• 한국산학기술학회논문지
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• 제16권12호
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• pp.8274-8283
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• 2015

텔레비전의 가스 스프링은 롱 스트로크 (200 ~ 300mm, TV 상승 변위) 하에서 작동 할 때 피스톤 속도의 제어가 가능하다. 이 원리에 의해서 사용자는 높낮이 조절이 가능하다. 먼저 피스톤의 흐름 해석을 수행하였다. 정확한 관형 단면을 위한 피스톤 속도 조절기술을 조사하였다. 유동률 제어 및 높낮이 작용을 위한 피스톤 구조를 제안되었다. 본 연구는 대형 텔레비전 스탠드를 통해 50 인치 이상 TV의 가스 스프링의 개발을 위한 것이다. 최적 피스톤 로드 제어를 위한 중공축(외경 19.9mm, 내경 13.9mm)에 질소 개스(0.3m/s)를 주입하였다. 그 결과, 유동율이 증대함에 따라 피스톤 로드의 압력강하는 외력의 변화 없이 증대되었다. 결과적으로, 가스스프링을 통한 변위의 제어는 가능하다.

• 한국추진공학회지
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• 제8권3호
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• pp.37-43
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• 2004

증기발생기 슬러지 세정을 위한 고압분사 실험의 분류궤적에 대한 가시화 및 속도분포를 측정함으로써 최적의 노즐형상을 찾기 위하여 플랜져방식의 고압펌프(사용압력 : 200 kg/$\textrm{cm}^2$, 15HP, 11kW. 토출유량 Q : 301/min)를 이용하였다. 가시화를 통하여 정성적인 분포를 비교분석할 수 있었고, 분류의 속도분포등을 통하여 노즐 형상비에 따른 유동의 차이를 2차원 PDPA 광학 계측장비를 사용하여 분석하였다. 고압 분사시 형상비에 관계없이 모든 경우에 있어서 중심축을 따라 모든 궤적들은 거의 유사함을 보였으나, 분류 중심에서 벗어난 외곽영역에서는 많은 차이가 있음을 알 수 있었다 이는 형상 비에 따른 주변 공기와의 마찰 및 분류 유입현상 때문이라 여겨진다.

• 대한기계학회논문집B
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• 제23권8호
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• pp.1048-1062
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• 1999

A numerical method and experiments for the aerodynamic design of high performance two-stage axial flow fans was carried out. A vortex ring element method used for the aerodynamic analysis of the propellers was extended to the fan-duct system. Fan Performance and velocity profiles at the fan inlet and outlet are compared with experimental data for the validations of numerical method. Performance test was done based on KS B 6311(testing methods for turbo-fans and blowers). The velocity profile was obtained using a 5-hole pitot tube by the non-nulling method. The two stage axial flow fan configurations for the optimal operation conditions were set by using the experimental results for the single rotating axial flow fan and the single stage axial flow fan. The single rotating axial flow fan showed relatively low efficiency due to the swirl velocities behind rotor exit which produced pressure losses. In contrast, the single stage and the two-stage axial flow fans showed performance improvements due to the swirl velocity reduction by the stator. The peak efficiency of the two stage axial flow fan was improved by 21% and 6%, compared to the single rotating axial flow fan and the single stage axial flow fan, respectively.

• 대한기계학회논문집B
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• 제38권8호
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• pp.715-720
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• 2014

좌심실보조장치(LVAD)가 심실부하감소에 미치는 영향을 극대화 하기 위해, 심실보조장치 치료를 위한 최적의 심부전 심각도 단계를 찾는 것은 중요하다. 우리는 심부전 정도에 따른 LVAD 의 박동효율을 이론적으로 예측하였다. 우리는 혈관시스템의 6 컴파트먼트의 Wind-kessel 모델과 연동된 심실의 삼차원 유한요소모델을 사용하였다. 이 모델을 이용하여, LVAD 치료 하에서 심부전의 정도에 따라 심실의 수축성 ATP 소모율, 좌심실압력, 심박출량, 심박출 분획, 1 회심박출량 등과 같은 심장응답을 예측하였다. LVAD 치료 중에 에너지학적 부하조건을 암시하는 수축성 ATP 소모율은 5 단계 심부전 조건에서 가장 크게 감소하였다. 따라서, 우리는 LVAD 를 회복으로의 가교로서 고려하고 있을 때, 심부전 5 단계에서 LVAD 치료를 시작하는 것이 가장 적절하다는 결론을 내린다.

