• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.70-78
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• 2014

A numerical study has been conducted to investigate flow and heat transfer characteristics of supersonic second throat exhaust diffusers for high altitude simulation. By changing pressure and configuration, flow and cooling characteristics of the diffuser have been studied. At the normal operation of the diffuser, there were high temperature regions over 3,000 K without cooling, especially near wall and in subsonic diffuser part. If the cooling system of the diffuser is added, flow velocity is increased due to the cooled wall temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.109-117
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• 2015

Aircraft needs an inlet duct to supply the airflow to engine face. A fighter aircraft that requires low radar observability has to hide the engine face in the fuselage to reduce the Radar Cross Section(RCS). Therefore, the flow path of the inlet duct is changed into S-shape. The performance of the aircraft engine is known to be influenced by the shape and the centerline curvature of the S-Duct. In this study, CFD analysis of the RAE M 2129 S-Duct has been performed to investigate the influence of aspect ratio of inlet geometry. The performance of the S-Duct is evaluated in terms of the distortion coefficient. To simulate the flow under adverse pressure gradient better, $k-{\omega}SST$ turbulence model is employed. The computational results are validated with the ARA experimental data. The secondary flow and the flow separation are observed for all computational cases, while the semi-circular geometry has been found to produce the best results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.596-604
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• 2010

In order to investigate the operating conditions and major design parameters of a dual ramjet propulsion system, an theoretical analysis of ramjet and scramjet propulsion systems was performed. The performance characteristics of each engine are delivered by thermo-dynamical cycle analysis, considering loss effects in a real engine. The performance sensitivity analysis is conducted by investigating various performance parameters, such as an intake efficiency, combustor inlet Mach number, configuration of the combustor, fuel flow rate, and exhaust nozzle efficiency. Based on these analysis results, the processes of application to dual ramjet cycle engines are specified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.4
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• pp.425-432
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• 2024

In this study, we propose a self-restoring friction slit damper by combining the concepts of self-restoring dampers, friction dampers, and steel dampers that are currently used and researched. For this purpose, an innovative damper structure was designed using superelastic shape memory alloy for automatic recovery and combining the concepts of friction damper and slit damper. Afterwards, detailed design was carried out and variables such as material, with of strut, and bolt fastening force were set. Modeling was performed using the ABAQUS program for a total of 12 dampers, and finite element analysis was performed by substituting the designed loading protocol. As a result, the self-recovering friction slit damper using superelastic shape memory alloy was excellent in terms of load, but the energy dissipation ability was not significantly secured due to the excellent recovery performance. However, friction slit dampers made of Gr.50 steel have dramatically improved performance in terms of load and energy dissipation through innovative structural improvements. Through this, the innovative structure of the damper, which combines the mechanisms of a friction damper and a steel damper, was demonstrated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.627-630
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• 2009

Ejector system can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an configuration and operating conditions for an ejector in the condition of sonic and subsonic. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Numerical simulation was adopted for an optimal geometry design and satisfying the required performance. Also, some ejectors with a various of nozzle throat and mixing chamber diameter were manufactured precisely and tested for the comparison with the calculation results.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.633-637
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• 2007

