• 지질공학
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• 제32권3호
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• pp.389-399
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• 2022

Observations on the influence of the fluid infiltration on the breakdown pressure during laboratory hydraulic fracturing tests, along with an analysis of the applicability of the breakdown pressure prediction for cylindrical samples using Quasi-static and Linear Elastic Fracture Mechanics approaches were carried out. These approaches consider fluid infiltration through the so-called radius of fluid infiltration or crack radius, a parameter that is not a material property. Two sets of tests under pressurization rate controlled and injection rate controlled tests were used to evaluate the applicability of these methods. The difficulty of the estimation of the radius of fluid infiltration was solved by back calculating this parameter from an initial set of tests, and later, the obtained relationships were used to predict breakdown pressures for a second set of tests. The results showed better predictions for the injection rate than for the pressurization rate tests, with average errors of 3.4% and 18.6%, respectively. The larger error was attributed to differences in the testing conditions for the pressurization rate tests, which had different applied vertical pressures. On the other hand, for the tests carried out under constant injection rate, the Linear Elastic Fracture Mechanics solution reported lower errors compared to the Quasi-static solution, with values of 3% and 3.8%, respectively. Moreover, a sensitivity analysis illustrated the influence of the radius of fluid penetration or crack radius and the tensile strength on the breakdown pressure, suggesting a need for a careful estimation of these values. Then, the calculation of breakdown pressure considering fluid infiltration in cylindrical samples under triaxial conditions is possible, although larger data sets are desirable to validate and derive better relations.

• 한국분무공학회지
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• 제10권4호
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• pp.47-53
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• 2005

This paper presents the effects of ambient pressure on atomization characteristics of high-Pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a shadowgraph technique. In order to investigate the atomization process numerically, the LISA-DDB hybrid model was utilized. This breakup model assumes that the primary breakup occurs when the amplitude of the unstable waves is equal to the radius of the ligament of liquid sheet near the nozzle and the droplet deformation induces the secondary breakup. The results provide the effect of ambient pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is also revealed that the accuracy of prediction of LISA-DDB hybrid model is pretty good in terms of spray developing process, spray tip penetration, and SMD distribution.

• Nuclear Engineering and Technology
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• 제35권2호
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• pp.144-153
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• 2003

The object of this paper is the probabilistic failure analysis on the cladding performance of WPF(Whole Pin Furnace) test fuel pins under transient conditions, and analysis of the KALIMER fuel pin using the preceding analysis. The cumulative damage estimation and Weibull probability estimation of WPF test are performed. The probabilistic method was adapted for these analyses to determine the effective thickness thinning due to eutectic penetration depth. In the results, it is difficult to assume that a brittle layer depth made by eutectic reaction is all of the thickness reduction due to cladding thinning. About 93% cladding thinning of the eutectic penetration depth is favorable as an effective thickness of cladding. And the unreliability of the KALIMER driver fuel pin under the same WPF test condition is lower than that of the WPF pin because of the higher plenum-fuel volume ratio and lower cladding inner radius vs. thickness ratio. KALIMER fuel pin developed from conceptual design has a more stable transient performance for a failure mechanism due to fission gas buildup than the WPF pin.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1434-1439
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• 2004

CFRP composite materials have wide application in structure materials of airplane, ships, and aero space vehicles because of their high strength and stiffness. This paper is to study the effects of curvature and orientation angle on the penetration characteristics of CFRP laminate shell. They are staked with 8 Ply specimens [0$_2$/90$_2$]$_{s}$, [0/90$_2$/0]$_{s}$ and the stacked of outer plates degree with 12 Ply specimens [0$_3$/90$_3$]$_{s}$, [0$_2$/90$_2$/0]$_{s}$ and [90$_3$/0$_3$], [90$_2$/0$_2$/90]S. They are manufactured to varied curvature radius (R=100,150,200mm and $\infty$). They are cured by heating to the appropriate harding temperature(13$0^{\circ}C$) by mean of a heater at the vaccum bag of the autoclave. Test specimens were prepared with dimensions 100mm$\times$140mm. When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determining the time for it to pass two ballistic-screen sensor located a known distance apart. In general, kinetic energy after impact-kinetic energy before impact rised in all specimens. This study observed a fracture mode inside the specimen after a penetration test using a digital camera and it examined a fracture mode and a penetration mode to stack of outer orientation angle and curvature.rvature.

