• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.64-69
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• 1997

정격속도 100,000RPM용 원심분리기(centrifuge) 로터베어링계에 대해 회전체동역학 해석이 수행된다. 시스템은 원심분리기 로터, 유연축, 모터 로터와 축, 그리고 모터축 지지용 두 개의 구름베어링으로 구성된다. 설계목표는 정격속도가 위험속도(critical speed)에 대해 충분한 분리여유를 갖고, 위험속도에서 로터의 양호한 불균형응답특성을 이루어 내는 것이다. 후자의 요구조건은, 시스템이 다수의 위험속도를 통과하며 정격속도 주위에서 충분한 분리 여유를 갖지 않을 수도 있기 때문에 특히 중요하다. 시스템에 초유연축(extra-flexible shaft)을 도입함으로써, 비록 1차 위험속도에서 만족스럽지 못한 큰 불균형응답을 가질지라도 고차 위험속도에서 만족스런 작은 불균형응답을 보인다. 1차 위험속도에서 로터의 큰 변위를 억제하기 위해서 범퍼링(bumper ring) 또는 안내베어링(guide bearing)을 유연축의 적절한 위치에 설치할 필요가 있다. 비록 유연축계라 할지라도 정격속도와 가까운 4차 이상의 고차 위험속도를 정확히 규명하기 위해서는 모터의 동역학을 전체시스템에 결합하여야 함을 볼 수 있다. 해석은 유한요소법(finite element method)에 의해 수행된다.

• 한국소음진동공학회논문집
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• 제11권7호
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• pp.275-286
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• 2001

The research presents an analytical theory to calculate the characteristics of the bal bearing with waviness in its rolling elements considering the centrifugal force and gyroscopic moment of bal. The effects of centrifugal force and gyroscopic moment are introduced to the kinematic constraints and force equilibrium equations. and the waviness of rolling elements is modeled by sinusoidal function to calculate the contact force at each ball. The numerical solutions of governing equation of berating due to waviness are calculated by using the Newton-Raphson method. The accuracy of the research is validated by comparing the contact force. contact angle in case of considering the centrifugal force and gyroscopic moment of bal and the contact force and vibration frequencies in cases of considering waviness with the prior researches respectively. It investigates the stiffness, contact force. displacement and vibration frequencies of the ball bearing considering not only the centrifugal force and gyroscopic moment of ball but also the waviness of the rolling elements.

• Tribology and Lubricants
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• 제39권4호
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• pp.123-132
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• 2023

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×10⁶ DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 ㎛, and the operating clearance decreases to 0.5 ㎛ at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.

• Tribology and Lubricants
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• 제29권4호
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• pp.218-222
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• 2013

Water-lubricated ball bearings consist of rolling elements, an inner raceway, an outer raceway, a retainer, and an operating lubricant. In the water environment, ball bearings are required to sustain high loads at high speeds under poorly lubricated conditions. For the analysis of bearing behavior, friction torque is considered as the main factor at various flow rates, rotating speeds, and roughnesses between the rolling element and raceways. When the bearing operates at high rotating speeds, the friction torque between the raceway and rolling elements increases considerably. This frictional torque is an important factor affecting bearing reliability and life cycle duration. For understanding the flow conditions in the inner part of the bearing, this study focuses on the flow around the rotating and revolving rolling elements. A simple model of fluid flow inside the ball bearing is designed using the commercial CFD program ANSYS.

