• Journal of the Korean Geotechnical Society
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• v.27 no.1
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• pp.77-86
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• 2011

The advanced geotechnical information has been required to determine the accurate design parameters for complex construction. However, the Standard Penetration Test (SPT), which has low reliability, has been used to estimate the subsurface condition in the field. The objective of this paper is development and application of the Static-Dynamic penetrometer, which detects the resistances in soft clay, sand and rock. The energy losses according to the rod connection methods (perfect or non-perfect connection, and number rods) are experimentally evaluated. The reflection and transmission ratios are used to investigate the energy loss by a simulation. The static-dynamic cone penetrometer, in which the accelerometers and strain gauges are installed on the cone tip and the rod head, is used to estimate the energy loss during penetration by impacts. The experimental and simulation studies show that the transferred energy through rods with non-perfect connection dramatically decreases. Furthermore, the transferred energy on the rod head is not the same as that on the cone tip. This study demonstrates that the energy loss should be evaluated on the cone tip.

• 대한공업교육학회지
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• v.41 no.1
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• pp.147-169
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• 2016

This study analyzed the international research trend of the secondary school level engineering education published from 2004 to 2014 in four major journals associated with technology education. The findings of this study were as followings First, regarding the published year, the studies related to the secondary school level engineering education were started from 2004 and had been conducted most actively from 2007 to 2011 (32 pieces). However, the number of studies decreased after 2012. Second, regarding the research topic, the number of study followed by 'survey/investigation' (16 pieces), 'establishment of concept/theoretical discussion' (11 pieces), 'verification of teaching method/models' effect' (10 pieces), 'teaching method/model observation' (7 pieces), 'development of concept/teaching method/model' (4 pieces). Third, regarding the research subject, the number of study followed by 'high school student' (17 pieces), 'literature' (16 pieces), 'teacher' (12 pieces), 'professor' (5 pieces). Fourth, regarding the research method, the number of study followed by 'survey research' (13 pieces), 'literature research' (12 pieces), 'qualitative research' (12 pieces), 'experimental research' (6 pieces), 'integrated research' (5 pieces). Based on the conclusion of this study, there are the needs for further studies to establish theoretical foundation on the engineering concept and content elements in secondary school level, investigate technology teachers' perception toward the implementation of engineering education, and analyze secondary school students' problem solving process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.712-722
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• 2018

This paper conducts parametric studies on flapping wing design, one of the most important design parameters of insect-mimicking aerial vehicles. Experimental study on wing shape was done through comparison and analysis of thrust, pitching moment, power consumption, and thrust-to-power ratio. A two-axis balance and hall sensor measure force and moment, and flapping frequency, respectively. Wing configuration is biplane configuration which can develop clap and fling effect. A reference wing shape is a simplified dragonfly's wing and studies on aspect ratio and wing area were implemented. As a result, thrust, pitching moment, and power consumption tend to increase as aspect ratio and area increase. Also, it is found that the flapping mechanism was not normally operated when the main wing has an aspect ratio or area more than each certain value. Finally, the wing shape is determined by comparing thrust-to-power ratio of all wings satisfying the required minimum thrust. However, the stability is not secured due to moment generated by disaccord between thrust line and center of gravity. To cope with this, aerodynamic dampers are used at the top and bottom of the fuselage; then, indoor flight test was attempted for indirect performance verification of the parametric study of the main wing.

• Journal of Biomedical Engineering Research
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• v.21 no.4
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• pp.391-401
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• 2000

Flow through compliant tubes with linear taper in wall thickness is numerically simulated by finite element analysis. For verification of the numerical method, flow through a compliant stenotic vessel is simulated and the results are compared to the existing experimental data. Steady two-dimensional flow in a collapsible channel with initial tension is also simulated and the results are compared with numerical solutions from the literature. Computational results show that as cross-sectional area decreases with the reduction in downstream pressure, flow rate increases and reaches the maximum when the speed index (mean velocity divided by wave speed) is near the unity at the point of minimum cross-section area, indicating the flow limitation or choking (flow speed equals wave speed) in one-dimensional studies. for further reductions in downstream pressure, flow rate decreases. The flow limitation or choking consist of the main reasons of waterfall effect which occurs in the airways, capillaries of lung, and other veins. Cross-sectional narrowing is significant but localized. When the ratio of downstream-to-upstream wall thickness is 2, the area throat is located near the downstream end. As this ratio is increased to 3, the constriction moves to the upstream end of the tube.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.479-488
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• 2001

