• Water Engineering Research
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• 제1권2호
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• pp.159-168
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• 2000

In this paper, the increment of the local scour depth at piers by constructing the bridge between existing bridges is examined through the experiments in which 5 piers in the non-cohesive bed material in the experimental flume were installed. In the experiments the maximum distance of 25 times of the pier length and the maximum distortion width of 8 times of the pier width were utilized. Through the experimental studies, it was indicated that low flow, which can be characterized as the flow having low Froude numbers, the maximum bed configuration change is obtained when the piers are installed in the straight line in the flor direction without any distortion. However, In the high flow, which can be characterized as the flow having high Froude numbers, the maximum bed configuration change is obtained when the piers are installed with some distortion from the flow direction. The influence of the bed configuration by interaction between bridge piers is changed depending upon the Froude numbers, the distance between piers, and the distortion width between adjacent bridge piers. Also, because the scour patterns are affected by the bed configuration, the maximum scour should be increased by about 60% compared to that in a single pier if the interaction between bridge piers exists. It can be suggested that the maximum scour depth at bridge piers predicted by applying the existing equations should be increased if the interaction between bridge piers exist. Those cases are found when new bridges are constructed successively in the river in the urban area.

• 콘크리트학회논문집
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• 제11권6호
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• pp.13-24
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• 1999

The external, unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of internal bonded PSC members because of eccentricity change and slip occurrence during loading process. The purpose of the present study is to propose the ultimate failure stresses of prestressing (PS) steels for those external unbonded PSC members. To this end, a comprehensive analysis has been made using the nonlinear finite element analysis program developed recently for external unbonded PSC members by authors. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, load geometry, amount of ordinary steel, and prestressing steel ration have great influence for the ultimate failue stress of PS steel is preposed and is compared with experimental dat as well as existing formulas for internal unbonded members. The Comparison indicates that the proposed equation agrees relatively well with experimental data and that existing formulas including ACI and AASHTO equations show some discrepancies from experimental ones. The present study allows more realistic analysis and design of prestressed concrete structures with external unbonded tendons.

• Journal of Periodontal and Implant Science
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• 제30권3호
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• pp.639-650
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• 2000

The purpose of this study was to evaluate clinical changes in graft size after treatment with connective tissue autograft in human. 40 premolar teeth in 23 patients having the following mucogingival problemswere selected. The width of extension, attached gingiva including free marginal gingiva, width of transplant and clinical sulcus depth were measured at the initial examination, 2, 12 and 24 weeks following the connective tissue autograft and free gingival autograft. The change of width of extension, attached gingiva including free marginal gingiva, width of transplant and clinical sulcus depth according to healing process in both graft procedures was statistically analyzed by ANOVA test and independent ttest using SPSS program. The results were as follows : 1. The change of keratinized gingiva in both grafting procedures was increased significantly at 24 weeks post-op. 2. The clinical sulcus depth exhibited no marked changes throughoutthe entire investigation in both grafting procedures. 3 . After 12 weeks, no dimensional variation was seen in graft size in both grafting procedures. 4. Shrinkage differs significantly in both grafting procedures. From the day of graft to 24 weeks after surgery the percentages of shrinkage were connective tissue autograft 55% and free gingival autograft 29%.

• Journal of Periodontal and Implant Science
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• 제24권2호
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• pp.376-389
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• 1994

A study was conducted to compare the effects of chlorhexidine mouthrinse and chlorhexidine acetate powder with periodontal pack during 4 weeks following periodontal surgery. Twelve patients were treated with Modified Widman flap procedures and devided into three groups of four patients each; control group, chlorhexidine mouthrinse group, chlorhexidine acetate powder group. Each group wasn't significant difference in clinical and microbiologic parameters at preoperation. Examination regarding plaque index, gingival index, pocket depth, change of gingival color postsurgically, pain index were performed by each methods and observed bacteria in gingiva by phase contrast microscope. Evaluations were made at 7, 14 and 28 days postsurgically. The results were as follows: l. In comparison of results revealed no significant differences in Plaque Index, Gingival Index, pocket depth and change of gingival color postsurgically. 2. The pocket depth of three experimental groups were significant reduced at 4 weeks. 3. Chlorhexidine mouthrinse group and chlorhexidine acetate powder group with periodontal pack were significant differences in pain index at 3, 4 days postsurgically. 4. Cocci and Non-motile rods were increased at 1, 2 weeks. But, motile rod and spirochete were increased at 4 weeks.

• 대한조선학회논문집
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• 제52권6호
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• pp.494-500
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• 2015

It has been reported that a ship sailing in shallow water possesses better straight-line stability due to the change of fluid flow around the ship. This tendency affects manoeuvring characteristics of the ship. To investigate this phenomenon, indoor free running model test(FRMT) on KVLCC2 was carried out in three water depth conditions(H/T = 1.2, 1.5 & 2.0). Turning circle tests(± 35° ) and zigzag tests(± 20° /5° and ± 20° /10° ) were conducted with newly developed indoor FRMT system, and the manoeuvring results were compared with test results from other institutes. As the water depth decreased, the yaw rate of the ship decreased, and the distances of circular trajectories at the same heading angle increased in the turning circle tests. The first overshoot angles of the zigzag tests decreased. From both tests, the time for course change increased as the water depth decreased. These manoeuvring characteristics show that KVLCC2 in shallow water becomes more stable in terms of straight-line stability.

