• Title/Summary/Keyword: 시변 동특성

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An Analysis of the Acoustical Source Characteristics in the Time-varying Fluid Machines (유체기계 덕트 내 시변 음원의 음향 특성에 관한 연구)

  • 장승호;이준신;이정권
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.2
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    • pp.104-112
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    • 2003
  • The in-duct acoustical sources of fluid machines are often characterized by the source impedance and strength using the linear time-invariant model. However, negative resistances, which are physically unreasonable, have been found throughout various measurements of the source properties in IC-engines and compressors. In this paper, the effects of the time-varying nature of fluid machines on the source characteristics are studied analytically. For this purpose, the simple fluid machine consisting of a reciprocating piston and an exhaust is considered as representing a typical periodic, time-varying system and the equivalent circuits are analyzed. Simulated measurements using the analytic solutions show that the time-varying nature in the actual sources is one of the main causes of the negative source resistances. It is also found that, for the small magnitude of the time-varying component, the source radiates large acoustic power if the piston operates at twice the natural frequency of the static system. or integral submultiples of that rate.

Temporal Variability of Acoustic Arrivals in the East Sea of Korea Using Tomographic Method (한국 동해에서 토모그래피용 신호를 이용한 음파 도달시간의 시변동성)

  • 오선택;나정열;오택환;박정수;나영남;김영규
    • The Journal of the Acoustical Society of Korea
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    • v.20 no.5
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    • pp.92-99
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    • 2001
  • To measure temporal variability of long- range transmission in northern part of the East Sea of Korea, low frequency acoustic sources were deployed on the continental shelf 0.4km south of Cape Shultz near the port of Vladivostok during October 1999. The transmissions of the phase modulated signals were recorded by VLA moored on the northern slope of Ulleung-do. The measured signals were processed for the acoustic arrivals and their variability in time. The temporal signal processing involves pulse compression of the phase-encoded signal, time spread and temporal coherence processing. Variability of the ocean sound speed field in time scales of short period seems to be dominated by random fluctuations caused by sound speed perturbation due to the vertical displacements associated with internal waves.

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The Simulator Design for the Analysis of Aircraft Longitudinal Dynamic Characteristics (항공기 세로 동특성 해석을 위한 시뮬레이터 설계)

  • Yoon, Sun-Ju
    • Journal of the Korea Computer Industry Society
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    • v.7 no.4
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    • pp.427-436
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    • 2006
  • State-space method for the analysis of the dynamic characteristics of a body motion is set up as mathematical tool for the solution of differential equation by computer. Representation of a system is described as a simple form of matrix calculation and unique form of model is available for the linear or nonlinear, time variant or time invariant, mono variable or multi variable system etc. For the analysis of state-space method a complicated vector calculation is required, but this analysis can be simplified with the specific functions of a software package. Recently as the Graphical User Interface softwares are well-developed, then it is very simplified to execute the simulation of the dynamic characteristics for the state-space model with the interactive graphics treatment. The purpose of this study is to developed the simulator for the educational analysis of the dynamic characteristics of body motion, and for the analysis of the longitudinal dynamic characteristics of an aircraft that is primarily to design the simulator for the analysis of the transient response of an aircraft longitudinal stability.

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Design of an OPtimal Controller for the Nonlinear Robot Manipulators with the Actuator Dynamics (조작기의 동특성을 고려한 비선형 로봇 매니퓰레이터의 최적 제어기 설계)

  • 김학범;이양범
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.18 no.9
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    • pp.1376-1385
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    • 1993
  • This paper presents a new dynamic model which is represented by the second order differenatial equation and itcludes the robot arm dynamics as well as the actuator dynamics. The model exhibits excellent performance in the steady state and transient response. In addition the time varing nonlinear and coupled dynamic system has been linearized and decoupled by using nonlinear feedback and linearization method. In this case a pole assignment law is used to improve stability, and the optimal control altorithm is applied to the error equation to minimize the path error. In applying the proposed algorithm to the three joint manipulator with actuators, we obtained very encouraging results.

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Doppler Frequency Estimation for Time-Varying Underwater Acoustic Communication Channel (시변 수중음향통신 채널을 위한 도플러 주파수 추정)

  • Hwang, Chan-Ho;Kim, Ki-Man
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.1
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    • pp.187-192
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    • 2015
  • Underwater acoustic communication channels have very complex channel characteristics caused by time-varying sea surface, submarine topography, sound speed, and geometry between transmitter and receiver. Especially, the channel has time-variance and doppler effect due to wind and sea current. We have to recognize the channel state and apply it to communication technique for increasing transmission efficiency in the underwater acoustic channel. In this paper, we present the frame recursive modulation and demodulation method using ambiguity function and autocorrelation function to estimate the doppler frequency. Furthermore, we conducted the simulation and sea experiment to evaluate the performance of the proposed method. When the channel coding technique was not used, the bit error rate performance of the proposed method was improved about 32 % compared with conventional method.

