• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.37-46
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• 2013

Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.175-186
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• 2010

When a rigid post is exposed to traffic, it is hazardous not only to head-on impacts but also to side impacts. Clip-type slip base is an effective measure to reduce the severity of head-on impacts and side impacts as well because of its multi-directional release mechanism. Side impact tests were conducted and the results were analysed to demonstrate the hazardousness of a rigid post to a side impact and the crash worthiness of a post having clip-type slip base. For that, side impact test standard was made adapting the NCHRP Report 350, and 820kg-50km/h side impact tests were made for posts of D101.6mm(t=4.2mm) with and without slip base. Additionally, 35km/h side impact to the same post with slip base was conducted to check whether the clip-type slip base release mechanism works properly to the low impact speed. The tests revealed that the rigidly connected post was very hazardous to side impact while the post with the clip-type slip base reduced the impact severity tremendously.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1017-1026
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• 2014

A multi-perforated tube is generally installed between the muffler inlet and in front of selective catalytic reduction (SCR) catalysts in the integrated urea-SCR muffler system in order to disperse the urea-water solution spray uniformly and to make better use of the SCR catalyst, which would result in an increase nitrogen oxide ($NO_x$) reduction efficiency and a decrease in the ammonia slip. The effects of the multi-perforated tube orifice area ratios on the internal flow characteristics were investigated analytically by using a general-purpose commercial software package. From the results, it was clarified that the multi-perforated tube geometry sensitively affected the generation of the bulk swirling motion inside the plenum chamber set in front of the SCR catalyst and to the uniformity index of the velocity distribution produced at the inlet of the catalyst. To verify the analytical results, engine tests were carried out in the ESC and ETC modes. Results of these tests indicated that the larger flow model in the longitudinal direction showed the highest NOx reduction efficiency, which was a good agreement with the analytical results.

• Journal of Drive and Control
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• v.13 no.1
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• pp.1-9
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• 2016

Nowadays automatic transmission equipped vehicles prevail in construction and agricultural equipment due to their convenience in driving and operation. Though domestic vehicle manufacturers install imported electronic controlled transmissions at present, overseas products will be replaced by domestic ones in the near future owing to development efforts over the past 10 years. For passenger cars, there are many kinds of shift control algorithms that enhance the shift quality such as feedback and learning control. However, since shift control technologies for heavy duty vehicles are not highly developed, it is possible to improve the shift quality with an organized control method. A feedback control algorithm for neutral-into-gear shift, which is enabled during the inertia phase for the master clutch slip speed to track the slip speed reference, is proposed based on the power transmission structure of TH100. The performance of the feedback shift control is verified by a vehicle test which is implemented with firmware embedded TCU. As the master clutch engages along the predetermined speed trajectory, it can be concluded that the shift quality can be managed by a shift time control parameter. By extending the proposed feedback algorithm for neutral-into-gear shift to gear change and shuttle shift, it is expected that the quality of the shift can be improved.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.124-131
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• 2019

A design study of gas turbine engine simulation duct was conducted to investigate the operating characteristics and control gain tunning of the Altitude Engine Test Facility(AETF). The simulation duct design involved testing variable spike nozzle and ISO standard choking nozzle to verify the measurements such as mass flow rate and thrust. The simulation duct air flow area was designed to satisfy Ma 0.4 at the aerodynamic interface plane(AIP) at engine design condition. The test conditions for verifying the AETF controls and measurement devices were deduced from 1D analysis and CFD calculation results. The spike-cone driving part was designed to withstand the applied aero-load, and satisfy the axial traversing speed of 10 mm/s at whole operation envelops.

