• International Journal of Fluid Machinery and Systems
• /
• v.2 no.1
• /
• pp.31-39
• /
• 2009

The flow instability in a low specific speed mixed-flow pump, having a positive slope of head-flow characteristics was investigated. Based on the static pressure measurements, it was found that a rotating stall in the vaned diffuser occurs at about 65% flow rate of best efficiency point (BEP). A dynamic Particle Image Velocimetry (DPIV) measurement and the numerical simulations were conducted in order to investigate the flow fields. As a result, the diffuser rotating stall was simulated even by Computational Fluid Dynamics (CFD) and the calculated periodic flow patterns agree well with the measured ones by DPIV. It is clarified that a periodical large scaled backflow, generated at the leading edge of the suction surface of the diffuser vane, causes the instability. Furthermore, the growth of the strong vortex at the leading edge of the diffuser vane induces the strong backflow from the diffuser outlet to the inlet. The scale of one stall cell is covered over four-passages in total thirteen vane-passages.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.1
• /
• pp.1-8
• /
• 2002

Metal surface temperatures around the combustion chamber in a gasoline engine directly affect thermal durability and performance of the engine. Metal surface temperatures are influenced by many cooling factors such as drilled water passage, deflector, combustion chamber wall thickness, pillar, and coolant flow pattern. The object of this study is to learn how the coolant passages and coolant flow pattern in an engine influence to the engine metal surface temperature at engine full load and speed. From the test result, it is suggested a plan to reinforce the engine stiffness and to reduce the thermal stress simultaneously. Also, approaches are introduced to reduce the thermal load on the engine by adjusting the discharging direction from the water pump and by optimizing the water transfer holes in the cylinder head gasket. These methods and the optimized engine cooling system, which were suggested in this paper, were adapted for an engine in progress to eliminate the exhaust valve seat wear.

• English Language & Literature Teaching
• /
• v.9 no.spc
• /
• pp.79-98
• /
• 2003

This article reports that a testee's content schemata have detrimental effects on the validity of standardized reading comprehension tests. in case that the reading passages constitute his prior background knowledge framed by regular academic pursuits focused on a major field of study. The empirical research findings on such a reliability issue have shown that the Korean subjects' familiarity with the content domain of the reading materials may substantially enhance their test performance, operated as unfair advantages over the other participants at the same level of English proficiency who do not possess technical knowledge closely related to the contents of the test passages. Based on these results, it may be argued that the reading text should be composed of maximally neutral contents to every testee to avoid the possible overlapping between a test-taker's content schemata and the content domain of the materials. Therefore, this article claims that the tenets of schema theory with its long-standing foundation on culturally predetermined content and formal schemata need to be expanded to cover professional knowledge structures, like those acquired by higher education, as the hard-wired framework of an individual's original culture-specific background knowledge.

• The KIPS Transactions:PartB
• /
• v.12B no.1 s.97
• /
• pp.57-68
• /
• 2005

It is important to segment a text, which is independent upon any text-embedded auxiliary information. This paper presents a technique for dividing the text into field-coherent passages. The presented method is based upon extracting field-associated terms from the text measuring how the topics grow, shrink and shift from sentence to sentence. We propose measures of topic continuity and of topic transition and suggest how those could be used to find the boundaries among passages. After collecting 12,500 documents, we obtain $88{\%}$ for average precision and $78{\%}$ for recall in Korean training set.

• Wind and Structures
• /
• v.22 no.4
• /
• pp.409-428
• /
• 2016

The mechanical and aerodynamic effect of building shape plays a dominate role in the pedestrian level wind environment. These effects have been presented in numerous studies and are available in many wind codes. However, most studies have focused on wind flow around conventional buildings and are limited to few wind directions. The present study investigated wind circulation in the re-entrant corners of cross-shaped high-rise buildings from various wind directions. The investigation focused on the pedestrian level wind environment in the re-entrant corners with different aspect ratios of building arrangements. Ninety cases of case study arrangements were evaluated using wind tunnel experimentation. The results show that for adequate wind circulation in the re-entrant corners, building orientations and separations play a critical role. Furthermore, in normal wind incident directions and at a high aspect ratio, poor wind flow was observed in the re-entrant corners. Moreover, it was noted that an optimized building orientation and aspect ratio significantly improved the wind flow in re-entrant corners and through passages. In addition, it was observed that oblique wind incident direction increased wind circulation in the re-entrant corners and through passages.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.587-598
• /
• 2008

In the trackbed design using elastic multi-layer model, the stress-dependent resilient modulus is an important input parameter, which reflects substructure performance under repeated traffic loading. The resilient moduli of crushed stone and weathered granite soil were developed using nonlinear dynamic stiffness, which can be measured by in-situ and laboratory seismic tests. The prediction models of resilient modulus varying with the deviatoric or bulk stress were proposed (Park et al., 2008). To investigate the performance of the prediction models proposed herein, the elastic response of the test trackbed near PyeongTaek, Korea was evaluated using a 3-D nonlinear elastic computer program (GEOTRACK) and compared with measured elastic vertical displacement during the passages of freight and passenger trains. The material types of the test sub-ballasts are crushed stone and weathered granite soil, respectively. The calculated vertical displacements within the sub-ballasts are within the order of 1mm, and agree well with measured values with the reasonable margin. The prediction models are thus concluded to work properly in the preliminary investigation. The prediction models proposed for resilient modulus were verified by the comparison of the calculated vertical displacements with measured ones during train passages.

