• Title/Summary/Keyword: n-coupling problem

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GRADIENT PROJECTION METHODS FOR THE n-COUPLING PROBLEM

  • Kum, Sangho;Yun, Sangwoon
    • Journal of the Korean Mathematical Society
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    • v.56 no.4
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    • pp.1001-1016
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    • 2019
  • We are concerned with optimization methods for the $L^2$-Wasserstein least squares problem of Gaussian measures (alternatively the n-coupling problem). Based on its equivalent form on the convex cone of positive definite matrices of fixed size and the strict convexity of the variance function, we are able to present an implementable (accelerated) gradient method for finding the unique minimizer. Its global convergence rate analysis is provided according to the derived upper bound of Lipschitz constants of the gradient function.

Design and Fabrication of Side-illuminated p-i-n Photodetectors with High Responsivity and Coupling Tolerance (높은 Responsivity와 광결합 공차를 가지는 면입사형 p-i-n 광검출소자의 설계 및 제작)

  • 이도영;강화영;전병옥;양승기;이은화;김태진;장동훈;김태일
    • Proceedings of the Optical Society of Korea Conference
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    • 2003.07a
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    • pp.104-105
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    • 2003
  • We have fabricated a side-illuminated p-i-n photodetectors with evanescently-coupled waveguides for surface hybrid integration in low-cost modules. We adopted WGPD of evanescently-coupled type to have high responsivity and coupling tolerance, and to avoid any reliability problem. This proposed photodetectors have a high responsivity of 1.10 A/W at a wavelength of 1.55 ${\mu}{\textrm}{m}$. The 1dB coupling tolerance to cleaved fiber and photodetectors is $\pm$3.5 ${\mu}{\textrm}{m}$ in the vertical direction and $\pm$11 ${\mu}{\textrm}{m}$ in the horizontal direction.

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A P-HIERARCHICAL ERROR ESTIMATOR FOR A FEM-BEM COUPLING OF AN EDDY CURRENT PROBLEM IN ℝ3 -DEDICATED TO PROFESSOR WOLFGANG L. WENDLAND ON THE OCCASION OF HIS 75TH BIRTHDAY

  • Leydecker, Florian;Maischak, Matthias;Stephan, Ernst P.;Teltscher, Matthias
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.17 no.3
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    • pp.139-170
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    • 2013
  • We extend a p-hierarchical decomposition of the second degree finite element space of N$\acute{e}$d$\acute{e}$lec for tetrahedral meshes in three dimensions given in [1] to meshes with hexahedral elements, and derive p-hierarchical decompositions of the second degree finite element space of Raviart-Thomas in two dimensions for triangular and quadrilateral meshes. After having proved stability of these subspace decompositions and requiring certain saturation assumptions to hold, we construct a local a posteriori error estimator for fem and bem coupling of a time-harmonic electromagnetic eddy current problem in $\mathbb{R}^3$. We perform some numerical tests to underline reliability and efficiency of the estimator and test its usefulness in an adaptive refinement scheme.

A Study on the Relationship between the Cutting Force and the Critical Ejecting Distance of Disk for a Mill Turret (복합공구대 디스크임계돌출거리와 절삭력과의 관계에 관한 연구)

  • Choi, Ji-Hwan;Kim, Chae-Sil;Cho, Su-Yong
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.12 no.1
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    • pp.110-116
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    • 2013
  • Curvic coupling of mill turret should maintain disk weight and the cutting resistance which occurs the machining operation and must also have power transmission function. In order to improve machining operation range, the ejecting distance from curvic coupling to the disk must increase as much as possible. But moment is increased by the lack of capacity of the curvic coupling. Increase of moment is the cause of vibration/noise and degradation of machining performance not only stability problem. The manufacturer of mill turret has no the design information between the ejecting distance and the cutting resistance with safety of curvic coupling. Therefore this study describes a finite element analysis model of mill turret using ANSYS workbench. The structural analyses and modal analyses with varying of the ejecting distances and cutting resistances are performed. Finally the equation for relationship between the critical ejecting distance and the cutting resistance is defined under 5 of the safety factor for the maximum von-Mises stress at the curvic coupling.

Numerical Investigation of Purcell Enhancement of the Internal Quantum Efficiency of GaN-based Green LED Structures

  • Choi, Young-Hwan;Ryu, Guen-Hwan;Ryu, Han-Youl
    • Current Optics and Photonics
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    • v.1 no.6
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    • pp.626-630
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    • 2017
  • GaN-based green light-emitting diode (LED) structures suffer from low internal quantum efficiency (IQE), known as the "green gap" problem. The IQE of LED structures is expected to be improved to some extent by exploiting the Purcell effect. In this study, the Purcell effect on the IQE of green LED structures is investigated numerically using a finite-difference time-domain simulation. The Purcell factor of flip-chip LED structures is found to be more than three times as high as that of epi-up LED structures, which is attributed to the high-reflectance mirror near the active region in the flip-chip LED structures. When the unmodified IQE is 20%, the relative enhancement of IQE can be greater than 50%, without utilizing the surface-plasmon coupling effect. Based on the simulation results, the "green gap" problem of GaN-based green LEDs is expected to be mitigated significantly by optimizing flip-chip LED structures to maximize the Purcell effect.

