• Smart Structures and Systems
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• v.23 no.6
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• pp.579-587
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• 2019

In this paper, pounding tuned mass dampers (PTMDs) were designed to mitigate the multi-mode vortex-induced vibration (VIV) of stay cable utilizing the viscous-elastic material's energy-dissipated ability. The PTMD device consists of a cantilever metal rod beam, a metal mass block and a specially designed damping element covered with viscous-elastic material layer. Wind-tunnel experiment on VIV of stay cable model was set up to validate the effectiveness of the PTMD on multi-mode VIV mitigation of stay cable. By analyzing and comparing testing results of all testing cases, it could be verified that the PTMD with viscous-elastic pounding boundary can obviously mitigate the VIV amplitude of the stay cable. Moreover, the installed location and the design parameters of the PTMD device based on the controlled modes of the primary stay cable, would have a certain extent suppression on the other modal vibration of the stay cable, which means that the designed PTMDs are effective among a large band of frequency for the multi-mode VIV control of the stay cable.

• Coupled systems mechanics
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• v.8 no.3
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• pp.199-218
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• 2019

This paper studies the forced vibration of the hydro-elastic system consisting of the anisotropic (orthotropic) plate, compressible viscous fluid and rigid wall within the scope of the exact equations and relations of elastodynamics for anisotropic bodies for describing of the plate motion, and with utilizing the linearized exact Navier-Stokes equations for describing of the fluid flow. For solution of the corresponding boundary value problem it is employed time-harmonic presentation of the sought values with respect to time and the Fourier transform with respect to the space coordinate on the coordinate axis directed along the plate length. Numerical results on the pressure acting on the interface plane between the plate and fluid are presented and discussed. The main aim in this discussion is focused on the study of the influence of the plate material anisotropy on the frequency response of the mentioned pressure. In particular, it is established that under fixed values of the shear modulus of the plate material a decrease in the values of the modulus of elasticity of the plate material in the direction of plate length causes to increase of the absolute values of the interface pressure. The numerical results are presented not only for the viscous fluid case but also for the inviscid fluid case.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.8 no.2
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• pp.51-73
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• 2004

A boundary layer analysis is used to study the effects of Hall and ion-slip currents on the steady magneto-micropolar of a viscous incompressible and electrically conducting fluid over a horizontal plate. By means of similarity solutions, deviation of fundamental equations on the assumption of small magnetic Reynolds number are solved numerically by using the shooting method. The effects of various parameters of the problem, e.g. the magnetic parameter, Hall parameter, ion-slip parameter, buoyancy parameter and material parameter are discussed and shown graphically.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.277-284
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• 1986

A numerical procedure (integral method) for calculating the interacting turbulent boundary layer is set up. With this method, some free interactions with various upstream conditions are simulated in order to investigate the influence of upstream state on the interacting turbulent boundary layer. The results obtained by this numerical simulation can be summarized as follows; Free interaction of upstream unstabilized (or separated) turbulent boundary layer is subcritical regardless of its external Mach number, while free interaction of upstream stabilized turbulent boundary layer has two different characteristics (subcritical, supercritical) according to the external Mach number.

• Journal of computational fluids engineering
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• v.20 no.1
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• pp.32-38
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• 2015

A 3-dimensional compressible turbulent boundary layer solver has been developed. A time marching method is used to integrate the turbulent boundary layer equations. While the direct integration of the boundary layer equations is performed for unseparated flow regions, the inverse integration is performed for separated flow regions. The program is verified for flows that have analytical solutions or other numerical results. The solver will be merged with an Euler solver for viscous-inviscid interaction.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1133-1152
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• 2015

