Su-Kyum Kim

Manufacture and Industrial Application of Fe-Based Metallic Glasses

Metallic glass alloys have been considered as attractive materials due to their excellent mechanical and magnetic properties. However, commercial application of metallic glasses has been limited not only because of high production cost, but because of low market demands. A critical production cost factor was raw material since ferrous metallic glasses were made from high purity electrolytic iron. An idea to reduce the cost was to utilize the raw materials which were taken directly from molten iron and steel manufactured at the existing steel plants. Investigations have been performed to find whether metallic glasses made of molten iron and steel demonstrated appropriate mechanical and magnetic performance. Pilot scale equipments were designed to produce amorphous metallic fibers and strips continuously under the atmospheric condition. Process conditions were optimized by controlling process variables such as alloying and nozzle design, feeding temperature, speed and so on. The glass formability was tested by XRD and DSC analysis. Possibilities of application of Fe-based metallic glasses to reinforced concrete were also evaluated. It was confirmed that a small addition of metallic glass fibers in concrete increased the mechanical performance compared to that of commercial concrete reinforced with steel wires. In addition, amorphous strips were manufactured to apply them to the transformer core. It has been demonstrated that the magnetic properties were equivalent to those of commercial products.

Life Firing Test of 1 N-class Monopropellant Thruster Development Model -Part I: Environmental Test and Steady State Performance

ABSTRACT Acceptance level random vibration and life firing test for development model of 1N-class monopropellant thruster have been performed. From the results o f random vibration, the natural frequency of the dual thurst module composed of 1N-class develo pment model thrusters was higher than the part level requirement(>100Hz) and the structural robu stness was verified. Thrust decrease of steady sate was below 7% and thrust instability was within ±5% in the life firing test using over 20kg propellant throughput. The computerized tomography for catalyst bed showed a less than 7% of catalyst loss and it revealed the design appropriateness of the current thruster development model.초 록 1N급 단일추진제 하이드라진 추력기 개발모델에 대한 인수수준 랜덤 진동시험과 장기수명 연소시험이 수행되었다. 랜덤 진동시험 결과로부터 1N급 추력기 개발모델로 구성된 이중추력기모듈의 고유진동수는 부품수준 요구조건(100Hz)을 상회하였으며, 구조적으로 강건함을 확인하였다. 또한 20kg 이상의 추진제가 사용된 장기수명 연소시험 결과 연속모드 추력 감소는 약 7% 이하, 추력 불안정 현상은 ±5% 이내로 나타났다. 컴퓨터단층촬영을 이용해 추력기 내부의 촉매를 촬영한 결과 촉매의 손실은 약 7% 이하로 추력기 개발모델의 설계가 적절함을 보여주었다.Key Words: Monopropellant Thruster(단일추진제 추력기), Random Vibration Test(랜덤 진동시험), Life Firing Test(장기수명 연소시험), Steady State Performance(연속모드 성능)1. 서 론 한국항공우주연구원과 ㈜한화는 1990년대 미

Study on Spray Phenomena and Optimal Design of Injector for Improving Small Thruster Performance

This work studies the performance of an injector for a monopropellant thruster, comparing a conventional and new injector types. The conventional injector consists of 8 nozzles on a convex surface allowing the jet to be diverged. The new injector, we suggested, is an impinging type with nozzle holes on a concave surface. The fuel streams through the nozzle holes are collide at a point on an axial direction, which allow to atomize the liquid streams and to spray more uniformly along circular direction. The performance of the injectors is investigated by using computational fluid dynamics, particle image velocimetry and high speed camera visualization.

Detailed Analysis of Thrust Plume and Satellite Base Region Interaction

The interaction between thrust plume and satellite base region was investigated by using direct simulate Monte-Carlo calculations. For the accurate simulation of N2 and H2 collisions and rotation-translation transition, a variable soft-sphere model and a recent rotational relaxation model of N2 and H2 were used. For the investigation of the interaction between thrust plume and base region, the number density distribution for each species, translational and rotational temperature distributions, heat flux, and pressure were examined by direct simulation of Monte-Carlo calculations. It was found that most of the surface properties are affected by H2 collisions and a strong non-equilibrium state is observed at the base region. It was demonstrated that an accurate model is needed to simulate H2 collisions and the rotation-translation transition. The results by the present calculation are more accurate than previous direct simulation Monte-Carlo calculations because more accurate rotational relaxation models were used in simulating the inelastic collisions.