• Interaction and multiscale mechanics
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• 제4권1호
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• pp.1-16
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• 2011

The inverse problem about the theoretical analysis of a drill string bending in a channel of an inclined bore-hole with localized geometrical imperfections is studied. The system of ordinary differential equations is first derived based on the theory of curvilinear flexible elastic rods. One can then use these equations to investigate the quasi-static effects of the drill string bending that may occur in the process of raising, lowering and rotation of the string inside the bore-hole. The method for numerical solution of the constructed equations is described. With the proposed method, the phenomenon of the drill column movement, its contact interaction with the bore-hole surface, and the frictional seizure can be simulated for different combinations of velocities, directions of rotation and axial motion of the string. Geometrical imperfections in the shape of localized smoothed breaks of the bore-hole axis line are considered. Some numerical examples are presented to illustrate the applicability of the method proposed.

• 대한토목학회논문집
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• 제28권5B호
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• pp.575-589
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• 2008

본 연구는 지진해일단파(tsunami bore) 혹은 조석단파(tidal bore)와 같은 단파의 동수역학적인 거동특성을 검토할 목적으로, 댐파괴류에서 단파의 형성과 동일한 방법, 즉 수조의 한쪽 끝단에 있는 고수위의 저수조(貯水槽) 게이트를 순간적으로 제거하는 방법으로 단파를 발생시킨다. 이러한 단파의 형성과 전파에 관한 수치시뮬레이션에 이상유(二相流)모델에 기초한 Navier-Stokes식을 적용하며, 이 때 비압축성 및 비혼합성의 액체와 기체흐름을 각각 고려한다. 기체와 액체의 접면을 VOF법으로 추적하고, Navier-Stokes방정식을 수치적으로 풀기 위하여 MCIP법을 적용한다. 1차원인 CIP법을 분할스텝기법을 사용하여 고차원으로 확장한 MCIP법은 수치확산이 매우 작고, 또한 안정된 스킴으로 알려져 있다. 게다가, 난류를 시뮬레이션하기 위하여 그의 유용성이 잘 알려져 있는 LES모델을 사용한다. 단파의 형성과 전파에 관한 수치해석결과를 검증하기 위하여 수리실험을 수행하였으며, 시간경과에 따른 수위변동과 평균유속변동에 대한 수치해석결과 및 실험결과를 비교하여 매우 양호한 상호대응관계를 확인할 수 있었다.

• Tribology and Lubricants
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• 제22권3호
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• pp.155-163
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• 2006

Ring, groove and cylinder bore wear may not be a problem in most current automotive engines. However, a small change in ring face, groove geometry and cylinder bore diameter can significantly affect the lubrication characteristics and ring axial motion. This in turn can cause to change inter-ring pressure, blowby and oil consumption in an engine. Therefore, by predicting the wear of piston ring face, ring groove and cylinder bore altogether, the changed ring end gap and the changed volume of gas reservoir can be calculated. Then the excessive oil consumption can be predicted. Being based on the calculation of gas flow amount by the theory of piston ring dynamics and gas flow, and the calculation of oil film thickness and friction force by the analysis of piston ring lubrication, the calculation theory of oil amount through top ring gap into combustion chamber will be set. This is estimated as engine oil consumption. Furthermore, the wear theories of ring, groove and cylinder bore are included. Then the each amount of wear is to be obtained. The changed oil consumption caused by the new end gap and the new volume of oil reservoir around second land, can be calculated at some engine running interval. Meanwhile, the wear amount and oil consumption occurred during engine durability cycle are compared with the calculated values. Next, the calculated amount of oil consumption and wear are compared with the guideline of each part's wear and oil consumption. So, the timing of part repair and engine life cycle can be predicted in advance without performing engine durability test. The wear data of rings, grooves and cylinder bore are obtained from three engines before and after engine durability test. The calculated wear data of each part are turn out to be around the band of averaged test values or a little below.

• Journal of Chest Surgery
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• 제44권6호
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• pp.418-422
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• 2011

Background: It has recently become most general to use the small bore catheter to perform closed thoracostomy in treating iatrogenic pneumothorax. This study was performed for analysis of the efficacy of treatment methods by using small bore catheter such as 7 F (French) central venous catheter, 10 F trocar catheter, 12 F pigtail catheter and for analysis of the appropriateness of each procedure. Materials and Methods: From March 2007 to February 2010, Retrospective review of 105 patients with iatrogenic pneumothorax, who underwent closed thoracostomy by using small bore catheter, was performed. We analyzed the total success rate for all procedures as well as the individual success rate for each procedure, and analyzed the cause of failure, additional treatment method for failure, influential factors of treatment outcome, and complications. Results: The most common causes of iatrogenic pneumothorax were presented as percutaneous needle aspiration(PCNA) in 48 cases (45.7%), and central venous catheterization in 26 cases (24.8%). The mean interval to thoracostomy after the procedure was measured as 5.2 hours (1~34 hours). Total success rate of thoracostomy was 78.1%. The success rate was not significantly difference by tube type, with 7 F central venous catheter as 80%, 10 F trocar catheter as 81.6%, and 12 F pigtail catheter as 71%. Twenty one out of 23 patients that had failed with small bore catheter treatment added large bore conventional thoracostomy, and another 2 patients received surgery. The causes for treatment failure were presented as continuous air leakage in 12 cases (52.2%) and tube malfunction in 7 cases (30%). The causes for failure did not present significant differences by tube type. Statistically significant factors affecting treatment performance were not discovered. Conclusion: Closed thoracostomy with small bore catheter proved to be effective for iatrogenic pneumothorax. The success rate was not difference for each type. However, it is important to select the appropriate catheter by considering the patient status, pneumothorax aspect, and medical personnel in the cardiothoracic surgery department of the relevant hospital.

