• Journal of the Korean Society for Railway
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• v.18 no.4
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• pp.289-300
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• 2015

An important source of noise from railways is rolling noise caused by wheel and rail vibrations induced by acoustic roughness at the wheel-rail contact. In conventional approaches to predicting rail noise, the rail is regarded as placed in a free space so that the reflection from the ground is not included. However, in order to predict rail noise close to the rail, the effect of the ground should be contained in the analysis. In this study the rail noise reflected from the ground is investigated using the wavenumber domain finite element and boundary element methods. First, two rail models, one using rail attached to the rigid ground and one using rail located above rigid ground, are considered and examined to determine the rigid ground effect in terms of the radiation efficiency. From this analysis, it was found that the two models give considerably different results, so that the distance between the rail and the ground is an important factor. Second, an impedance condition was set for the ground and the effect of the ground impedance on the rail noise was evaluated for the two rail models.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.54-60
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• 2003

The characteristics of radiation impedance for piston source on a spherical baffle are analyzed by algorithms which consists of Finite Element Method (FEM) and Hybrid type Infinite Element Method (HIEM). The results of self-radiation impedance for radiation angle and mutual radiation impedance between piston sources coincided with other reports on the spherical rigid baffle. For the spherical non-rigid baffles, the variations of self-radiation impedance and mutual-radiation impedance are identified. Therefore, these results can be applied to design and radiation characteristics analysis of acoustic transducers.

• The Journal of the Acoustical Society of Korea
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• v.21 no.1
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• pp.73-81
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• 2002

The transmission of vibration energy through beam-plate junctions in vibration intensity analysis called power new analysis (PFA) has been studied. PFA is an analytic tool for the prediction of frequency averaged vibration response of built-up structures at medium to high frequency ranges. The power transmission and reflection coefficients between the semi-infinite beam and plate are estimated using the wave transmission approach. For the application of the power coefficients to practical complex structures, the numerical methods, such as finite element method are needed to be adapted to the power flow governing equation. To solve the discontinuity of energy density at the joint, joint matrix is developed using energy flow coupling relationships at the beam-plate joint. Using the joint matrix developed in this paper, an idealized ship stem part is modeled with finite element program, and vibration energy density and intensity are calculated.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.12-18
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• 1995

Capactive miro pressure sensor is simulated with finite element methods to analyze the effect of geometrical variation on its performace. Sensor material is th silicon single crystal. The sensor consists of a disk type diaphragm and several bridges connected to a rigid frame. Structural variables in consideration are the thickness of the diaphragm and the bridges, radius of the circular plate, and the number of bridges. Results of static, dynamic and sensitivity analyses reveal the best structure of the sensor among the fifteen cases under investigation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.23-27
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• 1991

각종 홀 (음악홀, 극장, 사무실건물)의 공조 덕트계에는 미로형소음챔버가 설 치되는 경우가 많다. 이러한 소음장치를 건물내부에 설치하는 경우에는 건물 설계단계에서부터 소음챔버로 인한 감음양(투과손실 : Transmission Loss)의 예측계산이 중요하다. 그렇지만, 일반적인 소음장치는 그 형상이나 내표면의 흡음조건이 아주 복잡하기 때문에, 현단계에서는 간단한 이론만으로 투과손 실예측이 거의 불가능하다. 지금까지 이 문제에 대해서 유한요소법(Finite Element Method : FEM)을 이용해 검토한 예가 종종 소개되었으나, 대부분 소음챔버의 입구와 출구에서의 임의의 점에 대한 음압비를 투과손실로서 구 하고 있다. 그러나, 소음기자체의 실질적인 투과손실특성을 알기 위해서는 소음기의 입력 파워에 대한 출력파워의 비로서 구하지 않으면 안된다. 따라 서, 본 연구에서는 유한요소법에 의한 복소음향인텐시티(Complex sound intensity)의 수치계산법을 각종소음기 (팽창형, 미로형)의 투과손실해석에 적 용하기 위하여 이론적인 면에서 고찰했으며, 프로그램도 개발하여 모델해석 에 적용하였다. 또한, 위에서 언급된 수치해석법의 타당성의 검증을 위하여, 측정에 의한 투과손실예측방법으로서 크로스스펙트럼(Cross Spectrum)법에 의한 음향인텐시티계측법의 이용에 대해서 이론적으로 고찰했으며, 그 이론 을 기초로 한 축척 모형실험을 병행하였다.

