Longitudinal System Identification of an Avian-Type UAV Considering Characteristics of Actuator

Hakseong Gim,ByoungJu Lee,Jaeyeon Huh,Seungkeun Kim,JinyoungSuk 한국항공우주학회 2018 International Journal of Aeronautical and Space Sc Vol.19 No.4

To develop autonomous flapping aircraft, basic mathematical modeling is essential to solve the problem of “uncertainty models” in biomimetic flight dynamics. This study identified the longitudinal linear model of an ornithopter via automated flight tests and sensors onboard the ornithopter to measure angular rates, Euler angles, and total velocity. For accurate flight tests, automated signal input was designed for elevator deflection: doublet and multistep 3211 maneuver. Furthermore, because the flapping motion of the ornithopter’s main wings generates oscillations during cruise flight, fast Fourier transform is used to analyze flight data in the frequency domain, and a Butterworth filter is used to filter out the flapping motion from the data. The characteristics of the actuator are then analyzed using a motion capture camera and applied to the system identification. The structure of the ornithopter linear model is found to be similar to that of a fixed-wing aircraft, which has a periodic oscillation. The results from the flight tests and analysis manifest that an ornithopter has unstable characteristics due to a single right-half plane real pole.

수평 구동형 MEMS 관성 스위치 설계 및 성능해석

김학성(Hakseong Gim),장승교(Seung-gyo Jang) 한국항공우주학회 2020 韓國航空宇宙學會誌 Vol.48 No.7

스프링-메스 시스템의 원리를 이용하여 수평 구동형 MEMS 관성 스위치를 설계하였다. 본 MEMS 스위치는 외부에서 발생하는 가속도를 감지하여 점화안전장치를 장전시키는 역할을 한다. 성능 모델링을 통하여 다양한 가속도 조건에서의 구동 양상을 분석하였다. 시뮬레이션 결과 가속도의 기울기가 10g/msec 이하인 경우에 MEMS 스위치는 10g에서 잘 작동하는 것으로 나타났다. 반면에, 설계변수들의 공차를 10%로 고려한 시뮬레이션 결과 스프링 폭과 길이에 의해 임계 동작 가속도가 규격(10±2g)을 벗어났다. 제작 공정상 10% 이하의 공차 관리가 어려운 스프링 폭을 두 배로 늘렸을 때 규격을 만족하는 것을 확인하고 설계보완을 제안하였다. A lateral type MEMS inertial switch was designed on the same principle as spring-mass system. The MEMS switch is used for arming mechanism of the arm-fire device by sensing the applied acceleration. We analyzed the switching capability of the MEMS switch under various acceleration conditions via performance model. Simulation results showed that the MEMS switch works very well at 10 g when the applied acceleration slope does not exceed 10g/msec. On the other hand, the threshold operating acceleration level simulation exceeded the requirement (10±2 g) due to the width and length of the spring by considering 10% tolerance of the design values. Design modification of doubling the width of the spring, which is difficult to reduce less than 10% tolerance in fabrication process, was proposed after confirming the simulation results comply the requirement.

Accurate and Precise Determination of Mechanical Properties of Silicon Nitride Beam Nanoelectromechanical Devices

Kim, Hakseong,Shin, Dong Hoon,McAllister, Kirstie,Seo, Miri,Lee, Sangik,Kang, Il-Suk,Park, Bae Ho,Campbell, Eleanor E. B.,Lee, Sang Wook American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8

<P>Accurate and precise determination of mechanical properties of nanoscale materials is mandatory since device performances of nanoelectromechanical systems (NEMS) are closely related to the flexural properties of the materials. In this study, the intrinsic mechanical properties of highly stressed silicon nitride (SiN) beams of varying lengths are investigated using two different techniques: Dynamic flexural measurement using optical interferometry and quasi-static flexural measurement using atomic force microscopy. The resonance frequencies of the doubly clamped, highly stressed beams are found to be inversely proportional to their length, which is not usually observed from a beam but is expected from a string-like structure. The mass density of the SiN beams can be precisely determined from the dynamic flexural measurements by using the values for internal stress and Young's modulus determined from the quasi-static measurements. As a result, the mass resolution of the SiN beam resonators was predicted to be a few attograms, which was found to be in excellent agreement with the experimental results. This work suggests that accurate and precise determination of mechanical properties can be achieved through combined flexural measurement techniques, which is a crucial key for designing practical NEMS applications such as biomolecular sensors and gas detectors.</P>