• Journal of computational fluids engineering
• /
• v.6 no.3
• /
• pp.41-50
• /
• 2001

Effects of rotor-stator blade count ratio on the unsteady aerodynamic characteristics of a cascade was studied by using a Navier-Stokes code. Present Navier-Stokes code is a parallel code and works on a multi-cpu machine. It is based on the SIMPLE algorithm and uses QUICK scheme for convection terms and second order back difference for all temporal derivatives. Computations were carried out for two cases : case 1 is for 3 stator cascade passages subjected to two upstream wakes while case 2 is for 2 stator cascade passages subjected to three upstream wakes. Numerical solutions show that rotor-stator blade count ratio plays a significant role in the unsteady aerodynamic characteristics of the stator cascade. Case 2 shows smaller unsteady fluctuation than case 1, even if they show the same time averaged value. The smaller fluctuation of case 2 is believed due to strong interaction between unsteady vortices. The unsteady lift variation of case 2 is shown to have many high frequency fluctuations as more unsteady vortices travel around the cascade. The unsteady turbulent kinetic energy due to the upstream wake is also shown to decay faster through the cascade passage than in the free stream.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.610-615
• /
• 2001

Effects of rotor-stator blade count ratio on the unsteady aerodynamic characteristics of a cascade was studied by using a Navier-Stokes code. Present Navier-Stokes code is a parallel code and works on a multi-cpu machine. It is based on the SIMPLE algorithm and uses QUICK scheme for convection terms and second order back difference for all temporal derivatives. Computations were carried out for two cases : case 1 is for 3 stator cascade passages subjected to two upstream wakes while case 2 is for 2 stator cascade passages subjected to three upstream wakes. Numerical solutions show that rotor-stator blade count ratio plays a significant role in the unsteady aerodynamic characteristics of the stator cascade. Case 2 shows smaller unsteady fluctuation than case 1, even if they show the same time averaged value. The smaller fluctuation of case 2 is believed due to strong interaction between unsteady vortices. The unsteady lift variation of case 2 is shown to have many high frequency fluctuations as more unsteady vortices travel around the cascade. The unsteady turbulent kinetic energy due to the upstream wake is also shown to decay faster through the cascade passage than in the free stream.

• Phonetics and Speech Sciences
• /
• v.6 no.4
• /
• pp.151-159
• /
• 2014

The study investigated the effects of reading intervention to enhance reading fluency for children from low-income families. The participants were 20 children from low-income families who are in grades 1 to 3. To qualify for participation in this study, all children had to score below 30 % ile on the Receptive vocabulary Test of the Expressive and Receptive Vocabulary Test or the Word reading fluency of the Korean Language-Based Reading Assessment. Participants were randomly assigned to the intervention (n=10) or control (n=10) group. The intervention group participated in the individualized intervention program using the guided repeated reading and the corrective feedback strategies. The results showed that participants in the intervention group performed better on reading fluency than those in the control group after participating in the intervention program. Specifically, guided repeated reading with corrective feedback strategies produced significant improvement on generalization to unpracticed passages as well as practiced passages. The results of this study suggest that guided repeated reading with corrective feedback is effective for enhancing reading fluency for children in Korea. Further study is needed in order to develop language-specific reading intervention.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
• /
• v.9 no.1
• /
• pp.27-31
• /
• 1998

Nasal sounds include nasalized vowels and consonants. Nasal cavity is important for the acoustics of nasal sounds. Evaluating the effects of site-specific nasal obstruction on nasal sound will help us to understand the importance of nasal geometry for the nasal sound and to foretell voice change after nasal surgery This study was designed to analyze the change of nasality and formant characteristics of nasal sound by obstructing different sites around the ostiomeatal unit(OMU). Ten adult male and female volunteers participated. The nasal formants and bandwidths of nasal consonant /n/ were checked in various conditions of nasal obstruction. The nasalance of rabbit, baby, and mama passages were compared in each conditions. Nasalance of all passages decreased when anterior portion of OMU was obstructed. Center frequency of first nasal formant(NF1) of /n/ has decreased in the order of anterior, inferior obstruction. The bandwidth of NF1 decreased in female with anterior obstruction. Anterior portion of OMU is most critical to the change of nasality and acoustics of nasal consonant. When anterior portion of OMU is obstructed, the shift of NF1 to a lower frequency and the narrowing of NF1 bandwidth are the major acoustic changes of nasal consonant /n/.