• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.176-179
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• 2008

In a numerical simulation of open channel turbulent flows, the determination of wall roughness height for wall function was studied. The roughness constant, based on the law-of-the -wall for flow on rough walls, obtained by experimental works for pipe flows is employed in general wall functions. However, this constant of wall function is the function of Froude number in open channel flows. Thus, the wall roughness should be determined by taking into account the effect of Froude number. In addition, the wall roughness should be corresponding to Manning's roughness coefficient widely used for open channels. In this study, the relation between wall roughness height as an input condition and Manning's roughness coefficient was investigated, and an equation for effective wall roughness height considering the characteristics of numerical models was proposed as a function of Manning's roughness coefficient.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6B
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• pp.627-634
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• 2008

In a numerical simulation of open channel turbulent flows using RANS (Reynolds averaged Navier-Stokes) equations model equipped with VOF (Volume of Fluid) scheme, the determination of wall roughness for wall function was studied. The roughness constant, based on the law-of-the-wall for flow on rough walls, obtained by experimental works for pipe flows is employed in general wall functions. However, this constant of wall function is the function of Froude number in open channel flows. Thus, the wall roughness should be determined by taking into account the effect of Froude number. In addition, the wall roughness should be corresponding to Manning's roughness coefficient widely used for open channels. In this study, the relation between wall roughness height as an input condition and Manning's roughness coefficient was investigated, and an equation for effective wall roughness height considering the characteristics of numerical models was proposed as a function of Manning's roughness coefficient.

• Korean Journal of Hydrosciences
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• v.1
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• pp.49-60
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• 1990

Manning's roughness factor to flow in sand-bed channels may be divided into the grain roughness factor nd the form roughness factor. The grain roughness factor may be dedermined by using Keulegan's formula. By using available experimental data, it was found there is a unique relationship between the form roughness and the hydraulic radius to sediment particle size ratio for a given value of the Froude number. The form roughness and the bed form may be determined by using this unique relationship. The technique for engineering applications of the results appears to be quite simple.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.3
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• pp.287-294
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• 2007

When we use the circular pipes for wastewater and storm water, we should be known the characteristics of the flow for accurate design. To elevate the design accuracy, we want to know the profile of flow. The roughness coefficient in the Manning equation is constant, but in actuality changed with the relative depth in circular pipe. This study was conducted to calculate the relative normal depth in changing the roughness coefficient (named relative roughness coefficient) with the relative depth in the analysis of gradually varied flow in the circular pipe by Newton-Raphson method. We performed the analysis of gradually varied flow using the relative normal depth and the relative roughness coefficient. We presented the 12 flow profiles with the relative depth and the relative roughness coefficient in circular pipe. The flow classification considering relative depth in circular pipe is available to analyse gradually varied flow profiles.

• Journal of Korea Water Resources Association
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• v.46 no.12
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• pp.1209-1220
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• 2013

Roughness coefficients calibrated by flow modeling using the 1-dimensional numerical model were analyzed for the downstream section of Naesung Stream in this study. Also, the bedform configuration at the Hyangseok Station was predicted for measured and simulated hydraulic conditions of flows and total flow roughness was estimated with the coefficient of grain roughness. The Manning's n coefficients calibrated by numerical modeling and estimated by considering of grain and bedform roughness were compared and examined. As a result, the Manning's n by numerical modeling was greater than the coefficient range estimated by grain and bedform roughness at the low flow regime due to the other factors such as vegetation, sinuosity, and sand bar. However, the Manning's n by numerical modeling was included in the coefficient range by grain and bedform roughness at the transition and high flow regime over $500m^3/s$ of flow discharge.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.113-121
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• 2012

The study was carried out to investigate the dimension of irrigation canal, and measure the water flow of those diverted from Kimje main canal in Dongjin irrigation area. The rating curves indicating the relationships between water level and discharge of the lateral canals were induced using the measured data with high regression coefficients of 0.957~0.999 at inlet points and 0.932~0.998 at end points, respectively. And Manning's roughness coefficients were estimated as the ranged from 0.015 to 0.074 at inlet points and 0.056 to 0.089 at end points with rectangular type of concrete open irrigation canals, the Manning's roughness coefficients of the end points were less than those values of the end points, which may be considered as the deposition of the bottom sediments.

