• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.766-774
• /
• 2017

Software has been developed for simulating particle dispersion in a circular pipe with sudden-expansion, which models the fuel feeding system of a combustor that uses metal powder like aluminum as fuel. The Lagrangian based discrete tracer point method was employed for a plug flow of particles that satisfies local turbulent velocity fluctuations. A radial velocity component was created to improve the flow turning outwards in the recirculation zone. The particle distribution patterns from both with and without the component were directly compared with the experiments near the reattachment.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.20 no.4
• /
• pp.104-111
• /
• 2016

The flame stabilization is one of the topics which have to be solved for the airbreathing propulsion systems, using the entering air which is supersonic velocity as an oxygen sources. Making a recirculation zone with an eddy flow, installed the reducing velocity devices such as the bluff body, is the typical method of the flame stabilization. Recently using a cavity flame stabilization at the wall is an emerging technique as an effective method which extends the stabilization zone, and the related research papers have been published on the flow separation and reattachment, pressures and oscillations including length/depth ratios in the cavities. Even though, still there are lots of topics to study more in the cavity flame stabilization field as the preceding techniques, as well as the research and the development of the airbreathing propulsion system itself.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.109-111
• /
• 2020

본 논문에서는 ESS용 전류원 Dual-Active-Bridge 컨버터의 저 부하 및 고 부하에서의 효율 향상을 위한 하이브리드 스위칭 알고리즘을 제안하고자 한다. 전류원 DAB 컨버터는 인터리브 구조를 이용하여 배터리 단의 입력 전류 리플을 저감할 수 있고, 전력 변환 효율 개선을 위한 다양한 제어 변수를 도입할 수 있는 등의 장점으로 인해 DC 마이크로그리드에서 ESS용 절연형 양방향 DC/DC 컨버터로 주목받고 있다. 그러나 전류원 DAB에서 종래의 전력 제어 방법인 펄스폭 변조 방식과 위상천이가 결합된 방법 (PWM plus Phase Shift, PPS)의 경우 저 부하 조건에서 높은 피크 전류로 인해 도통 손실이 크며, 펄스폭 변조 방식과 이중 위상천이가 결합된 방법(PWM plus Dual Phase Shift, PPDPS)의 경우 고 부하 조건에서 영전압 스위치 영역이 좁아져 효과적이지 않다. 따라서 본 논문에서는 2차 측의 펄스폭과 위상천이를 독립적으로 제어하는 하이브리드 스위칭 알고리즘을 통해 순환전류를 감소시키고 영전압 스위치 영역을 확장시켜 저 부하 및 고 부하 모두에서 효율을 향상시키고자 한다. 1-kW급 전류원 DAB 컨버터 시작품을 통해 제안된 하이브리드 스위칭 알고리즘의 효율성과 타당성을 검증한다.

• Geophysics and Geophysical Exploration
• /
• v.14 no.1
• /
• pp.50-57
• /
• 2011

For effective and accurate prediction of overpressure in the Efomeh field, located in the Niger delta basin of Nigeria, integrated seismic and borehole analyses were undertaken. Normal and abnormal pore pressure zones were delineated based on the principle of normal and deviation from normal velocity trends. The transition between the two trends signifies the top of overpressure. The overpressure tops were picked at regular intervals from seismic data using interval velocities obtained by applying Dix's approximation. The accuracy of the predicted overpressure zone was confirmed from the sonic velocity data of the Efomeh 01 well. The variation to the depth of overpressure between the predicted and observed values was less than 10mat the Efomeh 01 well location, with confidence of over 99 per cent. The depth map generated shows that the depth distribution to the top of the overpressure zone of the Efomeh field falls within the sub-sea depth range of 2655${\pm}$2m (2550 ms) to 3720${\pm}$2m (2900 ms). This depth conforms to thick marine shales using the Efomeh 01 composite log. The lower part of the Agbada Formation within the Efomeh field is overpressured and the depth of the top of the overpressure does not follow any time-stratigraphic boundary across the field. Prediction of the top of the overpressure zone within the Efomeh field for potential wells that will total depth beyond 2440m sub-sea is very important for safer drilling practice as well as the prevention of lost circulation.

