• 한국전산유체공학회지
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• 제18권3호
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• pp.34-41
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• 2013

We develop a novel immersed boundary (IB) method based on implicit direct forcing scheme for incompressible flows. The proposed IB method is based on an iterative procedure for calculating the direct forcing coupled with the momentum equations in order to satisfy no-slip boundary conditions on IB surfaces. We perform simulations of two-dimensional flows over a circular cylinder for low and moderate Reynolds numbers. The present method shows that the errors for estimated velocities on IB surfaces are significantly reduced even for low Reynolds number with a fairly large time step while the previous methods based on direct forcing failed to provide no-slip boundary conditions on IB surfaces.

• 한국전산유체공학회지
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• 제15권2호
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• pp.55-61
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• 2010

A dependence of weighting parameter in preconditioning method for solving low Mach number flow with incompressible flow nature is investigated. The present preconditioning method employs a finite-difference method applied Roe‘s flux difference splitting approximation with the MUSCL-TVD scheme and 4th-order Runge-Kutta method in curvilinear coordinates. From the computational results of benchmark flows through a 2-D backward-facing step duct it is confirmed that there exists a suitable value of the weighting parameter for accurate and stable computation. A useful method to determine the weighting parameter is introduced. With this method, high accuracy and stable computational results were obtained for the flow with low Mach number in the range of Mach number less than 0.3.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.70-77
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• 2002

Since our physical world cannot be modeled as rigid body, deformable object models are important. For real-time simulation of elastic object, it must be guaranteed by its exact solution and low-latency computational cost. In this paper, we describe the boundary integral equation formulation of linear elastic body and related boundary element method(BEM). The deformation of elastic body can be effectively solved with 1ow run-time computational costs, using precomputed Green Function and fast low-rank updates based on Capacitance Matrix Algorithm.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2009년도 정기 학술대회
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• pp.135-138
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• 2009

Most of the studies use model order reduction for low frequency (LF) response analysis due to their high computational efficiency. In LF response analysis, one of model order reduction, algebraic substructuring (AS) retains all LF modes when using the modal superposition. However, in mid-frequency (MF) response analysis, the LF modes make very little contribution and also increase the number of retained modes, which leads to loss of computational efficiency. Therefore, MF response analysis should consider low truncated modes to improve the computational efficiency. The current work is focused on improving the computational efficiency using a AS and a frequency sweep algorithm. Finite element simulation for a MEMS resonator array showed that the performance of the presented method is superior to a conventional method.

• 한국공간구조학회논문집
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• 제23권1호
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• pp.35-43
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• 2023

Microclimate analysis was conducted through actual measurement according to land use status in urban, and CFD analysis was conducted to analyze and predict the microclimate characteristics of urban, and compared and analyzed with the actual measurement results. It was measured in high-rise areas and parks, and the temperature of the park area was 0.4 to 0.6℃ lower, and the relative humidity was 1.0 to 3.0% higher. The correlation coefficient was obtained by comparing the results of the computational fluid analysis with the results of the computational fluid analysis at the actual location located within the CFD analysis area for validation. The seasonal correlation coefficients are all higher than 0.8, so it is judged that they can be applied to microclimate analysis in urban area. The computational fluid analysis was divided into three areas (low-rise, low and high-rise, and high-rise) centered on the A2 point. On average, the low-rise area was 0.1 to 0.4% higher than the high-rise area. In the low and high-rise area and high-rise area, the pith of buildings are wide, so the airflow is smooth, so it is judged that the temperature is relatively low.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.127-153
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• 2012

This paper presents an advanced computational method for the prediction of the responses in the frequency domain of general linear dissipative structural-acoustic and fluid-structure systems, in the low-and medium-frequency domains and this includes uncertainty quantification. The system under consideration is constituted of a deformable dissipative structure that is coupled with an internal dissipative acoustic fluid. This includes wall acoustic impedances and it is surrounded by an infinite acoustic fluid. The system is submitted to given internal and external acoustic sources and to the prescribed mechanical forces. An efficient reduced-order computational model is constructed by using a finite element discretization for the structure and an internal acoustic fluid. The external acoustic fluid is treated by using an appropriate boundary element method in the frequency domain. All the required modeling aspects for the analysis of the medium-frequency domain have been introduced namely, a viscoelastic behavior for the structure, an appropriate dissipative model for the internal acoustic fluid that includes wall acoustic impedance and a model of uncertainty in particular for the modeling errors. This advanced computational formulation, corresponding to new extensions and complements with respect to the state-of-the-art are well adapted for the development of a new generation of software, in particular for parallel computers.

