• 한국시뮬레이션학회논문지
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• 제29권4호
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• pp.85-94
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• 2020

철도교통사업의 계획 및 시행 가능 여부를 판단 하는 데 있어, 다양한 의사결정 과정이 필수적으로 요구되며, 그 결과로 총사업비, 운영비 등을 포함한 LCC(Life Cycle Cost) 값을 예측한다. 본 연구에서는 철도교통사업 의사결정 및 LCC 도출과정을 지원하기 위한 모델링 및 시뮬레이션 기반의 분석 방식을 제안한다. 먼저, 수치적 데이터 기반의 분석이 가능하도록 기존 다양한 철도교통사업 자료를 취합하여 Cost Analysis 모델을 구성하였으며, 실험계획법 및 반응표면법 기반의 근사모델링 기법을 통해 시뮬레이션을 수행, 결과를 도출하여 분석하였다. 모델 구성 및 시뮬레이션을 효과적으로 수행하기 위해 전문적인 상용 소프트웨어 도구를 사용하였다. 연구 결과 검증을 위해 실제 추진되고 있는 철도교통사업을 선정하여 분석결과를 비교하였고, 이를 각 분야 전문가 검증 과정을 거쳐 연구 성과의 신뢰성을 검토하였다.

• 한국해양공학회지
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• 제36권2호
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• pp.101-107
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• 2022

Dean (1965) proposed the use of the root mean square error (RMSE) in the dynamic free surface boundary condition (DFSBC) and kinematic free-surface boundary condition (KFSBC) as an error evaluation criterion for wave theories. There are well known wave theories with RMSE more than 1%, such as Airy theory, Stokes theory, Dean's stream function theory, Fenton's theory, and trochodial theory for deep-water waves. However, none of them can be applied for deep-water breaking waves. The purpose of this study is to provide a closed-form solution for deep-water waves with RMSE less than 1% even for breaking waves. This study is based on a previous study (Shin, 2016), and all flow fields were simplified for deep-water waves. For a closed-form solution, all Fourier series coefficients and all related parameters are presented with Newton's polynomials, which were determined by curve fitting data (Shin, 2016). For verification, a wave in Miche's limit was calculated, and, the profiles, velocities, and the accelerations were compared with those of 5^th-order Stokes theory. The results give greater velocities and acceleration than 5^th-order Stokes theory, and the wavelength depends on the wave height. The results satisfy the Laplace equation, bottom boundary condition (BBC), and KFSBC, while Stokes theory satisfies only the Laplace equation and BBC. RMSE in DFSBC less than 7.25×10^-2% was obtained. The series order of the proposed method is three, but the series order of 5^th-order Stokes theory is five. Nevertheless, this study provides less RMSE than 5^th-order Stokes theory. As a result, the method is suitable for offshore structural design.

• 한국해안해양공학회지
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• 제6권1호
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• pp.12-22
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• 1994

외력에 의해 생성된 일정 수심 위를 전파하는 파랑변위의 시간변화를 점근 근사법을 사용하여 분석하였다. Stationary Phase 방법, Steepest Descents 방법 그리고 선두파랑 근사법을 사용하였다. 1차원 파랑과 2차원 파랑의 해면변위에 대한 근사법을 검증하기 위해 근사식과 수치적분으로 계산한 변위를 도시하였다. 파고 감소율에 대한 기존의 결과인 1차원 선두파랑의 감소율은 t$^{-1}$3/, 후속파랑은 t$^{-1}$2 그리고 2차원 후속파낭은 t$^{-1}$로 이들 근사식의 타당함을 입증하였다. 그러나 2차원 선두파랑의 감소율은 기존 Kajiura의 결과인 t$^{-4}$ 3/과 다른 t$^{-5}$6/이 적합함을 나타내었다.

• Journal of Advanced Research in Ocean Engineering
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• 제2권1호
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• pp.1-11
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• 2016

The objective of this paper is to present an analytical solution in deep water waves and verify the validity of the theory (Shin, 2015). Hence this is a follow-up to Shin (2015). Instead of a variational approach, another approach was considered for a more accurate assessment in this study. The products of two coefficients were not neglected in this study. The two wave profiles from the KFSBC and DFSBC were evaluated at N discrete points on the free-surface, and the combination coefficients were determined for when the two curves pass the discrete points. Thus, the solution satisfies the differential equation (DE), bottom boundary condition (BBC), and the kinematic free surface boundary condition (KFSBC) exactly. The error in the dynamic free surface boundary condition (DFSBC) is less than 0.003%. The wave theory was simplified based on the assumption tanh $D{\approx}1$ in this paper. Unlike the perturbation method, the results are possible for steep waves and can be calculated without iteration. The result is very simple compared to the 5th Stokes' theory. Stokes' breaking-wave criterion has been checked in this study.

