• 소음진동
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• 제11권3호
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• pp.428-436
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• 2001

The rotating inner cylinder executes a periodic translational motion in concentric annulus while the outer one is stationary. In the study of flow-induced vibrations and relaxed instabilities, it is of interest to evaluate the fluid-dynamic forces acting on the rotating inner cylinder. In the present work, the governing equations for the confined flow are expressed as Navier-Stokes equations, including the steady and unsteady terms. The fluid parameters for steady flow generated by the rotating cylinder are determined analytically while the unsteady ones by the oscillatory motion are evaluates by a numerical method based on the spectral collocation method. In order to validate the numerical approach, the numerical results are compared wish the analytical ones given by existing theories, for simple cases where the both approaches are applicable. Good agreement was found between the results. It is found the effects of the Reynolds number, defined by rotating velocity, on the fluid-dynamic forces are important for the case of relatively low oscillatory Reynolds number, defined by oscillatory frequency : j.e., in case of $Re_\omega\gg Re_S$.

• 대한전기학회논문지:전력기술부문A
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• 제55권8호
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• pp.322-328
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• 2006

In this paper, The impulse un-tripping characteristics and the electro magnetic compatibility characteristics are compared with each other. The performance of impulse un-tripping test exists at domestic standard (KSC 4613). However test items are insufficient because the more test items such as EMC exist at international standard (IEC). Also, Electric Appliances Safety Certificate has taken the certificate test since July 2004 in Korea but did not confirm the EMC performance for RCCBs made in Korea. Thus, in this paper, We experiment with Oscillatory waves immunity test and the 7 EMC tests for 32 RCCBs of 4 types (mini, home standard, plug, outlet) for 16 brands according to IEC standard 61009-1 and 61008-1. As a result, 24 RCCBs proved to be poor for surge immunity test. However the RCCBs operating incorrectly for surge immunity test operate correctly for oscillatory waves immunity test. Thus, the correlation between oscillatory waves immunity test and EMC test is little and standard for compatibility of combination surge at IEC 61000-4-5 should be added to KS standard as soon as possible.

• 제어로봇시스템학회논문지
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• 제19권4호
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• pp.299-305
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• 2013

The complexity and severe nonlinearity of multi-machine power systems make it difficult to design a control input for voltage regulation using modern control theory. This paper presents a model-based PID control scheme for the regulation of the bus voltage to a desired value. To this end, a fourth-order linear system is constructed using input and output data obtained using the TSAT (Transient Security Assessment Tool); the input is assumed to be applied to the grid through the STATCOM (STATic synchronous COMpensator) and the output from the grid is a bus voltage. On the basis of the model, it is identified as to which open-loop poles of the system make the response to a step input oscillatory. To reduce this oscillatory response effectively, a model-based PID control is designed in such a way that the oscillatory poles are no longer problematic in the closed loop. Simulation results show that the proposed PID control dampens the response effectively.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권7호
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• pp.370-378
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• 2002

As resent trends in structural construction have been to build taller and larger structures than any time in the past, they have had high flexibility and low damping that can cause large vibration response under severe environmental loading such as earthquakes, winds, and mechanical excitations. The damper with mass and spring is one approach to safeguarding the structure against excessive vibrations. In this paper, the lumped electrical circuit approach of mass/spring system is used to model the mechanical aspects according to the frequency. Therefore, the mass/spring system can be dealt with here and linked with the equivalent circuit of electric linear oscillatory actuator(LOA). Analysis models are two types of vibration control system, active mass damper(AMD) and hybrid mass damper(HMD). AMD consists of the moving coil LOA with mass only The LOA of HMD with mass and spring is composed of the fixed coil and the movable permanent magnet(PM) field part. The PM field part composed magnet modules and iron coke, is the damper marts itself. We Present the motional resistance and reactance of mass/spring system and the system impedance of AMD and HMD according to the frequency.

• 한국지능시스템학회논문지
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• 제16권1호
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• pp.24-29
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• 2006

연산기능을 갖는 새로운 진동성 신경회로를 설계하여 $0.5{\mu}m$ CMOS 공정으로 칩 제작을 하였다. 제안하는 진동성 신경회로는 흥분성 시냅스를 가진 3개의 신경진동자와 억제성 시냅스를 가진 1개의 신경진동자로 이루어진다. 사용된 진동자는 가변 부성저항과 트랜스콘덕터를 이용하여 설계하였다. 진동자의 입력단으로 사용되는 가변 부성저항은 가우시안 분포의 전류전압 특성을 지니는 범프 회로를 이용하여 구현하였다. 뉴럴 회로의 SPICE 모의실험결과 간단한 연산기능을 확인하였다. 제작된 칩을 ${\pm}$ 2.5 V 의 전원전압 조건에서 측정하였고 이를 모의실험결과와 비교 분석하였다.

