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3D 프린팅을 이용한 소형 무인기 설계·제작 교육 프로그램을 위한 수업자료 개발과 적용
김시태(Kim, Sitae),김민성(Kim, Minseong),공동재(Kong, Dongjae) 한국공학교육학회 2021 공학교육연구 Vol.24 No.5
This study introduces the development and application of instructional materials for a micro-UAV (unmanned aerial vehicle) design and manufacturing program in university education for freshman/sophomore students. The ADDIE methodology was applied to the development of educational materials, which consist of 15 lessons including the aircraft design theory, 3D CAD modeling, 3D printing production, and UAV flight control. The validity of the program was evaluated with 8 expert panels. A total of 82 participants from engineering and social science grouped the 16 teams for the creative UAV wing design and cooperative interactions. The results of overall program satisfaction survey was measured highly as the average 4.54 (out of 5), so that the students were content with the professional engineering knowledge, 3D digital tools, and the opportunity to design and manufacture airplanes on their own. In conclusion, it can be confirmed that the developed program is effective for UAV education for junior level college student.
블레이드 손상에 따른 이축식 터보팬 엔진의 동적 안정성 해석
김시태(Sitae Kim),정기현(Kihyun Jung),이준호(Junho Lee),박기현(Kihyun Park),양광진(Kwangjin Yang) 한국트라이볼로지학회 2020 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.36 No.2
This paper presents a numerical study on the rotordynamic analysis of a dual-spool turbofan engine in the context of blade defect events. The blades of an axial-type aeroengine are typically well aligned during the compressor and turbine stages. However, they are sometimes exposed to damage, partially or entirely, for several operational reasons, such as cracks due to foreign objects, burns from the combustion gas, and corrosion due to oxygen in the air. Herein, we designed a dual-spool rotor using the commercial 3D modeling software CATIA to simulate blade defects in the turbofan engine. We utilized the rotordynamic parameters to create two finite element Euler–Bernoulli beam models connected by means of an inter-rotor bearing. We then applied the unbalanced forces induced by the mass eccentricities of the blades to the following selected scenarios: 1) fully balanced, 2) crack in the low-pressure compressor (LPC) and high pressure compressor (HPC), 3) burn on the high-pressure turbine (HPT) and low pressure compressor, 4) corrosion of the LPC, and 5) corrosion of the HPC. Additionally, we obtained the transient and steady-state responses of the overall rotor nodes using the Runge–Kutta numerical integration method, and employed model reduction techniques such as component mode synthesis to enhance the computational efficiency of the process. The simulation results indicate that the high-vibration status of the rotor commences beyond 10,000 rpm, which is identified as the first critical speed of the lower speed rotor. Moreover, we monitored the unbalanced stages near the inter-rotor bearing, which prominently influences the overall rotordynamic status, and the corrosion of the HPC to prevent further instability. The high-speed range operation (>13,000 rpm) coupled with HPC/HPT blade defects possibly presents a rotor–case contact problem that can lead to catastrophic failure.
비선형 로터 다이나믹스에 적용되는 슈팅 알고리즘의 초기조건 생성 효과 분석 연구
김시태 ( Kim Sitae ) 공군사관학교 2018 군사과학논집 Vol.69 No.2
슈팅 알고리즘은 비선형 미분방정식의 경계값 문제를 수치적으로 풀이하는 방법으로 다중해 식별 및 안정성 해석에 주로 적용된다. 본 연구는 비선형 로터 다이나믹 시스템에 적용되는 슈팅 방법의 연산 효율화를 위하여 여러 초기조건 생성 방안을 적용하고 그 효과를 분석하는 것을 목표로 한다. 로터-플로팅 링 베어링 시스템을 모델링한 후, 시스템 자유도와 가동영역을 고려하여 격자형 분포와 랜덤형 분포로 초기조건을 생성시키고, 각각의 해 수렴률과 다중해 식별과정을 분석하였다. 그 결과, 로터-베어링 간 윤활유 압력이 집중되는 구역 주변으로 해 수렴률이 급격히 증대되는 것으로 나타났다. 반면, 다중해 식별 확률을 높이기 위해서는 가동구역 전반에 걸쳐 정규 분포화하는 것이 필요하다는 것을 확인하였다. 이러한 분석을 토대로 슈팅 알고리즘의 효과적인 초기값 설정 방안을 제시하였다. Shooting algorithm is a numerical method to solve the boundary value problem of a nonlinear differential equation, and it is capable of identifying multiple roots and analyzing stability of the response. This research aims to find an effective intial condition generation process of the shooting for solving nonlinear rotordynamic problem with an efficient computing manner. A Jeffcott rotor-floating ring bearing system is employed as a mechanical model to investigate the convergence rate of the generated initial conditions to one or all orbital equilibrium states, OES. As results, the convergence rate to one OES drastically increased when the initial conditions are near the maximized hydrodynamic pressure area. On the other hand, discovering all OES shows advantages when initial conditions has normal distribution along the all bearing clearance area. A guideline for the setting initial condition is suggested based on the numerical investigation results.
