• Smart Structures and Systems
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• 제1권3호
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• pp.257-266
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• 2005

In Lamb wave detection of damages in smart structures, the excitation pulse is usually designed as a narrow band burst wave for the convenience of analysis and recognition. However, the wideband excitation can excite more modes in plate/shell structure and thus provides extra information for changes of the structure. This paper presents a method that can extract information in wideband Lamb wave signals. By transforming the detected signals into various sub-frequency band, the measured signal can be converted to its equivalences of narrow band excitations, therefore, the information in different frequency bands can be acquired from a single test and in the same time the complicity of wideband signal can be simplified. Some test results are provided to verify this method.

• 한국자동차공학회논문집
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• 제12권1호
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• pp.209-215
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• 2004

This paper presents the frequency range and an analysis method to find the dominant source of electro-magnetic wave which originates from a spark ignition in engine room. Applying the distributed constant equivalent circuit theory the radiation of probable electro-magnetic wave around an ignition plug and a high voltage cable is studied analytically. Experimental studies are also conducted by measuring the frequency spectrum to obtain the radiating characteristics of electro-magnetic wave. Results from both analytical and experimental studies confirm that an ignition plug and a high voltage cable are dominant sources of electro-magnetic wave and that the radiating frequency is ranged from 1.3[GHz] to 2[GHz] band.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1313-1315
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• 2002

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency inverter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AD filter. The high frequency inverter bridge switching at 20kHz is used to generate bipolar PWM pulse, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60Hz sine wave power output. In this paper, the control algorithm for synchronous current feedback control method and a maximum power point tracking (MPPT) method using DSP are described. And, the simulation and experimental results are shown to verify the validity of the proposed system.

• 전기학회논문지
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• 제57권11호
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• pp.2041-2046
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• 2008

A frequency-dependent slow-wave factor (SWF) and equivalent circuit model of transmission line with defected ground structures (DGS) is described. Once S-parameters of a DGS transmission line are given, the conventional frequency -independent equivalent circuit elements are extracted using 3dB cutoff and resonant frequencies (Fc and Fo) as the first step. Using the initial equivalent elements and simple transmission line theories, a frequency-dependent equivalent transmission line model is established through an analytical method, and finally the frequency dependent SWF is calculated. The proposed equivalent circuit model and SWF are frequency-dependent and more reliable because even small insertion loss within available passband is considered, while they have been independent of frequency.

• 대한예방한의학회지
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• 제4권1호
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• pp.152-162
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• 2000

The present condition of study on the wave-resonance for the bio-KI is observed. The results are as follows: 1. Tn the wave-resonant stand point, the tendency of studying on KI is showed in the several field all over the world. 2. Because it is originated radionics, the wave-resonant tools of MRA insistenting minute-magnetism-resonance-apparatus need the more severe data in the side of electric circuit. 3. The wave resonance apparatus according to the frequency occurance transmits low-frequency's vibration ratio to the electric stimulating aspect. 4. The wave-water is considered on the application of wave-resonance transcription on the water, and needs the comprehension of torsion-field level.

• 한국가시화정보학회지
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• 제18권3호
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• pp.14-22
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• 2020

An experiment, in the cases that satisfies deep water condition, has been performed to observe the strongly nonlinear sloshing flow in a rectangular tank. A variety of parametric study on oscillating frequency and amplitude was conducted and we found that two types of wave motions, sloshing wave and Faraday wave, could be persisting simultaneously even in horizontal sloshing problem. Moreover, it is observed both of symmetric and skewed symmetric Faraday wave exist. A comprehensive explanation is given to the generation mechanism of those waves and how to interact among them.

• 한국해양공학회지
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• 제12권2호통권28호
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• pp.33-42
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• 1998

In the presence of incident waves with different frequencies, the second order sum and difference frequency waves due to the nonlinearity of the incident waves come into existence. Although the magnitudes of the forces produced on a Tension Leg Platform(TLP) by these nonlinear waves are small, they act on the TLP at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency wave loads produced close to the natural frequencies of TLPs often give greater contributions to high and low frequency resonant responses. The second order wave exciting forces and moments have been obtained by the method based on direct integration of pressure acting on the submerged surface of a TLP. The components of the second order forces which depend on first order quantities have been evaluated using the three dimensional source distribution method. The numerical results of time domain analysis for the nonlinear wave exciting forces in regular waves are compared with the numerical ones of frequency domain analysis. The results of comparison confirmed the validity of the proposed approach.

• 한국인터넷방송통신학회논문지
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• 제13권2호
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• pp.121-125
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• 2013

무배전기식 불꽃 점화 시스템의 스파크 플러그 케이블에서 발생되는 전자파에 대한 분석이다. 무배전기식 불꽃 점화 시스템인 경우에는 점화코일이 고주파 발생원이고 스파크 플러그 케이블과 스파크 플러그는 전자파를 복사하는 안테나로 동작 할 수 있다. 스파크플러그 케이블과 스파크 플러그의 길이를 측정하여 ${\lambda}/4$ 수직 접지 안테나로 동작하는 안테나로 고려하여 HFSS를 이용하여 공진주파수를 계산하였다. 계산된 공진주파수와 엔진룸에서 복사되는 전자파의 전력 스펙트럼 분포를 측정한 결과를 분석하여 무배전기식 불꽂 점화 시스템이 특정한 주파수 대역에서 고주파 에너지를 복사한다는 것을 알 수 있다.

• Geomechanics and Engineering
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• 제28권1호
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• pp.25-33
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• 2022

The energy transferred on drill rods by dynamic impact mainly determines the penetration depth for in-situ tests. In this study, the dynamic response and transferred energy of drill rods are determined from the frequency of the stress waves. AW-type drill rods of lengths 1 to 3 m are prepared, and strain gauges and an accelerometer are installed at the head and tip of the connected rods. The drill rods are hung on strings, allowing free vibration, and then impacted by a pendulum hammer with fixed potential energy. Increasing the rod length L increases the wave roundtrip time (2L/c, where c is the wave velocity), and hence the transferred energy at the rod head. At the rod tip, the first velocity peak is higher than the first force peak because a large and tensile stress wave is reflected, and the transferred energy converges to zero. The resonant frequency increases with rod length in the waveforms measured by the strain gauges, and fluctuates in the waveforms measured by the accelerometer. In addition, the dynamic response and transferred energy are perturbed when the cutoff frequency is lower than 2 kHz. This study implies that the resonant frequency should be considered for the interpretation of transferred energy on drill rods.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1303-1313
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• 2002

Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Wavier-Stokes code. The Wavier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.