• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1071-1074
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• 2006

The frequency response functions and loss factors, $\eta$, of structurally hollowed, rectangular, metal cantilever beams have been measured in bending vibrations within low strain amplitudes. The beams were heat treated or fined with aluminum to vary the material conditions. The measured frequency response functions at the end of the cantilevered beam were processed to calculate the structural damping ratios. The results showed that the modal frequencies and damping ratios of heat treated beam are increased due to the increase of beam rigidity with the predictions of the classical beam theory. When the beams are fined with aluminum, however, the frequencies are decreased due to the increase of mass, while the damping ratios are increased. As the agreement between measurement and classical theory is good, the performance of a beam with heat treated or fined with dissimilar material can be duplicated, for industrial and most practical purposes, by the theory developed for an internally damped homogeneous beam.

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

• 전기학회논문지
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• 제66권11호
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• pp.1591-1599
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• 2017

In power electronics applications which switching frequency is below audible frequency, the acoustic noise and vibration design of magnetics are as important as the efficiency. In the case of the powder core, which is widely used in grid-connected inverters, many researches have been progressed in terms of efficiency. However, there are only few research have been progressed related with acoustic noise and vibrations. In this paper, the Sendust(Fe-Si-Al) powder core material which has low magnetostriction and low core loss is analyzed in terms of acoustic noise and vibration induced by Maxwell force and magnetostriction. Three building structures such as, rectangular, toroidal, and oval shape are designed for 4kW grid-connected inverter, because magnetic properties and the audible noises of the inductor are varied by magnetic core building structures. The effects of the Maxwell force and magnetostriction behaviors varied with core shapes are analyzed by finite element method and experiments. In addition, experiment results of the inductor efficiency are presented according to core building structures.

• 대한의용생체공학회:의공학회지
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• 제24권2호
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• pp.121-126
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• 2003

본 연구는 진동형 장치의 활용을 통해 혈관 내 폐 보조장치의 기체전달 효율을 향상시키고자 시도하였으며, 진동에 따른 혈액의 용혈 문제에 있어서 한계 용혈이 발생하는 영역을 선정하고자 하였다. 가진 주파수가 0 Hz일 때를 기준으로 하여 중공사 수의 변화에 따라 산소전달속도를 측정하였다. 최대의 산소전달속도를 나타내는 중공사 모듈에서 가진 주파수의 변화에 따른 산소전달속도를 측정하고 혈액의 용혈도를 측정하였다. 측정결과 액체 유속의 변화에 따라 최대 산소전달속도를 나타내는 중공사 모듈은 type 6으로 이때의 중공사 개수는 675개이다. 또한, 중공사를 가진하지 않았을 때 최대의 산소전달속도를 보여주는 모듈은 type 6이었다. 모듈 type 6의 가진 주파수의 변화에 따른 산소전달속도는 7 Hz에서 최대산소전달속도를 나타내었으며 최대산소전달속도를 나타내는 7 Hz의 가진 주파수에서의 혈액 용혈도를 측정한 결과 혈액의 용혈도는 낮았다. 그러므로 최대 흔들림이 일어나는 7 Hz를 한계 용혈 주파수로 결정할 수 있었다.

• 한국음향학회지
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• 제27권2호
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• pp.80-86
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• 2008

유방초음파 검사는 유방암 검사에 있어 유방촬영술에 비하여 많은 장점이 있으나, 미세석회화 발견에는 적합하지 않은 단점이 있다. 이에 유방초음파 검사에서 기존의 7.5 MHz 선형 탐촉자를 사용하여 파워도플러와 매질의 공명현상을 이용한 유방조직 석회화 병변을 관측할 수 있는 방법을 연구하였다. 먼저 gelatin을 이용하여 유방조직 팬텀을 제작하였으며, 외부 진동을 변화시켜 가며 석회화 병변을 관측하였다. 유방조직 팬텀 안에 주입된 석회화는 주변 조직과 다른 공명을 일으키면서 외부진동에 따라 음향공명의 정도가 파워도플러의 ROI 영역 내의 색상의 밝기와 영역의 차이로 나타내었다. 낮은 주파수 영역에는 음향공명이 거의 나타나지 않았으며, 약 $300{\sim}600\;Hz$ 사이에서 일정한 플래토우 영역을 나타내었으며, 이후 주파수가 증가함에 따라 색상이 사라짐을 확인하였다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권7호
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• pp.370-378
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• 2002