• The Journal of the Acoustical Society of Korea
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• v.19 no.4
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• pp.107-114
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• 2000

This work is aimed to develop a new type of the Push-Pull ultrasonic transducer that can provide higher sound pressure level and simpler internal structure than conventional types. The driving part of the newly designed transducer is positioned in the middle of the cylinder, and its optimum geometry is determined by using the FEM package, ANSYS. Through FEM model analysis, the effects of all of its geometrical variables such as transducer length, transducer radius, and the edge shape of the end cap have been examined, and the results have led to the optimum geometry. The newly designed transducer has been found to give better performance than that of traditional ones.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.365-371
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• 2008

In this study, beat control method using an equivalent ring model is proposed to control beat period of a slightly asymmetric ring. Slight asymmetry in a ring generates mode pair and the interaction of the mode pair makes beat in vibration and sound. In a ring, as a simplified bell type structure, mode data are measured and an equivalent ring is determined so that the measured mode condition is satisfied. By the finite element analysis on the equivalent ring, changes of mode pair condition are predicted when local mass is attached or the local thickness is decreased. The predicted results are compared with the experimental result and the validity of the proposed method is verified.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.184-189
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• 1995

자동차 흡배기계의 음향성능 해석에 일반적으로 사용되고 있는 방법은 평면과 이론에 의한 1차원적인 해석방법이다. 그러나 관심 주파수 대역이 높거나 대상물의 형상이 복잡한 경우, 또는 내부에 흡음재가 부착되어 있는 경우에는 이러한 1차원 해석으로는 만족할만한 결과를 얻을 수 없으므로 경계요소법(BEM), 유한요소법(FEM) 등과 같은 수치해석 방법이 이용되고 있다. 본 연구에서는 축대칭 단순팽창형, 연장관형, 다공형등 반사형 소음기와 흡음형 소음기의 음향성능을 해석하기 위한 경계요소법 프로그램을 개발하고, 소음기 성능의 주파수 특성을 구하여 실험결과 및 1차원 해석 결과와 비교 고찰하였다.

• The Journal of the Acoustical Society of Korea
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• v.30 no.6
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• pp.344-352
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• 2011

In this paper, the resonant characteristic of a Tonpilz transducer with a fixed tail mass has been studied by means of an equivalent circuit approach. An equivalent circuit has been designed to describe the characteristic of a Tonpilz transducer that has an additional resonance because of its fixed tail mass. The transmitting voltage response of the transducer calculated by the designed circuit has been compared with that by the FEA (finite element analysis) to confirm the validity of the circuit. This equivalent circuit approach produces identical results with the FEA, in which the variation of resonant frequencies and TVR has been clearly figured out in relation to the stiffness of the mounting fixture and the mass of the tail mass. The suggested equivalent circuit can be utilized to figure out the characteristics of the Tonpilz transducer more efficiently than FEA that requires much calculation time and revision of the models in accordance with the variation of design variables.

• The Journal of the Acoustical Society of Korea
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• v.12 no.2
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• pp.28-36
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• 1993

임의의 형상을 갖는 진동체에 의한 방사 음장해석은 경계요소법에 의하여 이미 많은 해석이 시도되었다. 그러나, 진동체의 형상이 매우 복잡한 경우에는 겉표면의 요소수가 크게 증가할 뿐만 아니라 각 요소에서의 경계조건을 모두 알아내어야 하므로, 저주파에 국한된 해석일지라도 엄청난 시간과 노력이 필요하게 된다. 이러한 어려움을 극복하기 위하여 경계요소법을 사용하되, 복잡한 형상의 진동체를 둘러싸는 가상적인 표면을 매우 간단하게 설정한 후 그 표면상의 경계조건인 음압을 측정한다. 임의의 형상에 대한 파수 영역에서의 감쇠파의여파작업을 위하여 특이값 분리를 사용하였다. 특이값 분리에 의하여 음압분포를 측정위치에서 설정된 일반 좌표계에서의 고유모드로 분해한다. 각 고유모드의 원거리 음장의 기여도에 해당하는 각 특이벡터에 대한 특이값의 크기를 비교하여, 유한개의 고유모드만을 포함시킴으로써 원거리 음장을 예측한다. 몇 개의 예제를 통하여 해석적 방법의 기존의 경계요소법에 의한 결과를 본 연구 방법의 결과와 비교하여 잘 일치함을 확인하였다.