• Wind and Structures
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• 제19권4호
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• pp.421-441
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• 2014

With the assistance of typhoon field data at aerial elevation level observed by meteorological satellites and wind velocity and direction records nearby the ground gathered in Guangzhou Weather Station between 1985 and 2001, some key wind field parameters under typhoon climate in Guangzhou region were calibrated based on Monte-Carlo stochastic algorithm and Meng's typhoon numerical model. By using Peak Over Threshold method (POT) and Generalized Pareto Distribution (GPD), Wind field characteristics during typhoons for various return periods in several typical engineering fields were predicted, showing that some distribution rules in relation to gradient height of atmosphere boundary layer, power-law component of wind profile, gust factor and extreme wind velocity at 1-3s time interval are obviously different from corresponding items in Chinese wind load Codes. In order to evaluate the influence of typhoon field parameters on long-span flexible bridges, 1:100 reduced-scale wind field of type B terrain was reillustrated under typhoon and normal conditions utilizing passive turbulence generators in TJ-3 wind tunnel, and wind-induced performance tests of aero-elastic model of long-span Guangzhou Xinguang arch bridge were carried out as well. Furthermore, aerodynamic admittance function about lattice cross section in mid-span arch lib under the condition of higher turbulence intensity of typhoon field was identified via using high-frequency force-measured balance. Based on identified aerodynamic admittance expressions, Wind-induced stochastic vibration of Xinguang arch bridge under typhoon and normal climates was calculated and compared, considering structural geometrical non-linearity, stochastic wind attack angle effects, etc. Thus, the aerodynamic response characteristics under typhoon and normal conditions can be illustrated and checked, which are of satisfactory response results for different oncoming wind velocities with resemblance to those wind tunnel testing data under the two types of climate modes.

• 한국지반공학회논문집
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• 제37권5호
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• pp.47-63
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• 2021

최근 디지털 트윈 관점의 3차원 지하공간 지도의 수요 및 유관분야의 연계 활용 요구가 증대되고 있다. 그러나 전국단위의 지반조사 자료의 방대함과 이를 활용함에 있어 공간적/추계학적 기법 적용의 불확실성으로 인해 신뢰도 높은 지역적 지반특성화 연구와 그에 따른 최적화 모델 제시에 어려움이 있다. 따라서 본 연구에서는 서울지역 3차원 지하공간의 공학적 지층분류를 위해 다층 퍼셉트론(MLP) 기반의 최적 학습모델을 구축하였다. 먼저, 서울지역에 분포하는 시추공별 층상구조 및 3차원 공간좌표를 표준화 서식에 따라 지반정보 데이터베이스로 구축하고 기계학습을 위한 결측치 보정, 정규화 등의 데이터 전처리를 하였다. MLP 모델의 파라미터 최적화와 정밀도 및 정확도 관련 모델 성능 평가를 통해 최적의 피팅 모델을 설계하였다. 이후 3차원 지반 공간레이어 구축을 위한 수치표고모델 기반 격자망을 구성하고, 단위격자별 MLP기반 예측모델 적용을 통한 층상구조를 결정하고 이를 가시화하였다. 구축된 3차원 지반모델은 범용적인 지구통계학적 공간보간 기법의 적용 결과 및 지질도의 표토층 성상과 비교하여 그 성능을 평가하였다.

• 한국건설관리학회논문집
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• 제16권5호
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• pp.114-122
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• 2015

많은 부동산 개발 사업에서 초기 사업부지 확보를 통한 토지매입 후 인허가 지연 및 사업비 부족에 따른 지연이 빈번하게 일어나고 있다. 이렇게 사업기간이 길고 외부요인의 변동성에 따라 사업의 성패가 좌우되는 부동산 개발 사업은 미래의 불확실성을 반영한 전략적인 투자가치 평가가 필요하다. 그러나 일반적으로 사용하는 현금흐름할인법(DCF)은 미래의 불확실성을 반영하지 못하는 한계를 지니고 있다. 이 연구의 목적은 미래의 불확실성을 고려할 수 있는 실물옵션, 더 나아가 다양한 상황을 고려한 다중 실물옵션을 활용한 가치평가 방법을 제시하여 부동산 개발 사업의 의사결정을 하는 의사결정권자가 전략적이고 유연한 결정을 내릴 수 있도록 도움을 주고자 함이다. 부동산 개발 사업 프로젝트 중 오피스 개발 사업을 선택하여 다중 실물옵션 모델을 적용하고 기존의 현금흐름할인법과 단일 실물옵션 모델의 결과값과 비교하였다. 연구 결과 다중 실물옵션의 가치가 현금흐름할인법과 단일 실물옵션의 가치보다 높게 나타났고, 이러한 상황변화에 따른 유연성이 실물옵션 가치평가에서 사업의 가치를 증가시킴을 알 수 있었다. 의사결정권자는 본 연구와 같이 프로젝트의 가치를 다양한 상황에서 고려함으로써 의사결정의 유연성을 보다 높일 수 있을 것이다.