Control of Time-varying and Nonstationary Stochastic Systems using a Neural Network Controller and Dynamic Bayesian Network Modeling (신경회로망 제어기와 동적 베이시안 네트워크를 이용한 시변 및 비정치 확률시스템의 제어)

  • Cho, Hyun-Cheol;Lee, Jin-Woo;Lee, Young-Jin;Lee, Kwon-Soon
    • Journal of the Korean Institute of Intelligent Systems
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    • v.17 no.7
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    • pp.930-938
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    • 2007
  • Captions which appear in images include information that relates to the images. In order to obtain the information carried by captions, the methods for text extraction from images have been developed. However, most existing methods can be applied to captions with fixed height of stroke's width. We propose a method which can be applied to various caption size. Our method is based on connected components. And then the edge pixels are detected and grouped into connected components. We analyze the properties of connected components and build a neural network which discriminates connected components which include captions from ones which do not. Experimental data is collected from broadcast programs such as news, documentaries, and show programs which include various height caption. Experimental result is evaluated by two criteria : recall and precision. Recall is the ratio of the identified captions in all the captions in images and the precision is the ratio of the captions in the objects identified as captions. The experiment shows that the proposed method can efficiently extract captions various in size.

The Experimental Verification of Adaptive Equalizers with Phase Estimator in the East Sea (동해 연근해에서 위상 추정기를 갖는 적응형 등화기의 실험적 성능 검증)

  • Kim, Hyeon-Su;Choi, Dong-Hyun;Seo, Jong-Pil;Chung, Jae-Hak;Kim, Seong-Il
    • The Journal of the Acoustical Society of Korea
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    • v.29 no.4
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    • pp.229-236
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    • 2010
  • Phase coherent modulation techniques in underwater acoustic channel can improve bandwidth efficiency and data reliability, but they are made difficult by time-varying intersymbol interference. This paper proposes an adaptive equalizer combined with phase estimator which compensates distortions caused by time-varying multipath and phase variation. The experiment in the East sea demonstrates phase coherent signals are distorted by time-varying multipath propagation and the proposed scheme equalizes them. Bit error rate of BPSK and QPSK are 0.0078 and 0.0376 at 300 meter horizontal distance and 0.0146 and 0.0293 at 1000 meter respectively.

Adaptive Chaos Control of Time-Varying Permanent-Magnet Synchronous Motors (시변 영구자석형 동기 전동기의 적응형 카오스 제어)

  • Jeong, Sang-Chul;Cho, Hyun-Cheol;Lee, Hyung-Ki
    • Journal of the Institute of Convergence Signal Processing
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    • v.9 no.1
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    • pp.89-97
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    • 2008
  • Chaotic behavior in motor systems is undesired dynamics in real-time implementation since the speed is oscillated in a wide range and the torque is changed by a random manner. We present an adaptive control approach for time-varying permanent-magnet synchronous motors (PMSM) with chaotic phenomenon. We consider that its parameters are changed randomly within certain bounds. First, a nonlinear system model of a PMSM is transformed to derive a nominal linear control strategy. Then, an auxiliary control for compensating real-time control error occurred by system perturbation due to parameter change is designed by using Lyapunov stability theory. Numerical simulation is accomplished for evaluating its efficiency and reliability comparing with the traditional control method. Additionally, we test our control method in real-time motor experiment including a PSoC based drive system to demonstrate its practical applicability.

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Tracking Performance Improvement of Discrete Signal using Neural Networks and Self Tuning Controller (신경망모델과 자기 동조 제어기를 이용한 이산신호의 추적 성능 개선)

  • 최수열;정연만;최부귀
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.2 no.1
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    • pp.19-26
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    • 1998
  • In this paper, Simulation result was studied by PID controller in series to the estblised neural networks controller. Neural network model is composed of two layers to evaluate tracking performance improvement. The regular dynamics was also studied for the expected error to be minimized by using Widrow-Hoff delta rule. As a result of the study, We identified that tracking performance improvement was developed more in case of connecting PID than conventional neural network controller and that tracking plant parameter in 251 sample was approached rapidly in case of time varying.

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Robust frame synchronization algorithm in time-varying underwater acoustic communication channel (수중 음향통신에서 채널 시변동성에 강인한 프레임 동기 알고리즘)

  • Ko, Seokjun;Kim, Wan-Jin
    • The Journal of the Acoustical Society of Korea
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    • v.39 no.1
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    • pp.8-15
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    • 2020
  • In this paper, we propose a frame synchronization algorithm for robust to the combined effects of large Doppler fluctuations and extended, time-varying multipath in the underwater acoustic communication. From the algorithm, we can recover a high timing error which is occurred from an acoustic propagation delay and uncertainty of oscillator between transmitter and receiver. In order to verify the performance of the synchronization algorithm, the lake trial results are used. The lake experiments are performed in a Gyeongcheonho located in Mungyeong-si, Gyeongsangbuk-do. We can see that the start position of frame is adjusted after the frame synchronization while the receiver moving.