• 한국정밀공학회지
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• 제33권9호
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• pp.707-714
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• 2016

This paper describes analysis results of vibration characteristics and modal test for a small-scale quad-rotor drone. The rotor arm has a slender body with a propeller and motor at its tip. Rotor system generates excitation for an unbalanced mass. Therefore, the drone platform is involved in the possibility of resonance. For advance identification of the possibility of resonance, confirmation of eigen-mode being closest to the propeller operation range is necessary. Material properties of CFRP tubes used for the rotor arm were acquired by finding the natural frequency based on Rayleigh method. A simplified quad-rotor FE model consisting of rotor arm assembly with tip mass was built to perform numerical analysis, and a free-free boundary condition was applied to provide flight status. Modal tests for the actual platform with impact hammer instrument were performed to verify analysis results. Separation margin from hazardous eigen-mode was checked on the propeller operation range.

• 전기학회논문지
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• 제58권3호
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• pp.566-572
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• 2009

This paper has studied breakage possibility of glass insulators by resonance and accelerated deterioration through the comparison of the natural vibration and on site vibration. The natural frequencies of the strut tube glass insulator was measured within a range of less than 1kHz. In the on site vibration, the largest frequency that was imposed on strut tube glass insulators was 80Hz with 1.13g of vertical vibration in the viaduct section, the largest vertical vibration (0.38g) was detected at 103Hz in the open route section. When site vibration and natural vibration of strut tube glass insulators were compared in terms of characteristics, the resonance frequency was not the same. In both the viaduct and open route sections, it seems that the impact by vertical vibration in strut tube glass insulators is large. It's very unlikely that glass insulators were damaged by fatigue accumulation of vibration since the possibility of damage by resonance was very low in consideration of the characteristics of natural vibration and site vibration of glass insulators. In addition, no damage was detected in the accelerated deterioration test.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.39-40
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• 2006

Diesel power plant(DPP) with the medium speed diesel engine is operated under the very severe condition in aspect of load and operating time as compared with the marine diesel generator set. So, minimized vibration level have to be insured for the more stable operation of engine and generator. The vibration of generator set mainly comes from the resonance between the rigid modes by resilient mount or distortion modes by structural stiffness and the excitation forces of engine. Then, avoidance of resonance with structural modification is generally well known. In this paper, the first order vibration in non-resonance range and local vibration modes were investigated by impact test, response/ODS(operational deflection shape) measurement and 3D finite element analysis for the additional reduction of vibration. The proposed countermeasures were actually applied and their final effects were verified through the in-situ measurement.

• 대한조선학회 특별논문집
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• 대한조선학회 2005년도 특별논문집
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• pp.69-75
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• 2005

Recently it was reported that the vibration problems on the oil pipe support structure of the crude oil carrier were occurred. in order to investigate the vibration characteristics and the causes of the vibration occasionally. the vibration measurements and impact tests for the oil Pipe structure were carried out. From the measurement results severe vibration was caused by the resonance between the transversal natural frequency of the structure and $6^{th}$ order excitation force of the main engine. Providing the proper countermeasures a series of the vibration analyses were carried out based on the measurement results. From the analysis results, it was concluded that the vibration characteristics of the oil pipe structure were affected by the oil pipes, support structure itself, upper deck structure and the installation spaces and the standard design was established for the crude oil carriers.

• 한국음향학회지
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• 제26권6호
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• pp.235-242
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• 2007

공동주택의 바닥충격음 측정 및 평가는 주로 입주 전에 이루어지고 있으나 실제 충격음 발생은 입주 후 커튼과 가구와 같은 중량물이 설치되어 있는 조건이므로 입주 전 후 음원세대(음원실)와 수음세대(수음실)의 상황은 다르다고 할 수 있다. 본 연구에서는 음원실에 가구 등과 같은 하중 설치에 따른 중량충격음 변화정도를 파악하기 위하여 바닥충격음 시험동과 현장에서 활하중($200kg/m^2$) 설치 전 후의 음원실 바닥슬래브 하부 진동가속도레벨 및 수음실 충격음레벨 변화를 측정하였다. 측정결과 하중설치를 통하여 진동가속도레벨 및 충격음레벨이 다소 저감되었으나 큰 영향은 받지 않는 것으로 나타났으며, 슬래브의 공진주파수도 변화하지 않았다.

