• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.1
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• pp.3642-3654
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• 1975

The purpose of this thesis is to derive a unit hydrograph which may be applied to the ungaged watershed area from the relations between directly measurable unitgraph properties such as peak discharge(qp), time to peak discharge (Tp), and lag time (Lg) and watershed characteristics such as river length(L) from the given station to the upstream limits of the watershed area in km, river length from station to centroid of gravity of the watershed area in km (Lca), and main stream slope in meter per km (S). Other procedure based on routing a time-area diagram through catchment storage named Instantaneous Unit Hydrograph(IUH). Dimensionless unitgraph also analysed in brief. The basic data (1969 to 1973) used in these studies are 9 recording level gages and rating curves, 41 rain gages and pluviographs, and 40 observed unitgraphs through the 9 sub watersheds in Nak Oong River basin. The results summarized in these studies are as follows; 1. Time in hour from start of rise to peak rate (Tp) generally occured at the position of 0.3Tb (time base of hydrograph) with some indication of higher values for larger watershed. The base flow is comparelatively higher than the other small watershed area. 2. Te losses from rainfall were divided into initial loss and continuing loss. Initial loss may be defined as that portion of storm rainfall which is intercepted by vegetation, held in deppression storage or infiltrated at a high rate early in the storm and continuing loss is defined as the loss which continues at a constant rate throughout the duration of the storm after the initial loss has been satisfied. Tis continuing loss approximates the nearly constant rate of infiltration (${\Phi}$-index method). The loss rate from this analysis was estimated 50 Per cent to the rainfall excess approximately during the surface runoff occured. 3. Stream slope seems approximate, as is usual, to consider the mainstreamonly, not giving any specific consideration to tributary. It is desirable to develop a single measure of slope that is representative of the who1e stream. The mean slope of channel increment in 1 meter per 200 meters and 1 meter per 1400 meters were defined at Gazang and Jindong respectively. It is considered that the slopes are low slightly in the light of other river studies. Flood concentration rate might slightly be low in the Nak Dong river basin. 4. It found that the watershed lag (Lg, hrs) could be expressed by Lg=0.253 (L.Lca)0.4171 The product L.Lca is a measure of the size and shape of the watershed. For the logarithms, the correlation coefficient for Lg was 0.97 which defined that Lg is closely related with the watershed characteristics, L and Lca. 5. Expression for basin might be expected to take form containing theslope as {{{{ { L}_{g }=0.545 {( { L. { L}_{ca } } over { SQRT {s} } ) }^{0.346 } }}}} For the logarithms, the correlation coefficient for Lg was 0.97 which defined that Lg is closely related with the basin characteristics too. It should be needed to take care of analysis which relating to the mean slopes 6. Peak discharge per unit area of unitgraph for standard duration tr, ㎥/sec/$\textrm{km}^2$, was given by qp=10-0.52-0.0184Lg with a indication of lower values for watershed contrary to the higher lag time. For the logarithms, the correlation coefficient qp was 0.998 which defined high sign ificance. The peak discharge of the unitgraph for an area could therefore be expected to take the from Qp=qp. A(㎥/sec). 7. Using the unitgraph parameter Lg, the base length of the unitgraph, in days, was adopted as {{{{ {T}_{b } =0.73+2.073( { { L}_{g } } over {24 } )}}}} with high significant correlation coefficient, 0.92. The constant of the above equation are fixed by the procedure used to separate base flow from direct runoff. 8. The width W75 of the unitgraph at discharge equal to 75 per cent of the peak discharge, in hours and the width W50 at discharge equal to 50 Per cent of the peak discharge in hours, can be estimated from {{{{ { W}_{75 }= { 1.61} over { { q}_{b } ^{1.05 } } }}}} and {{{{ { W}_{50 }= { 2.5} over { { q}_{b } ^{1.05 } } }}}} respectively. This provides supplementary guide for sketching the unitgraph. 9. Above equations define the three factors necessary to construct the unitgraph for duration tr. For the duration tR, the lag is LgR=Lg+0.2(tR-tr) and this modified lag, LgRis used in qp and Tb It the tr happens to be equal to or close to tR, further assume qpR=qp. 10. Triangular hydrograph is a dimensionless unitgraph prepared from the 40 unitgraphs. The equation is shown as {{{{ { q}_{p } = { K.A.Q} over { { T}_{p } } }}}} or {{{{ { q}_{p } = { 0.21A.Q} over { { T}_{p } } }}}} The constant 0.21 is defined to Nak Dong River basin. 11. The base length of the time-area diagram for the IUH routing is {{{{C=0.9 {( { L. { L}_{ca } } over { SQRT { s} } ) }^{1/3 } }}}}. Correlation coefficient for C was 0.983 which defined a high significance. The base length of the T-AD was set to equal the time from the midpoint of rain fall excess to the point of contraflexure. The constant K, derived in this studies is K=8.32+0.0213 {{{{ { L} over { SQRT { s} } }}}} with correlation coefficient, 0.964. 12. In the light of the results analysed in these studies, average errors in the peak discharge of the Synthetic unitgraph, Triangular unitgraph, and IUH were estimated as 2.2, 7.7 and 6.4 per cent respectively to the peak of observed average unitgraph. Each ordinate of the Synthetic unitgraph was approached closely to the observed one.

