• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1332-1336
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• 2005

It could make the LIghtweight Piezoelectric Composite Actuator (LIPCA) damageable by the cyclic large deformation. If the progressive microvoid coalescence of LIPCA interlaminar took place, the decrease of the stiffness and the weakness of stress transmission and fiber bridging effect would make the fatigue characteristics worse suddenly. Therefore, it is required to study the variation of fatigue behavior and interlaminar condition in LIPCA under resonant frequencies. These studies such as the changeable fatigue phase and interlaminar behavior of LIPCA affected by the resonant frequencies should be carried out due to the strong anisotropy of CFRP layer. Hence, these studies are as follows. 1) The residual stresses distribution of interlaminar in LIPCA using the Classical Lamination Theory (CLT). 2) Comparative analysis of interlaminar behavior for the intact LIPCA versus LIPCA containing an artificial delamination during resonant frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.5
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• pp.467-472
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• 2004

This paper presents the normalized site attenuation characteristics for frequencies below 80 ㎒ using forced resonant type EMI dipole antennas. The coupled integral equations for unknown current distribution are solved by the Galerkin's method of moments with piecewise sinusoidal functions. The results show that the forced resonant type EMI dipole antenna for frequencies below 80 ㎒ can be used effectively for the measuring normalized site attenuation. The calculated normalized site attenuation curves for the forced resonant type EMI dipole antenna are useful in determining the suitability of open area test sites.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.431-434
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• 2002

In this paper, The resonant frequencies of any modes in the dielectric resonator filter is determined by numberical analysis. The theoretical analysis for the dielectric resonator filter used Ansoft HFSS. We designed the dielectric resonator filter with resonant frequency 4.5 GHz. We describe the characteristics of delivering Power to resonator in different shaped coupling loops. Tile resonant mode of T $E_{01{\delta}}$ and T $E_{01{\delta}}$ could be selected by the horizontal and the vertical coupling loop.p.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.390-396
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• 2000

The dynamic elastic constants of the simulated weld HAZ (heat-affected zone) of SA 508 Class 3 reactor pressure vessel (RPV) steel were investigated by resonant ultrasound spectroscopy (RUS). The resonance frequencies of rectangular parallelepiped samples woe calculated from the initial estimates of elastic stiffness $c_{11},\;c_{12}\;and\;c_{44}$ with an assumption of isotropic property, dimension and density. Through the comparison of calculated resonant frequencies with the measured resonant frequencies by RUS, very accurate elastic constants of SA 508 Class 3 steel were determined by iteration and convergence processes. Clear differences of Youngs modulus and shear modulus were shown from samples with different thermal cycles and microstructures. Youngs modulus and shear modulus of samples with fine-grained bainite were higher than those with coarse-grained tempered martensite. This tendency was confirmed from other results such as micro-hardness test.

• International Journal of Fluid Machinery and Systems
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• v.7 no.4
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• pp.160-173
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• 2014

Surge phenomena in multi-stage axial flow compressors were studied with attention to the frequency behaviors. A new parameter "volume-modified reduced surge frequency" was introduced, which took into consideration the essential surge process, i.e., emptying and filling of the working gas in the delivery plenum. The behaviors of the relative surge frequencies at the stall stagnation boundaries, compared with the corresponding duct resonance frequencies, have demonstrated the existence of two types of surges; i.e., a near-resonant surge and a subharmonic surge. The former, which has fundamentally a near-resonance frequency, occurs predominantly at the stall stagnation boundary for the short -and-fat plenum delivery flow-path and the long-and-narrow delivery duct flow-path, and possibly in the intermediate conditions. The latter, which has a subharmonic frequency of the fundamental near-resonant one and occurs mainly in the intermediate zone, is considered to be caused by the reduced frequency restricted to a limited range. In relation with those dimensionless frequencies at the stall stagnation boundary, the surge frequency behaviors in more general situations away from the boundaries could be estimated, though very roughly.

