• 한국소음진동공학회논문집
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• 제26권6_spc호
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• pp.714-720
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• 2016

Rubbing and misalignment are the most usual faults that occurs in rotating machinery and with them severe effect on power plant availability. Especially blade rubbing is hard to detect on FFT spectrum using the vibration signal. In this paper, the possibility of feature analysis of vibration signal is confirmed under blade rubbing and misalignment condition. And the lab-scale rotor test device provides the blade rubbing and shaft misalignment modes. Feature selection based on GA (genetic algorithm) is processed by the extracted feature of the time domain. Then, classification of the features is analyzed by using SVM (support vector machine) which is one of the machine learning algorithm. The results of features selection based on GA compared with those based on PCA (principal component analysis). According to the results, the possibility of feature analysis is confirmed. Therefore, blade rubbing and shaft misalignment can be diagnosed by feature of vibration signal.

• 한국해양공학회지
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• 제33권2호
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• pp.196-202
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• 2019

In this study, the excessive noise and vibration phenomena of a high-speed Ro/Ro passenger ship were analyzed, and a countermeasure was taken based on them. This ship was granted a comfort class notation by the classification society, which was COMFORT-VIBRATION-II and COMFORT-NOISE-CREW-II. However, unfortunately, excessive noise and vibration in the aft part of the ship were delivered from the twin shaft propellers, and therefore the Class Requirement was not satisfied before delivery. In order to obtain the class notation, all of the concerned parties came to an agreement to reduce the noise and vibration level during operation after delivery because a seasonal ferry service was already scheduled and the cabin was fully booked. The root cause of the massive amount of noise and vibration was mainly the propeller-induced excitation pulse and beating that occurred from the mismatch of the rotating speeds of the two shaft lines. A 1st order vibrating force and beating phenomena existed in the propeller. Thus, a reduction of the excitation force, elimination of the beating phenomena, and decrease of the noise level at the aft area cabins and public spaces were required. In addition, structural reinforcements were conducted using pillars and additional girders at the aft part of the decks.

• Journal of Biosystems Engineering
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• 제33권2호
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• pp.94-100
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• 2008

Present chemical application method using a power sprayer has been labor intensive, costly and ineffective. Therefore, a small agricultural unmanned helicopter was suggested to replace the conventional spray system. In this study, conceptual design for developing the helicopter and a consequential prototype were reported. The overall conceptual design was initiated by deciding the type of agricultural helicopter, as the single rotor helicopter with a tail system. As the first step of the designing, an air-cooled, 2-stroke engine was selected and a prototype transmission was designed by determining the rotating speed of main rotor shaft. A 'pusher' type tail rotor system was adapted to balance the reaction torque and reduce the power use. The tail boom length was designed to avoid the rotating trajectory of the main rotor. The RF console consisted of the engine control, attitude control, and emergency control modules. Assembling the prototype concluded the mechanical development of the agricultural helicopter.

• 대한기계학회논문집B
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• 제24권1호
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• pp.114-123
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• 2000

The flow structure around a rotating axial-fan was experimentally investigated using a phase averaging velocity field measurement technique. The fan blades were divided into 4 different phases, for which 500 velocity fields were acquired for each phase angle with a 2-frame PTV system. Velocity field measurements were also carried out at two planes parallel to the axis of rotation, with offsets toward the radial direction of the fan. For accurate synchronization of the PTV system with the phase of the axial fan, two synchronization circuits were employed with a photo-detector attached to the rotating shaft. The phase averaged velocity fields show periodic variations with respect to the blade phase. The periodic formation of vortices at the blade tip is also observed in vorticity contour plots. Locations of local maximum turbulence intensities in the axial and radial directions are found to be located in an alternating pattern. These experimental results can be used to validate numerical calculations and to understand the flow characteristics of an axial fan.

• 대한산업공학회지
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• 제27권1호
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• pp.61-68
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• 2001

A rotor system is composed of a rotating shaft with supporting bearings. The rotor system is widely used in every rotating machinery such as the turbine generator and the high precision machine tools. A negligible error or malfunction in the rotor, however, can cause a catastrophic failure in the system then result in the environmental and economic disasters. A diagnosis of the rotor system is important in preventing these kinds of failures and disasters. Up to now, many researchers have devoted in the development of diagnosing tools for the system. The basic principles behind the tools are to retrieve the data through the sensors for a specific state of the system and then to identify the specific state through the heuristic methods such as neural network, fuzzy logic, and decision matrix. The proper usage of the heuristic methods will enhance the performance of the diagnostic procedure when together used with the statistical signal processing. In this paper, the methodologies in using the above 3 heuristic methods for the diagnostics of the rotor system are established and also tested and validated for the data retrieved from the rolling element bearing and journal bearing supported system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.863-868
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• 2008

This paper investigates the abnormal noise of polygon mirror scanner motor due to the mechanical contact. In the high speed polygon mirror scanner motor the vibration of polygon mirror scanner motor is one of the main sources of abnormal noise, because structure-borne noise due to the vibration is bigger than aerodynamic noise, especially when the rotating part contacts the stationary parts. This research determines the main harmonics of structure-borne noise by using sound quality evaluation. It also develops an experimental set-up to measure the mechanical contact and vibration of polygon mirror scanner motor simultaneously. This paper also show that mechanical contact between rotating shaft and stationary sleeve is one of the dominant vibration sources of structure-borne noise which cause the abnormal noise of the high speed polygon mirror scanner motor by using the developed experimental set-up.

