• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.48-49
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• 2003

원자가 전자기파와 상호작용할 때 원자 전이의 결맞음 여기 (coherent excitation of atomic transitions)는 일반적인 현상이다. 이 상호작용은 라비 진동 (Rabi oscillation), 자유 유도 감쇠 (free induction decay), 단열 밀도 이송 (adiabatic population transfer), 결맞음 과도 (coherent transients； CT) 등 다양한 결과를 가져온다. 특히, 전자기파의 주파수가 원자의 공진주파수를 중심으로 스윕될 때 결맞음 과도 현상 (coherent transient phenomenon)은 밀도 반전 (population reversal)을 유도하기도 한다. (중략)

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.12
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• pp.874-880
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• 2015

This paper presents the vibration analysis of a deploying beam with spin when the beam has a time-dependent spinning speed. In the previous studies for the deploying beams with spin, the spinning speed was time-independent. However, it is more reasonable to consider the time-dependent spinning speed. The present study introduces the time-dependent spinning speed in the modeling. The Euler-Bernoulli beam theory and von Karman nonlinear strain theory are used together to derive the equations of motion. After the equations of motion are transformed into the weak forms, the weak forms are discretized. The natural frequency and dynamic response are obtained. The effect of the time-dependent spinning speed on the dynamic response is studied.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.73-76
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• 2004

에밀레종은 서기 771년도(신라 혜공왕 7년)에 완성한 것으로 성덕대왕의 공적을 기리기 위해 34년간 주조(높이 3.663m, 최대지름 2.227 m, 무게 18.900, 두께 $7.7\~21.5m$)한 에밀레종의 과학성은 놀랄만하다. 외형도 미려하지만 종소리는 천, 지, 인을 뒤흔드는 신비감을 갖추고 있다. 에밀레 종소리는 끊어질 듯 이어지는 소리, 애끓는 소리, 심금을 울리는 소리 등의 특징을 갖는데 끊어질듯 이어지는 소리는 맥놀이 현상으로 나타난다. 지금까지 에밀레 종소리 규명에 대한 많은 연구가 있었다. 본 연구에서는 스펙트럼 분석을 통하여 에밀레 종소리에서 나타난 기본 주파수 64Hz, 168Hz, 360Hz, 480Hz 특성과 중년 남성의 목소리를 음성 분석기의 분석한 파형, 스펙트럼, 스펙트로그램으로 상호간의 비교 분석을 통하여 유사성을 규명하였다.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.68-75
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• 1997

In this study, to investigate vibration response of piping systems due to pulsation flow, a transfer matrix method is presented. Fluid-pipe interaction is formulated using wave equation for flow velocity and pressure, which depends on position and time. From the wave equation, transfer matrix is obtained. The dynamic responses of piping systems induced by pulsation flow appeared to depend upon fluctuation fluid velocity and pressure occurrnece from pulsation, and beating phenomena were observed near the resonance. Consequently, the dynamic behaviors of piping systems appeared to the same as response characteristics of the inside flow pattern of the pipe, and are determined by the inside fluid flow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.836-841
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• 2002

The nonlinear vibration of moving viscoelastic belts excited by the eccentricity of pulleys is investigated through experimental and analytical methods. Laboratory measurements demonstrate the nonlinearities in the responses of the belt, particularly in the resonance region and with the variation of tension. The measurements of the belt motion were made using a noncontact laser sensor Jump and hysteresis phenomenon are observed experimentally and are studied with a model which considers the nonlinear relation of belt stretch. An ordinary differential equation is derived as a working form of the belt equation of motion. Numerical results show good agreements with the experimental observations, which demonstrates the nonlinearity of viscoelastic moving belts

• The Journal of the Acoustical Society of Korea
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• v.30 no.5
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• pp.249-254
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• 2011

Inquiring activities on the acoustic phenomena have been carried out by using a sound card installed in a personal computer. A sound card is cheaper and more accessible to the students than the precision equipment such as a function generator or an oscilloscope. The students record the sounds from various acoustic phenomena to the sound card. Then they analyze the frequency spectrums of that sounds by using a program. Inquired phenomena include beat by two tuning forks, sound from Rijke tube, pouring sound, breaking of a wine glass and pop-up sound of a wine bottle. Through these activities students perform quantitative analysis of various phenomena due to superposition, resonance and standing wave.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.91-92
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• 2011

Beat is a phenomenon, where the magnitudes and frequencies of the voltage and the current fluctuate. This paper describes a quantitative analysis of the beat phenomenon of a wind farm using the envelope of a current during intertie/grid fault conditions. In this paper, the ratio of the crest to the trough of the envelope curve and the time interval between adjacent troughs are defined and used to evaluate the beat phenomenon quantitatively. Beat phenomena under various fault and wind conditions are analyzed. The proposed quantitative analysis seems simple but effective in the more understanding of beat phenomenon of a wind farm, and thus can be used as a basis for operation and/or protection of an intertie.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.82-89
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• 2014

This paper discusses the methods for reducing the sampling time quantization errors of the body dither type ring laser gyroscope. A ring laser gyroscope has the angle quantization error which is generated by the frequency counting method of the laser beat signal and sampling time quantization error which is generated by the demodulation method for eliminating the body dithering in which the sampling periods are fitted to the dither periods. Generally, because the dither periods are longer than the calculation periods of the inertial navigation system, vehicle navigation errors are produced by long time attitude update missing during the vehicle move with a high dynamical motion. In this paper, the double demodulation method is proposed for reducing the sampling time quantization error and its effects under the dynamic situation are confirmed by simulation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.463-470
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• 2013

In this paper, 2D simple analyses were performed in order to predict the large torsional oscillations in a suspension bridge based on Makenna and Tuama model(2001). The existing model(Makenna and Tuama, 2001) has shown unrealistic results as the wind speed increases and frequency decreases. Furthermore, resonance could not be simulated by the existing model. Therefore, in this study, new model was proposed with a consideration of the torsional resistance. The vertical and rotational behaviors of the deck in the suspension bridge were analyzed. Analysis results showed that at first vertical oscillations were observed and it was gradually transformed to the rotation oscillations. With the consideration of the torsional resistance, it was shown that vertical behavior were stabilized as time passed. However, the rotational behavior was not stabilized and was kept until the end of analysis. Beat periods decreased while the wind speed increased. The resonance of the rotational mode was dependent to the rotational resistance. Obtained results could be applied for the design of the suspension bridge under the wind load.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.275-282
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• 2009

Generally, the sinusoidal cavity dither is adopted to ring laser gyroscope for eliminating the lock-in which is non-linear effect at the small rotation input. Despite this method, there are some remained errors which are generated at the dither turnaround, and those errors produce random walk which is a general character of a ring laser gyroscope. As one of the numerous research results for compensating these errors, there is a special lock-in compensation method which is the method of error estimation and compensation by comparing the beat signal periods of before and after the dither turnarounds. In this paper, by ring laser gyroscope modeling and numerical analysis, we verified the theoretical validity and confirmed the effectiveness of this method in expectation of the possible beat signal measurement time resolution. As a result, we confirmed the random walk decreases from a-half to a-third by this lock-in compensation method. So, it is expected to be a remarkable method for reducing the INS alignment time.