As resent trends in structural construction have been to build taller and larger structures than any time in the past, they have had high flexibility and low damping that can cause large vibration response under severe environmental loading such as earthquakes, winds, and mechanical excitations. The damper with mass and spring is one approach to safeguarding the structure against excessive vibrations. In this paper, the lumped electrical circuit approach of mass/spring system is used to model the mechanical aspects according to the frequency. Therefore, the mass/spring system can be dealt with here and linked with the equivalent circuit of electric linear oscillatory actuator(LOA). Analysis models are two types of vibration control system, active mass damper(AMD) and hybrid mass damper(HMD). AMD consists of the moving coil LOA with mass only The LOA of HMD with mass and spring is composed of the fixed coil and the movable permanent magnet(PM) field part. The PM field part composed magnet modules and iron coke, is the damper marts itself. We Present the motional resistance and reactance of mass/spring system and the system impedance of AMD and HMD according to the frequency.

• Steel and Composite Structures
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• 제45권1호
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• pp.119-131
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• 2022

Due to the complexity of the structure and the limits of classical SEA, a combined SEA approach is employed, with angle-dependent SEA in the low- and mid-frequency ranges and advanced SEA (ASEA) considering indirect coupling in the high-frequency range. As an important component of the steel box girder, the dynamic response of an L-junction periodic ribbed plate is calculated first by the combined SEA and validated by the impact hammer test and finite element method (FEM). Results show that the indirect coupling due to the periodicity of stiffened plate is significant at high frequencies and may cause the error to reach 38.4 dB. Hence, the incident bending wave angle cannot be ignored in comparison to classical SEA. The combined SEA is then extended to investigate the vibration properties of the steel box girder. The bending wave transmission study is likewise carried out to gain further physical insight into indirect coupling. By comparison with FEM and classical SEA, this approach yields good accuracy for calculating the dynamic responses of the steel box girder made of periodic ribbed plates in a wide frequency range. Furthermore, the influences of some important parameters are discussed, and suggestions for vibration and noise control are provided.

• 대한토목학회논문집
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• 제31권4A호
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• pp.287-293
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• 2011

본 연구에서는 교량의 진동을 이용한 압전 외팔보 에너지 수확장치의 적용성을 연구하였다. 이를 위하여 압전 소자의 구성방정식과 외팔보의 진동방정식을 결합하여 외팔보의 단일 모드에 대한 연성 방정식을 행렬 형태로 구성하였다. 그리고 에너지 수확장치의 가진기 실험을 통하여 해석 모델의 타당성을 검증하였다. KTX, 새마을, 무궁화 열차가 주행할 때 측정된 교량 가속도를 바탕으로 수치해석을 통하여 산정한 에너지 수확장치의 최대 전력은 각각 28.5 mW, 0.65 mW, 0.51 mW로 나타났다. 이를 볼 때 철도와 같은 이동하중에 의한 교량의 진동은 가진 진동수와 가속도가 낮고 지속시간이 짧아서 에너지 공급원으로서 효율성이 떨어지는 것으로 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.24-29
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• 2007

Low-speed Diesel Engine, 7K60MC-S, in Power Plant have been experienced high vibration frequently since these units were completed the construction works, but they did not have any fundamental vibration solutions up to date. Therefore, several vibration tests and analyses are conducted to identify the root cause of high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25Hz & 25.4Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude at 9.25Hz occurs due to the inertia momentum added by SCR duct system with the same vibration phase angle. It is analyzed that the excess structural vibration be occurred when the natural frequency of engine body is accessed the exciting sources due to the explosion pressure and the discharge pulsation of 7 cylinders in resonance range.

• 한국소음진동공학회논문집
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• 제17권9호
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• pp.826-834
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• 2007

A 7K60MC-S low speed diesel engine in a power plant has frequently experienced high vibration since the unit completed construction works. Up to date, no fundamental vibration solutions were reached. Hence, several vibration tests and analyses were conducted to identify the root cause of this high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25 Hz and 25.4 Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude with the same vibration phase angle at 9.25 Hz occur due to the explosion pulsations of 7 cylinders and the Inertia momentum added by the SCR (selective catalytic reduction) duct system. It was analyzed that the excess structural vibration occurred when the natural frequency of engine body is affected by the exciting sources due to the explosion pressure and the discharge pulsation of the seven cylinders in resonance range.