비선형 로터 다이나믹스에 적용되는 슈팅 알고리즘의 초기조건 생성 효과 분석 연구
김시태 ( Kim Sitae ) 공군사관학교 2018 空士論文集 Vol.69 No.2
Shooting algorithm is a numerical method to solve the boundary value problem of a nonlinear differential equation, and it is capable of identifying multiple roots and analyzing stability of the response. This research aims to find an effective intial condition generation process of the shooting for solving nonlinear rotordynamic problem with an efficient computing manner. A Jeffcott rotor-floating ring bearing system is employed as a mechanical model to investigate the convergence rate of the generated initial conditions to one or all orbital equilibrium states, OES. As results, the convergence rate to one OES drastically increased when the initial conditions are near the maximized hydrodynamic pressure area. On the other hand, discovering all OES shows advantages when initial conditions has normal distribution along the all bearing clearance area. A guideline for the setting initial condition is suggested based on the numerical investigation results.
유승훈,김시태,김동수,이영건,Yoo, Seunghoon,Kim, Sitae,Kim, Dongsoo,Lee, Younggun 한국정보통신학회 2021 한국정보통신학회논문지 Vol.25 No.12
최근 다양한 분야에 적용되고 있는 딥러닝을 활용한 알고리즘 개발을 위해서는 양질의 풍부한 학습데이터가 갖춰져야 한다. 본 논문은 딥러닝 알고리즘 개발 시 활용도가 높고 정보 도출 시 유용한 광학 영상, 열화상, 음성 등의 생체신호 데이터를 동시에 수집하여 서버에 전송하는 생체신호 수집시스템을 제안한다. 수집기의 이동성을 높이기 위해 라즈베리 파이를 기반으로 제작하였고, 수집한 데이터는 무선 인터넷을 통해 서버로 전송한다. 복수의 수집기에서 동시에 데이터 수집이 가능하도록 피실험자별로 로그인을 위한 아이디를 부여했고, 이를 데이터베이스에 반영하여 데이터 관리가 용이하게 하였다. 제안하는 수집시스템의 활용방안을 보이기 위해 피로도 측정을 위한 생체신호 데이터 수집의 예시를 보인다. In order to develop an algorithm using deep learning, which has been recently applied to various fields, it is necessary to have rich, high-quality learning data. In this paper, we propose an acquisition system for biological signals that simultaneously collects bio-signal data such as optical videos, thermal videos, and voices, which are mainly used in developing deep learning algorithms and useful in derivation of information, and transmit them to the server. To increase the portability of the collector, it was made based on Raspberry Pi, and the collected data is transmitted to the server through the wireless Internet. To enable simultaneous data collection from multiple collectors, an ID for login was assigned to each subject, and this was reflected in the database to facilitate data management. By presenting an example of biological data collection for fatigue measurement, we prove the application of the proposed acquisition system.
날아가는 섬광탄이 연료탱크 수평핀에 미치는 복사열전달 연구
정대한,강치행,김시태,Jung, Daehan,Kang, Chihang,Kim, Sitae 한국군사과학기술학회 2014 한국군사과학기술학회지 Vol.17 No.2
In this paper, the effect of unsteady radiation on the horizontal fin of an external fuel tank by flame of a flying flare was analysed to see the temperature increase of the fin and the thermal impact on the fin. Radiation between two surfaces was calculated using the concept of radiation resistance of surface and space including radiation, irradiation and shape factor for two flying trajectories of a flare, maximum temperature of 2200 K, emissivity of 0.95, flying velocity of 30 m/s, and thermal surface area of $0.01m^2$. The result shows that the temperature increase of the fin is 0.236 K, and the thermal effect on the fin is ignorable. And it was found that temperature is increased a little because small amount of heat energy can be radiated due to the short exposure time to the heat source.