• Journal of Biosystems Engineering
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• 제34권6호
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• pp.397-403
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• 2009

This study was carried out to investigate the present status of subsoil compaction, and subsoil compaction management in orchard as a basic study for developing a self-propelled explosive subsoiler. Subsoil compaction was evaluated using the soil penetration resistance. Soil cone index was measured using the DIK 5520 type cone penetrometer in several fruit farms such as apple, pear, peach and grapes during growing seasons of these fruit in Jecheon, Gamgok, Choongju, Cheonan and Hwasung areas. Most of the subsoil managing machinery were either explosive type or digging type attached to the tractor or power tiller and turning radius of this machine was more than 3-5 m. Many of the farmers wanted to use the subsoiler which can put lime into soil and rupture soil at the same time. For most of the orchard fields, soil penetration resistance in vehicle traffic area was increased quickly and reached about 1.0 MPa in 5 cm soil depth. As the soil depth increased to 15-20 cm, cone penetration resistance reached about 2.0-2.5 MPa which restricted root growth seriously. Thus it was concluded that one of the main reason for increasing the soil compaction in orchard fields is agricultural vehicle traffic. In the vicinity of fruit trees, compaction is not so serious compared to that of the vehicle traffic area, but as the soil depth increased to 20-25 cm, in most of the orchard fields soil penetration resistance reached about 2.0-2.5 MPa which is the root growth-limiting value. Considering the rooting depth of fruit trees which ranged 30-60 cm for apple, pear and peach, and 20-30 cm for grape, it is necessary to loosen the subosoil and improve the subsoil conditions using subsoiler.

• 한국지반공학회논문집
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• 제34권10호
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• pp.51-60
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• 2018

최근 해상 작업을 위한 새로운 시공기술로서 대형원형강재 가물막이 공법이 제안되었다. 본 구조물은 원형 형상의 가물막이이기 때문에 가물막이의 형상에 따른 침투해석 연구가 필요하다. 그러므로, 본 연구에서는 흐름해석을 수행하여 원형 가물막이에 대하여 벽체 내부로의 침투 유량을 산정하였다. 흐름해석에 이용된 수치모델링은 2열의 널말뚝을 가진 가물막이에 대하여 제안된 이론해와 비교하여 검증하였다. 흐름조건의 경우 축대칭 흐름조건의 침투유량이 2차원 흐름조건의 침투유량과 비교하여 1.55배 크게 나타났으므로 2차원 축대칭 흐름조건을 적용하였다. 벽체 반경, 벽체의 지중 근입깊이 그리고 벽체 내외부의 수위차 등을 변화시키며 변수연구를 수행한 결과, 침투유량은 벽체의 근입깊이와 벽체 반경이 증가할수록 감소하는 것으로 나타났다. 최종적으로, 대형원형강재 가물막이의 침투유량을 산정할 수 있는 간이식을 제안하였다.

• Journal of Biosystems Engineering
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• 제34권6호
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• pp.404-410
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• 2009

This study was carried out to develop a self-propelled type explosive subsoiler for improving the root zone soil conditions in orchard and other forest fields. Prototype was designed to be able to inject air and other soil improving material such as lime into soil at the same time, and thus improve the air permeability and drainage of orchard soils to promote the root growth of tree for high quality fruit production. Soil penetration device of explosive subsoiler is composed of air hammer, penetration rob and air injection nozzle. To support the soil penetration device of explosive subsoiler to penetrate vertically, modified Scott-Russel mechanism was used. Timing control device for simultaneous injection of soil improving material with air was attached to the out side wall of air cylinder and as the cylinder move, the soil improving material was injected into soil at the same time. Turning radius of prototype was 2.2-2.3 m with good mobility in sloped land. It took approximately 1 minute for lime injection system to reach the optimum pressure of 9.9 kg/$cm^2$, average 10-20 seconds were required to rupture soil with the depth of 50 cm and 2-3 seconds were required for explosion, so all in all about 1 minute and 20 seconds were required for one cycle of explosion. Maximum soil rupture depth and diameter were 50 cm and 3-4 m respectively depending on the soil type and soil moisture content. For final design of explosive subsoiler inclination angle of lime hopper was increased from 60 degree to 70 degree and the shape of hopper was changed from rectangular cone to circular cone to solve the clogging problem of lime at out let. Agitating system operated by compressed air was attached to the metering device of the prototype, thus more than 90 cc of lime was discharged per cycle from metering device without clogging problems.