• Journal of the Society of Disaster Information
• /
• v.15 no.3
• /
• pp.339-346
• /
• 2019

Purpose: In fact, to manage response and recovery successfully, although mitigation and preparedness should be accomplished naturally and automatically through thorough analysis and assessment, response, recovery, mitigation, and preparedness have not done in the way of virtuous cycles and continued broken disaster management repeatedly. Method: By Analysis through the critical methods, to enhance the community disaster resilience centered by social disaster management system in Korea, Result: (1) public training & education preparing for emergency or disaster (2) supplying public with disaster, or hazards information, and sharing at real time (3) networking emergency and disaster informational communication system & alarm system (4) analysis and assessment of risk(or disaster) in community (5) inter-governmental cooperative relationship and agreements (6) adopting and implementing disaster or hazards mitigation plan Conclusion: These will be able to be fully melt down into and specifically focused in the disaster policies in Korea for the better disaster management.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.29 no.2
• /
• pp.101-115
• /
• 2024

The ocean heatwave is emerging as a major issue due to global warming, posing a direct threat to marine ecosystems and humanity through decreased food resources and reduced carbon absorption capacity of the oceans. Consequently, the prediction of ocean heatwaves in the vicinity of the Korean Peninsula is becoming increasingly important for marine environmental monitoring and management. In this study, an LSTM model was developed to improve the underestimated prediction of ocean heatwaves caused by the coarse vertical grid system of the Korean Peninsula Ocean Prediction System. Based on the results of ocean heatwave predictions for the Korean Peninsula conducted in 2023, as well as those generated by the LSTM model, the performance of heatwave predictions in the East Sea, Yellow Sea, and South Sea areas surrounding the Korean Peninsula was evaluated. The LSTM model developed in this study significantly improved the prediction performance of sea surface temperatures during periods of temperature increase in all three regions. However, its effectiveness in improving prediction performance during periods of temperature decrease or before temperature rise initiation was limited. This demonstrates the potential of the LSTM model to address the underestimated prediction of ocean heatwaves caused by the coarse vertical grid system during periods of enhanced stratification. It is anticipated that the utility of data-driven artificial intelligence models will expand in the future to improve the prediction performance of dynamical models or even replace them.

• Journal of Elementary Mathematics Education in Korea
• /
• v.19 no.3
• /
• pp.323-345
• /
• 2015

This study is intended to establish and apply a program created with RME for mathematising instruction and learning and identify how it influences on the mathematical thinking process in the field. In order to deal with this study inquiries, related theories have been analyzed establishing a program for mathematising instruction and learning method based on a model of them and RME theory principles and re-organizing education courses for instruction on the fields concerned. Study subjects were limited to two classes consisting of fifth graders in S elementary school located in the city of Daegu and divided them in an experiment group and a control group. An experiment group was given a mathematising learning method applied with RME, while a control group had a class with regular methods of learning and instruction during the period of experiment. As a summary of aforementioned results of the study, mathematising learning method applied with RME had an effect on improving mathematical thinking ability for students and also on promoting mathematising outcome through a repetitive experience in each procedure obtained on a regular basis.

• The Journal of the Korea Contents Association
• /
• v.17 no.3
• /
• pp.462-473
• /
• 2017

This study suggested appropriate media educational model for the Korean situation based on the two previous research results concerning Korean media mental model which have abstracted from elementary schoolers and parents respectively living in and around Seoul. This looked through typical media educational model being in effect in Western countries such as Buckingham's creation-centered model, Hobbs' action-centered model, Potter's analysis-centered model and Vanhoozer's worldview-centered model, synthesized all the strengths of each model, and finally modified and reorganized this new model to reflect demanders' needs. Newly developed demander-centered educational model is a kind of circulation model consisting of a chain of the steps: worldview and viewpoints, use(access), analysis and evaluation, reflection, and social act; Each step borrowed the essential contents of each domain of objectives and tried to reflect the specific situations for Korean demanders. The needs for media use etiquette against addiction and cyberbullying were applied to the step of 'worldview and viewpoint', the needs for the educational status of books as media to 'use(access)', and the reality of highly used digital media to 'social act.'

• Proceedings of KOSOMES biannual meeting
• /
• 2005.11a
• /
• pp.153-158
• /
• 2005

The turbulent shear flaw around a surface-mounted vertical wall was investigated using the two-frame PIV(CACTUS 3.1) system. From this study, it is revealed that at least 500 instantaneous velocity field data are required for ensemble average to get reliable turbulence statistics, but only 200 field data are sufficient for the time-averaged mean velocity information The flow has an unsteady recirculation region post vertical wall with bottom gap, followed by a slow relaxation to the fiat-plate boundary layer flow. The time-averaged reattachment length estimated from the streamline distribution is about x/H=3H. The large eddy structure in the separated shear layer seems to have signification influence on the development of the separated shear layer and the reattachment process.

• Journal of The Korean Association For Science Education
• /
• v.22 no.3
• /
• pp.550-559
• /
• 2002

This study is to investigate the type, process and context of inquiry activities in life science textbooks based on the seventh curriculum. Six kinds of science textbooks were analysed. Three units of life science were analysed; 'the structure of living things', 'digestion and circulation' and 'respiration and excretion', As result of analysis, types, processes and skills, and context of inquiry were not balanced, it is suggested that learners be educated with complementary of this aspects. To develope the science textbook on the basis of aims and objectives of curriculum, it is proposed that the inquiry activities presented in science textbooks be examined, and the framework to evaluate inquiry activities be reflected on the standard of science textbook authorization