적함수를 최적화시키는 설계변수를 찾는데 반해, 목표지향 교통망설계(target NDP)는 사전에 설정된 목표수준(target level)을 달성하기 위한 설계변수를 구하는 문제이다. 본 연구에서 제시된 목표지향 교통망설계모형을 교통수단분담문제에 적용하여 모형을 평가한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.689-694
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• 1994

In this paper, to develop a smart CAD/CAM system for systematically performing from the 3-D solid shape design of products to the CNC cutting operation of products by a machining center, a B-Rep solid modeler is realized based on the half edge data structure. Because the B-Rep solid modeler has the various capabilities related to the solid definition functions such as the creation operation of primitives and the translational and rotational sweep operation, the solid manipulation functions such as the split operation and the Boolean set operation, and the solid inversion function for effectively using the data structure, the 3-D solid shape of products can be easily designed and constructed. Also, besides the automatic generation of CNC code, the B-Rep solid modeler can be used as a powerful tool for realizing the automatic generation of finite elements, the interference check between solids, the structural design of machine tools and robots and so on.