• 소성∙가공
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• 제21권3호
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• pp.202-206
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• 2012

Marking is a process that engraves letters or a pattern onto the surface of sheet metal. During marking, it is important to set the proper working conditions for clarity of the letters. In this study a simple case for forming circular protrusions by half-piercing and embossing was initially attempted to determine the working conditions which gave good results with respect to shape accuracy. Corner-radius and flatness of circular protrusions made under several experimental conditions were measured and compared. It is shown that the precision of protrusions by half-piercing is superior to that of embossing, and the clearance between punch and die exerts a strong influence on the shape accuracy rather than the penetration percentage into the thickness of the sheet metal. The marking dies for "SNUT" letters, as an example, by applying the above results were manufactured with four different clearances. The working variables for the experiment were clearance and marking depth. For the very shallow depth of 0.1mm the letters were not clearly read. Letters marked under other conditions were easily distinguished with increasing marking depth. It was confirmed that the half-piercing technique with proper values of the working variables gives good quality for the marking of sheet metal.

• 한국해안해양공학회지
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• 제5권2호
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• pp.143-150
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• 1993

이중 주파수(Dual Frequency)를 사용한 Prototype형 천해 지층 탐사기를 사용하여 얻은 탐사 기록지가 제시되었다. 이중 주파수로는 3.5/100KHz 혹은 15/100KHz를 이용해서 고주파수에 의한 고해상도(High Resolution)을 얻고 동시에 저주파수(3.5~15KHz)에 의한 심층 투과력을 높이는데 본 연구의 목적이 있다. 특히 탐지하는 목표물이 Fresnel 반경에 비해서 매우 작을 때는 쌍곡선형 회절무늬(Hyperbolic Diffraction)가 나타나기 때문에 쉽게 목표물을 찾을 수 있다. 감쇠상수가 큰 모래층은 작은 감쇠상수를 갖고 있는 점토보다 지진파의 투과력을 약하게 만든다. 이와같이 이중 주파수의 동시 운용은 해저 지질. 모래와 점토(Silt/Clay) 분포 오니토 및 해양고고학 유물 탐사에 크게 활용할 수 있다.

• 한국실천공학교육학회논문지
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• 제2권1호
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• pp.154-163
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• 2010

본 연구에서는 터보차저 및 인터쿨러, 블루 오프 밸브 등 튜닝 부품을 장착한 스쿠푸 알파 차량의 경우 N/A엔진에 비해 흡입 공기량의 변화가 오게 되고 이에 따른 연료 보정 및 ECU의 튜닝을 목적으로 연구되었다. 이와 같은 터보 엔진은 압축압력의 변화가 있게 되며 이때 인위적으로 개스킷의 두께를 조절하여 압축비에 변화를 주게 되면 엔진의 출력 특성 변화를 살펴볼 수 있다. 시험은 제동압력이나 마력 측정이 불가능하므로 ECU튜닝 장비인 모텍 라서치(주)의 Engine Management System장비를 기본으로 시험하였고 성능 공식 전개를 통하여 출력의 변화를 살펴보았다. 엔진 다이나모미터 시험보다 엔진 ECU데이터를 사용하기 때문에 개발된 ECU 데이터를 이용하면 튜닝엔진에 바로 접목시킬 수 있어 앞으로 튜닝 정비 분야에서 많이 필요로 할 것으로 예측된다. 또한 본 연구를 통하여 학생들은 전자제어엔진에 대해 섬도 있는 학습이 되었으며, 정비 관련 산업체에서도 ECU데이터를 이용하여 엔진의 성능을 점검하고 체계적으로 제어할 수 있는 기술의 방향과 토대를 마련하였다고 본다.