• Title/Summary/Keyword: spatial grid model

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Influence of TVD Schemes on the Spatial Accuracy of Turbulent Flows Around a Hull When Using Structured and Unstructured Grids (정렬 및 비정렬 격자를 이용한 선체 주위 유동에서 TVD 기법이 공간 정확도에 미치는 영향)

  • Sim, Min Gyeoung;Lee, Sang Bong
    • Journal of the Society of Naval Architects of Korea
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    • v.58 no.3
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    • pp.182-190
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    • 2021
  • Computational simulations of turbulent flows around a model ship have been performed to investigate an influence of TVD schemes on the accuracy of advective terms associated with ship resistances. Several TVD schemes including upwind, second-order upwind, vanLeer, and QUICK as well as a nonTVD linear scheme were studied by examining temporal and spatial characteristics of accuracy transition in adjacent cells to the hull. Even though vanLeer scheme was the most accurate among TVD schemes in both structured and unstructured grid systems, the ratio of accuracy switch from 2nd order to 1st order in vanLeer scheme was considerable compared with the 2nd order linear scheme. Also, the accuracy transition was observed to be overally scattered in the unstructured grid while the accuracy transition in the structured grid appeared relatively clustered. It concluded that TVD schemes had to be carefully used in computational simulations of turbulent flows around a model ship due to the loss of accuracy despite its attraction of numerical stability.

Behavior and stress check of concrete box girders strengthened by external prestressing

  • Zhang, Yu;Xu, Dong;Liu, Chao
    • Computers and Concrete
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    • v.22 no.2
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    • pp.133-142
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    • 2018
  • The deterioration of existing bridges has become a major problem around the world. In the paper, a new model and an associated stress checking method are proposed for concrete box girders strengthened by external prestressing. The new model called the spatial grid model can analyze all the spatial behaviors clearly by transforming the box girder into discrete orthogonal grids which are equivalent to plate elements. Then the three-layer stresses are employed as the stress checking indices to evaluate the stress state of the plate elements. The initial stress check before strengthening reveals the cracked and potential cracking areas for existing bridges, making the strengthening design more targeted and scientific; the subsequent stress check after strengthening evaluates the strengthening effect and ensures safety. A deficient bridge is selected as the practical example, verifying the accuracy and applicability of the proposed model and stress checking method. The results show that principal stresses in the middle layer of plate elements reflect the main effects of external prestressing and thus are the key stress checking indices for strengthening. Moreover, principal stresses check should be conducted in all parts of the strengthened structure not only in the webs. As for the local effects of external prestressing especially in the areas near anchorage and deviator, normal stresses check in the outer and inner layers dominates and local strengthening measures should be taken if necessary.

Grid-Based Soil-Water Erosion and Deposition Modeling sing GIS and RS

  • Kim, Seong-Joon
    • Proceedings of the Korea Water Resources Association Conference
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    • 2001.05a
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    • pp.25-34
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    • 2001
  • A grid-based KIneMatic wave soil-water EROsion and deposition Model (KIMEROM) that predicts temporal variation and spatial distribution of sediment transport in a watershed was developed. This model uses ASCII-formatted map data supported from the regular gridded map of GRASS (U.S. Army CERL, 1993)-GIS (Geographic Information Systems), and generates the distributed results by ASCIIl-formatted map data. For hydrologic process, the kinematic wave equation and Darcy equation were used to simulate surface and subsurface flow, respectively (Kim, 1798; Kim et al., 1993). For soil erosion process, the physically-based soil erosion concept by Rose and Hairsine (1988) was used to simulate soil-water erosion and deposition. The model adopts sing1e overland flowpath algorithm and simulates surface and subsurface water depth, and sediment concentration at each grid element (or a given time increment. The model was tested to a 162.3 km$^2$ watershed located in the tideland reclaimed area of South Korea. After the hydrologic calibration for two storm events in 1999, the results of sediment transport were presented for the same storm events. The results of temporal variation and spatial distribution of overland flow and sediment areas are shown using GRASS.