• Journal of Advanced Marine Engineering and Technology
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• 제33권5호
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• pp.672-678
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• 2009

Acoustic Emission (AE) technique is a non-destructive testing method and widely used for the early detection of faults in rotating machines in these days, because the sensitivity of AE transducers is higher than normal accelerometers. So it can detect low energy vibration signals. The faults in the rotating machines are generally occurred at bearings and gearboxes which are the principal parts of the machines. It was studied to detect the bearing faults by envelop analysis in several decade years. And the researches showed that AE had a possibility of the application in condition monitoring system(CMS) using the envelope analysis for the rolling bearing. And peak ratio (PR) was developed for expression of the bearing condition in condition monitoring system using AE. Noise level is needed to reduce to take exact PR value because the PR is calculated from total root mean square (RMS) and the harmonics peak levels of the defect frequencies of the bearing. Therefore, in this paper, the discrete wavelet transform (DWT) was added in the envelope analysis to reduce the noise level in the AE signals. And then, the PR was calculated and compared with general envelope analysis result and the result of envelope analysis added the DWT. In the experiment result about inner fault of bearing, defect frequency was difficult to find about only envelop analysis. But it's easy to find defect frequency after wavelet transform. Therefore, Envelop analysis added wavelet transform was useful method for early detection of default in signal process.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.585-590
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• 2004

Many machine failures are not detected well in advance due to the masking of background noise and attenuation of the source signal through the transmission mediums. Advanced signal processing techniques using adaptive filters and higher order statistics have been attempted to extract the source signal from the measured data at the machine surface. In this paper, blind deconvolution using the eigenvector algorithm (EVA) technique is used to recover a damaged bearing signal using only the measured signal at the machine surface. A damaged bearing signal corrupted by noise with varying signal-to-noise (s/n) was used to determine the effectiveness of the technique in detecting an incipient signal and the optimum choice of filter length. The results show that the technique is effective in detecting the source signal with an s/n ratio as low as 0.21, but requires a relatively large filter length.

• 한국소음진동공학회논문집
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• 제23권2호
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• pp.131-143
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• 2013

대부분의 철강산업 기계 등에 설치되어 사용되는 선회베어링은 교체를 위한 정확한 정비계획이 필요하기 때문에 저속회전체의 선회베어링에 대한 진동 상태감시가 매우 중요하게 되었다. 지금까지 음향방출(AE)법이 저속베어링의 상태감시에 가장 많이 사용되는 기술이고 몇몇의 경우는 진동을 사용한다. 음향방출을 사용하는 일반적인 이유는 저속에서 구름요소와 결함위치 사이의 충격에 의하여 발생되는 신호가 약하고 때때로 노이즈나 다른 간섭 주파수에 결함신호가 묻혀 검출이 어렵기 때문이다. 따라서 쉽게 특정 결함에 대한 결함주파수의 동정을 위하여 몇몇 연구자들은 충격에너지를 증가시키기 위하여 인위적으로 미리 정해진 길이, 넓이와 깊이의 결함을 베어링의 내, 외부 레이스에 인가하기도 한다. 이 논문에서는 15 rpm에서 운전하는 저속 선회베어링의 진동신호에 EMD와 EEMD를 적용하였고 논문에서 사용한 진동결함 신호는 국내 산업체에서 공급받은 것이다. 이 논문에서는 베어링결함 주파수 동정을 위하여 EEMD를 사용하여 결함신호의 FFT처리 결과를 입증하고 설명하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.319-323
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• 1996

정격속도 80,000 rpm 초고속 원심분리기(ultra-centrifuge)의 회전체동역학 설계가 수행된다. 설계목표는 충분한 위험속도(critical speed)의 분리여유(separation margin)와 함께, 다수의 고차 위험속도 통과시 원심분리기 로터의 위치에서 양호한 불균형응답특성을 갖는 로터-베어링 시스템의 최적구성을 이루어 내는 것이다. 후자의 특성은 불균형에 의해 가진될 때 로터의 질량중심이 회전축에 가능한 한 근접하도록 함으로써 만족시킬 수 있으며, 이를 위해 초유연축(extra slender shaft)이 적용된다. 이와 더불어, 특히 1차 위험속도에서 공진에 기인한 로터의 큰 변위를 방지하기 위해 범퍼링(bumper ring) 또는 안내베어링(guide bearing)의 설치가 필요하다. 유한요소법(finite element method)에 의한 회전체동역학 모델링이 수행되며, 지지 구름베어링의 강성과 함께 소량의 감쇠(damping)가 고려된다.