• Title, Summary, Keyword: linear time-varying system

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ATTITUDE STABILITY OF A SPACECRAFT WITH SLOSH MASS SUBJECT TO PARAMETRIC EXCITATION (계수자극을 받는 유동체를 포함한 위성체의 자세 안정도 해석)

  • Kang, Ja-Young
    • Journal of Astronomy and Space Sciences
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    • v.20 no.3
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    • pp.205-216
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    • 2003
  • The attitude motion of a spin-stabilized, upper-stage spacecraft is investigated based on a two-body model, consisting of a symmetric body, representing the spacecraft, and a spherical pendulum, representing the liquid slag pool entrapped in the aft section of the rocket motor. Exact time-varying nonlinear equations are derived and used to eliminate the drawbacks of conventional linear models. To study the stability of the spacecraft's attitude motion, both the spacecraft and pendulum are assumed to be in states of steady spin about the symmetry axis of the spacecraft and the coupled time-varying nonlinear equation of the pendulum is simplified. A quasi-stationary solution to that equation and approximate resonance conditions are determined in terms of the system parameters. The analysis shows that the pendulum is subject to a combination of parametric and external-type excitation by the main body and that energy from the excited pendulum is fed into the main body to develop the coning instability. In this paper, numerical examples are presented to explain the mechanism of the coning angle growth and how angular momenta and disturbance moments are generated.

Coordinated Beamforming Systems with Channel Prediction in Time-varying MIMO Broadcast Channel (시변 다중입출력 방송 채널을 위한 채널예측이 적용된 협력 빔형성 시스템)

  • Kim, Jin;Kang, Jin-Whan;Kim, Sang-Hyo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.5C
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    • pp.302-308
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    • 2011
  • In this paper we propose a coordinated beamforming(CBF) scheme considering the effects of feedback quantization and delay in time-varying multiple-input multiple-output(MIMO) broadcast channels. By equal power allocation per data stream, the proposed CBF scheme transmits multiple data streams per user terminals without additional feedback overhead when quantized feedback information is used. The proposed CBF scheme also applies a linear channel predictor to each user terminals to prevent errors due to feedback delays that are not evitable in practical wireless systems. Each user terminal utilizes Wiener filter to predict future channel responses and generates feedback information based on the predicted channels. Consequently the proposed CBF scheme adapting Wiener filter improves system performances compared with the conventional scheme using delayed feedback.

Time Series Prediction of Dynamic Response of a Free-standing Riser using Quadratic Volterra Model (Quadratic Volterra 모델을 이용한 자유지지 라이저의 동적 응답 시계열 예측)

  • Kim, Yooil
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.4
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    • pp.274-282
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    • 2014
  • Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

Analysis of the Ultrasonic Beam Profile Due to Variation of the Inter-Element Spacing for the Phased Array Transducer (페이즈드 어레이 트랜스듀서에 있어서 구성 압전소자의 간격 변화에 따른 초음파 빔 전파 특성 해석)

  • Choe, Sang-U;Lee, Jun-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.4
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    • pp.972-981
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    • 2000
  • The phased array transducer has two distinct advantages. One is rapid scanning comparing with the conventional mechanical or manual scanning system. Therefore, output image is represented in real-time. The other is the dynamic focusing and the dynamic steering of ultrasonic beam. Only the delay times that are controlled electrically are used to focus and to steer beam without any lenses or wedges. In this study, the profile of the ultrasonic beam for the phased array transducer has been simulated in the Huygens principle with varying the inter-element spacing of the linear phased array transducer. From the result of this study, it was found that the ultrasonic beam spread wider as the inter-element spacing was decreased. However, the focusing effect was improved, even when the number of the element was not big. In addition, there was grating lobes that are constructed when the inter-element spacing is more than half wavelength. However, this grating lobe has lower amplitude than the main lobe.

Impact of Sea Surface Scattering on Performance of QPSK (해면산란이 QPSK 성능에 미치는 영향)

  • Xue, Dandan;Seo, Chulwon;Park, Jihyun;Yoon, Jong Rak
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.8
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    • pp.1818-1826
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    • 2014
  • Time-variant sea surface causes a forward scattering and Doppler spreading in received signal on underwater acoustic communication system. This results in time-varying amplitude, frequency and phase variation of the received signal. In such a way the channel coherence bandwidth and fading feature also change with time. Consequently, the system performance is degraded and high-speed coherent digital communication is disrupted. In this paper, quadrature phase shift keying (QPSK) performance is examined in two different sea surface conditions. The impact of sea surface scattering on performance is analyzed on basis of the channel impulse response and temporal coherence using linear frequency modulation (LFM) signal. The impulse response and the temporal coherence of the rough sea surface condition were more unstable and less than that of the calm sea surface condition, respectively. By relating these with time variant envelope, amplitude and phase of received signal, it was found that the bit error rate (BER) of QPSK are closely related to time variation of sea surface state.