• Journal of Biosystems Engineering
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• 제27권1호
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• pp.67-76
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• 2002

This study was conducted to investigate the effects of impact conditions on the acoustic characteristics of a watermelon. The study was crucial to develop a device for nondestructive internal quality evaluation of a watermelon by an acoustic impulse response method. An impact device was constructed with a pendulum to hit the watermelon, a microphone to detect the acoustic impulse responses, and a digital oscilloscope and computer to store and analyze the data. The selected samples were Guemcheon cultivar watermelons(Citrulus Vulgaris Schrad) harvested on Oct. 20,1998. Sixty watermelons were tested on flour different types of sample holders, with four kinds of ball made of different materials, at four bevels of the angular position of the pendulum and distance from the watermelon to the microphone. Since the magnitudes of frequencies obtained by hitting with the steel and rubber ball were relatively small at the bandwidths of above 500 Hz, it was shown that the steel and rubber ball were not suitable far a hitting ball in the pendulum to get informations on internal quality of the watermelon. In case of using broth of the wood and acryl ball, almost the same and good acoustic responses were shown on the wide range of frequency bandwidth. Therefore, it seemed that the acryl ball was more suitable to the test than the wood ball in considering its mechanical properties. The acoustic characteristics of the watermelon were not shown a significant difference between the types of sample holder. The amplitudes of the acoustic signals and the magnitudes of frequencies from the whole samples increased with increase of the angular position of pendulum and with decrease of the distance from the watermelon to the microphone. However, the resonance resonance of the sample were almost the same regardless of the angular positions and the distances.

• 한국전자통신학회논문지
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• 제19권2호
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• pp.361-370
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• 2024

본 논문에서는 저비용 제작이 가능한 직렬 공진형 한류기를 스마트 그리드 배전 계통에 적용하기 위한 방법을 연구하였다. 먼저, 한류기의 직렬 공진 회로에 주입되는 단락 전류의 고조파 성분들이 과도 응답의 피크 값에 미치는 영향에 대해서 분석하였으며, 퍼센트 임피던스 기반 고장 전류 계산법을 적용하여 정상 상태 응답을 결정하는 방법을 연구하였다. 다음, 시험 배전 선로에 적용하여 채택된 방법의 유효성을 검증하였다. 설계된 한류기를 적용한 시험 배전계통을 EMTP_RV를 이용하여 모델링하였으며 3상 단락 고장 시나리오를 모의하였다. 고장 모의 결과에서 한류기 적용 후 고장 전류의 정상 상태 응답이 설계 목표 값을 정확하게 추종하는 것을 확인하였다. 또한 한류기 적용 전과 후의 고장전류 파형 비교에서 고장 전류가 크게 억제되는 것을 확인함으로써 배전 계통에 대한 직렬 공진형 한류기 적용 효과를 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.107-112
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• 2012

All chemical processes are centered in the chemical reactor. Chemical reactions are often accompanied by mixing. Mixing can influence not just reaction rate but also product distribution if more than one product is possible. So, reactor agitator is more critical in industrial reactions. High vibration was occurred on reactor agitator which is critical equipment in HDPE plant. This paper describes analysis and diagnosis for agitator vibration throughout some tests. High vibration has been occurred by misalignment and resonance. Through the correction it could be stable.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.416-421
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• 2001

It was firstly issued that frequently broken of Encoder installed at travelling motor during RTGC operation. Estimated as broken due to excessive vibration of traveling and motor manufacturer claimed it as resonance of motor base. The principal vibration of Encoder was caused by the rotating vibration component of motor and by traveling wheel. The component transmitted from the wheel didn't have great vibration by the resonance with motor and other parts. Therefore, the plans was tried to add the support point to prevent the Encoder shaft vibrated greatly and inhibit the vibration. These showed good results.

• 대한기계학회논문집
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• 제13권5호
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• pp.875-885
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• 1989

본 연구에서는 이러한 경우를 대상으로 하여, 채터발생의 주원인이 공구가 되도록 돌출길이를 충분히 길게 한 상태에서 공구체결부에 점탄성재료를 삽입하고 채터진동 억제 효과를 검토하였다. 또한 점탄성 재료 삽입으로 인한 공구 고정부의 강성 및 감쇠의 변화를 공구고정부에 대한 유한요소해석(FEA) 및 충격실험 등을 수행 하여 알아보았으며, 정적 강성의 저하로 인해 안정절삭조건에서 발생할 수 있는 정밀 도저하를 검토하여 보았다.