• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.1
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• pp.63-69
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• 1998

A rotating shaft system subjected to seismic motions has been investigated for the various operating modes at start-up. During an earthquake excitation, the rotor may hit the stator of machines due to the excessive deformation of shaft, and thus the response of rotating shaft system of which foundation is supported by the vibration isolation devices has been simulated. In order to examine the transient response of the rotating shaft system at the start-up to both the various operating conditions and the seismic excitation simultaneously, nonlinear equations of motion are derived and solved numerically using Runge-Kutta method. The response of the rotating shaft system is calculated according to the operating modes as recommended by the machine and the system parameters such as the spring stiffness of isolation devices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.9-17
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• 2005

The wake patterns and thrust characteristics of dual flapping airfoils in a biplane configuration are investigated using an unsteady panel method. To trace complicated wake shapes behind airfoils, a core addition scheme, a vortex core model, and the fourth order Runge-Kutta convection scheme are employed. Present results are verified by comparing them with flow visualization, exact solution and published computed results. The thickness and camber of thick airfoils has an effect of decreasing thrust. The airfoils produce maximum thrust when the phase angles between plunging and pitching motions are both 90 and 120 degrees. Thrust increases as the plunge velocity is increased, which is also found as the pitch amplitude is stepped up. Thrust decreases when the distance between the airfoils is less than 0.6c.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.2
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• pp.70-79
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• 2024

In this study, we introduce a linear spectral method capable of simulating wave generation and transformation caused by a moving bottom in a 3-dimensional space. The governing equations are linear dynamic free-surface boundary conditions and linear kinematic free-surface boundary conditions, which are solved in Fourier space. Solved velocity potential and free-surface displacement should satisfy continuity equation and kinematic bottom boundary condition. For numerical analysis, a 4th order Runge-Kutta method was utilized to analyze the time integral. The results obtained in Fourier space can be converted into velocity potential and free-surface displacement in a real space using inverse Fourier transform. Regular waves generated by various types of moving bottoms were simulated with the linear spectral method. Additionally, obliquely generated regular waves using specified bottom movements were simulated. The results obtained from the spectral method were compared to analytical solutions, showing good agreement between the two.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1383-1393
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• 2014

Recently, with rapid improvement in computer hardware and theoretical development in the field of computational fluid dynamics, high-order accurate schemes also have been applied in the realm of computational hydraulics. In this study, numerical solutions of 1D shallow water equations are presented with TVD Runge-Kutta discontinuous Galerkin (RKDG) finite element method. The transcritical flows such as dam-break flows due to instant dam failure and transcritical flow with bottom elevation change were studied. As a formulation of approximate Riemann solver, the local Lax-Friedrichs (LLF), Roe, HLL flux schemes were employed and MUSCL slope limiter was used to eliminate unnecessary numerical oscillations. The developed model was applied to 1D dam break and transcritical flow. The results were compared to the exact solutions and experimental data.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.679-690
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• 1997

The risk assessment model for hydrlolgic safety analysis of dam and levee in developed by using Monte-Carlo and AFOSM (Advanced First-Order Second-Moment) method. The fault tree analysis and four phases approach are presented for the safety eveluation of risk of dam and levee. The risk model consists of rainfall-runoff analysis, reservoir routing and channel routing considering the variations in the model parameter. For the rainfall-runoff analysis, KRRL method is adopted with 200-year precipitation and PMP (Probable Maximum Precipitation). Reservoir routing is performed by fourth order Runge-Kutta method and channel routing by standard step method. The suggested model will contribute to safety evaluation of dam and levee and their rehabilitation decision problem.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.1
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• pp.1-8
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• 2001

The computations of the turbulent flow around the ship models with the free-surface effects were carried out. Incompressible Reynolds-Averaged Navier-Stokes equations were solved by using an explicit finite-difference method with the nonstaggered grid system. The method employed second-order finite differences for the spatial discretization and a four-stage Runge-Kutta scheme for the temporal integration. For the turbulence closure, a modified Baldwin-Lomax model was exploited. The location of the free surface was determined by solving the equation of the kinematic free-surface condition using the Lax-Wendroff scheme and a free-surface conforming grid was generated at each time step so that one of the grid boundary surfaces always coincides with the free surface. An inviscid approximation of the dynamic free-surface boundary condition was applied as the boundary conditions for the velocity and pressure on the free surface. To validate the computational method developed in the present study, the computations were carried out for beth Wigley and Series 60 $C_B=0.6$ ship model and the computational results showed good agreements with the experimental data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.2
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• pp.187-193
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• 2023

This paper presents the buckling behavior of a pile considering its self-weight. The differential equation and boundary conditions governing the buckling of partially embedded piles in nonhomogeneous soils are derived. The buckling load and mode shape of the pile are numerically computed by the Runge-Kutta method combined with the Regula-Falsi algorithm. The obtained numerical solutions for bucking loads agree well with the results available from the literature. Numerical examples are given to analyze the buckling load and mode shape of the piles as affected by the self-weight, embedment ratio, slenderness ratio and boundary condition of the pile as well as the aspect ratio and rigidity ratio of the subgrade reaction. It is found that the self-weight of the pile leads to the reduction of the buckling load, indicating that neglecting the effect of self-weight may overestimate the buckling load of partially embedded piles.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.266-273
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• 1981

갑자기 작용하는 외압을 받는 직교이방성원통쉘의 동적좌굴을 해석하였다. Donnell-Karnam 형의 비선형방정식을 유도하였으며 쉘의 초기불완전성도 고려하였다. Galerkin의 방법을 사용하여 운동방정식을 구하고 Runge-Kutta 수직해법으로 비선형방정식을 풀었다. 쉘의 직교이방성특성이 처짐-하중 관계식의 비선형성에 미치는 영향을 검토하였으며 동적산출하중의 판별법을 정의하였다. 본 연구의 결과, 직교이방성원통쉘은 쉘의 초기불완전성에 그리 민감하지 않음을 보여주었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.264-273
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• 1984

초기경향이 있는 보강평판의 비선형 운동 방정식을 Galerkin method에 의하여 유도하였다. Runge Kutta method를 사용하여 step-load를 받고 있는 보강평판의 동적 좌굴문제의 수치해를 구하였다. 정적 좌굴실험에 의하여 좌굴하중을 결정함에 있어 동적 해석법을 응용할 수 있음을 입증하였으며, step-load를 받는 보강평판의 동적 좌굴해석으로 정적좌굴의 초기결함 민감성을 해 석하였다. 보강평판의 초기결함민강성은 평판보다 훨씬 낮으며 보강재의 편심비가 높을수록 민감 성은 둔화된다.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.411-416
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• 2004

This paper introduces a fast Fourier transform (FFT)-based spectral analysis method for the transient responses as well as the steady-state responses of linear dynamic systems with non-proportional damping. The force vibration of a non-proportionally damped three-DOF system is considered as the illustrative numerical example. The proposed spectral analysis method is evaluated by comparing with the numerical solution obtained by the Runge-Kutta method