• Journal of Korea Water Resources Association
• /
• v.40 no.12
• /
• pp.943-956
• /
• 2007

Among various statistics, the spatial correlation function, that is "correlogram", is frequently used to evaluate or design the rain gauge network and to model the rainfall field. The spatial correlation structure of rainfall has the significant variation due to many factors. Thus, the variation of spatial correlation structure of rainfall causes serious problems when deciding the spatial correlation function of rainfall within the basin. In this study, the spatial rainfall structure was modeled using bivariate mixed distributions to derive monthly spatial correlograms, based on Gaussian and lognormal distributions. This study derived the correlograms using hourly data of 28 rain gauge stations in the Keum river basin. From the results, we concluded as following; (1) Among three cases (Case A, Case B, Case C) considered, the Case A(+,+) seems to be the most relevant as it is not distorted much by zero measurements. (2) The spatial correlograms based on the lognormal distribution, which is theoretically as well as practically adequate, is better than that based on the Gaussian distribution. (3) The spatial correlation in July exponentially decrease more obviously than those in other months. (4) The spatial correlograms should be derived considering the temporal resolution(hourly, daily, etc) of interest.

• The Journal of Korean Academy of Prosthodontics
• /
• v.34 no.4
• /
• pp.746-754
• /
• 1996

The purpose of this study was to evaluate the fracture strength of porcelain laminate veneer with various lingual extention length when incisal restoring. Sixty recently extracted, intact maxillary incisors were used and stored in a physiologic saline solution from the time of extraction. Seating form was preparation at the labial surface of each tooth with a water-cooled round diamond bur. Standard block was formed with 32 gauge and 24 gauge wax at tooth labial and lingual surface. Lingual extention length differed according to each group. (group I : 0.5mm, group II : 1 mm, group III : 2mm, group IV : 0mm) All tooth specimens were impressioned with examix(GC Inc., Japan). Refractory cast were maked with refractory die material(Ceramco Inc., U.S.A.) Laminate porcelain (Ceramco II Veneer porcelain, Ceramco Inc., U.S.A.) was condensed in refractory die cast and baked according to the manufacturer's recommendations. Each surface was contoured with low speed diamond bur according to guide block. All porcelain specimens were sandblasted and ultrasonically cleaned in distlled water for 3 minutes. Then, all porcelain specimen were etched with 8% hydrofluoric acid for 5 minutes. Sixty specimens were bonded with composite resin cement(Choice Porcelain Veneer System, Bisco Inc., U.S.A.) according to manufacture's directions. The fracture loads of the specimen were measured by Instron universal testing machine. The mean values of fracture loads for the groups were statistically compared by Duncan's multiful range test. The result were as follows : Mean fracture strengths of each group were 86.95Mpa in no lingual extention group, 44.98Mpa in 0.5mm lingual extention group, 27.47Mpa in 1mm lingual extention group, 19.61Mpa in 2mm lingual extention group. There was a statistically significant difference between all group(p<0.01).

• Journal of Korea Water Resources Association
• /
• v.48 no.4
• /
• pp.309-319
• /
• 2015

River characteristics in South Korea has been affected by seasonal climatic variability due to climate change and by remarkable land cover change due to rapid economic growth. In this regard, the roles of river management is getting more important to eco-system and human community in watersheds of South Korea. Understanding river characteristics including direct runoff and baseflow, the first step of river management, can give a significant contribution to sustainable river environment. Therefore, the objective of this study is to quantify the contributions of the direct runoff and baseflow to river streamflow. For this, we used the BFLOW and WHAT programs to conduct baseflow separation for 71 streamflow gauge stations in Han River system, South Korea. The results showed that baseflow index for 71 stations ranges from 0.42 to 0.78. Also, gauge stations which have baseflow index more than 0.5 occupied 76% of a total stations. However, baseflow index can be overestimated due to human impacts such as discharge from dams, reservoirs, and lakes. This study will be used as fundamental information to understand river characteristics in river management at the national level.

• Journal of Korea Water Resources Association
• /
• v.45 no.7
• /
• pp.657-674
• /
• 2012

This paper presents the effect of spatially-distributed rainfall on both rainfall-sediment-runoff and erosion or deposition in the experimental Cheoncheon catchment: upstream of Yongdam dam basin. The rainfall fields were generated by three rainfall interpolation techniques (Thiessen polygon: TP, Inverse Distance Weighting: IDW, Kriging) based only on ground gauges and two radar rainfall synthetic techniques (Gauge-Radar ratio: GR, Conditional Merging: CM). Each rainfall field was then assessed in terms of spatial feature and quantity and also used for rainfall-sediment-runoff and erosion-deposition simulation due to the spatial difference of rainfall fields. The results showed that all the interpolation methods based on ground gauges provided very similar hydrologic responses in spite of different spatial pattern of erosion and deposition while raw radar and GR rainfall fields led to underestimated and overestimated simulation results, respectively. The CM technique was acceptable to improve the accuracy of raw radar rainfall for hydrologic simulation even though it is more time consuming to generate spatially-distributed rainfall.