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An Arrangement Technique for Fine Regular Triangle Grid of Network Dome by Using Harmony Search Algorithm (화음탐색 알고리즘을 이용한 네트워크 돔의 정삼각형 격자 조절기법)

  • Shon, Su-Deok;Jo, Hye-Won;Lee, Seung-Jae
    • Journal of Korean Association for Spatial Structures
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    • v.15 no.2
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    • pp.87-94
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    • 2015
  • This paper aimed at modeling a fine triangular grid for network dome by using Harmony Search (HS) algorithm. For this purpose, an optimization process to find a fine regular triangular mesh on the curved surface was proposed and the analysis program was developed. An objective function was consist of areas and edge's length of each triangular and its standard deviations, and design variables were subject to the upper and lower boundary which was calculated on the nodal connectivity. Triangular network dome model, which was initially consist of randomly irregular triangular mesh, was selected for the target example and the numerical result was analyzed in accordance with the HS parameters. From the analysis results of adopted model, the fitness function has been converged and the optimized triangular grid could be obtained from the initially distorted network dome example.

Discontinuous Grids and Time-Step Finite-Difference Method for Simulation of Seismic Wave Propagation (지진파 전파 모의를 위한 불균등 격자 및 시간간격 유한차분법)

  • 강태섭;박창업
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2003.03a
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    • pp.50-58
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    • 2003
  • We have developed a locally variable time-step scheme matching with discontinuous grids in the flute-difference method for the efficient simulation of seismic wave propagation. The first-order velocity-stress formulations are used to obtain the spatial derivatives using finite-difference operators on a staggered grid. A three-times coarser grid in the high-velocity region compared with the grid in the low-velocity region is used to avoid spatial oversampling. Temporal steps corresponding to the spatial sampling ratio between both regions are determined based on proper stability criteria. The wavefield in the margin of the region with smaller time-step are linearly interpolated in time using the values calculated in the region with larger one. The accuracy of the proposed scheme is tested through comparisons with analytic solutions and conventional finite-difference scheme with constant grid spacing and time step. The use of the locally variable time-step scheme with discontinuous grids results in remarkable saving of the computation time and memory requirement with dependency of the efficiency on the simulation model. This implies that ground motion for a realistic velocity structures including near-surface sediments can be modeled to high frequency (several Hz) without requiring severe computer memory

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Application of Grid-based Kinematic Wave Storm Runoff Model

  • Kim, Seong-Joon;Kim, Sun-Joo;Chae, Hyo-Seok
    • Proceedings of the Korea Water Resources Association Conference
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    • 2000.05a
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    • pp.20-27
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    • 2000
  • The grid-based KlneMatic wave STOrm Runoff Modei (Kim, 1998; Kim, et al., 1998) which predicts temporal variation and spatial distribution of saturated overland flow, subsurface flow and stream flow was evaluated at two watersheds. This model adopts the single overland flowpath algorithm and simulates surface and/or subsurface water depth at each cell by using water balance of hydrologic components. The model programed by C-language uses ASCII-formatted map data supported by the irregular gridded map of the GRASS (Geographic Resources Analysis Support System) GIS and generates the spatial distribution maps of discharge, flow depth and soil moisture of the watershed.

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Development and Application of Grid-Based Urban Surface Runoff Model (격자기반의 도시유역 지표면 유출모형의 개발 및 적용)

  • Kim, Mun-Mo;Lee, Jeong-Woo;Yi, Jae-Eung
    • Journal of Korea Water Resources Association
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    • v.40 no.1 s.174
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    • pp.25-38
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    • 2007
  • A grid-based urban surface runoff model for simulating the temporal variation and spatial distribution of overland flow in a drainage area was developed. The process of routing of overland flow is modeled by the nonlinear storage equation which is composed of the continuity equation and the Manning's equation. For model operation, the drainage area is divided into grid areas, and spatially distributed topographical and hydrological information for model inputs is provided. Then overland flow is routed for each of the discretized cells of the area. In order to test the applicability of this model, temporal variations and spatial distributions of flow depth and overland flow was simulated in a fictitious and a real urbanized Kunja drainage area. Results indicate that the model can simulate reasonably well the urban runoff hydrograph.