As the SoC designs complexity constantly increases, the simulation that uses their software models simply takes too much time. To solve this problem, FPGA-based logic emulators have been developed and commonly used in the industry. However, FPGA-based logic emulators are facing with the problems of which not only very low FPGA resource usage rate due to the very limited number of pins in FPGAs, but also the emulation speed getting slow drastically as the complexity of designs increases. In this paper, we proposed a new innovative emulation architecture and its software that has high FPGA resource usage rate and makes the emulation extremely fast. The proposed emulation system has merits to overcome the FPGA pin limitation by pipelined ring which transfers multiple logic signal through a single physical pin, and it also makes possible to use a high speed system clock through the intelligent ring topology. In this topology, not only all signal transfer channels among EPGAs are totally separated from user logic so that a high speed system clock can be used, but also the depth of combinational paths is kept swallow as much as possible. Both of these are contributed to achieve high speed emulation. For pipelined singnals transfer among FPGAs we adopt a few heuristic scheduling having low computation complexity. Experimental result with a 12 bit microcontroller has shown that high speed emulation possible even with these simple heuristic scheduling algorithms.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.189-199
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• 1999

The resonance scattering of acoustic waves from the cylindrical shells of nuclear fuel rods coated with oxide layers has been theoretically modeled and numerically analyzed for the propagation characteristics of the circumferential waves. The normal mode solutions of the scattering pressure of the coated shells have been obtained. The pure resonance components have been isolated using the newly proposed inherent background coefficients. The propagation characteristics of resonant circumferential waves for the shells coated with oxide layers are affected by the presence and the thickness of an oxide layer. The characteristics have been experimentally confirmed through the method of isolation and identification of resonances. The change of the phase velocity of the $A_1$ circumferential wave mode for the coated shell is negligible at the specified partial waves in spite of the presence of the oxide layer and the increase in coating thickness. Utilizing the invariability characteristics of the phase velocity of the $A_1$ mode, the oxide layer thickness of the coated shells can be estimated. A new nondestructive technique for the relative measurement of the coating thickness of coated shells has been proposed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.34-44
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• 2016

This study is an experimental study about a facility for preventing the accumulation of floating debris at a bridge by flooding at a small river. Generally, structures installed at a small river are damaged frequently by floating debris during typhoons or localized rainfall events. On the other hand, there is no method available for preventing such damage. The facilities used in other countries to prevent such damage by the accumulation of floating debris include debris fins, deflectors, and sweeper. Among these facilities, the present study was conducted with a sweeper to investigate the damage-reducing capability through a real-scale accumulation experiment. A sweeper was installed in front of a bridge to bypass floating debris by self-rotation so that the floating debris may not be accumulate at the bridge. A small bridge model was prepared in a real-scale for the real-scale experiment. The accumulation reducing capability was compared through an accumulation experiment before and after the sweeper installation depending on the length of the debris and flow conditions. The result showed that the accumulation rate increased with increasing length of the debris or decreasing flow rate. The installation of a sweeper decreased the debris accumulation rate by a minimum of 55% to a maximum of 88% compared to the case without an installed sweeper. The result of the present study showed that the installation of a sweeper at a small river having a high potential of generating floating debris may help secure the stability of a bridge in the case of floating debris accumulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.265-278
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• 2016

In this study, an ascending capability experiment was performed with largemouth bass and bluegill, which are exotic fish species inhabiting (the freshwaters) in Korea. The experiment was performed by dividing the subject fish into four groups according to their size and at four flow rates for each group. The number of fish passing through a reference line was analyzed by recording videos, and their swimming and ascending capabilities were observed by the naked eye. The number of fish passing through the reference line did not include those returning downstream within five minutes due to the high flow rate. The flow rate used for the analysis was the mean of the flow rate values measured at the left bank, the right bank, and in the middle of the stream. The results showed that the number of exotic fish migrating upstream decreased as the flow rate increased, regardless of the species and size of the fish. The comparison between the fish species showed that the ascending capability of bass was higher than that of bluegill, but the difference was not significant when considering the difference in the size of the fish. In addition, the upper limit flow velocity allowing the ascending of the exotic fish species was 1.11 m/s, when considering the fish returning to the downstream after the upstream migration and experimental error. The results of the experiment may be used as fundamental data for the blocking of fish and the management of exotic fish species by means of a high flow rate current. Further experiments, verification, and monitoring may need to be conducted continuously to determine whether the fish are able to pass through the reference line at a high flow rate, when they attain a high or cruising velocity. Additionally, the reaction of the fish species should be investigated by considering the response to external forces as well as pressure differences due to the flow rate.

