• 한국정밀공학회지
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• 제15권5호
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• pp.120-127
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• 1998

Differential inequalities occurring in problems of obstacle contact problems are recast into variational inequalities and analyzed by finite element methods. A new a posteriori error estimator, which is essential in adaptive finite element method, is introduced to capture the errors in finite element approximations of these variational inequalities. In order to construct a posteriori error estimates, saddle point problems are introduced using Lagrange parameters and upper bounds are provided. The global upper bound is localized by a special mixed formulation, which leads to upper bounds of the element errors. A numerical experiment is performed on an obstacle contact problem to check the effectivity index both in a local and a global sense.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제27권4호
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• pp.245-271
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• 2023

In this paper we discuss some recovery of H(div)-conforming flux approximations from the equilibrated fluxes of Ainsworth and Oden for quadratic finite element methods of second-order elliptic problems. Combined with the hypercircle method of Prager and Synge, these flux approximations lead to a posteriori error estimators which provide guaranteed upper bounds on the numerical error. Furthermore, we prove some superconvergence results for the flux approximations and asymptotic exactness for the error estimator under proper conditions on the triangulation and the exact solution. The results extend those of the previous paper for linear finite element methods.

• The Journal of the Acoustical Society of Korea
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• 제18권1E호
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• pp.3-6
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• 1999

In digital mobile communication system, the transmission errors affect the quality of output speech seriously. There are many error concealment techniques using a posteriori probability which provides information about any transmitted parameter. They need knowledge about channel transition probability as well as the 1st order Markov transition probability of codec parameters for estimation of transmitted parameters. However, in applications of mobile communication systems, the channel transition probability varies depending on nonstationary channel characteristics. The mismatch of designed channel transition probability of the estimator to actual channel transition probability degrades the performance of the estimator. In this paper, we proposed a new parameter estimator which adapts to the channel characteristics using short time average of maximum a posteriori probabilities(MAPs). The proposed scheme, when applied to the LSP parameter estimation, performed better than the conventional estimator which do not adapt to the channel characteristics.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제17권3호
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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.

• Structural Engineering and Mechanics
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• 제6권1호
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• pp.115-124
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• 1998

A novel boundary stress resolution method is suggested in this paper, which is based upon the displacements of finite element analysis and of high precision with stress boundary condition strictly satisfied. The method is used to modify the Zienkiewicz-Zhu ($Z^2$) a posteriori error estimator and for the h-version adaptive finite element analysis of crack problems. Successful results are obtained.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.87-90
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• 1988

This paper reports a simple posteriori error estimate method for adaptive finite element mesh generation using quadratic shape function especially for the magnetic field problems. The elements of quadratic shape function have more precise solution than those of linear shape function. Therefore, the difference of two solutions gives error quantity. The method uses the magnetic flux density error as a basis for refinement. This estimator is tested on two dimensional problem which has singular points. The estimated error is always under estimated but in same order as exact error, and this method is much simpler and more convenient than other methods. The result shows that the adaptive mesh gives even better rate of convergence in global error than the uniform mesh.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.273-282
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• 2022

In this paper, we propose a new concept for error estimation in finite element solutions, which we call mode-based error estimation. The proposed error estimation predicts a posteriori error calculated by the difference between the direct finite element (FE) approximation and the recovered FE approximation. The mode-based FE formulation for the recently developed self-updated finite element is employed to calculate the recovered solution. The formulation is constructed by searching for optimal bending directions for each element, and deep learning is adopted to help find the optimal bending directions. Through various numerical examples using four-node quadrilateral finite elements, we demonstrate the improved predictive capability of the proposed error estimator compared with other competitive methods.

• 한국통신학회논문지
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• 제25권4A호
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• pp.546-552
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• 2000

터보부호의 복호기는 두 개이상의 연판정 입출력이 가능한 복호기로 구성되며, 이러한 복호기는 일정길이의 비트열에서 최적의 사후확률(a posteriori robability)을 이용한 MAP(maximum-a-posteriori) symbol estimator를 이용한다. 기존의 radix-2 MAP복호기는 아주 큰 인터리버 블록 크기로 인해 고속 통신시스템의 적용에는 문제점이 있다. 따라서 본 논문에서는 인터리버 블록크기를 줄일 수 있는 radix-2 MAP복호기를 기바으로 하는 새로운 radix-4 MAP복호기를 제안하였다. Radix-4 MAP 복호기 구조에 적용하기 위해 순방향, 역방향 state metric과 채널 metric을 제안하였으며, 가우시안 채널에서 기존의 radix-2 기반의 MAP 복호기와 성능을 비교하였다.

• ETRI Journal
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• 제36권5호
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• pp.721-729
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• 2014

We propose a novel phase-based method for single-channel speech enhancement to extract and enhance the desired signals in noisy environments by utilizing the phase information. In the method, a phase-dependent a priori signal-to-noise ratio (SNR) is estimated in the log-mel spectral domain to utilize both the magnitude and phase information of input speech signals. The phase-dependent estimator is incorporated into the conventional magnitude-based decision-directed approach that recursively computes the a priori SNR from noisy speech. Additionally, we reduce the performance degradation owing to the one-frame delay of the estimated phase-dependent a priori SNR by using a minimum mean square error (MMSE)-based and maximum a posteriori (MAP)-based estimator. In our speech enhancement experiments, the proposed phase-dependent a priori SNR estimator is shown to improve the output SNR by 2.6 dB for both the MMSE-based and MAP-based estimator cases as compared to a conventional magnitude-based estimator.

• 한국통신학회논문지
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• 제32권3C호
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• pp.338-347
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• 2007

본 논문에서는 순환 보호 구긴(cyclic-prefix)을 사용하는 시공간 블록 부호 (STBC: Space-Time Block-Coding) 단일 반송파 시스템에서 향상된 채널 성능을 위한 가중된 블록 적응형 주파수 영역 채널 추정기를 제안한다. 제안된 채널 추정기 구조는 필터 입력 신호에 대해 STBC로 구성된 블록을 형성하며, 이후 형성된 입력 블록에 대해 사후 오차 (a posteriori error)를 이용하는 가중된 LS (least-square) 규준을 적용하여 알고리즘을 유도한다. 또한 정적 채널에서 steady-state EMSE (excess mean-square error) 분석을 통해 블록 길이가 늘어남에 따라 EMSE를 분석한다. 전산 모의실험에서는 시변 TU (typical urban) 채널에서 블록 길이를 증가시킬수록 제안한 채널 추정기는 기존 NLMS와 RLS 채널 추정기들 보다 우수한 성능을 나타냄을 확인 할 수 있다.