• 대한기계학회논문집A
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• 제27권3호
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• pp.381-386
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• 2003

Gradually engineering designers are determined based on computer simulations. Modeling of the computer simulation however is too expensive and time consuming in a complicate system. Thus, designers often use approximation models called metamodels, which represent approximately the relations between design and response variables. There arc general metamodels such as response surface model and kriging metamodel. Response surface model is easy to obtain and provides explicit function. but it is not suitable for highly nonlinear and large scaled problems. For complicate case, we may use kriging model that employs an interpolation scheme developed in the fields of spatial statistics and geostatistics. This class of into interpolating model has flexibility to model response data with multiple local extreme. In this study. metamodeling techniques are adopted to carry out the shape optimization of a funnel of Cathode Ray Tube. which finds the shape minimizing the local maximum principal stress Optimum designs using two metamodels are compared and proper metamodel is recommended based on this research.

• 대한기계학회논문집
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• 제8권6호
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• pp.591-598
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• 1984

본 논문에서는 고체상호간 미끄름접촉에 의해 발생하는 진동과 소음의 특성을 조사하기 위해서 실험과 이론해석을 행하였다. 미끄름접촉과 관련된 소음에는 brake squeal 혹은 wheel screech등과 같이 stick-slip 형태의 동적 불안정 상태와 관련이 있는 squeal noise와, 겉보기로 동적 안정 상태에 있으나 미끄름접촉면간에 내재하는 미끄름접촉 고유의 불규칙한 동특성에 기인하여 발생하는 rubbing noise가 있다. 본 연구의 대상은 보다 기본적인 형태인 후자에 한한다.

• International Journal of CAD/CAM
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• 제3권1_2호
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• pp.97-109
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• 2003

A large scale polygon models are often used to approximately represent 3D CAD models in Digital Engineering environment such as DMU (Digital Mockups) and network based collaborative design. However, they are not suitable for distribution on the network and for interactive rendering. We introduce a new coding system based on subdivision schemes called S-CODE system. In this system, it is possible to highly compress the model with sufficient accuracy and to view the model efficiently in a level of detail (LOD) fashion. The method is based on subdivision surface fitting by which a subdivision surface and curves which approximate a face of a CAD model are generated. We also apply a subdivision method to analytic surfaces such as conical and cylindrical surfaces. A prototype system is developed and used for evaluation with reasonably complicated data. The results show that the method is useful as a CAD data coding system.

• 한국해양학회지
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• 제29권4호
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• pp.383-391
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• 1994

해면고도계 인공위성에 의하여 지오이드의 형상에 직접관련된 양질의 관측자료가 대량으로 수집되고 있다는 점에 주목하여 이를 이용한 중력이상, 지오이드 기복의 변 환관계를 논하였다. 또한, 실제문제로서 해상중력장의 연구에 있어 활용이 기대되는 해면고도 관측자료를 중력이상으로 변환하고 선상측정치를 위주로 하는 기존자료와 비 교하였다. 해면고도로서는 2년간의 GEOST 관측자료를 이용하였다. 지오이드, 중력이상 의 변환은 Fast Fourier Transform을 이용하였으며 정밀성을 기하기 위하여 관측치로 부터 범지구중력모델에 의한 추정치를 remove-restore 하는 방법을 채용하였다. 해면 고도로부터 구한 계산치와 기존자료와의 차이는 10 mgal 정도로서, 선상중력 관측치의 정밀도와 비교할 만한 수준으로 나타났다.

• 한국정밀공학회지
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• 제10권4호
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• pp.81-93
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• 1993

The three dimensional(3D) shape reconstruction from two dimensional(2D) cross-sections can be completed through three main phases : the input compilation, the triangular grid formation, and the smooth surface construction. In the input compilation phase, the cross-sections are analyzed to exctract the input data required for the shape reconstruction. This data includes the number of polygonized contours per cross-section and the vertices defining each polygonized contour. In the triangular grid formation phase, a triangular grid, leading to a polyhedral approximations, is constructed by extracting all the information concerning contour links between two adjacent cross- sections and then performing the appropriate triangulation procedure for each contour link. In the smooth surface construction phase, a smooth composite surface interpolating all vertices on the triangular grid is constructed. Both the smooth surface and the polyhedral approximation can be used as reconstructed models of the object. This paper proposes a new method for reconstructing the geometric model of a 3D objdect from a sequence of planar contours representing 2D cross-sections of the objdect. The method includes the triangular grid formation algorithms for contour closing, one-to-one branching, and one-to-many braanching, and many-to-many branching. The shape reconstruction method has been implemented on a SUN workstation in C.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.568-571
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• 2008

The computation of moving interface by the level set method typically requires reinitializations of level set function. An inaccurate estimation of level set function ${\phi}$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, accurate and robust reinitialization process is essential to the free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates directly level set function ${\phi}$ using a normal vector in the interface without solving the re-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1splitting FEM are adopted to discretize advection equation of the level set function and the Navier-Stokes equation, respectively. Advection equation of free surface and re-initialization process are validated with benchmark problems, i.e., a broken dam flow and time-reversed single vortex flow. The simulation results are in good agreement with the existing results.