• 한국광학회지
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• 제11권4호
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• pp.294-298
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• 2000

반도체레이저로 단면 여기시킨 Nd:VAP 레이저의 내부공진기 제2고조파 출력특성을 조사하였다. 유도방출 단면적과 형광수명의 곱이 커 낮은 발진문턱 특성을 갖는 Nd:S-VAP 매질은 컴팩트한 마이크로칩 레이저에 적합하다. 내부공진기를 이용한 제2고조파 발진문턱에너지가 81 uJ로 측정되어 쉽게 발진됨을 확인하였다. 여기에너지 $2\mu\textrm{J}$에서 제2고조파 에너지 $126\mu\textrm{J}$을 얻었고, 내부공진기 제2고조파의 출력을 계산하여 이론적인 해석 근거를 제시하였다. Q-스위치된 제2고조파 출력은 펄스폭 26ns에 펄스당 에너지 $15\mu\textrm{J}$로 저출력에서도 시.공간적으로 깨끗한 펄스를 얻었으며, $M^2$도 1.47로 우수한 빔 특성을 나타내었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권3호
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• pp.392-403
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• 2013

For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave's directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.719-724
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• 2001

The study on reducing vehicle noise and vibration has gained much attention to ensure the comfortability as well as the safety. These days. in this paper, we applied Statistical Energy Analysis(SEA) to characterize the tire assembly, which is useful analytical tool for mid- and high-frequency range. First, the SEA tire model was developed by dividing the tire and the wheel into several subsystems. The material properties were estimated experimentally. Finally. the SEA model was validated by comparing the estimated and the measured. In addition, we investigated the energy level and the energy transfering paths through the tire assembly in different frequency region.

• Smart Structures and Systems
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• 제3권3호
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• pp.263-280
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• 2007

In this paper, an improved GA-based damage detection algorithm using a set of combined modal features is proposed. Firstly, a new GA-based damage detection algorithm is formulated for beam-type structures. A schematic of the GA-based damage detection algorithm is designed and objective functions using several modal features are selected for the algorithm. Secondly, experimental modal tests are performed on free-free beams. Modal features such as natural frequency, mode shape, and modal strain energy are experimentally measured before and after damage in the test beams. Finally, damage detection exercises are performed on the test beam to evaluate the feasibility of the proposed method. Experimental results show that the damage detection is the most accurate when frequency changes combined with modal strain-energy changes are used as the modal features for the proposed method.

• 한국태양에너지학회 논문집
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• 제30권1호
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• pp.7-12
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• 2010

As many grid-connected photovoltaic power conditioning systems (PVPCS)are installed in many residential areas simultaneously, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. In this paper, active frequency drift (AFD) method, one of the anti-islanding methods which is analyzed by current magnitude compensation and calculation of the fundamental component. Both harmonic component and RMS value of the output current for THD analysis are provided and verified by simulation.

• Structural Engineering and Mechanics
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• 제86권2호
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• pp.237-247
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• 2023

Fourier series-based models in the time domain are frequently established to represent individual bouncing loads, which neglects the stochastic property of human bouncing activity. A power spectral density (PSD) model in the frequency domain for individual bouncing loads is developed herein. An experiment was conducted on individual bouncing loads, resulting in 957 records linked to form long samples to achieve a fine frequency resolution. The Welch method was applied to the linked samples to obtain the experimental PSD, which was normalized by the bouncing frequency and the harmonic order. The energy, energy distribution center, and energy distribution shape of the experimental PSD were investigated to establish the PSD model. The proposed model was used to analyze structural vibration responses using stochastic vibration theory, which was verified via field measurements. It is believed that this framework can evaluate the vibration capacity of structures excited by bouncing crowds, such as concert halls and grandstands.

• Journal of Mechanical Science and Technology
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• 제15권4호
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• pp.482-491
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• 2001

An experimental study has been carried out to investigate an I-type sparger-performance in view of pressure oscillation and thermal mixing in a pool. Its pitch-to-hole diameter, P/D, varies from 2 to 5. The test conditions are restricted to the condensation oscillation regime. In the present study, two different hole patterns, staggered and parallel types, are employed under various test conditions. The amplitude of the pressure pulse shows a peak for pool temperatures of 45∼85$\^{C}$, which depends on P/D and the steam mass flux. The effect of hole pattern on the pressure load is smaller than that of P/D. The dominant frequency increases with the subcooling temperature of pool water and P/D. A correlation for the dominant frequency is proposed in terms of the pitch-to-hole diameter ratio and other dimensionless thermal hydraulic parameters.

• 한국전기전자재료학회논문지
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• 제23권5호
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• pp.424-428
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• 2010

This paper describes the design and analysis of AlN piezoelectric micro energy harvester. The harvester was designed to convert ambient vibration energy to electrical power as a AlN piezoelectric material compatible with CMOS (complementary metal oxide semiconductor) process. To cut off the leakage current, AlN was used as the insulating layer. Also, Mo was used for the excellent c-axis crystal growth as the bottom electrode. The AlN harvester which it has the low operating frequency was designed by using the ANSYS FEA (finite element analysis). From the simulation results, the resonance frequency of designed model is about 360 Hz and analyzed the bending mode, displacement and expectation output.

• 한국소음진동공학회논문집
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• 제12권4호
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• pp.272-279
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• 2002

The time-dependent frequency and energy of free vibration of the spagetti problem, that is the axially moving continuum with time-varying length, are investigated. Exact expressions for the natural frequency and time-varying vibration energy are derived by dealing with traveling waves. The vibration period increases with increasing length, but the free vibration energy decreases. When the string undergoes retraction, the vibration energy increases with time. The free response of the time-varying string is represented by superposing two traveling waves.

• 한국통신학회논문지
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• 제22권11호
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• pp.2470-2476
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• 1997

We propose a simle scheme for detecting tone signals narrowly spaced in the frequency by employing a nonlinear device called Teager's energy tracker. When the input signal is a tone signal, the output of Teager's energy tracker is proportional to the energy and tone frequency of the input signal. When the envelope of the input tone is varying, this tracker can also track the energy of the envelope. By employing Teager's algorithm as a preprocessor, the detector for narrowly spaced tone signals can be implemented without the use of sharp notch filters. As an example, the proposed detector is applied to distinguishing ITU-T V.8 and V.25 tone signals. The detector perfodrmance is analyszed and is verified by computer simulation.