원심압축기의 선회실속특성에 관한 연구

모양우,나기대,유영태,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

In the present study, the performance characteristics and the number of stall cell during rotating stall of a centrifugal air compressor were experimentally investigated. Rotating stall in the vaneless diffuser were investigated by measuring unsteady pressure fluctuations at several different diffuser radius using a high frequency pressure transducer. The number of stall cell and their rotational speeds are distinctive features of the rotating stall phenomenon. The present study is mainly forced on the analysis for the stall cell number and its propagation speed unstable operating region of the compressor. The interpretation method of visualization is based on the pressure distribution in the circumference pressure fields while plotting the pressure and its harmonics variations in time in polar coordinates. To obtain the visualize the existence rotating stall, auto-correlation function and the frequency spectra of the pressure fluctuations were measured at rh-2 = 1.52. When the flow coefficient is lower than 0.150, the static pressure at impeller inlet is higher than that at inlet duct of the Compressor. And the flow coefficient is lower than 0.086, several stall cell groups of discrete frequencies are observed.

압박 고 나사로 치료한 대퇴골 전자부 골절 : 고정 실패의 인자에 대한 분석 Analysis of Factors associated with Failure of Fixation

유찬훈,김홍태,변영수,남준모,조영호,문성건 대한골절학회 2002 대한골절학회지 Vol.15 No.4

목 적 : 압박 고 나사로 치료한 대퇴골 전자부 골절의 고정 실패에 영향을 미치는 요소에 대하여 분석하고자 하였다. 대상 및 방법 : 1995년 5월부터 2000년 7월까지 대퇴골 전자부 골절을 압박 고 나사를 이용하여 치료하고 1년 이상 추시가 가능했던 97예를 대상으로 하였다. 골절의 분류는 Jensen 분류법을, 골다공증의 정도는 Singh 지수를 이용하였다. 술후 방사선 검사에서 경체각, 정복 상태, 지연 나사의 대퇴골 두 내 위치, tip-apex distance(TAD) 및 지연 나사의 활강 거리를 측정하였고 고정 실패에 미치는 영향을 통계학적으로 분석하였다. 결 과 : 97예 중 17예(17%)에서 고정 실패가 발생하였고 그 중 지연 나사의 과도한 활강으로인한 경우가 15례(15.4%), 골두 천공 1얘, 10도 이상의 외반 변형 1예였다. 고정 실패의 발생과 80세 이상의 고령, 불안정성 골절, telescoping 정복, 원위 골편의 내측 혹은 전방 전위, 대퇴골 두 내 지연 나사의 위치와 밀접한 관계가 있었다. 결 론 : 압박 고 나사를 이용한 대퇴골 전자부 골절의 치료에서 고정 실패를 방지하기 위해서는 정확한 정복이 필요하고 대퇴골 두 내에서 지연 나사의 전방 위치를 피하는 것이 좋을 것으로 사료된다. Purpose : This study was performed to analyze the significant factors that may affect failure of fixation in trochanteric fractures of the femur treated with the compression hip screw. Materials and Methods : From May 1995 to July 2000, the authors analyzed 97 cases of trochanteric fracture of the femur treated with the compression hip screw and followed more than one year. We classified the fracture type by Jensen's method. We used Singh index for the degree of osteroporosis. In the post-operative radiograph, we checked neck-shaft angle, state of reduction, position of the lag screw within the femoral head, tip-apex distance, and sliding distance of the lag screw. The relationship between these factors and failure of fixation was statistically analyzed. Results : There were 17 cases(17.5%) of failure of fixation ; 15 cases(15.4%) of excessive sliding of the lag screw, 1 case (1%) of cutting out of the lag screw, and 1 case (1%) of valgus malunion. There were significant relationship between failure of fixation and old age over 80 , unstable fracture, telescoping reduction, anterior or medial displacement of the distal fragment, and anterior placement of the lag screw within the femoral head. Conclusion : Accurate reduction and avoidance of the placement of the lag screw in the anterior part of the femoral head were important factors to prevent failure of fixation in trochanteric fractures of the femur treated with the compression hip screw.

고출력 레이저에 의한 이종금속 용접시험평가에 관한 연구

유영태,신호준,송성욱,모양우 朝鮮大學校 機械技術硏究所 2004 機械技術硏究 Vol.7 No.1

Laser welding techniques have been characterised for various materials. In this paper. the laser weldability of STS304 stainless steel and Inconel 600 at dissimilar metal welds using a continuous wave Nd:YAG laser are experimentally investigated. Inconel 600 is being used in a steam generator tubing of pressurized water reactor(PWR) exposed to some corrosion. Stress corrosion cracking can occur on this material. An experimental study was conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser were tested.

