• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.1
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• pp.15-28
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• 1992

Temporal variations of the path of the East Korea Warm Current(EKWC) which flows northward along the east coast of Korea were analysed to investigate whether the EKWC directly influences the existence of the so-called Warm Core in the Ulreung basin. From the 13 years(1975-1987) data of the Fisheries Research and Development Agency(FRDA), the $10^{\circ}C$ isotherm at the 100m depth and the depth of $2^{\circ}C$ isotherm and the temperature field at the 200m depth were used for identification of the path and the central position of the Warm Core. Sea surface winds computed from the surface pressure charts gave the monthly-averaged wind stress curl over the East Sea which was used for determination of the Sverdrup transport. And the mass transport stream functions were computed by use of the Sverdrup balance. The variations of the path show that the EKWC does not always have a fixed path and fluctuates with time. And the existence of the Warm Core is independent upon the presence of the EKWC even when the EKWC doesn't flow northward along the east coast of Korea. In view of the mass transport stream functions, the influences of the sea surface winds on the branching of the Tsushima Warm Currents and the presence of the EKWC were investigated. The presence of the EKWC may be hindered by the southward flow driven by the sea surface winds when the Tsushima currents are rather weak. A very weak correlation exists between the north-south component of the Sverdrup transport and the position of the Warm Core. However, a small but significant part of the southward transport across the latitudinal line of $38^{\circ}N$ indicates that cold water from the northern part of the East Sea may be driven and be forced to flow beneath the permanent thermocline in such a way that the thermal structure of the Warm Core and its position might be changed.

• Journal of Korea Water Resources Association
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• v.56 no.1
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• pp.23-34
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• 2023

This study analyzed the bed load transport and channel change on the vegetation zone through laboratory experiments and numerical simulations. To examine the effect of vegetation zone in the laboratory experiment, artificial vegetation zones made of acrylic sticks were installed in the experimental channel, and discharge conditions were adjusted to examine the bed load transport and channel change in the vegetation zone. Next, numerical simulations were performed by applying the same conditions as those of the laboratory experiment to the Nays2D model, a two-dimensional numerical model, and the applicability of the numerical model was examined by comparing the results with the results of the laboratory experiment. Finally, by applying a numerical model, the bed load transport and channel change according to the change in vegetation density were examined. As a result of examining the bed load transport and channel change in the vegetation zone according to the discharge condition change by applying the laboratory experiment and the numerical model, the results of the two application methods were similar. As the discharge increased, bed load from the upper stream was deposited inside the vegetation zone. On the other hand, on the other side of the vegetation zone, the flow was concentrated and erosion occurred. Also, the range of erosion increased in the downstream direction. As a result of examining the bed load transport and channel change according to the change in vegetation density, as the vegetation density increased, the bed load from the upper stream was deposited inside the vegetation zone. On the other hand, due to the increase in vegetation density, the flow was concentrated to the opposite side of the vegetation zone, erosion occurred.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.887-894
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• 2006

Water quality in the Daecheong reservoir has been deteriorated by algal bloom every year. Algal bloom is propagated from eutrophicated tributary into the main body of the reservoir during the wet season. Nutrients from diffuse sources trigger the propagation of the algal bloom. This study is aimed to analyze relationship between the water current by the simulation and algae transport from the main body in the Daecheong reservoir including tributary where algal bloom has occurred seriously every year. Water quality model CE-QUAL-W2 was applied to analyze water movement in draught season (2001) and flooding season (2003). The result of simulation corresponded with the observed water elevation level, 63~80 m and showed stratification of the Daecheong reservoir. In the draught season, as velocity and direction off low in the reservoir was estimated to affect algae transport including nutrient supply from small tributary, algal blooms occurred in the stagnate zone of middle stream of the reservoir. On the other hand, in the flooding season, it was resulted in nutrient transport from upstream of main reservoir and nutrients were delivered up to downstream by fast water velocity. In result, algal blooms occurred in stagnate zone of reservoir downstream as the current of downstream was retarded according to dam outflow control.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.43-48
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• 2004

RTP that is proposed supplement of real-time services on internet environment, as Real-time Transport Protocol, is the protocol that for the purpose of sending data of stream type. RTP and RTCP(Real-time Transport Control Protocol) basically work at the same time, RTCP serves with state information of network at present. RTP has important properties of a transport protocol that runs on end-to-end systems and provides demultiplexing. It also offer reliability and protocol-defined flow／congestion control that transport protocol like TCP can not provides. In this paper, we look around concept and construction of Differentiated sen1ice tint run on RTP and by setting parameters of packet transfer method be used CBQ(Class-Based Queuing) for packet transfer on Differentiated service, each service queue controls properly through packet scheduling method, such as WRR(Weighted Round Robin) and PRR(Packet-by-packet Round Robin) all service classes do not experience the starvation and confirm the performance through computer simulation to achieve fairly scheduling.

