• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.312-316
• /
• 2002

Recently, mixers are being widely used in the water purification plant in order to increase the filtration efficiency. It has been found that a severe vibration was being felt on a upper structure of a mixer facility during steady state operation. The cause of the excessive vibration of the structure to which the mixer's shaft is supported has been evaluated through modal analysis on the shaft and vibration measurements during operation. The fundamental natural frequency of the mixer's shaft is found to be around 1.8 Hz and the main vibratory frequency around 30 Hz. It has been tuned out that the main vibratory frequency, 30 Hz is coincident with the fundamental holding frequency of the upper structure, and that the acceleration signal of the upper structure and the displacement signal of the mixer's shaft showed highly coherent to each other. Accordingly, it reveals that the main cause of the excessive vibration is due not to the mixer's vibration but to the natural frequency of the upper structure excited by flow turbulence.

• Advances in aircraft and spacecraft science
• /
• 제4권5호
• /
• pp.543-553
• /
• 2017

Vibration is a source of performance degradation in all optical imaging systems. Performance of high resolution remote sensing payloads is often limited due to satellite platform vibrations. Effects of Linear and high frequency sinusoidal vibrations on the system MTF are known exactly in closed form but the low frequency vibration effects is a random process and must be considered statistically. Usually the vibration MTF budget is defined based on the mission requirements and the overall MTF limitations. For analyzing low frequency effects, designer must know all the systems specifications and parameters. With a good understanding of harmful vibration frequencies and amplitudes in the system preliminary design phase, their effects could be removed totally or partially. This procedure is cost effective and let the designer to eliminate just harmful vibrations and avoids over-designing. In this paper we have analyzed the effects of low-frequency platform vibrations on the payload's modulation transfer function. We have used a statistical analysis to find the probability of imaging with a MTF equal or greater than a pre-defined budget for different missions. The worst and average cases have been discussed and finally we have proposed "look-up figures". Using these look-up figures, designer can choose the electro-optical parameters in such a way that vibration effects be less than its pre-defined budget. Furthermore, using the results, we can propose a damping profile based on which vibration frequencies and amplitudes must be eliminated to stabilize the payload system.

• Structural Engineering and Mechanics
• /
• 제64권3호
• /
• pp.279-285
• /
• 2017

Modal expansion technique (MET) is a method to estimate the vibration fields of flexible structures by using eigenmodes of the structure and the signals of sensors. It is the useful method to estimate the vibration fields but has the truncation error since it only uses the limit number of the eigenmodes in the frequency of interest. Even though block-wise MET performed frequency block by block with different valid eigenmodes was developed, it still has the truncation error due to the absence of other eigenmodes. Thus, this paper suggested an improved block-wise modal expansion technique. The technique recovers the truncation errors in one frequency block by utilizing other eigenmodes existed in the other frequency blocks. It was applied for estimating the vibration fields of a cylindrical shell. The estimated results were compared to the vibration fields of the forced vibration analysis by using two indices: the root mean square error and parallelism between two vectors. These indices showed that the estimated vibration fields of the improved block-wise MET more accurately than those of the established METs. Especially, this method was outstanding for frequencies near the natural frequency of the highest eigenmode of each block. In other words, the suggested technique can estimate vibration fields more accurately by recovering the truncation errors of the established METs.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 추계학술대회논문집
• /
• pp.517-520
• /
• 2004

The power flow analysis(PFA) can be effectively used to predict structural vibration in medium-to-high frequency ranges. In this paper, vibration experiment has been performed to observe the analytical characteristics of the power flow analysis of the vibration of a plate. In the experiment, the loss factor of the plate and the input mobility at a source point have been measured. The data for the loss factor has been used as the input data to predict the vibration of the plate with PFA. The frequency response functions have been measured over the surface of the plate. The comparison between the experimental results and the predicted results for the frequency response functions showed that PFA can be an effective tool to predict structural vibration in medium-to-high frequency ranges.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.283-288
• /
• 2006

This study developes the vibration model to estimate the vibration energy of damper/spring assembly(mainbase assembly) for car CD player, and this model is verified by experiment. From frequency response, response, we investigate the natural frequency and mode shape in the up/down direction. In order to determine the analysis frequency band, we investigate the excitation frequency from the vehicle test. As the characteristics of damper and spring is changed, we carry out the vibration test(transmissibility) and investigate the change of transmissibility.