하천환경 복원사업이나 자연형하천 정비사업의 근본 목표는 그 하천 고유의 하천경관이나 생태계 등 특성을 회복(Rehabilitation)시키거나 복원(Restoration)하는 것이다. 현재 이 치수기능 확보를 위한 댐 보의 건설, 하천정비 및 골재채취 등 하천의 인공화가 계속되고 있으며, 이에 따른 하천 및 하도의 물리, 화학, 생물에 미치는 영향은 심각한 수준이다. 이러한 하천의 인위적 교란은 요인, 규모, 빈도 및 강도는 다르지만 하천생태 서식처의 물리적, 화학적 특성이 변형, 변질되어 하천생태계가 변화, 단절, 절멸되는 심각한 상태가 빈발하고 있다. 하천교란(River disturbance)은 요인에 따라 유량 및 유사량 변화, 하상변동, 하도준설, 인공호안, 생태통로 차단 등 하천의 물리적 환경 변화를 초래하고, 그에 따른 영향으로 생물종의 감소 및 단순화, 개체수 감소 등과 같이 하천 생태계가 변화하게 된다. 그러나 하천의 교란평가에 대한 연구가 미흡하고, 또한 표준화된 평가체제가 구축되어 있지 않을 뿐 만 아니라 하천환경의 복원에 대한 의식 보급도 부족한 것이 현실이다. 따라서, 본 연구에서는 하천의 교란정도를 파악하기 위한 하천교란평가기법 개발을 위한 전단계로서 일본의 하천수변 국세조사, 영국의 River Habitat Survey, 호주의 River Assessment System, 미국의 Stream Corridor Restoration 등에서 제시하는 하천모니터링 및 평가체제를 비교, 분석하였다. 외국사례 분석 결과를 토대로 하천교란 요인을 하천정비, 댐건설, 골재채취로 유형화하고 교란요인별 조사해야 할 물리적 인자로서 유량, 유사량, 하도 제원, 특징적 내용, 하도형상, 여울과 소, 점사주, 인공구조물, 제방 호안의 재료 및 특징 등으로 선정, 검토하였으며, 생태계 인자로서는 제방 마루의 토지이용 및 식생구조, 하도의 식생유형, 하도주변 토지이용, 하안(bank) 형상 및 구조, 수종 및 구조, 하도 및 하안 특징 및 구조 등으로 선정, 검토하였다. 이상의 하천교란과 관계되는 지표를 선정하여 물리적, 생태적 조사 및 교란평가기법(안)을 개발, 제시하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.346-351
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• 2017

A numerical study has been conducted to investigate flow characteristics of STED with ram structure shape. By increasing the attack angle of shock cone, vacuum pressure is increased because of oblique shock at ram structure and separation point moved to the downstream of the second throat. By increasing blockage ratio, expansion wave angle is increased at ram structure while vacuum pressure is constant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.150-156
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• 2017

This study examined the stress recovery length due to the local damage of a 7-wire strand, which is applied widely to PSC (Post Tensioned Concrete) bridges and cable-stayed bridges. The 7-wire strand is a multiple stranded steel of PC prestressing strand. Owing to the nature of the material, it is damaged continuously after completion with corrosion being the main cause of damage. On the other hand, due to its structural characteristics, it is difficult to grasp the degree of damage inside the cable and the pattern of stress variation. In the case of cables applied to bridges, the parts that are susceptible to corrosion are generated depending on the water supply and installation shape, which may cause local damage. This study analyzed the tendency of performance degradation and stress recovery length according to local damage of a 7-wire strand, which is applied mainly to bridge post-tensioning or stay cables. This study developed a computer-based simulation model that was validated with experimental results. The model developed in this study can be used to evaluate the safety level and estimate the remaining life span of P SC bridges or cable-stayed bridges.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.3 s.40
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• pp.47-51
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• 2006

Recently, CMP (Chemical Mechanical Polishing) is one of very important processing in semiconductor technology because of large integration and application of design role. CMP is a planarization process of wafer surface using the chemical and mechanical reactions. One of the most important components of the CMP system is the polishing pad. During the CMP process, the pad itself becomes smoother and glazing. Therefore it is necessary to have a pad conditioning process to refresh the pad surface, to remove slurry debris and to supply the fresh slurry on the surface. A conditioning disk is used during the pad conditioning. There are diamonds on the surface of diamond disk to remove slurry debris and to polish pad surface slightly, so density, shape and size of diamond are very important factors. In this study, we characterized diamond disk with 9 kinds of sample.

• Journal of Biomedical Engineering Research
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• v.19 no.4
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• pp.333-339
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• 1998

The effect of heat treatment conditions on the properties of tungsten(W) embolization coils has been evaluated. The W embolization coils were fabricated by coiling the primary W coil with a diameter of 30.mm on a alumina rod mandrel with a diameter of 2.92mm. The secondary coils were then heat treated at 475$^{\circ}C$and 600$^{\circ}C$ for various heat treatment time ranging from 5 minutes to 36hours. The pitch distance, diameter and shape retention capability of the W embolization coils were characterized after the heat treatment. The pitch distance of the W embolization coils increased with the heat treatment time. The diameter of W emboliazation coils decreased continuously with heat treatment time. The shape retention capability of the W embolization coils increased with the heat treatment time due to an increase in elasticity by formation of tungsten oxide film on W coil surface during the heat treatment. The heat treatment condition of W embolization Col at 600$^{\circ}C$ for 20 minute was considered desirable based on the optimization of the shape retention capability, pitch distance and secondary coil diameter after heat treatment.