• Bulletin of the Korean Chemical Society
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• 제21권7호
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• pp.697-700
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• 2000

A method of calculating the excess Helmholtz free energy from the average of the bent effective acceptance ratio for two-center-Lennard-Jones liquids has been presented. The bent effective acceptance ratio has been newly composed from the acceptan ce ratio for the potential energy difference between a configuration in the Metropolis Monte Carlo procedure and random virtual configuration generated by the separate parallel Monte Carlo procedure and the Boltzmann factor for half the potential energy difference. The excess Helmholtz free energy was calculated directly from the average of the bent effective acceptance ratio through a single Metropolis Monte Carlo run. Because the separate parallel Monte Carlo procedure was used, this method can be applied to molecular dynamics simulations. For two-center-Lennard-Jones liquids, the average of the bent effective acceptance ratio gave better results than use of the modified effective acceptance ratio in the previous work.

• The Korean Journal of Ceramics
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• 제2권2호
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• pp.102-110
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• 1996

The Mg-PSZ/$Al_2O_3$ fibers were fabricated by the sol-gel method. The added $Al_2O_3$ amounts were varied from 5 to 20 mol%. The phase transformation studies of a drawn Mg-PSZ/$Al_2O_3$ fibers were investigated by use of X-ray diffraction, IR and Raman spectroscopy. Microstructure and tensile strength of fibers were subjected to scanning electron microscopy and tensile strength tester. When $Al_2O_3$ was added to the Mg-PSZ fibers, it was found out from the analysis of XRD patterns and Raman spectra that a small amount of crystalline spinel($MgAl_2O_4$) started to form due to the reaction between $Al_2O_3$ and MgO, at $1000^{\circ}C$, and the phase transformation temperature of $ZrO_2$ crystal phase at different sintering temperatures increased. Also, the rapid grain growth with average size of 2.0 ${\mu}m$ shown in Mg-PSZ fiber at $1500^{\circ}C$ was considerably suppressed to 0.39 ${\mu}m$ by adding $Al_2O_3$ at the same temperature. When the Mg-PSZ/$Al_2O_3$ fibers containing 5 mol% $Al_2O_3$ were sintered $800^{\circ}C$ for 1 hr, average tensile strength of fibers was 0.9 GPs at diameters of 20 to 30 ${\mu}m$, but as the sintering temperatures was increased to $1000^{\circ}C$ for 1 hr, average tensile strength of fibers increased to 1.2 GPa in the same diameter range.

• 한국세라믹학회지
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• 제44권3호
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• pp.175-181
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• 2007

Molecular dynamics simulation (MD) of $(62-x)CaO{\cdot}38Al_{2}O_{3}{\cdot}xBaO$ glasses has been carried out using empirical potentials with the covalent term. The simulations closely reproduce the total neutron correlation functions of glass with 5 mol% BaO and physical properties of these glasses such as elastic constants. For these glasses, aluminum is tetrahedrally coordinated by oxygen, but there is a part of five-fold and six-fold coordination of aluminum. There are no major changes to the mid-range structure of glass, as barium is substituted for calcium. To predict the barium coordination number, we have used the bond valence (BV) theory and also compared the results of simulation with Bond valence. The coordination number for oxygen around barium atoms is close to 8 and the average distance of barium and oxygen is nearly 2.80 A. The viscosity of these glasses increases with the content of barium oxide substituted for calcium oxide.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2009년도 학술발표회 초록집
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• pp.52-56
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• 2009

In this study a dynamic modeling scheme is presented to derive the probabilistic structure of soil water and plant water stress when subject to stochastic precipitation conditions. The newly developed model has the form of the Fokker-Planck equation, and its applicability as a model for the probabilistic evolution of the soil water and plant water stress is investigated under climate change scenarios. This model is based on the cumulant expansion theory, and has the advantage of providing the probabilistic solution in the form of probability distribution function (PDF), from which one can obtain the ensemble average behavior of the dynamics. The simulation result of soil water confirms that the proposed soil water model can properly reproduce the results obtained from observations, and it also proves that the soil water behaves with consistent cycle based on the precipitation pattern. The plant water stress simulation, also, shows two different PDF patterns according to the precipitation. Moreover, with all the simulation results with climate change scenarios, it can be concluded that the future soil water and plant water stress dynamics will differently behave with different climate change scenarios.

