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Data Transfer Schemes in Rotorcraft Fluid-Structure Interaction Predictions
You, Young H.,Na, Deokhwan,Jung, Sung N. Hindawi Limited 2018 International journal of aerospace engineering Vol.2018 No.-
<P>For a CFD (computation fluid dynamics)/CSD (computational structural dynamics) coupling, appropriate data exchange strategy is required for the successful operation of the coupling computation, due to fundamental differences between CFD and CSD analyses. This study aims at evaluating various data transfer schemes of a loose CFD/CSD coupling algorithm to validate the higher harmonic control aeroacoustic rotor test (HART) data in descending flight. Three different data transfer methods in relation to the time domain airloads are considered. The first (method 1) uses random data selection matched with the timewise resolution of the CSD analysis whereas the last (method 2) adopts a harmonic filter to the original signals in CFD and CSD analyses. The second (method 3) is a mixture of the two methods. All methods lead to convergent solutions after a few cycles of coupling iterations are marched. The final converged solutions for each of the data transfer methods are correlated with the measured HART data. It is found that both method 1 and method 2 exhibit nearly identical results on airloads and blade motions leading to excellent correlations with the measured data while the agreement is less satisfactory with method 3. The reason of the discrepancy is identified and discussed illustrating CFD-/CSD-coupled aeromechanics predictions.</P>
OFDMA uplink performance for interactive wireless broadcasting
You, Y.-H.,Jeon, W.-G.,Wee, J.-W.,Kim, Sang-Tae,Hwang, Intae,Song, H.-K. IEEE 2005 IEEE transactions on broadcasting Vol.51 No.3
A combination of orthogonal frequency division multiplexing (OFDM) with frequency-division multiple access (FDMA) called OFDMA is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. This work focuses on the performance of OFDM when used as a modulation and access technique for the uplink of an interactive wireless broadcasting system. In such an application, we present our investigations of the effects of symbol timing misalignments and peak-to-average power ratio (PAR). Under the condition of the same side information bits, the selective mapping (SLM) approach can be implemented by decimating OFDM samples, which is less complex compared to the ordinary SLM incurring a slight degradation of the PAR performance. Taking into account the effects of clipping operation and symbol timing misalignment, the bit error rate (BER) and throughput performances are investigated for a typical OFDMA uplink scenario.
MOKE Studies of the Magnetic Anisotropy of Epitaxial Ni/Cu(001) Structure on HF-Treated Si(001)
H.M.Hwang,I.S.Kim,D.G.You,H.S.Park,M.C.Sung,K.Jeong,J.Lee,T.G.Kim,J.H.Song 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.41 No.1
We present various hysteresis loops of epitaxial Ni/Cu(001) grown on HF-treated Si(001). Re ection high-energy electron diraction (RHEED) and X-ray diraction (XRD) measurements show that the Cu and the subsequently deposited Ni lms are epitaxial and have fcc structures. Magnetooptic Kerr eect (MOKE) measurements from the step-wedged Ni lms show the double transitions of a magnetic anisotropy (in-plane!perpendicular!in-plane). In polar MOKE measurements, at remanence, a 100 % of the magnetization is found for Ni thicknesses in the range of 2075 A. The remanence measurement on the 200-A Ni lm clearly showed fourfold magnetic in-plane anisotropy, which is a direct magnetic conrmation of a fcc epitaxial structure.
YOU, Young H.,JUNG, Sung N.,KIM, Chang J. Elsevier 2017 Chinese journal of aeronautics Vol.30 No.4
<P>The best active twist schedules exploiting various waveform types are sought taking advantage of the global search algorithm for the reduction of hub vibration and/or power required of a rotor in high-speed conditions. The active twist schedules include two non-harmonic inputs formed based on segmented step functions as well as the simple harmonic waveform input. An advanced Particle Swarm assisted Genetic Algorithm (PSGA) is employed for the optimizer. A rotorcraft Computational Structural Dynamics (CSD) code CAMRAD II is used to perform the rotor aeromechanics analysis. A Computation Fluid Dynamics (CFD) code is coupled with CSD for verification and some physical insights. The PSGA optimization results are verified against the parameter sweep study performed using the harmonic actuation. The optimum twist schedules according to the performance and/or vibration reduction strategy are obtained and their optimization gains are compared between the actuation cases. A two-phase non-harmonic actuation schedule demonstrates the best outcome in decreasing the power required while a four-phase non-harmonic schedule results in the best vibration reduction as well as the simultaneous reductions in the power required and vibration. The mechanism of reduction to the performance gains is identified illustrating the section airloads, angle-of-attack distribution, and elastic twist deformation predicted by the present approaches. (C) 2017 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.</P>
You, Sung H.,Bunker, Linda K. 한국전문물리치료학회 2002 한국전문물리치료학회지 Vol.9 No.4
Lesch-Nyhan 증후군(LNS)은 hypoxanthine guanine phosphoribosyle transferase (HGPRT) 효소를 암호화 하는 X 염색체가 불완전해서 일어나는 유전적인 추제외로계(또는 기저핵)의 드문 병변이다. 출생시 LNS 유아는 정상적인 운동발달이 관찰되어진다. LNS에게서 현저하게 진단적인 특징으로 보여지는 운동심리적 행동인 self-mutilating 행위는 4살 이후에나 나타난다. LNS 아이들은 오히려 초기에 Rett's 증후근, 뇌성마비, 자폐, 다운증후근과 유사한 운동행위를 보인다. 그래서 LNS 아이들은 앞에 기술한 신경학적 장애로 오진을 받을 수가 있다. 오진으로 인해 초기에 적절한 치료를 받지 못한다면 LNS는 결과적으로 합병증(신장부전)과 self-mutilating 행위로 인하여 치명적일 수가 있다. 그러므로, 이 연구의 목적은 LNS 평가 동안 더 나은 진단을 하도록 하기 위하여 LNS와 관련된 기능부전에 대한 지식을 임상가들에게 제공하고자 함이었다. 연구 대상자는 10살인 2명의 쌍둥이 남아이었으며 실험은 뻗기 과제 수행 (reaching task)시 움직임 특성을 보기 위하여 운동형상학적과 비디오 분석을 사용하였다. 기술통계로 분석 결과 움직임 시간과 단위가 증가됨을 보였고 사지의 분절적 움직임이 협응되지 않음을 보였다. ballistic과 jerky 움직임 양상은 dysmetric과 비긴장성 운동 행위에서 우세하였다. LNS은 추체로계 운동 장애 (과근긴장도나 저긴장도) 와 추체외로계의 운동 장애 (dystonia와 choreoathetosis)의 혼합된 형태를 보였다. 결론으로 이 연구는 운동발달 장애를 가진 아이들을 치료하고자 할 때 임상가들한테 LNS 아이들의 움직임 장애의 다른 진단적 특징을 알아야 한다는 것을 제시하고자 한다.