• Tribology and Lubricants
• /
• v.33 no.4
• /
• pp.141-147
• /
• 2017

The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.5
• /
• pp.198-205
• /
• 2005

Many precedent investigations hate been made for the reliable assessment of the insulation state of large power apparatus for which partial discharge detection is one of tile plausible way. In this work, experimental investigations have been carried out to make the comparison on the PD(partial discharge) pattern analysis related to the five different types of artificial defects such as SFMP (Single Free Moving Particle), MFMP (Multi Free Moving Particle), Void, CFP (Conductor-Fixed Protrusion), EP (Enclosure Protrusion). For each PD pattern, PD detection has been done by tee different types of PD sensors such as HFCT(High Frequency Current Transformer), AE(Acoustic Emission) and UHF(Ultra High Frequency). And, in addition, frequency spectrum by the UHF sensor has been also made for each defect respectively. As a result, it is observed that the possibility of obtaining PD pattern based on PRPD(Phase Resolved Partial Discharge) in connection with the defects tinder investigation is dependant on the type of the sensor while the spectrum analysis is always successful to be achieved for every defect. Therefore, it could be suggested that the nature of PD source can be identified more distinctively when the conventional PRPDA is combined with spectrum analysis.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.1
• /
• pp.78-85
• /
• 1986

This study has been made to investigate Behavior of the fatigue crack propagation for the purpose of taking into consideration the fatigue behavior Which initiate and propagate in tip of defect of the defected specimens, Which Contain the micro-hole or micro-slit. Especially, the specimens have been conducted with high-freguency heat treatment of 850.deg. C, 1050.deg. C to consider strength elevation of defected specimens. The results of this study are as follow; (1) The case of the same in the length of crack, the fatigue crack propagation rate of the micro-slit is always faster than that of micre-hole. But, the first step of the fatigue crack propagation it is not always so. (2) Fatigue crack propagation rate of specimens with micro-slit or micro-hole which have been treated with high-frequency heat treatment satisfy the following formula between the fatigue crack propagation rate and nominal stress; dl/dN .var..sigma.$^{m}$ *l$^{n}$ .

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.322-326
• /
• 2008

In this paper, we have studied the images which have been reconstructed by using combination of images acquired by the variation of operating frequency. When inner images have been reconstructed, they have been superposed by the surface state effect. In this case, the images of the phase object can be enhanced by the contrast of inner images. There is a kind of specimen, one is a reference block having 1/4T, 1/2T, 3/4T side drilled holes as main run piping material of the steam generator in nuclear power plants. It has been shown that the two results of defect shapes have better than before in this processing and phase contrast grow about twice. And we have constructed the acoustic microscope by using a quadrature detector that enables to acquire the amplitude and phase of the reflected signal simultaneously. Further more we have studied the reconstruction method of the amplitude and phase images, the enhancement method of the defect images' contrast.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.147-153
• /
• 2009

In this paper, FSS(Frequency Selective Surface) using defect mode characteristic is proposed. The unit cell using defect mode characteristic of the proposed FSS is offered lower resonant frequency in the same cell size. The number of suitable array is optimized 13 by 13. Also, the patch antennas operated in WCDMA(Wideband Code Division Multiple Access) Tx band and Rx band are designed for the comparison. The gain value of proposed FSS-1 complex structure (the patch antenna of Tx band and FSS) is improved 3.3 dB from 9.98 dBi to 13.28 dBi in Tx band. The gain value of proposed FSS-2 complex structure(the patch antenna of Rx band and FSS) is improved 5.53 dB from 9.81 dBi to 15.34 dBi in Rx band. Also the measured impedance bandwidth($VSWR{\leq}2$) of manufactured $13{\times}13$ array antenna is from 337 MHz(1.87 to 2.21 GHz). The measured radiation gain is 11.39 dBi(1.94 GHz), 13.11 dBi(2.05 GHz), 11.09 dBi(2.14 GHz). The measured radiation efficiency is 81 %. Because the proposed FSS structure has more higher gain, it will be applied to antenna of WCDMA repeater system.

