• Journal of Astronomy and Space Sciences
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• v.16 no.1
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• pp.79-88
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• 1999

The satellite experiences the severe launch environment such as vibration, acceleration, shock, and acoustics induced by rocket. Therefore, the satellite should be designed and manufactured to endure such severe launch environments. In this paper, we describe the structure of the KITSAT-3 FM(Flight Model) and the processes and results of the launch environmental test to ensure the reliability during launch period.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.65-70
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• 1993

본 연구에서는, 제철 열간 압연기에서 slab가 진입, 추출시 충격으로 인한 진 동에 의해 두께 조절용 위치센서가 오작동을 하는 원인을 규명하고 그 해결 책을 제시하고자, 기존 AGC Top Plate와 위치 감지센서의 작동 상태 및 진 동특성을 검정하였고, 문제점을 발견하여 각각의 구조를 개선, 재측정하여 개선정도를 확인하였다. Disk형 AGC Top Plate는 직경을 줄이고, 두께를 늘 여 자체 진동을 감소시켜, Plate 진동에 의한 위치센서의 오작동 원인 및 이 에 의해 제어 유압펌프에 Feedback되어 top부 제어계에 발생하는 Hunting현 상을 줄였다. 위치센서는 내부 Spring의 초기변형량을 증가시켜 내탄성에너 지량을 증가시켜, 센서자체의 진동 및 측정시 나타나는 여진현상을 제거하였 다. 본 연구를 통한 측정결과로는 최대 82.7%의 제진효과와 여진현상의 제거 효과를 보았다.

• Computational Structural Engineering
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• v.10 no.3
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• pp.233-240
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• 1997

The study presents the linear dynamic analysis of multi-girder steel bridges under vehicular movement to examine the performance characteristics due to the various structural and loading conditions. The road surface roughness and bridge-vehicle interactions are considered. The road surface profiles for the approaching roadway and bridge decks are generated from power spectral density functions for different road roughness conditions. A new filtering method using the wheel trace is proposed to obtain the more rational bridge-vehicle interactions from the randomly generated road surface. The possible settlement condition between the bridge deck and approaching roadway is also included. The dynamic responses of various bridges designed according to current design practice are examined, in which important structural parameters(such as span length, girder spacing, etc.) are considered systematically. In addition to the basic loading conditions due to a single truck passing on the bridge, the traffic conditions of multi-truck traveling either consecutively on the same lane or side-by-side on the adjacent lanes are also evaluated.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.119-129
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• 1994

The aim of the present study is to derive an empirical formula relating the absorbed energy and the cutting length for longitudinally stiffened steel palates which are cut by a wedge, idealizing the ship bottom stiffened platings in groundings. This study is based on the test results and the investigations of some parameters affecting the cutting response, described in Part I. By dimensionless ana1ysis of the test results obtained in a quasi-static loading condition, the energy absorbed while a longitudinally stiffened plate is cut by a wedge is expressed as functions of the cutting length, the yield stress, the equivalent plate thickness and the wedge angle. Also, the dynamic effects are incorporated into the static formula such that the proposed formula can be applied to the impact loading situations. The validity of the proposed formula is checked by comparing with the results obtained by the other existing formulas or by the drop-hammer tests.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.507-513
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• 2021

This study examined the final stop position and posture of both vehicles, the damaged part of the vehicle, the road surface, the specifications of the vehicle, and the angle of impact, centering on the case of a collision in which no surface trace was found. As a result of the simulation, the impact velocity of an SM5 and Lexus was 131 km/h and 74 km/h, respectively, and the impact angle of the SM5 and Lexus was 0.91° and -161.07°, respectively. The cause of the accident was that the SM5 passed through the intersection exceeding the maximum speed limit of 61 km/h and entered the Lexus' left turn lane. Lexus collided during the evacuation to avoid the collision. The collision trajectory error rate of the simulation was approximately 1.4%. Of the subjective experience of accident investigators, the collision dynamics and vehicle engineering aspects and simulations were actively utilized to provide close-to-fact cause identification.

