• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.5-8
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• 2000

This paper proposes GaN film as a piezoelectric material for SAW(surface acoustic wave) filters. The fabricated GaN SAW filter exhibited a very high velocity of 5800 ㎧and relatively low insertion loss of -9.9 dB without matching circuit. From Smith's equivalent circuit model, the calculated electromechanical coupling factor (K$^2$) was about 4.$\pm$03％. which is larger than those obtained from other thin film piezoelectric materials and allows the realization of wider filter fractional bandwidths.

• Steel and Composite Structures
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• 제21권2호
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• pp.249-266
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• 2016

The interest of this article lies in the proposition of using bionic method to develop a new sound absorber and analyze the efficient of this absorber in a ski cabin. Inspired by the coupling absorption structure of the skin and feather of a typical silent flying bird - owl, a bionic coupling multi-layer structure model is developed, which is composed of a micro-silt plate, porous fibrous material and a flexible micro-perforated membrane backed with airspace. The finite element simulation method with ACTRAN is applied to calculate the acoustic performance of the multi-layer absorber, the vibration modal of the ski cabin and the sound pressure level (SPL) near the skier's ears before and after pasting the absorber at the flour carpet and seats in the cabin. As expected, the SPL near the ears was significantly reduced after adding sound-absorbing material. Among them, the model 2 and model 5 showed the best sound absorption efficiency and the SPL almost reduced 5 dB. Moreover, it was most effctive for the SPL reduction with full admittance configuration at both the carpet and the seats, and the carpet contribution seems to be predominant.

• Coupled systems mechanics
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• 제7권6호
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• pp.649-668
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• 2018

In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy's law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot's porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.

• 해양환경안전학회지
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• 제26권7호
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• pp.915-921
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• 2020

연소실 내 공조현상으로 인해 발생되는 열음향 불안정성은 안정적인 연소시스템을 구현하기 위해 해결해야 하는 고질적인 문제로 제기되어 왔다. 열음향 불안정성은 크게 1차 2차 열음향 불안정성으로 나뉘며, 본 연구에서는 열음향 불안정성 중 2차 열음향 불안정성의 천이에 관해 열손실이 미치는 영향에 대한 실험적 연구를 진행하였다. 2차 열음향 불안정성을 발생시키기 위해 한쪽 끝이 열린 1/4 파장 공명기를 채택하여 수직으로 설치하였고, 공명기 내부에는 예혼합 가스를 주입하였다. 또한 공명기 상단으로 발생하는 열손실 효과를 비교하기 위해 추가적으로 외부 동축류 관을 설치하였다. 연료 농후조건의 예혼합 가스만을 채택하여 주입하였기 때문에 동축관에 주입되는 기체에 따라 공명기 상부에 추가적인 확산화염이 형성될 수 있다. 그 결과 확산화염이 발생되었을 경우 공명기 상단으로의 열손실이 감소하며 2차 열음향 불안정성이 발현되었으며, 확산화염이 억제되어 공명기 상단으로의 열손실이 증가하였을 경우 2차 열음향 불안정성의 발현이 억제되는 결과를 도출하였다.

• Coupled systems mechanics
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• 제7권3호
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• pp.297-319
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• 2018

In this paper, the vibro-acoustic behaviors of vibrational cylindrical shells are investigated by using structural intensity approach. The reducing interior noise method for vibrating cylindrical shells is proposed by altering and redistributing the structural intensity through changing the damping property of the structure. The concept of proposed novel method is based on the properties of structural intensity distribution on cylindrical shells under different load and damping conditions, which can reflects power flow in the structures. In the study, the modal formulas of structural intensity are developed for the steady state vibration of cylindrical shell structures. The detailed formulas of structural intensity are derived by substituting modal quantities, in which the effect of main parameters such as weight coefficients and distribution functions on structure intensity are analyzed and discussed. Numerical simulations are first carried out based on the structural intensity analytical solutions of modal formulas. Through simulating the coupling vibration and acoustical radiation problems of cylindrical shell, the relationship between vibro-acoustic and structural intensity distribution is derived. We find that for cylindrical shell, by properly arranging damping conditions, the structural intensity can be efficiently changed and further the noise property can be improved. The proposed methodology has important implications and potential applications in the vibration and noise control of fuselage structure.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.756-762
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• 2012

A method of the low-frequency noise reduction in an enclosure by using an array of Helmholtz resonator is presented. An integral form of equation, which represents the acoustical coupling between the internal sound field and the resonator array, is formulated so that the boundary element method can be applied to solve the coupling problem. It is shown that the resonator array on the surface of the enclosure can be regarded as impedance patches on the boundary element. Experiments on a simple enclosure acoustically coupled with an array of resonators are conducted to verify the method. The predicted noise reduction by the boundary element method shows good agreement with the measured one. The effects of the resistance of resonators as well as the number of resonators on the noise reduction are demonstrated. As a practical example, the presented method is applied to the payload fairing of a space launcher with resonator arrays. It is demonstrated that the resistance of resonators affects significantly the required number of resonators to achieve a desired noise reduction.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.51-55
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• 2007

