• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.44-54
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• 2018

In a spray experiment using a venturi mounted on a lean premixed LPP injector, droplets appear to have non-uniform distributions. To solve this problem, the exit angle of the venturi was changed to form a dump surface on the nozzle neck. The dump surface improved the atomization performance and minimized droplet loss while forming recirculation zone in the venturi exit. In order to solve the non-uniform spray of the injector, the flow characteristics inside the venturi and SMD of the spray are compared. Finally, an optimum venturi shape is selected to minimize the spray loss and improve the spray performance.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.84-93
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• 1994

The purpose of present study is to investigate the surface roughness on tip-vortex cavitation and its induced noise, emanating from an elliptic wing of NACA 0012 section. Roughness elements of $200{\mu}m$ are applied to the 10% portion of wing tip, and then, the wing tip as well as the leading edge. It is shown from cavitation observation that the cavitation inception is first visible at about half chord downstream of wing tip for most experimental conditions, and developed into the tip-vortex cavitation and finally the fully developed cavitation as cavitation number is decreased. Acoustic noise generated by a tip-vortex cavitation has its frequency range of 3 kHz to 50 kHz, while the fully-developed cavitation at lower cavitation number induces a broad band spectrum. It is also shown that, when the roughness elements are applied to the wing tip and the leading edge, the cavitation characteristics and its induced noise are improved. Moreover, it is appeared that the condition at which the rough surface is at pressure side gives a better result. although its lift-drag ratio is reduced.

• Solar Energy
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• v.11 no.1
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• pp.27-40
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• 1991

Research and development works on practical application of natural energy utilization systems involving solar, wind and sea wave energies are under promoting for the purpose of improving the energy consumption structure. These natural energies, made available with the use of relatively simple apparatus, are clean economically efficient and highly effective in the conservation of environment. However, these natural energies also have low energy density, randomness and regional variations. To compensate for these characteristics, hybrid utilization of solar and wind energies is currently under study. The introduction of a plural number of the natural energy hybrid utilization systems into a specific area will affect the economic efficiency, reliability and environmental conservation. Evaluation method of such effects has been examined in this study. The present method consisted of the steps described below. First, available energy was calculated from insolation distribution and wind velocity distribution in the specified area, and then the effect on the configuration of the power system load was obtained. This was followed by the determination of the optimal power dispatch over the specified period and by evaluations in light of economic efficiency, reliability and environmental indices.

• Journal of the Korean Magnetics Society
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• v.26 no.1
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• pp.24-30
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• 2016

MFL (Magnetic flux leakage) type nondestructive testing has been used for inspection of underground gas pipelines to find metal defects by detecting magnetic leakage signal. Because the underground gas pipeline is exposed by environment such as high pressure with great humidity, external defects are easily formed on the surface of pipelines and they are being grouped respectively. These adjacent defects cause the signal distortion of leakage flux so that it is hard to estimate the shape information of defects. In this paper, we performed to study of the signal distortion and compensating method for multiple defects in MFL type nondestructive testing system by using 3D FEM simulation. This paper proposes the basic algorithm of defect signal analysis on multiple defects on the surface of 30 inch diameter pipeline.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.6
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• pp.397-404
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• 2019

Linear Shaped Charge (LSC) that is widely used as separation system in aerospace system has to charge lots of explosives due to lack of uniformity. In addition, it is hard to optimize shape of liner and explosives because of manufacturing process. In order to overcome aforementioned drawbacks, Precision Linear Shaped Charge (PLSC) is currently under development. PLSC is made in two steps: prepare liner independently and charge explosive uniformly. In this study, PLSC is designed to have proper amount of explosives and penetration test of PLSC with different stand-off distance from liner to target is conducted to confirm penetration performance. Based on the penetration test results of PLSC, the numerical analysis method using AUTODYN is established and verified. Penetration mechanism and characteristics of PLSC is analyzed from the numerical and experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.347-352
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• 2019

This study focused on improving the cast quality of small-sized induction motor rotors during the die casting process. A new rotor core cast model was proposed based on previous research results and parametric studies. Numerical analyses using 3-dimensional half models were performed to evaluate the filling patterns of aluminum molten metals into a mold and on-site experiment performed to verify the newly proposed cast model. The following were obtained from numerical filling analyses and experimental results. First, molten metals started to fill the lower end ring, then moved on to fill the core slot and upper end ring and finally stopped to fill at the rotor core slot. Second, significant circulation of molten metals was not observed on the lower end ring, resulting in fewer defects at the section of the lower end ring from the experimental results. Third, the new shape of a rotor core cast was effective in producing rotors with sound cast quality, and reducing the end ring cast defect area by approximately 70 %.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.214-214
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• 2017