• 대한기계학회논문집
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• 제10권5호
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• pp.593-600
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• 1986

본 연구에서는 베어링과 같은 기계 회전부품의 정밀진동분석을 위한 구동장치 로서 평판 자기결합기를 갖는 회전장치를 제작하였다. 이 회전장치의 진동특성을 고 찰하기 위해 Weinmann 등의 연구결과에 따라 자기 결합기의 전달 토오크가 그대로 피 동축에 전달됨을 이용하여 이론전개를 하였으며 이 결과를 실험치와 비교하였다.

• 대한기계학회논문집A
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• 제34권11호
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• pp.1757-1763
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• 2010

플라이휠 에너지 저장 장치는 잉여 전기를 회전관성을 통해 운동 에너지로 저장하는 장치로, 회전의 중심이 되는 축과 외부의 플라이휠로 구성이 된다. 수치해석을 위한 일반적 프로그램들은 3차원의 모델을 통하여 구조해석 및 주파수 응답 등의 해석을 수행하게 된다. 허나 상용 프로그램을 이용한 동역학적 해석의 응용은 매우 어려운 실정이며, 사용자가 그 방법을 익히는 것 또한 쉽지 않다. 이러한 문제들을 보완하고자 동역학적 해석을 위한 프로그램을 2차원의 모델을 사용하여 구축하였다. 본 논문에서 제시한 모델링은 회전체를 2차원으로 표현함으로써 3차원에 비해 시스템의 표현을 보다 단순화하여 시스템의 구조를 쉽게 이해할 수 있도록 하였으며, 회전체를 서로 다른 재질의 다중 레이어로 모델이 가능하게 하였다. 또한 축계에 추가적 강성의 영향을 줄 수 있는 열박음 부분에 대하여, 그 영향 정도를 선택적으로 입력할 수 있게 하여 열박음에 대한 효과를 조정할 수 있도록 하였다. 따라서 본 논문에서 제시하는 2차원 모델을 이용한 동특성 해석 프로그램의 해석 오차를 알아보기 위해 상용 프로그램의 해석 결과와 비교하였으며, 모델링을 위한 시간과 해석 수행 시간 역시 비교하였다.

• 대한기계학회논문집A
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• 제37권5호
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• pp.707-713
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• 2013

커플링 볼트는 조립, 분해 시 작업자의 안전이 고려되는 부분이나 공정 중단의 비용이 중요한 부분에서 기존의 일반볼트를 대체한다. 해양과 발전분야에서 세계적으로 광범위하게 적용되어, 회전하는 플랜지 결합에 사용되어 왔고, 국제적인 국가 선급 협회나 규제기관의 사용을 승인받아 왔었다. 커플링 볼트는 유압식으로 인장되어 플랜지 사이를 안정적으로 단단히 결합한다. 본 논문에서는 발전소 커플링 볼트의 국산화를 위해, 역설계를 통해 현재 사용 중인 볼트의 치수를 측정, 역학적인 수식을 통해 권장 체결하중의 기준을 살펴보았다. 마찰계수는 실험을 통해 선정하였고, 구조해석을 통해 체결상태를 확인하였다. 형상변수에 따른 접촉압력의 변화를 볼트 재설계시 참고할 수 있도록 나타내었다.

• 한국정밀공학회지
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• 제27권8호
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• pp.42-47
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• 2010

In this paper, the characteristics of contact surface damage due to fretting in a press-fitted shaft below the fretting fatigue limit are proposed by experimental methods. A series of fatigue tests and interrupted fatigue tests of small scale press-fitted specimen were carried out by using rotating bending fatigue test machine. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that fretting fatigue cracks were initiated even under the fretting fatigue limit on the press-fitted shafts by fretting damage. The fatigue cracks of press-fitted shafts were initiated from the edge of contact surface and propagated inward in a semi-elliptical shape. Furthermore, the fretting wear rates at the contact edge are increased rapidly at the initial stage of total fatigue life. After steep increasing, the increase of wear rate is nearly constant under the load condition below the fretting fatigue limit. It is thus suggested that the fretting wear must be considered on the fatigue life evaluation because the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in the press-fitted structures.