• Journal of Korean Society for Atmospheric Environment
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• v.18 no.5
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• pp.401-410
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• 2002

Concerns for energy conservation, environmental pollution, and the fact that organic wastes account for a major portion of our waste materials, have created the interest of biogas, which usually contains about 60 to 70 percent methane, 30 to 40 percent carbon dioxide, and other gases, including ammonia, hydrogen sulfide, mercaptans and other noxious gases. Cyclone combustors are used for homing a wide range of fuels such as low calorific value gas, waste water, sludge. coal, etc. The 3-dimensional swirling flow, combustion and emission in a tangential inlet cyclone incinerator under different inlet conditions are simulated using a standard k-s turbulence model and ESCRS (Extended Simple Chemically-Reacting System) model. The commercial code Phoenics Ver.3.4 was used for the present work. The main parameters considered in this work are inlet velocity and air to fuel ratio. The results showed that the change of operating conditions had an influence on the shape and size of recirculation zones, mixture fraction and axial velocity which are important factors for combustion efficiency and emission behavior. The application of this kind of computer program seams to be promising as a potential tool for the optimum design of a cyclone combustor with low emission.

• Wind and Structures
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• v.21 no.2
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• pp.241-272
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• 2015

In the current study, dynamic and quasi-static analyses were performed to investigate the response of multiple-spanned and single-spanned transmission line conductors under both downburst and synoptic winds considering different wind velocities and different length spans. Two critical downburst configurations, recommended in the literature and expected to cause maximum conductor reactions, were considered in the analyses. The objective of the study was to assess the importance of including the dynamic effect when predicting the conductor's reactions on the towers. This was achieved by calculating the mean, the background and the resonant reaction components, and evaluating the contribution of the resonant component to the peak reaction. The results show that the maximum contribution of the resonant component is generally low (in the order of 6%) for the multiple-spanned system at different wind velocities for both downburst and synoptic winds. For the single-spanned system, the result show a relatively high maximum contribution (in the order of 16%) at low wind velocity and a low maximum contribution (in the order of 6%) at high wind velocity for both downburst and synoptic winds. Such contributions may justify the usage of the quasi-static approach for analyzing transmission line conductors subjected to the high wind velocities typically used for the line design.

• The Journal of Churna Manual Medicine for Spine and Nerves
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• v.10 no.1
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• pp.15-33
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• 2015

Objectives : The aim of this systemic review was to summarize and compare adverse effect of spinal manipulation at domestic and abroad. Methods : We searched articles in Korean databases and Pubmed. We selected and analysed the articles met inclusion criteria. Results : 51 cases were included. 32 cases in Pubmed show that adverse effect related to cervical rotation and high velocity low amplitude(HVLA) thrust manipulation. It leads to severe adverse effect and sequela about vascular. While, 19 cases in Korean articles shows that domestic spinal manipulation is more safe becase of lower use of high velocity low amplitude(HVLA) thrust. It leads to low incidence of vascular adverse effect and no sequela. Conclusions : We concluded that Chuna is difficult manipulation because of possibility of adverse effect. Chuna is recommended to be taken by licensed medical practitioners who are skilled and complete the regular curriculum. Further studies like meta analysis about spinal manipulation are needed to estimate incidence of adverse effect. And adverse effects are going to be collected continually through randomized controlled trials(RCT) related to spinal manipulation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.6
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• pp.782-793
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• 2018

A small-scale horizontal axis hydrokinetic turbine is designed, manufactured and studied both experimentally and numerically in this study. The turbine is expected to work in most of China's sea areas where the ocean current velocity is low and to supply electricity for remote islands. To improve the efficiency of the turbine at low flow velocities, a magnetic coupling is used for the non-contacting transmission of the rotor torque. A prototype is manufactured and tested in a towing tank. The experimental results show that the turbine is characterized by a cut-in velocity of 0.25 m/s and a maximum power coefficient of 0.33, proving the feasibility of using magnetic couplings to reduce the resistive torque in the transmission parts. Three dimensional Computational Fluid Dynamics (CFD) simulations, which are based on the Reynolds Averaged Navier-Stokes (RANS) equations, are then performed to evaluate the performance of the rotor both at transient and steady state.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.278-283
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• 2003

A generation rate of sludge in Korea had increased dramatically about 200 % for a decade. A requirement for high efficiency dewatering system being possible to produce the low water content cake have suggested due to the appearanceof commercial and social problems about handling of dewatered cake. The conventional dewatering system with mechanical compression device was not suitable to produce the low water content cake and didn'tcope with lots of requirements. Therefore, this paper was to develop the high efficient filter press with the compressive and heating forces through the heating plate to be built between membrane filter plates. It is possible to produce the low water content cake and improve the dewatering rate, so this equipment positively coped with several types of problems related to the sludge dewatering. The plate heated by heat transfer materials such as steam, hot water and thermo-oil made the sludge make the residual moisture within the cake to discharge easilyand to improve the dewatering efficiency of equipment. The pilot scale experiment with 500kg of cake production showed that the dewatering efficiency determined by the final water content and dewatering velocity was improved 30% more than the conventional dewatering equipment.

