• Journal of Microbiology and Biotechnology
• /
• 제20권5호
• /
• pp.904-907
• /
• 2010

The vibration of fungal cultures was evaluated to determine its potential effect on the dispersal of airborne fungal microorganisms suspected of being pathogens. An artificial vibration system, which simulates the actual environmental vibration of fungal structures, was designed and constructed for this purpose. Experiments featured the use of low-frequency vibrations similar to those induced by earthquakes. Within the range of conditions tested, the vibration of fungal cultures was found to affect the airflow-driven generation of bioaerosols.

• International Journal of Safety
• /
• 제6권1호
• /
• pp.22-25
• /
• 2007

Damping out high frequency low amplitude structural vibrations using PZT bimorph is presented. Static and Dynamic analyses of the piezoelectric bimorph bender were performed. Three layer piezoelectric actuators were modeled with SOLID5 coupled-field elements using ANSYS. Static deflection and modal analyses of the piezoelectric bimorph bender are presented. Proper tuning of the values of the resistor and inductor in the shunt circuit is required for maximum vibration suppression.

• 국제초고층학회논문집
• /
• 제1권1호
• /
• pp.15-19
• /
• 2012

Occupant footfalls are often the most critical source of floor vibration on upper floors of buildings. Floor motions can degrade the performance of imaging equipment, disrupt sensitive research equipment, and cause discomfort for the occupants. It is essential that low-vibration environments be provided for functionality of sensitive spaces on floors above grade. This requires a sufficiently stiff and massive floor structure that effectively resists the forces exerted from user traffic. Over the past 25 years, generic vibration limits have been developed, which provide frequency dependent sensitivities for wide classes of equipment, and are used extensively in lab design for healthcare and research facilities. The same basis for these curves can be used to quantify acceptable limits of vibration for human comfort, depending on the intended occupancy of the space. When available, manufacturer's vibration criteria for sensitive equipment are expressed in units of acceleration, velocity or displacement and can be specified as zero-to-peak, peak-to-peak, or root-mean-square (rms) with varying frequency ranges and resolutions. Several approaches to prediction of floor vibrations are currently applied in practice. Each method is traceable to fundamental structural dynamics, differing only in the level of complexity assumed for the system response, and the required information for use as model inputs. Three commonly used models are described, as well as key features they possess that make them attractive to use for various applications. A case study is presented of a tall building which has fitness areas on two of the upper floors. The analysis predicted that the motions experienced would be within the given criteria, but showed that if the floor had been more flexible, the potential exists for a locked-in resonance response which could have been felt over large portions of the building.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2005년도 춘계학술대회 논문집
• /
• pp.718-721
• /
• 2005

The purpose of the study is to evaluate the usage of microtremor in estimation of subsurface structure and ground response to ground motion. Ground motion amplification based on site condition of an area is an important parameter for dynamic design. Microtremor cover the characteristics in a low frequency range, while forced vibrations cover them in a high-frequency range. Microtremor consider ground characteristics and offer transfer function in area. To determine the dominant frequency, the passive microtremor measurement is performed and to determine the transfer function of test site, active microtremor measurement is performed. Microtremor measurement in the site is compared with theoretical transfer function calculated from the known structures.

• Nuclear Engineering and Technology
• /
• 제56권5호
• /
• pp.1712-1724
• /
• 2024

Spiral tubes are used in a wide range of applications and it is significant to understand the vibration introduced by two-phase flow in spiral tubes. In this paper, the numerical method is used to study the vibration induced by the gas-liquid two-phase flow in a spiral tube with different flow regimes. The pressure fluctuation characteristics at the pipe wall and the solid vibration response characteristics are obtained. The results show that the motion of small bubbles in bubbly flow leads to small pressure fluctuations with low-frequency broadband (0-50 Hz). The motion of the gas plug in the plug flow causes small amplitude periodic pressure fluctuation with a shortened low-frequency broadband (0-15 Hz) compared to the bubbly flow. The motion of the gas slug in the slug flow causes large periodic fluctuations in pressure with a significant dominant frequency (6-7 Hz). The wavy flow is very stable and has a distinct main frequency (1-2 Hz). The vibration regime in the bubbly flow and wave flow are close to the first-order mode, and the vertical vibrating component is dominant. The plug flow and slug flow excite higher-order vibration modes, and the lateral vibration component plays more important part in the vibration response.