• 한국공작기계학회논문집
• /
• 제14권6호
• /
• pp.117-124
• /
• 2005

This study developes the vibration model to estimate the vibration energy of compact disc player's mainbase assembly which is supported by dampers and springs, and this model is verified by experiment. From frequency response function, we investigate the natural frequency and mode shape in the up/down direction for mainbase assembly. In order to determine the analysis frequency band, we investigate the excitation frequency of road from the vehicle test. As the characteristics of dampers and springs are changed, we carry out the sensitivity analysis of vibration energy for mainbase assembly which include optical pick-up and feeding system. And we found out that the properties of damper were dominant element in the vibration energy of mainbase assembly's CG(center of gravity).

• 한국소음진동공학회논문집
• /
• 제11권6호
• /
• pp.163-168
• /
• 2001

Vibration problems occurred in an air cooled heat exchanger with axial flow fan for a petrochemical plant were investigated. Experimental field test and theoretical verification were performed. To find the main cause of the high vibration of the fan at the air inlet of the axial fan, the frequency spectrum was measured. The natural frequency of the driving support of the heat exchanger was numerically calculated. Both of the measured and the natural frequency were approximately equal to the blade passing frequency. Because it was difficult to modify the structure of the driving support during the normal operation of the plant, the blade number of the fan was increased, which greatly reduced the vibration level of the heat exchanger.

• 한국지진공학회논문집
• /
• 제3권1호
• /
• pp.103-112
• /
• 1999

본 연구는 두 지점간의 진동수 응답함수를 이용하여 시간 및 진동수 영역에서의 원심펌프(20Hp. 50Hp) 가진력을 추정하기 위한 것이다. 진동수 응답함수는 실수부와 허수부에 대한 신호정보를 가지고 있으며 응답함수 역시 실수부와 허수부에 대한 신호정보를 가지고 있다 따라서 이들 진동수 응답함수 및 응답함숴의 복소수 계산으로부터 가진력을 실험적으로 구하였으며 이론적인 방법에 의하여 구한 가진력과 실험적으로 구한 값을 비교함으로서 펌프에 의한 주진동수 성분의 크기는 펌프 및 모터중량의 10-25% 정도가 됨을 제시하였다. 가진력 산정을 위한 시간영역에서의 불평형질량의 크기는 펌프 및 모터중량의 약 30-60%임을 알수 있었다 한편 펌프회전에 의한 진동은 주진동수 이외에도 주진동수의 2-3배의 크기를 갖는 성분이 있음을 알 수 있었으며 대상 콘크리트 슬래브의 고유진동수와의 가진진도수비를 달리함에 따라 정확한 진동전달률을 조절하는데 활용할 수 있다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.1285-1289
• /
• 2006

In a large diameter piping system, high frequency energy can produce excessive noise, high vibration, and failures of thermo-well, instrumentation, and attached small-bore piping. High frequency energy is generated by flow induced vibration like vortex shedding in orifices and valves. Once this energy is generated, amplification may occur from acoustical and/or structural resonances, resulting in high amplitude vibration and noise. At low frequencies, pipe vibration occurs laterally along the pipe's length, but at higher frequencies, the pipe shell wall vibrates radially across its cross-section. The simple beam analogy which is based on the beam mode vibration can not be applied to evaluate shell mode vibration. ASME OM3 recommends that the stress be measured directly by strain gauge and be evaluated according to the fatigue curves of the piping material. This Paper discusses the excitation and amplification mechanism relevant to high frequency energy generation in piping system, the monitoring method of the shell mode vibration in ASME OM3, the evaluation method generally used in the industry. Finally this paper presents the stress evaluation of the cavitating venturi down stream piping, where high frequency shell mode vibrations were observed during the operation.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
• /
• pp.283-284
• /
• 2002

Ball bearings (BB) are generally used in spindle of‘ disk drives at present, but they have been known that BB generate high frequency vibration. Fluid dynamic bearings (FDB) having high-rotational accuracy and small vibration characteristics have been developed as next generation spindles. Especially. a ferro fluid bearing (FFB) spindle has the advantage to prevent leakage and dispersion of lubricating oil using a ferro seal. In this study, we measured damping characteristics and frequency characteristics of these bearing spindles using a high-frequency vibration base. High frequency excitation was added to these bearing spindles mounted on the vibration base, and we proved that FFB and FDB spindles have effective damping.