• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.234-239
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• 2002

Acoustic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=200 are simulated using finite difference lattice Boltzmann method. A third-order-accurate up-wind scheme is used for spartial derivatives, and a second-order-accurate Runge-Kutta scheme is used for time marching. The results show that in capturing very small acoustic pressure fluctuation with same frequency of Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of acoustic sound is presented that acoustic which approaches tire upstream due to Doppler effect in the uniform flow slowly propagates, while that for the downstream quickly propagates. It is also apparent that the size of sound pressure is proportional for central distance $r^{-1/2}$ of the cylinder.

• Journal of applied mathematics & informatics
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• v.39 no.3_4
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• pp.419-435
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• 2021

This paper deals with numerical treatment of singularly perturbed differential equations involving small delays. The highest order derivative in the equation is multiplied by a perturbation parameter 𝜀 taking arbitrary values in the interval (0, 1]. For small 𝜀, the problem involves a boundary layer of width O(𝜀), where the solution changes by a finite value, while its derivative grows unboundedly as 𝜀 tends to zero. The considered problem contains delay on the convection and reaction terms. The terms with the delays are approximated using Taylor series approximations resulting to asymptotically equivalent singularly perturbed BVPs. Inducing exponential fitting factor for the term containing the singular perturbation parameter and using central finite difference for the derivative terms, numerical scheme is developed. The stability and uniform convergence of difference schemes are studied. Using a priori estimates we show the convergence of the scheme in maximum norm. The scheme converges with second order of convergence for the case 𝜀 = O(N^-1) and for the case 𝜀 ≪ N^-1, the scheme converge uniformly with first order of convergence, where N is number of mesh intervals in the domain discretization. We compare the accuracy of the developed scheme with the results in the literature. It is found that the proposed scheme gives accurate result than the one in the literatures.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.3
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• pp.535-544
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• 2023

In this paper, we study the effect of gradient vector calculation method(analytical method, central finite difference method) on adaptive beamforming to control weight distribution during iterated calculation when LMS algorithm (repeating method) is used to realize desired beam pattern. To this end, a quasi-ideal beam having an arbitrarily set beam width, a rotating beam, and a multi-beam were reviewed as examples. Numerical experiments applied the step parameters of the appropriate values to the adaptive beamforming system through trial and error equally to the two calculations, and compared the convergence characteristics of objective functions that evaluate adaptability and error using two methods for calculating gradient vectors.

• Structural Engineering and Mechanics
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• v.47 no.4
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• pp.559-573
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• 2013

Geometrically non-linear axisymmetric bending of a shallow spherical shell with a clamped or a simply supported edge under axisymmetric load was investigated numerically. The partial load was introduced by the Heaviside step function, and the solution was obtained by the finite difference and the Newton-Raphson methods. The thickness of the shell was considered to be uniform and the material was assumed to be homogeneous and isotropic. Sensitivity analysis was made for three geometrical parameters. The accuracy of the algorithm was checked by comparing the central deflection, the radial membrane stress at the edge, or the transverse shear force with the solutions of plates and shells in the literature and good agreement was obtained. The main findings of the study can be outlined as follows: (i) If the shell is fully loaded the central deflection of a clamped shell is larger than that of a simply supported shell provided that the shell is not very shallow, (ii) if the shell is partially loaded the central deflection of the shell is sensitive to the parameters of thickness, depth, and partial loading but the influence of the boundary conditions is negligible.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.185-197
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• 2001

This paper presents the effect of axial stretching on large amplitude free vibration of an extensible suspended cable supported at the same level. The model formulation developed in this study is based on the virtual work-energy functional of cables which involves strain energy due to axial stretching and work done by external forces. The difference in the Euler equations between equilibrium and motion states is considered. The resulting equations govern the horizontal and vertical motion of the cables, and are coupled and highly nonlinear. The solution for the nonlinear static equilibrium configuration is determined by the shooting method while the solution for the large amplitude free vibration is obtained by using the second-order central finite difference scheme with time integration. Numerical examples are given to demonstrate the vibration behaviour of extensible suspended cables.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2252-2263
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• 1993

The purpose of this study is to verify the vibration and damping characteristics of elastic-viscoelastic-elastic structures, theoretically and experimentally. The forth-order differential equations of motion are derived for the transverse vibration of three-layered plates with viscoelastic core layer. The equations consider both transverse displacements of the constraining layer and the bare base plate as variable and account for the effect of the transverse normal strain and the shear strain of viscoelastic core layer on the vibration of the plates. Finite difference analysis of the equations and experimental measurements are performed on the three-layered plates of completely free boundary condition. Comparative investigations on the theory and the results of direct frequency analysis of NASTRAN are carried out on the same structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1996.10a
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• pp.210-217
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• 1996

Under strong shock loads including earthquake or blast, structures may start to crack in stress concentrated members. The continuous behavior of the structure changes to the discontinuous. In this study, numerical method analyzing continuous and discontinuous behavior of a structure is developed using a modified distinct element method. Equations of motion of each distinct element are integrated using the central difference method, one of the finite difference methods. Interactions between he elements are considered by an element and pore spring. The forces acting in the center of an element include contact stress transferred by element spring; tensile stress by pore spring; and external traction such as earthquake or blast load. To verify the proposed method, the behavior of the cantilever beam subject to the quasi-static concentrated force at the end is investigated. The failure behavior of the simply supported beam subject to the strong shock at the center is studied. The proposed method can predict the failure behavior of the structure due to the shock loading and the post-failure discontinuous behavior of the structure.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.3
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• pp.37-47
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• 1989

A calcuation method of the temperature distribution for various shape due to the constant heat input is studied in this paper. So far, the method of try and error is carring out on the mould design. The reason of adopting this method is due to hardly estimate the cooling system in the mould base. As above description, the most part of the mould is supposed as a rectangular, cylinderical and triangular shape and made a governing equation of heat transfer and solved it to numerical analysis by finite-difference method(central- difference). After that in order to confirm that the temperatures are measured on different shape specimens from the part of frequent usage of which are carbon, crome-molybden, tool and stainless steel those were compared with the results of calculations presented in this paper.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.11
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• pp.1538-1551
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• 1997

Kinetic energy conservation for fixed and moving grids is examined in time-accurate finite element computation of fully unsteady inviscid flows. As numerical algorithms, fractional step method (FSM) and modified SIMPLE are used. To simulate the flow in moving grid system, arbitrary Lagrangian-Eulerian (ALE) method is adopted. In the present study, the energy conserving time integration rule for finite element algorithm is proposed and discussed schematically. It is shown that the discretization by Crank-Nicolson in time and Galerkin (central difference) in space must be used to ensure energy conservation. The developed code has been tested for a standing vortex in fixed or moving grid system, sloshing in a tank and propagation of a solitary wave, and has been shown to be a completely energy conserving algorithm.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.4
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• pp.19-30
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• 2000

A finite-volume method is developed to solve turbulent flows around modern commercial hull forms with bow and stern bulbs. The RANS equations are solved. The cell-centered finite-volume method employs QUICK and central difference scheme for convective and diffusive flux discretization, respectively. The SIMPLEC method is adopted for the velocity-pressure coupling. The developed numerical methods are applied to calculate turbulent flow around KRISO 3600TEU container ship. Surface meshes are generated into five blocks: bow and stern bulbs, overhang, fore and afterbody. 3-D field grid system with O-H topology is generated using elliptic grid generation method. Surface friction lines and wake distribution at propeller plane is compared with experiment. The calculated results show that the present method can be used to predict flow around a modern commercial hull forms with bulbs.