• 한국해양공학회지
• /
• 제22권3호
• /
• pp.1-7
• /
• 2008

In this study, a mathematical model for flaw with silt protector is proposed that adds a second-order energy loss term in the momentum equation. The three-dimensional numerical model was developed based on mathematical models and verified through comparison with flume test results. Loss coefficients were evaluated through the flume tests and applied to the numerical model. It was found through the investigation of various example cases that the downstream flow pattern was affected mainly by penetration of the silt curtain, not by the approach velocity, and also that the blocking effect of velocity was increased by the increase in mesh density of the silt curtain, below a certain mesh density. The blocking effect did not increase further above a certain mesh density.

• 한국농공학회논문집
• /
• 제46권3호
• /
• pp.3-14
• /
• 2004

A two-dimensional numerical model based on a finite volume method was formulated to solve the shallow water equations and applied for evaluating drainage characteristics at large-sized paddy fields. Manning roughness coefficient was calibrated using the observed inundating depths at drainage tests, and used for validating the model with the results from another drainage test. The simulated results were in good agreement with the observed inundating depths. The result of surface drainage showed that the longer width of the outlet was or the more the number of drainage outlet was, the shorter the drainage time was taken, and the larger the size of the field become, the longer the drainage time was taken, and the field shape had little effect on drainage time. To reduce the drainage time to 24 hours, the outlet is located lower than the elevation of the basin and small drainage ditch is constructed at the field. The results showed that the drainage time was taken short as the small drainage ditch was constructed. The comparison of drainage time as to the size of field constructed small drainage ditch showed the field, 100m ${\times}$ 200 m, can be drained in 24 hours.

• Journal of Advanced Research in Ocean Engineering
• /
• 제1권2호
• /
• pp.115-133
• /
• 2015

This paper describes an approach for the numerical analysis of container ship slamming and whipping and various parameters that influence slamming and whipping. For validation purposes, the numerical analysis results were compared with experimental results obtained as part of the Wave-Induced Loads on Ships Joint Industry Project. Water entry problems for two-dimensional (2D) sections were first solved using a 2D generalized Wagner model (GWM) for various drop conditions and geometries. As the next step, the hydroelastic numerical analysis of a 10,000-TEU container ship subjected to slamming and whipping loads in waves was performed. The analysis method used is based on a fully coupled model consisting of a three-dimensional (3D) Rankine panel model, a 3D finite element model (FEM), and a 2D GWM, which are strongly coupled in the time domain. Parametric studies were carried out in both numerical and experimental tests with various forward speeds, wave heights, and wave periods. The trends observed and the validity of the numerical analysis results are discussed.

• Computers and Concrete
• /
• 제1권3호
• /
• pp.261-284
• /
• 2004

Two enhancements to a recently developed plastic-damage-contact model for concrete are presented. The model itself, which uses planes of degradation that can undergo damage and separation but that can regain contact according to a contact law, is described. The first enhancement is a new damage evolution function which provides a completely smooth transition from the undamaged to the damaged state and from pre-peak to post-peak regions. The second is an improved contact function that governs the potential degree of contact with increasing opening on a crack plane. The use of a damage evolution function with a pre-peak has implications for the consistent tangent matrix/stress recovery algorithm developed for the model implementation, and amendments to this algorithm to accommodate the new function are described. A series of unpublished experimental tests on notched specimens undertaken in Cardiff in the mid 1990s are then described. These include notched beam tests as well as prismatic and cylindrical torsion tests. The tests are then considered in three dimensional finite element analyses using the modified Craft model implemented in the finite element program LUSAS. Comparisons between experimental and numerical data show reasonable agreement except that the numerical simulations do not fully describe the latter stages of the softening responses for the torsion examples. Finally, it is concluded that the torsion tests described provide useful benchmark examples for the validation of three-dimensional numerical models for concrete.

