• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.161-164
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• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/e, of 2,0%. This squealer tip has a indent-to-chord ratio, $h_{st}/c$, of 5.5%. The results are compared with those for a plane tip ($h_{st}/c\;=\;0.0%$). The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• Journal of applied mathematics & informatics
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• v.36 no.3_4
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• pp.181-203
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• 2018

In this paper, we have constructed an overlapping Schwarz method for singularly perturbed second order convection-diffusion equations. The method splits the original domain into two overlapping subdomains. A hybrid difference scheme is proposed in which on the boundary layer region we use the central finite difference scheme on a uniform mesh while on the non-layer region we use the mid-point difference scheme on a uniform mesh. It is shown that the numerical approximations which converge in the maximum norm to the exact solution. When appropriate subdomains are used, the numerical approximations generated from the method are shown to be first order convergent. Furthermore it is shown that, two iterations are sufficient to achieve the expected accuracy. Numerical examples are presented to support the theoretical results. The main advantages of this method used with the proposed scheme is it reduces iteration counts very much and easily identifies in which iteration the Schwarz iterate terminates.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.913-920
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• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/c, of 2.0%. This squealer tip has a indent-to-chord ratio, $h/{st}/c$, of 5.5%. The results are compared with those for a plane tip $(h_{st}/c=0.0%)$. The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• Korean Journal of Remote Sensing
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• v.36 no.4
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• pp.527-534
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• 2020

This study aims to monitor the displacement of the bridges using Stanford Method for Persistent Scatterers (StaMPS) time-series Persistent Scatterer Interferometric Synthetic Aperture Radar analysis. For case study bridges: Kimdaejung bridge and Deokyang bridge, we acquired 60 and 33 Cosmo-Skymed Synthetic Aperture Radar (SAR) data over the Mokpo region and Yeosu region, respectively from 2013 to 2019. With single-look interferograms, we estimated the long-term time-series displacements over the bridges. The time-series displacements were estimated as -8.8 mm/year and -1.34 mm/year at the mid-span over the selected bridges: Kimdaejung and Deokyang bridge, respectively. This time-series displacement provides reliable and high spatial resolution information to monitor the structural behavior of the bridge for preventing structural behaviors.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1026-1030
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• 2010

The Geum river being used as drinking water sources has contaminated due to inflow of inadequately treated wastewater from the tributaries into the river. The characteristics of water quality in the upper regions showed good grade(BOD<3mg/L) in the Geum river, the Mankyung river and the Dongjin river, while that in the lower regions and the upper region of the Sapkyo river did not achieve the good grade. This resulted in the inflow of domestic, industrial and livestock wastewater not adequately treated by wastewater treatment systems. For lakes, the mouth of the kyungchun lake, the Sapkyo lake and the Yedane lake showed the eutrophication phenaminon with higher COD concentration. In particular, total phosphorus and chlorophyll-a concentration were higher in the Sapkyo lake than other lake.

• Steel and Composite Structures
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• v.32 no.1
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• pp.21-35
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• 2019

This study investigates the flexural behavior of steel-concrete composite beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. An innovative mechanical anchorage system was developed. The components of the system can be easily assembled on site before applying a prestressing force, and removed from the structures after strengthening is completed. A total of seven steel-concrete composite specimens including four simply supported beams strengthened at the positive moment region and three continuous beams strengthened at the negative moment region were tested statically until failure. Experimental results showed that the use of prestressed CFRP plates enhanced the flexural capacity and reduced the mid-span deflection of the beams. Furthermore, by prestressing the CFRP laminates, the material was used more efficiently, and the crack resistance of the continuous composite specimens at the central support was significantly improved after strengthening. Overall, the anchorage system proved to be practical and feasible for the strengthening of steel-concrete composite beams. The theoretical analysis of ultimate bearing capacity is reported, and good agreement between analytical values and experimental results is achieved.

• Journal of the Korean Society of Visualization
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• v.20 no.1
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• pp.29-37
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• 2022

We carried out a laboratory experiment about the thermo-fluidic characteristics of natural convection boundary layer over a vertical heated plate under constant heat flux condition. Particle image velocimetry has been applied to observe the surface convection velocity close to the vertical plate submerged in the water chamber with the condition of Ra = 7 × 10⁹ and Pr = 8.1. The velocity distributions indicate that the distinct stripe-like structures appears in the upstream (earlier transition region) and the distinct negative-positive and Λ(λ)-shaped flow structures in the downstream (mid-transition region). In addition, the temporal variation of spanwise and streamwise velocity is also presented.