Flood Impact Pressure Analysis of Vertical Wall Structures using PLIC-VOF Method with Lagrangian Advection Algorithm

  • Phan, Hoang-Nam;Lee, Jee-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.6
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    • pp.675-682
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    • 2010
  • The flood impact pressure acting on a vertical wall resulting from a dam-breaking problem is simulated using a navier-Stokes(N-S) solver. The N-S solver uses Eulerian Finite Volume Method(FVM) along with Volume Of Fluid(VOF) method for 2-D incompressible free surface flows. A Split Lagrangian Advection(SLA) scheme for VOF method is implemented in this paper. The SLA scheme is developed based on an algorithm of Piecewise Linear Interface Calculation(PLIC). The coupling between the continuity and momentum equations is affected by using a well-known Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. Several two-dimensional numerical simulations of the dam-breaking problem are presented to validate the accuracy and demonstrate the capability of the present algorithm. The significance of the time step and grid resolution are also discussed. The computational results are compared with experimental data and with computations by other numerical methods. The results showed a favorable agreement of water impact pressure as well as the global fluid motion.

Numerical Analysis of Solidification and Melting Phase Change Using Modified PISO algorithm (수정된 PISO 알고리즘을 이용한 응고 및 융해 현상의 수치해석)

  • Kang K. G;Ryou H. S;Hur N.
    • Journal of computational fluids engineering
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    • v.8 no.3
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    • pp.12-20
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    • 2003
  • A numerical procedure for the calculation of solidification and melting phase change using PISO algorithm is presented. In case of phase change problem, the coupling between velocity/pressure/temperature and liquid fraction is important. The converged temperature and liquid fraction solution which satisfies the energy balance is acquired by applying enthalpy method into inner iteration in matrix solver. And a modified PISO algorithm version is introduced to properly solve the coupling between velocity/pressure/temperature and liquid fraction. A comparison of the proposed procedure with a standard iterative method shows improvement both in terms of computing speed and robustness.

Influence of Initial Diameter on the Combustion Characteristics of n-heptane Droplet (초기 직경이 n-heptane 액적 연소 특성에 미치는 영향)

  • Suh, Hyun Kyu
    • Journal of ILASS-Korea
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    • v.18 no.2
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    • pp.94-99
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    • 2013
  • The spherically-symmetric burning of an isolated droplet is a dynamic problem that involves the coupling of chemical reactions and multi-phase flow with phase change. For the improved understanding of these phenomena, this paper presents the numerical results on the n-heptane droplet combustion conducted at a 1 atm ambient pressure in three different initial droplet diameter ($d_0$). The main purpose of this study is to provide basic information of droplet burning, extinction and flame behavior of n-heptane and improve the ability of theoretical prediction of these phenomena. To achieve these, the numerical analysis was conducted in terms of normalized droplet diameter ($d/d_0$), flame diameter ($d_f$) and flame standoff ratio (FSR) under the assumptions that the droplet combustion can be described by both the quasi-steady behavior for the region between the droplet surface and the flame interface and the transient behavior for the region between the flame interface and ambient surrounding.

Urban Inundation Modeling and Its Damage Evaluation Based on Loose-coupling GIS (Loose-coupling GIS기반의 도시홍수 모의 및 피해액산정)

  • Kang, Sang-Hyeok
    • Spatial Information Research
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    • v.18 no.1
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    • pp.49-56
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    • 2010
  • Considering the flood problem in urban areas, it is important to estimate disaster risk using accurate numerical analysis for inundation. In this study, it is carried out to calculate inundation depth in Samcheok city which suffered from serious flood damage in 2002. The urban flood model was developed by cording Manning n, elevation, and building's rare on ArcGIS for reducing error on data exchange, and applied for estimating flood damage by grid. This paper describes the extraction of sewer lines and buildings area, estimates its influence on flood inundation extent, and integrated 1D/2D flow to simulate inundation depth in high-density building area. This paper shows an integrated urban flood modeling including rainfall-runoff, inundation simulation, and mathematical flood damage estimation, and will serve drainage design for reducing its damage.

Device Miniaturization using Butterfly Grating-Assisted MMI Couplers (나비형 격자구조 다중모드 간섭 결합기를 사용한 소자의 소형화)

  • Ho, Kwang-Chun
    • Korean Journal of Optics and Photonics
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    • v.19 no.1
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    • pp.25-30
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    • 2008
  • In this paper, a novel architecture for device miniaturization of multimode interference-based (MMI) couplers is proposed. The coupling length of $N{\times}N$ MMI couplers scales as the square of the MMI region width so that the use of these structures with large-N ports can require large chip size. To solve the design problem, the butterfly grating-assisted MMI couplers, that have smaller device dimensions than conventional MMI couplers, are discussed and evaluated. Numerical simulations and novel design rules for such structures derived through theoretical analysis are presented.