• Journal of Korea Water Resources Association
• /
• v.54 no.spc1
• /
• pp.1155-1166
• /
• 2021

In this study, statistical analysis was performed to suggest the optimal analysis techniques for the main measuring instruments of the fill dam, such as seepage, crest settlement, and porewater pressure gauge. In addition, correlation analysis with water level and rainfall data was performed. Based on the results of descriptive statistical analysis for each instrument, porewater pressure gauges could be classified into 3 groups or 2 groups through principal component analysis, In the case of the group having a high correlation with the water level instrument, the correlation between the gauges was also large. In the case of seepage instrument, the distribution showed an extremely asymmetric distribution, so for quantitative analysis, the average seepage during non-precipitation and precipitation could be estimated through decision tree analysis. In the case of the crest settlement instrument, the correlation analysis showed that the correlation between the gauges was large, but the relationship with the water level instrument did not show a significant linear relationship, so EMD analysis was performed to analyze it in more detail. It is judged that principal component analysis, decision tree analysis, and data filtering method can be applied to analyze the behavior of pore water pressure meters, seepage, and crest settlement instrument as major measurement items of fill dam.

• Journal of Korea Water Resources Association
• /
• v.55 no.11
• /
• pp.913-922
• /
• 2022

The purpose of this research is to propose the measurement of improving DEM by using the water surface range of SAR image analysis for river corridors and to suggest the construction of satellite-based 3D river spatial information of inaccessible regions such as North Korea. For this research, it has been progressed from the accessible area, watershed of Namgang river, the branch of Nakdonggang river. The satellite image was collected from SAR satellite image data for a year in 2021 which was provided by ESA from Sentinel-1A/B data and extracted from the seasonal water surface area. Ground gauge water level was collected from hourly intervals data by WAMIS. The DEM was improved by analysis of the river altitude of water surface area change by the combination of the ground water level of minimum to maximum water surface area data extracted from SAR image analysis. After the improvement of DEM, the altitude of the river varied that it is defined to comprise more natural form of river DEM than the existing DEM. The correction validation of improvement DEM was necessary in field survey elevation data; however, the correction validation was not progressed due to the absence of the data. Although, the purpose of this research is to provide the improvement of DEM by using the analyzed water surface by existing DEM data and SAR image analysis. After the progression of additional correction validation research, we would plan to examine the application in other places and to progress the additional methodological research to apply in inaccessible and unmeasured area including the North Korea.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.2
• /
• pp.203-212
• /
• 2010

Water spray cooling has been widely used in a variety of industrial applications. The present study concentrated on quantitative measurements of the heat flux and heat transfer coefficient by water spray as it impinges on the rough surface of a hot steel plate at $900^{\circ}C$. A novel experimental technique was developed for a hightemperature heat flux gauge with a test block, cartridge heaters, and thermocouples that was used to measure the surface heat flux information on the hot steel plate for local heat flux measurements. The roles of the surface roughness on heat transfer are presented in this paper for well-characterized four rough surfaces with average rms roughness heights of $40-80{\mu}M$. The results show that the local heat transfer for rough surfaces is higher than that for a smooth surface. Heat transfer can be significantly increased by the presence of surface roughness elements, which can disrupt the thin thermal boundary layer. In addition, the heat transfer enhancement mechanism on a rough surface can be investigated by a different boiling regime.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.3
• /
• pp.293-300
• /
• 2013

This study used a water tank and wave maker to generate conditions similar to the real ocean environment. Given that the waves were properly generated in the water tank, a precise analysis indicated the quantitative value of the wave force acting on a body. A high-speed camera and wave-level gauge were used to measure the temporal wave motion and period. A series of artificial water waves were successfully generated using three different wave periods and amplitudes. Each of the waves captured by a high-speed camera was sinusoidal and did not maintain its shape properly without a wave absorber, but it was substantially improved and well shaped when the wave absorber was installed.

• Journal of Korean Society on Water Environment
• /
• v.26 no.2
• /
• pp.215-224
• /
• 2010

This study was carried out to estimate effects of sediment reduction with net type sediment settling pond at highland agricultural areas. Flow and sediment monitoring system with rainfall gauge were installed at the study area for real-time monitoring and analysis. It was found that amount and intensity of rainfall events strongly affect sediment yield from the study area. With net type sediment settling pond, it was expected that approximately 61% of sediment could be removed. The correlation between heavy metals and SS were analyzed in this study. $R^2$ values were 0.644, 0.876, 0.945, and 0.928 for Fe, Mn, Al, and Si, respectively. This results indicate that heavy metals also could be removed with net type sediment settling pond. As shown in this study, the sediment settling pond will be an efficient sediment reduction facility at highland agricultural areas. For maximum reduction efficiencies of sediment and other pollutants at agricultural fields, simplified sediment settling pond should be designed and implemented.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.1
• /
• pp.5-12
• /
• 2014

In this study, we developed the electric heating equipment and applied for soft ground improvement. The developed heat pipe is 4 m-length and consumes 1 kW/m, which is consisted of Ni-Cr wire. It was installed in 3.5~4.5 m below ground surface and heated for 96 hours (48 hours, 2 times). The temperature variation and vapor pressure caused by electric heating was measured by the thermometer and pressure gauge which were installed in the ground (5.0 m), and the tip resistances were measured by static electronic piezo-cone penetration test (CPT). As the results of experiments, 2-order polynomial curve was shown to adjust the variation of tip resistance and the temperature distribution with the horizontal distance from electric heater, whose R2 value is close to 1. In addition, in-situ pore-water pressure and water content was decreased.