• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.125-138
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• 2001

An efficient correction storage scheme on a structured grid is applied to a sequence of approximate Jacobian systems arising at each time step from a linearization of the discrete nonlenear system of equations, obtained by the implicit time discretization of the conservation laws for unsteady fluid flows. The contribution of freezing the Jacobian matrix to computing costs is investigated within the correction storage scheme. The performance of the procedure is exhibited by measuring CPU time required to obtain a fully developed laminar vortex shedding flow past a circular cylinder, and is compared with that of a collective iterative method on a single grid. In addition, some computed results of the flow are presented in terms of some functionals along with measured data. The computational test shows that the computing costs may be saved in favor of the correction storage scheme with the frozen Jacobian matrix, to a great extent.

• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.985-996
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• 2000

The issue of quench is related to safety operation of large-scale superconducting magnet system fabricated by cable-in-conduit conductor. A numerical method is presented to simulate the thermal hydraulic quench characteristics in the superconducting Tokamak magnet system, One-dimensional fluid dynamic equations for supercritical helium and the equation of heat conduction for the conduit are used to describe the thermal hydraulic characteristics in the cable-in-conduit conductor. The high heat transfer approximation between supercritical helium and superconducting strands is taken into account due to strong heating induced flow of supercritical helium. The fully implicit time integration of upwind scheme for finite volume method is utilized to discretize the equations on the staggered mesh. The scheme of a new adaptive mesh is proposed for the moving boundary problem and the time term is discretized by the-implicit scheme. It remarkably reduces the CPU time by local linearization of coefficient and the compressible storage of the large sparse matrix of discretized equations. The discretized equations are solved by the IMSL. The numerical implement is discussed in detail. The validation of this method is demonstrated by comparison of the numerical results with those of the SARUMAN and the QUENCHER and experimental measurements.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.639-647
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• 2019

A realistic numerical simulation technology using a Lagrangian Fluid-Structure Interaction (FSI) model was combined with a fracture algorithm to predict the fluid-ice-structure interaction. The failure of ice was modeled as the tensile fracture of elastic material by applying a novel FSI model based on the Moving Particle Semi-implicit (MPS) method. To verify the developed fracture algorithm, a series of numerical simulations for 3-point bending tests with an ice beam were performed and compared with the experiments carried out in an ice room. For application of the developed FSI model, a dropping water droplet hitting a cantilever ice beam was simulated with and without the fracture algorithm. The simulation showed that the effects of fracture which can occur in the process of a FSI simulation can be studied.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.117-122
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• 1998

A numerical study is carried out to investigate the transient process of combustion phenomena associated with hypersonic propulsion devices. Reynolds averaged Navier-Stokes equations for reactive flows are used as governing equations with a detailed chemistry mechanism of hydrogen-air mixture and two-equation SST turbulence modeling. The governing equations are discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit time accurate method. At first, oscillating shock-induced combustion is analyzed and the comparison with experimental result gives the validity of present computational modeling. Secondly, the model ram accelerator experiment was simulated and the results show the detailed transient combustion mechanisms. Thirdly, the evolution of oblique detonation wave is simulated and the result shows transient and final steady state behavior at off-stability condition. Finally, shock wave/boundary layer interaction in combustible mixture is studied and the criterion of boundary layer flame and oblique detonation wave is identified.

• Coupled systems mechanics
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• v.1 no.4
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• pp.361-379
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• 2012

This paper presents a fully coupled three-dimensional solver for the analysis of interaction between pulsatile flow and large deformation structure. A partitioned time marching algorithm is employed for the solution of the time dependent coupled discretised problem, enabling the use of highly developed, robust and well-tested solvers for each field. Conservative transfer of information at the fluid-structure interface is combined with an effective multi-predict-correct iterative scheme to enable implicit coupling of the interacting fields at each time increment. The three-dimensional unsteady incompressible fluid is solved using a powerful implicit time stepping technique and an ALE formulation for moving boundaries with second-order time accurate is used. A full spectrum of total variational diminishing (TVD) schemes in unstructured grids is allowed implementation for the advection terms and finite element shape functions are used to evaluate the solution and its variation within mesh elements. A finite element dynamic analysis of the highly deformable structure is carried out with a numerical strategy combining the implicit Newmark time integration algorithm with a Newton-Raphson second-order optimisation method. The proposed model is used to predict the wave flow fields of a particular flow-induced vibrational phenomenon, and comparison of the numerical results with available experimental data validates the methodology and assesses its accuracy. Another test case about three-dimensional biomedical model with pulsatile inflow is presented to benchmark the algorithm and to demonstrate the potential applications of this method.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.145-162
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• 1995

A damped trapezoidal rule method for numerical time-integration is presented, and its application in analyses of dynamic response of damped structures is discussed. It is shown that the damped trapezoidal rule method has features that make it an attractive approach for applications in dynamic analyses of structures. Accuracy and stability analyses are developed for the damped single-degree-of-freedom systems. Error analyses are also performed for the Newmark beta method and compared with the damped trapezoidal rule method as a basis for discussion of the relative merits of the proposed method. The procedure is fully explicit and easy to implement. However, since the method is an explicit method, it is conditionally stable. The methodology is applied to several example problems to illustrate its strengths, limitations and inherent simplicity.

• Journal of Korean Port Research
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• v.13 no.1
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• pp.167-174
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• 1999

Numerical analysis of two-fluid flows for both water and air is carried out. Free-Surface flows with an arbitrary deformation have been simulated around two dimensional submerged hydrofoil. The computation is performed using a finite volume method with unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell-wise local mesh refinement. the integration in space is of second order based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels The linear equation systems are solved by conjugate gradient type solvers and the non-linearity of equations is accounted for through picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations the continuity equation the conservation equation of one species and the equations or two turbulence quantities.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.789-795
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• 2000

Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell wise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.

• Nuclear Engineering and Technology
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• v.45 no.4
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• pp.439-458
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• 2013

REX-10 is a fully-passive small modular reactor in which the coolant flow is driven by natural circulation, the RCS is pressurized by a steam-gas pressurizer, and the decay heat is removed by the PRHRS. To confirm design decisions and analyze the transient responses of an integral PWR such as REX-10, a thermal-hydraulic system code named TAPINS (Thermal-hydraulic Analysis Program for INtegral reactor System) is developed in this study. Based on a one-dimensional four-equation drift-flux model, TAPINS incorporates mathematical models for the core, the helical-coil steam generator, and the steam-gas pressurizer. The system of difference equations derived from the semi-implicit finite-difference scheme is numerically solved by the Newton Block Gauss Seidel (NBGS) method. TAPINS is characterized by applicability to transients with non-equilibrium effects, better prediction of the transient behavior of a pressurizer containing non-condensable gas, and code assessment by using the experimental data from the autonomous integral effect tests in the RTF (REX-10 Test Facility). Details on the hydrodynamic models as well as a part of validation results that reveal the features of TAPINS are presented in this paper.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1215-1220
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• 2008

To obtain the shape of the free surface more accurately, computations are carried out by a finite volume method using unstructured meshes and an interface capturing method. Free-surface flow, which is very important in the fields of ship and marine engineering, is numerically simulated for flows of both water and air. Control volumes are used with an arbitrary number of faces and allows a local mesh refinement. The integration is of second order, with a midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation. The solution method of pressure-correction type solves sequentially equations of momentum, continuity, conservation, and two-equations turbulence model. Comparison are quantitatively made between the computation and experiment in order to confirm the solution method.