• Wind and Structures
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• 제22권4호
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• pp.503-524
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• 2016

The suitability of Computational Fluid Dynamics (CFD) simulations on the built environment for the purpose of estimating average roughness characteristics and for studying wind flow patterns within the environment is assessed. Urban models of various levels of complexity are considered including an empty domain, array of obstacles arranged in regular and staggered manners, in-homogeneous roughness with multiple patches, a semi-idealized built environment, and finally a real built environment. For each of the test cases, we conducted CFD simulations using RANS turbulence closure and validated the results against appropriate methods: existing empirical formulas for the homogeneous roughness case, empirical wind speed models for the in-homogeneous roughness case, and wind tunnel tests for the semi-idealized built environment case. In general, results obtained from the CFD simulations show good agreement with the corresponding validation methods, thereby, giving further evidence to the suitability of CFD simulations for built environment studies consisting of wide-ranging roughness. This work also provides a comprehensive overview of roughness modeling in CFD-from the simplest approach of modeling roughness implicitly through wall functions to the most elaborate approach of modeling roughness explicitly for the sake of accurate wind flow simulations within the built environment.

• 한국데이터정보과학회:학술대회논문집
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• 한국데이터정보과학회 2005년도 춘계학술대회
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• pp.145-154
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• 2005

There have been some controversies on the use of the coefficient of determination for linear no-intercept model. One definition of the coefficient of determination, $R^2=\sum\;{y}{^{\hat{2}}/\sum\;{y^2}$, is being widely accepted only for linear no-intercept models though Kvalseth(1985) demonstrated some possible pitfalls in using such $R^2$. Main objective of this article is to provide a cautionary notice for use of the $R^2$ by pointing out its tricky aspects by means of empirical simulations.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.93-93
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• 2010

In this talk, I will introduce a reactive force field (ReaxFF) molecular dynamics (MD) simulation. In contrast to common MD simulations with empirical FFs, we can predict chemical reactions (bond breaking and formation) in large scale systems with the ReaxFF simulation where all of the ReaxFF parameters are from quantum mechanical calculations such as density functional theory to provide high accuracy. Accordingly, the ReaxFF simulation provides both accuracy of quantum mechanical calculations and description of large scale systems of atomistic simulations at the same time. Here, I will first discuss a theory in the ReaxFF including the differences from other empirical FFs, and then show several applications for studying chemical reactions of SiHx radicals on Si surfaces, which is an important issue in Si process.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.231-232
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• 2002

Various methods that utilize erosion rate measurement of standard cannon, 155mm Howitzer M185, as reference, are being used to calculate erosion rate of an interested unknown cannon tubes. We know ten measured erosion values of the standard cannon from 391 rounds to 4.000. An approximate function fitting these value s is derived. The new erosion equation is also suggested and computer simulations arc presented.

• Journal of the Korean Statistical Society
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• 제30권4호
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• pp.563-571
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• 2001

In this paper, we study selecting a transformation so that the transformed variable is nearly symmetrically distributed. The large sample properties of an M-estimator of transformation parameter that is obtained by minimizing the integrated square of the imaginary part of the empirical characteristic function are investigated when a random sample is selected from some unspecified distribution. According to influence function calculations and Monte Carlo simulations, these estimates are less sensitive, than the normal model maximum likelihood estimates, to a few outliers.

• IEIE Transactions on Smart Processing and Computing
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• 제4권2호
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• pp.89-96
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• 2015

In this paper, time-frequency analysis algorithms, empirical mode decomposition and local mean decomposition, are reviewed and their applications to nonlinear and nonstationary real-world data are discussed. In addition, their generic extensions to complex domain are addressed for the analysis of multichannel data. Simulations of these algorithms on synthetic data illustrate the fundamental structure of the algorithms and how they are designed for the analysis of nonlinear and nonstationary data. Applications of the complex version of the algorithms to the synthetic data also demonstrate the benefit of the algorithms for the accurate frequency decomposition of multichannel data.