• Bulletin of the Korean Chemical Society
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• 제29권2호
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• pp.363-371
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• 2008

As a computational method for the discovery of the effective agonists for PPARd, we address the usefulness of molecular dynamics free energy (MDFE) simulation with explicit solvent in terms of the accuracy and the computing cost. For this purpose, we establish an efficient computational protocol of thermodynamic integration (TI) that is superior to free energy perturbation (FEP) method in parallel computing environment. Using this protocol, the relative binding affinities of GW501516 and its derivatives for PPARd are calculated. The accuracy of our protocol was evaluated in two steps. First, we devise a thermodynamic cycle to calculate the absolute and relative hydration free energies of test molecules. This allows a self-consistent check for the accuracy of the calculation protocol. Second, the calculated relative binding affinities of the selected ligands are compared with experimental IC50 values. The average deviation of the calculated binding free energies from the experimental results amounts at the most to 1 kcal/mol. The computational efficiency of current protocol is also assessed by comparing its execution times with those of the sequential version of the TI protocol. The results show that the calculation can be accelerated by 4 times when compared to the sequential run. Based on the calculations with the parallel computational protocol, a new potential agonist of GW501516 derivative is proposed.

• 한국진공학회지
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• 제19권2호
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• pp.121-127
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• 2010

소형위성의 추력시스템으로 사용되어지는 홀 추력기의 중성 기체 시뮬레이션을 수행하였다. 홀 추력기의 채널 내부에서의 난반사효과 및 초기 가스의 온도, 그리고 채널의 길이 등을 변수로 하여 계산되어진 밀도, 압력, 속도, 온도를 분석 하였다. 시뮬레이션에서 얻어진 결과를 통해 홀 추력기의 방전 시뮬레이션의 정확성을 높이는 동시에 실제 시스템의 이해에 기여할 것으로 예상되어 진다.

• 한국전자통신학회논문지
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• 제14권2호
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• pp.425-432
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• 2019

노즐모양이 터빈의 회전력과 축동력에 미치는 영향을 분석하기 위해, 분자 동력학 시뮬레이션을 수행하였다. 3 개의 파라메타, 노즐모양, 터빈의 회전속도 w, 분자들의 초기 속도 ($V_x,V_y$) 값들을 변화하면서, 시뮬레이션을 수행하여 터빈입구와 출구에서 분자들의 터빈 회전방향으로의 속도를 계산하였다. 이 두 영역에 걸쳐 평균 운동량을 각각 계산하고 그 차이(AMD)를 비교 분석하였다. 사용한 노즐 모양을 대상으로 AMD를 향상할 수 있는 w의 최적의 범위 도출하였으며, 터빈의 축동력 형성에 더 많이 기여할 수 있는 우수한 노즐 모양을 파악하였다.

• 풍력에너지저널
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• 제5권1호
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• pp.22-32
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• 2014

The structural design of a wind turbine must show the verification of the structural integrity of all load-carrying components. Also, design load calculations shall be performed using appropriate and accurate methods. In this study, advanced numerical approach for the calculation of design loads based on unsteady computational fluid dynamics (CFD) is presented considering extreme design load conditions such as the extreme coherent gust (ECG) and the 50 year extreme operating gust (EOG). Unsteady aerodynamic loads are calculated based on Reynolds average Navier-Stokes (RANS) equations with shear-stress transport k-ω(SST k-ω) turbulent model. A full three-dimensional 5 MW offshore wind-turbine model with rotating blades, hub, nacelle, and tower configuration is practically considered and its aerodynamic interference effect among blades, nacelle, and tower is also accurately considered herein. Calculated blade loads based on unsteady CFD method with respect to blade azimuth angle are compared with those by NREL FAST code and physically investigated in detail.

• 한국지열·수열에너지학회논문집
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• 제3권1호
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• pp.11-16
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• 2007

The purpose of this study is to use the CFD(Computational Fluid Dynamics) method for the ground source heat pump(GSHP) system with vertical U-tube ground heat exchangers. In order to predict LWT(leaving water temperature) in the length of time, This simulation is used by utilizing FLUENT which is commercial CFD code. It was performed by based on four boreholes in the field. Comparing with the results of CFD and field measurement for LWT, the results of CFD was presented very good agreement with 1.0% average difference.

• Journal of Advanced Marine Engineering and Technology
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• 제36권5호
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• pp.609-617
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• 2012

The flow characteristics of polluted air are analysed by comparing the results obtained from PIV(Particle Image Velocimetry) experiment and CFD(Computational Fluid Dynamics) commercial code. In order to simulate the polluted air flow, the olive oil has been used as tracer particles with the kinematic viscosity of air, $1.51{\times}10^{-5}m^2/s$. The investigation has done in the range of Reynolds numbers of 870, 1730 and 2890 due to the inlet flow velocities of 0.3, 0.6, and 1.0 m/s, respectively. The average velocity and the pressure distributions are comparatively discussed with respect to the three different Reynolds numbers. The results show that the outlet flow rates at three different Reynolds numbers are equivalent of 165 to 167 percent of the inlet ones. The pressure drop occurs in the model closed at both end sides and the highest pressures at each Reynolds number are positioned at the top of the tunnel between the inlet and outlet.