• 한국지진공학회논문집
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• 제10권6호
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• pp.57-65
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• 2006

본 논문에서는 구조물의 전역적인 손상도 평가와 국부 구조 연결부의 손상 검색을 동시에 수행할 수 있는 하이브리드 구조 손상 모니터링 체계가 제시되었다. 하이브리드 손상 모니터링 체계는 진동기반 기법과 전기/역학적 임피던스 기법으로 구성되었다. 진동기반 기법은 구조물의 모드특징의 변화를 사용하여 구조물의 전역적 특성의 변화를 감지하고, 전기/역학적 임피던스 기법은 PZT 센서의 저항 변화를 사용하여 국부 구조 연결부의 손상 여부를 검출한다. 제안된 하이브리드 모니터링 체계를 검증하기 위해 구조 연결부의 볼트 풀림 상황을 손상 시나리오로 선택하였으며, 가속도 응답과 임피던스 응답 신호가 계측되었다. 실험 결과, 제안된 하이브리드 모니터링 체계를 통해 구조물의 전역적 손상 상태와 국부 구조 연결부의 손상을 정확하게 모니터링 할 수 있었다.

• Journal of Dental Anesthesia and Pain Medicine
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• 제21권4호
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• pp.345-355
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• 2021

Background: This study aimed to evaluate the efficacy of external vibrating devices and counterstimulation on a child's dental anxiety, apprehension, and pain perception during local anesthetic administration. Methods: This was a prospective, randomized, parallel-arm, single-blinded interventional, clinical trial. One hundred children aged 4-11 years, requiring pulp therapy or extraction under local anesthesia (LA), were recruited and allocated equally into two groups (1:1) based on the interventions used: Group BD (n = 50) received vibration using a Buzzy^® device {MMJ Labs, Atlanta, GE, USA} as a behavior guidance technique; Group CS (n = 50) received counterstimulation for the same technique. Anxiety levels [Venham's Clinical Anxiety Rating Scale (VCARS), Venham Picture Test (VPT), Pulse oximeter {Gibson, Fingertip Pulse Oximeter}, Beijing, China)] were assessed before, during, and after LA administration, while pain perception [Wong-Baker Faces Pain Rating Scale (WBFPS), Visual Analogue Scale (VAS)] was evaluated immediately after injection. Statistical analysis was performed using the Student's t-test to assess the mean difference between the two groups and the repeated measures ANOVA for testing the mean difference in the pulse rates. Statistical significance was set at P < 0.05. Results: Significant differences in mean pulse rate values were observed in both groups. In contrast, the children in the BD group had higher diminution (P < 0.05), whereas the mean VCARS and VPT scores were conspicuous (P < 0.05). Based on the mean WBFPS and VAS scores, delayed pain perception after LA injection was more prominent in the BD group than in the CS group. Conclusion: External vibration using a Buzzy^® device is comparatively better than counterstimulation in alleviating needle-associated anxiety in children requiring extraction and pulpectomy.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.380.2-380
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• 2002

SRM(Switched Reluctance Motor) 내부의 Radial Force는 소음ㆍ진동의 주원인이 되는 가진력으로 작용하는 것으로 알려져 있다. 따라서 본 논문에서는 Radial Force의 주 요인인 Motor 내부의 Air Gap 편심에 따른 반경방향의 전자기 가진력을 전자장 수치해석을 통하여 해석하고 소음ㆍ진동에 미치는 영향을 분석하였다. Air Gap 편심량을 변화시켜 가면서 Stator, Rotor의 Local Force와 Gloval Force인 Torque Fluctuation을 해석하고 이를 실험 결과와 비교함으로서 해석결과의 타당성을 입증하였다.

• 화약ㆍ발파
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• 제19권3호
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• pp.91-104
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• 2001

As in Korean environments with mountainous and hilly areas, the rock generally has to be removed in construction or civil engineering work in tunnelling or excavation for development in urban area. Explosives should be used for blasting, which may cause serious problems on local people for their claim for compensation due to ground vibration, noise. For safe and economic blasting, geology and engineering characteristics of rocks such as discontinuities of rock or weathering are very important factors, together with site characteristics for prediction of ground vibration. In this study, conducted were the detailed study for major rocks most widely distributed in the South-east area, in-situ geological survey, geological and geochemical analysis, and further laboratory uniaxial rock stress, seismic velocity of core samples together with in-situ seismic velocity measurements. Regulations on ground vibration and noise were reviewed for assessing their adaptabilities, and a total of 4,856 measured blasting vibration data were examined for enhancing the confidence level in estimating the predictive formulation using scaled distance statistically.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.848-854
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• 2006

In this study, a computational analysis system has been developed in order to investigate flow-induced vibration(FIV) phenomenon for general stator-rotor cascade configurations. Relative movement of the rotor with respect to stator is reflected by modeling independent two computational domains. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming methods. Unsteady, Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation SST $k-\omega$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used flow computing the coupled governing equations of the fluid-structure interaction problem. Detailed FIV responses for different flow conditions are presented with respect to time and vibration characteristics are also physically investigated in the time domain.

