• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.2
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• pp.29-37
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• 2001

The application of laser in pipelines was started from the base of using laser in nuclear facilities industries and power plants. Because laser can be delivered to a remote area without any difficulties, the application of laser in many industries can solve many difficulties from limitation of access in danger area and reduced the risks of workers. Therefore, we developed a new experimental technique to measure internal defects of pressure vessels with a combination of shearog-raphy and image processing technique. Conventional NDT methods have been taken relatively much time, money and manpower because of performing as the method of contact with objects to be inspected. But digital shearography is laser-based optical method which allows full-field observation of surface displacement derivatives. This method has many advantages in practical use, such as low sensitivity to environmental noise, simple optical configuration and real time mea-surement. In this paper, we find the optimum shearing magnitude with EFM and experiment and measured internal crack length of the pressure vessels at a real time and estimated the error of the results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.5
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• pp.473-481
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• 2007

Compared to other types of fuel cells, SOFC has advantages like a wide output range and the direct use of hydrocarbon fuel without the process of external reforming. Particularly because the direct use of fuel without reforming reaction is closely linked to overall system efficiency, it is a very attractive advantage. We tried the operation with methane. However, although methane has a small number of carbons compared to other hydrocarbon fuels, our experiment found the deposition of carbon on the surface of the SOFC electrode. To overcome the problem, we tried the operation through activating internal reforming. The reason that internal reforming was possible was that SOFC runs at high temperature compared to other fuel cells and its electrode is made of Ni, which functions as a catalyst favorable for steam reforming.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.5
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• pp.401-412
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• 2013

The paper is to study on the simulation of the micro/macroscale thermo-electrochemical model of a single cell of anode-supported SOFC with direct internal reforming. The coupled heat and mass transport, electrochemical and reforming reactions, and fluid flow were simultaneously simulated based on mass, energy, charge conservation. The micro/macroscale model first calculates the detailed electrochemical and direct internal reforming processes in porous electrodes based on the comprehensive microscale model and then solve the macroscale processes such as heat and mass transport, and fluid flow in SOFCs with assumption of fully-developed flow in gas channel. The simulation results evaluate the overall performance by analyzing distributions of mole fraction, current density, temperature and microstructural design in co/counter flow configurations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.2
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.773-783
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• 2005

Internal flow measurement of very low specific-speed semi-open impellers has been carried out by PIV in order to understand better the internal flow patterns that are responsible fur the unique performance of these centrifugal pumps operating in the range of very low specific speed. Two types of impellers, one equipped with six radial blades (Impeller A) and the other with four conventional backward-swept blades (Impeller B), are tested in a centrifugal pump operating at a non-dimensional specific-speed of $n_s=0.24$. Complex flow patterns captured by PIV are discussed in conjunction with the overall pump performance measured separately. It is revealed that Impeller A achieves higher effective head than Impeller B even though the flow patterns in Impeller A are more complex, exhibiting secondary flows and reverse flows in the impeller passage. It is shown that both the localized strong outward flow at the pressure side of each blade outlet and the strong outward through-flow along the suction side of each blade are responsible for the better head performance of Impeller A.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.6
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• pp.660-667
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• 2016

Maintaining proper tire air pressure is an essential element in ensuring vehicle safety. UHP Tires that boast of many safety features are increasing in the market. In particular, the development of "Self-Inflating Tire" technology is accelerating around the globe. Self-inflating tire refers to a technique for maintaining appropriate tire pressure. An internal regulator senses when tire inflation pressure has dropped below the set air pressure. The tire boosts air through the valve when rolling and compressed air enters into the tire. This procedure keeps the tire air pressure at an appropriate level and increases tire safety. Flow analysis of the internal tube is required to examine self-inflating tires. In this study, a method of tube flow analysis using the FSI Method is proposed. The valve system is also implemented to optimize the regulator and sensor.

• Transactions of Materials Processing
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• v.18 no.1
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• pp.59-66
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• 2009

In this study, V-notch part has been considered as one of safety components in rectangular cup used for mobile device. This kind of safety component in rectangular cup with the V-notch part, which controls adequately the increased internal pressure in the rectangular cup, plays an important role to prevent the explosion from the excessive internal pressure. The protecting mechanism on the mobile device against the explosion is that a series of fracture on the V-notch part at the critical internal pressure level occurs. Therefore, it is very crucial to estimate accurately the working pressure range of the safety device. Relationship between the working internal pressure and fracture phenomenon at V-Notch part was investigated through numerical analysis using ductile fracture criteria. Integral value, I, of the used ductile fracture criteria was calculated from effective stress and strain, and then the bursting pressure of the V-notch part was extracted. Comparisons between the estimated and experimental results show that this systematic approach to predict bursting pressure using the ductile fracture criteria gives fairly good agreements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1399-1406
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• 2005

Recently authors have proposed a new method to estimate failure strength of a pipe with local wall thinning subject to either internal pressure or global bending. The proposed method was based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region, and the simple scheme to estimate the equivalent stress in the minimum ligament was proposed, based on the reference stress concept. This paper extends the new method to combined internal pressure and global bending. The proposed method is validated against FE results for various geometries of local wall thinning under combined loading. The effect of internal pressure is also investigated in the present study. Comparison of maximum moments, predicted according to the proposed method, with published full-scale pipe test data fur locally wall-thinned pipes under combined internal pressure and global bending, shows good agreement.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1801-1806
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• 2012

This paper presents a simple and practical method which enables to prevent malfunction of protection relay due to differential current caused by one end CT saturation in case of external fault. This method uses difference of magnitude(instantaneous value) between the both end current just before the occurrence of differential current without a separate method to CT staturation detection. One end CT saturation is simulated by current transformer model using type-96 component and the presented method is verified by using EMTP MODELS with respect to internal and external fault with one end CT staturation. The presented method distinguished rightly bewteen external and internal fault with one end CT saturation. This information can be used to prevent malfunction of current differential protection relay in case of external fault. And this method is not affected by sampling rate and has no calculation burden, so it will be applicable to differential current protection relay with ease.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.4
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• pp.175-185
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• 2002

In this paper, a new fully digital current control method of UPS inverter, which is based on an internal model control, is proposed. In the proposed control system, overshoots and oscillations due to the computation time-delay are compensated by explicit incorporation of the time-delay in the current control loop transfer function. The internal model controller is adopted to a second order deadbeat reference-to-output response which means that its response reaches the reference in two sampling time including computational time-delays. That is, the average current of filter capacitor is been exactly equal to the reference current with a time lag of two sampling intervals. Therefore, this method has an essentially overshoot free reference-to-output response with a minimum possible rise time. The effectiveness of the proposed control system has been verified by the simulation and experimental respectively. From the simulation and experimental results, the proposed system is achieved the robust characteristics to the calculation time delay and parameter variation as well as very fast dynamic performance, thus it can be effectively applied to the power supply for the critical load.