• Journal of the Korean Institute of Gas
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• v.16 no.2
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• pp.18-24
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• 2012

This research seeks to evaluate damage on type II gas cylinder by an acoustic emission test when executing 20000 cycles fatigue test and thereafter burst test. Used gas cylinders in the experimental are three types as follows; one is sound cylinder, others are cylinders which contain longitudinal and transverse artificial defect. The size of artificial defect is a depth of 3 mm, width of 3 mm and length of 50 mm. In the case of the cylinder which artificial defect, unlike the expectation that it will burst in low pressure, the burst pressure of the cylinder did not differ much according to whether or not there were defects. However, when there was longitudinal defect, the location of burst was near the location of defect. This leads to the effect in which the thickness of the composite material becomes thinner according to the length of the longitudinal defect and this is judged to have an effect on the location of initiation and growth of crack in the liner. Also, for the acoustic emission signal, when there is longitudinal defect, the ratio of an event occurring at defect position among overall hits is more than 50 %, and the source location also accords very precisely with defect position.

• Journal of Chest Surgery
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• v.29 no.9
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• pp.945-950
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• 1996

Twelve patients with left ventricular-right atrial shunt (LV-RA shunt) underwent surgical correction be- tween April 1982 and March 1995. Seven patients were male and five patients were female. Age ranged from 3 to 26 years with mean age of 8.5 years. On the preoperative chest PA views, increased pulmonary vascularity was noted in 3 cases and enlargement of right atrium in 4 cases. The mean preoperative cardiothoracic ratio was 0.59. Echocardiographic studies were obtained in 9 patients and the preoperative echocardiographic diagnoses were LV-RA shunt in 2 cases, ventricular septal defect (VSD) in 6 casei, and atrial septal defect (ASD) in 1 case. The preoperative ngiographic diagnoses which were obtained in all patients were LV-RA shunt in 5 cases, VSD in 5 cases, ASD in 1 case, and VSD with ASD in 1 case. The descriptions of defect of LV-RA shunt according to intraoperative findings were supravalvular defect in 5 cases(42%), infravalvular defect in 4 cases (33%), and combined defect in 3 cases (25%). Associated anomalies of tricuspid valve in 4 cases of infravalvular defect were perforation (3 cases) and cleft (1 case). Primary closure of the septal defect was performed through the right atriotomy in all but one patient. There was no operative death. One patient underwent reoperation because of the residual interventricular shunt. All patients have been in good condition.

• Journal of Chest Surgery
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• v.29 no.2
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• pp.147-152
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• 1996

his study was undertaken to assess the residual interventricular shunt following surgical closure of the isolated ventricular septal defect. From January 1989 through December 1993, 211 patients underwent surgical closure of the isolated ventricular septal defect. All patients had 2D-Echocardlo-graphic study after operation to rule out residual ventricular septal defect. There was a 9.5% incidence of a definite residual shunt. The type of ventricular septal defect, closure method of the defect and cardiopulmonary bypass time showed no significant differences between two groups. The sue of ventricular septal defect (6.3 $\pm$ 3.7mm versus 10.6 $\pm$ 5.8mm : p : 0.0034), aortic cross-clamping time(32.6 $\pm$ 15.0 minutes versus 48.5 $\pm$ 20.0 minutes, p : 0.0003), pulmonary-to-systemic pressure ratio(0.31 $\pm$ 0.22 versus 0.51 $\pm$ 0.33, p=0.019) and mean pulmonary artery pressure(20.3 $\pm$ 11.9 mmHg versus 29.1 $\pm$ 16.2 mmHg, p : 0.009) were meaningfully different between two groups. There were 9 insta ces of spontaneous closure of the residual shunts at mean 21 months of following up (ranged 1 ~43 months). In conclusion, we suggest that the size of ventricular septal defect, aortic cross-clamping time and mean pulmonary artery pressure may play an important role in occurance of residual ventricular septal defect.

