• 대한수학회지
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• 제43권5호
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• pp.1081-1098
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• 2006

Mathematical analysis is made on a mesh free method for the compressible Euler equations. In particular, the Moving Least Square Reproducing Kernel (MLSRK) method is employed for space approximation. With the backward-Euler method used for time discretization, existence of discrete solution and it's $L^2-error$ estimate are obtained under a regularity assumption of the continuous solution. The result of numerical experiment made on the biconvex airfoil is presented.

• Journal of the Korean Data and Information Science Society
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• 제18권1호
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• pp.195-210
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• 2007

This paper develops a consistent nonparametric test for Granger causality in the context of strong-mixing process, which covers a large class of stationary processes including ARMA and ARCH models. The previously proposed tests require absolute regularity ($\beta$-mixing) more stringent than the strong-mixing condition. We prove the consistency of the test under a high level assumption on the approximation error of U statistic by its projection. Due to the sample splitting, the test statistic we propose is asymptotically normally distributed under the null.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1569-1572
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• 2003

Meshfree approximations exhibit significant potential to solve partial differential equations. Meshfree methods have been successfully applied to various problems which the traditional finite element methods have difficulties to handle, including the quasi-static and dynamic fracture. large deformation problems, contact problems, and strain localization problems. A meshfree method based on the reproducing kernel particle approximation(RKPM) is applied to sheet metal forming analysis in this research. Metal forming examples, such as stretch forming and flanging operation, are analyzed to demonstrate the performance of the proposed meshfree method for largely deformed elasto-plastic material.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2007년도 가을 학술발표논문집 Vol.34 No.2 (C)
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• pp.485-489
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• 2007

Gaussian process classifiers (GPCs) are fully statistical kernel classification models which have a latent function with Gaussian process prior Recently, EP approximation method has been proposed to infer the posterior over the latent function. It can have a special hyperparameter which can treat outliers potentially. In this paper, we propose the outlier robust algorithm which alternates EP and the hyperparameter updating until convergence. We also show its usefulness with the simulation results.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.567-574
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• 2002

새로운 자유격자 관사를 이용한 점별 계산법을 제안한다 이동 최소 자승법을 이용한 기저의 생성과 기저의 근사적 미분을 동시에 구해내는 자유격자 근사를 유도하여, 직접 점별 계산법을 고안하였다. 기존의 자유 격자 법에서는 기저의 직접 미분을 사용하므로 높은 계산 비용이 필요하지만, 이 논문에서 제안된 방법은 기저의 생성과 동시에 기저의 근사적 미분을 구하게 된다. 또한 기존의 방법에서 필요하였던, 창 함수(window function)의 미분가능성을 연속성으로 대치할 수 있으므로, 주어진 문제에 따라 다양한 창 함수를 이용할 수 있다. 기저의 재생성과 interpolation의 수렴성을 소개하고, 수치 예제로서, Poisson 문제를 통해 이 방법의 유효함을 보인다.

• 한국해양공학회지
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• 제28권2호
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• pp.93-101
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• 2014

In general, particle simulation methods such as the MPS(Moving Particle Simulation) or SPH(Smoothed Particle Hydrodynamics) methods have some serious drawbacks for pressure solutions. The pressure field shows spurious high fluctuations both temporally and spatially. It is well known that pressure fluctuation primarily occurs because of the numerical approximation of the partial differential operators. The MPS and SPH methods employ a pre-defined kernel function in the approximation of the gradient and Laplacian operators. Because this kernel function is constructed artificially, an accurate solution cannot be guaranteed, especially when the distribution of particles is irregular. In this paper, we propose a particle simulation method based on the moving least-square technique for solving the partial differential operators using a Taylor-series expansion. The developed method was applied to the hydro-static pressure and dam-broken problems to validate it.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.173-195
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• 2013