• 자원환경지질
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• 제37권4호
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• pp.375-381
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• 2004

장주기 방사성 폐기물인 악티나이드 원소들을 고정화시킬 수 있는 파이로클로어 (pyrochlore; CaCeH$f_xTi_{2-x}O_7$=0.2, 0.6, 1.0, 1.4, 1.8, 2.0)를 합성하여 상평형 관계 및 특성을 연구하였다. 혼합된 시료는 상온에서 400kg/$cm^2$의 압력으로 성형한 후, 산소분위기에서 1200∼1$600^{\circ}C$ 범위로 소결온도를 변화시키면서 소성하였다. 합성된 시료는 XRD를 사용하여 상분석을 실시하였다. 실험결과, 파이로클로어의 최적 합성조건은 산소분위기 하에서, 각각의 조성에 따라, 1300∼150$0^{\circ}C$로 매우 다양하였다. 합성시 생성된 상으로는 페롭스카이트, 파이로클로어 및 $A_{2}BO_{5}$산화물 등이 있으며, 본 계의 특성은 Hf의 함량증가에 따라 페롭스카이트 및 파이로클로어의 격자상수가 증가한다는 점이다. 이같은 현상은 육배위 자리를 차지하고 있는 Hf와 Ti의 이온반경의 차이에서 비롯된 것이다.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.233-242
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• 2007

We performed a numerical investigation to find out the optimal choice of the spatial discretization in the distributed-Lagrangian-multiplier/fictitious-domain (DLM/FD) method for the solid/fluid interaction problem. The elastic solid bar attached on the bottom in a pressure-driven channel flow of a Newtonian fluid was selected as a model problem. Our formulation is based on the scheme of Yu (2005) for the interaction between flexible bodies and fluid. A fixed regular rectangular discretization was applied for the description of solid and fluid domain by using the fictitious domain concept. The hydrodynamic interaction between solid and fluid was treated implicitly by the distributed Lagrangian multiplier method. Considering a simplified problem of the Stokes flow and the linearized elasticity, two numerical factors were investigated to clarify their effects and to find the optimum condition: the distribution of Lagrangian multipliers and the solid/fluid interfacial condition. The robustness of this method was verified through the mesh convergence and a pseudo-time step test. We found that the fluid stress in a fictitious solid domain can be neglected and that the Lagrangian multipliers are better to be applied on the entire solid domain. These results will be used to extend our study to systems of elastic particle in the Stokes flow, and of particles in the viscoelastic fluid.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1051-1057
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• 2011

최근 개발된 GMP공정의 활용으로 디지털 카메라, 광저장기기, 각종 전자기기 등의 광응용 기기에서 비구면 유리렌즈가 폭넓게 활용되고 있다. GMP공정은 복잡한 형상의 유리렌즈를 정밀하면서도 경제적으로 생산할 수 있다. 본 연구에서는 다구치 실험계획법을 이용하여 순차이송형 GMP공정에서 비구면 유리렌즈의 성형 조건을 최적화 하였다. 냉각 1단계에서의 압력과 온도, 시간을 3가지 주요 공정변수로 정하였으며, 3캐비티 금형을 이용하여 실험한 결과 순차이송형 유리렌즈 성형공정에서 냉각시간이 비구면 유리렌즈의 형상정밀도(PV)에 가장 큰 영향을 미치는 것을 알 수 있었다.

