• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.423-430
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• 2014

Noise and vibration, which occur in a pipe, are usually caused by the interaction between the turbulent flow and nearby wall. Although it can be estimated by a simple case of expanded pipes having complex turbulent flow, the radiated noise is highly dependent upon the size, shape, and thickness of the given model. In addition, the radiated noise propagates and has serious interference and destabilization effects on the surrounding systems, which can lead to fatigue fracture and failure. This study took advantage of the variety of commercial programs, such as FLUENT (flow solver), NASTRAN (dynamic motion solver of complex structures) and VIRTUAL LAB (radiated noise solver) based on the boundary element method (BEM), to understand the underlying physics of flow noise. The expanded pipe has separation and a high pressure drop because of the abrupt change in the cross-section. Based on the radiated noise calculations, the noise level was reduced to around 20 dB in the range of 100-500 Hz.

• Journal of the Korean Institute of Gas
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• v.15 no.4
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• pp.21-26
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• 2011

Type-3 cylinder liner has a limitation of machining the standard specimen for fracture toughness test because it has approximately 5 mm in thickness as well as a curvature. Hence, it needs to be employed a miniature specimen test technique to evaluate fracture toughness of the cylinder liner. In this study, small punch (SP) test method was employed to evaluate fracture toughness of the cylinder liner. Load-displacement curve result measured from the SP test showed that the liner material was failed during membrane stretching in the general SP load-displacement curve. Additionally, it was shown that liner material was isotropic although the amount of plastic deformation was different depending on the direction due to manufacturing process characteristics. Fracture toughness, $J_{Ic}$, was evaluated using the SP test data. The value of fracture toughness obtained was $13.0kJ/m^2$. This value was similar to that of the same kind of materials. Therefore, the fracture toughness evaluated using the SP test data was reasonable.

• Composites Research
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• v.24 no.5
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• pp.39-43
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• 2011

For the last twenty years, nanocomposites composed of polymer matrices reinforced with carbon nanotubes (CNTs) have been an active research area. Also, the polymeric nanocomposites reinforced with CNTs are being investigated to be used matrices of carbon fiber composites. Carbon tiber composites have achieved advanced properties in the direction of carbon fibers due to enhanced carbon fiber properties. However, the matrix dominated properties need to be improved further to fully utilize the advanced carbon fiber properties. In particular, delamination is a typical and critical reason for fracture of carbon fiber composites. Mode I fracture toughness test which is also often called double cantilever beam (DCB) test shows the resistance to delamination of carbon fiber composites and this test is performed on carbon fiber composite samples incorporated with carbon nanotubes functionalized with various functional groups. The specimens with mat-like CNT layers showed the increased fracture toughness by 10.6%.

• Journal of Korea Multimedia Society
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• v.9 no.9
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• pp.1131-1138
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• 2006

This paper proposes a novel method for grading of underground communication conduits by laser projection image analysis. The equipment thrust into conduit consists of a laser diode, a light emitting diode and a camera, the laser diode is utilized for generating projection image onto pipe wall, the light emitting diode for lighting environment and the image of conduit is acquired by the camera. In order to segment profile region, we used a novel color difference model and multiple thresholds method. The shape of profile ring is represented as a minimum diameter and the Fourier descriptor, and then the pipe status is graded by the rule-based method. Both local and global features of the segmented ring shaped, the minimum diameter and the Fourier descriptor, are utilized, therefore injured and distorted pipes can be correctly graded. From the experimental results, the classification is measured with accuracy such that false alarms are less than 2% under the various conditions.

• Composites Research
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• v.17 no.3
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• pp.1-7
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• 2004

In the vacuum assisted RTM (VARTM) process that has become the center of attention for manufacturing massive composite structures, a good evacuation of air in the fiber preform is recognized as the prime factor. The microvoids, or the dry spots, are formed as a result of improper gate/vent locations and the mold geometry. The non-uniform resin velocity at the flow front leads to the formation of microvoids in the fibers, whereas the air in the microvoids can migrate along with the resin flow during mold filling. The residual air in the internal voids of a composite structure may cause a degradation of the mechanical properties as well as the structural failure. In this study, a unified macro- and micro analysis methods were developed to investigate the formation and transport of air in resin during VARTM process. A numerical simulation program was developed to analyze the three-dimensional flow pattern as well as the macro- and microscopic distribution of air in a composite part fabricated by VARTM process.

• Composites Research
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• v.31 no.1
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• pp.37-41
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• 2018

The aim of the current work is to characterise a piecewisely-integrated composite bumper beam based on the IIHS bumper crash protocol. IIHS bumper crash FE analysis for an aluminium type bumper beam was carried out to get the information about the dominant loading types at several regions in the bumper beam during crash. In the meantime, robust stacking sequences against tension and compression have been searched for using FE analysis of a coupon type model. After determining most effective stacking sequences for tension and compression, three-point bending simulation was preliminarily carried out to investigate the combination performance of them. Finally, IIHS bumper crash FE analysis for the piecewisely-integrated composite bumper beam, which consisted of the combination of tension effective stacking sequence and compression efficacious stacking sequence, was conducted and the result was compared with other types of composite bumper beams. It was found that the newly suggested piecewisely-integrated composite bumper beam showed superior crashworthy behaviour to those of uni-modal stacking sequence composite bumper beams.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2016.11a
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• pp.299-301
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• 2016