• 한국농림기상학회지
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• 제12권2호
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• pp.122-131
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• 2010

본 논문은 가상 생태계의 개념과 가상생태계를 구현하는데 중요하게 사용되어 질 수 있는 세 가지 수학적-물리학적 접근법을 응용 예와 함께 소개 하였다. 가상생태계란 개체기반 모델로써 인공생명체들이 가상 환경하에서 스스로 행동하면서 살아가는 것을 모사하는 컴퓨터 내에 구현된 생태계를 의미한다. 생물의 무리행동을 전산 모사하는 분자동역학모사 접근법과, 흰개미 영토를 전산 모사하는 확률적 격자모델 접근법, 그리고 생물막 성장을 전산 모사하는 규칙기반-세포자동자모델 접근법을 소개하였다. 실 생태계와의 유사성을 높이기 위해 가상생태계 모델은 많은 변수들을 사용하여야 하지만, 기술적인 측면에서 이러한 변수들을 모두 결정하기는 어렵다. 그러나 현재의 눈부신 컴퓨터 성능향상에 힘입어 많은 부분이 극복 되어 지고 있다. 특히, 가상생태계는 기후변화와 같은 환경재앙을 포함하여 많은 복잡한 생태학적 현상을 개체수준의 낮은 계층에서부터 생물집단 또는 외부 환경수준과 같은 높은 계층까지를 통합적으로 이해하는데 큰 도움을 줄수 있을 것이다. 마지막으로 논문에서는 높은 수준의 계층인 기후변화가 낮은 수준의 계층인 개체기반의 흰개미 생태계에 미치는 복잡한 문제를 어떻게 다룰 수 있는지에 대한 예를 들고 간략하게 논의하였다.

• 청정기술
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• 제28권3호
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• pp.249-257
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• 2022

Grand canonical Monte Carlo 전산모사 방법에 의하여 77.16 K에서 국부분자배향 모델을 가지는 나노 기공 탄소 흡착제에 대한 질소의 평형 흡착량을 계산하였다. 국부분자배향 모델은 일정한 공간을 가지는 규칙적인 격자에 동일한 크기를 배열하였다. 국부분자배향 영역의 연속적인 평면의 직교(out-of-plane)의 제거에 의해 미세기공을 도입하였고, 기본구조단위의 기울임을 통해 기울어진 기공을 도입하였다. 이런 기공 구조는 틈새형 기공 구조보다 나노기공을 가지는 탄소계 흡착제의 흡착 연구에 보다 현실적인 모델이 된다. 또한 이들 기공 구조에 대해 기공도, 표면적 그리고 제한된 비선형 최적화 기법을 활용하여 기공크기분포에 구하였다. 또한 참고 자료로써 틈새형 기공에서의 등온 평형흡착량도 계산하였다. 틈새형 기공에서는 질소분자의 5배 이상의 기공에서 hysteresis 루프가 관찰되었고, 모세관 응축과 응축의 역과정인 증발이 한 압력에서 한 번에 일어났다. 국부분자배향 기공모델에서는 질소분자의 크기의 6배 큰 기공에서 기저 슬립면, armchair 슬립면 그리고 상호연결된 채널에서 각각 세 가지 연속적인 응축이 관찰되었다. 탈착 과정의 hysteresis 루프에서는 단일 또는 두 압력에서 응축의 반대인 증발이 관찰되었다.

• 한국수소및신에너지학회논문집
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• 제16권3호
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• pp.244-252
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• 2005

It is very interesting and important in the academic point of view and in practical use the hydrogen-induced phase separation(HIPS) which appears during hydrogen heat treatment. Since hydrogen can be removed very fast by pumping it out the hydrogen-induced new lattice phase which can not be obtained without hydrogen can be preserved as meta-stable state. In this study it has been investigated whether the HIPS appear in Pd-Al, Pd-Co, Pd-Cr, Pd-Ti, Pd-V and Pd-Zr alloys and discussed thermodynamic representation of the HIPS. The Pd alloys were arc-melted under argon atmosphere and remelted 4 or 5 times for homogenization. The alloys were annealed at 600$^{\circ}C$ under vacuum for 24 hrs and then subjected to pressure-composition isotherm measurements at 100$^{\circ}C$. The hydrogen heat treatment(HHT) of samples was carried out at 600$^{\circ}C$ under hydrogen pressure of 70 bar for 6 days and PC isotherms at 100$^{\circ}C$ were measured. By comparing the PC isotherms measured before and after HHT, occurrence of phase separation was determined. The experimental results showed that the HIPS appeared only in Pd-0.05Co alloy. For Pd-Co alloys with various composition the PC isotherms were measured. By adopting Park-Flanagan model for ternary thermodynamics the Gibbs free energy change for Pd-Co-H solid solution was calculated and subsequently with this the HIPS in Pd-Co alloy was explained fairly.