Use of Geographic Information System Tools for Improving Atmospheric Emission Inventories of Biogenic Source

  • Shin, Tae-joo
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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    • v.3 no.3
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    • pp.151-158
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    • 1999
  • Biogenic source emissions refer to naturally occuring emissions from vegetation, microbial activities in soil, lightening, and so on. Vegetation is especially known to emit a considerable amout of volatile organic compounds into the atmosphere. Therefore, biogenic source emissions are an important input to photochemical air quality models. since most biogenic source emissions are calculated at the county-level, they should be geographically allocated to the computational grid cells of a photochemical air quality model prior to running the model. The traditional method for the spatial allocation for biogenic source emissions has been to use a "spatial surrogate indicator" such as a county area. In order to examine the applicability of such approximations, this study developed more detailed surrogate indicators to improve the spatial allocation method for biogenic source emissions. Due to the spatially variable nature of biogenic source emissions, Geographic Information Systems(GIS) were introduced as new tools to develop more detailed spatial surrogate indicators. Use of these newly developed spatial surrogate indicators for biogenic source emission allocation provides a better resolution than the standard spatial surrogate indicator.indicator.

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Numerical Study on Atmospheric Flow Variation Associated With the Resolution of Topography (지형자료 해상도에 따른 대기 유동장 변화에 관한 수치 연구)

  • Lee, Soon-Hwan;Kim, Sun-Hee;Ryu, Chan-Su
    • Journal of Environmental Science International
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    • v.15 no.12
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    • pp.1141-1154
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    • 2006
  • Orographic effect is one of the important factors to induce Local circulations and to make atmospheric turbulence, so it is necessary to use the exact topographic data for prediction of local circulations. In order to clarify the sensitivity of the spatial resolution of topography data, numerical simulations using several topography data with different spatial resolution are carried out under stable and unstable synoptic conditions. The results are as follows: 1) Influence of topographic data resolution on local circulation tends to be stronger at simulation with fine grid than that with coarse grid. 2) The hight of mountains in numerical model become mote reasonable with high resolution topographic data, so the orographic effect is also emphasized and clarified when the topographic data resolution is higher. 2) The higher the topographic resolution is, the stronger the mountain effect is. When used topographic data resolution become fine, topography in numerical model becomes closer to real topography. 3) The topographic effect tends to be stronger when atmospheric stability is strong stable. 4) Although spatial resolution of topographic data is not fundamental factor for dramatic improvement of weather prediction accuracy, some influence on small scale circulation can be recognized, especially in fluid dynamic simulation.

A Study on the Analysis of Correlation Decay Distance(CoDecDist) Model for Enhancing Spatial Prediction Outputs of Spatially Distributed Wind Farms (풍력발전출력의 공간예측 향상을 위한 상관관계감소거리(CoDecDist) 모형 분석에 관한 연구)

  • Hur, Jin
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.29 no.7
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    • pp.80-86
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    • 2015
  • As wind farm outputs depend on natural wind resources that vary over space and time, spatial correlation analysis is needed to estimate power outputs of wind generation resources. As a result, geographic information such as latitude and longitude plays a key role to estimate power outputs of spatially distributed wind farms. In this paper, we introduce spatial correlation analysis to estimate the power outputs produced by wind farms that are geographically distributed. We present spatial correlation analysis of empirical power output data for the JEJU Island and ERCOT ISO (Texas) wind farms and propose the Correlation Decay Distance (CoDecDist) model based on geographic correlation analysis to enhance the estimation of wind power outputs.