• Korean Chemical Engineering Research
• /
• v.46 no.2
• /
• pp.286-290
• /
• 2008

Small amounts of CO in reformate fuel gas effectively block platinum catalysts by strong adsorption on the platinum surface at the operation temperature of $60{\sim}80^{\circ}C$ in PEMFC. To oxidate CO, Ru/C layer (CO filter) was placed between Pt/C layer and GDL (gas diffusion layer) in this study. Ru/C filter provided good CO-tolerant PEMFC anode, but decreased the performance of unit cell about 10% at 0.6 V due to mass transfer resistance from Ru/C filter thickness and increase of charge transfer resistance. Membrane degradation is one of the most important factors limiting the life-time of PEMFCs. Membrane durability would be dependent on the electrode catalyst type. It seemed that Ru catalyst layer would shorten the life time of PEMFC as enhanced the fluoride emission rate of membrane in acceleration test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.159-159
• /
• 2010

We conducted bum-in test by current stress to evaluate acceleration reliability characteristics about p-resistivity influence of GaN-based light-emitting diodes. The LEDs used in this study are the polarization field-induced LED(PF-LED) having low p-resistivity and the highly resistive LED(HR-LED) having high p-resistivity. The result of high stress experiment shows that current crowding phenomenon is occurred from the center of between p-bonding pad and n-bonding pad to either electrodes. In addition, series resistance and optical power decrease dramatically. These results means that the resistance of between p-bonding pad and p-GaN affect reliability. That's why we need to consider the ohmic contact of p-bonding pad when design the high efficiency and high reliability LEDs.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.24 no.3
• /
• pp.123-128
• /
• 2020

Analysis of the 2016 Gyeongju earthquake and the 2017 Pohang earthquake showed the characteristics of a typical high-frequency earthquake with many high-frequency components, short time strong motion duration, and large peak ground acceleration relative to the magnitude of the earthquake. Domestic nuclear power plants were designed and evaluated based on NRC's Regulatory Guide 1.60 design response spectrum, which had a great deal of energy in the low-frequency range. Therefore, nuclear power plants should carry out seismic verification and seismic performance evaluation of systems, structures, and components by reflecting the domestic characteristics of earthquakes. In this study, high-frequency amplification factors that can be used for seismic verification and seismic performance evaluation of nuclear power plant systems, structures, and equipment were analyzed. In order to analyze the high-frequency amplification factor, five sets of seismic time history were generated, which were matched with the uniform hazard response spectrum to reflect the characteristics of domestic earthquake motion. The nuclear power plant was subjected to seismic analysis for the construction of the Korean standard nuclear power plant, OPR1000, which is a reactor building, an auxiliary building assembly, a component cooling water heat exchanger building, and an essential service water building. Based on the results of the seismic analysis, a high-frequency amplification factor was derived upon the calculation of the floor response spectrum of the important locations of nuclear power plants. The high-frequency amplification factor can be effectively used for the seismic verification and seismic performance evaluation of electric equipment which are sensitive to high-frequency earthquakes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.2
• /
• pp.120-126
• /
• 2013

Increasing numbers of space debris around the earth now pose a major threat to satellites as their impact velocity may reach up to several km/s. We use a pulse laser to accelerate a miniflyer for mimicking the space debris. The multi-layer coat on the confined medium is known to promote a higher acceleration. However, it requires some special techniques which take somewhat long time and cost to coat. Instead, we devised a simple concept to coat by the black lacquer paint on a flyer. It shows improvement in the flyer velocity by 1.5-2 times the uncoated, and the resulting velocity reached 1.42km/s with Nd:YAG laser energy under 1.4 joules. The resulting velocity is suitable for satellite vulnerability test for debris impact in the geostationary orbit.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.15 no.6
• /
• pp.1-8
• /
• 2016

As demand for paper cups markedly increases, this has brought about a requirement to develop fast paper cup forming machines. However, the fast manufacturing speed of these machines causes faults to occur more frequently in the final product. To reduce the possibility of producing faulty products, it is necessary to develop technologies to monitor the manufacturing process and diagnose the machine status. In this research, we selected the main driving axis of the forming machine for fault diagnosis. We searched the states of rotational elements related to the driving axis and suggested a fault diagnostic system based on spectrum analysis consisting of a real-time data acquisition device, accelerometers, and a diagnosis algorithm. To evaluate the developed fault diagnostic system, we performed experiments using a test station which resembles the actual paper cup forming machine. As a result, we were able to confirm that the proposed system was sufficiently feasible to diagnose any abnormalities in the operation of the paper cup forming machine.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1299-1306
• /
• 2011

In this study, crack-growth model parameters subjected to variable amplitude loading are estimated in the form of a probability distribution using the method of Bayesian parameter estimation. Huang's model is employed to describe the retardation and acceleration of the crack growth during the loadings. The Markov Chain Monte Carlo (MCMC) method is used to obtain samples of the parameters following the probability distribution. As the conventional MCMC method often fails to converge to the equilibrium distribution because of the increased complexity of the model under variable amplitude loading, an improved MCMC method is introduced to overcome this shortcoming, in which a marginal (PDF) is employed as a proposal density function. The model parameters are estimated on the basis of the data from several test specimens subjected to constant amplitude loading. The prediction is then made under variable amplitude loading for the same specimen, and validated by the ground-truth data using the estimated parameters.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.10
• /
• pp.1644-1652
• /
• 2003

