• Proceedings of the KIPE Conference
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• 전력전자학회 2003년도 추계학술대회 논문집
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• pp.238-243
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• 2003

The solar cells should be operated at the maximum power point because its output characteristics are greatly fluctuated on the variation of insolation, temperature and load. The output power of solar cell is DC, therefore it is necessary to install an inverter among electric power converts. The inverter have to supply a sinusoidal current and voltage to the load and the interactive utility line. In the paper, the proposes a photovoltaic system designed with a step up chopper and single phase PWM voltage source inverter. Synchronous signal and control signal was processed by microprocessor for stable modulation. The step up chopper operates in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature because solar cell has typical dropping character. The single phase PWM voltage source inverter consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be developed continuously by connecting with the source of electric power, from 10 to $20\%$. The single phase PWM voltage source inverter operates in situation that its output voltage is in same phase with the utility voltage. The inverter supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.69-74
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• 2006

An Experimental study was conducted on $CO_2$ recycle combustion heating system using pure oxygen instead of conventional air as an oxidant, which is thereby producing a flue gas of mostly $CO_2$ and water vapor($H_2O$) and resulting in higher $CO_2$ concentration. The advantages of the system are not only the ability to control high temperatures characteristic of oxygen combustion with recycling $CO_2$. but also the possibility to reduce NOx emission in the flue gas. A small scale industrial reheating furnace simulator and specially designed variable flame burner were used to characterize the $CO_2$ recycle oxy-fuel combustion, such as the variations of furnace pressure, temperature and composition in the flue gas during recycle. It was found that $CO_2$ concentration in the flue gas was about 80% without $CO_2$ recycle, but increased to $90{\sim}95%$ with $CO_2$ recycle. The furnace temperature and pressure was decreased due to recycle and the NOx emission was also reduced to maintain under 100ppm.

• Journal of Sensor Science and Technology
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• 제21권1호
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• pp.46-52
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• 2012

The rapid water pollution in stream, river, lake and sea in recent years raises an urgent need for continuous monitoring and policymaking to conserve the global clean environment. In particular, the increasing water pollution in coastal marine areas adds to the importance of the environmental monitoring systems. In this paper, the mobile server is designed to gathers information of the water quality at coastal areas. The obtained data by the server is transmitted from field servers to the base station via multi-hop communication in wireless sensor network. The information collected includes dissolved oxygen(DO), hydrogen ion exponent(pH), temperature, etc. By the information provided the real-time monitoring of water quality at the coastal marine area. In addition, wireless sensor network-based flooding routing protocol was designed and used to transfer the measured water quality information efficiently. Telosb sensor node is programmed using nesC language in TinyOS platform for small scale wireless sensor network monitoring from a remote server.

• 한국석유지질학회:학술대회논문집
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• 한국석유지질학회 2000년도 제7차 학술발표회 발표논문집
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• pp.47-56
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• 2000

The northwestern part of Kyongsang Basin largely comprises interbedded sandstone and mudstone with local conglomeratic deposits in the basin margin, representing marginal alluvial fans and fluvial depositional environments. The non-marine successions are divided into successive stratigraphic units, each of which is unique in facies assemblages and architecture of sandstone bodies. Two stratigraphic units, i.e., Sinpyong-Anpyong and Jotap units are examined in terms of stratigraphic architecture and its causative processes. Detailed architectural analysis reveals that the channel systems of Sinpyong-Anyong unit were of braided patterns, whereas those of Jotap unit were dominated by small-scale bedforms. The difference in fluvial styles can be attributed to the changes in amount and caliber of sediment load and water discharge, which might have been ultimately governed by basin tectonics, climate, and base level. Along with the marked change in fluvial style, the two successive units show repeated expansions of distal, water-logged floodplains and lacustrine facies in the basal and uppermost parts of Sinpyong-Anpyong unit, where the proportion of channel sandstone bodies is relatively low. These stratigraphic intervals are succeeded by the sequences with proximal, well-drained floodplain facies and relatively coarser-grained channel sandstone bodies of higher proportion, reflecting the progradation of proximal systems (the middle part of Sinpyong-Anpyong unit and Jotap unit). The overall stratigraphic architecture can be ascribed to the fluctuations in accommodation space and sediment supply induced by repeated basin subsidence.

