• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1280-1290
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• 2016

This paper presents an advanced estimation method for obtaining the probability density functions of a damage parameter for valve leakage detection in a reciprocating pump. The estimation method is based on a comparison of model data which are simulated by using a mathematical model, and experimental data which are measured on the inside and outside of the reciprocating pump in operation. The mathematical model, which is simplified and extended on the basis of previous models, describes not only the normal state of the pump, but also its abnormal state caused by valve leakage. The pressure in the cylinder is expressed as a function of the crankshaft angle, and an additional volume flow rate due to the valve leakage is quantified by a damage parameter in the mathematical model. The change in the cylinder pressure profiles due to the suction valve leakage is noticeable in the compression and expansion modes of the pump. The damage parameter value over 300 cycles is calculated in two ways, considering advance or delay in the opening and closing angles of the discharge valves. The probability density functions of the damage parameter are compared for diagnosis and prognosis on the basis of the probabilistic features of valve leakage.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.595-600
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• 2016

In this paper, the oxide currents of thin silicon oxides is investigated. The oxide currents associated with the on time of applied voltage were used to measure the distribution of voltage stress induced traps in thin silicon oxide films. The stress induced leakage currents were due to the charging and discharging of traps generated by stress voltage in the silicon oxides. The stress induced leakage current will affect data retention in memory devices. The oxide current for the thickness dependence of stress current and stress induced leakage currents has been measured in oxides with thicknesses between $109{\AA}$, $190{\AA}$, $387{\AA}$, and $818{\AA}$ which have the gate area $10^{-3}cm^2$. The oxide currents will affect data retention and the stress current, stress induced leakage current is used to estimate to fundamental limitations on oxide thicknesses.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.433-434
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• 2007

This paper describes a low-voltage dynamic random-access memory (DRAM) focusing on subthreshold leakage reduction during self-refresh (sleep) mode. By sharing a power switch, multiple iterative circuits such as row and column decoders have a significantly reduced subthreshold leakage current. To reduce the leakage current of complex logic gates, dual channel length scheme and input vector control method are used. Because all node voltages during the standby mode are deterministic, zigzag super-cutoff CMOS is used, allowing to Preserve internal data. MTCMOS technique Is also used in the circuits having no need to preserve internal data. Sub-1.2-V 1-Gb mobile DDR DRAM employing all these low-power techniques was designed in a 60 nm CMOS technology and achieved over 77% reduction of overall leakage current during the self-refresh mode.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.2
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• pp.207-214
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• 2006

The current paper focuses the analysis of leakage detection in water pipeline systems by means of the transient method. In order to obtain essential data for evaluation the existing methodology, an extensive experimental process has been carried out in a single pipeline system, Several experimental tests were performed with and without a leakage in the system. Using the unsteady friction and improved unsteady friction factors gives reasonable match between the computed and measured results on the condition of the flow situations presented in the paper. The transient method attempts to estimate the leakage in water pipelines using observed pressure data collected during transient events on the system.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3594-3601
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• 2024

It is difficult to detect a small-scale leakage in a nuclear power plant (NPP) quickly and take appropriate action. Delaying these procedures can have adverse effects on NPPs. In this paper, we propose leak flow rate prediction using the bidirectional gated recurrent unit (Bi-GRU) method to detect leakage quickly and accurately in small-scale leakage situations because large-scale leak rates are known to be predicted accurately. The data were acquired by simulating small loss-of-coolant accidents (LOCA) or small-scale leakage situations using the modular accident analysis program (MAAP) code. In addition, to improve prediction performance, data were collected by distinguishing the break sizes in more detail. In addition, the prediction accuracy was improved by performing both LOCA diagnosis and leak flow rate prediction in small LOCA situations. The prediction model developed using the Bi-GRU showed a superior prediction performance compared with other artificial intelligence methods. Accordingly, the accurate and effective prediction model for small-scale leakage situations proposed herein is expected to support operators in decision-making and taking actions.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.42-47
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• 2012

The containment local leakage rate testing in nuclear power plants is performed in accordance with ANSI/ANS 56.8-1994 in Korea. Two methods, the make-up flow rate and the pressure decay, are used for local leakage rate testing. Though ANSI/ANS 56.8-1994 does not define clearly the minimum test duration for the make-up flow rate method, it requires obtaining the data after reaching the stable condition. Thus the prerequisite stable condition for data acquisition and the testing time is differently applied to each NPPs. Therefore, this study presents a standardized test procedure for data stabilization and testing time through experiments to improve the test reliability.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1189-1194
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• 2002

Acoustic intensity is usually estimated by the cross-spectrum of acoustic pressure at two adjacent micrphones. The cross-spectrum calculated by digital Fourier transform technique will unavoidally have leakage error since the period of signal will not be usually coincident with record length. Therefore, the acoustic intensity estimated by the conventional r]n analyzer will show distorted value. In this paper the expression of the Fourier transformed data of a harmonic signal is formulated when there is leakage error. The method to elimate the effect of leakage error from the contaminated data is also proposed. Some numerical examples show the validation of the proposed method.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1969-1971
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• 2000

This paper presents a data acquisition and analysis program modules that has been developed using the Labview program. These program modules can use to acquire and analyze leakage current data of insulator under different contamination conditions. The experimental hardware made up salt fog chamber, AC/DC power supply, transducer (shunt resistor), measurement devices and PC with the GPIB (General Purpose Interface Bus). And analysis program modules can calculate pulse level count, accumulated charge, average leakage current, power spectrum, and harmonics. The result of applying these analytical program modules to polymeric insulator is available for evaluation of leakage current characteristic of outdoor insulators.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.311-317
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• 2005

Measurements of the leakage flow in the shrouded cavity were performed in axial compressor cascades at $Re=2.6{\times}10^5$. This paper describes the effects of the leakage flow tangential velocity on kinematics of the leakage flow in the shrouded cavity and consequent overall loss and exit flow turning at stator blade row downstream. Flow data and flow visualization images consistently indicate that leakage flow circumferentially migrates 2, 4 and 5 blade passages in the direction of rotation for ${\upsilon}_y/c=0.09$, 0.35 and 0.45, respectively where ${\upsilon}_y$ is the leakage tangential velocity and c is the mainstream velocity. The leakage flow contracts to a jet across the seal-tooth resulting in an increase in the leakage axial velocity-doubling the leakage axial velocity in upstream cavity compared to that in the downstream cavity. Consequently, two flow regions are distinguished before and after the seal-tooth. As increasing the leakage tangential velocity, the overall loss downstream of stator blade row decreases and the exit flow turning in the range of span. from the hub endwall to 15% increases while the decreases in the flow turning from 15% to 30% span is observed.

• Journal of Applied Reliability
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• v.14 no.4
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• pp.230-235
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• 2014

The failure modes of pneumatic directional control valves include leakage, wear of the spool seal, and sticking of the spool. Among them, the main failure mode of the valve is leakage. The leakage is caused by the wear of the spool seal. However, due to the characteristics of the seal material, the leakage rate is fluctuated a lot rather than constantly increased over time. If life analysis is performed using the first time data of leakage failure, predicted life cycles can be different from the real life cycles. This paper predicts life cycles of the pilot pneumatic directional control valve based on the three point moving average which considers the average of the fluctuating leakage rate.