• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.108-115
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• 1995

An efficient model for the dynamic analysis of caisson breakwaters under impulsive wave loadings is presented. The caisson structure is. regarded as a rigid body, and the rubble mound foundation is idealized as virtual added masses, springs, and dampers using the elastic half-space theory. The frequency-dependent hydrodynamic added mass and damping coefficients are considered by using the time memory functions and added mass at infinite frequency. To simulate the permanent sliding phenomenon of the caisson, the horizontal spring is modeled as a nonlinear spring with plastic behaviors. Comparisons with experimental results show that the present model gives fairly good results. Sensitivity analysis is performed for the relevant parameters affecting the dynamic responses of a caisson breakwater. Numerical experiments are also carried out to investigate the applicability to the prediction of permanent sliding distance and critical weight of the caisson.

• Structural Engineering and Mechanics
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• v.20 no.1
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• pp.111-121
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• 2005

The dynamic interaction of vehicle-bridge is studied by using transfer matrix method in this paper. The vehicle model is simplified as a spring-damping-mass system. By adopting the idea of Newmark-${\beta}$ method, the partial differential equation of structure vibration is transformed into a differential equation irrelevant to time. Then, this differential equation is solved by transfer matrix method. The prospective application of this method in real engineering is finally demonstrated by several examples.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.103-107
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• 2001

When ship claps against the ocean structure sited at shallow water, the time simulation of motion responses of dolphin-moored ocean structure is presented. The equatien of motion based on Cummin's theory of impulse responses are employed, and solved in time domain by using the Newmark $\beta$ method. The added mass and damping coefficients involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The impact forces due to ship collision are modeled as two method, and those are elastic and non-elastic collisions. The mooring forces for dolphin systems of scean structure are considered as linear spring system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.816-816
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• 2009

In order to attenuate structural waves in railway track, damped mass-spring absorber system and spring supported system are considered that are attached continuously along the beam length. A mathematical model is presented for the propagation of structural waves on a finitely long, periodically supported classical beam. The model in this paper could represent a railway track where the beam represents the rail and an appropriately chosen support type represents the pad/sleeper/ballast system of a railway track. And in this study, it is presented that the measurement method of health monitoring of railway track.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1942-1949
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• 2004

SLA(Scanned Linear Array) is a portable display unit for implementing next-generation virtual realities, utilizes a design that light generated by a line of LEDs is reflected from the rapidly oscillating mirror to generate a raster display. Reaction forces generated by the motions of the mirror and counter-balance mass cancel each other at the device base, reducing vibration. Metal leaf springs have been extensively applied in such portable units. Magnetic springs have been developed and adopted that can replace the metal spring and can avoid many disadvantages of metal springs. We model and analyze the dynamics of the structure with magnetic springs and present the simulation and experimental analysis results, which can be utilized for identifying and eliminating possible problem sources in removing shaking forces and moments, and oscillating the mirror at the required amplitude and frequency. Finally, we present the improved novel magnetic actuator model which can be applied in portable display units.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1065-1070
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• 2004

When the track designer analyze the track structure uses many known & unknown parameters. Unknown parameters, equivalent rail support spring factor, unit rail support spring factor, track damping coefficient, should be assumed. Known parameters are section properties (area, section factor, etc), material properties(modulus of elasticity, mass, etc) and track conditions(wheel load, loading conditions, gauge, etc.). In the assumption of track design parameters, some parameters can be overestimated or under estimated. The purpose of this study is to verify design parameters used in track design, in the way of experimental measurements. Data of displacements, banding stresses, loads, accelerations are measurable at track site. From these data, unknown parameters are derived. Compare these assumed and derived parameters, estimate the entire track stability.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.1021-1026
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• 1995

The seismic responses of a base isolated Pressurized Water Reactor (PWR) are investigated using a mathematical model which expresses the superstructure as lumped mass-spring model and the seismic isolator as an equivalent spring-damper. Time history analyses are performed for the 1940 E1 Centre earthquakes in both horizontal and vertical directions. In the analysis, structural damping of 5% is used for the superstructure. The isolator damping ratios of 12% for horizontal and 5% for vertical directions are used. The acceleration responses in base isolated PWR superstructure with high damping rubber bearings are much smaller than those in fixed base structure in horizontal direction. However, the vertical acceleration responses at the superstructure in the base isolation system are amplified to some extent. It is suggested that the vertical seismic responses at the superstructure should be reduced by introducing a soft vertical isolation device.

• Structural Engineering and Mechanics
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• v.29 no.4
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• pp.355-380
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• 2008

In this study, the new three-dimensional finite element analysis model of guideway structures considering ultra high-speed magnetic levitation train-bridge interaction, in which the various improved finite elements are used to model structural members, is proposed. The box-type bridge deck of guideway structures is modeled by Nonconforming Flat Shell finite elements with six DOF (degrees of freedom). The sidewalls on a bridge deck are idealized by using beam finite elements and spring connecting elements. The vehicle model devised for an ultra high-speed Maglev train is employed, which is composed of rigid bodies with concentrated mass. The characteristics of levitation and guidance force, which exist between the super-conducting magnet and guideway, are modeled with the equivalent spring model. By Lagrange's equations of motion, the equations of motion of Maglev train are formulated. Finally, by deriving the equations of the force acting on the guideway considering Maglev train-bridge interaction, the complete system matrices of Maglev train-guideway structure system are composed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.766-772
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• 2012

Spring supported piezoelectric cantilever structures (SPCS) were fabricated for vibration-based energy harvester application. We selected four elastic springs (A, B, C, and D type) as cantilever's supporter, each elastic spring has a different spring constant (S). The C type of SPCS ($S_C$: 4,649 N/m) showed a extremely low resonance frequency of 81 Hz along with the highest power output of 38.5 mW while the A type of SPCS ($S_A$: 40,629 N/m) didn't show a resonance frequency while. Therefore, it is considered that the lower spring constant lead to a lower resonance frequency of the SPCS. In addition, a tip mass (18 g) at one end of the SPCS could further reduce the resonance frequency without heavy degradation of power output.

• International Journal of Control, Automation, and Systems
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• v.4 no.3
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• pp.382-393
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• 2006

Mechanical system dynamics plays an important role in the area of computational structural biology. Elastic network models (ENMs) for macromolecules (e.g., polymers, proteins, and nucleic acids such as DNA and RNA) have been developed to understand the relationship between their structure and biological function. For example. a protein, which is basically a folded polypeptide chain, can be simply modeled as a mass-spring system from the mechanical viewpoint. Since the conformational flexibility of a protein is dominantly subject to its chemical bond interactions (e.g., covalent bonds, salt bridges, and hydrogen bonds), these constraints can be modeled as linear spring connections between spatially proximal representatives in a variety of coarse-grained ENMs. Coarse-graining approaches enable one to simulate harmonic and anharmonic motions of large macromolecules in a PC, while all-atom based molecular dynamics (MD) simulation has been conventionally performed with an aid of supercomputer. A harmonic analysis of a macroscopic mechanical system, called normal mode analysis, has been adopted to analyze thermal fluctuations of a microscopic biological system around its equilibrium state. Furthermore, a structure-based system optimization, called elastic network interpolation, has been developed to predict nonlinear transition (or folding) pathways between two different functional states of a same macromolecule. The good agreement of simulation and experiment allows the employment of coarse-grained ENMs as a versatile tool for the study of macromolecular dynamics.