• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.53-58
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• 1998

In this paper, we study the response of several anisotropic systems to buried transient line loads. The problem is mathematically formulated based on the equations of motion in the constitutive relations. The load is in form of a normal stress acting with arbitrary axis on the plane of monoclinic symmetry. Plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in reference coordinate system, where the line load is coincident with symmetry axis of the orthotrioic material. Then the equation of motion is transformed with respect to general coordiante system with azimuthal angle by using transformation tensor. The load is first described as a body force in the equations of the motion for the infinite media and then it is mathematically characterized. Subsequently the results for semi-infinite spaces is also obtained by using superposition of the infinite medium solution together with a scattered solution from the free surface. Consequently explicit solutions for the displacements are obtained by using Cargniard-DeHoop contour. Numerical results which are drawn from concrete examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• Journal of KSNVE
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• v.11 no.1
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• pp.156-166
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• 2001

This work uses tensor calculus to derive a complete set of three-dimensional field equations well-suited for determining the behavior of thick shells of revolution having arbitrary curvature and variable thickness. The material is assumed to be homogeneous, isotropic and linearly elastic. The equations are expressed in terms of coordinates tangent and normal to the shell middle surface. The relationships are combined to yield equations of motion in terms of orthogonal displacement components taken in the meridional, normal and circumferential directions. Strain energy and kinetic energy functionals are also presented. The equations of motion and energy functionals may be used to determine the static or dynamic displacements and stresses in shells of revolution, including free and forced vibration and wave propagation.

• Journal of Ship and Ocean Technology
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• v.4 no.3
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• pp.21-32
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• 2000

In the present paper, the sloshing flow in the liquid holds of a large tanker is simulated using a numerical method. In the fluid domain, the three-dimensional Navier-Stokes equation with free surface is solved using a finite difference method, and the realistic shapes of multi holds are modeled including the internal members. The time-history of the tank motion is obtained using a time-domain program for ship motion. In order to computer the impulsive pressures on internal structures, a concept of buffer zone is adopted near the tank ceiling during impact occurrence. This study demonstrates that the global fluid motion in the multi liquid holds of ships and FPSO's can be simulated using the numerical method and the corresponding local pressure can be predicted with reasonable accuracy.

• Bulletin of the Society of Naval Architects of Korea
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• v.18 no.3
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• pp.29-38
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• 1981

In general the drift result in ship heeling, thus it seems to be necessary to analyze the ship motion by considering both the drifting and heeling phenomena. In this paper, a drift velocity and a heeling angle are given as prior conditions, and then within the linear potential theory the hydrodynamic coefficients and wave exciting forces and moments are derived for a ship advancing and drifting with constant speeds. And numerical calculations are preformed for a cylindrical body of shiplike cross section at zerp forward velocity. The 2-D hydrodynamic forces and moments of a heeled cylinder are calculated by using the Frank Close-Fit method. These numerical results for the oscillating cylinder without drift velocity have shown better agreements with experimental data than the numerical results of Kobayashi[2]. The motion responses for a drifting cylinder are calculated ignoring the drift velocity effect in the free surface condition. The accuracy of these calculations can not be verified, because the experimental data are not available. Through these numerical calculations to so concluded that drift velocity effects on the body motion are signiffcant.

• Geomechanics and Engineering
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• v.7 no.2
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• pp.149-164
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• 2014

One of the most advanced classes of techniques for ground response analysis is based on the use of Transfer Functions. They represent the ratio of Fourier spectrum of amplitude motion at the free surface to the corresponding spectrum of the bedrock motion and they are applied in frequency domain usually by FFT method. However, Fourier spectrum only shows the dominant frequency in each time step and is unable to represent all frequency contents in every time step and this drawback leads to inaccurate results. In this research, this process is optimized by decomposing the input motion into different frequency sub-bands using Wavelet Multi-level Decomposition. Each component is then processed with transfer Function relating to the corresponding component frequency. Taking inverse FFT from all components, the ground motion can be recovered by summing up the results. The nonlinear behavior is approximated using an iterative procedure with nonlinear soil properties. The results of this procedure show better accuracy with respect to field observations than does the Conventional method. The proposed method can also be applied to other engineering disciplines with similar procedure.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.3
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• pp.247-253
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• 2012