• 한국유체기계학회 논문집
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• 제4권4호
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• pp.37-42
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• 2001

In the present study, flow characteristics of turbulent oscillatory flow in an oscillator connected to square-sectional $180^{\circ}$ curved duct are investigated experimentally. In order to investigate wall shear stress and pressure distributions, the experimental studies for air flows we conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisitions and the processing system. The wall shear stress at bend angle of the $150^{\circ}$ and pressure distribution of the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) by $10^{\circ}$ intervals of the duct are measured. The results obtained from the experiment are summarized as follows : wall shear stress values in the inner wall we larger than those in an outer wall, except for the phase angle (${\omega}t/{\pi}/6$) of 3, because of the intensity of secondary flow. The pressure distributions are the largest in accelerating and decelerating regions at the bend angle(${\phi}$) of $90^{\circ}$ and pressure difference of inner and outer walls is the largest before and after the ${\phi}=90^{\circ}$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.294-298
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• 2003

The complex, unsteady, self-sustained pressure oscillations induced by supersonic flow past a rectangular cavity is investigated using numerical simulations. The present numerical study is performed using a parallel, multiblock solver for the two-dimensional, compressible Navier­Stokes equations. Open cavities with length-to-depth (L / D) ratio in the range 0.5 - 3.3 are considered. This paper sheds light on the cavity physics, cavity oscillatory mechanism, and the organisation of vortical structures inside the cavity. The vortex shedding phenomenon, the shear layer impingement event at the aft wall and the movement of the acoustic/compression wave within the cavity are well predicted. The vortical structures· and the source of the acoustic disturbances are found to be located near the aft wall of the cavity. With the increase in the cavity length, strong recompression of the flow near the aft wall leading to a sudden jump in the cavity form drag is observed. The estimated cavity tones are in good agreement with the available semi­empirical relation. Multiple peaks are noticed in deep and long cavities. For the present free­stream Mach number 1.71, it is observed that around L/D=2.0, the cavity oscillatory mechanism changes from the transverse to longitudinal oscillatory mode. The effects of this transition on various fluid dynamics and acoustic properties are also discussed.

• 디지털산업정보학회논문지
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• 제11권1호
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• pp.171-182
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• 2015

The general wavelet transform has profitable property in non-stationary signal analysis specially. The tunable Q-factor wavelet transform is a fully-discrete wavelet transform for which the Q-factor Q and the asymptotic redundancy r, of the transform are easily and independently specified. In particular, the specified parameters Q and r can be real-valued. Therefore, by tuning Q, the oscillatory behavior of the wavelet can be chosen to match the oscillatory behavior of the signal of interest, so as to enhance the sparsity of a sparse signal representation. The TQWT is well suited to fast algorithms for sparsity-based inverse problems because it is a Parseval frame, easily invertible, and can be efficiently implemented. The transform is based on a real valued scaling factor and is implemented using a perfect reconstruction over-sampled filter bank with real-valued sampling factors. The transform is parameterized by its Q-factor and its over-sampling rate, with modest over-sampling rates being sufficient for the analysis/synthesis functions to be well localized. This paper describes filter design of 2D discrete-time wavelet transform for which the Q-factor is easily specified. With the advantage of this transform, perfect reconstruction filter design and implementation for performance improvement are focused in this paper. Hence, the 2D transform can be tuned according to the oscillatory behavior of the image signal to which it is applied. Therefore, application for performance improvement in multimedia communication field was evaluated.

• 디지털산업정보학회논문지
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• 제10권3호
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• pp.237-247
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• 2014

This paper describes a 2D discrete-time wavelet transform for which the Q-factor is easily specified. Hence, the transform can be tuned according to the oscillatory behavior of the image signal to which it is applied. The tunable Q-factor wavelet transform (TQWT) is a fully-discrete wavelet transform for which the Q-factor, Q, of the underlying wavelet and the asymptotic redundancy (over-sampling rate), r, of the transform are easily and independently specified. In particular, the specified parameters Q and r can be real-valued. Therefore, by tuning Q, the oscillatory behavior of the wavelet can be chosen to match the oscillatory behavior of the signal of interest, so as to enhance the sparsity of a sparse signal representation. The TQWT is well suited to fast algorithms for sparsity-based inverse problems because it is a Parseval frame, easily invertible, and can be efficiently implemented. The TQWT can also be used as an easily-invertible discrete approximation of the continuous wavelet transform. The transform is based on a real valued scaling factor (dilation-factor) and is implemented using a perfect reconstruction over-sampled filter bank with real-valued sampling factors. The transform is parameterized by its Q-factor and its oversampling rate (redundancy), with modest oversampling rates (e. g. 3-4 times overcomplete) being sufficient for the analysis/synthesis functions to be well localized. Therefore, This method services good performance in image processing fields.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권11호
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• pp.533-539
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• 2005

In the previous work, we performed the analysis of a tubular type moving-magnet linear oscillatory actuator (LOA) with cylindrical Halbach array by using 2-d analytical formulas and confirmed validity of analytical results by comparison of those with both finite element (FE) computation and experimental results. This paper deals with the dynamic characteristic analysis of the moving-magnet LOA with cylindrical Halbach array. Control parameters such as the thrust constant, the back-emf constant, resistance and inductance are obtained from both analytical and experimental results. And then, the dynamic simulation algorithm is established by the state and output equation obtained from voltage and motion equation. Finally, for various values of frequency, the dynamic simulation and experimental results for the characteristics of the voltage, current and displacement of moving-magnet LOA are presented. The simulation results are validated extensively by experiments. The experimental and simulation results for the variation of stroke according to control voltage are also presented for various values of frequency.