• Structural Engineering and Mechanics
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• v.47 no.5
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• pp.599-622
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• 2013

Seismic response of two dimensional liquid tanks is numerically simulated using fully nonlinear velocity potential theory. Galerkin-weighted-residual based finite element method is used for solving the governing Laplace equation with fully nonlinear free surface boundary conditions and also for velocity recovery. Based on mixed Eulerian-Lagrangian (MEL) method, fourth order explicit Runge-Kutta scheme is used for time integration of free surface boundary conditions. A cubic-spline fitted regridding technique is used at every time step to eliminate possible numerical instabilities on account of Lagrangian node induced mesh distortion. An artificial surface damping term is used which mimics the viscosity induced damping and brings in numerical stability. Four earthquake motions have been suitably selected to study the effect of frequency content on the dynamic response of tank-liquid system. The nonlinear seismic response vis-a-vis linear response of rectangular liquid tank has been studied. The impulsive and convective components of hydrodynamic forces, e.g., base shear, overturning base moment and pressure distribution on tank-wall are quantified. It is observed that the convective response of tank-liquid system is very much sensitive to the frequency content of the ground motion. Such sensitivity is more pronounced in shallow tanks.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.54-62
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• 2008

A new solution method was developed to solve the free surface flow around a hull and named as 'Variable Free Surface Panel Method'. In the method the non-linearity of the free surface boundary conditions was fully taken into account and the raised panel method was employed to effectively solve the problem. The transom stern flow was also considered and the panel on the hull was generated using the panel cutting method. Numerical calculations were performed for KCS(KRISO Container Ship) hull form and compared with the experimental data to confirm the validity of the method. The comparison with the conventional free surface panel method was also accomplished. It is confirmed that new method gives more reliable results than the conventional method.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.107-112
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• 2011

The aim of this study is to analyze the hydrodynamic properties of a 2D floating body with moon pool using a 2D fully nonlinear Numerical Wave Tank(NWT). This NWT was developed based on the Boundary Element Method(BEM) with potential theory and fully nonlinear free surface boundary conditions. Free surface elevations in the moon pool were calculated in the time domain for various frequencies of forced body motions. The added-mass and damping coefficients of the heaving body were also obtained. The present numerical results were compared with the analytic and experimental results and their accuracy was verified.

• Journal of Ocean Engineering and Technology
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• v.21 no.5
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• pp.1-8
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• 2007

A long wave induced by a Gaussian-shape submarine landslide is simulated by a 2D fully nonlinear numerical wave tank (NWT). The NWT is based on the boundary element method and the mixed Eulerian/Lagrangian approach. Using the NWT, physical characteristics of land-slide tsunami, including wave generation, propagation, particle kinematics, hydrodynamic pressure, run-up and depression, are simulated for the early stage of long wave generation and propagation. Various sliding mass heights are applied to the developed model for a systematic sensitivity analysis. In particular, the fully nonlinear NWT results are compared with linear results (exact body-boundary conditions with linear free-surface conditions) to identify the nonlinear effects in the respective cases.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.631-636
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• 2006

In this paper, the wave pattern around the hull with the transom stern advancing on the free surface with a constant speed was taken into consideration. To solve the problem the numerical analysis program was developed using Rankine source panel method based on potential flow analysis technique. The non-linearity of the free surface boundary conditions was fully satisfied. To verify the validity of the developed program the numerical calculations for Athena hull and KCS(KRISO container ship) hull was performed. The results of the numerical computation was compared with the ones of the model test experiment.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.281-290
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• 2012

Hydrodynamic analysis of a surface-piercing body with an open chamber was performed with incident regular waves and forced-heaving body motions. The floating body was simulated in the time domain using a 2D fully nonlinear numerical wave tank (NWT) technique based on potential theory. This paper focuses on the hydrodynamic behavior of the free surfaces inside the chamber for various input conditions, including a two-input system: both incident wave profiles and forced body velocities were implemented in order to calculate the maximum surface elevations for the respective inputs and evaluate their interactions. An appropriate equivalent linear or quadratic viscous damping coefficient, which was selected from experimental data, was employed on the free surface boundary inside the chamber to account for the viscous energy loss on the system. Then a comprehensive parametric study was performed to investigate the nonlinear behavior of the wave-body interaction.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.80-89
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• 1992

This paper deals with the open boundary problems, and two numerical schemes are used for the implementation of open boundary condition. One is to add the artificial damping term to dynamic free-surface boundary condition. Determination of suitable damping coefficient and the damping cone is the most important in this scheme. The other scheme is a modified Orlanski's method. This will be useful for the problems with unidirectional waves. A few typical free-surface wave problems are modeled for the numerical test. Method of solution is fundamental source-distribution method and the fully nonlinear boundary conditions are applied. The computed results are compared with those of others for the proof of practicality of these schemes.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.38-52
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• 1991

In this paper, a semi-Lagrangian method is used to solve the nonlinear hydrodynamics of a three-dimensional body beneath the free surface in the time domain. The boundary value problem is solved by using the boundary integral method. The geometries of the body and the free surface are represented by the curved panels. The surfaces are discretized into the small surface elements using a bi-cubic B-spline algorithm. The boundary values of $\phi$ and $\frac{\partial{\phi}}{\partial{n}}$ are assumed to be bilinear on the subdivided surface. The singular part proportional to $\frac{1}{R}$ are subtracted off and are integrated analytically in the calculation of the induced potential by singularities. The far field flow away from the body is represented by a dipole at the origin of the coordinate system. The Runge-Kutta 4-th order algorithm is employed in the time stepping scheme. The three-dimensional form of the integral equation and the boundary conditions for the time derivative of the potential Is derived. By using these formulas, the free surface shape and the equations of motion are calculated simultaneously. The free surface shape and fille forces acting on a body oscillating sinusoidally with large amplitude are calculated and compared with published results. Nonlinear effects on a body near the free surface are investigated.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.6 s.150
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• pp.638-646
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• 2006

In this paper a new hull-panel generation algorithm named 'Panel Cutting Method' was developed to solve the flow phenomena around a ship advancing on the free surface with a constant speed. In this algorithm the non-linearity of the free surface boundary conditions was taken into account using the iterative method and the raised panel was used at each iteration step. Numerical calculations were performed to investigate the validity of the developed algorithm using the series $60(C_B=0.60)$ hull The wave resistance coefficients, the wave patterns and the wave heights were compared between the computed and the experimental results at Fn=0.25 and 0.316. The comparison showed good agreement between computation and experiment.