• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.367-370
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• 2011

A high-resolution numerical study is carried out to investigate the transient process of the combustion and the shock-train developments in an ethylene-fueled direct-connect dual-mode scramjet combustor. Air-throttling is then applied at the expansion part of the combustor to provide mass addition to block the flow to subsonic speed, hence to enhance the fuel-air mixing and ignition. Present simulation shows the detailed results for the better understanding of transient processes of the operation regimes in the dual-mode scramjet combustor.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.6
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• pp.569-576
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• 2021

Radar is a ground defense system that detects enemy aircraft and receives power from a mobile power supply in an emergency. Serious problems may occur if the equipment is damaged by impact during transportation for use. The US military standard MIL-STD-810H contains information on environmental tests such as shock and vibration applied to munitions. Therefore, in this study, the transient analysis of ANSYS 19.2 was performed using the impact data specified in MIL-STD-810H as an input value. Through this, the maximum stress generated in the impact environment of the mobile power supply container was derived, and the safety margin was calculated to confirm the reliability of the container.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.72-77
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• 2011

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FEM building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FEM reflecting the results of the modal testing of a pod is built through the optimization, applied to the structural dynamic model of an Aircraft, used to verified the stability of vibration and flutter of an aircraft.

• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.162-167
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• 2005

An optical directional coupler, which consists of quantum wells with nanothickness, is designed by using Modal Transmission Line Theory (MTLT). To demonstrate the validity and usefulness, the propagation characteristics and the coupling efficiencies are rigorously evaluated at nanoscale couplers, which consist of double quantum wells with different effective masses. The numerical result reveals that the coupling efficiency of nanoscale couplers is maximized at a coupling length 2052.3 nm, if the total electron energy is 83.9 meV. Furthermore, the coupler operates as a filter with narrower band as the barrier thickness increases.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.74-74
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• 2011

본 연구에서는 중앙경간 54m, 교폭 4m의 사장교형식의 보도교로 측경간은 계단으로 이루어진 1경간 케이블교량을 대상으로 보행하중에 의한 수직진동을 제어하기 위해 제진장치(TMD)를 적용하기로 하고 실물 TMD의 설계 및 제작 그리고 설치 및 제어성능실험을 수행하였다. 우선 사장교형식의 교량. 그리고 1경간 교량이라는 점에서 상대적으로 감쇠율이 낮을 것으로 예측되었고 또한 54m의 경간장이 보행자가 가진 주파수에 근접한 고유진동수를 나타낼 것으로 사료되어 Eurocode 2 part 2(EC5-2)의 규준에 따라 1인 및 다수 보행하중에 의한 보도교의 발생가속도를 산출하였다. 이 경우 최대가속도는 다수의 보행자가 연속적으로 진행할 때 발생하였으며, 수직방향의 가속도가 사용성기준을 초과하는 것으로 나타났다. 또한 구조해석프로그램에 의한 고유치 해석결과, 보행하중의 주파수대역내에 진동모드가 존재하는 것으로 나타났다. 따라서 본 교량의 설계단계에 있어서 보행진동을 제어하기 위하여 유지관리가 용이한 수동형의 동조질량감쇠장치(Tuned Mass Damper)를 적용하기로 하였으며 TMD의 설계에서는 TMD의 제어목표를 만족시킬 수 있는 TMD의 가동질량(moving mass)을 우선적으로 결정하였고, 이로부터 Den Hartog의 제안식에 따라 TMD의 고유진동수비, 유효감쇠비를 산정하였다. 산정된 변수들을 이용하여 설계된 TMD는 현장설치 및 튜닝의 편의성을 고려하여 수평 외팔보형식으로 설계, 제작되었으며 제작된 TMD의 경우 회전축에 대해 질량, 스프링, 댐퍼의 중심거리를 조정함으로써 TMD의 진동수, 강성, 감쇠력을 상대적으로 매우 용이하게 조절할 수 있으며, 조정범위 또한 광범위하여 일반 TMD에 비해 현장설치시 대상구조물에 동조시키기가 용이하며, 작동시 마찰감쇠가 거의 없다는 장점이 있다. 현장설치전에 제작된 TMD를 대상으로 자유진동 시험을 통하여 질량의 중심거리, 스프링 크기 그리고 댐퍼의 설치유무를 각각 변화시키며 TMD의 자유진동 데이터를 취득하였다. 각각의 시험에서 얻어진 데이터로부터 스펙트럼해석을 통하여 고유진동수를 구하였고, 자유진동 파형으로 부터 감쇠비를 구하였다. TMD는 일반적으로 제어모드의 변형형상이 가장 큰 곳에 설치되었을 때 최대의 제진효과를 발휘할 수 있다. 그러나 현장여건상 설치가 불가능하거나 미관을 해치는 경우에는 가능한 범위 내에서 TMD 제어효율이 가장 크게 발휘할 수 있는 곳을 선택하여야 한다. 본 보도교의 경우, 중앙경간 중심부에서 가장 큰 모드변형형상을 나타내지만, 보도교의 상판 연결부 등에 따른 TMD 시공문제로 인하여 TMD 설치위치는 교량 중앙에서 양 방향으로 1.25m 떨어진 곳에 대칭으로 총 2기를 설치하기로 하였다. 일반적으로 TMD의 모든 설계변수는 구조물의 설계단계에서 수행된 구조해석결과에 근거하여 설정하므로 완공된 구조물, 즉 실제보도교의 동적특성을 계측하여 정확하게 진동수를 튜닝하여야 한다. 구조해석에 의한 보도교의 수직방향(TMD 작동방향) 고유진동수는 1.5225 Hz이며, 감쇠비는 규준에 의하여 0.6 %로 가정하였다. 그러나 이 값들은 구조해석모델 및 재료적 특성과 시공상의 오차에 의하여 실제와 다를 수 있으므로 현장계측에 의한 확인이 요구된다. 또한 TMD의 제진효율이 설계시의 목표대로 확보되었는지도 확인해야 하므로 현장튜닝 및 성능시험을 실시하였다. 보도교의 가진은 사전에 실시한 상시 미진동계측결과를 토대로 2Hz를 목표로 하여 인력가진실험을 수행하였고, 탁월진동 주파수는 1.9896Hz로 나타나 구조해석결과와 오차가 있음을 알 수 있다. 가진실험결과를 토대로 TMD의 진동수를 최적진동수비로 튜닝하고 인력가진 실험을 다시 실시하여 TMD의 진동제어성능을 검토하였다. TMD 튜닝 전, 후의 보도교 감쇠비를 비교한 결과, TMD를 설치함으로써 약 4.218%의 감쇠비 증가가 있음을 알 수 있다.

