• Wind and Structures
• /
• 제17권1호
• /
• pp.1-19
• /
• 2013

A multiscale finite element method is applied to the Spalart-Allmaras turbulence model based detached-eddy simulation (DES). The multiscale arises from a decomposition of the scalar field into coarse (resolved) and fine (unresolved) scales. It corrects the lack of stability of the standard Galerkin formulation by modeling the scales that cannot be resolved by a given spatial discretization. The stabilization terms appear naturally and the resulting formulation provides effective stabilization in turbulent computations, where reaction-dominated effects strongly influence near-wall predictions. The multiscale DES is applied in the context of high-Reynolds flow over the Commonwealth Advisory Aeronautical Council (CAARC) standard tall building model, for both uniform and turbulent inflows. Time-averaged pressure coefficients on the exterior walls are compared with experiments and it is demonstrated that DES is able to resolve the turbulent features of the flow and accurately predict the surface pressure distributions under atmospheric boundary layer flows.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제3권1호
• /
• pp.107-114
• /
• 1999

In many applications (e,g., identification of non-destructive testing signal and biomedical signal and multiscale analysis of image), it is of interest to analyze and identify phenomena occurring at the different scales. The recently introduced wave let transforms provide a time-scale decomposition of signals that offers the possibility of such signals. However, there is no corresponding statistical properties to development of multiscale statistical signal processing. In this paper, we derive such properties of random signals in wavelet domain.

• Computers and Concrete
• /
• 제31권3호
• /
• pp.197-206
• /
• 2023

In this paper, the bending performance of a MSFRHPC (containing steel fiber, polyvinyl alcohol (PVA) fiber, and CW)-reinforced beam was studied for the first time. Introducing a multiscale fiber system increased the first crack load (up to 150%), yield load (up to 50%), and peak load (up to 15%) of reinforced beams. The multiscale fiber system delays cracking of the reinforced beam, reduces crack width of the reinforced beam in normal use, and improves the durability of the beam. Considering yield load and peak load, the reinforcing effect of multiscale fiber on the high-reinforcement ratio beam (1.00%) is better than that on the low-reinforcement ratio beam (0.57%). Introducing fibers slowed the development of cracks in the reinforced beam under bending. With the added hybrid fiber, the deformation concentration of reinforced beams after yield was more significant with concentration in 1 or 2 cracks. A model for predicting the flexural capacity of MSFRHPC-reinforced beams was proposed, considering the action of multiscale hybrid fibers. This research is helpful for structure application of MSFRHPC-containing CW.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제16권2호
• /
• pp.544-564
• /
• 2022

Underwater images often suffer from color distortion, blurring and low contrast, which is caused by the propagation of light in the underwater environment being affected by the two processes: absorption and scattering. To cope with the poor quality of underwater images, this paper proposes a multiscale fusion underwater image enhancement method based on channel attention mechanism and local binary pattern (LBP). The network consists of three modules: feature aggregation, image reconstruction and LBP enhancement. The feature aggregation module aggregates feature information at different scales of the image, and the image reconstruction module restores the output features to high-quality underwater images. The network also introduces channel attention mechanism to make the network pay more attention to the channels containing important information. The detail information is protected by real-time superposition with feature information. Experimental results demonstrate that the method in this paper produces results with correct colors and complete details, and outperforms existing methods in quantitative metrics.

• 한국전산유체공학회지
• /
• 제15권2호
• /
• pp.35-40
• /
• 2010

In the present work, LES with new variational multiscale method is conducted on the fully developed channel flow with Reynolds number, 180 based on the friction velocity and the channel half width. Incompressible Navier-Stokes equations are integrated using finite element method with the basis function of NURBS. To solve space-time equations, Newton's method with two stage predictor multicorrector algorithm is employed. The code is parallelized using MPI. The computational domain is a rectangular box of size $2{\pi}{\times}2{\times}4/3{\pi}$ in the streamwise, wall normal and spanwise direction. Mean velocity profiles and velocity fluctuations are compared with the data of DNS. The results agree well with those of DNS and other traditional LES.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 추계학술대회논문집
• /
• pp.56-59
• /
• 2009

