• Composites Research
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• 제24권4호
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• pp.23-28
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• 2011

최근 항공용 재료 산업 분야에서 널리 사용되고 있는 CFRP의 활용이 증가되고 있다. 하지만, CFRP와 같은 복합재료 부품의 결합 시에 단점이 있다. 복합재료를 이용한 다양한 구조를 제조하기 위해선 많은 홀 가공이 필요하다. 일반적으로 CFRP 홀 가공시 내구성이 매우 강한 polycrystalline crystalline diamond (PCD) 드릴을 사용한다. 하지만, 단가가 비싸고 가공 속도가 느리기 때문에 내구성은 PCD 드릴에 비해 약하나 드릴 형상 변화를 통해 가공 속도를 조절 할 수 있고, 비교적 가격이 저렴한 chemical vapor deposition (CVD) 다이아몬드 코팅 드릴의 사용량이 증가 되고 있다. 본 연구에서는. PCD 드릴과 CVD 다이아몬드 코팅 드릴의 홀 가공성을 비교 평가하였다. 먼저, 홀 가공 조건 식 (날당 이송량, 절삭 속도)을 이용하여 CFRP 홀 가공성을 평가했으며, CFRP 가공 시 드릴링 과정에서 발생하는 시편 내부의 열적 손상 정도를 비교했다. 열화상 카메라 촬영한 홀 가공 시 발생되는 온도를 이용한 경험식을 만들어 두 드릴의 발열 정도에 따른 홀 가공성을 비교 평가하였다. 또한, 홀 가공 시 발생하는 칩(chip) 배출 여부에 따른 홀 내부의 상태를 평가하여 CVD 다이아몬드 코팅 드릴과 PCD 드릴의 CFRP 홀 가공성을 비교했다. 전반적으로 PCD 드릴의 홀 가공성이 CVD 다이아몬드 드릴에 비해 우수한 성능을 나타냈지만, 홀 생성 속도는 CVD 다이아몬드 드릴이 PCD 드릴에 비해 빠른 결과를 나타냈다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권7호
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• pp.854-867
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• 2014

지속적인 유가의 상승에 따라 국제 석유 자본들의 유전개발에 대한 투자가 활발하고 지속적으로 증가하고 있는 추세에 있다. 최근 5년 동안(2008~2013)에 인도된 드릴쉽(drill-ship)은 67척으로 그 이전 30년 동안에 인도된 척수의 두 배에 이른다. 그리고 최근에는 3,000 m 내외의 심해유전 개발이 증가하고 있다. 이에 따라 시추 장비와 시스템이 대형화 추세에 있으며, 이들의 운전을 위한 디젤발전기의 용량이 증가하였다. 디젤발전기 용량은 일반 상선과는 달리 고출력 및 고전압이 요구되며, 이를 충족시키기 위하여 V-type 320 mm 실린더 내경의 고출력 엔진에 대한 수요가 증가하게 되었다. 드릴쉽의 경우 일반 상선 대비 선박건조 기간이 길어짐에 따라 커미셔닝 기간 중 장시간 저 부하 운전이 불가피하여 엔진 윤활유 관리의 중요성이 대두되었다. 최근에는 선박인도 전 크랭크핀에 캠마모(Cam wear)와 같은 이상마모가 발생하였으며 시리즈 호선 및 관련 호선들에 대한 크랭크핀의 전수 검사 결과 정도의 차이가 있었으나 모두 크랭크핀에 이상마모가 발생한 것이 확인되었다. 본 논문은 실제 호선에 적용된 엔진 크랭크핀의 이상마모 발생 원인에 대해 이상마모 메커니즘 분석과 실증결과 분석을 통하여 재발방지를 위한 대책 방안에 대하여 논하였다.

