• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.3
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• pp.233-245
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• 2011

A new BWIM(bridge weigh-in-motion) algorithm using both measured strain and acceleration data is proposed. To consider the effects of bridge vibration on the estimation of moving loads, the dynamic governing equation is applied with the known stiffness and mass properties but damping is ignored. Dynamic displacements are computed indirectly from the measured strains using the beam theory and accelerations are measured directly by accelerometers. To convert a unit moving load to its equivalent nodal force, a transformation matrix is determined. The incompleteness in the measured responses is considered in developing the algorithm. To examine the proposed BWIM algorithm, simulation studies, laboratory experiments and field tests were carried. In the simulation study, effects of measurement noise and estimation error in the vehicle speed on the results were investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.1038-1043
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• 2002

The floating ring journal bearing is attraction for high-speed turbo machinery applications, including turbochargers and aircraft accessory equipment, because it is not only simple and easy to make and to replace in the field but also it seems to have adequate high speed stability characteristics. Therefore, an analysis method of dynamic properties of floating ring journal bearing is presented. The static equilibrium locus of inner film and outer film are calculated by using the impedance description. The equivalent stiffness and damping coefficients of floating ring journal bearing are composed by using the equilibrium of torque between inner film and outer film. Then, a stability analysis of turbocharger shaft system supported with floating ring journal bearing has been performed.

• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.15-38
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• 2018

Negative stiffness dampers (NSDs) have been proven an efficient solution to vibration control of stay cables. Although previous studies usually assumed a linear negative stiffness behavior of NSDs, many negative stiffness devices produce negative stiffness with nonlinear behavior. This paper systematically evaluates the impact of nonlinearity in negative stiffness on vibration control performance for stay cables. A linearization method based on energy equivalent principle is proposed, and subsequently, the impact of two types of nonlinear stiffness, namely, displacement hardening and softening stiffness, is evaluated. Through the Hilbert transform (HT) of free vibration responses, the effects of nonlinear stiffness of an NSD on the modal frequencies, damping ratios and frequency response functions of a stay cable is also investigated. The HT analysis results validate the accuracy of the linearization method.

• Structural Engineering and Mechanics
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• v.2 no.1
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• pp.95-112
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• 1994

This paper describes the formulation and application of a dynamic model for a conventional rail track subjected to arbitary loading functions that simulate wheel/rail impact forces. The rail track is idealized as a periodic elastically coupled beam system resting on a Winkler foundation. Modal parameters of the track structure are first obtained from the natural vibration characteristics of the beam system, which is discretized into a periodic assembly of a specially-constructed track element and a single beam element characterized by their exact dynamic stiffness matrices. An equivalent frequency-dependent spring coefficient representing the resilient, flexural and inertial characteristics of the rail support components is introduced to reduce the degrees of freedom of the track element. The forced vibration equations of motion of the track subjected to a series of loading functions are then formulated by using beam bending theories and are reduced to second order ordinary differential equations through the use of mode summation with non-proportional modal damping. Numerical examples for the dynamic responses of a typical track are presented, and the solutions resulting from different rail/tie beam theories are compared.

• Structural Engineering and Mechanics
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• v.21 no.1
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• pp.101-119
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• 2005

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequency-dependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

• Journal of Power Electronics
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• v.12 no.4
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• pp.559-566
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• 2012

A new design method for the LCL filters of three-phase voltage source PWM rectifiers is presented in this paper. Based on the single-phase harmonic equivalent model, the harmonic voltage of the rectifier side is calculated to design the LCL filter parameters by an iterative algorithm, in which the resonance frequency $f_{res}$ and the ratio r between the grid-side inductance and the rectifier-side inductance are selected as known constants. The design criteria and process are introduced and the influence on the design result by the value of the resonance frequency $f_{res}$, ratio r is analyzed. Finally an example (600V, 500kW) is tested by simulation and experiment to verify the validity of the new design method.

• 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.

• Selected Papers of The Society of Naval Architects of Korea
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• v.2 no.1
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• pp.47-62
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• 1994

Herein the surge-heave-pitch motion of a ship in harbor has been analyzed within the framework of linear potential theory. The ship is assumed to be slender and moored at an arbitrary position in a rectangular harbor with a constant depth. The coast line is assumed to be straight. The ship and harbor responses to incident long waves are represented in terms of Green's function, which is the solution of tole Helmholtz equation satisfying necessary boundary conditions. An integral equation is obtained from matching condition between harbor and ocean solutions, and it is replaced by an equivalent variational form. Numerical results sallow that the ship motion can be highly amplified at the frequencies, where the harbor is resonated by the incident wave. At the resonant frequencies, the added mass for vertical motions becomes negative and the damping forte changes abruptly.

• International Journal of Concrete Structures and Materials
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• v.7 no.2
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• pp.135-153
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• 2013

This study investigates the direct displacement based design (DDBD) approach for different types of reinforced concrete structural systems including single moment-resisting, dual wall-frame and dual steel-braced systems. In this methodology, the displacement profile is calculated and the equivalent single degree of freedom system is then modeled considering the damping characteristics of each member. Having calculated the effective period and secant stiffness of the structure, the base shear is obtained, based on which the design process can be carried out. For each system three frames are designed using DDBD approach. The frames are then analyzed using nonlinear time-history analysis with 7 earthquake accelerograms and the damage index is investigated through lateral drift profile of the models. Results of the analyses and comparison of the nonlinear time-history analysis results indicate efficiency of the DDBD approach for different reinforced concrete structural systems.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.6
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• pp.794-805
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• 1999

Pneumatic cushioning cylinders are commonly employed for vibration and shock control. A mathematical simulation model of a double acting pneumatic cushioning cylinder designed to absorb shock loads is presented which is based on the following assumptions; ideal equation of state isentropic flow through a port conservation of mass polytropic thermodynamics single degree of freedom piston dynamics and energy equivalent linear damping. These differential equation can be solved through numerical integration using the fourth order Runge-Kutta method. An experimental study was conducted to validate the results obtained by the numerical integra-tion technique. Simulated results show good agreement with experimental data. The computer simulation model presented here has been extremely useful not only in understanding the has been extremely useful not only in understanding the basic cushioning but also in evaluating different designs.