In the present work, LES with new variational multiscale method is conducted on the fully developed channel flow with Reynolds number is 180 based on the friction velocity and the channel half width. Incompressible Navier-Stokes equations are integrated using finite element method with the basis function of NURBS. To solve space-time equations, Newton's method with two stage predictor multicorretor algorithm is employed. The code is parallelized using MPI. The computational domain is a rectangular box of size $2{\pi}{\times}2{\times}4/3{\pi}$ in the streamwise, wall normal and spanwise direction. Mean velocity profiles and velocity fluctuations are compared with the data of DNS. The results agree well with those of DNS and other traditional LES.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.547-550
• /
• 2004

We present a multiscale scheme which describes the dynamic pictures of atoms in the multiple length-scale systems. Large-scale atomic systems are reduced to coarse grained system by the quasicontinuum, of which the dynamic pathways are rendered by the action-derived molecular dynamics proved effective for multiple time-scale problems such as rare events. Adatom diffusions on the metal (001) surface are selected for our numerical examples. The energy barriers of the diffusions and the real dynamic trajectories of the adatoms are calculated.

• 한국통신학회논문지
• /
• 제28권10C호
• /
• pp.1023-1032
• /
• 2003

MPEG-4와 같은 객체 기반 부호화는 멀티미디어 응용을 위한 다양한 내용 기반 기능들을 제공한다. 압축 효율의 향상과 더불어 이러한 기능들이 지원되도록 하기 위해서는 비디오 데이터의 각 프레임은 비디오 객체로 분할되어야 한다. 본 논문에서는 비선형 다중스케일 필터링과 시공간 정보를 사용한 효과적인 비디오 객체 분할 기법을 제안한다. 제안된 방법은 안정화된 역 확산 방정식(Stabilized Inverse Diffusion Equation : SIDE)에 기반한 비선형 다중스케일 필터링을 사용하여 공간적 분할을 수행한다. 또한 구해진 초기 분할된 영역들은 인접 영역 그래프 (Region Adjacency Graph : RAG)를 사용하여 병합된다. 본 논문에서는 통계적 유의성 검사(Statistical significance test)와 시변 메모리(Time-variant memory)를 시간적 분할 방법으로 사용하며 구해진 공간적 분할과 시간적 분할을 결합하여 최종 객체 영역을 효과적으로 분할한다. 본 논문에서 제안된 공간적 분할 방법은 기존의 형태학적 Watershed 알고리즘에 비해 잡음에 강인한 분할 특성을 나타내었으며 기존의 A. Neri의 방법과 비교하였을 때, 최종 분할된 객체 영역의 정확도 비율이 Akiyo는 43%, Claire는 29% 정도 향상됨을 확인할 수 있었다.

• 정보과학회 컴퓨팅의 실제 논문지
• /
• 제20권10호
• /
• pp.534-542
• /
• 2014

멀티스케일 모델링은 시공간적으로 서로 다른 규모의 시스템을 다룰 수 있는 시뮬레이션 기법이다. 본 연구에서는 멀티스케일 모델링 연구의 일환으로 서로 다른 시뮬레이션 기법인 분자동역학과 확률회전동역학을 결합할 수 있는 방법을 제안한다. 분자동역학 프로그램 중 잘 알려진 오픈 소스인 LAMMPS를 기반으로 멀티스케일링 모델링을 구현하였으며 LAMMPS에서 정의한 제3자를 위한 표준 확장 방법을 따랐다. 제안된 방법에서는 확률회전동역학 모델을 기본으로 경계 영역은 분자동역학으로 해석 가능하게 하였고 심리스한 해석을 보장하기 위하여 중첩 영역과 정보 교환 영역을 함께 구현하였다. 예비실험을 수행한 결과, 제안된 멀티스케일 방법론이 기존 분자동역학 시뮬레이션 결과와 일치된 해석 결과를 보여주었으며 실행 시간 또한 단축시킬 수 있음을 확인하였다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.241-245
• /
• 2011

엔진 시험과정에서 데이터는 시계열 형태로 수집된다. 보통 그러한 시계열들의 섭동보다는 시간평균에 더 관심을 가진다. 본 논문에서는 공기 흡입식 엔진의 시험에서 측정된 압력과 유량 데이터의 섭동에 시계열의 복잡성의 척도로 제안된 개념인 multiscale sample entropy라는 분석법을 적용해본다. 분석 결과, 서로 다른 물리량은 각각의 시간척도에서 다른 복잡성을 가진다는 것을 보였고, 이를 잘 이용하면 엔진 시험의 성패 여부를 즉각적으로 알려주는 도구를 만들 수 있을 것이다.