• Title, Summary, Keyword: numerical methods

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Validation of Numerical Codes Applied to Floating Offshore Structures

  • Choi, Hang S.
    • Journal of Hydrospace Technology
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    • v.2 no.1
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    • pp.55-64
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    • 1996
  • Herein a review is made on the validation problem of numerical codes applied to floating offshore structures. Since the dynamic behaviour of offshore floating structures in water waves is in general complex and nonlinear, a numerical approach seems to be promising. However, numerical codes are likely involved with uncertainties and they at the present status show apparent scatterness in typical bechmark tests, particularly in second-order wave forces. Convergence test is the minimum requirement for the validation of numerical codes. Some other practical check points are introduced to clarify the potential error sources. It is concluded that a standard procedure for validation must be urgently established sothat numerical methods can safely be used as a rational design tool.

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Numerical Simulation of Ballast Water Exchange

  • Kamada, Koichi;Minami, Kiyokazu;Shiotani, Shigeaki;Shoji, Kuniaki
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • pp.157-165
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    • 2006
  • In February,2004, at International Maritime Organization (IMO), LONDON, a new international convention 'International Convention fur the Control and Management of Ship's Ballast Water and Sediment 2004' was adopted. It is called 'Ballast Water Management Convention (BWM)'. Ballast water means charged seawater or fresh water in ship's special tanks (ballast tank) to keep safety navigation and ship's maneuverability. However, from 1980, it was point out the serious problem for marine ecosystem and human life that ballast water includes harmful marine species (and small organisms) and these species are also discharged along with ballast water. These species were released with discharged ballast water in water areas, where species are different from discharged ballast water. The problem is that released species increase when released species are more powerful than native species and consequently, marine ecological system is destroyed in released water area. Authors have inspected the validity of the ballast water exchange using pumping-through method that is one of the methods of ballast water management. In this paper, the numerical simulation of the motion and density of the fluid at the time of exchange of the fluid in a 2-dimensional tank using the pumping-through method was carried out by using two different type numerical methods. One method is MPS method that is one of the particle methods. Other one is Finite Different Method (FDM). Authors were compared with result of two numerical method calculations and experiment result and reported some knowledge from these results.

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Estimation of groundwater inflow into an underground oil storage facility in granite

  • Wang, Zhechao;Kwon, Sangki;Qiao, Liping;Bi, Liping;Yu, Liyuan
    • Geomechanics and Engineering
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    • v.12 no.6
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    • pp.1003-1020
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    • 2017
  • Estimation of groundwater inflow into underground opening is of critical importance for the design and construction of underground structures. Groundwater inflow into a pilot underground storage facility in China was estimated using analytical equations, numerical modeling and field measurement. The applicability of analytical and numerical methods was examined by comparing the estimated and measured results. Field geological investigation indicated that in local scale the high groundwater inflows are associated with the appearance of open joints, fractured zone or dykes induced by shear and/or tensile tectonic stresses. It was found that 8 groundwater inflow spots with high inflow rates account for about 82% of the total rate for the 9 caverns. On the prediction of the magnitude of groundwater inflow rate, it was found that could both (Finite Element Method) FEM and (Discrete Element Method) DEM perform better than analytical equations, due to the fact that in analytical equations simplified assumptions were adopted. However, on the prediction of the spatial distribution estimation of groundwater inflow, both analytical and numerical methods failed to predict at the present state. Nevertheless, numerical simulations would prevail over analytical methods to predict the distribution if more details in the simulations were taken into consideration.

Analytical and numerical simulation on charging behavior of no-insulation REBCO pancake coil

  • Quach, Huu Luong;Kim, Ji Hyung;Chae, Yoon Seok;Moon, Jae Hyung;Ko, Jung Hyup;Kim, Hyung-Wook;Kim, Seog-Whan;Jo, Young-Sik;Kim, Ho Min
    • Progress in Superconductivity and Cryogenics
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    • v.20 no.4
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    • pp.16-19
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    • 2018
  • This paper presents analytical and numerical simulation approaches on charging characteristics of no-insulation (NI) REBCO pancake coil by using the equivalent circuit model to estimate magnetic performance response in the coil. The analytical methods provide closed form or definite solution in the form of complete mathematical expressions but they are hard to solve the complex problems. Numerical methods have become popular with the development of the computing capabilities to solve the problems which are impossible or very hard to solve analytically. First of all, the equivalent circuit model are proposed to develop the simulation code for both analytical and numerical method. The charging test was performed under critical current to obtain magnetic field induced and terminal voltage through the radial as well as spiral current paths within the coil. To verify the validity of both proposed methods, the simulation results were compared and discussed with the experimental results.