우리나라는 도시화 및 산업화로 도시지역의 대부분이 불투수층으로 변화하였으며, 국지성 호우의증가로 홍수 저감시설의 방어능력이 취약한 실정이다. 따라서 홍수방어 개선을 위한 여러 방안들이 이루어지고 있으며, 그 중 저류지는 도시지역에서 유역 하류의 홍수피해 저감 및 흐름을 지체시켜 유출률을 감소시키는 시설물로 홍수 저감을 위한 시설물로 가장 많이 사용되고 있다. 저류지는 큰 규모일수록 유역의 하류지역에 설치할 경우 가장 큰 유출저감효과를 가지는 것으로 알려져 있다. 하지만 저류지의 위치를 유역의 하류가 아닌 상류지역에 설치할 경우에는 단기간 강우의 시간적 분포가 강우 초기에 집중될 경우 저류지의 허용용량이 초기에 도달하게 되어 추가적인 강우가 발생할 경우 본래의 역할을 하지 못하는 경우가 빈번하게 발생하고 있다. 그러므로 다양한 강우강도 및 시간적 분포를 고려하여 유역의 특성 및 저류지의 설치위치에 따른 관계를 분석할 필요가 있다. 본 연구에서는 도시화, 산업화 인구집중으로 인해 동일규모의 강우에서도 우수유출이 증대되고 있는 도시지역에서 원활한 내수배제를 위해 기존의 우수관거를 연계한 저류시스템인 간선저류지 개념을 적용하여 강우강도 및 시간적 분포에 따른 간선저류지의 관련매개변수를 분석하였다. 대상유역은 세장형, 집중형, 중앙형의 3가지 형상의 가상유역으로 선정하여 다양한 지속기간의 강우량을 적용하였으며, 간선저류지의 설치위치는 전체 유역면적에 대한 저류지 상류부 면적의 비(저류지 상류부 면적비, DUAR ; Dimensionless Upstream Area Ratio)를 20%, 40%, 60%, 80%로 변화시키면서 강우의 시간적 분포에 따른 간선저류지의 매개변수 분석에 관한 연구를 진행하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.391-399
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• 2020

In this study, the behaviors of a suction cap shaped as an arch were analyzed using finite element models. The fundamental structural behaviors of both flat- and arch-type caps were compared, and the advantages of the arch-shaped cap were explained. Moreover, the effects of geometric parameters and stiffener arrangements on the stress and deformation of the arch-shaped caps were investigated by comparisons of the changes in the behaviors of the caps. Additionally, the effects of boundary condition at the edge of the cap were analyzed to study the interactions between the cap and cofferdam walls; these results were used to derive the fundamental structural design of stiffened arch caps. Unlike flat caps, the results showed that ring stiffeners could improve the structural behaviors of arch caps remarkably, while the contributions of the radial stiffeners to the structural behaviors of the caps are dependent on constraints at the edges of the caps.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.199-207
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• 2021

This study aimed to improve the performance of the KTX (Korea Train Express) brake system. To develop a braking disc-hub for the high-speed rail, the model performance was analyzed by finite element analysis, and the analysis results were verified using the braking test results. In addition, heat transfer analysis, thermal stress analysis, natural frequency analysis, and static analysis were conducted to examine the mechanical performance of the braking system. By deriving the design factors and conducting parametric analyses according to the shape of the hub, this study derived the optimal specifications that could improve heat dissipation and reduce weight. The cooling efficiency and structural performance of the optimization model were improved during braking compared to the existing model. It is expected that the design verification will be carried out through analyses of the optimal specifications so that it can be used in the development of brakes in railway vehicles and motor vehicles.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.66-73
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• 2022

In this study, the experimental results of 7 dampers with the same strut height and similar cross-sectional area were compared based on the existing research results on steel dampers with rocking behavior. As steel plate dampers, SI-260, SV-260, SS-260 without Lateral deformation prevention detail(Ldpd), I-1, V-1, S-1 with Ldpd, and R20-260 with steel rod damper were evaluated. In addition, R15-260, which has a cross-sectional area of 0.56 times than other dampers, was also reviewed to appropriately evaluate the behavior of the steel rod damper. An important study result is the application superiority of the steel rod damper, which improved the unidirectional behavior of the steel plate dampers. This was proved in the moment-resistance capacity and displacement ratio evaluation. As a result of the evaluation, the R20-260, a steel bar damper, was evaluated as having the best performance. In addition, it is judged to have sufficient seismic resistance as it shows deformability up to a displacement ratio of 2.0.