• Journal of Ship and Ocean Technology
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• 제8권2호
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• pp.61-69
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• 2004

Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory is employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with other existing experimental results. Agreement between the experimental data and the computation results is good.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.407-413
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• 2011

VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.448-448
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• 2000

This paper deals with dynamic behaviour analysis for pipeline inspection gauge (PIG) flow control in natural gas pipeline. The dynamic behaviour of the PIG is depending on the different Pressure between the rear and nose parts, which is generated by injected gas flow behind PIG's tail and expelled gas flow in front of its nose. To analyze the dynamic behaviour characteristics such as gas flow in pipeline, and the PIG's position and velocity, mathematical model is derived as two types of a nonlinear hyperbolic partial differential equation for unsteady flow analysis of the PIG driving and expelled gas, and nonhomogeneous differential equation for dynamic analysis of PIG. The nonlinear equation is solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used when we solve the steady flow equations to get initial flow values and the dynamic equation of PIG. The gas upstream and downstream of PIG are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of PIG with different operational conditions of pipeline.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• Journal of Biosystems Engineering
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• 제31권3호
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• pp.188-193
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• 2006

Elevation differences within a paddy field relate strongly to plant health, crop homogeneity, and pest control. For precision agriculture (PA), the elevation within a field should be precisely controlled. We analyzed variation in elevation within a rice paddy field over one crop cycle. The study took place in a rectangular plot (100 m x 30 m). Elevations within the a plots was measured by a laser-equipped surveying instrument, that could determine elevations to precisions of I mm. The test field was divided into grids with 30 squares; elevation was measured at the center of each 5 x 10-m grid square. This study measured elevation during nine observation periods from pre-plowing to post-harvest. Descriptive statistics showed the highest elevations after plowing due to soil disturbance. One-way analysis of variance (ANOVA) revealed significant elevation differences before and after plowing and transplanting, although elevations were similar over the period of crop growth. Comparison of pre-plowing and post-harvest data showed differences in elevations, indicating that elevation changes occurred during plowing, rice transplanting, plant growth, and harvesting. In summary, the above statistical analysis indicated that elevation changes occurred due to plowing but not during the plant growth season or due to harvesting.

• 대한조선학회논문집
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• 제47권2호
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• pp.188-195
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• 2010

Green water load is an important parameter to be considered in designing a modern ship or offshore structures like FPSO and FSRU. In this research, a numerical simulation method for green water phenomenon is introduced. The Navier-Stokes equations and the continuity equation are used as governing equations. The equations are calculated using Finite Difference Method(FDM) in rectangular staggered grid system. To increase the numerical accuracy near the body, the Cartesian cut cell method is employed. The nonlinear free-surface during green water incident is defined by Marker-density method. The green waters on a box in regular waves are simulated. The simulation results are compared with other experimental and computational results for verification. To check the applicability to moving ship, the green water of the ship which is towed by uniform force in regular wave, is simulated. The ship is set free to heave and to surge.

• Structural Engineering and Mechanics
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• 제41권1호
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• pp.25-41
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• 2012

Kriging surrogate model provides explicit functions to represent the relationships between the inputs and outputs of a linear or nonlinear system, which is a desirable advantage for response estimation and parameter identification in structural design and model updating problem. However, little research has been carried out in applying Kriging model to crack identification. In this work, a scheme for crack identification based on a Kriging surrogate model is proposed. A modified rectangular grid (MRG) is introduced to move some sample points lying on the boundary into the internal design region, which will provide more useful information for the construction of Kriging model. The initial Kriging model is then constructed by samples of varying crack parameters (locations and sizes) and their corresponding modal frequencies. For identifying crack parameters, a robust stochastic particle swarm optimization (SPSO) algorithm is used to find the global optimal solution beyond the constructed Kriging model. To improve the accuracy of surrogate model, the finite element (FE) analysis soft ANSYS is employed to deal with the re-meshing problem during surrogate model updating. Specially, a simple method for crack number identification is proposed by finding the maximum probability factor. Finally, numerical simulations and experimental research are performed to assess the effectiveness and noise immunity of this proposed scheme.

• 한국해안해양공학회지
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• 제10권3호
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• pp.125-131
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• 1998

본 논문은 경계처리 및 계산과정에 있어서 좀더 개선된 파랑 예측이 보장되도록 기존의 정방형 좌표계에서 수립된 포물선형 및 쌍곡선형 파랑 모델을 경계고정좌표계에 적용하였다. 일정 수심의 만곡 수로를 따라 진행 및 반사하는 파랑에 대한 이론해와 비교하여 수치 모델 결과는 모두 만족할만하였다. 포물선형 모델의 반사 파랑 모의는 반사물에 접근한 입사파를 다시 외해 경계 쪽으로 역계산하여 수행된다.

• 대한조선학회논문집
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• 제35권1호
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• pp.1-14
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• 1998

2차원 천수방정식에 기초한 조류계산 수치모델을 개발하였다. 복잡한 해안선의 입력을 단순화할 수 있는 직각격자를 사용하였으며, 방정식은 효율이 뛰어난 것으로 알려져 있는 인수분해음해법(Implicit Factorization Method)에 의하여 수치적으로 풀었다. 대류항은 상류차분법으로 처리하여 수치소산이 자동적으로 들어가도록 하였으며, 따라서 수치불안정에 의한 발산을 억제할 수 있었다. 모델의 검증을 위하여 선형화된 천수방정식을 풀고 계산결과를 해석해와 비교하였으며 잘 일치하고 있음을 확인하였다. 수치모델의 응용 예로서 인천항부근의 경인운하 개발예정인 수로에서의 조류 계산결과를 보였다.

• 한국지리정보학회지
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• 제17권3호
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• pp.160-174
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• 2014

본 연구의 목적은 광역의 일단위 수문순환을 모의할 수 있는 격자기반의 분포형 모델을 구축한 후, 이를 미래 기후변화에 따른 광역적 수문영향을 평가하는데 있다. 격자별로 지표 유출층, 지표하 불포화 및 포화 토양층의 3단으로 구성하여 일별 물수지를 계산하며, 증발산량은 Penman-Monteith방법을 사용하였고, 지표 및 지표하유출은 지체계수(lag coefficient)와 감수곡선 계수(recession curve slope)를 적용하였다. 모델의 검보정을 위하여 한강유역의 충주댐과 소양강댐을 대상으로 9개년(2001-2009)의 댐유입량 자료를 이용하여 모델의 6개 주요매개변수를 보정하였으며, Nash-Sutcliffe 모델효율 (NSE)은 각각 0.57, 0.71의 값을 보였으며, 결정계수($R^2$)는 각각 0.65, 0.72의 값을 보였다. 5개의 IPCC SRES A1B 기후변화 시나리오자료(CSIRO MK3, GFDL CM2_1, CONS ECHO-G, MRI CGCM2_3_2, UKMO HADGEMI)를 적용한 결과, 미래 유출량의 변화는 강수량과 비슷한 경향을 보이면서 전체적으로 7.0%~27.1% 증가하였고, 증발산량도 미래 기온의 증가경향으로 일부 경우를 제외하고 증가하는 경향을 나타내었으며, 이들의 공간적 변화를 제시하였다.