• 융합보안논문지
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• 제17권1호
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• pp.63-68
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• 2017

2011년 1월 튀니지에서 시작된 재스민혁명은 북아프리카와 중동지역 국가들에 많은 변화를 가져왔으며, 우리는 그 원인을 살펴볼 필요가 있다. 우선, 이 지역의 왕정과 독재체제 국가들은 장기집권을 위하여 야당, 언론 등을 탄압하였고, 특권계층에 집중된 권력은 부정부패를 양산하였다. 다음으로, 이 지역 국가들의 국가수입 대부분은 왕실과 독재자에게 귀속되었고, 이를 배분하는 과정에서 문제가 발생하기 시작하였다. 특히, 1990년대 유가하락과 2000년대 생필품 가격 상승은 정부에 대한 불신을 초래하는 계기가 되었다. 마지막으로, 2000년부터 2010년까지 이 지역 국가들의 인터넷 사용자가 평균 4,863% 증가하였고, 페이스북(Facebook), 트위터(Twitter) 등과 같은 소셜 네트워크 서비스(SNS)의 증대도 국가차원의 정보 통제를 어렵게 한 요인이 되었다. 그렇다면, 과연 북한의 급변사태 가능성은 어떠한가에 대한 고민을 해야 한다고 본다. 이를 위해 재스민혁명이 발생 국가들과 북한의 정치, 경제, 사회적 특성 등을 비교 분석할 필요가 있으며, 그 시사점을 도출하고자 한다.

• 국제지역연구
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• 제13권3호
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• pp.385-412
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• 2009

본 연구는 일본기업의 해외진출 결정요인 및 영향력 분석에 있어 투자국인 일본 및 일본기업의 경제적 환경 변화(요인)을 선행적으로 분석한다. 최근 일본기업의 해외진출의 특징은 과거 "노동집약적 산업"이라는 점과 "사양 산업"의 해외투자라는 전통적인 형태를 유지하고 있다. 또한 중소 제조업의 경우 "비용 절약형"이라는, 그리고 대기업은 "시장 확보형"의 투자요인이 상대적으로 중요했다. 반면에 비제조업 대기업의 특징은 "전문가 확보 및 시장 관련형"이, 그리고 중소 비제조업 경우 "사회자본의 정비와 수준"이 해외진출에 주요한 요인으로 작용한다. 한편 1990-96년과 1998-2006년까지 일본기업의 해외진출에 관한 요인분석의 결과, 공통적으로 적용되는 요인은 엔환율, 금리, 임금, 기업이익, 설비투자, 소비지출이었다. 특히 회귀분석의 결과, 1990-96년에는 "저금리"의 급변이 일본기업의 해외진출에 주요하게 작용했고, 1998-2006년에는 일본의 "엔환율"이 중요한 요인으로 추출되었다. 즉, 1990-96년까지 엔화가치의 폭등에 따른 충격은 1998-2006년에 이르러 서서히 일본경제 내부에 체화 및 완충되었고 볼 수 있다. 반면에 1998-2006년에는 엔화가치의 상승 요인과 더불어 일본정부의 해외지원정책과 "저금리"하에서 일본기업의 해외진출은 가속화되었다고 말할 수 있다.

• 대한설비공학회지:설비저널
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• 제14권4호
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• pp.293-299
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• 1985

This paper describes an economical prediction procedure for heat transfer phenomenon through a channel containing an abrupt asymmetric expansion in flow cross-seetional area. Numerical solutions for the flow field are obtained by the finite difference numerical method applied to the modified boundary layer equations. Modified boundary energy equation is used to analyze heat transfer as modified boundary momentum equation. Predictions of the method compare very favorable with exprimental data. Results of this study by modified boundary layer equation are as follows : 1. The computation time required for the scheme is at least an order of magnitude less than for the numerical solution of the full Navier-stokes and Energy eguations. 2. In laminar flow, the maximum heat transfer occurs downstream of the reattachment point.

• 한국해양공학회지
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• 제21권4호
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• pp.1-7
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• 2007

Based on the eigenfunction expansion method, the wave-absorbing performance of a square or circular pile breakwater was investigated. Flow separation resulting from sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of an exact energy loss coefficient is critical to enhancing the reliability of the mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code, and the energy loss coefficient can be obtained from the pressure difference between upstream and downstream. It was found that energy loss coefficient of circular pile is 20% that of a square pile. To validate the fitting equation for the energy loss coefficient, comparison between the analytical results and the experimental results (Kakuno and Liu, 1993) was made for square and circular piles with good agreement. The array of square piles also provides better wave-absorbing efficiency than the circular piles, and the optimal porosity value is near P=0.1.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.1-10
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• 1999

In this study, a numerical analysis is made on the ice-formation for laminar water flow inside a stenotic tube. The study takes into account the interaction between the laminar flow and the stenotic port in the circular tube. The purpose of the present numerical investigation is to assess the effect of a stenotic shape on the instantaneous shape of the flow passage during freezing upstream/downstream of the stenotic channel. In the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. In a channel flow between parallel plates, the agreement between the of predictions and the available experimental data is very good. Numerical analyses are performed for parametric variations of the position and heights of stenotic shape and flow rate. The results show that the stenotic shape has the great effect on the thickness of the solidification layer inside the tube. As the height of a stenosis grows and the length of a stenosis decreases, the ice layer thickness near the stenotic port is thinner, due to backward flow caused by the sudden expansion of a water tunnel. It is found that the flow passage has a slight uniform taper up to the stenotic channel, at which a sudden expansion is observed. It is also shown that the ice layer becomes more fat in accordance with its Reynolds number.