• Journal of Advanced Marine Engineering and Technology
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• 제11권2호
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• pp.51-60
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• 1987

Recently, the problem of the axial vibration for the marine diesel engine shafting has become important due to the increased exciting forces resulting from high supercharging and large output, and the reduced natural frequencies resulting from long stroke and show speed. The effects of the axial vibration on the propulsion shafting induce cracks of the connecting point of crankpin and crankarm, the severe wear of thrust bearing, the fatigue failure of each fixing bolt and jointed parts, the hull and local hull vibrations, and also the wear and the noise due to intense hammering phenomena of thrust collar. Therefore, each classification society requires the calculation of natural frequencies and their amplitudes and also measurements of the forced damped axial vibration. At present, the technical and theoretical level is at the stage of estimating the resonant points and their maximum displacements, but the estimated displacements of the resonant points are not so reliable as the torsional one. In this study, induced stresses and amplitudes of the forced damped axial vibration are calculated. For this purpose, the equation of forced axial vibration with damping for the propulsion shafting is derived and its steady-state response is calculated by the mechanical impedance method. A computer program for above calculations is developed. The measured values are analyzed and the calculated results are compared with the measured ones. They show fairly good agreements and the reliability of developed program is confirmed.

• 한국해양공학회지
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• 제34권5호
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• pp.325-333
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• 2020

As regulations concerning ship vibration and noise are becoming stricter, considerable attention is being drawn to prediction technologies for ship vibration and noise. In particular, the resonance and lock-in phenomena caused by vortex-induced vibration (VIV) have become considerably important with increases in the speed and the size of ships and ocean structures, which are known to cause structural problems. This study extends the fluid-structure interaction (FSI) analysis method to predict resonances and lock-in phenomena of high modes and VIV of ship rudders. Numerical stability is secured in underwater conditions by implementing added mass, added damping, and added stiffness by applying the potential theory to structural analysis. An expanded governing equation is developed by implementing displacements and twist angles of high modes. The lock-in velocity range and resonant frequencies of ship rudders obtained using the developed FSI method agree well with the experimental results and the analytic solution. A comparison with local vibration guidelines published by Lloyd's Register shows that predictions of resonances and lock-in phenomena of high modes are necessary in the shipbuilding industry due to the possible risks like fatigue failure.

• 한국가스학회지
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• 제12권1호
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• pp.13-18
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• 2008

지진 및 외부 진동에 의하여 구조물에 발생하게 되는 진동량은 진동 속도와 피해규모가 비례하는 관계에 있음을 고려하여 일반적으로 진동속도로 나타내어진다. 본 연구에서는 진동 속도 기반의 구조물 진동기준을 검토하고, 이를 고려하여 도로 하부 매설 가스 강관의 안정성 평가를 수행하였다. 가스공사 주사용 배관인 762 mm API 5L Gr. X65 강관을 해석 대상 배관으로 선정하였으며 도로설계기준에 의하여 지반 매설 조건 및 DB-24 하중을 다양한 속도에 대한 시간 함수로 고려하여 재하하였다. 진동속도는 차량 진행 속도 80 km/h까지 증가하다가 이후 감소하는 경향을 보였으며, 차량 진행 속도 80 km/h에서 0.034 cm/s의 진동 속도를 보임으로서 진동 기준 대비 매우 작은 값임을 확인하였다. 또한 감쇄법칙을 적용하여 진행파의 속도를 분석한 결과, 차량 진행 속도 80 km/h에서 가장 작은 속도를 나타내었다.

• 한국음향학회지
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• 제23권5호
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• pp.340-352
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• 2004

28.5 ㎑의 초음파의 미세 수직진동에 의해서 유도된 음향유동 (acoustic streaming)을 레이저를 이용한 입자 영상. 유속계에 의하여 고정 유리 평판과 초음파 진동자의 사이에서의 공기 유동을 가시화 하였다. 음향유동에 의한 공기의 유동 속도의 증가를 측정하기 위해 고정 유리 평판과 초음파 진동자의 사이에서의 속도변화를 실시간으로 측정하였다. 진동자와 고정 평판의 사이의 gap에 따른 음향유동의 세기의 변화를 정량적인 공기의 유동 속도의 변화에 의해 관찰되었고 고정판과 초음파 진동자 사이의 gap에서 공진 상태를 야기시키는 공진 Gap (H=18, 24, 30, 36㎜)중에서 공진 Gap (H)이 18m일 때 최대의 음향속도가 존재함을 알 수 있었고 진동자 표면부근에서부터 고정평판사이까지의 국소 최대 난류강도의 축 방향 위치에 따른 변화는 gap의 크기에 따라 8%∼70% 이었다. 전단응력값은 반경방향 위치의 중심영역에서 최대전단응력을 가지며 와도 분포도 반경방향 위치에서 진동자 중심영역에 최대 및 최소와도 값을 가짐을 알 수 있었다.

• Smart Structures and Systems
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• 제13권2호
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• pp.203-217
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• 2014

Due to the shift in paradigm from passive control to adaptive control, smart tuned mass dampers (STMDs) have received considerable attention for vibration control in tall buildings and bridges. STMDs are superior to tuned mass dampers (TMDs) in reducing the response of the primary structure. Unlike TMDs, STMDs are capable of accommodating the changes in primary structure properties, due to damage or deterioration, by tuning in real time based on a local feedback. In this paper, a novel adaptive-length pendulum (ALP) damper is developed and experimentally verified. Length of the pendulum is adjusted in real time using a shape memory alloy (SMA) wire actuator. This can be achieved in two ways i) by changing the amount of current in the SMA wire actuator or ii) by changing the effective length of current carrying SMA wire. Using an instantaneous frequency tracking algorithm, the dominant frequency of the structure can be tracked from a local feedback signal, then the length of pendulum is adjusted to match the dominant frequency. Effectiveness of the proposed ALP-STMD mechanism, combined with the STFT frequency tracking control algorithm, is verified experimentally on a prototype two-storey shear frame. It has been observed through experimental studies that the ALP-STMD absorbs most of the input energy associated in the vicinity of tuned frequency of the pendulum damper. The reduction of storey displacements up to 80 % when subjected to forced excitation (harmonic and chirp-signal) and a faster decay rate during free vibration is observed in the experiments.