현대 사회에서 테러는 국제적으로 매우 빈번하게 일어나고 있으며, 대한민국도 더 이상 테러의 안전지대가 아니라는 뉴스가 보도되고 있다. 하지만 우리에 테러의 인식에 따른 시각은 다소 편협하여 성별, 나이, 직위, 장소등 많은 부분에서 갈등을 갖으며, 또한 한반도는 남북한의 갈등으로 인한 특수성은 게릴라 전을 테러라고 인식하는 시각이 있다. 국내 특수성으로 인해 테러를 전쟁의 영역으로 보고 테러대응 전략은 국가 안보로 많이 치우쳐져 있다. 역사와 정치적으로 또한 테러는 이념대립으로 인한 전쟁으로 치우쳐 전쟁의 전략에 한 부분으로 인식 되어 왔다는 것이 사실이다.(Rumyana G., 2014) 이는 전쟁의 시각에서 테러를 잘 설명하고 있다. 한편, 테러의 개념은 시간이 지남에 따라 기존의 안보의 개념뿐 아니라 재난의 개념에서도 찾을 수 있다. "불평등한 사회에 대한 민중의 분노로 이해하여야 한다"고 스위스 진보적 사회학자 장 징글러(Jean Ziegler) 는 말하며 무고한 사람들을 타겟으로 한 정치적 목적을 이루기 위한 비합법적 무력 사용으로 보았다. 즉, 비합법적 무력사용으로 무고한 다중(Innocent people)에게 폭력을 행사한 것이다. 젠킨스와 라쿼르의 정의를 살펴보면 "테러리즘이란 폭력 혹은 폭력의 위협이다"라고 정하였다.(Jenkins 2004) 폭력이란 형법에서는 다른 사람에게 상해를 입히거나 협박하거나 하는 등의 행위와 함께 다른 사람을 감금하는 행위, 주거에 침입하는 행위, 기물의 파손 등에 대해서도 폭력이라 표현한다. 철학, 정치학 등의 학문에서는 다른 사람 또는 국가나 세력을 제압하는 힘을 일반적으로 지칭하기도 한다. 힘자랑이나 힘겨루기가 이에 속한다. 무력의 사용으로 사회에 심리적인 영향을 끼치며 사회적 파괴를 일으키는 것을 보편적 테러의 개념으로 볼 수 있다. 테러는 국가 통치 질서와 사회질서 안정에 큰 위협과 혼란을 초래하는 파괴행위의 무력행사로 국가의 재난 상황을 유발하는 인류가 만든 재난으로 볼 수 있다. 자연현상으로 발생하는 자연재해는 인류의 시점에서 재난으로 해석된다. 마찬가지로 사회현상으로 발생하는 폭력적 파괴행위에 대한 피해는 인류의 시점에서 재난의 현상으로 해석 되어야 한다. 과학기술이 발달하면서 첨단기술을 이용한 폭력행위와 파괴의 두려움은 정보통신 기술의 발달로 두려움의 전파 속도도 빨라 질 것이다. 따라서 테러행위의 극복을 위해서는 테러를 인적재난(Man-made Disaster)로 보고 재난의 범주로 포함하여 미래의 테러를 위한 대비전략을 수립해야 할 것이다. 이를 위해 본 논문에서는 학계의 학자들과 기관 및 민간 의 전문기관들에 따른 테러의 정의를 분석하고 재난정의를 고찰하여 시사점을 제시하고, 대테러 대비 전략의 방향에 기틀을 마련하고자 테러정의를 도출하였습니다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.88-94
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• 2002

For the pressurized propellant supply system of liquid rocket, feed pressure is determined with respect to the chamber pressure of normal combustion state. However, during ignition period the initial chamber pressure is atmosopheric. This may cause overflow, hard-start and even critical damage for the engine. This paper proposes an improved propellant feed system for the stable combustion of liquid rocket. The proposed system utilizes the cavitating venturi to provide stable mass flow rate. Cavitating venturi offers unique flow control capabilities at normal and abnormal combustion state, because flow rate is soley dependent on the upstream absolute pressure and fluid properties, but independent on th downstream condition. Experimental variables are propellant feed pressure and chamber pressure. The effectiveness of cavitating venturi increased when the ratio of actual feed pressure to the cavitating venturi design pressure is increased. It is also found that Kerosene if more effective to supply stable mass flow rate than LOx.

• KIISE Transactions on Computing Practices
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• v.22 no.1
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• pp.8-19
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• 2016

Potholes are caused by the presence of water in the underlying soil structure, which weakens the road pavement by expansion and contraction of water at freezing and thawing temperatures. Recently, automatic pothole detection systems have been studied, such as vibration-based methods and laser scanning methods. However, the vibration-based methods have low detection accuracy and limited detection area. Moreover, the costs for laser scanning-based methods are significantly high. Thus, in this paper, we propose a new pothole detection system using a commercial black-box camera. Normally, the computing power of a commercial black-box camera is limited. Thus, the pothole detection algorithm should be designed to work with the embedded computing environment of a black-box camera. The designed pothole detection algorithm has been tested by implementing in a black-box camera. The experimental results are analyzed with specific evaluation metrics, such as sensitivity and precision. Our studies confirm that the proposed pothole detection system can be utilized to gather pothole information in real-time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4B
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• pp.227-235
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• 2012

Holes that generated by the unpredictable and harsh nature application environment or uneven energy consumption are an inevitable phenomenon in wireless sensor networks. Most of the existing schemes for this hole problem tend to use a static detour path to bypass a hole. The static detour path may lead to uneven energy consumption of the nodes on the boundary of the hole, thus it may enlarge the region of holes. At the same time, traffic would concentrate on the nodes on the boundary of the hole and tend to be depleted quickly. To solve this problem, we introduce energy-efficient grid-based geographic routing and hole-detouring scheme by taking advantage of grid anchor point in wireless sensor network with holes. The location of hole detour anchor node is dynamically shifted in grid cell. just generating dynamic hole detour paths to reduce total energy consumption. Simulation results are provided to validate the claims.