Tracking Control of Variable Structure System with a New Variable Boundary Layer (새로운 가변 경계층을 갖는 가변 구조 제어 시스템의 추적 제어)

  • Lee, Hui-Jin;Kim, Eun-Tae;Kim, Dong-Yeon
    • Journal of the Institute of Electronics Engineers of Korea SC
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    • v.37 no.3
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    • pp.19-32
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    • 2000
  • This paper suggests the variable structure controller with a new variable boundary layer for the accurate tracking control of the variable structure systems. Up to now, variable structure controller (VSC) applying the variable boundary layer did not remove chattering from an arbitrary initial state of the system trajectory because VSC has the limited initial state according to the fixed sliding surface. But, by using the linear time-varying sliding surfaces, the scheme has the robustness against chattering from all states. The suggested method can be applied to the second-order nonlinear systems with parameter uncertainty and extraneous disturbances, and has better tracking performance than the conventional method. To demonstrate the advantages of the proposed algorithm, it is applied to a two-link manipulator.

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The Development of a learning Control Method for the Application to Industrial Robots (로봇트에의 적용을 위한 학습제어 방법 개발)

  • 허경무;원광호
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.1 no.2
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    • pp.49-55
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    • 2000
  • In this paper, we show that our previously proposed second-order iterative learning control method with feedback is more effective and has better convergence performance than the second-order iterative learning control method without feedback, particularly in the case of the existence of initial condition errors. Also the convergence proof of the proposed method is given. And through the simulation result of applying the proposed method to the linear time-varying system, we show that our proposed method has enhanced robustness and stability in case of the existence of initial condition errors.

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A Study on the Fliker Effect of SVC in Electric Arc Furnace Loads (전기로 부하에서 SVC의 플리커 효과에 관한 연구)

  • Kim, Kyung-Chul;Jin, Seong-Eun;Lee, Il-Moo
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.20 no.8
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    • pp.48-53
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    • 2006
  • An electric arc furnace being used in the steel industry is a time-varying non-linear load causing voltage fluctuations to the power system. Flicker can be defined as the effect produced on the human visual perception by a changing emission of light lamps subjected to magnitude fluctuations of their supply voltage. The level of flicker depends on the amplitude, frequency and duration of the voltage fluctuations. In this paper, the voltage fluctuation problem in an 154[kV] system due to the electric arc furnace loads is investigated and the analysis results of the static var compensator application for the voltage flicker mitigation are presented and evaluated by the IEC 61000-3-7.

A Study of Position Control Performance Enhancement in a Real-Time OS Based Laparoscopic Surgery Robot Using Intelligent Fuzzy PID Control Algorithm (Intelligent Fuzzy PID 제어 알고리즘을 이용한 실시간 OS 기반 복강경 수술 로봇의 위치 제어 성능 강화에 관한 연구)

  • Song, Seung-Joon;Park, Jun-Woo;Shin, Jung-Wook;Lee, Duck-Hee;Kim, Yun-Ho;Choi, Jae-Soon
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.57 no.3
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    • pp.518-526
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    • 2008
  • The fuzzy self-tuning PID controller is a PID controller with a fuzzy logic mechanism for tuning its gains on-line. In this structure, the proportional, integral and derivative gains are tuned on-line with respect to the change of the output of system under control. This paper deals with two types of fuzzy self-tuning PID controllers, rule-based fuzzy PID controller and learning fuzzy PID controller. As a medical application of fuzzy PID controller, the proposed controllers were implemented and evaluated in a laparoscopic surgery robot system. The proposed fuzzy PID structures maintain similar performance as conventional PID controller, and enhance the position tracking performance over wide range of varying input. For precise approximation, the fuzzy PID controller was realized using the linear reasoning method, a type of product-sum-gravity method. The proposed controllers were compared with conventional PID controller without fuzzy gain tuning and was proved to have better performance in the experiment.

Speech Dereverberation using Improved Linear Prediction Residual (개선된 선형예측 잔여를 이용한 음성의 잔향음 제거)

  • Park, Chan-Sub;Kim, Ki-Man;Kang, Suk-Youb
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.11 no.10
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    • pp.1845-1851
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    • 2007
  • Background noise and room reverberation are two causes of degradation in speech in listening situations. Many algorithms developed to enhance reverberant speech. In this paper we propose a dereverberation method for enhancement of speech using modified the linear prediction(LP) residual in reverberant room condition. The proposed dereberberation method based on the fact that the signification excitation of the vocal tract system takes place at the instant of glottal closure in voiced speech. Our method used delay information form each sensor, and we need reverberant signals from 3 sensors. We obtain a new LP residual signal using modified IP residual combination which derived form weighting of the LP residual and the Hilbert transform of LP residual. The nature of the coherently added Hilbert envelop has several large amplitude spikes because of the effects of noise and reverberation. This residual of the clean speech is used to excite the time-varying all-pole filter to obtain the enhanced speech. We achieved simulation of proposed algorithm for performance analysis in reverberation environment. The proposed algorithm improves substantially the quality of reverberant speech.