• 한국해양학회지
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• v.18 no.2
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• pp.104-110
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• 1983

The Intermittent phenomena of the turbulent momentrm transports were closely examined in order to know the nature of intermittency and its fluid dynamic implications in the oceanic turbulent boundary layer. Also the connection between the observed intermittency and the bursting phenomenon was studied in detail. In this investigation, strong intermittency of turbulent momentum transports were found and the peak values of Reynolds stress (i,e., u'w') was about 408 times greater than average Reynolds stress (u',w') in the mid-layer and 270 times greater in the uppcrlayer of the turbulent boundary layer. These values are far greater than presently known maximum value, namely 30 times greater than the average Reynolds stress reported by Gordon (1974) and Heathersaw (1974). The distribution of Reynolds stress were extremely non-normal with the mean peak occurrence period of 5 minutes in the mid-layer and 1. 1 minutes in the upper layer of the turbulent boundary layer. Each teak lasted about 2 seconds in the mid-layer and 1.1 seconds in the upper layer of the turbulent boundary layer. Our dimensionless period of peak occurrence are found to be 33.3 in the mid-layer and 7.3 in the upper-layer, which are substantially larger than the often quoted values of 3.2-6.8 for the bursting period (Jackson, 1976). Some workers have interpreted that the intermittency phenomenon is the retlect of burst across their probe of the currentmeter (Gordon, 1974; Heathersaw, 1974). However, it was known that the burst can be found very near bottom boundary with smoothed bottom (i,e., friction Reynolds number$\leq$3,000) in the laboratory experiments. Through this investigation, it was found that the intermittent strength of the turbulent momentum transports does not conclusively indicate the characteristic feature of the boundary layer turbulence with a rough bottom (i,e., friction Reynolds number$\geq$10$\^$5/).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3B
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• pp.193-201
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• 2012

In the last decade, heavy rainfall induced debris flow events have been remarkably occurred in Korea. Consequently, debris flow is becoming one of the most dangerous natural phenomena in mountainous area. Understanding and correct predicting of the runout distance of debris flow is an essential prerequisite for developing debris flow hazard map and prevention technology. Based on the simple and widely used sled model, in this study, we analyse the net efficiency of debris flows which is a dimensionless constant (=1/R) and defined by the ratio of the horizontal runout distance L from the debris flow source to deposit and the vertical elevation H of the source above the deposit. The analysis of field data observed in total 238 debris flow events occurred from 2002 to 2011 reveals that the representative value of the net efficiency of debris flows in Korea is 4.3. The data observed in Gangwon province where is the most debris flow-prone area in Korea shows that debris flows in Inje area have the runout distance longer than those in Pyongchang and Gangneung. Overall features of the net efficiency of debris flows observed in the central Korea are similar to those in the southern Korea. The estimation based on aerial photographs and available depositional conditions appears to overestimate the net efficiency compared to estimation based on the field observations, which indicates that appropriate depositional conditions need to be developed for debris flows in Korea.