• Transactions of Materials Processing
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• 제17권8호
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• pp.570-578
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• 2008

A flexible forming apparatus is composed a number of punches which have spherical pin tip shape instead of conventional solid die. The flexible forming tool consisted of punch array in a matrix form was proposed as an alternative forming method to substitute the conventional line heating method which use heat source to induce residual stress along specified heating lines. In this study, application of the flexible forming process to the small scale curved plate forming was conducted. Numerical simulations for both solid and flexible die forming process were carried out to compare the shape of the products between flexible and conventional die forming process. In addition, spring-back analysis was conducted to figure out the feasibility of the flexible forming process comparing with the die forming process in view of final configuration of the specimens. Moreover, experiment was also carried out to confirm the formability of the process. Consequently, it was confirmed that the flexible die forming method has capability and feasibility to manufacture the curved plates for shipbuilding.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.318-321
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• 2009

Transformation plasticity is that when a phase transformation of ferrous or non-ferrous alloys progresses even under an extremely small applied stress compared with a yield stress of the material, a permanent deformation occurs. One of widely accepted description for the transformation was proposed by Greenwood and Johnson [1]. Their description is based on an assumption that a weaker phase of an ideal plastic material could deform plastically to accommodate the externally applied stress and the internal stress caused by the volumetric change accompanying the phase transformation. In this study, an implicit finite element model was developed to simulate the deformation behavior of a low carbon steel during phase transformation. The finite element model was coupled with a phase field model, which could simulate the kinetics for ferrite to austenite transformation of the steel. The thermo-elasto-plastic constitutive equation for each phase was adopted to confirm the weaker phase yielding, which was proposed by Greenwood and Johnson [1]. From the simulation, the origin of the transformation plasticity was quantitatively discussed comparing with the other descriptions of it.

• Journal of Microbiology and Biotechnology
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• 제6권1호
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• pp.30-35
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• 1996

Distillery wastewater was used in a thermophilic laboratory-scale two stage anaerobic digester to test the effects of the redox potential of the first acidogenic reactor on the performance of the system. The digester consisted of first a acidogenic reactor and the an upflow anaerobic sludge blanket (UASB) reactor. The digestor was operated at a hydraulic retention time (HRT) of 48 h. Under these conditions, about 90% of the chemical oxygen demand as measured by the chromate method ($COD_{cr}$) was removed with a gas production yield of 0.4 l/g-COD removed. The redox potential of the acidogenic reactor was increased when the reactor was purged with nitrogen gas or agitation speed was increased. The increase in reduction potential was accompanied by an increase in acetate production and a decrease in butyrate formation. A similar trend was observed when a small amount of air was introduced into the acidogenic reactor. It is believed that the hydrogen partial pressure in the acidogenic reactor was decreased by the above mentioned treatments. The possible failure of anaerobic digestion processes due to over-loading could be avoided by the above mentioned treatments.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.8-15
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• 2002

For the large scale computation of turbulent flows around an arbitrarily shaped body, a parallel LES (large eddy simulation) code has been recently developed in which domain decomposition method is adopted. METIS and MPI (message Passing interface) libraries are used for domain partitioning and data communication between processors, respectively. For unsteady computation of the incompressible Wavier-Stokes equation, 4-step splitting finite element algorithm [1] is adopted and Smagorinsky or dynamic LES model can be chosen fur the modeling of small eddies in turbulent flows. For the validation and performance-estimation of the parallel code, a three-dimensional laminar flow generated by natural convection inside a cube has been solved. Then, we have solved the turbulent flow around MIRA (Motor Industry Research Association) model at $Re = 2.6\times10^6$, which is based on the model height and inlet free stream velocity, using 32 processors on IBM SMP cluster and compared with the existing experiment.

• Publications of The Korean Astronomical Society
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• 제30권2호
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• pp.461-462
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• 2015

Quasars are among the farthest and brightest objects known in the universe. Because quasars are mostly observed in the redshift range between 1 and 3, they can be used to study large scale structure in the universe, and its evolution over the past billion years. An important issue is the evolution of the quasar luminosity function, which has been investigated for relative small samples of the 2QZ catalog. Here we extend the study to 3 quasar samples, the most recent data of the Milliquas, Master and 2QZ quasar catalogs to determine the luminosity function of quasars and its evolution, using the Standard cosmological ${\Lambda}CDM$ model with ${\Omega}_{\Lambda}=0.73$, ${\Omega}_M=0.27$, and $H_0=70kms^{-1}Mpc^{-1}$. For the purpose of this analysis we initially used 0.25-mag bins and approximately 0.180-redshift bins, then calculated the comoving distance and comoving volume for each bin of redshift and calculated the number of objects in each bin per unit volume, in order to find the number density per absolute magnitude bin. Our analysis on the basis of these new and much more complete datasets is largely in agreement with earlier studies of the luminosity evolution of quasars.

• Structural Engineering and Mechanics
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• 제48권3호
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• pp.351-365
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• 2013

In this paper, unified nonlocal shear deformation theory is proposed to study bending, buckling and free vibration of nanobeams. This theory is based on the assumption that the in-plane and transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. In addition, this present model is capable of capturing both small scale effect and transverse shear deformation effects of nanobeams, and does not require shear correction factors. The equations of motion are derived from Hamilton's principle. Analytical solutions for the deflection, buckling load, and natural frequency are presented for a simply supported nanobeam, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory and Reddy beam theories.