• Explosives and Blasting
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• v.19 no.3
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• pp.105-113
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• 2001

채석, 굴착, 가공과 같은 워터젯 응용분야에서 대상재료에 깊은 홈(kerf)을 절단할 수 있는 실험실용 회전식 슬로터(slotter)를 제작하여 암석을 대상으로 워터젯 시스템의 절단효율을 시험하였다. 고압펌프는 유율 7.5 l/min, 압력 379 MPa, 용량 75 kW급의 JETPAC을 주로 사용하였고, 암석시료는 화강석인 제천석, 거창석을 사용하였다. 시험과정에서는 물과 연마재 투입에 의한 절단 및 진동식 슬로터에 의한 슬롯절단 기초시험을 먼저 수행하고, 그 결과를 토대로 회전식 슬로터에 의한 절단시험을 실시하였다. 순수한 물에 의한 시험의 결과 고압수류의 토출압력은 절단심도에 정비례하였고, 노즐의 이송속도는 이차함수 형태의 반비례 관계를 보였다. 연마재 투입시험에서는 순수한 물에 의한 경우에 비해 연마재로 인한 충격력의 증가로 절단심도가 크게 증가하였는데, 유사한 조건하에서 3~5배 이상의 절단심도의 증가를 보였다. 진동식 슬로터에 의한 슬롯절삭에서는 생성된 슬롯의 내벽면이 바닥으로 갈수록 좁아짐으로써 넓은 폭의 슬롯형성은 가능하나 절삭심도가 제한되었다. 회전식 슬로터에 의한 시험에서 생성된 슬롯들은 평균 22 mm의 폭으로 내벽면이 바닥까지 서로 평행하여 깊은 심도까지 비트진입이 가능하였다. 절단율은 16~32 mm/sec의 속도범위에서 $40~160{\;}\textrm{mm}^2/sec$로 나타났다. 한편, 최대유율 24 l/min의 HUSKY S-200 펌프에 의한 시험결과 JETPAC 펌프에 비해 1.13~3.47 배의 절단심도를 보였다

• Journal of the Korean earth science society
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• v.42 no.6
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• pp.688-699
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• 2021

On September 23, 2020, at 1:39 a.m., a bright fireball above Seocheon was observed across the country. Two fireball explosions were identified in the images of the All-Sky Camera (ASC), and the shock waves were recorded at seismic and infrasound stations in the southwestern Korean Peninsula. The location of the explosion was estimated by a Bayesian-based location method using the arrival times of the fireball-associated seismic and infrasound signals at 17 stations. Realistic azimuth- and rang-dependent propagation speeds of sound waves were incorporated into the location method to increase the reliability of the results. The location of the sound source was found to be 36.050°N, 126.855°E at an altitude of 35 km, which was close to the location of the second fireball explosion. The two explosions were identified as sequential infrasound arrivals at local infrasound stations. Simulations of waveforms for long ranges explain the detection results at distant infrasound stations, up to ~266 km from the sound source. The dominant period of the signals recorded at five infrasound stations is about 0.4 s. A period-energy relation suggests the explosion energy was equivalent to ~0.3 ton of TNT.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.89-96
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• 2013

Combustion pressures were measured to study combustion stability for an oxygen rich preburner by both of static and dynamic pressure sensors. The resolutions of each static and dynamic pressure sensor are the 1,000 Hz and 25,600 Hz, respectively. The nominal combustion pressure of the preburner was 200 bar but 80 bar was used at the several initial tests for the safety reason. Two stage ignition was applied to reduce the ignition impact for every tests including the tests with 200 bar combustion pressure. The tests lasted for 10 sec. max. and a little fluctuations of pressure was observed during the main mode. The measured pressures were studied by FFT analysis and no noticeable frequency coupling was found. Thus the preburner can be regarded as stable and it can be utilized for further study on staged combustion cycle liquid rocket engine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.103-113
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• 2004

The satellite is exposed to the severe vibration environments such as random vibration environments such as random vibration, acceleration, shock, and acoustics during launch ascent and transportation. It is also faced with various space environments such as thermal vacuum, radiation and microgravity during the mission life. The satellite should be designed, manufactured, assembled and tested to be able to endure in these harsh environments. This paper addresses the results of the structural and thermal design and analyses for the HAUSAT-1 picosatellite which is scheduled to launch in the first quarter of 2005 by Russian launch vehicle "Dnepr". The qualification vibration and thermal vacuum tests have been conducted and passed at the satellite level to ensure that the HAUSAT-1 mechanical system was designed to be stable with enough margin.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.1-6
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• 2017

Recently, the brittle materials such as ceramics, glass, sapphire and textile material have been widely used in semiconductors, aerospace and automobile owing to high functional characteristics. On the other hand, it has the characteristics of difficult-to-cut material relative to all materials. In this study, diamond electro-deposited band-saw machine was developed to operate stably using water-coolant type through relative motion between band-saw tool and $Al_2O_3$ material. High densified $Al_2O_3$ material was manufactured by spark plasma sintering method. The bulk density was observed by the Archimedes law and the theoretical density was estimated to be $3.88g/cm^3$ and its hardness 14.7 MPa. From the dicing sawing test of $Al_2O_3$ specimen, behavior of surface roughness and band-saw wear are dominantly affected by the increase of the band-saw linear velocity. Additionally, an continuous pattern type of diamond band-saw was a very effective due to entry impact as a one-off for brittle material.