• Journal of Korea Water Resources Association
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• v.45 no.3
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• pp.275-290
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• 2012

In this study, we have developed an optimal time distribution model through extraction of peaks over threshold (POT) series. The median values for annual maximum rainfall dataset, which are obtained from the magnetic recording (MMR) and the automatic weather system(AWS) data at Seoul meteorological observatory, were used as the POT criteria. We also suggested the improved methodology for the time distribution of extreme rainfall compared to Huff method, which is widely used for time distributions of design rainfall. The Huff method did not consider changing in the shape of time distribution for each rainfall durations and rainfall criteria as total amount of rainfall for each rainfall events. This study have suggested an extracting methodology for rainfall events in each quartile based on interquartile range (IQR) matrix and selection for the mode quartile storm to determine the ranking cosidering weighting factors on minutely observation data. Finally, the optimal time distribution model in each rainfall duration was derived considering both data size and characteristics of distribution using kernel density function in extracted dimensionless unit rainfall hyetograph.

• Journal of Korea Water Resources Association
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• v.45 no.2
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• pp.151-163
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• 2012

The distribution of gravel-bed materials in mountainous river is formed by the process of deposition and transportation of sediment responding to stream power of the latest flood that is over the certain scale. The particle size of bed material was surveyed in the longitudinal points of river and detail points of a specific meandering section and used to estimate the critical velocity and stream power. Yang's critical unit stream power and Bagnold's critical stream power for gravel-bed materials increased with the distance from downstream to upstream. Dimensionless shear stress based on the designed flood discharge in Shields diagram was evaluated that the gravel-bed materials in most survey points may be transported as form of bedload. The mean diameter in the meandering section was the biggest size in first water impingement point of inflow water from upstream and the second big size in second water impingement point by reflection flow. The mean diameters were relatively the small sizes in points right after water impingement. The range of mean critical velocity was 0.77~2.60 m/s and critical unit stream power was big greatly in first water impingement point. The distribution of critical stream power, range of 7~171 $W/m^2$, was shown that variation in longitudinal section was more obvious than that of cross section and estimated that critical stream power may be affected greatly in first and second water impingement point.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.706-711
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• 2016

Characteristics of solid circulation rate in the liquid-solid circulating fluidized beds with viscous liquid medium were investigated. Effects of primary and secondary liquid velocities, particle size, liquid viscosity and height of solid particles piled up in the solid recycle device on the solid circulation rate were considered. The solid circulation rate increased with increasing primary and secondary liquid velocities, liquid viscosity and height of solid particles in the downcommer, but it decreased with increasing particle size. The particle rising velocity in the riser decreased with increasing the ratio of $U_{L1}/U_{L2}$ and particle size. The slip velocity of liquid and particle, $U_L/U_S$, decreased with increasing liquid viscosity but it increased with increasing particle size. The values of solid circulation rate were well correlated in terms of operating variables and dimensionless groups.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.3
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• pp.179-189
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• 2014

Pyroprocessing has been developed for the purpose of resolving the current spent nuclear fuel management issue and enhancing the recycle of valuable resources. An electrolytic reduction of the pyroprocessing is a process to reduce oxides into metals using LiCl as an electrolyte and requires a post-treatment process due to the inclusion of residual salt in porous metal products. A vacuum distillation has been adopted for various molten salt systems and could be applied to the post-treatment process of the electrolytic reduction. The residual salt in the metal products includes LiCl, alkali chlorides, and alkaline earth chlorides. In this paper, vapor pressures of chlorides have been estimated and the composition changes on the residual liquid during the vacuum distillation process have been calculated. A model combining a material balance and vapor-liquid equilibrium relations has been proposed under a constant vapor discharging flow rate and liquid composition changes have been calculated using the vapor pressures with respect to a dimensionless time. The behaviors have been compared with temperature and molten salt composition changes to simulate the process condition variation. The distillation of the residual salt has been dominated by LiCl which is the main component of the salt and CsCl of which vapor pressure is higher than that of LiCl would be readily removed. RbCl exhibits similar vapor pressure with LiCl and maintains its composition. However, $SrCl_2$ and $BaCl_2$ of which vapor pressures are much lower than that of LiCl are concentrated with time and expected to be possibly precipitated during the distillation when the initial compositions are increased.