• 한국자동차공학회논문집
• /
• 제9권4호
• /
• pp.148-156
• /
• 2001

Brake judder, one of low Sequency vibrations in brake system is determined by the excitation of Brake Torque Variation (BTV). The largest contributor to BTV is disc thickness variation. In this study, the static loads of brake torque at Suspension Mounting Points (SW) are obtained by the quasi-static analysis using DADS. The dynamic loads with frequency of BTV at SW are derived from correlation between forced vibration analysis with static loads and brake test results. And the accelerations at steering wheel were analyzed by forced vibration analysis with dynamic loads using commercial finite element program MSC/NASTRAN so that vibration characteristics of vehicle due to brake judder were investigated. Reliability of analysis results was verified through comparing the brake test results. Also, a parametric study with natural frequencies of frame, such as the 1st torsional mode and 1st bending mode, was conducted to reduce vibration amplitudes. As a result we could detect frame natural frequency conditions to improve vibration characteristics and obtained the frame model to reduce vibration amplitude.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2010년도 춘계학술대회 논문집
• /
• pp.1287-1292
• /
• 2010

Recently, many railway stations are built under the railway line in urban area. The passage of railway vehicles generates mechanical vibrations of a wide range of frequency. Thus, it is required to place structural vibration isolation systems to reduce vibration and noise originating from surrounding environments. This study utilizes elastometric bearings as a vibration isolation system. The slab track system on elastometric bearings is called "low vibration track" or "floating slab track." In this low vibration track system, dowel bars or plates can be installed to minimize the discontinuity of displacement between adjacent floating slab tracks. This study is to numerically investigate the effects of dowel members on static behavior of the low vibration track. The study involves two steel dowel systems including dowel bars and dowel plates. Each dowel system is analyzed under the service load condition to assess load transfer efficiency (LTE).

• 한국항공우주학회지
• /
• 제35권3호
• /
• pp.218-224
• /
• 2007

PZT와 같은 압전 재료는 능동 진동 억제 분야에서 널리 사용되고 있지만 단일 PZT의 경우 장착 과정에서의 손상, 전기 누전, 낮은 피로 성능과 같은 문제가 지적되고 있다. 이러한 문제를 해결하기 위하여 개발된 LIPCA 작동기는 여러 층의 복합재료와 PZT 층으로 구성되어 있다. 본 연구에서는 LIPCA 작동기를 끝단 질량이 부착된 알루미늄 외팔보의 진동을 억제하는데 적용하였다. 양변위 되먹임 제어 알고리듬을 사용하였으며, 필터 주파수를 대상 모드의 첫 번째 고유진동수에 맞추었다. 실험적으로 구한 알루미늄 보의 고유 진동수는 유한요소 해석의 결과와 잘 일치하였다. LIPCA 작동기를 능동 진동제어에 적용할 때 효율성을 시간과 주파수 영역에서 확인하고자 하였는데, 실험 결과 PPF제어를 사용한 LIPCA 작동기가 자유 진동의 안정화 시간과 강제 진동의 진폭을 효과적으로 제어할 수 있었다. 사례 연구로 다른 두께를 가지는 보의 강제 진동 제어를 수행하였다.

• 소음진동
• /
• 제8권6호
• /
• pp.1158-1165
• /
• 1998

실내 저주파 소음은 도로가진, 차량 현가 또는 엔진 마운트와 같은 차량 샤시 부품의 진동인 구조 진동에 기인한다. 실내 저주파 소음을 줄이려는 노력의 일환으로 소음 원의 위치 및 소음 전달경로를 추적하는 기술인 TPA (Transfer Path Analysis) 를 소개하였다. 본 연구에서는 TPA 기술을 이론적으로 고찰해보고 이를 실제로 적용하여, 도로가진에 의해 앞 좌석에서의 실내 소음에 기여도가 가장 큰 샤시 부품을 찾는 Case Study를 소개하였다. TPA를 적용하기 위한 데이터를 얻기 위해. 도로가진에서 소음으로 연결되는 계측과 실차 운행 상태의 진동 데이터 계측을 실시하였다. 또한 아스팔트 도로에서 시속 30 km/h로 달리면서 관능 평가와 진동 소음 계측 평가 모두를 실시하여 문제가 되는 저주파 실내 소음을 확인하였다. 시험 분석 결과 Trailing Arm을 통해 전달되는 소음이 앞 좌석 저주파 실내 소음에 대한 기여도가 가장 크게 나타났다.

• 한국해양공학회지
• /
• 제19권6호통권67호
• /
• pp.58-63
• /
• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.