Meshfree methods are known to have the capability to overcome the strict regularization requirements and numerical instabilities that encumber the finite element method (FEM) in large deformation problems. They are also more naturally suited for problems involving material perforation and fragmentation. To take advantage of the high efficiency of FEM and high accuracy of meshfree methods, a coupled finite element (FE) and reproducing kernel (RK, one of the meshfree approximations) formulation is described in this paper. The coupling of FE and RK approximation is implemented in an evolutionary fashion, where the extent and location of the evolution is dependent on a triggering criteria provided by the material constitutive laws. To enhance computational efficiency, Gauss quadrature is applied to integrate both FE and RK domains so that no state variable transfer is required when mesh conversion is performed. To control the hourglassing that might occur with 1-point integrated hexahedral grids, viscous type hourglass control is implemented. Meanwhile, the FEM version of the K&C concrete (KCC) model was modified to make it applicable in both FE and RK formulations. Results using this code and the KCC model are shown for the modeling of concrete responses under quasi-static, blast and impact loadings. These analyses demonstrate that fragmentation phenomena of the sort commonly observed under blast and impact loadings of concrete structures was able to be realistically captured by the coupled formulation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1998년도 제13차 학술회의논문집
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• pp.280-284
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• 1998

Many classes of nonlinear systems can be represented by Volterra kernel expansion. Therefore, identification of Volterra kernels of nonlinear system is an important task for obtaining the nonlinear characteristics of the nonlinear system. Although one of the authors has recently proposed a new method for obtaining the Volterra kernels of a nonlinear system by use of M-sequence and correlation technique, our mettled of nonlinear system identification is limited to Wiener-type nonlinear system and we can not apply this method to the identification of Hammerstein-type nonlinear system. This paper describes a new mettled for obtaining Volterra kernels of Hammerstein nonlinear system by adding a linear element in front of tile Hammerstein system. First we calculate the linear element of Hammerstein system by use of conventional correlation method. Secondly, we put a linear element in front of Hammerstein system. Then the total system becomes Wiener-type nonlinear system. Therefore we can use our method on Volterra kernel identification by use of M-sequence. Thus we get the coefficients of the approximation polynomial of nonlinear element of Hammerstein system. From the results of simulation, a good agreement with theoretical considerations is obtained, showing a wide applicability of our method.

• 수산해양기술연구
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• 제23권3호
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• pp.111-116
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• 1987

이상으로부터 다음의 결론을 얻는다. 조파저항 이론의 전개에서 Michell 적분보다 더욱 정밀한 Neumann-Kelvin 문제가 복잡한 kernel 함수 때문에 많은 시간과 노력이 필요하지만, 원점 부근에서 Kelvin 소오스의 점근거동을 조사하여 세장체 근사를 행함으로 N-K 문제의 kernel 함수에 대한 근사와 동등하게 처리될 수 있었다. 조파저항의 계산 결과가 Michell 적분과 비슷한 경향을 보이나, 실험치와의 정확한 비교를 할 수 없었다. 그러나 세장선 이론을 적용함으로써 훨씬 복잡하고 지루한 작업을 들 수 있었다. 전진 속도를 갖는 경우에는 수정된 Green정리를 이용하면 될 것으로 기대된다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제31권5호
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• pp.595-604
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• 2004

문서 집합 내의 개념 또는 의미 관계의 자동 분석은 보다 효율적인 정보 획득과 단어 이상의 개념 수준에서의 문서간 비교를 가능케 한다. 본 논문에서는 다중요인모델에 기반 하여 텍스트 문서로부터 토픽들을 추출하고 이로부터 의미 커널(semantic kernel)을 구축하여 문서간 유사도를 측정하는 방안을 제시한다. 텍스트 문서는 내재된 토픽들의 다양한 결합에 의해 생성된다고 가정하며 하나의 토픽은 공통 주제에 관련되거나 적어도 자주 같이 나타나는 단어들의 집합으로 정의한다. 다중요인모델은 은닉층을 갖는 하나의 네트워크 형태로 표현되며, 토픽을 표현하는 단어 집합은 은닉노드로부터의 가중치가 높은 단어들로 구성된다. 일반적으로 이러한 다중요인 네트워크에서의 학습과 추론과정을 용이하게 하기 위해서는 근사적 확률 추정 기법이 요구되는데, 본 논문에서는 헬름홀츠 머신에 의한 방법을 활용한다. TDT-2 문서 집합에 대한 실험에서 토픽별로 관련 있는 단어 집합들을 추출할 수 있었으며, 4개의 텍스트 집합에 대한문서 검색 실험에서는 다중요인모델의 분석결과에 기반 한 의미 커널을 사용함으로써 기본 벡터공간 모델에 비해 평균정확도 면에서 통계적으로 유의한 수준의 성능 향상을 얻을 수 있었다.