• Wind and Structures
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• v.9 no.2
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• pp.95-108
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• 2006

Wind turbines are highly complex structures for numerical flow simulation. They normally comprise of a turbine mounted on a tower thus the movement of the turbine blades and the blade/tower interaction must be captured. In addition the ground effect should also be included. There are many more important features of wind turbines and it is difficult to include all of them. A simplified set of features is chosen here for both the turbine and the tower to show how the method can begin to identify the main points connected with wind turbine wake generation and tip vortex tower interaction. An approach to modelling the rotating blades of a turbine is proposed here. The model uses point forces based on blade element theory to model the blades and takes into account their time dependent motion. This means that local instantaneous velocities can be used as a basis for the blade element theory. The model is incorporated into a large eddy simulation code and, although many important features are left out of the model, the velocity/power performance relation is generally of the correct order of magnitude. Suggested improvements to the method are discussed.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.43-48
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• 2009

In this study, through case studies, solar energy systems were coordinated with architectural plan elements and the others in apartment complex, and the energy performance was evaluated quantitatively through computer simulation PVSYST and RETScreen. As a results, in plan process of the application of solar energy systems in apartment complex, solar energy system should be considered as not only energy reducing technical element but also part of architectural plan element. And it must be considered with architectural plan elements, composition methods, energy storage methods, technical elements from the early basic plan stage. Photovoltaic system was installed on the wall facing the south and rooftop. The energy ratio of electric load was shown to be 5.5%. The result showed 7.2% when adding it to shading device additionally, and 6.4% in case of putting extra translucent module on windows. Active solar collecting system was applied on roof with the angle of 45. Maximum number of solar collector was 10 in a row, and the total solar collecting area was $915.00m^2$. The energy ratio of domestic water heating load by active solar hot water system is shown to be 11.4%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.1217-1219
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• 2003

상용화되어 있는 이동통신 기기의 Front-end 부분은 듀플렉서와 필터를 포함하는 수동소자로 구성되어 있다. 듀플렉서의 임피던스 정합선로는 전송선로 이론으로부터 설계하며, 단순하게 ${\lambda}=1/4$ 파장 길이의 정합 선로를 설치하는 것이기 때문에 정합선로를 이용한 듀플렉서 성능을 극대화하기 위한 설계의 융통성이 없는게 현실이다. 이런 문제점을 해결하기 위하여 집중소자(lumped element)인 R L C를 탄성 표면파 듀플렉서 대신 스위치 모들에 적용하게 된다면 여러 가지 다양한 형태의 회로를 구현할 수 있고 회로망 내에 위치하는 집중소자의 정격을 최적화하여 스위치 모듈의 성능을 향상시킬 수 있는 가능성이 있다. 본 연구에서는 $900 MHz{\sim}2.2 GHz$의 대역에서 소형화 집적화에 적용 가능한 디바이스를 개발하기 위하여 고주파, 저진압, 저손실 스위치 모듈의 제조와 구성되는 커패시터와 인덕터의 제조와 특성에 관하여 연구하였다.

• Geomechanics and Engineering
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• v.5 no.3
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• pp.195-221
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• 2013

A centrifuge model study is carried out to investigate the behavior of pile subject to negative skin friction induced by pile installation, ground water drawdown and surcharge loading. A single end-bearing pile is examined as the induced negative skin friction would induce the most severe stress on the pile structural material as compared to friction piles. In addition, the behavior of the pile under simultaneous negative skin friction and dead/live loads is examined. To facilitate detailed interpretations of the test results, the model setup is extensively instrumented and involves elaborate test control schemes. To further examine the phenomenon of negative skin friction on an end-bearing pile, finite element analyses were conducted. The numerical analysis is first validated against the centrifuge test data and subsequently extended to examine the effects of pile slenderness ratio, surcharge intensity and pile-soil stiffness ratio on the degree of mobilization of negative skin friction induced on the pile. Finally experimental and numerical studies are conducted to examine the effect of applied transient live load on pile subject to negative skin friction.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.261-268
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• 2012

The effects of thickness, base element and additive to inoculant on the number of eutectic cells and chill depth of thin-section gray cast iron were investigated. Meanwhile the number of eutectic cells increased by inoculation, chill depth decreased. The former decreased and the latter increased by holding the melt at the temperature range between 1,450 and $1,500^{\circ}C$. The former was more for the thinner casting with the thickness of 5 mm than the other. The result of thermal analysis coincided well with the change of macrostructure. The former increased and the latter decreased with the increased contents of carbon, silicon and the silicon content by inoculation. The former decreased and the latter increased with increased manganese content. The number of eutectic cells decreased as the amounts of rare earth and the bismuth added to this inoculant increased. With the addition of sulfur of 0.10 wt% of the weight of this inoculant, the maximum number of eutectic cells was obtained.