• Journal of Soil and Groundwater Environment
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• v.18 no.1
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• pp.123-128
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• 2013

Water quality and contamination of sediment is a growing concern in the Iksan stream of Korea. Heavy metal contamination and changes in the physicochemical properties of the stream were evaluated. Water and sediment samples were collected from six sites during the dry and rainy seasons; pH, DO, EC, ORP, turbidity, $PO_4$-P, $NO_3$-N and selected heavy metals (Cu, Pb, Ni, As, Zn, Cd, Hg) were measured. Results showed almost no change in pH between seasons. DO was highest at site 2 (~2.63 mg/L) in the dry season; EC (1,540 ms/m) was greatest at site 1 in both seasons. The ORP gradually increased from the dry to rainy season at most of the sites and was highest at site 5. Turbidity was highest at site 1 and gradually decreased from the dry to rainy season at all sites except site 3. $PO_4$-P ranged from a high of 1,193mg/L at site 1 to in the dry season to a low of ~1.2 mg/L at site 4. In contrast, $NO_3$-N was highest at site 3 in the rainy season (12,531 mg/L). Among the heavy metals measured, Cu and Zn concentrations were highest at all sediment sites. Cu and Zn are added to livestock feed to improve reproductive rates and can be carried to the stream with manure. Transport of sediment and heavy metals during the rainy season is the major source of stream contamination and it is important to continue monitoring and take necessary action in these areas.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1209-1219
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• 2003

The dynamic behaviors of the single vortex interacting with $CH_4-Air$ jet diffusion flame are investigated numerically. The numerical method is based on a predict-corrector scheme for a low Mach number flow. A two-step global reaction mechanism is adopted as a combustion model. Studies are conducted in fixed initial velocities for the three cases according as where $CO_2$ is added; (1) without dilution, (2) dilution in fuel stream and (3) dilution in oxidizer stream. A single vortex is generated by an axisymmetric jet, which is made by an impulse of a cold fuel when a flame is developed entirely in a computational domain. The simulation shows that $CO_2$ dilution in fuel stream results in somewhat larger vortex radius, and greater amount of entrainment of surrounding fluid than in other cases. Thus, the dilution of $CO_2$ in fuel stream enhances the mixing in single vortex and increases the stretching of the flame surface. The budgets of the vorticity transport equation are examined to reveal the mechanism of vortex formation when $CO_2$ is added. It is found that, in the case of $CO_2$ dilution in fuel stream, the vortex destruction due to volumetric expansion and the vortex production due to baroclinic torque are more dominant than in other cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.371-381
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• 2004

Numerical simulation of $CO_2$ addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H$_2$-O$_2$ diffusion flames of a counterflow configuration. An artificial species, which displaces added $CO_2$ in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added $CO_2$, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added $CO_2$ causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of $CO_2$ addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, $CO_2$＋H=CO＋OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added $CO_2$ mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position.

• Journal of Korea Multimedia Society
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• v.20 no.6
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• pp.853-864
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• 2017

HD padding area is essential redundancy in HD broadcasting. It is possible to use this padding area for the purpose of improving DTV broadcasting services. For utilization of this area, The bit of a service data was converted to black and white $8{\times}8$ block image. Converted block images are compressed with active video and are delivered to a receiver as only DC coefficients in a video stream. video quality is not effected by the proposed method, and service data was perfectly recovered in receiver without errors by using block average and threshold. The proposed utilization of HD essential padding area can possibly overcome the limited transmission stream rate with the bandwidth of HD broadcasting. If service data in transport or video stram were transferred using this padding area, it is possible to improve video quality with expanded video stream rate. Additionally, because the proposed methods are based on well-established standards, it is also useful for world-wide HD broadcasting systems such as ATSC, DVB, and IPTV.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.509-517
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• 1997

Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

• Journal of The Geomorphological Association of Korea
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• v.23 no.3
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• pp.57-66
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• 2016

The objective of this study is to find out geomorphological characteristics of historical ruins where people produced and consumed large jar coffins excavated in the Yeongsan river basin using the map of old drainage network to restore distribution network. For this purpose, we chose the 21 consumption sites. The results are as follows. First of all, large jar coffins(relics, 47.6% of total) in the Yeongsan River basin were located in Sampo stream basin, almost all of them were located within the Yeongsan River main stream basin and Sampo stream basin. Also, distance from all consumption site to river was within about 2km. Therefore, it is thought that the all consumption sites are located at the place of the gift of nature that was very favorable to water transport of jar coffins. The results of this study may be used as basic data for research of cultural relics in the Yeongsan river basin.