• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.601-606
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• 2004

Vibration spectrums of the test loop according to flow conditions were analyzed in order to identify the sources of vibration at peak frequencies. While a flow condition of the sweep test was changed by varying pump rotational speed from 450 rpm to 1500 rpm by the step 150 rpm, midspan acceleration of the test section in width-direction and dynamic pressure perturbation in the test section were measured. Other sources of vibration due to the flow structure interactions, such as acoustic resonance, blade pulsing frequency and bellows wrinkles, were investigated. Pressure perturbation in the section and acoustic resonance due to branch pipe give major effects to the vibration of the test section in high frequency range of 1.5 kHz to 2.8 kHz.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.335-340
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• 2005

Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.149-151
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• 2014

The blowoff phenomenon was experimentally investigated in a ducted combustor according to the acoustic excitation. The blowoff equivalence ratio rapidly increases at specific acoustic excitation frequencies. A resonance phenomenon occurs when the excitation frequency approaches the harmonic frequency of the combustor. The resonance increases the velocity fluctuation in the combustor and the infiltration velocity of the unburned gas in the shear layer. Consequently, the mixture velocity exceeds the burning velocity and the blowoff occurs at the higher equivalence ratio.

• 소음진동
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• 제9권6호
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• pp.1200-1209
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• 1999

This paper reports a peculiar example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration was dtected at all around the plant. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34 Hz. To identify the vibration, frequency analysis on the response vibration as well as on the expected excitation forces and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.377-382
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• 2000

Film bulk acoustic resonator (FBAR) using AIN reactively sputtered at room temperature was fabricated. The FBAR is composed of a piezoelectric aluminium nitride thin film, top electrode of Al and bottom electrode of Au connected by a short (200${\mu}{\textrm}{m}$) transmission line on both sides and reflector layers of SiO$_2$- W Pair. The active areas of Al and Au were patterned using 150${\mu}{\textrm}{m}$ diameter shadow mask. The series resonance frequency (fs) and the parallel resonance frequency (fp) were measured at 1.976 GHz and 2.005 GHz, respectively. The minimum insertion loss and return loss were 6.1 dB and 37.19 dB, and the quality factor (Q) was 4261.

• 한국분무공학회지
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• 제29권1호
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• pp.23-31
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• 2024

This study conducted a 3D thermo-acoustic analysis based on the helmholtz solver to analyze the major resonance modes causing combustion instability in a single-can combustor. The experimental investigations were carried out on a test rig designed by the Korea Institute of Machinery & Materials (KIMM) under various conditions of hydrogen co-firing and fuel staging. Through these experiments, two primary unstable frequencies were identified. To determine the resonance modes of these frequencies, a 3D thermo-acoustic analysis was conducted using temperature information from the test rig. The results confirmed that the unstable frequencies observed in the experiments were all longitudinal modes. Additionally, the mode shapes identified in the analysis facilitated a simplification of the exit geometry for the low-order network model, confirming that this did not significantly affect the fundamental resonance modes.

• 조명전기설비학회논문지
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• 제15권6호
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• pp.8-14
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• 2001

메탈핼라이드램프는 고효율, 고연색성이며 집광능력이 좋다. 그러나 메탈핼라이드 램프의 단점은 아크튜브내에서 음향공명현상이 발생되는 것으로 알려져 있다. 이러한 음향공명은 점등상태의 불안정과 기체의 심한 파동을 일으킨다. 심한 파동과 불안정한 점등으로 아크가 소멸되는 부위는 전압이 상승되고, 방전관내벽에 근접된 아크는 국부의 과열로 튜브를 금가게한다. 이 연구의 목적은 펄스스타트 메탈핼라이드램프 MH200[W]의 아크튜브내에서 음향공명을 감소시키는 것이다. 음향공명현상을 감소시키기 위하여 전자식안정기가 84.6[kHz]에서 94.2[kHz] 대역내에 있는 89[kHz]의 단독주파수인 정현고주파를 램프에 공급하기 위하여 설계되었다. 실험결과 고효율 펄스스타트 MH200[W] 램프의 방전관내에 음향공명 현상이 없었다.

• 한국음향학회지
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• 제14권4호
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• pp.12-20
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• 1995

본 논문은 충격 음향법에 의한 원통형 물체의 결함 검출 방법에 관한 원리와 실험 결과를 기술한다. 원통형 물체가 가지게 되는 공진 주파수는 물체의 직경, 길이 등의 물리적 크기에 따라 결정되며 이러한 원통형 물체를 자유 공진 시킬 경우 구조물 고유에 주파수 및 고조파 성분이 내포된 음향을 방생시킨다. 결함이 존재하는 물체에 충격ㄷ이 가해질 경우 발생하는 음향은 정상의 경우와 구별되며, 주파수 성분 분석을 통해 보다 명확한 식별이 가능하다. 본 연구에서 적용된 음향 충격법에 의한 결함 검출 기법은 연구 대상 물체의 경우 결함 유무를 완벽하게 판정할 수 있었으며, 차후 유사한 형태의 구조물에 대한 결함 검출에도 응용될 수 있다.

• 조명전기설비학회논문지
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• 제27권2호
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• pp.69-76
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• 2013

In this paper, electronic ballast using resonant inverter for HID lamp is designed and implemented. The proposed electronic ballast is used the soft switching technology ZVS(Zero Voltage Switching) to reduce turn-on and turn-off loss. The ignition of proposed electronic ballast is achieved by controlling a full bridge inverter which is consisted of LC filter for resonance. After ignition the ballast operates as a low frequency square wave inverter by controlling a full bridge inverter as a buck converter. After ignition at resonant frequency of $f_o$=160kHz, the switching frequency of a buck converter is consisted of 50kHz of high frequency and 170Hz of low frequency. This is for attenuating high frequency harmonics and avoiding acoustic resonance. The experimental results show that electronic ballast using resonant inverter is operated stably.

• 한국태양에너지학회 논문집
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• 제32권2호
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• pp.105-112
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• 2012

The conversion of solar energy into acoustic waves is experimentally studied. Measurements were made on the Sound Pressure Level (SPL), frequency, onset time and the temperature gradient across the stack. A pyrex resonance tube is used with a honey-comb structure ceramic stack along with Ni-Cr and Cu wires. An AL1 acoustical analyzer was used to measure the SPL and frequency of acoustic waves whereas K-type thermocouples were hired to estimate temperature gradients. For a resonance tube of 100 mm, no acoustic waves were generated with a power input of 25W. By increasing its length to 200 mm, however, maximum SPLs of 96.4 dB, 106.3 dB and 112.8 dB were detected for the tubes of 10mm,20mm and 30mm in IDs and their respective stack positions of 70mm, 60mm and 50mm from the closed end.