Comparative studies on numerical optimal design techniques (수치해석에 의한 최적화 설계 기법의 비교 연구)

  • 조선휘;박종근
    • Journal of the korean Society of Automotive Engineers
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    • v.4 no.2
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    • pp.79-85
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    • 1982
  • Computer codes on two numerical optimization methods-Sequentially Unconstrained Minimization Technique (SUMT) and Gradient Projection Method-are constructed and tested with several test problems. Design formulation of tension - compression coil spring is set up and the solution is obtained. Consequently, the feature, the advantage and the limitation of these methods, made clear through the tests, are discussed.

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전산구조의 과거와 미래

  • 김형열
    • Computational Structural Engineering
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    • v.9 no.3
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    • pp.60-64
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    • 1996
  • 본 기사에서는 International Journal for Numerical Methods in Engineering(이하 IJNME로 표기)의 창간호에 실린 편집자 논설("Editorial," Vol.1, pp.1-2, 1969)과 창간 25년이 지난 IJNME의 과거와 미래에 관하여 기술한 글(O.C.Zienkiewicz, R.H. Gallagher and R.W.Lewis, "International Journal for Numerical Methods in Engineering: The First 25 Years and the Future," Vol.37, pp.2151-2158, 1994)의 일부분을 각각 2장과 3장에 옮겨 적고자 한다.

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Generalized runge-kutta methods for dynamical systems

  • Yu, Dong-Won
    • Bulletin of the Korean Mathematical Society
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    • v.35 no.1
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    • pp.157-172
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    • 1998
  • A numerical method is proposed for dynamical systems. We utilize the fact that special matrix exponentials can be exactly evaluated by the intrinsic library functions. Numerical examples are given, which show that the relative error s of the proposed method converge to a small constant and that the method faithfully approximates the dynamics of the nonlinear differential equations.

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Analysis of 2-Dimensional Shallow Water Equations Using Multigrid Method and Coordinate Transformation

  • Lee, Jong-Seol;Cho, Won-Cheol
    • International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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    • v.26 no.1
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    • pp.1-14
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    • 1998
  • Various numerical methods for the two dimensional shallow water equations have been applied to the problems of flood routing, tidal circulation, storm surges, and atmospheric circulation. These methods are often based on the Alternating Direction Implicity(ADI) method. However, the ADI method results in inaccuracies for large time steps when dealing with a complex geometry or bathymetry. Since this method reduces the performance considerably, a fully implicit method developed by Wilders et al. (1998) is used to improve the accuracy for a large time step. Finite Difference Methods are defined on a rectangular grid. Two drawbacks of this type of grid are that grid refinement is not possibile locally and that the physical boundary is sometimes poorly represented by the numerical model boundary. Because of the second deficiency several purely numerical boundary effects can be involved. A boundary fitted curvilinear coordinate transformation is used to reduce these difficulties. It the curvilinear coordinate transformation is used to reduce these difficulties. If the coordinate transformation is orthogonal then the transformed shallow water equations are similar to the original equations. Therefore, an orthogonal coorinate transformation is used for defining coordinate system. A multigrid (MG) method is widely used to accelerate the convergence in the numerical methods. In this study, a technique using a MG method is proposed to reduce the computing time and to improve the accuracy for the orthogonal to reduce the computing time and to improve the accuracy for the orthogonal grid generation and the solutions of the shallow water equations.

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Stability of onshore pipelines in liquefied soils: Overview of computational methods

  • Castiglia, Massimina;de Magistris, Filippo Santucci;Napolitano, Agostino
    • Geomechanics and Engineering
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    • v.14 no.4
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    • pp.355-366
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    • 2018
  • One of the significant problems in the design of onshore pipelines in seismic areas is their stability in case of liquefaction. Several model tests and numerical analyses allow investigating the behavior of pipelines when the phenomenon of liquefaction occurs. While experimental tests contribute significantly toward understanding the liquefaction mechanism, they are costly to perform compared to numerical analyses; on the other hand, numerical analyses are difficult to execute, because of the complexity of the soil behavior in case of liquefaction. This paper reports an overview of the existing computational methods to evaluate the stability of onshore pipelines in liquefied soils, with particular attention to the development of excess pore water pressures and the floatation of buried structures. The review includes the illustration of the mechanism of floating and the description of the available calculation methods that are classified in static and dynamic approaches. We also highlighted recent trends in numerical analyses. Moreover, for the static condition, referring to the American Petroleum Institute (API) Specification, we computed and compared the uplift safety factors in different cases that might have a relevant practical use.