• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.3
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• pp.254-260
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• 2002

In this study, two types of mobile robotic systems using NDT (Non-destructive testing) method are developed for automatic diagnosis of the boiler tubes and large size pipelines. The developed mobile robots crawl the outer surface of the tubes or pipelines and detect in-pipe defects such as pinholes, cracks and thickness reduction by corrosion and/or erosion using EMAT (Electro-magnetic Acoustic Transducer). Automation of fault detection by means of mobile robotic systems for these large-scale structures helps to prevent significant troubles without danger of human beings under harmful environment.

• Tunnel and Underground Space
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• v.17 no.5
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• pp.337-349
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• 2007

Yearly, it seems the fact that the numbers of tunnels with wide sections are on the rise as the length of tunnel and number of lanes continues increasing. According to these trends, well-schemed plans of design, construction and management related with tunnel safety has become to be crucial. It is a high possibility to be observed by the fact that the direct effects of casualties and property damages are caused by the situations of car collisions, bump to solid structures by careless driving and the outbreak on vehicles by mechanical fault. Therefore, in order to prevent these types of accidents, we would make issues md adopt appropriate mechanical and management plans of emergency exits and disaster prevention equipments inside of tunnel, based on up-to dated experiences and study of foreign cases, to structural design technology. The objectives of this study are to recognize related actual problems and suggest improvement plans.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.983-989
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• 2015

Power transformer is one of the major and key apparatus in electric power system. Monitoring and diagnosis of transformer fault is necessary for improving the life period of transformer. The failures caused by short circuits are one of the causes of transformer outages. The short circuit currents induce excessive forces in the transformer windings which result in winding deformation affecting the mechanical and electrical characteristics of the winding. In the present work, a transformer producing only the radial flux under short circuit is considered. The corresponding axial displacement profile of the windings is computed using Finite Element Method based transient structural analysis and thus obtained displacements are compared with the experimental result. The change in inter disc capacitance and mutual inductance of the deformed windings due to different short circuit currents are computed using Finite Element Method based field analyses and the corresponding Sweep Frequency Responses are computed using the modified electrical equivalent circuit. From the change in the first resonant frequency, the winding movement can be quantified which will be useful for estimating the mechanical withstand capability of the winding for different short circuit currents in the design stage itself.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.10
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• pp.832-839
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• 2007

The geometry and dimensions of an expansion chamber are decisive factors in thermal puffer plasma chamber designs. Because they together dominate the temperature and speed at which the cooling gas from the chamber flows back through a flow channel to the arcing zone for the successful interruption of fault currents. In this study, we calculated the flow and mass transfer driven by arc plasma, and investigated the effects of a flow guide installed inside a thermal puffer plasma chamber. It is found that the existing cold gas of the chamber mixes with hot gases entrained from the arcing zone and is subjected to compression due to pressure build-up in the chamber. The pressure build-up with the flow guide is larger than that without due to a vortex which rotates clockwise around the chamber center. By the reverse pressure gradient, the mixing gas of the chamber flows back out for cooling down the residual plasma near current zero. In the case with the flow guide, the temperature just before current zero is lower than that without, and the Cu concentration with high electrical conductivity is also less than that without the flow guide.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.965-970
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• 2011

We develop a diagnostic system to monitor failures in an engine-assembly line. Existing techniques such as sensory analysis, time domain analysis, frequency analysis, and statistical analysis have limitations in the diagnosis of engine-assembly failure when there are abnormal vibration waveforms (crashing and damping signals) during the assembly. We use a wavelet technique to deal with crashing and damping signals. We also implement a new technique for developing diagnostic rules from sensor data, and we demonstrate its validity.

• Progress in Superconductivity
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• v.13 no.1
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• pp.24-27
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• 2011

High voltage insulation in cryogenic environment is one of big issues for development of superconducting power application, such as superconducting fault current limiter, transformer, transmission cable, and so on. We had proposed a composite solid insulator composed of plastics and polymer insulation sheets for a use of high voltage superconducting power applications. It is well known that the G10 FRP keeps its mechanical strength at very low temperature and the PPLP is very good insulator adopted as insulations for superconducting transmission cables. The composition of these two materials will show very good electrical and mechanical properties adequate for the insulation components of superconducting power applications, such as bushing, insulation barrier, and even for a cryostat. Dielectric strengths of prepared samples were measured at the temperature of boiling point of liquid nitrogen at atmospheric pressure, which will be presented in this paper to show a usefulness of this technique.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.8
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• pp.780-788
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• 2005

Two different types of algorithms were developed and applied to detect the partial faults of a multi-type air conditioning system. Partial faults include the compressor valve leakage, the refrigerant pipe partial blockage, the condenser fouling, and the evaporator fouling. The first algorithm was developed by using mathematical models and parity relations, and the second algorithm was developed by using mathematical models and a RBF neural network. Test results showed that the second algorithm was better than the first algorithm in detecting various partial faults of the system. Therefore, the algorithm developed by using mathematical models and a RBF neural network may be used for the detection of partial faults of an air-conditioning system.

• Journal of Hydrogen and New Energy
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• v.27 no.1
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• pp.36-41
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• 2016

The development need of new renewable energy is more and more important to resolve exhaustion of chemical fuels and environmental pollution. Polymer electrolyte membrane fuel cell has been widely studied to the extent that it can be used commercially. But there are many problems to be solved. One of them is to enhance the stability of fuel cell stacks. This paper proposes a new fault diagnosis method using Least Square Method (LSM) which is one of parameter estimation methods. The proposed method extracts equivalent circuit parameters from on-line measurements. Parameters of the circuit are estimated according to normal and abnormal states using simulation. The variation of parameters estimated in each states enables the estimation of state in fuel cells. Thus the LSM presented can be a suitable on-line parameter estimation method in PEMFC.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.8
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• pp.351-356
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• 2014

Typical trouble patterns in solar thermal systems include working fluid leakage and freezing other than breakdown of pump. A fluid sensor for measuring electric resistance of fluid was developed and installed at the top of the collector piping in order to check the fault of solar system. Working fluid level in the pipe was determined by measuring electric resistance from a fluid sensor. On the base of this, it was confirmed that the fluid sensor diagnoses leakage of fluid. Electric resistance of propylene glycol aqueous solution was measured in the range of $0{\sim}70^{\circ}C$ and 0~40% of concentration. The response surface analysis was performed by using a central composite design, and the regression equation was derived from the relationship between electric resistance, temperature, and concentration. Through the experiment in a real solar system, we can estimate a concentration of working fluid when a pump is not operating and predict a possibility of freezing. Finally, an effective algorithm for trouble shooting was proposed to operate and maintain the solar system.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.894-903
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• 2018

In the case of helicopters, the development of parts technology is rapidly changing, and the complexity is rapidly increasing. Particularly, the surge of various electric and electronic systems is recognized as a problem that is directly related to the safety of the helicopter. Due to these problems, there is a growing interest in reliability evaluation in the face of the problem of confirming and certifying the reliability of parts in the development stage. In this paper, the analysis of the failure mechanism of the wiper system was carried out, and the priority and importance of each failure mode were checked by using the results, and major stress factors were derived and the corresponding acceleration model was selected. Also, the accelerated lifetime test time was calculated according to the life test time, acceleration status and acceleration level of the steady state by using the selected acceleration model and characteristic values.