• Journal of Korea Water Resources Association
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• v.50 no.4
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• pp.223-232
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• 2017

The ability to defend against floods in urban areas was weakened, because the increase in the impervious rate of urban areas due to urbanization and industrialization and the increase in the localized torrential rainfall due to abnormal climate. In order to reduce flood damage in urban areas, various runoff reduction facilities such as detention ponds and infiltration facilities were installed. However, in the case of domestic metropolitan cities, it is difficult to secure land for the installation of storm water reduction facilities and secure the budget for improving the aged pipelines. Therefore, it is necessary to design a storage system (called the detention pond in trunk sewer) that linked the existing drainage system to improve the flood control capacity of the urban area and reduce the budget. In this study, to analyze the effect of reducing runoff amounts according to the volume of the detention pond in trunk sewer, three kinds of virtual watershed (longitudinal, middle, concentration shape) were assumed and the detention pond in trunk sewer was installed at an arbitrary location in the watershed. The volume of the detention pond in trunk sewer was set to 6 cases ($1,000m^3$, $3,000m^3$, $5,000m^3$, $10,000m^3$, $20,000m^3$, $30,000m^3$), and the installation location of the detention pond in trunk sewer was varied to 20%, 40%, 60%, and 80% of the detention pond upstream area to the total watershed area (DUAR). Also, using the results of this study, a graph of the relationship and relational equation between the volume of the detention pond in trunk sewer and the installation location is presented.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.29-39
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• 2017

In this research, thermal design data such as heat transfer coefficient on the wall surface required for ventilation system design which is to prevent the temperature rise in the underground utility tunnel that three sides are adjoined with the ground was investigated in numerical analalysis. The numerical model has been devised including the tunnel lining of the underground utility tunnel in order to take account for the heat transfer in the tunnel walls. The air temperature in the tunnel, wall temperature, and the heating value through the wall based on heating value(117~468 kW/km) of the power cable installed in the tunnel and the wind speed in the tunnel(0.5~4.0 m/s) were calculated by CFD simulation. In addition, the wall heat transfer coefficient was computed from the results analysis, and the limit distance used to keep the air temperature in the tunnel stable was examined through the research. The convective heat transfer coefficient at the wall surface shows unstable pattern at the inlet area. However, it converges to a constant value beyond approximately 100 meter. The tunnel wall heat transfer coefficient is $3.1{\sim}9.16W/m^2^{\circ}C$ depending on the wind speed, and following is the dimensionless number:$Nu=1.081Re^{0.4927}({\mu}/{\mu}_w)^{0.14}$. This study has suggested the prediction model of temperature in the tunnel based on the thermal resistance analysis technique, and it is appraised that deviation can be used in the range of 3% estimation.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.82-87
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• 2014

MLI(Multi-layer Insulation) is widely used to get highly insulating on cryogenic system in order to reduce heat loads. MLI for satellites thermal performance is changed by materials and laminated method. In this study, a composite multilayer insulation by application of heat stroage tank performance were compared with materials and laminated to change the way. Experimental methods of the KS C 9805 was used, the composite multilayer insulation and EPS was compared with the insulation performance. A method for analysis of experimental results is the equivalent thickness about CMI and the insulation performance were used to compare thermal conductance. As a results, the equivalnet thickenss and the thermal conductance of the composite multilayer insulation were smaller than the EPS and the thermal performance are more excellent. In addition, the configuration of the composite multilayer insulation materials and laminated method varies depending on the overall heat transfer coefficient was confirmed.