조류모방형 비행체 구동기 특성 분석

김학성(Hakseong Gim),유연아(Yeona Yoo),김승균(Seungkeun Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.5

Accurate Gap Determination in Monolayer and Bilayer Graphene/<i>h</i>-BN Moiré Superlattices

Kim, Hakseong,Leconte, Nicolas,Chittari, Bheema L.,Watanabe, Kenji,Taniguchi, Takashi,MacDonald, Allan H.,Jung, Jeil,Jung, Suyong American Chemical Society 2018 Nano letters Vol.18 No.12

<P>High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. One of the methods used to create gaps in the spectrum of graphene systems is to form long period moiré patterns by aligning the graphene and hexagonal boron nitride (<I>h</I>-BN) substrate lattices. Here, we use planar tunneling devices with thin <I>h</I>-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single-layer and bilayer graphene-<I>h</I>-BN superlattice structures at charge neutrality (first Dirac point) and at integer moiré band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene, we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to a zero magnetic field and are as large as ≈17 meV for devices in near-perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field.</P> [FIG OMISSION]</BR>

모션캡쳐 실험을 통한 조류모방 날갯짓 비행체 구동 특성 분석

김학성(Hakseong Gim),김승균(Seungkeun Kim),석진영(Jinyoung Suk) 한국항공우주학회 2017 韓國航空宇宙學會誌 Vol.45 No.3

본 논문에서는 모션캡쳐 카메라를 사용한 실험을 통해 날갯짓 비행체의 주 날개, 꼬리날개 구동기 특성 분석에 대하여 기술하였다. 실험은 빛이 차단된 실내에서 진행되었고 지그에 기체를 고정하여 날갯짓으로 인한 영향을 줄였다. 주 날개와 꼬리날개 끝단에 마커를 부착하였고 모션캡쳐 카메라는 입력 신호에 대한 각각의 반응을 측정한다. 실험 결과 주 날개는 날갯짓의 주파수에 따라 진폭이 변하는 경향을 보였고, Modified Strip Theory에 실험 결과와 비행체 제원을 적용하여 양력 및 추력 발생 시뮬레이션을 구현 하였다. 꼬리날개는 종·횡축별로 스텝 신호를 인가하여 이에 따른 결과를 2차 전달함수 형태로 정의하였고, 각 축별로 구동기의 구조 차이로 인하여 최종 응답시간, 오버슈트, 최대값등에서 차이를 나타내는 것을 확인하였다. This paper analyzes actuator characteristics for main wing and tail surfaces of an ornithopter by using a motion capture test. Experiments with the ornithopter are conducted indoor, and its fuselage is held on a jig to reduce interaction with vibration generated by flapping motion. The motion capture system detects the movement of markers attached on the main wing and tail wing tip. Experimental results show that the main wings tend to change its amplitude according to the flapping frequency, and the lift and thrust generation simulation is implemented by applying the experimental results and the ornithopter specification to Modified Strip Theory. Step input excitation is applied for experimental analysis of the tail wing in horizontal and vertical directions. As a result, horizontal and vertical tail wings have different characteristics in terms of overshoot, final value, damping ratio and natural frequency because they have different wing structures and linkages.

Integrating ZnO Microwires with Nanoscale Electrodes Using a Suspended PMMA Ribbon for Studying Reliable Electrical and Electromechanical Properties

Kim, Hakseong,Yun, Hoyeol,Yoon, Ho Ang,Lee, Sang Wook Wiley (John WileySons) 2014 Advanced Energy Materials Vol.4 No.11

광대역 CDMA 시스템을 위한 Transmit Adaptive Array와 전송 안테나 선택 다이버시티 결합 기법

김학성(Hakseong Kim),이원철(Woncheol Lee),신요안(Yoan Shin) 한국통신학회 2002 한국통신학회 학술대회논문집 Vol.2002 No.7