• 한국건축시공학회지
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• 제5권2호
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• pp.161-166
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• 2005

This study is to evaluate on the increased cost of construction according to the depth change of concrete slabs in apartment building. When we increased the depth of concrete slab from 150mm to 180, 210mm, the qualitative and cost of construction were calculated by the high-rise type, the unit-size type. As a result of this study, in 32 Pyong type, increment of construction cost rate appeared by $5.1\%$ in case of increase from slab 150mm to 180mm, and $10.0\%$ in case of increase from slab 150mm to 210mm. In 45 Pyong type, Increment of construction cost rate appeared by $5.7\%$ in case of increase from slab 150mm to 180mm, and $10.2\%$ in case of increase from slab 150mm to 210mm. In 55 Pyong type, Increment of construction cost rate appeared by $2.4\%$ in case of increase from slab 150mm to 180mm, and $8.9\%$ in case of increase from slab 150mm to 210mm.

• Ocean and Polar Research
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• 제24권3호
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• pp.189-196
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• 2002

A multichannel seismic survey was conducted in the southern Ayu Trough which is the only spreading boundary between the Philippine Sea and Caroline plates. The seismic system used in this study comprises of 2.46-l sleeve gun and a 12-channel streamer with a group interval of 6.25m. Migration technique was used to analyze seismic velocity, and poststack depth migration was applied to the stacked data. The sediment thickness obtained from the depth section tends to increase with distance from the spreading axis. Sedimentation rates are poorly constrainted in the study area. The apparent half-spreading rates estimated from the sediment thickness and sedimentation rate from DSDP hole on the caroline plate are 4.7mm/yr and 7.9mm/yr at $1^{\circ}24'N\;and\;0^{\circ}42'N$, respectively, which are fester than Previously suggested. On the basis of new oblique spreading geometry, the recalculated spreading rates are 5.4mm/yr and 9.1mm/yr at $1^{\circ}24'N\;and\;0^{\circ}42'N$, respectively. Seismic sections show that the topography is asymmetric across the Ayu Trough and the acoustic basement is rough. These features are consistent with the earlier suggestion that the Ayu Trough is a slow-spreading divergent boundary. A detailed examination of seismic profiles away from the axis shows that sediments can be divided into two layers which implies a possible change in the spreading rate anuor sedimentation condition during the formation of the trough.

• 공학교육연구
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• 제18권1호
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• pp.54-60
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• 2015

본 논문은 자기주도학습과 심층면담 프로그램이 이공계 학습부진학생의 학업성취도에 미치는 영향을 연구한 것이다. 본 연구는 학점평균 2.5미만의 학생들 17명의 신청을 받아 진행하였으며, 15주 동안의 자기주도학습 프로그램 참여와 3차의 심층면담 결과, 평균 평점(GPA, grade point average)의 변화를 분석하였다. 그 결과 참여 과목의 학업성취도, 평균 평점(GPA, grade point average)이 높아지는 효과가 있었으며, 학습 필요성에 대한 인식이 긍정적으로 변화한 것을 확인할 수 있었다.

• 한국정밀공학회지
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• 제19권1호
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• pp.186-195
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• 2002

The mechanism of micro machining of reacted layer on silicon surface were proposed. The depth of reacted layer and the change of mechanical property were measured and analyzed. Depth of hydrated layer which is created on the surface of silicon by potassium hydrate was analyzed with SEM and XPS. The decrease of the micro victors hardness of silicon surface was shown with the increase of the concentration of potassium hydrate and the change of the dynamic friction coefficient by chemical reacted layer was measured due to the readiness of machining. The experiment of groove machining was done with 3-axis machine with constant load. With chemical mechanical micro machining the surface crack and burrs generated by both brittle and ductile micro machining were diminished. And the surface profile and groove depth was shown in accordance with the machining speed and reaction time with SEM and AFM.

• 한국전산구조공학회논문집
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• 제17권4호
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• pp.451-458
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• 2004

본 연구는 동결토의 동결심도 및 매설된 파이프라인의 온도분포를 예측하기 위하여 유효열용량 개념 반영한 수치해석 모델의 개발에 초점이 맞추어져 있다. 이를 위하여 저자는 사용코드인 ANAQUS를 활용하여 파이프라인이 매설된 폐쇄형 시스템의 화강 동결토에 대하여 비정상 열전달 수치해석을 수행하였다. 제안된 수치해석 모델은 Frozen Fringe에서 간극수의 상변화 효과가 반영되었다. 제안된 수치해석 모델과 실내 실험으로부터 얻어진 결과들을 비교함으로써 유효열용량 모델의 적용성을 검증하였다.