The monitor product is packed by cushioning materials because the monitor can be broken during transportation. However, the addition of the cushioning material increased the volume of the product. Therefore, it is required that the usage of cushioning material be minimized. In practice, design engineers have followed the ad hoc design with experiences of predecessors. Automation of the design process is very important for the reduction of engineering cost, and can be achieved by an excellent design process and software development. According to Axiomatic design, a design flow is defined and a software system is developed for automated design. At first, a basic model is defined. A user can modify the model from menus and design is carried out according to the input from the user. Finite element models are automatically generated based on the design. A nonlinear finite element analysis program called LS/DYNA3D is linked for the impact analysis. The process of Design of Experiments using orthogonal array is installed to minimize the maximum acceleration in drop test. Therefore, a new design can be proposed by the system. The program is designed according to the Independence Axiom of Axiomatic design. FRs and DPs of the software system are defined and decomposed by zigzagging process. Independent modules can be generated by analysis of the full design matrix and each module is coded as class in Object Oriented Programming (OOP). Design results are discussed.

• Smart Structures and Systems
• /
• v.20 no.2
• /
• pp.151-162
• /
• 2017

In practical engineering, the friction damper is a widely used energy dissipation device because of its large deformation capacity, stable energy dissipation capability, and cost effectiveness. While based on conventional friction dampers, the double-sliding friction damper (DSFD) being proposed is different in that it features two sliding friction forces, i.e., small and large sliding friction forces, rather than a single-sliding friction force of ordinary friction dampers. The DSFD starts to deform when the force sustained exceeds the small-sliding friction force, and stops deforming when the deformation reaches a certain value. If the force sustained exceeds the large sliding friction force, it continues to deform. Such a double-sliding behavior is expected to endow structures equipped with the DSFD better performance in both small and large earthquakes. The configuration and working mechanism of the DSFD is described and analyzed. Quasi-static loading tests and finite element analyses were conducted to investigate its hysteretic behavior. Finally, time history analysis of the single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems were performed to investigate the seismic performance of DSFD-equipped structures. For the purpose of comparison, tests on systems equipped with conventional friction dampers were also performed. The proposed DSFD can be realized perfectly, and the DSFD-equipped structures provide better performances than those equipped with conventional friction dampers in terms of interstory drift and floor acceleration. In particular, for the MDOF system, the DSFD helps the structural system to have a uniform distributed interstory drift.

• Geomechanics and Engineering
• /
• v.15 no.3
• /
• pp.851-859
• /
• 2018

There are two primary causes of the ground movement due to tunnelling in urban areas; firstly the lost ground and secondly the groundwater depression during construction. The groundwater depression was usually not considered as a cause of settlement in previous research works. The main purpose of this study is to analyze the combined effect of these two phenomena on the transverse settlement trough. Centrifuge model tests and numerical analysis were primarily selected as the methodology. The characteristics of settlement trough were analyzed by performing centrifuge model tests where acceleration reached up to 80g condition. Two different types of tunnel models of 180 mm diameter were prepared in order to match the prototype of a large tunnel of 14.4 m diameter. A volume loss model was made to simulate the excavation procedure at different volume loss and a drainage tunnel model was made to simulate the reduction in pore pressure distribution. Numerical analysis was performed using FLAC 2D program in order to analyze the effects of various groundwater depression values on the settlement trough. Unconfined fluid flow condition was selected to develop the phreatic surface and groundwater level on the surface. The settlement troughs obtained in the results were investigated according to the combined effect of excavation and groundwater depression. Subsequently, a new curve is suggested to consider elastic settlement in the modified Gaussian curve. The results show that the effects of groundwater depression are considerable as the settlement trough gets deeper and wider compared to the trough obtained only due to excavation. The relationships of maximum settlement and infection point with the reduced pore pressure at tunnel centerline are also suggested.

• Journal of IKEEE
• /
• v.19 no.3
• /
• pp.455-459
• /
• 2015

This paper proposes a dispatch unit of GP-GPU with SIMT architecture to support the acceleration of general-purpose operation as well as graphics processing. If all the information of an operand used instructions issued from the warp scheduler is decoded, an unnecessary operand load occurs, resulting in register loads. To resolve this problem, this paper proposes a method that can reduce the operand load and the load on the resister by decoding only the information of the operand using a pre-decoding method. The operand information from the dispatch unit is passed to the operand selection unit with preventing register bank collisions. Thus the overall performance are improved. In the simulation test, the total clock cycles required by processing 10,000 arbitrary instructions issued from the wrap scheduler using ModelSim SE 10.0b are measured. It shows that the application of the dispatch unit equipped with the pre-decoding function proposed in this paper can make an improvement of about 12% in processing performance compared to the conventional method.