조선시기 京畿 島嶼지역의 空間認識 변화

임학성(Lhim, Hakseong) 목포대학교 도서문화연구소 2014 島嶼文化 Vol.0 No.43

조선시대 島嶼지역에 대한 중앙 정부의 空間認識은 시기별로 뚜렷한 차이를 보였다. 조선전기에는 空島政策으로 代辯되듯이 도서지역을 범죄자의 소굴 또는 敎化가 미치지 못하는 변방 정도로 인식하였던 반면, 조선 후기에는 도서의 중요성 및 활용성이 제대로 인식되면서 入島政策으로 전환하였던 것이다. 아울러 이러한 공간인식의 변화와 연동하여 조선 전기에는 도서지역에 적잖은 國營牧場이 설치되었던 반면, 조선 후기에는 국영목장을 폐장하고 목장터를 농지로 개간함은 물론 水軍鎭을 설치하여 방어체제를 강화하는 것으로 전환하였다. 조선 정부가 취한 도서정책의 결과와 영향은 경기도의 도서지역에서도 그대로 확인되었다. 첫째, 조선 정부가 파악하고 있었던 경기지역의 도서 수가 조선 전기(15세기 전반)에는 20여개에 불과했으나, 조선 후기(18세기 후반)에는 80여 개로 무려 4배가량이나 급증하였다. 둘째, 조선 전기(15세기 후반)에 20여 개였던 경기 도서지역의 국영목장 수가 조선 후기(18세기 중엽)에 이르러 그 절반 이하인 9개로 급감하였다. 셋째, 공도정책 폐지 및 국영목장 폐장의 결과 주민의 입도가 활발히 전개되어 경기지역의 일부 도서에서는 조선 후기(18세기 중엽)에 이미 적잖은 주민이 거주(예를 들어 자연도의 경우 850戶)하고 있었으며 이러한 주민 증가추세는 이후에도 계속 진행되고 있었다. 넷째, 조선 후기(17세기 중엽) 이후 경기 서해 水路의 요충지에 위치한 도서지역에 수군진이 설치되기 시작했으며, 일부 수군진의 경우 保障處이자 咽喉處로 인식된 江華島를 外護하기 위해 獨鎭으로 재편되어 운영되기도 하였다. 이상 조선시기 경기 도서지역에서 확인되는 여러 현상, 즉 국영목장의 설치와 폐장, 도서주민 및 농지의 多大한 증가, 수군진의 설치 및 독진 운영 등은 도서지역에 대한 조선 정부의 空間인식 및 도서정책이 변환한 결과였다. Between the early Joseon Dynasty and the late one, there was a distinct difference how the government treated islands. In the early period, as we know from the empty-island policy, they were viewed as the hotbed of crime or frontier beyond the edification. On the contrary, the government realized their importance and encouraged people to migrate to there in the late days. According to this change, it closed state-owned ranch which had been built before, changed ranch into agricultural land, and built naval bases to reinforce the defense system. The results and influences of the governmental policy on islands can be seen islands in Gyeonggi Province. First, the government estimated that there would be about 20 islands in the early 15th century, while about 80 ones in the late 18th century. Secondly, it removed state-owned ranch from 20 (late 15th century) to 9 (mid-18th century). Thirdly, lots of people moved to islands after abolition of the empty-island policy and state-own ranch. For example, there were 850 households residing and the population growth in an island. Finally, naval bases had been built in the islands located in the strategic points of sea route of the Yellow Sea since mid-17th century, and some of them were run independently in order to preserve Ganghwa Island, which was viewed as a wartime shelter and the throat-like spot. In conclusion, some phenomena were the results of change of the governmental view and policy on islands in Gyeonggi Province in the Joseon dynasty, which were installation and closing of state-owned ranch, remarkable growth of residents and agricultural land, and establishment and independent operation of naval bases.

Design and Implementation of a Body Fat Classification Model using Human Body Size Data

Taejun Lee,Hakseong Kim,Hoekyung Jung The Korea Institute of Information and Commucation 2023 Journal of information and communication convergen Vol.21 No.2

Recently, as various examples of machine learning have been applied in the healthcare field, deep learning technology has been applied to various tasks, such as electrocardiogram examination and body composition analysis using wearable devices such as smart watches. To utilize deep learning, securing data is the most important procedure, where human intervention, such as data classification, is required. In this study, we propose a model that uses a clustering algorithm, namely, the K-means clustering, to label body fat according to gender and age considering body size aspects, such as chest circumference and waist circumference, and classifies body fat into five groups from high risk to low risk using a convolutional neural network (CNN). As a result of model validation, accuracy, precision, and recall results of more than 95% were obtained. Thus, rational decision making can be made in the field of healthcare or obesity analysis using the proposed method.