• Structural Engineering and Mechanics
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• v.74 no.1
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• pp.33-54
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• 2020

The aim of this study is to calculate natural frequencies and harmonic responses of cracked frames with general boundary conditions by using transfer matrix method (TMM). The TMM is a straightforward technique to obtain harmonic responses and natural frequencies of frame structures as the method is based on constructing a relationship between state vectors of two ends of structure by a chain multiplication procedure. A single variable shear deformation theory (SVSDT) is applied, as well as, Timoshenko beam theory (TBT) and Euler-Bernoulli beam theory (EBT) for comparison purposes. Firstly, free vibration analysis of intact and cracked frames are performed for different crack ratios using TMM. The crack is modelled by means of a linear rotational spring that divides frame members into segments. The results are verified by experimental data and finite element method (FEM) solutions. The harmonic response curves that represent resonant and anti-resonant frequencies directly are plotted for various crack lengths. It is seen that the TMM can be used effectively for harmonic response analysis of cracked frames as well as natural frequencies calculation. The results imply that the SVSDT is an efficient alternative for investigation of cracked frame vibrations especially with thick frame members. Moreover, EBT results can easily be obtained by ignoring shear deformation related terms from governing equation of motion of SVSDT.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.5
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• pp.605-615
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• 2017

A multi-resonant broadband acoustic transducer with six Tonpilz elements operating at different resonant frequencies in a transducer assembly was fabricated, tested, and analyzed. A compensated transducer, modified by adding series inductance to the developed multi-resonant broadband transducer, was shown to provide improved bandwidth performance with a relatively more uniform frequency response compared with the uncompensated transducer. By controlling the series inductance, flat frequency response characteristics at two frequency bands were obtained over the range 38-52 kHz with 1.1 mH inductance and 50-60 kHz with 0.4 mH inductance. These results suggest that the operating frequency of the developed multi-resonant broadband transducer in a chirp echo sounder can be shifted to a different frequency band that is optimized according to the environment for more effective echo surveys of fishing grounds.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.726-730
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• 2001

Temperature stabilities of dielectric constraints and resonant frequencies of the substrates are very important in piezoelectric ceramics oscillators and filters. In this study, it was investigated temperature stability of the length-extensional vibration mode of Pb(Zr$\_$y/Ti$\_$1-y/)O$_3$+x[wt%]Cr$_2$O$_3$ ceramics. The mode can be utilized in fabricating ultra-small 455 kHz IF devices. Addition of Cr$_2$O$_3$ in morphotrophic phase PZT decreased the variations of dielectric constant, electro-mechanical coupling factor k$\_$31/ and resonant frequency by thermal shock. As additive weight of Cr$_2$O$_3$increased, the temperature coefficient of resonant frequency changed from positive number to negative one. And the composition tith temperature coefficient of resonant frequency was shifted to the one with increased Cr$_2$O$_3$ additive weigh by thermal aging.

• Structural Engineering and Mechanics
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• v.32 no.6
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• pp.725-740
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• 2009

A new simple relation for the estimation of modal correlation coefficients is presented. It is obtained from the decomposition of covariances of modal responses into background and resonant contributions, as it is commonly done for the variances. Thanks to appropriate assumptions, the modal correlation coefficients are estimated as weighted sums of two limit values, corresponding to the background and resonant responses respectively. The weighting coefficients are expressed as functions of the background-to-resonant ratios, which makes the proposed formulation convenient and easily accessible. The simplicity of the mathematical formulation facilitates the physical interpretation. It is for example proved that modal correlation coefficients can be non negligable even in case of well separated natural frequencies, which is sometimes unclear in the litterature. The new relation is mainly efficient in case of large finite element models. It is applied and validated on a finite element buffeting analysis of the Viaduct of Millau, the highest bridge deck ever built so far.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.4
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• pp.173-178
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• 2003

The rotational force of ultrasonic motors is able to get from the frictional force of elliptical vibration by contact between rotor and stator. Generally, ultrasonic motors are suitable for driving at resonant frequencies of about 20∼80［KHz］. The driving characteristics of ring type ultrasonic motors are the object of this study. A two-phase driving signal is delivered to the tested ultrasonic motor, which has a $90^0$ phase difference respectively with both sine and cosine voltage waveforms. The driving frequency is almost equal to the mechanical resonant frequency for the proper operation, and the driving signal is supplied by the two-phase parallel resonant inverter. The validity of the proposed driving method is verified by experimental results with stable operation.