• 대한의용생체공학회:의공학회지
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• 제41권6호
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• pp.219-227
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• 2020

In this study, we tried to quantify the actual cross-sectional area inside the bore when scanning by the MRI system with various bore sizes. To this end, a comparative analysis was conducted by both of blueprint of each MRI equipment and actual measurement in the field. As a result of analysis, ACSA(Actual Cross-Sectional Area) in Ingenia CX, Elition X, uMR 780, Omega, Vida, Lumina, Architect, Premier is recorded as 171230, 232150, 242100, 309332, 230760, 230760, 229380 and 235990 ㎟, respectively ACSA% was 60.6, 60.3, 73.0, 70.0, 60.0, 60.0, 59.6, and 61,3%. In addition, DTB (Distance from Table top to Bore top) recorded 400, 407, 445, 495, 405, 405, 405, 403, and 412 mm. Through this study, it was confirmed that there is a difference between the bore size according to each MRI system and the actual cross-sectional area during MRI scanning. Accordingly, if we consider the internal actual area just not bore size at the clinical site, useful diagnostic images can be obtained in the end with better convenience.

• 한국수자원학회논문집
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• 제52권5호
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• pp.313-323
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• 2019

대심도 터널은 기 개발된 도시의 부족한 배수관망 능력을 보강하기 위하여 지하에 설치하는 대규모 도시홍수 배제 시설물로 역 사이펀 관로 형태를 하고 있는 시설물이다. 대심도 터널과 같은 구조에서는 하류에서 발생한 불규칙 단파에 의하여 터널의 수리적 안정성에 문제가 발생한다. 본 연구에서는 국내 최초로 건설 중인 '신월 빗물저류배수시설'의 수리적 안정성에 불규칙 단파가 미치는 영향을 알아보기 위하여 다양한 홍수유입 시나리오에 대하여 수리모형실험을 실시하였다. 본 연구에서 수행한 수리모형실험 결과 하류에서 발생한 불규칙 단파가 상류로 이동하면서 관 내 포집되어 압축상태인 공기덩어리를 밀어내는데, 이 공기덩어리가 상류 수직유입구를 통하여 급배기 되는 과정에 수직유입구를 질식시키고 홍수유입을 차단하여 월류가 발생하는 것으로 판단된다. 또한 불규칙 단파의 이동속도를 분석한 결과 불규칙 단파가 이동하면서 에너지를 전달하고 이때 관 내 압력 상승 및 불규칙 단파의 속도 증가분이 발생하는 것으로 판단된다. 대심도 터널의 수리적 안정성에 중요한 역할을 하는 불규칙 단파의 크기 및 속도 예측을 위한 추가 연구가 필요할 것으로 판단된다.

• Corrosion Science and Technology
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• 제12권5호
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• pp.227-232
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• 2013

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one (1) inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1,000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed on in front of the orifice. This paper deals with UT (Ultrasonic Test) thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

• 소음진동
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• 제9권4호
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• pp.714-719
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• 1999

Because the residual vibration of a gun barrel acts negatively on the firing of a large calibers gun, the fast stabilization of theresidual vibration is indispensible to the precise and successive firing. In this study, the residual vibrations of a gun barrel carrying a bore evacuator and a muzzle brake are investigated by the experimental method. The influence of the eigenfrequencies and the mode shapes of gun barrel on the fast stabilization of the residual vibration is studied for the various masses of bore evacuator and muzzle brake, the possition of bore evacutor. Also the relationships between the funcamental frequencies and the settling times of the gun barrel are investigated for the various parameters. The experiments to reduce the residual vibration using the viscoelastic damping treatment gives the best result among the various treatments for the reduction of residual vibration of the system.

• International Journal of Automotive Technology
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• 제2권2호
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• pp.47-52
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• 2001

For the wear protection of cylinder bore in aluminum cast material the internal plasma spraying technology offers a new economical solution. The size and the weight of the engine blocks significantly can be decreased in comparison with the traditional cast iron sleeves. The coefficient of friction between piston ring and cylinder wall sensitively can be reduced and the wear resistance increased from several factors. The paper gives an overview of the technology from the AlSi cast alloys for engine block to the non destructive testing technology used after the machining by diamond honing. The actual results in engines of different types also will be shown. The economical advantages of the plasma spraying (or the internal coating in cylinder bore also will be discussed in comparison with the different alternatives of technology. The aspect of the market introduction also will be discussed in this paper.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.174-181
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• 2002

Dynamic deformation of the cylinder bore during actual engine operation has an important effect on the combustion gas sealing, oil consumption, friction and so on. The dynamic analysis using the finite element method is performed to investigate the dynamic deformation of the cylinder bore subjected to forced vibration under excitation of the combustion gas pressure. However, this analysis requires large computer memory and tremendous solving time. The pseudo-static analysis can be an alternative to the dynamic analysis at the expense of accuracy. Dynamic analysis and static analysis results are presented for both closed-deck block and open-deck block that are respectively combined with the cylinder block, cylinder head, transmission, and oil pan.