• Journal of the Korean Society for Railway
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• v.8 no.1
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• pp.41-50
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• 2005

Steel -Concrete Composite two girder railway bridges applying high performance steel with extra thick plate have economic and aesthetic advantages due to the simplification of manufacturing and construction process. However, steel bridges are seldom adopted in domestic railway bridge, since steel bridges are not efficient as R.C bridges considering dynamic characteristics and noise, etc. While highway bridges do not have lower horizontal bracing and larger interval of diaphragm cross beam, railway bridges install lower horizontal bracings to control the torsion due to heavy eccentrical line load. Accurate finite element analysis were performed with the parameters of existence of bracing and bracing shape, with the cross beam interval and stiffness, etc. To find out the effects of secondary members such as horizontal bracings and diaphragms, static md dynamic analysis have been performed by using finite element method. In this study, few member plate-girder bridges are analyzed with variable span lengths to examine the dynamic behavior and limits of damping. And though lateral bracings are members against torsion, but lateral bracing's absence is no big problem. Time history analysis using mode superposition method makes proof of this result.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1258-1270
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• 2009

Recently, the earthquakes activities are more of frequency occurred in the country. In case of nomal or large magnitude earthquakes, which cause a rising number of life loss or widespread loss of property. It must be considered how to cope with the situperty of dpmage in the country ty account of ay earthquake. Consequently, the public works have currently ensured against a lot of risk about seismism not only on large scale structures but also relatively small structures. Therefore, in this study, in order to make the seismic stability safe, it has been evaluated by the seismic performance for caisson-type breakwater. The seismic response analyses have conducted on the caisson-type breaker under long-period, short-period and artificial seismic wave. The liquefaction potential of the foundation, which is caisson-type, is also estimated by using the simplified assessment method. Finally, the result of the numerical analysis by PENTAGON 2D finite element method(FEM) program are presented for 3 cases with time-history seismic analysis under the seismic load.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.179-187
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• 2003

Vertical reinforcement of soft ground using granular column is a very effective ground improvement technique which is being used fur increasing bearing capacity and decreasing settlement. In this study, the theories of elasticity and plasticity including the upper bound theorem of limit analysis were used to derive the equations for obtaining elastic properties and shear strength parameter of equivalent ground of composite foundation. The developed equations were verified using the finite element computer program, SAGE CRISP. For validation, finite element analyses were conducted f3r the various different cases including different type of soil and replacement ratios. The results of the analysis show that the proposed equation could determine the properties of equivalent ground material for practical application effectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.201-211
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• 2011

Many reinforced concrete structures have been constructed at the offshore in Korea and those are exposed in environments for long period. Due to that, the reinforcement of the structure faces possibility of corrosion by the salt damage. Such corrosions are effects on the bond performance between concrete and reinforcing bar as well as the performance of the structure. In this study, the performance of RC structure has been investigated when the reinforcing bars are totally bonded and unbonded in the structure. Through the experimental tests and finite element analyses of beam-column joint with bond and unbonded reinforcing bar, the energy dissipation capacity, strength, and crack distribution are compared and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.291-294
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• 2003

The circuit substrate was made from the Low Temperature Cofired Ceramics(LTCC) that a $\varepsilon_\gamma$ was 7.8. Accumulated Varactor and the low noise transistor which were a Surface Mount Device-type element on LTCC substrate. Let passive element composed R, L, C with strip-line of three dimension in the multilayer substrate circuit inside, and one structure accumulate band-pass filter, resonator, a bias line, a matching circuit, and made it. Used Screen-Print process, and made Strip-line resonator. A design produced and multilayer-type VCO(Voltage Controlled Oscillator), and recognized a characteristic with the Spectrum Analyzer which was measurement equipment. Measured multilayer structure VCO is oscillation frequency 1292[MHz], oscillation output -28.38[dBm], hamonics characteristic -45[dBc] in control voltage 1.5[V], A phase noise is -68.22[dBc/Hz] in 100 KHz offset frequency. The oscillation frequency variable characteristic showed 30[MHz/V] characteristic, and consumption electric current is approximately 10[mA].