• Journal of Energy Engineering
• /
• v.10 no.4
• /
• pp.335-341
• /
• 2001

Pressure pulsations generated by the blade-tongue interaction induce vibration of the piping systems and the structure connected to pumps, resulting in the severe noise and fatigue fracture. Experiments were made on the natural frequencies of liquid columns in piping systems with a single suction, single stage, centrifugal volute pump. Experimental results show that the natural frequencies of the liquid columns in the pump piping systems depend on the dimensions of the pipes and the impeller shapes, and are not affected substantially by the rate of discharge and the rotating speed of the pump.

• Journal of the Korean Institute of Telematics and Electronics T
• /
• v.36T no.1
• /
• pp.71-78
• /
• 1999

This paper presents a new type of energy generative ER suspension system which does not require external power sources. This is accomplished by converting vibration energy(kinetic energy) into electrical energy. In order to undertake this, an appropriate size of the ER damper is manufactured by incorporation a mechanism which changes the linear motion of the ER damper to the rotary motion. This rotary motion is amplified by gears and activates a generator to produce the electrical energy. The efficiency of energy generation is evaluated and the level of damping force with generated power is also investigated. Then, the ER suspension system is applied to the quarter car model, and its vibration isolation is experimentally evaluated with respect to the piston speed.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.2
• /
• pp.63-70
• /
• 2014

Design sensitivity analysis and topology design optimization for a piezoelectric crystal resonator are developed. The piezoelectric crystal resonator is deformed mechanically when subjected to electric charge on the electrodes, or vice versa. The Mindlin plate theory with higher-order interpolations along thickness direction is employed for analyzing the thickness-shear vibrations of the crystal resonator. Thin electrode plates are masked on the top and bottom layers of the crystal plate in order to enforce to vibrate it or detect electric signals. Although the electrode is very thin, its weight and shape could change the performance of the resonators. Thus, the design variables are the bulk material densities corresponding to the mass of masking electrode plates. An optimization problem is formulated to find the optimal topology of electrodes, maximizing the thickness-shear contribution of strain energy at the desired motion and restricting the allowable volume and area of masking plates. The necessary design gradients for the thickness-shear frequency(eigenvalue) and the corresponding mode shape(eigenvector) are computed very efficiently and accurately using the analytical design sensitivity analysis method using the eigenvector expansion concept. Through some demonstrative numerical examples, the design sensitivity analysis method is verified to be very efficient and accurate by comparing with the finite difference method. It is also observed that the optimal electrode design yields an improved mode shape and thickness-shear energy.

• Proceedings of the Optical Society of Korea Conference
• /
• 2002.07a
• /
• pp.98-99
• /
• 2002

대표적인 II-VI족 극성 반도체 결정인 ZnTe[001]와 ZnCdTe MQW에서 시료의 에너지 띠보다 낮은 에너지의 펨토초 티타늄 사파이어 레이저를 이용하여 결맞는 포논을 발생시키고 그 특성을 관찰하였다. 결맞는 포논의 신호는 그림1)과 같이 반사 및 투과형 전기 광학적 샘플링(Reflective/Transmissive Electro-Optic Sampling： REOS/TEOS)방법과 여기-탐사광 방법으로 시간 영역에서 측정하였다. (중략)

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.2
• /
• pp.131-143
• /
• 2013

Vibration condition monitoring of low-speed rotational slewing bearings is essential ever since it became necessary for a proper maintenance schedule that replaces the slewing bearings installed in massive machinery in the steel industry, among other applications. So far, acoustic emission(AE) is still the primary technique used for dealing with low-speed bearing cases. Few studies employed vibration analysis because the signal generated as a result of the impact between the rolling element and the natural defect spots at low rotational speeds is generally weak and sometimes buried in noise and other interference frequencies. In order to increase the impact energy, some researchers generate artificial defects with a predetermined length, width, and depth of crack on the inner or outer race surfaces. Consequently, the fault frequency of a particular fault is easy to identify. This paper presents the applications of empirical mode decomposition(EMD) and ensemble empirical mode decomposition(EEMD) for measuring vibration signals slewing bearings running at a low rotational speed of 15 rpm. The natural vibration damage data used in this paper are obtained from a Korean industrial company. In this study, EEMD is used to support and clarify the results of the fast Fourier transform(FFT) in identifying bearing fault frequencies.