• 한국초지조사료학회지
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• 제41권3호
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• pp.205-209
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• 2021

Barnyard millet (Echinochloa esculenta) can be processed through soiling, hay, and silage, depending on the weather conditions during harvesting. However, research on barnyard millet is insufficient, and standards for cultivar, seeding density, and fertilizers have not been established. This study was conducted to examine the effects of seeding density and seeding methods on dry matter yields. For this, we used the early-maturing (Shirohie millet) variety of the barnyard millet. The experimental design included different seeding density (10 kg/ha, 15 kg/ha, 20 kg/ha (standard seeding density), 25 kg/ha and 30 kg/ha), and different methods of seeding (drill seeding and broadcast seeding). The seeding date was May 13, 2021, and the harvest date was July 13, 2021. Harvesting was carried out when the heading reached 40 %. Lodging occurred at 5, 9 and 7 at 20, 25 and 30 kg/ha densities in the broadcast seeding, but not in the drill seeding. With decreasing density of seeding, tillage number showed an increasing trend in both drill seeding and broadcast seeding (p>0.05). The plant heights were comparable in both drill seeding and broadcast seeding (p>0.05). The heading stage of barnyard millet was checked July 7 for drill seeding, and, on July 8 for broadcast seeding. It took 62 days, i.e., till July 13 for the heading to reach 40 % of the output. The dry matter yield of barnyard millet was significantly higher at the seeding density of 30 kg/ha, for both the methods of seeding (p<0.05). There was no difference in the chemical composition of grain, based on the seeding method and seeding density. However, as the seeding density increased, the CP, NDF, ADF, and TDN contents increased in both drill seeding and broadcast seeding. We found that, the dry matter content was the highest at the seeding density of 30 kg/ha for both the methods of seeding, but this was only 1.3 times higher than that of 10 kg/ha. Considering the seed price and labor force involved in seeding, it is advisable to have a seeding density of 15-20 kg/ha.

• 한국구조물진단유지관리공학회 논문집
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• 제27권1호
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• pp.64-70
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• 2023

본 연구에서는 1.04배 드릴비트 직경 및 1.02배 드릴비트 직경 시 앵커의 신뢰성시험을 수행하였다. 각 변수별 시험을 통해 앵커의 표준편차 및 변동계수를 검토하였고, 기준시험 결과와 비교 평가하였다. 1.04배 드릴비트 직경을 가진 M12 및 M16 앵커의 신뢰성시험결과, 극한 인장하중 허용기준 변동계수 값인 20% 이내의 값을 나타내어 시험기준을 만족하였다. 또한, 1.04배 드릴비트 직경을 가진 앵커의 성능은 기준시험 대비 M12 앵커는 약 74%, M16 앵커는 약 55% 정도로 나타나 앵커의 내력이 다소 부족한 성능을 나타냈지만, 설계강도 대비 약 253% 및 210%로 나타나 1.04배 드릴비트 직경에 설치된 앵커의 인발성능은 충분히 확보하고 있음을 알 수 있었다. 1.02배 드릴비트 직경을 가진 M12 및 M16 앵커의 신뢰성시험결과, 극한인장하중 허용기준 변동계수 값인 20% 이내의 값을 나타내어 시험기준을 만족하였다. 또한, 1.02배 드릴비트 직경을 가진 앵커의 성능은 기준시험 대비 M12 앵커는 약 48%, M16 앵커는 약 53% 정도로 나타나 다소 부족한 성능을 나타냈지만, 설계강도 대비 약 136% 및 168% 로 나타나 1.02배 드릴비트 직경에 설치된 앵커의 인발성능은 충분히 확보하고 있음을 알 수 있었다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2018년도 공동국제학술발표회
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• pp.62-62
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• 2018

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.115-121
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• 1993

The carbon fiber epoxy composite materials have some problems, for example, seperation between carbon fiber and epoxy, delamination of lamina etc. Also, the tool wear is very serious. Therefore, we need to improve the shape of drill and condtion of drilling if possible. In this study, machinability of the carbon fiber epoxy composite materials in drilling was experimentlly investigated to establish the efficient shape of drill.

