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연소실 및 추진제 변화에 따른 고체로켓 모터의 L<sup>*</sup> 불안정에 관한 연구
이동희,류승현,주성민,김준성,문희장,성홍계,양준서,Lee, Donghee,Ryu, Seunghyun,Joo, Seongmin,Kim, Junseong,Moon, Heejang,Sung, Honggye,Yang, Juneseo 한국항공운항학회 2015 한국항공운항학회지 Vol.23 No.4
In this paper, a theoretical study of low frequency non acoustic instability, the $L^*$ instability, of a solid rocket motor is investigated. The $L^*$ stability criterion is determined by analysing the $L^*$ stability curves of two very distinct propellants for five different geometrical combustors. The $L^*$ instability of two extreme fuels showed totally different behavior in terms of operating pressure of the combustor. A parametric study on the stability for different chamber volume and different throat area keeping constant $L^*$ is conducted and analyzed. It was found that one of the main parameters, the non-dimensional critical characteristic time, requires an enough margin from the critical $L^*$ stability curve.
생체 다공성 매질에서 분자 확산 측정을 위한 영상 기반 형광 광표백 기법 개발
이동희(Donghee Lee),이정훈(Jeonghoon Lee),박춘호(Choonho Park),김중경(Jung Kyung Kim) 한국가시화정보학회 2009 한국가시화정보학회지 Vol.7 No.1
Fluorescence recovery after photobleaching (FRAP) has been widely used for the measurement of molecular diffusion in living cells and tissues. We developed an image-based FRAP (iFRAP) technique using a modified real-time microscope and a 488 ㎚ Ar-ion laser. A fractional intensity curve was obtained from the time-lapse images of fluorescence recovery in the bleached spot to determine the diffusion coefficient of fluorescently labeled macromolecules in porous medium. We validated iFRAP through experiments with agar gels (0.5% and 1.5% w/v) containing FITC-Dextrans (10, 70 and 500 kDa ㎿). Further validation was performed by a Monte Carlo approach, where we simulated the three-dimensional random walk of macromolecules in agar gel model. Diffusion coefficients were deduced from the mean square displacement curves and showed good agreements with those measured by iFRAP.
고속 모듈 스케줄러를 이용한 스트림 기반 네트워크의 성능 향상
이동희(Donghee Lee),진영택(Youngtaek Jin),조유근(Yookun Cho) 한국정보과학회 1996 정보과학회논문지 : 시스템 및 이론 Vol.23 No.2
UNIX System V에서 제공하는 스트림 기법(STREAMS mechanism)은 모듈화와 계층화를 지원하여, 네트워크 소프트웨어의 구현에 적합한 기본 구조를 제공한다. 한편 네트워크의 고속화에 대응하여 네트워크 프로토콜을 처리하는데 소요되는 시간이 극적으로 감소하면서, 스트림이 제공하는 기본 구조에 의한 지연 시간이 차지하는 비중이 상대적으로 증가하여 전체 네트워크 지연 시간에서 많은 부분을 차지하게 되었다. 본 논문에서는 전체 네트워크 지연 시간에서 스트림 구조로 인한 지연이 차지하는 비율을 제시하고, 스트림 구조의 장점을 유지하면서 이러한 지연 시간을 감소시키기 위하여 스케줄 지역성을 이용 하는 고속 모듈 스케줄러를 제안한다. SVR 4.0에서 제안된 고속 모듈 스케줄러를 구현하고 일부 모듈의 스케줄 경로를 개선하여, TCP/IP의 네트워크 지연 시간과 스트림 구조로 인한 지연 시간의 감소 정도를 측정함으로써 네트워크 성능이 향상됨을 검증한 내용을 제시한다. The STREAMS mechanism provides a flexible framework for network protocols and services under UNIX System V Recently networks are getting faster and the processing time of network protocols have decreased. As a result, the relative ratio of the STREAMS overhead to the network delay is increasing In this paper, we quantify the STREAMS overhead which consists of queueing and scheduling delays in SVR 4.0. To reduce the overhead and maintain the merits of the STREAMS mechanism, we propose a fast module scheduler which exploits locality of scheduling. Performance of the proposed fast scheduler is measured in various configurations.
차량 충돌 모델 최적화를 위한 개선된 Solution space 탐색 기법
이동희(Donghee Lee),이익진(Ikjin Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
In the early phase for crashworthiness design, the classical optimization method is limited due to the lack of information. Even though simple vehicle design is provided, the optimization process is still time-consuming and inefficient problem because the performance and constraint functions of vehicle design are highly non-linear. And various factors that influence the crash performance are coupled, which means that a variation in one component leads to the change of the global performance. In order to handle these difficulties, the solution space has been proposed, which makes the different components independent to each other when it comes to crashworthiness. The solution space is the product of permissible intervals in the design space. Every design within the solution space delivers the required crash performance. In this paper, a sequential sampling method enhanced with surrogate model is introduced to get the solution space in efficient way.