• Journal of Information Management
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• v.41 no.4
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• pp.227-249
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• 2010

Scholarly information has increased tremendously according to the development of IT, especially the Internet. However, simultaneously, people have to spend more time and exert more effort because of information overload. There have been many research efforts in the field of expert systems, data mining, and information retrieval, concerning a system that recommends user-expected information items through presumption. Recently, the hybrid system combining a content-based recommendation system and collaborative filtering or combining recommendation systems in other domains has been developed. In this paper we resolved the problem of the current recommendation system and suggested a new system combining collaborative filtering and Naive Bayes Classification. In this way, we resolved the over-specialization problem through collaborative filtering and lack of assessment information or recommendation of new contents through Naive Bayes Classification. For verification, we applied the new model in NDSL's paper service of KISTI, especially papers from journals about Sitology and Electronics, and witnessed high satisfaction from 4 experimental participants.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.447-447
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• 2016

홍수 시 하천을 따라 유하되는 유송잡물(잡목, 생활쓰레기 등)은 구조물에 집적이 이루어지며 이로 인해 물의 흐름을 방해하고 구조물 주변의 지반을 약화시키거나 월류로 인해 심각한 피해를 야기 시킨다. 교량의 경우 유송잡물의 집적은 교각의 항력을 증가시켜 전도파괴를 유발시킬 수 있으며, 교각주변 흐름교란을 통한 하상세굴로 인해 기초부를 파괴시키기도 한다. 또한 통수단면적 증가로 인해 높아진 수위는 제방을 월류시켜 재산 및 인명피해를 유발하기도 한다. 암거의 경우 유송잡물을 포함한 토사로 인해 단면폐색 및 침식으로 암거의 파괴를 발생시키고 이로인해 도로의 단절을 가져오기도 한다. 이러한 유송잡물에 대한 차단대책은 현재 까지 유지관리를 통한 방법만이 최선책으로 제시되고 있다. 본 연구는 국외에서 소개되고 있는 유송잡물 피해저감시설을 대상으로 축소모형실험을 통해 효과를 확인하고 이를 통해 저감시설의 효율에 대해 소개하고자 하는 것이 주목적이다. 유송잡물 저감시설은 교량의 경우 수직분리대 방법, 우회말뚝 방법, 스위퍼를 이용한 방법으로 소개하고 있으며 이들 방법의 특징은 유송잡물 우회를 통해 집적을 저감하는 방식이다. 암거의 경우 수직분리대 방법, 스크린 방법, 우회스크린을 이용하는 방법 등이 있으며 수직분리대는 교량과 마찬가지로 우회방식을 기본방식으로 스크린 방식은 유송잡물의 차단을 원칙으로 하고 있다. 실험의 결과는 교량과 암거의 차단시설 유무에 따른 유송잡물의 집적률을 대상으로 하였다. 차단시설이 없는 경우 교량에서의 집적률은 97.9% ~ 99.2%의 집적률로 나타났다. 수직분리대의 경우 유송잡물 집적률은 49.3%, 우회말뚝은 0.0% ~ 4.2%의 범위로 매우 높은 차단효과를 보이고 있었다. 스위퍼방식의 경우 집적률은 5.3% ~ 20.9%로 나타났다. 이러한 결과로 판단하였을 때 차단시설 설치로 인한 교량에 대한 직접적인 차단효과는 수직분리대 < 스위퍼 < 우회말뚝 순으로 높은 차단효과를 보이는 것으로 나타났다. 그러나 우회말뚝에서의 집적률이 한계치를 넘어선다면 유송잡물로 인해 흐름교란, 수위 및 하상변동, 말뚝의 유실 등으로 인한 피해가 예상된다. 암거대상 유송잡물 차단시설 실험결과는 수직분리대의 경우 type과 투하방법에 따라 차이가 있지만 집적률은 14.7% ~ 64.9%의 범위로 나타났다. 스크린과 우회스크린 방식은 유송잡물의 우회가 아닌 차단이 목적이므로 유송잡물 집적에 의한 수위상승이 우려되는바 수위영향을 검토하였다. 검토결과 스크린 설치로 인한 수위상승이 우회스크린보다 높게 상승하는 것으로 나타났다. 이러한 결과는 스크린의 형태적인 측면에서 2면을 통해 집적되는 특성을 갖는 우회스크린이 통수단면적을 많이 확보하기 때문이다. 따라서 국부적인 수위상승으로 인한 피해를 저감하기 위해서는 설치여건이 허용된다면 통수단면적 확보가 유리한 우회스크린 설치가 유리할 것으로 판단된다.