• 기술사
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• 제24권3호
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• pp.43-50
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• 1991

On the ground foundation works for Bldg site, Rock classification test can be obtained as follows due to the International Society for Rock Mechanics. 1. In-take test ; Compression strength, Point load test. 2. In-situ test : Schmidt hammer test. Burden test finaly the convinient co-relation table between strength and S.H. test were carried out for site-engineer. This project is one of contineous works regarding to Burden test from Jack leg drill( ø 36mm) to Crawler drill( ø 75mm) use.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 추계학술대회 논문집
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• pp.298-301
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• 1992

A digital image processing approach has been adopted to measure the flank wear area, which is very difficult to measure using conventional techniques. Automatic thresholding of the gray-level values of an image is very useful in automated analysis of image. 1-D entropy thresholding technique is used for image processing and analysis of the flank wear area. This strategy provides more information about drill wear conditions and should therefore have a higher reliability than previous methods. This study calulated quantitatively the flank were area of drill by computer program.

• 한국작물학회지
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• 제43권2호
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• pp.124-127
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• 1998

Since weedy rice problems have emerged with the recent advent of direct seeding cultivation in Korea, the establishment of effective control strategies for weedy rice is considered to be one of the urgent issues to be solved for widely practiced direct seeding rice cultivation. A three year experiment was conducted to investigate the occurrence pattern of weedy rice in four different rice cultivation practices: high ridged dry seeding, wet drill seeding, water seeding, and machine transplanting. The highest weedy rice occurrence of 11.0% was observed in high ridged dry seeding practice followed by 9.6% in wet drill seeding, 6.4% in water seeding practice, and 0.2% in machine transplanting practice, respectively. The same trend was observed when we examine the occurrence of contamination of panicle and rice grain by weedy rice. More contamination was observed in high ridged dry seeding than any other practices. It was also found that the possible emergence depths from the soil surface was deeper in both in ridged dry seeding and wet drill seeding practice (0-5 cm from the soil surface) than those in water seeding (0-4 cm), and machine transplanting practice (0-3 cm). The highest yield reduction of 19.5% was observed in high ridged dry seeding practice followed by 13.0% in wet drill seeding, 6.3% in water seeding practice. The reduction may have occurred to the competition between weedy rice and cultivated rice, These findings suggest that among the four cultural practices examined, the machine transplanting practice is the most effective method to control and reduce the weedy rice occurrence and weedy rice seed in soil.

• Structural Engineering and Mechanics
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• 제49권4호
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• pp.427-448
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• 2014

At present, the time of easy oil and gas is over. Now, the largest part of fossil fuels is concentrated in the deepest levels of tectonic structures and in the sea shelves. One of the most cumbersome operations of their extraction is the bore-hole drilling. In connection with austere tectonic and climate conditions, their drivage every so often is associated with great and diversified technological difficulties causing emergencies on frequent occasions. As a rule, they are linked with drill string accidents. A key role in prediction of these situations should play methods of theoretical modelling. For this reason, there is a growing need for development and implementation of new numerical methods for computer simulation of critical and post-critical behavior of drill strings (DSs). In this paper, the processes of non-linear deforming of a DS in cylindrical cavity of a deep bore-hole are considered. On the basis of the theory of curvilinear flexible rods, non-linear constitutive differential equations are deduced. The effects of the longitudinal non-uniform preloading, action of torque and interaction between the DS and the bore-hole surface are taken into account. Owing to the use of curvilinear coordinates in the constraining cylindrical surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equation system. To solve it, the method of continuation the solution by parameter and the transfer matrix technique are applied. As a result of the completed numerical analysis, the critical states of the DS loading in the cylindrical channels of inclined bore-holes are found. It is shown that the modes of the post-critical deforming of the DS are associated with its irregular spiral curving prevailing in the zone of bottom-hole-assembly. The possibility of invariant state generation during post-critical deforming is established, condition of its bifurcation is formulated. It is shown that infinite variety of loads can correspond to one geometrical configuration of the DS. They differ each from other by contact force functions.