• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1026-1031
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• 2002

This paper shows the effect of mean flow in duct. The potential equation of duct with mean flow is obtained. A finite element method(FEM) is used to predict acoustic performance of duct with mean flow. The formulation of the finite element method is derived for duct taking into consideration of the convective effect of mean flow. A simple duct, simple expansion chamber and a duct with resonator are implemented to show the effects of the mean flow.

• 한국소음진동공학회논문집
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• 제23권10호
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• pp.909-919
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• 2013

Pneumatic exciters can be good replacements of electrodynamic, piezoelectric and hydraulic exciters owing to simple structure and large exciting force. One problem to be solved is a slow response caused by compressibility of air. Desirable frequency response characteristics of exciter are constant magnitude and zero degree phase, because users want no time delay between input signal and output force. For this reason, frequency range of pneumatic exciters is limited about 0~1 Hz. Therefore, expansion of frequency range is an important issue when designing the pneumatic exciter. In this paper, the pneumatic exciter which has same structure with active pneumatic isolator is dealt with. The dynamic characteristics are presented, and its limitation of expanding frequency range is shown based on analytical studies. Then the pneumatic exciter with dual-chamber is suggested to overcome this problem. Based on simulation study, a design method is presented.

• 한국음향학회지
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• 제21권5호
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• pp.503-509
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• 2002

입력단 및 출력단이 동심을 이루어 원형 확장관 안으로 연장되어 있는 소음기가 관내 전달 소음저감을 위해 널리 사용되고 있다. 이 소음기의 저주파수 영역에서의 소음저감 효과는 음파 진행 단면의 확장-축소와 입력단 및 출력단의 상대적 위치 등으로 발생되는 소음기의 리액티브 성분에 의해 설명이 된다. 본 논문에서는 입력단 및 출력단에 동심으로 배치된 연장관이 단순 팽창형 소음기 내부에 삽입되어 있는 경우에 대한 음향해석을 수행하였다. 해석방법으로는 음장을 분리좌표계로 표현될 수 있는 몇개의 경계 표면으로 나누고, 각 표면에서의 음압 및 입자속도를 정규화 된 음향 고유 모드로 전개하여 간단한 대수식으로 표현하였다. 이 해석적인 방법을 사용하여 소음기의 투과손실을 예측하였으며, 실험과도 잘 일치함을 관찰할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1648-1653
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• 2000

Theoretical analysis of noise reduction by a membrane-duct system is presented. When acoustic waves propagate in the membrane-duct, the part of membrane is also excited and its motion is coupled with interior medium. For an infinite plane membrane-duct system, a simple coupled governing equation is derived and solved. One of the characteristics of dispersion relation is that evanescent waves occur below critical frequency. Attaching damping materials to the membrane may improve the absorption efficiency of acoustic energy. The results show that the membrane-duct system can be applied to diminish and absorb low frequency noise in duct instead of passive muffler, such as simple expansion chamber or absorption material.

• 대한기계학회논문집B
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• 제33권2호
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• pp.79-84
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• 2009

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within a compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation is associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in a turbocharger system. In this study, a expansion muffler with lids is devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler are investigated which are related to the unsteadiness of turbulence and pressure in the turbocharger system. A transfer matrix method is used to analyze the transmission loss of the muffler. A simple expansion muffler with lids is proposed for the reduction of high frequency component noise. Turbulence simulation is carried out by a standard k - ${\varepsilon}$ model. An optimal design condition of the muffler is obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise is achieved at the optimal design of the muffler as compared with the conventional muffler.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1999년도 학술발표대회 논문집 제18권 2호
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• pp.397-400
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• 1999

본 연구에서는 기존의 모드적합법의 단점을 개선하여 각 관에 임의의 모드갯수를 선택할 수 있고, 동심관형 단순확장관의 음향특성뿐만 아니라 입$\cdot$출구가 임의의 위치에 있는 경우에도 모드적합법을 적용할 수 있는 방안을 제시한다. 그리고 제시한 방안으로 프로그램을 작성하여, 각각 임의의 모드와 임의의 입$\cdot$출구의 위치를 가지는 원형 소음기의 4단자 정수를 구하고, 이로부터 임의의 입$\cdot$출구 위치에 따른 소음기의 음향특성을 구하여 유한요소법과 비교하여 제안하는 방법의 유용성을 검증하고 고차모드의 영향을 조사하였다.

• 한국자동차공학회논문집
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• 제3권1호
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• pp.13-19
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• 1995

The objective of this study is do obtain the relationship between the acoustic mode and cavity tone induced in a perforated tube exhaust muffler. First, the modal frequency for the axisymmetric radial mode and the mode shape have been computed using the impedance model for the perforated tube. Then, experiment has been perfonned for the onset frequencies of the cavity tone for various design parameters and through-flow. The theoretically obtained modal frequencies are well consistent with the measured onset frequencies of the cavity tone, showing that the cavity tone is induced by the axisymmetric radial mode. And it is found that the modal frequency of a perforated tube muffler is much lower than that of a simple expansion chamber.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.420-425
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• 2001

Theoretical analysis of noise reduction by a membrane-duct system is presented. When acorn waves propagate in the membrane-duct, the membrane is also excited and its motion is coup with interior medium. It has been shown that propagating waves with supersonic wave speed exist beyond a certain critical frequency that is determined from the mass ratio of the me and the fluid. Also found are subsonic waves which couple strongly wi th the membrane a provide a powerful mechanism of energy dissipation. Existence of an exterior medium alter dispersion characteristics. It provides additional mass loading and reduces the subsort speed further. The effect of mean flow speed on dispersion characteristics is also consider results show that the membrane-duct system can be applied to diminish and absorb 1 frequency noise in duct instead of passive muffler, such as a simple expansion chamber absorption material.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2913-2917
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• 2007

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within the compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation was associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in turbocharger system. In this study, a sharp-edged reactive-type muffler was devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler were investigated which is related to the unsteadiness of turbulence and pressure in turbocharger system. A transfer matrix method was used to analyze the transmission loss of the muffler. Simple expansion muffler with extended tube of the reactive type is proposed for the reduction of high frequency component noise. Turbulence computation was carried out by a standard ${\kappa}-{\varepsilon}$ model. An optimal design condition of the muffler was obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise was achieved at the optimal design of the muffler as compared with the conventional turbocharger system.

• 대한기계학회논문집B
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• 제33권10호
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• pp.778-782
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• 2009

Recently, we developed a simple thermopneumatic micropump having neither a membrane nor a valve. This micropump discharges liquid by a thermopneumatic pressure and refill by a capillary attraction. In case of the micropump driven by the capillary attraction, the flow characteristic depends mainly on the geometry of the micropump. In this paper, we investigated the influence of the geometry of the micropump on the performance of the micropump to illustrate the properness of the micropump shape. We analyzed the micropump characteristics of six types having different geometries by FVM simulation with a commercial CFD tool. Also we fabricated the micropumps with PDMS and glass by micromachining, and tested the performances. The simulation and the test results illustrate that the discharge volume and the discharge time depend on the chamber volume. The expansion angle of the inlet channel location has influence on the refill time, while the front air channel direction has influence on the backward flow loss.