유압관로에서 맥동유동의 유량특성

유영태,모양우,김지환 朝鮮大學校 機械技術硏究所 2001 機械技術硏究 Vol.4 No.2

The measurement of unsteady flow rate is importance to clarify and improve the dynamic characteristics in pipeline, hydraulic components and systems. There is also demand for a real time flow at the sensor in order to measure unsteady flow rate with high accuray and fast response to realize feedback control of flow rate in fluid power systems therefore We propose an approch for estimating unsteady flow rate through a pipeline and dynamic characteristics of pulsting flow rate components under high pressure condition. Unsteady flow rate is estimated by using semiconductor type pressure transducers and the measured pressure values at two distant points along the pipeline.

고출력레이저에 의한 인코넬600의 맞대기용접 시험 평가

유영태,신호준,모양우 조선대학교 에너지.자원신기술연구소 2004 에너지·자원신기술연구소 논문지 Vol.26 No.1

Welding characteristics of Inconel 600 Alloy using a continuous wave Nd:YAG laser are experimentally investigated. The major process parameters studied in the present laser welding experiment were position of focus, laser power, travel speed. The gap and offset maintained as small as possible. Optical microscope were used to investigate the microstructures of the welded zone. This study shows the result of the tension experiments. And then this paper used the Electronic Speckle Pattern Interferometry to present the welding residual stress in welds. The follow conclusions can be drawn the laser power and travel speed have a pronounced effect the fusion zone size and shape.

유압관로의 임피던스 전달특성

유영태,나기대,모양우,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

Design for quite operation of fluid power system requires t h understanding of noise and vibration characteristics of t h system This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation characteristics of pressure ripple in automotive power steering hydraulic pipe with dynamic response of hydraulic pipe line is examined.

정사각 덕트의 출구 영역에서 속도분포에 대한 실험적 연구

유영태,모양우,나기대,임인호 朝鮮大學校 機械技術硏究所 2002 機械技術硏究 Vol.5 No.2

A numerical simulation has been performed with the non-linear turbulence model proposed by Speziale(1987) coupled with the k-ε equations coming from the renormalization group theory(RNG) derived by Yakhot et al(1992). The fully developed turbulent flow through a straight square duct, involing secondary motion is simulated. This paper represent computations of the interaction between measurement and numerical computation of turbulent flow on velocity distribution of outlet region in a square duct. RNG turbulent model was adapted and compared with the experimental data and the result of Standard k-ε turbulent model. The predictions obtained with the RNG k-ε model show improvements when compared with the Standard k-ε model. Mean velocity, turbulence kinetic energy and Reynolds shear stresses are in quantitiative agreement with the experimental data. We feel that the RNG k-ε model suggested in this paper can be a useful turbulence model for practical engineering

유압관로의 비정상유동에 따른 임피던스 전달특성

모양우,유영태,나기대,김지환 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.6

Design for quite operation of fluid power system requires the understanding of noise and vibration characteristics of the system. This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation of pressure ripple in automotive power steering hydraulic pipe line is examined. Also, a mathematical model of hydraulic pipe is proposed to support a design of the hydraulic circuit. and the impedance characteristics of pressure ripple is analyzed. It is experimentally shown that power steering hydraulic pipe attenuates pressure ripple with high frequency.

Finn Chamber Occlusion 과 Histometry 를 사용한 수종 스테로이드제의 표피 위축에 대한 관찰

천영일(Young Il Chun),양준모(Joon Mo Yang),서명수(Myoung Soo Suh),은희철(Hee Chul Eun),이유신(Yoo Shin Lee) 대한피부과학회 1986 大韓皮膚科學會誌 Vol.24 No.5

The aim of this stud y was to compare the epidermal thinning properties of four corticosteroid ointments applied under occlusion, using histology and histometry. The results were surnmerized as follows: 1.The stratum corneurn was dramatically thinned, appearing as a wispy layer of horny cells as apposed to the norrnal basket-weave configuration. this effect was prominent at sites treated with clobestasol propionate, fluocinonide, and fluocinolone acetonide. 2. With the histometry, visible epidermal thickness wa.s markedly reduced. This effect w is prominent in the following ascending order: fluocinolone acetonide, fluocienonide, clobestasol-17-propionate. Hydrocortisone was the least atrophogenic. 3. Clohestasol-17-propionate and fluocinonide caused significant flattening of der- mo-epidermal junction, Fluocinolone acetonide and hydrocortisone caused less pronounced cbanges. 4. Marked capillary dilation af papilly dermis is caused by clobestasol-17-propionate, fluocinonide and fluocinolone acetonide.