• Journal of the Korea Convergence Society
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• v.12 no.3
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• pp.141-149
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• 2021

3D printers, which emerged in the late 20th century, have become a key part of the fourth industrial revolution in the 21st century. Although 3D printers, the key equipment of the maker movement and the starting point of the new cottage industry in the 21st century, still reveal the limitations of mass production with low output speed and limited filament materials, the use of 3D printers by ceramic craftsmen has recently increased exponentially. However, as part of a way to overcome the discord between craftsmanship and the new technology, which has been repeated over and over in the past in craft history, the study focused on the 'plaster mold casting' technique using 3D printers. Therefore, after analyzing casting techniques of Tony Hansen, Webe van Gansbeck, Jade Crompton, and Ryu Hee-do, the potters who actively developed gypsum techniques in the world's ceramic crafts field and applied them to their own designs, I tried to find the point of convergence between 3D printers and ceramic crafts by presenting examples of effective 3D modeling methods and optimal slip casting methods using 3D printers.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.11a
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• pp.72-72
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• 1998

원자력발전소 1차계통내 밸브의 경면처리(hardfa따1잉에 사용되는 재료는 $90~343^{\circ}C$의 고온과 높은 접촉응력 그리고 급격한 압력변화가 일어나는 환경에서 사용되기 때문에 내마모성과 내식성 그리고 cavitation erosion 저항성이 우수한 Co계 Stellite 합금이 현재 사용되어진다. 그러나 Co가 원력발전소 1차계통의 방사선장을 형성하는 주요 원소로 알려지면서 S Stellite 합금을 대체할 수 있는 Fe계 경면처리용 합금을 개발하려는 연구가 진행되고 있다. 현재 Fe계 경면처리용 합금의 개발은 적절환 팝금원소를 첨가하여 적충결함에너지를 낮춤 으로써 전위의 교차슬립을 억제하여 표면을 경화시키고, 소성변형을 억제하여 마모저항성을 향상시키려는 방법으로 연구가 진행되고 있다. 본 연구에서는 Fe-Cr-Ni-Si-C 합금에 Fe계 합금의 적충결함에너지를 감소시키는 것으로 알려진 vanadium을 0, 1, 2wt%첨가하여 첨가량의 변화가 cavitation erosion 저항성에 미치 는 영향을 조사하였다. Cavitation erosion 실험은 초음파를 이용하여 미세한 기포를 발생시키는 vibratory type으로 A ASTM G-32 규격에 따라 제작된 실험장치를 이용하여 $25{\pm}2^{\circ}C$의 온도의 증류수 속에 잠긴 상태에서 실시하였다. 시면은 지름 16mm, 두게 7mm의 버턴형태로 vanadium 첨가량을 변화시킨 조성을 아크 용융 방법을 이용하여 제작하였으며 hom끝단부에 부착하여 cavitation e erosion 저항성 살험을 하였다. 시편의 cavitation erosion 실험시간에 따른 무게감소량을 측 정하였으며 cavitation erosion 시킨 시편의 표면을 SEM으로 관찰하였다.겨지는 열전달 매체액 과 신규 부식억제제가 적용된 시스템 등 객관적으로 확인된 부식억제제 시스랩에 대 하여 다양한 평가 방법을 동원 비교분석하고자 하였다. 실험은 KSM 2142에 의한 무게감량법, 분극곡선 측정에 의한 $E_P$(공식개시전위), $E_R$(재부동태화전위) 측정, 시간에 따른 자연전위 변화 측정 빛 이때의 부식속도(선형분극법), 인위적인 피막 파괴 전,후 의 전위 변화 및 부식속도 측정법에 의한 국부부식 발달 저지능 등을 평가하여 각 실험결과를 비교분석하여 보았다. 수록 민감하여 304 의 IGSCC 와 매우 유사한 거동을 보인다. 본 강연에서는 304 와 600 의 고온 물에서 일어나는 IGSCC 민감도에 미치는 환경, 예민화처리, 합금원소의 영향을 고찰하고 이에 대한 최근의 연구 동향과 방식 방법을 다룬다.다.의 목적과 지식)보다 미학적 경험에 주는 영향이 큰 것으로 나타났으며, 모든 사람들에게 비슷한 미학적 경험을 발생시키는 것 이 밝혀졌다. 다시 말하면 모든 사람들은 그들의 문화적인 국적과 사회적 인 직업의 차이, 목적의 차이, 또한 환경의 의미의 차이에 상관없이 아름다 운 경관(High-beauty landscape)을 주거지나 나들이 장소로서 선호했으며, 아름답다고 평가했다. 반면에, 사람들이 갖고 있는 문화의 차이, 직업의 차 이, 목적의 차이, 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lrcorner$의 범위를 벗어나지 않는다. 그렇기 때문에도 $\ulcorner$

