• Proceedings of the KSME Conference
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• 2000.11b
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• pp.609-614
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• 2000

This numerical study investigate resonance frequency of natural convection for steady state, periodic flow and chaotic flow in two-dimensional direct numerical simulations, differentially heated, vertical cavities having aspect ratios near unity. The enclosure cavity has isothermal and time dependent temperature side walls and adiabatic top/bottom walls. The aspect ratio is 1/3, 1/2, 1, 2, and 3 for the varying Rayleigh number. Resonance frequency for AR=1 has decrease as the aspect ratio and the Rayleigh number are increasing.

• Journal of KSNVE
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• v.7 no.6
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• pp.1039-1048
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• 1997

This paper describes the effects of dual dynamic vibration absorbers attached to a primary vibration system with damping. The efficiency of dual dynamic vibration absorbers was investigated with the height of amplitude ratio at the resonance frequency ratio of the damped vibration system according to mass ratio, natural frequency ratio and damping ratio. The variation of amplitude ratio related to frequency ratio of primary vibration system is verified experimentally and theoretically according to dual dynamic vibration systems using computer program designed to find mutual relationship between two absorbers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.688-692
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• 2003

For high voltage operation, a new type of piezoelectric transformer using radial vibration of disk, poled with the same direction was proposed. The piezoelectric ceramics was composed to PZT-PMN-PSN. The diameter and thickness of a disk type piezoelectric transformer were 45［mm］and 4［mm］, respectively The surface ratio of driving electrode and generating electrode of the piezoelectric transformer was 2 : 1. The resonance characteristics of input admittance, step-up voltage ratio and power transmission efficiency of the piezoelectric transformer were measured by varying the load resistance(0.1∼70［kΩ］). As a result, both resonance frequency and step-up voltage ratio increased with increasing load resistance. The step-up voltage ratio was reached more than 60 times under no load resistance. The maximum efficiency of 97% at load resistance of 2kΩ was obtained.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.129-135
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• 1996

This paper presents the effectiveness of the dynamic vibration absorber consisting of a single mass, coil springs and oil damper on the resonance freauency ratio and amplitude ratio for damped linear systems, that is, primary vibration system with damping. The effects of the dynamic vibration absorber are investigated numerically and experimentally for values of mass ratio, natural frequency ratio, and damping ratio. The experimental results show good agreement with calculated ones. As a result, the characteristics shown by the present work are useful in optimal tuning the dynamic vibration absorber in practice.

• Electrical & Electronic Materials
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• v.9 no.1
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• pp.24-29
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• 1996

A composite piezoelectric ceramic transducer is fabricated with three piezoelectric ceramic disk vibrators and two sheets of thin insulator. Its equivalent circuit is derived from the Mason's model of a thickness-driven piezoelectric vibrator. When the electric input near its fundamental resonance frequency is applied to the center vibrator and the output voltages across the left and the right vibrators are connected in series to the resistor loads, the load characteristics at resonance frequencies under the various resistor loads and the frequency characteristics near the resonance frequency without load are investigated. Furthermore, symbolic expressions for input impedances, voltage ratios, resonance frequencies, and bandwidths are derived. The data calculated from those symbolic expressions are agreed well with the measurement data.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.81-87
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• 2011

The characteristics of vertical to horizontal ratio of response spectrum from 20 recent earthquakes were analysed. Response spectrum of 260 horizontal and 130 vertical ground motions were normalized by peak ground acceleration at each resonance frequency from 0.1 to 50Hz. It has been identified that the ratio of vertical to horizontal response spectrum has strong dependancy on epicentral distance and resonance frequency. The ratio of vertical to horizontal response spectrum for the 0-50km epicentral distance group are larger than 2/3 values, which is a standard engineering rule-of-thumb V/H=2/3, at resonance frequency above 7-8Hz. All the 3 groups such as 50-100, 100-150- and 150-200km epicentral distance have shown larger values of vertical to horizontal ratio than 2/3 at resonance frequency above 15Hz and also are larger than 2/3 at resonance frequency below 8-10Hz. Even though there are differences in specific resonance frequency values which depend on the epicentral distance group, we should be careful of seismic design of vertical component of the structures winch are located within the range of about 200km distance. form the potentially seismic causative faults.

• Wind and Structures
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• v.38 no.1
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• pp.59-74
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• 2024

Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios f_e / f_o = 0.8-1.2 (f_e : oscillation frequency; f_o : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes A_h/D = 0.05 - 0.3. The individual influences of f_e / f_o and A_h/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C₁ and displacement-proportional component C₂ of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C₁ and C₂ on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• 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.

• Journal of the Korean Wood Science and Technology
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• v.39 no.5
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• pp.398-405
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• 2011

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for woodceramics made by different phenol resin impregnation ratios (40, 50, 60, 70%) for Broussonetia Kazinoki Sieb. Dynamic modulus of elasticity increased with increasing resin impregnation ratios. There was a close relationship between dynamic modulus of elasticity and static bending modulus of elasticity and between dynamic modulus of elasticity and MOR and between static bending modulus of elasticity and MOR. Therefore, the dynamic modulus of elasticity using resonance frequency mode is useful as a nondestructive evaluation method for predicting the MOR of woodceramics made by different impregnation ratios.