• Structural Engineering and Mechanics
• /
• v.23 no.1
• /
• pp.1-13
• /
• 2006

Structural cracks may cause variations in structural stiffness and thus produce bilinear vibrations to structures. This study examines the dynamic behavior of structures with breathing cracks. A generalized algorithm based on the finite element method and bilinear theory was developed to study the influence of a breathing crack on the vibration characteristic. All the formulae derived in the time domain were applied to estimate the period of the overall bilinear motion cycle, and the contact effect was considered in the calculations by introducing the penetration of the crack surface. Changes in the dynamic characteristics of cracked structures are investigated by assessing the variation of natural frequencies under different crack status in either the open or closed modes. Results in estimation with vibrational behavior variation are significant compared with the experimental results available in the literature as well as other numerical calculations.

• Proceedings of the KSR Conference
• /
• 2003.10c
• /
• pp.22-27
• /
• 2003

The running safety of the rolling stock depends on the design characteristics and the contact condition between wheel and railway. In this study, the effect of the conicity of wheel tread on the running safety is analyzed. The modal analysis results in $0.5\~0.6Hz$ natural frequency with lateral modes. However, the frequency analysis for the running simulation shows the frequency components near 1Hz. The running simulation shows that the KTX with GV40 wheel has less lateral vibration than that of XP55 as the KTX goes higher speed.

• Wind and Structures
• /
• v.3 no.1
• /
• pp.41-58
• /
• 2000

According to research currently developed by several authors (including the present ones) a multimode approach to the aeroelastic instability can be appropriate for suspension bridges with very long span and so with close natural frequencies. Extending that research, this paper deals in particular with: i) the role of along-wind modes, underlined also by means of the flutter mode representation; ii) the effects of a variation of the mean wind speed along the span. A characterisation of the response in the time domain by means of an energetic approach is also discussed.

• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.662-667
• /
• 2003

This paper presents a performance analysis of the 1st generation bump foil journal bearings for the micro gas turbine TG75. Static performances such as load capacity and attitude angle are estimated by using soft elasto-hydrodynamic analysis technique, and dynamic performances such as stiffness and damping coefficients are estimated by perturbation method. Rotordynamic analysis for TG75 is performed by using the bearing analysis results. TG75 rotor has 2 horizontal and vertical directional natural modes due to the bearing stiffness characteristics. TG75 rotor will be stably operated between the 1st bending mode at 33000cpm and the 2nd bending mode at 85500cpm. Unbalance response analysis results satisfy the API vibration criteria.

• Advances in concrete construction
• /
• v.4 no.4
• /
• pp.263-281
• /
• 2016

Concrete continues to be the most consumed construction material in the world, only next to water. Due to rapid increase in construction activities, Construction and Demolition (C&D) waste constitutes a major portion of total solid waste production in the world. It is important to assess the amount of C&D waste being generated and analyse the practices needed to handle this waste from the point of waste utilization, management and disposal addressing the sustainability aspects. The depleting natural resources in the current scenario warrants research to examine viable alternative means, modes and methods for sustainable construction. This study reports processing Recycled Coarse Aggregates (RCA) using a rod mill, for the first time. Parameters such as amount of C&D waste for processing, nature of charge and duration of processing time have been optimized for obtaining good quality RCA. Performance of RCA based concrete and performance enhancement techniques of 50% RCA based concrete are discussed in this paper.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.15 no.3
• /
• pp.83-90
• /
• 2001

This paper resents an algorithm for the optimal parameter selection of a power system stabilizer in a single machine-infinite bus system through the external equivalent transmission line. This method is one of the classical techniques by changing the PSS gain to allocate properly pole-zero positions. All the PSS parameters are obtained by solving a set of algebraic equations for the system constants depend on a variety of machine loadings and system external impedances, the natural oscillation modes, and the damping characteristics. And this algorithm was written in a simple software program using MATLAB.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.103-108
• /
• 2013

This paper describes basic properties tests and non-rotating dynamic test for rotor blade, flexbeam, and torque tube of which bearingless rotor in helicopter consists. A basic properties test are bending and twist test to find the flap stiffness, lag stiffness, and twist stiffness of specimens. The purpose of dynamic test is to find natural frequencies and modes in non-rotating state. The test results are used to update the analysis model. The updated analysis results using rotorcraft comprehensive code match the tests quite well. The updated model input based on the tests will be utilized to analysis the conditions of rotating whirl tower test before the whirl test and will be compared with the whirl tower test results.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.11
• /
• pp.204-212
• /
• 1999

In this paper, the vibrational motion of a flexible beam clamped on a translating base and carrying a moving mass is investigated. The equations of motion which describe the total dynamics of the beam-mass-cart system are derived and the coupled dynamic equations are solved by unconstrained modal analysis. In modal analysis, the exact normal mode solutions corresponding to the eigenfrequencies for the position of the moving mass and the ratios of the mass of the flexible beam, the moving mass and the base cart are used. Proper transformations of the time solutions between the normal modes for a position and those for the next position of the moving mass are also adopted. Numerical simulations are carried out to obtain the open-loop responses of the system in tracking the pre-designed path of the moving mass.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.12 no.7
• /
• pp.534-541
• /
• 2002

Vibration and sound characteristics of King Song-Dok Bell are ivesigated. Natural frequencies. vibration modes and beat period of the bell are precisely measured. The effect of striking position and the position of nodal lines on the beat characteristics is examined. It is first found that the beat characteristics are quote different according to the position on the bell surface and clear beat is periodically generated on the circumference. It turns out that in King Song-Dok Bell, Dangjwa(the present striking position) is located at the position which makes a beat in the first vibration mode, as welt as it produces very clear beat In the second vibration mode.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1026-1031
• /
• 2001

In this paper. the dynamic characteristics of a super high-speed tilting-pad air bearing(TPGB) used in a turbo expander with high expansion ratio are analyzed. The dynamic behavior and stability of a rotary system supported by two journal air bearings are investigated numerically. The transient response of the shaft is obtained by simultaneously solving the equation of motion of the shaft and the dynamic Reynolds equation. The stiffness and damping coefficients of the bearing are calculated from the loading coefficients of the bearing are calculated from the loading capacity. shaft velocity and displacement by using a curve fitting method. The natural frequencies of the 1st and 2nd rigid modes can be calculated from these coefficients. The theoretical method of a rigid rotor system is verified by experimentsut.