• Journal of Korean Neurosurgical Society
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• 제37권3호
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• pp.193-196
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• 2005

Objective: Strategies for managing supratentorial primitive neuroectodermal tumors(PNETs) in children include surgical resection, craniospinal irradiation and chemotherapy. This study is performed in order to compare the efficacy of various methods of treatment and to describe its optimal management. Methods: We have reviewed all medical records and pathology slides of six children(four males and two females) with supratentorial PNET from November, 1987 to May, 2003. The extent of resection was confirmed by computed tomography and magnetic resonance studies. Results: The patients were aged 1 to 13 years and treated postoperatively with/without adjuvant therapy. Tumor location included was four cortical, one gangliobasal, and one pineal region. The presenting symptoms and signs consisted of increased intracranial pressure and focal neurological deficits such as seizure and hemiparesis. The treatment consisted of surgical resection alone in one patient, postoperative radiotherapy in one patient, postoperative chemotherapy in one, and postoperative radiotherapy with chemotherapy in three. Five patients lived more than 12 months after diagnosis and one patient among them has been living more than 5 years after diagnosis. Conclusion: We can improve the survival and prognosis of supratentorial PNET patients by radical gross total resection of tumor followed by craniospinal irradiation and aggressive chemotherapy. First of all, gross total resection of tumor is the most important among many factors.

• 대기
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• 제29권4호
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• pp.451-461
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• 2019

Medium-range forecast is highly dependent on ensemble forecast data. However, operational weather forecasters have not enough time to digest all of detailed features revealed in ensemble forecast data. To utilize the ensemble data effectively in medium-range forecasting, representative weather patterns in East Asia in this study are defined. The k-means clustering analysis is applied for the objectivity of weather patterns. Input data used daily Mean Sea Level Pressure (MSLP) anomaly of the ECMWF ReAnalysis-Interim (ERA-Interim) during 1981~2010 (30 years) provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Using the Explained Variance (EV), the optimal study area is defined by 20~60°N, 100~150°E. The number of clusters defined by Explained Cluster Variance (ECV) is thirty (k = 30). 30 representative weather patterns with their frequencies are summarized. Weather pattern #1 occurred all seasons, but it was about 56% in summer (June~September). The relatively rare occurrence of weather pattern (#30) occurred mainly in winter. Additionally, we investigate the relationship between weather patterns and extreme weather events such as heat wave, cold wave, and heavy rainfall as well as snowfall. The weather patterns associated with heavy rainfall exceeding 110 mm day^-1 were #1, #4, and #9 with days (%) of more than 10%. Heavy snowfall events exceeding 24 cm day^-1 mainly occurred in weather pattern #28 (4%) and #29 (6%). High and low temperature events (> 34℃ and < -14℃) were associated with weather pattern #1~4 (14~18%) and #28~29 (27~29%), respectively. These results suggest that the classification of various weather patterns will be used as a reference for grouping all ensemble forecast data, which will be useful for the scenario-based medium-range ensemble forecast in the future.

• 한국정밀공학회지
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• 제26권7호
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• pp.44-50
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• 2009

High-pressured jetting is now widely used in the advanced cutting processes of polymers, metals, glass, ceramics and composite materials because of some advantages such as heatless and non-contacting cutting. Similarly to the focused laser beam machining, it is well known as a type of high-density energy processes. High-pressured jetting is going to be developed not only to minimize the cutting line width but also to achieve the short cutting time as soon as possible. However, the interaction behavior between a work piece and high-velocity abrasive particles during the high-pressured jet cutting makes the impact mechanism even more complicated. Conventional high-pressured jetting is still difficult to apply to precision cutting of micro-scaled thin work piece such as thin metal sheets, thin ceramic substrates, thin glass plates and TMM (Thin multi-layered materials). In this paper, we proposed the advanced high-pressured jetting technology by introducing a new abrasives supplying method and investigated the optimal process conditions of the cutting pressure, the cutting velocity and SOD (Standoff distance).