• The Journal of the Acoustical Society of Korea
• /
• v.16 no.5
• /
• pp.36-42
• /
• 1997

This paper purposes the measurement method of vibration intensity in building structure which is a method of measuring the intensity and the flow of vibration energy. We derived basic theory and measuring theory for a simple beam, and comparison of the experimental results with calculated results. As a result, according to the calculated value from acceleration distribution and the measurement result from the method of vibration intensity under the condition except near field of measurement zone. The measured results, show that this method is useful for measuring the vibration energy flow in building structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.171-177
• /
• 1995

환경 보호와 연비 향상을 목표로 한 고출력 엔진과 초경량 차체의 차량을 설계하려는 최근의 차량 개발 추세는 진동과 소음의 문제를 더욱 악화시키느 요인이 되었다. 이에 반해 차량을 구입하는 고객은 보다 정숙한 주행 성능을 요구하고 있다. 이런 상황에서 커다란 설계의 변경이나 차체의 중량 증가없이도 ㅈ거용가능한 능동 제어 기술(Active Control Technique)은 차량의 진동, 소음문제에서 훌륭한 해결책의 하나로 등장하였다. 최근까지 능동 소음제어와 관련한 연구는 여러 분야에서 수행되었으며, 실제로 시작차량뿐만 아니라 양산차에 적용된 사례가 있다. P.A.Nelson등은 음향 공동내의 음향 에너지를 최소화시키는 소음 제어에 관한 이론, 컴퓨터 시뮬레이션 및 실험에 대하여 발표하였다. 또한 최근의 디지탈 신호 처리기(DSP, Digital Signal Processor)의 개발에 힘입어 해석의 검즈외에도 실제 차량에 적용한 사례도 있다. 로터스(LOTUS,영)는 다양한 시작차를 제작하여 그 효과를 검증하였으며, 닛산(Nissan, 일)은 양산차에 적용하여 판매하고 있는 실정이다. 본 논문에서는 능동 소음 제어 장치를 개발하여 승용차에 적용한 결과를 보이도록 한다.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1079-1080
• /
• 2008

본 논문에서는 Piezoelectric effect를 이용하여 인체의 움직임에 의한 진동 에너지를 전기적 에너지로 변환, 저장하고 이를 사용하여 온도 정보를 RF신호로 약 20 m 거리의 수신기로 전송할 수 있는 ubiquitous 네트워크용 센서 모듈을 설계.제작하고, 그 동작을 확인하였다. 또한 가장 빈번하게 신호를 보내기 위한 저장커패시터의 용량과 충전전압의 조합을 수식적으로 유도하였고 이 결과를 실험적으로 확인하였다.

• Journal of the Institute of Convergence Signal Processing
• /
• v.6 no.3
• /
• pp.143-147
• /
• 2005

Monitoring and diagnosis of the operating machines are very important for safety operation and maintenance in the industrial fields. These machines are most rotating machines and the diagnosis of the machines has been researched for long time. We can easily see the faulted signal of the rotating machines from the changes of the signals in frequency. The Linear Predictive Coding(LPC) is introduced for signal analysis in frequency domain. In this paper, we propose fault detection and diagnosis method using the Linear Predictive Coding(LPC) and residual signal energy. We applied our method to the induction motors depending on various status of faulted condition and could obtain good results.

• The Journal of the Acoustical Society of Korea
• /
• v.33 no.1
• /
• pp.10-20
• /
• 2014

To study the water-entry impact noise, on-board experiment using a small launcher firing various objects was performed in the Yellow Sea. As the launcher fires a cylindrical object from the ship vertically, generated noise is measured with a hydrophone on the starboard of Chung-hae, Marine surveyor. Three types of cylindrical objects, which have noses of flat-faced, conical, and hemisphere, were used during the experiment. The measured noise exhibits a time-dependency which can be divided into three phases: (1) initial impact phase, (2) open cavity flow phase, (3) cavity collapse and bubble oscillation phase. In most cases, the waveform of bubble oscillation phase is dominant rather than that of initial impact phase. Pinch-off time, where a cavity begins to collapse, occurs at 0.18 ~ 0.2 second and the average lasting time of bubble was 0.9 ~ 1.3 second. The energy of water-entry impact noise is focused in the frequency region lower than 100 Hz, and the generated noise is influenced by the nose shapes, object mass, and launching velocity. As a result, energy spectral density on the bubble frequency is higher in the order of flat-faced, conical, hemisphere nose, and the increase of initial energy raises the energy spectral density on the bubble frequency in the cylinder body of same shape. Finally, we compare the measurements with the simulated signals and spectrum based on the bubble explosion physics, and obtain satisfactory agreements between them.