• 대한토목학회논문집
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• 제33권5호
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• pp.1777-1783
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• 2013

유량측정방법 중에서 파샬플륨을 이용하는 방법은 유속이 매우 느리거나 토사유입이 많은 지점에서 상대적으로 유리하다. 국제표준화기구(ISO : International Organization for Standardization)에 파샬플륨의 규모별 규격화된 경험식이 제시되어 있지만, 규격을 따르지 않는 파샬플륨에 대한 수리실험이나 수치모의를 통한 연구는 다소 부족한 실정이다. 따라서 본 연구에서는 ISO 규격 파샬플륨에 대하여 경험식과 수치모의를 비교하여 파샬플륨에 대한 수치모의의 적정성을 검토하였고 현장 여건 등의 이유로 ISO 규격을 따르지 않는 파샬플륨은 유량산정공식을 얻기 위해서 수리실험을 수행해야만 했다. 이러한 임의형상의 파샬플륨에 대하여 동일 조건의 수리실험 및 수치모의 결과를 비교 검토하였다. 그 결과 수치모의가 파샬플륨의 수심과 유량을 적절하게 모의하고 있음을 확인하였다. 이 결과를 이용하여 임의형상에 대한 무차원 유량산정공식을 도출하였으며, 식을 통해 산정된 값과 실험값을 비교하였다. 그 결과 오차는 최대 2.3%로 나타났다. 파샬플륨의 규모결정시 실제 지형과 유입부 형상 등을 고려한 수치모의를 수행한다면 수치모의에 기초한 유량산정공식을 쉽게 도출 할 수 있을 것이다. 또한, 복잡한 수행과정으로 인해 오차가 발생하기 쉬운 수리모형실험을 경제적으로 보완할 수 있을 것으로 판단된다.

• Wind and Structures
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• 제21권1호
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• pp.85-103
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• 2015

Aerodynamic forces of vortex-induced vibration and galloping are going to be coupled when their onset velocities are close to each other, which will induce the cross-wind amplitudes of the structures increased continuously with ever-increasing wind velocities. The main purpose of the present work is going to propose an empirical formula to predict the response amplitude of VIV-galloping interaction. Firstly, two typical mathematical models for the coupled oscillations, i.e., Tamura & Shimada model and Parkinson & Corless model are comparatively summarized. Then, the key parameter affecting response amplitude is determined through comparative numerical simulations with Tamura & Shimada model. For rectangular cylinders with the side ratio from 0.5 to 2.5, which are actually prone to develop the VIV and galloping induced interaction responses, an empirical amplitude prediction formula is proposed after regression analysis on comprehensively collected experimental data with the predetermined key parameter.

• KIEAE Journal
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• 제13권1호
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• pp.109-123
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• 2013

The study is to probe a technical alternative to enhance the reliability and accuracy of the results of various landscape simulations. This study to present technical criteria that are necessary in each stage of target site analysis, picture taking, and computer synthesis and, through these to present supplementary plans to enhance the reliability and accuracy of landscape simulations. In order to derive more practical and empirical results in terms of the reliability of the results of landscape simulations, examples that actually passed landscape review were selected. With regard to study process, an analysis was made first to analyze the landscape report data of designs that passed the review to analyze their characteristics, to be followed by an integrated analysis of problems that were revealed in various landscape simulations. Important factors that affect directly the work of landscape simulations such as the specification of camera lenses that were used in picture taking, distance, and angle. Design the work was carried out using Auto CAD, 3DS Max, and Photoshop program in the same way as in actual design. For verification of their accuracy and reliability, the results were entrusted to experts who have implemented similar jobs. To seduce differences from those too landscape simulations that conduct trial experiment of the virtual space that are to be created in the future with accurate numerical values.

• Structural Engineering and Mechanics
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• 제68권2호
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• pp.237-245
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• 2018

This study proposes an empirical formulation to predict the maximum deformation of offshore blast wall structure that is subjected to impact loading caused by hydrocarbon explosion. The blast wall model is assumed to be supported by a simply-supported boundary condition and corrugated panel is modelled. In total, 1,620 cases of LS-DYNA simulations were conducted to predict the maximum deformation of blast wall, and they were then used as input data for the development of the empirical formulation by regression analysis. Stainless steel was employed as materials and the strain rate effect was also taken into account. For the development of empirical formulation, a wide range of parametric studies were conducted by considering the main design parameters for corrugated panel, such as geometric properties (corrugation angle, breadth, height and thickness) and load profiles (peak pressure and time). In the case of the blast profile, idealised triangular shape is assumed. It is expected that the obtained empirical formulation will be useful for structural designers to predict maximum deformation of blast wall installed in offshore topside structures in the early design stage.