• Journal of Korea Water Resources Association
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• v.31 no.1
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• pp.115-120
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• 1998

In this paper, a depth-averaged two-dimensional transport model is introduced, and its error bound is presented as the results of sensitivity analysis. The results show that the calculated SS concentration is highly dependant on Manning roughness coefficient, mixing coefficient. fall velocity. and critical shear stress. On the other hand, water level and dispersion coefficient are proved to be less significant in the variation of SS concentration.

• Journal of Korea Water Resources Association
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• v.45 no.2
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• pp.137-149
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• 2012

Field measurements of resistance to flow are analyzed for 739 rivers vegetated with grass (281 channels), shrubs (150 channels) and trees (308 channels). The measured distribution of Manning roughness coefficients ranges from 0.015~0.250 for grass, 0.016~0.250 for shrubs, 0.018~0.310 for trees. Significant trends are obtained between Darcy-Weisbach (or Manning roughness coefficients) and flow discharge, friction slope, and relative submergence. The regression equations for Darcy-Weisbach and Manning roughness coefficients in vegetated rivers are: $f_{veg}=0.436Q^{-0.363}$, $f_{veg}=3.305S_f^{0.508}$, and $n_{veg}=0.061Q^{-0.124}$, $n_{veg}=0.144S_f^{0.199}$, $V=5.3(h/d_{50})^{1/8.3}{\sqrt{ghS_f}}$, $\sqrt{8/f}(=V/u*)=5.75log(5h/d_{50})$, respectively. These semi-empirical relationships should be useful for hydraulic engineering practice.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.553-563
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• 2011

According to the improvement of computer's performance, the development of Geographic Information System (GIS), and the activation of offering information, a distributed model for analyzing runoff has been studied a lot in recently years. The distribution model is a theoretical and physical model computing runoff as making target basin subdivided parted. In the distributed model developed by this study, the volume of runoff at the surface flow is calculated on the basis of the parameter determined by landcover data and a two-dimensional diffusion wave equation. Most of existing runoff models compute velocity and discharge of flow by applying Manning-Strickler's mean velocity equation and Manning's roughness coefficient. Manning's roughness coefficient is not matched with dimension and ambiguous at computation; Nevertheless, it is widely used in because of its convenience for use. In order to improve those problems, this study developed the runoff model by applying not only Manning-Strickler's equation but also Chezy's mean velocity equation. Furthermore, this study introduced a power law of exponential friction factor expressed by the function of roughness height. The distributed model developed in this study is applied to 6 events of fan-shape basin, oblong shape test basin and Anseongcheon basin as real field conditions. As a result the model is found to be excellent in comparison with the exiting runoff models using for practical engineering application.

• Journal of Korea Water Resources Association
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• v.40 no.10
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• pp.755-768
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• 2007

The purpose of this study is to analyse the characteristics of Manning's roughness coefficient according to change of discharge by using observed data obtained from a stable gravel-bed river and to investigate the applicability of the relevant existing empirical methods to it. Observed water level and discharge data are used as input data for the USGS computer program NCALC model for calculation of the roughness coefficient. Calculated values are compared with roughness values which are estimated with four widely used methods. The results show that though the empirical methods are able to give similar roughness values only for flood flow, they seem to have rather high uncertainty because of necessity of subjective judgement and differences of resultant values. Roughness coefficients for normal-low flow cannot be estimated from the existing empirical formulae. Especially, using the Manning equation for calculating them should be careful as this provides a wide range of estimated values in normal-low flow. The relations between the roughness coefficient and characteristic size of bed materials are different from them in flood flow even though they have a close relations.