• Composites Research
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• v.30 no.1
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• pp.52-58
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• 2017

This paper presents the optimum design methodology for composite wing structure which automatically calculates the safety margin using optimization framework integrating failure modes. Particularly, its framework is possible to optimize sizing procedure to prevent failure mode which has the greatest effect on reducing the sizing time of composite structure. The main failure mode was set as the first ply failure, buckling failure mode, and bolted joint stress field, and the margin was calculated to minimize the weight. The design variable is a laminate sequence database and the responses are strain, buckling, bolted joint stress field. The objective function is the mass of the wing structure. The results of buckling analysis were compared using the finite element model to verify the robustness and reliability of Composite Optimizer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.6
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• pp.495-501
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• 2012

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FE model building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FE model reflecting the results of the modal testing of a pod is built through the optimization and will be applied to the structural dynamic model of an aircraft which is used to verified the stability of vibration and flutter of an aircraft.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.325-331
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• 2013

In this study, a complex eigenvalue analysis is implemented to verify the unstable mode of a brake system using ABAQUS software. The component participation factors and component modal participation factors are used to analyze the total contributions from each component and each component mode to a particular unstable system mode. This study shows that the 1.4-kHz unstable system mode comes from mode coupling between the 2nd nodal diametric mode and 3rd lateral axial mode (LAM) in the baseline model. A sensitivity analysis with a linking index is performed to prevent the mode coupling of the component modes. This linking index analysis shows the optimum mass loading position to move away the natural frequency of the 3rd LAM, which contributes to the unstable mode. Finally, a complex eigenvalue analysis is implemented with mass loading in the tie bar position, and no unstable system mode is generated in the low-frequency range (below 2 kHz).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.26-32
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• 2021

The antenna is mounted on the vehicle and operated, so its components must be able to withstand the shock that may occur while driving. In this study, the stability of antenna mounted on the vehicle is verified through the connection between modal analysis and transient analysis. The shock data used was taken from MIL-STD-810H, METHOD 516.8. As a result of the analysis of antenna, the maximum equivalent stress 169.49MPa and minimum margin of safety 2.31 has occurred on the bracket of antenna. Thus, it was found that the antenna has enough stability during the operation.

• Journal of Convergence for Information Technology
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• v.11 no.2
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• pp.107-116
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• 2021

In this study, an analytical method was developed for estradiol-17��, testosterone, and progesterone, which are growth promoters as veterinary drug residues in animal food. The analytes were separated using liquid chromatography, and was injected into a mass spectrometer through the electrospray ionization(ESI) process and detected in multiple reaction monitoring(MRM) mode. As the method was validated by CODEX CAC/GL 71-2009 guideline, it met the acceptable. The analysis of beef, pork, and chicken distributed in Korea was conducted with an established method to confirm the applicability of the actual sample. It was confirmed that the developed method can be quickly and reliably in the analysis for the growth promoters identified in domestic distributed livestock products. Through subsequent research, a highly utilized analysis method will be completed if the number of growth promoters is expanded based on the method and the simultaneous analytical method is established by including all of it.