• Journal of the Korean Institute of Navigation
• /
• v.22 no.4
• /
• pp.59-67
• /
• 1998

A quick and automatic detection with no harm to the goods is very important task for improving quality control, process control and labour reduction. In real fields of industry, defect detection is mostly accomplished by skillful workers. A narrow band eliminating spatial filter having characteristics of removing the specified spatial frequency is developed by the author, and it is proved that the filter has an excellent ability for on-line and real time detection of surface defect. By the way,. this spatial filter shows a ripple phenominum in filtering characteristics. So, it is necessary to remove the ripple component for the improvement of filter gain, moreover efficiency of defect detection. The spatial filtering method has a remarkable feature which means that it is able to set up weighting function for its own sake, and which can to obtain the best signal relating to the purpose of the measurement. Hence, having an eye on such feature, theoretical analysis is carried out at first for optimal design of narrow band eliminating spatial filter, and secondly, on the basis of above results spatial filter is manufactured, and finally advanced effectiveness of spatial filter is evaluated experimentally.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05a
• /
• pp.35-39
• /
• 2002

A defect detection test was performed for a conductor using a amorphous wire sensor head. A uniform magnetic field was applied in the space between the most inner conductors of a spiral-typed coil. The conductor with a defect was placed on the space between the most inner conductors of spiral-typed coil. The defect can be detected from the differences of induced voltage measured in the vicinity of gap of the conductor. The induced voltage difference of 2.5mV was measured in the gap vicinity of the 1mm thick conductor having 0.5mm gap in the frequency region of 100kHz~600kHz.

• Journal of Chest Surgery
• /
• v.27 no.8
• /
• pp.650-655
• /
• 1994

The author analyzed 99patients with VSD weighting less than 10kg of body weight who underwent surgical correction from 1981 to 1992 at cardiovascular department of Hanyang University hospital. Patients occupied 29.3% of total cases who were underwent surgical corrections for congenital heart diseases during that time. Of the 99 patients, 51 patients were male [52%] and 48 patients[48%] were female. Age ranged from 28 days to 36 months with mean age of 13.6 months. Mean body weight was 7.53kg. According to Kirklin`s anatomical classification, type II defect was most common [61.6%]. Associated anomaly was found in 48 patients [48.5%]. Patent foramen ovale was most commonly associated cardiac anomaly [14.1%] and followed by atrial septal defect [12.1%], patent ductus arteriosus [10.1%]. Cardiac catheterization data were analyzed. The most common range of Qp/Qs, Rp/Rs, Pp/Ps were above 3.0, 0.1 - 0.25, and above 0.75 respectively. Among the indications of surgical correction, there were pulmonary hypertention in 69 patients, congestive heart failure in 44 patients, frequent respiratory infection in 47 patients, growth retardation in 33 patients. The most common surgical approach and method for VSD closure were right atriotomy[48.3%] and dacron patch closure[93.3%]. Complication rate was 13.1% [13 cases], and overall mortality was 17.1% [17 cases]. The cause of death consisted of low cardiac output syndrome[11 cases], acute renal failure[3 cases], sepsis[2 cases] and pulmonary insufficiency[1 case] in order of frequency.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.223-224
• /
• 2022

The occurrence of defect, one of the major risk elements, gives rise to construction delays and additional costs. Although construction companies generally prefer to use a method of identifying and classifying the causes of defects, a system for predicting the rise of defects becomes important matter to reduce this harmful issue. However, the currently used methods are kinds of reactive systems that are focused on the defects which occurred already, and there are few studies on the occurrence of defects with prediction systems. This paper is about preliminary study on the development of judgemental algorithm that informs us whether additional works related to defect issue are needed or not. Among machine learning techniques, deep neural network was utilized as prediction model which is a major component of algorithm. It is the most suitable model to be applied to the algorithm when there are 8 hidden layers and the average number of nodes in each hidden layer is 70. Ultimately, the algorithm can identify and defects that may arise in later and contribute to minimize defect frequency.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.12
• /
• pp.5-12
• /
• 2009

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.