• Wind and Structures
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• 제16권5호
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• pp.411-431
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• 2013

A computational study of vortex-induced transverse vibrations of a cylinder with low mass-damping is presented. An Arbitrary Lagrangian-Eulerian (ALE) formulation of the Unsteady Reynolds-Averaged Navier-Stokes equations (URANS), along with the Spalart-Allmaras (SA) one-equation turbulence model, are coupled conservatively with rigid body motion equations of the cylinder mounted on elastic supports in order to study the amplitude and frequency response of a freely vibrating cylinder, its flow-induced motion, Vortex Street, near-wake flow structure, and unsteady loading in a moderate range of Reynolds numbers. The time accurate response of the cylinder from rest to its limit cycle is studied to explore the effects of Reynolds number on the start of large displacements, motion amplitude, and frequency. The computational results are compared with published physical experiments and numerical studies. The maximum amplitudes of displacements computed for various Reynolds numbers are smaller than the experimental values; however, the overall agreement of the results is quite satisfactory, and the upper branch of the limit-cycle displacement amplitude vs. reduced velocity response is captured, a feature that was missed by other studies. Vortex shedding modes, lock-in phenomena, frequency response, and phase angles are also in agreement with experiments.

• 한국전자파학회논문지
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• 제22권7호
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• pp.705-710
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• 2011

본 논문에서는 Chase 알고리즘 기반의 연판정 e-BCH 복호시 계산량을 감소하는 알고리즘을 제시하였다. Chase 알고리즘 기반의 연판정 e-BCH 복호 방식은 test pattern을 만들기 위해 수신 데이터 중 신뢰성이 낮은 데이터를 순서대로 찾기 위해 ordering을 한다. 데이터를 ordering하는 과정과 test pattern 수 만큼을 수신 데이터와 비교함으로써 최적의 복호 열을 찾는 과정에서 높은 복잡도가 요구되며, 본 논문에서는 이러한 복잡도를 줄이는 방안을 제시하여 계산량 및 성능 관점에서 비교 분석하였다.

• 전산구조공학
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• 제12권2호
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• pp.85-91
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• 1999

• 정보처리학회논문지C
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• 제12C권2호
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• pp.157-168
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• 2005

그룹 키 동의 프로토콜은 공개된 통신망을 통해 안전하게 통신하려는 그룹 구성원들에게 세션키를 제공하기 위해 설계된다. 모바일 컴퓨팅 기술은 프로토콜 참가자의 계산적인 능력 측면에서 비대칭적이다. 즉 프로토콜 참가자는 충분한 계산 능력을 가진 고정된 서버(애플리케이션 서버)와 제한된 계산 자원을 가진 모바일 장치들(클라이언트)로 구성되어 있다. 스마트카드나 개인 휴대 정보 단말기(PDA)와 같은 저전력 모바일 장치를 포함하는 그룹에서는 각 구성원의 계산량을 최소화하는 것이 바람직하다. 또한 그룹 구성원이 현재의 그룹을 탈퇴하거나 다수의 새로운 구성원이 현재의 그룹에 참여할 필요가 있을 때 길은 계산 비용으로 그룹 키의 갱신이 요구된다. 본 논문에서는 저전력 모바일 장치인 클라이언트 쪽의 계산 효율성이 높은 동적 그룹 키 동의 프로토콜을 제안한다. 제안한 프로토콜과 기존 프로토콜을 통신과 계산 비용 측면에서 비교하고, 제안한 프로토콜의 안전성은 랜덤 오라클 모델에서 수동적인 공격자에 대하여 안전함을 증명한다.