• Journal of Chest Surgery
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• v.12 no.1
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• pp.33-42
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• 1979

The present study reports 41 cases of congenital and acquired heart diseases, who received open heart surgery under extracorporeal circulation [ECC] by Sarns Heart-Lung-Machine [HLM] at the Department of Thoracic and Cardiovascular Surgery, Hanyang University Hospital during the` period between July 1975 and February 1979. The priming of pump oxygenator was carried out by the hemodilution method using Hartman`s solution, whole blood, and fresh human plasma. The rate of hemodilution was in the average of 50.8 ml/kg. ECC was performed at the average perfusion flow rate of 85.0 ml/kg/min [2.43 L./ kg/2] and at moderate hypothermia. In the total cardiopulmonary bypass, arterial pressure ranged between 55 mmHg and 90 mmHg, but generally maintaining over 70 mmHg. Patient age ranged between 2 and 54 year old, in congenital heart diseases, between 2 and 28, in acquired heart diseases, between 17 and 54 Sex ratio of male to female was 20:21. The cases include a case of pulmonary valvular stenosis, 4 cases of atrial septal defect, 9 cases of ventricular septal defect, 9 cases of tetralogy of Fallot, 5 cases of pentalogy of Fallot, 3 cases of atypical multiple anomalies 7 cases of mitral stenosis or insufficiency, a case of myxoma in left atrium, and a case of ruptured aneurysm of Valsalva`s sinus. The surgical managements were 16 valvulotomy for pulmonary valvular stenosis, 2 Teflon patch graft closure and 5 simple suture closure of atrial septal defect, 16 Teflon patch graft closure and 5 simple suture closure of ventricular septal defect, 12 pericardial patch graft for infundibular stenosis of right ventricle, one anastomosis between left superior vena cava and right atrium, 2 open mitral commissurotomy, 5 mitral valve replacement using Starr-Edward`s ball valve, porcine xenograft by Hancock, by Carpentier-Edward, or Angell-Shiley, one removal of left atrial myxoma, and a repair of ruptured aneurysm of Valsalva`s sinus. Four [9.7%] out 41 cases expired postoperatively and the rest of 37 cases survived with satisfactory results. The causes of death were one coronary embolism in tetralogy of Fallot, 2 postoperative lower cardiac output in atypical multiple anomalies, and one right heart failure in large: ventricular septal defect with pulmonary hypertension.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.5
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• pp.415-419
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• 2008

Detecting and correcting defects on LCD glasses early in the manufacturing process becomes important for panel makers to reduce the manufacturing costs and to improve productivity. Many attempts have been made and were successfully applied to detect and identify simple defects such as scratches, dents, and foreign objects on glasses. However, it is still difficult to robustly detect low-contrast defect region, called Mura or blemish area on glasses. Typically, these defect areas are roughly defined as relatively large, several millimeters of diameter, and relatively dark and/or bright region of low Signal-to-Noise Ratio (SNR) against background of low-frequency signal. The aim of this article is to present a robust algorithm to segment these blemish defects. Early 90's, a highly robust estimator, known as the Model-Fitting (MF) estimator was developed by X. Zhuang et. al. and have been successfully used in many computer vision application. Compared to the conventional Least-Square (LS) estimator the MF estimator can successfully estimate model parameters from a dataset of contaminated Gaussian mixture. Such a noise model is defined as a regular white Gaussian noise model with probability $1-\varepsilon$ plus an outlier process with probability $varepsilon$. In the sense of robust estimation, the blemish defect in images can be considered as being a group of outliers in the process of estimating image background model parameters. The algorithm developed in this paper uses a modified MF estimator to robustly estimate the background model and as a by-product to segment the blemish defects, the outliers.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.291-298
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• 1995

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter $d/{\lambda}$; where d is transducer or defect size and ${\lambda}$ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the $d/{\lambda}$ is greater than 1.5, measured directivities almost agreed with the theoretical one.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.75-82
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• 2007

As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.218-218
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• 2003

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1078-1085
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• 2011

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor's "2.5D" model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44mm depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.5
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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.