• Journal of Biosystems Engineering
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• v.20 no.1
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• pp.13-21
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• 1995

This study was conducted to investigate the cutting mechanism of reciprocating knife of combine harvester. The cutting operation of reciprocating knife with the arrangement of the low-cutting and the double-cutting was demonstrated through cutting pattern diagram which was drawn by computer graphics. Various kinds and dimensions of reciprocating knives were analyzed using the developed program. The results are summarized as follows (1) The low-cutting type reciprocating knife was represented similar cutting characteristics to the standard type, but the maximum stalk-deflection was decreased as 1/2 level of the standard type. And the first ledger plate should be designed shorter than the second ledger plate. (2) The bunching area and the maximum stalk-deflection for the double cutting knife almost were not changed since cutting velocity ratio of 0.6, but the secondary cut were occurred at ratio of 0.8 and increased rapidly over these ratio. (3) The double cutting knife was recommended for the high speed combine, because its bunching area and the maximum stalk-deflection were decreased as 1/2 level of the standard type. (4) In order to maintain the proper cutting mechanism characterized by the bunching area, the maximum stalk-deflection and the secondary cutting length etc., the adequate cutting velocity at forward speed of 0.5㎧ to 1.2㎧ was from 0.3㎧ to 0.96㎧ for the double cutting knives.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.977-986
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• 2019

In the thermal-hydraulic system codes, such as MARS and RELAP5/MOD3, the Savannah River Laboratory (SRL) model has been adopted as a subcooled boiling model. It, however, has been shown that the SRL model cannot take into account appropriately the effects of inlet liquid velocity and hydraulic diameter on axial void fraction development. To overcome the problems, Ha et al. (2018) proposed a modified SRL model, which is applicable to low-pressure and low-Pe conditions (P < 9.83 bar and $Pe{\leq}70,000$) only. In this work, the authors extended the modified SRL model by proposing a new net vapor generation (NVG) model and a wall evaporation model so that the new subcooled boiling model can cover a wide range of thermal-hydraulic conditions with pressures ranging from 1.1 to 69 bar, heat fluxes of $97-1186kW/m^2$, Pe of 3600 to 329,000, and hydraulic diameters of 5-25.5 mm. The new model was implemented in the MARS code and has been assessed using various subcooled boiling experimental data. The results of the new model showed better agreements with measured void fraction data, especially at low-pressure conditions.

• Korean Journal of Applied Biomechanics
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• v.33 no.2
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• pp.52-61
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• 2023

Objective: This study aimed to investigate the effect of a combined functional intervention program on the pain-related questionnaire, the erector spinae contractile properties, and trunk extensor strength of prime-aged females with non-specific chronic low back pain. Method: 16 (female: 16) prime-aged subjects (age: 60.88 ± 6.09 years, height: 158.16 ± 5.58 cm, weight: 59.05 ± 9.44 kg) participated in this study. Results: Except for Tampa Scale of Kinesiophobia all pain-related questionnaires revealed a significant decrease after the intervention program (p<.001). Tensiomyography of the erector spinae revealed a significant post-intervention program increase in the maximum radial displacement (p<.05) and velocity of contraction (p<.05), however, there wasn't a significant post-intervention program change in the contraction time. Additionally, Trunk extensor strength showed a significant increase post-intervention program (p<.001). Conclusion: Our results indicated that the combined functional intervention program positively changed pain-related questionnaires and reduced erector spinae muscle stiffness, increasing the velocity of erector spinae contraction. Additionally, improved the trunk extensor strength.

• Journal of Korea Water Resources Association
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• v.40 no.9
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• pp.723-734
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• 2007

This study was to investigate the settling velocity which is an important factor for the prediction of cohesive deposition under the various densities of particle and dissolved ion addition$(Na^+,\;Cl^-,\;OH^-,\;H^+)$ in rivers, ports, reservoirs and lakes. Settling velocity of suspended fine particles in still water was measured with a pressure sensor (maximum 10 mbar). At the initial concentration of 20g/l of alumina and quartz the average settling velocities were high due to the aggregation behaviour of particles. At this point it was 0.185 mm/s (alumina) and 0.022 mm/s (quartz). Above this initial concentration it was on the decrease owing to the hindered settling. The higher the salinity is, the faster the settling velocity of alumina and quartz is. Furthermore, in an acid condition the average settling velocity of alumina was on the decrease. In an alkaline water, which causes strong flocculation, the average settling velocity of alumina it was observed on the increase. However, in an alkaline medium the low average settling velocity of quartz powder was measured.

• Journal of The Korean Astronomical Society
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• v.42 no.3
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• pp.61-69
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• 2009

Transverse velocity vectors can be determined from a pair of images successively taken with a time interval using an optical flow technique. We have tested the performance of the new technique called NAVE (non-linear affine velocity estimator) recently implemented by Chae & Sakurai using real image data taken by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. We have developed two methods of estimating the errors in the determination of velocity vectors, one resulting from the non-linear fitting ${\sigma}_{\upsilon}$ and the other ${\epsilon}_u$ resulting from the statistics of the determined velocity vectors. The real error is expected to be somewhere between ${\sigma}_{\upsilon}$ and ${\epsilon}_u$. We have investigated the dependence of the determined velocity vectors and their errors on the different parameters such as the critical speed for the subsonic filtering, the width of the localizing window, the time interval between two successive images, and the signal-to-noise ratio of the feature. With the choice of $v_{crit}$ = 2 pixel/step for the subsonic filtering, and the window FWHM of 16 pixels, and the time interval of one step (2 minutes), we find that the errors of velocity vectors determined using the NAVE range from around 0.04 pixel/step in high signal-to-noise ratio features (S/N $\sim$ 10), to 0.1 pixel/step in low signa-to-noise ratio features (S/N $\sim$ 3) with the mean of about 0.06 pixel/step where 1 pixel/step corresponds roughly to 1 km/s in our case.