• 한국구조물진단유지관리공학회 논문집
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• 제7권4호
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• pp.191-199
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• 2003

대부분 강구조 및 철근콘크리트 구조물은 탄소성 거동에 의해 극한강도가 지배된다. 비록 평상시에는 탄성 범위를 초과하는 진폭(振幅)이 발생하지 않지만 심각한 폭발이나 지진하중과 같은 극단적인 경우가 발생할 때, 엔지니어는 구조물에 영구적인 손상을 줄 수 있는 상황들을 접하게 된다. 이러한 상태 평가를 위해 본 연구는 폭발 등의 극한하중에 특성에 의해 발생되는 구조물의 동적거동을 분석하였다. 그리고 본 연구는 극한진동 특성을 분석하기 위해 비선형 유한요소프로그램(ATENA2D, FRANC2DL)을 사용하였다. 본 연구의 해석결과, 평상시와 횡하중시의 균열은 발생 위치와 양태가 매우 다르게 나타났다. 또한, 초기 손상균열이 있는 RC라멘의 보에 단면형상과 기하학적 형상비 변화를 고려하여 균열각의 변화를 분석하였으며 이를 통해 동적 횡하중 작용에 의한 피해여부를 판단할 수 있었다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.89-98
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• 1997

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.

• Journal of Korean Neurosurgical Society
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• 제53권1호
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• pp.46-48
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• 2013

Chondrosarcoma is a very uncommon malignant primary bone tumor, especially, it occurs extremely rare in the spine. A 52-year-old man was admitted to the emergency room with sudden paraplegia. Twelve hours prior to a paraplegic event, he visited an outpatient clinic with discomfort and tenderness around the medial border of the right scapular, and his neurologic status was absolutely intact. Magnetic resonance imaging showed a lobulated soft tissue mass from T3 to T5, which extended to the epidural space. Computed tomography scans showed soft tissue mass on the spinal posterior arch and osteolytic change of the adjacent bony structures. Emergent surgery was performed and the lesion was removed. Dark reddish blood and gel-like material were encountered around the dura and posterior arch during the operation. Multiple pulmonary nodules were found on a chest CT scan and a biopsy of one of them had been proven to be a metastasis of chondrosarcoma. The histologic examination showed dedifferentiated chondrosarcoma. The patient's neurologic deficit was improved slowly from ASIA A to ASIA D. Chondrosarcoma in the spine is extremely rare, even more with acute hemorrhage and sudden expansion into the epidural space. We named it chondrosarcoma apoplexy. We should consider the possibility of a hemorrhagic event when the patient's neurologic deficit worsens suddenly with spinal bone tumor.

• 산업기술연구
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• 제29권A호
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• pp.111-122
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• 2009

In this study, flood stage was computed by HEC-RAS, 1-D numerical analysis model and FESWMS-2DH, 2-D numerical model. Flood stages computed by two different models were compared for straight line, dot axle watercourse, dead-zone watercourse, section sudden-changing watercourse, and curved watercourse. From the results, flow velocity and water level were similar in straight watercourse and dot-reduction watercourse. However, there was difference of flow velocity and water level in dead-zone watercourse, sudden expansion, dot-reduction, and curve-watercourse. This result might be influenced by rapid change of watercourse due to dead-zone, the angle of inflow and outflow, and the curvature. Especially in this study, numerical model was applied to Wol-Song-Cheon at Chuncheon in order to analyze the effect of flood stage by two different models. By flowing properties around the bridge and confluence of rivers, it was found that flow velocity and water level was changed. Therefore, it was concluded that a lot of uncertainties are contained in the present bank.

• 한국해양공학회지
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• 제10권3호
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• pp.138-152
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• 1996

Many studies of heat transfer on the swirling flow or unswirled flow in a abrupt pipe expansion are widely carried out. The mechanism is not fully found evidently due to the instabilities of flow in a sudden change of the shape and appearance of turbulent shear layers in a recirculation region and secondary vortex near the corner. The purpose of this study is to obtain data through an experimental study of the swirling flow and heat transfer downstream of an abrupt expansion in a circular pipe with uniform heat flux. Experiments were carried out for the turbulent flow nd heat transfer downstream of an abrupt circular pipe expansion. The uniform heat flux condition was imposed to the downstream of the abrupt expansion by using an electrically heated pipe. Experimental data are presented for local heat transfer rates and local axial velocities in the tube downstream of an abrupt 3:1 & 2:1 expansion. Air was used as the working fluid in the upstream tube, the Reynolds number was varied from 60, 00 to 120, 000 and the swirl number range (based on the swirl chamber geometry, i.e. L/d ratio) in which the experiments were conducted were L/d=0, 8 and 16. Axial velocity increased rapidly at r/R=0.35 in the abrupt concentric expansion turbulent flow through the test tube in unswirled flow. It showed that with increasing axial distance the highest axial velocities move toward the tube wall in the case of the swirling flow abrupt expansion. A uniform wall heat flux boundary condition was employed, which resulted in wall-to-bulk temperatures ranging from 24.deg. C to 71.deg. C. In swirling flow, the wall temperature showed a greater increase at L/d=16 than any other L/d. The bulk temperature showed a minimum value at the pipe inlet, it also exhibited a linear increase with axial distance along the pipe. As swirl intensity increased, the location of peak Nu numbers was observed to shift from 4 to 1 step heights downstream of the expansion. This upstream movement of the maximum Nusselt number was accompanied by an increase in its magnitude from 2.2 to 8.8 times larger than fully developed tube flow values.