• The Korean Journal of Petroleum Geology
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• v.4 no.1_2 s.5
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• pp.1-11
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• 1996

Multichannel deep seismic reflection data in the Main Pass area of the northern Gulf of Mexico are interpreted in this study for the stratigraphy and the depositional history. Structural analysis of deep seismic reflection data provides new information on the locations of paleo-shelf margins and the basement. The basement occurs at about $7.5{\cal}km$ depth at the northern end of seismic line LSU-1 in the Mississippi shelf. The Jurassic and early Cretaceous shelf margins occupy approximately the same position, whereas the Oligocene shelf margin occurs about 28 km farther landward. Ten major seismic stratigraphic sequences are identified for the Mesozoic and Cenozoic sed-imentary section. Correlation of sequence boundaries defined in this study with those in other areas of the circum-Gulf region indicates that majo. regional unconformities formed at the mid-Miocene (10.5 Ma), mid-Oligocene (30 Ma), mid-Cretaceous (97 Ma), and top-Jurassic (131 Ma). Three distinct periods a.e recognized in the depositional history of the Main Pass area of the northern Gulf of Mexico: (1) shallow ma.me deposition du.ins the period from the opening of the Gulf to the mid-Cretaceous, (2) deep marine deposition in the Cretaceous to the mid-Oligocene, and (3) shallow marine deposition prevailed since the mid-Oligocene to present. A comparison of depositional rates between the Main Pass area and the Destin Dome area indicates that the northern Gulf of Mexico continental margin was initiated as a terrigenous sediment wedge province in the late Cretaceous.

• Journal of Astronomy and Space Sciences
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• v.28 no.3
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• pp.173-181
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• 2011

Korea Astronomy and Space Science Institute researchers have installed and operated magnetometers at Mt. Bohyun Observatory to measure the Earth's magnetic field variations in South Korea. We, in 2007, installed a fluxgate magnetometer (RFP-523C) to measure H, D, and Z components of the geomagnetic field. In addition, in 2009, we installed a Overhauser proton sensor to measure the absolute total magnetic field F and a three-axis magneto-impedance sensor for spectrum analysis. Currently three types of magnetometer data have been accumulated. In this paper, we provide the preliminary and the first statistical analysis using the BOH magnetometer installed at Mt. Bohyun Observatory. By superposed analysis, we find that daily variations of H, D, and Z shows similar tendency, that is, about 30 minutes before the meridian (11:28) a minimum appears and the time after about 3 hours and 30 minutes (15:28) a maximum appears. Also, a quiet interval start time (19:06) is near the sunset time, and a quiet interval end time (06:40) is near the sunrise time. From the sunset to the sunrise, the value of H has a nearly constant interval, that is, the sun affects the changes in H values. Seasonal variations show similar dependences to the sun. Local time variations show that noon region has the biggest variations and midnight region has the smallest variations. We compare the correlations between geomagnetic variations and activity indices as we expect the geomagnetic variation would contain the effects of geomagnetic activity variations. As a result, the correlation coefficient between H and Dst is the highest (r = 0.947), and other AL, AE, AU index and showed a high correlation. Therefore, the effects of geomagnetic storms and geomagnetic substorms might contribute to the geomagnetic changes significantly.

• Journal of environmental and Sanitary engineering
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• v.7 no.2
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• pp.29-36
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• 1992

Among the rivers in Korea, the Han River is the largest, most important one, which runs through the Seoul metropolitan region in the west toward the yellow sea. In the Han River basin there live as many as 17.1 mil. people including appr, 11 mil, citizens in Seoul. The Seoul Metropolitan region, already containing appr. 40% of the nation's total populating, expectedly poses an ever-growing polluting burden to the Han River. Due to Korea's vigorous industrialization and heavy urbanization in the past quarter century, water pollution was observed to be increasing in the Han River until the mid-1980's, but thereafter the Han River began to improve little by little by virtue of the government's massive investment and all-out efforts in water preservation. Public awareness on the importance of environmental protection is increasing unprecedentedly. With a view to meeting people's growing demand for clean water and pleasant environment, the government established the "Comprehensive Mid-Term Environmental Conservation Plan" (1992∼1993) in 1991. According to the plan, 1,315 bil.won(1.7 bil.us$ ) is to be poured into the Han River Basin to install 113 water pollutant abatement plants including 43 treatment facilities. To successfully cope with the future's challenging need for the environmentally sound sustainable development, a variety of measures and an array of policies are going to be incorporated with emphasis on, -redistributing such polluting sources as population and industries -tightening control of the water pollutant discharge -restricting the pollution-accompanying land use -enhancing the assimilation capacity of the river -stirring up the public awareness and participation in the environment protection We hopefully anticipate that with those e(forts the Han River will improve as drawn in the attached "1996's Envisioned Han River Quality".