임플란트의 collar design이 변연골과 연조직에 미치는 영향

유현상,강선녀,정창모,윤미정,허중보,전영찬 대한치과보철학회 2012 대한치과보철학회지 Vol.50 No.1

연구 목적: 임플란트 경부가 잘 설계된 경우 양호한 연조직 반응을 통해 변연골을 보존하는데 도움이 된다. 본 실험에서는 연, 경조직 경계부에 가장 가까이 위치하는 임플란트의 collar design이 변연골 변화와 연조직 반응에 미치는 영향을 동물실험을 통해 알아보고자 하였다. 연구 재료 및 방법: 2마리의 건강한 Beagle dog에 임플란트 collar design만 다른 두 종류의 임플란트(Neobiotech Co. Seoul, Korea)를 식립하였다. Collar에 bevel 을 부여한 군(Bevel 군)과 "S"자 형태를 부여한 군(Bioseal 군)으로 나누어 마리 당 7개, 군당 7개, 총 14개의 임플란트를 무작위로 식립한 후 Healing abutment를 즉시 체결하였다. 디지털 표준구내 방사선사진을 이용해 4주 간격으로 총 12주간 근원심 변연골 변화를 관찰하였고, 12주에 희생하여 조직학적 분석을 통해 협설 변연골 흡수 및 임플란트 주변 연조직 반응을 평가하였다. Mann-Whitney test를 통해 동일한 방사선 사진 촬영 시점에서 근원심 변연골 변화량 및 조직계측치를 군 간 비교하였고, Kruskal-Wallis test를 통해 방사선 사진상 근원심 변연골 변화량이 시간에 따른 차이가 있는지 군 내 분석 한 후 Duncan test를 통해 사후 검증하였다(α=.05). 결과: 방사선학적 분석 결과 각 촬영 시점에서 두 군간 근원심 변연골 변화량의 차이를 보이지 않았다(P>.05). 군 내에서 시간에 따른 근원심 변연골의 흡수량을 분석한 결과 Bevel 군에서는 시간에 따른 차이를 보이지 않았으나 (P>.05), Bioseal 군에서는 시간에 따른 차이를 보였으며, 4주및8주와 비교했을 때 12주에서 변연골의 증가를 보였다(P<.05). 조직학적 분석 결과 협설측 변연골 흡수량에서 두 군간 차이를 보이지 않았으나 (P>.05), Bevel 군에 비해 Bioseal 군에서 더 견고한 결합조직부착을 관찰할 수 있었으며, 생물학적 폭경의 값은 두 집단 간 차이를 보이지 않은 반면에 (P>.05), 접합상피부착은 Bevel 군에서 유의하게 길었고, 결합조직부착은 Bioseal 군에서 더 길게 나타났다(P<.05). 결론: Bevel 군에 비해 Bioseal 군에서 결합조직부착은 길게 형성된 반면에 접합상피부착은 더 짧게 나타났으며, 생물학적 폭경과 초기 변연골 흡수에는 차이가 없음을 알 수 있었다. 연조직 반응의 차이가 실제 기능하중 하에서 변연골 변화에 미치는 영향에 대해서 향후 연구가 필요할 것으로 생각된다. PURPOSE. The purpose of this study was to investigate the effects of implant collar design on marginal bone change and soft tissue response by an animal test. MATERIALS AND METHODS. Two types of Implant (Neobiotech Co. Seoul, Korea) that only differs in collar design were planted on two healthy Beagle dogs. The implants were divided into two groups, the first group with a beveled collar (Bevel Group) and the second group with "S" shaped collar (Bioseal group). Standardized intraoral radiographs were used to investigate the mesio-distal change of the marginal bone. Histological analysis was done to evaluate the bucco-lingual marginal bone resorption and the soft tissue response adjacent to the implant. Mann-Whitney test was done to compare the mesio-distal marginal bone change at equivalent time for taking the radiographs and the tissue measurements between the groups. RESULTS. Radiographic and histological analysis showed that there was no difference in marginal bone change between the two groups (P>.05). Histological analysis showed Bioseal group had more rigid connective tissue attachment than the Bevel group. There was no difference in biological width (P>.05). Bevel group showed significantly longer junctional epithelium attachment and Bioseal group showed longer connective tissue attachment (P<.05). CONCLUSION. For three months there were no differences in marginal bone change between the Bevel group and the Bioseal group. As for the soft tissue adjacent to the implant, Bioseal group showed longer connective tissue attachment while showing shorter junctional epithelium attachment. There were no differences in biologic width.