In this paper Statistical Energy Analysis has been considered to predict high frequency air borne interior noise. Dash panel Insulation is major part to reduce engine excitation noise. Transmission loss and absorption coefficient are considered to predict dash insulation performance. Transmission lose is derived from coupling loss factor and absorption coefficient is derived from internal damping loss factor. Material Biot properties were used to calculate each loss factors. Insulation geometry thickness distribution was hard to measure, so FeGate software was used to calculate thickness map from CAD drawing. Each predicted transmission losses between conventional insulation and light weight insulation were compared with SEA. Transmission loss measurement was performed to validate each prediction result, and it showed good correlation between prediction and measurement. Finally interior noise prediction was performed and result showed light weight insulation system can reduce 40% weight to keep similar performance with conventional insulation system, even though light weigh insulation system has lower sound transmission loss and higher absorption coefficient than conventional system.

• Journal of Astronomy and Space Sciences
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• 제26권3호
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• pp.287-294
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• 2009

In helioseismology it is normally assumed that p-mode oscillations are excited in a statistically independent fashion. Unfortunately, however, this issue is not clearly settled down in that two experiments exist, which apparently look in discrepancy. That is, Appourchaux et al. (2000) looked at bin-to-bin correlation and found no evidence that the assumption is invalid. On the other hand, Roth (2001) reported that p-mode pairs with nearby frequencies tend to be anti-correlated, possibly by a mode-coupling effect. This work is motivated by an idea that one may test if there exists an excess of anticorrelated power variations of pairs of solar p-modes. We have analyzed a 72-day MDI spherical-harmonic time series to examine temporal variations of p-mode power and their correlation. The power variation is computed by a running-window method after the previous study by Roth (2001), and then distribution function of power correlation between mode pairs is produced. We have confirmed Roth's result that there is an excess of anti-correlated p-mode pairs with nearby frequencies. On the other hand, the amount of excess was somewhat smaller than the previous study. Moreover, the distribution function does not exhibit significant change when we paired modes with non-nearby frequencies, implying that the excess is not due to mode coupling. We conclude that the origin of this excess of anticorrelations may not be a solar physical process, by pointing out the possibility of statistical bias playing the central role in producing the excess.

• International Journal of Automotive Technology
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• 제4권1호
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• pp.21-30
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• 2003

In this paper a systematic test procedure for evaluation of road-induced noise of a vehicle and guidelines for each test are presented. Also, a practical application of the test procedure to a small SUV is presented. According to the test procedure, all the tests were performed to evaluate road-induced booming noise that is in low frequency range. First of all the information on characteristics of road-induced noise was obtained through baseline test. Coupling effects between body structure and acoustic cavity of a compartment were obtained by means of modal tests for a structure and an acoustic cavity. Local stiffness of joint areas between chassis system and car-body was determined by test for measurement of input point inertance. Noise sensitivities of body joints to operational forces were obtained through test for measurement of noise transfer functions. Operational deflection shapes made us analyze behaviors of chassis system under running condition and then find sources of noise due to resonance of the chassis system. Finally, Principal Component Analysis and Transfer Path Analysis were utilized to investigate main paths of road-induced noise. In order to evaluate road-induced booming noise exactly, all of tests mentioned above should be performed systematically.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1991년도 추계학술대회 논문집
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• pp.68-72
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• 1991

In this study, to improve temperature stability 0.05 Pb(Sn$\_$$\frac{1}{2}$/Sb$\_$$\frac{1}{2}$/O$_3$ - 0.35PbTiO$_3$ - 0.60PbZrO$_3$ + 0.4[wt%]MnO$_2$ piezoelctric oeramics of low dielectric constant and large mechanical quality factor were manufactured with the addition of Cr$_2$O$_3$by Hot Press method. And the SAW delay line was fabricated and the propagation characteristics of SAW was investigated, and the SAW filter was fabricated on C4 added by 0.2[wt%] Cr$_2$O$_3$and its frequency characteristics was investigated. The specimen, whose propagation characteristics of surface acoustic wave were the best, was C4 added by 0.2[wt%] Cr$_2$O$_3$, and its electromechanical coupling factor(ks$^2$) was 3.11[%] and its temperature coefficient of the center frequency (C$\_$fo/) was -21.27[ppm/$^{\circ}C$]. The 31[MHz] SAW IF filter of C4 scarcely had diffraction phenomena and its group delay time was 1.4673 ${\pm}$40[ns] in the pass band, and the insertion loss was -24.419[dB] on no impedance matching.