• Nuclear Engineering and Technology
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• 제41권5호
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• pp.729-738
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• 2009

Given the evolution of High-Temperature Gas-cooled Reactor(HTGR) designs, the source terms for licensing must be developed. There are three potential source terms: fission products, actinides in the fuel and tritium in the coolant. It is necessary to provide first an inventory of the source terms under normal operations. An analysis of source terms has yet to be performed for HTGRs. The previous code, which can estimate the inventory of the source terms for LWRs, cannot be used for HTGRs because the general data of a typical neutron cross-section and flux has not been developed. Thus, this paper uses a combination of the MCNP, ORIGEN, and MONTETEBURNS codes for an estimation of the source terms. A method in which the HTR-10 core is constructed using the unit lattice of a body-centered cubic is developed for core modeling. Based on this modeling method by MCNP, the generation of fission products, actinides and tritium with an increase in the burnup ratio is simulated. The model developed by MCNP appears feasible through a comparison with models developed in previous studies. Continuous fuel management is divided into five periods for the feeding and discharging of fuel pebbles. This discrete fuel management scheme is employed using the MONTEBURNS code. Finally, the work is investigated for 22 isotope fission products of nuclides, 22 actinides in the core, and tritium in the coolant. The activities are mainly distributed within the range of $10^{15}{\sim}10^{17}$ Bq in the equilibrium core of HTR-10. The results appear to be highly probable, and they would be informative when the spent fuel of HTGRs is taken into account. The tritium inventory in the primary coolant is also taken into account without a helium purification system. This article can lay a foundation for future work on analyses of source terms as a platform for safety assessment in HTGRs.

• International Journal of Aeronautical and Space Sciences
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• 제15권4호
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• pp.345-355
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• 2014

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

• 열처리공학회지
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• 제31권6호
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• pp.275-282
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• 2018

Two different modes of rolling were applied to control the texture development in tantalum sheet. In the conventional uni-directional rolling, the typical rolling textures of a body-centered cubic metal which was primarily composed of <110>//(rolling direction) was developed. In a cross rolling where the specimen was rotated by $90^{\circ}$ between each pass, the rotated cube components, i.e. {100}<011> were greatly reinforced. The prediction of lattice rotation by the full-constraint Taylor model showed that the high stability and the symmetry of the rotated cube components caused their strengthening in cross-rolling. The two specimens were heated to $1,100^{\circ}C$ at $9^{\circ}C/min$and held for 1 hour for annealing, then cooled to room temperature in atmosphere. In spite of the significant difference in the deformation textures, the annealing textures were very similar. They developed strong <111>//(plane normal) components with negligible intensity at the rotated cube components, which was attributed to the negligible capability of the latter components to provide effective recrystallized grains.

• E2M - 전기 전자와 첨단 소재
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• 제16권9호
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• pp.64.2-65
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• 2003

A 4 nm layer of ZrOx (targeted x-2) was deposited on an interfacial layer(IL) of native oxide (SiO, t∼1.2 nm) surface on 200 mm Si wafers by a manufacturable atomic layer chemical vapor deposition technique at 30$0^{\circ}C$. Some as-deposited layers were subjected to a post-deposition, rapid thermal annealing at $700^{\circ}C$ for 5 min in flowing oxygen at atmospheric pressure. The experimental x-ray diffraction, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and high-resolution parallel electron energy loss spectroscopy results showed that a multiphase and heterogeneous structure evolved, which we call the Zr-O/IL/Si stack. The as-deposited Zr-O layer was amorphous $ZrO_2$-rich Zr silicate containing about 15% by volume of embedded $ZrO_2$ nanocrystals, which transformed to a glass nanoceramic (with over 90% by volume of predominantly tetragonal-$ZrO_2$(t-$ZrO_2$) and monoclinic-$ZrO_2$(m-$ZrO_2$) nanocrystals) upon annealing. The formation of disordered amorphous regions within some of the nanocrystals, as well as crystalline regions with defects, probably gave rise to lattice strains and deformations. The interfacial layer (IL) was partitioned into an upper Si $o_2$-rich Zr silicate and the lower $SiO_{x}$. The latter was sub-toichiometric and the average oxidation state increased from Si0.86$^{＋}$ in $SiO_{0.43}$ (as-deposited) to Si1.32$^{＋}$ in $SiO_{0.66}$ (annealed). This high oxygen deficiency in $SiO_{x}$ indicative of the low mobility of oxidizing specie in the Zr-O layer. The stacks were characterized for their dielectric properties in the Pt/{Zr-O/IL}/Si metal oxide-semiconductor capacitor(MOSCAP) configuration. The measured equivalent oxide thickness (EOT) was not consistent with the calculated EOT using a bilayer model of $ZrO_2$ and $SiO_2$, and the capacitance in accumulation (and therefore, EOT and kZr-O) was frequency dispersive, trends well documented in literature. This behavior is qualitatively explained in terms of the multi-layer nanostructure and nanochemistry that evolves.ves.ves.