A frequency-domain method is developed for evaluating the earthquake input energy to two building structures connected by viscous dampers. It is shown that the earthquake input energies to respective building structures and viscous connecting dampers can be defined as works done by the boundary forces between the subsystems on their corresponding displacements. It is demonstrated that the proposed energy transfer function is very useful for clear understanding of dependence of energy consumption ratios in respective buildings and connecting viscous dampers on their properties. It can be shown that the area of the energy transfer function for the total system is constant regardless of natural period and damping ratio because the constant Fourier amplitude of the input acceleration, relating directly the area of the energy transfer function to the input energy, indicates the Dirac delta function and only an initial velocity (kinetic energy) is given in this case. Owing to the constant area property of the energy transfer functions, the total input energy to the overall system including both buildings and connecting viscous dampers is approximately constant regardless of the quantity of connecting viscous dampers. This property leads to an advantageous feature that, if the energy consumption in the connecting viscous dampers increases, the input energies to the buildings can be reduced drastically. For the worst case analysis, critical excitation problems with respect to the impulse interval for double impulse (simplification of pulse-type impulsive ground motion) and multiple impulses (simplification of long-duration ground motion) are considered and their solutions are provided.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.410-415
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• 2001

An analytical and numerical examination of second-order fractional-step methods and boundary condition for the incompressible Navier-Stokes equations is presented. In this study, the compatibility condition for pressure Poisson equation and its boundary conditions, stability, and numerical accuracy of canonical fractional-step methods has been investigated. It has been found that satisfaction of compatibility condition depends on tentative velocity and pressure boundary condition, and that the compatible boundary conditions for type D method and approximately compatible boundary conditions for type P method are proper for divergence-free velocity for type D and approximately divergence-free for type P method. Instability of canonical fractional-step methods is induced by approximation of implicit viscous term with explicit terms, and the stability criteria have been founded with simple model problems and numerical experiments of cavity flow and Taylor vortex flow. The numerical accuracy of canonical fractional-step methods with its consistent boundary conditions shows second-order accuracy except $D_{MM}$ condition, which make approximately first-order accuracy due to weak coupling of boundary conditions.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.1-10
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• 2016

The analysis of characteristics of turbulent flow and thermal boundary layer for natural convection caused by fire along vertical wall is performed. The 4m-high vertical copper plate is heated and kept at a uniform surface temperature of $60^{\circ}C$ and the surrounding fluid (air) is kept at $16.5^{\circ}C$. The flow and temperature is solved by large eddy simulation(LES) of FDS code(Ver.6), in which the viscous-sublayer flow is calculated by Werner-Wengle wall function. The whole analyzed domain is assumed as turbulent region to apply wall function even through the laminar flow is transient to the turbulent flow between $10^9$<$Gr_z$<$10^{10}$ in experiments. The various grids from $7{\times}7{\times}128$ to $18{\times}18{\times}128$ are applied to investigate the sensitivity of wall function to $x^+$ value in LES simulation. The mean velocity and temperature profiles in the turbulent boundary layer are compared with experimental data by Tsuji & Nagano and the results from other LES simulation in which the viscous-sublayer flow is directly solved with many grids. The relationship between heat transfer rate($Nu_z$) and $Gr_zPr$ is investigated and calculated heat transfer rates are compared with theoretical equation and experimental data.

• Kyungpook Mathematical Journal
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• v.57 no.4
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• pp.651-665
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• 2017

Some computational fluid dynamics problems concerning the thin films flow of viscous fluid with a free surface and draining or coating fluid-flow problems can be delineated by third-order ordinary differential equations. In this paper, the aim is to introduce the numerical solutions of the boundary value problems of such equations by variational iteration method. In this paper, it is shown that the third-order boundary value problems can be written as a system of integral equations, which can be solved by using the variational iteration method. These solutions are gleaned in terms of convergent series. Numerical examples are given to depict the method and their convergence.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.3-8
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• 1998

The vortex particle method, which includes viscous effects, consists of diffusion of boundary vorticity and creation of the vortex particles, convection, particle strength exchange, and particle redistribution. Accuracy of the boundary element method is very important since it creates the particles around the body at every time step. A boundary element method based on source panel was investigated as part of computation of unsteady separated flows by rising the vortex particle method. The potential flows were computed around a circular cylinder and a square cylinder. The results around the circular cylinder were compared with the exact solution, and the distribution of vorticity, in particular near the sharp comers of the square cylinder, is scrutinized for different number of panels.