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.861-869
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• 2020

A dynamo set for a high-power induction motor drive is expensive and needs a long time to manufacture. Therefore, the development of a simulator that functions as the induction motor and load equipment is required. A load simulator of an inverter for a high-power three-phase induction motor consists of a reactor and three-phase PWM inverter. Therefore, it cannot simulate the dynamic characteristics of an induction motor and functions only as a load. In this paper, a real-time simulator is proposed to simulate a model of an induction motor and the load characteristics based on an LCL filter and three-phase PWM rectifier for a three-phase induction motor. The currents of a PWM inverter that simulate the stator currents of the motor are controlled by the inductor currents and capacitor voltages of the LCL filter. The capacitor voltages of the LCL filter simulate the induced voltages in the stator windings by the rotating rotor fluxes of the motor, and the capacitor voltages are controlled by the inductor currents and a PWM rectifier. The rotor currents, the stator and rotor flux linkages, the electromagnetic torque, the slip frequency, and the rotor speed are derived from the inverter currents and the motor parameters. The electrical and mechanical model characteristics and the operation of vector control were verified by MATLAB/Simulink simulation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.472-482
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• 2019

This paper describes the stabilization of underwater TAS winch system Deploy/Recover operation performance. TAS winch installed on the stern of submarine performs to deploy/recover sensor, towing cable and rope tail which is deployed from the stern and separated from submarine itself. Also TAS winch provides transmission path of power to the sensor and data transmitting/receiving path which data are acquired from underwater environment like sound, depth and temperature. At the step of TAS winch evaluation test, sporadic standstill and rotating speed oscillation phenomenon were occurred. Winch motor provides the available torque to deploy/recover TAS and root cause analysis to the winch motor was done to find exact reason to sporadic malfunction. When winch motor was disassembled, eccentricity of rotor, slip-ring and the other composition part for winch motor were found. These might cause magnetic field distortion. To make TAS winch system more stable and block magnetic field distortion, this paper suggests methods to enhance fixing status installed in winch motor. For reliable data acquisition for TAS winch operation, the deploy/recover function of the improved type of TAS winch was verified in LBTS making similar condition with sea status. At the end of stage, improved type of TAS winch was tested on some functions not only deploy/recover function, but sustainability of TAS operation on specific velocity, steering angle of submarine in the sea trial. Improved type of TAS winch was verified in accordance with design requirement. Also, validity of suggested methods were verified by the sea trial.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.208-215
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• 1999

The creep behavior of a rapidly solidified and consolidated Al-9.45wt%Fe-4.45wt%Cr alloy were investigated in the stress range 40 to 115 MPa and temperature range 300(0.53Tm) to 441$^{\circ}C$(0.66Tm). It is of use to available aerospace and automobile industries for the improved performance of materials used at high temperature. Because Al alloys with improved creep resistance offer the potential for lower weight and reduced costs in aerospace and automobile components (e.g., structural members and engine parts) through the replacement of heavier and more costly materials, the safety in use at high temperature is good. The alloy is characterized by high stress exponents and activation energies for creep, which are greatly dependent on the stress and temperature. Because the creep stress is seen to cause a strongly significant enhancement of coarsening, the coarsening rate of the dispersed particles in all crept specimens is faster than that in isothermally annealed specimens. Dislocations connecting dispersoids are observed more cofrequently in crept specimens with higher stress and lower temperature. The creep strain rates in the power law creep regime were found to be predicted much better by the Shorty and Rosler/Arzt equation with the inclusion of a threshold stress and dislocation detachment mechanism. The dispersoids in this alloy were acting a source of void nucleation that finally leaded to ductile fracture within the grain so called intergranular. Each void was initiated, grown and failed at the dispersoids in the aluminium matrix. Grain boundary accommodation of the slip produced, which result in initiation of the void and then final transgranular fracture. Therefore, it was confirmed that these dispersoids played an important role in the fracture mechanism by the formation of $Al_{13}Fe_4$, $Al_{13}Cr_2$ and $Al_2O_3$.