Dam-break flows, a type of very shallow gravity-driven flow, are substantially influenced by resistance forces due to viscous friction and turbulence. Assuming turbulent flow, the main focus of this study is to validate the increase of drag forces caused by surface roughness and especially turbulence intensity. A Reynolds Averaged Navier-Stokes(RANS) approach with the standard k-${\varepsilon}$ turbulence model is used for this study, where the free surface motion is captured by using a volume of fluid(VOF) method. Surface roughness effects are considered through the law of the wall modified for roughness, while the initial turbulence intensity which determines the lowest level of turbulence in the flow domain of interest is used for the variation of turbulence intensity. It has been found that the numerical results at higher turbulence intensities show a reasonably good agreement with the physical aspects shown by two different dam-break experiments without and with the impact of water.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.279-290
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• 2010

In this paper, a VOF method called RHRIC (refined high resolution intertace capturing) is introduced for solving the motion of the free surface and applied to the simulation of the advection of rigid interiaces of different shapes and a 20 dam-break problem, which are typical benchmark test cases. The numerical results for the interface advection cases are compared to the analytic solutions, while the available experimental data and other numerical results of various free surface methods for the dam-break problem are provided for the validation of the proposed VOF method. The same simulations were also carried out using the original HRIC scheme and a modified HRIC scheme called MHRIC for comparison. Although the RHRIC uses a simple order scheme, a basis of the original HRIC scheme, lower than the third-order ULTIMATE-QUICKEST used by the MHRIC, it provides an improved accuracy over the two previous HRIC methods.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1033-1048
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• 2016

An analytical solution based on the neutral surface concept is developed to study the free vibration behavior of simply supported functionally graded plate reposed on the elastic foundation by taking into account the effect of transverse shear deformations. No transversal shear correction factors are needed because a correct representation of the transversal shearing strain obtained by using a new refined shear deformation theory. The foundation is described by the Winkler-Pasternak model. The Young's modulus of the plate is assumed to vary continuously through the thickness according to a power law formulation, and the Poisson ratio is held constant. The equation of motion for FG rectangular plates resting on elastic foundation is obtained through Hamilton's principle. Numerical examples are provided to show the effect of foundation stiffness parameters presented for thick to thin plates and for various values of the gradient index, aspect and side to thickness ratio. It was found that the proposed theory predicts the fundamental frequencies very well with the ones available in literature.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.481-488
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• 2003

A fluid-structure-isolator interaction program was developed in this study. The behavior of liquid regions are simulated by the boundary element method, and then the technique of analyzing the free surface motion in time domain is developed by using the nonlinear free surface boundary condition(NFBC) and the condition of interface between the structure and the fluid. Structure regions are modeled by the finite element method. In order to construct the governing equation of the fluid structure interaction(FSI)problem in time domain, the finite elements for a structure and boundary elements for liquid are coupled using the equilibrium condition, the compatibility condition and NFBC. The isolator is simulated by equation proposedin 3D Basis Me. In order to verify the validity and the applicability of the developed fluid- structure -Isolator interaction program, The horizontal forced vibration analysis was performed. The applicability of the developed method is verified through the artificial seismic analysis of real size liquid storage tank.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.4
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• pp.382-390
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• 2009

The submerged body near the free surface is disturbed by the 1st and 2nd order wave forces, which results in unstable movements when no control is applied. In this paper, the vertical motions of the submerged body are analyzed, and the time-variant nonlinear system for the vertical motions of the submerged body is transformed to the time-invariant linear system in state space. Next, depth controller of the submerged body is designed by using LQR control, one of the modern optimal control technique. Numerical simulation shows that effective depth controls can be achieved by LQR control.