• 대한기계학회논문집B
• /
• 제24권7호
• /
• pp.916-923
• /
• 2000

Numerical study of three-dimensional turbulent flow in a forward curved centrifugal fan is presented. Standard $k-{\varepsilon}$ turbulence model and non-orthogonal curvilinear coordinates arc used to consider the turbulent flow field and complex geometry. Finite Volume approach is adopted for discretization scheme and structured grid system is used to help convergence. Multiblock grid system is used for flow field and divided into five domains that are inlet, outlet, impeller, tip clearance and scroll. It is assumed that the flow field is steady and incompressible. These numerical results are compared with the experimental data inside a rotor and at the fan outlet. Most important flow features are captured through this numerical approach. Finally details of flow field inside a fan are described and analyzed.

• Journal of Mechanical Science and Technology
• /
• 제20권8호
• /
• pp.1256-1265
• /
• 2006

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• Wind and Structures
• /
• 제11권3호
• /
• pp.241-256
• /
• 2008

This paper adopts autoregressive (AR) model to simulate the wind velocity of spatial three-dimensional fields in accordance with the time and space dependent characteristics of the 3-D fields. Based on the built MATLAB programming, this paper discusses in detail the issues of the AR model deduced by matrix form in the simulation and proposes the corresponding solving methods: the over-relaxation iteration to solve the large sparse matrix equations produced by large number of degrees of freedom of structures; the improved Gauss formula to calculate the numerical integral equations which integral functions contain oscillating functions; the mixed congruence and central limit theorem of Lindberg-Levy to generate random numbers. This paper also develops a method of ascertaining the rank of the AR model. The numerical examples show that all those methods are stable and reliable, which can be used to simulate the wind velocity of all large span structures in civil engineering.

• 대한수학회논문집
• /
• 제22권3호
• /
• pp.453-464
• /
• 2007

A computationally efficient numerical scheme is presented for the phase-field model of two-phase systems for anisotropic interfacial energy. The scheme is solved by using a nonlinear multigrid method. When the coefficient for the anisotropic interfacial energy is sufficiently high, the interface of the system shows corners or missing crystallographic orientations. Numerical simulations with high and low anisotropic coefficients show excellent agreement with exact equilibrium shapes. We also present spinodal decomposition, which shows the robustness of the pro-posed scheme.

• 대한기계학회논문집B
• /
• 제20권10호
• /
• pp.3272-3281
• /
• 1996

The flow analysis method which had been developed for the numerical calculation of 3-dimensional, incompressible and turbulent flow within an axial compressor was extended to the flow field within centrifugal impeller. In this method based on the SIMPLE(Semi Implicit Method Pressure Linked Equations) algorithm, the coordinate transformation was adopted and the standard k-.epsilon. model using wall function was used for turbulent flow analysis. The calculated flow fields have agreed very well with measurement results. Especially, 3-dimensional and viscous flow characteristics including secondary flows, jet-wake flow and decreased pressure rise along impeller passage, which can't be predicted by inviscid Q3D calculation were predicted very reasonably.

• 한국방재학회 논문집
• /
• 제8권2호
• /
• pp.159-164
• /
• 2008

본 연구에서는 경상남도 양산시를 통과하여 흐르는 양산천 유역에서의 홍수범람을 3차원 공간정보를 이용하여 모의하였다. Saint-Venant 방정식을 지배방정식으로 사용하였으며, 지배방정식의 선형항은 풍상차분기법을 이용하여 해석하였고 비선형항을 해석하기 위해서 Leap-frog 기법을 사용하였다. 홍수빈도에 따른 수치모의 결과는 3차원으로 가시화 되어 웹(web)상에서 제공되며 결과를 3차원적으로 가시화를 시킴으로서 2차원 도면상에 표시하여 제공하는 수치모의결과보다 대상 행정기관의 업무능률 향상과 대민서비스의 질을 향상시킬 수 있을 것이다. 본 연구를 통해 얻어진 수치모의 결과는 GIS를 이용한 3차원 홍수지도 작성에 사용될 수 있으며, 각 지방자치단체에 제공하므로서 홍수로 인한 피해를 감소시키는데 효율적일 것이다.