• 대한조선학회논문집
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• 제49권5호
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• pp.384-390
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• 2012

Power Flow Analysis (PFA) is introduced for solving the noise and vibration analysis of structures in medium-to-high frequency ranges. The vibration analysis software, $PFADS_{C{+}{+}}$ R4 based on Power Flow Finite Element Method (PFFEM) and the noise prediction software, $NASPFA_{C{+}{+}}$ R1 based on Power Flow Boundary Element Method (PFBEM) are developed. In this paper, the coupling equation which represents relation between structural energy and acoustic energy is developed for vibro-acoustic coupling analysis. And vibro-acoustic coupling analysis software based on PFA and coupling equation is developed. Developed software is composed of translator, cavity-finder, solver and post-processor over all. Translator can translate FE model into PFADS FE model and cavity-finder can automatically make NASPFA BE model from PFADS FE model for noise analysis. The solver module calculates the structural energy density, intensity of structures, the fictitious source on the boundary and the acoustic energy density at the field in acoustic cavities. Some applications of vibro-acoustic coupling analysis software to various structures and cruise ship are shown with reliable results.

• 한국추진공학회지
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• 제19권1호
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• pp.42-49
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• 2015

3차원 Large Eddy Simulation(LES)와 Proper Orthogonal Decomposition(POD) 기법을 이용하여 고체로켓의 인히비터에서 발생하는 연소실내 압력 진동 특성을 분석하였다. 인히비터 후방에서 발생한 와류는 Flow-acoustic coupling에 의해 주기적으로 반복하여 생성, 소멸이 이루어지는 것을 확인하였고, 이 와류가 내삽 노즐 입구 도출부에 충돌하면서 유동이 불균질하게 분해되고, 후방 돔으로 유입된 유동에 의한 압력 진동은 연소실 압력 진동 가진의 원인이 된다. 또한 인히비터에서 발생하는 와흘림(vortex shedding) 주기는 연소실내 와류 발생 주기와 일치하며, 실험에서 측정된 압력 진동 주파수와 비교 분석하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.253-257
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• 2011

고체로켓에서 발생하는 vortex shedding 현상 중 인히비터로 인해 발생하는 연소실내 와류(vortex)의 특성을 조사하기 위해 Large Eddy Simulation을 수행하였다. 해석의 결과는 기존 연구자들의 결과와 잘 일치하며 정략적 및 정성적 분석을 수행하였다. 인히비터 후방에서 발생하는 vortex는 Flow-acoustic coupling 에 의해 주기적으로 반복되며 생성, 소멸이 이루어지는 것을 확인 할 수 있었으며, 발생 주기는 연소실내 mode 2의 주파수와 일치하는 것을 확인하였다. 3차원 해석결과 인히비터 후방에서 Roll 발생은 비균일한 노즐 유동을 발생시킨다.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.423-439
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• 2006

This paper proposes a hybrid analytic method for the prediction of vibrational and acoustic responses of reverberant system in the medium-to-high frequency ranges by using the PFA(Power Flow Analysis) algorithm and SEA(Statistical Energy Analysis) coupling concepts. The main part of this method is the application of the coupling loss factor(CLF) of SEA to the boundary condition of PFA in reverberant system. The hybrid method developed shows much more promising results than the conventional SEA and equivalent results to the classical PFA for various damping loss factors in a wide range of frequencies. Additionally, this paper presents applied results of hybrid power flow finite element method(hybrid PFFEM) by formulating the new joint element matrix with CLF to analyze the vibrational responses of built-up structures. Finally, the analytic results of coupled plate structures and an automobile-shaped structure using hybrid PFFEM were predicted successively.

• The Journal of the Acoustical Society of Korea
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• 제19권1E호
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• pp.27-37
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• 2000

This paper presents a simplified analytical formulation for computing acoustic power radiation from a rectangular plate exposed to random forces such as turbulent boundary layer pressure fluctuations and arbitrary mechanical force in a subsonic flow field. The expression for the acoustic power is derived using modal expansion method and light fluid loading is assumed on the plate. In order to simplify the formulation for acoustic power due to combined excitations of mechanical forces and turbulent pressures, it is assumed that the structural damping of the plate is small and excitations are broadband random forces having frequency spectra above the convective coincidence. Under these assumptions, an approximate solution for the broadband acoustic power radiation from a plate excited by both turbulent pressures and arbitrary mechanical forces is obtained and evaluated considering the effect of modal coupling on the radiated acoustic power. An efficient method is also suggested to compute modal acoustic impedance in a moving fluid medium by using averaged Green function.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.83-87
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• 2009

램제트 엔진은 다른 공기흡입식 엔진에 비해 상대적으로 매우 긴 유로를 지니고 있음으로 인해 저주파 연소불안정에 취약한 단점을 지니고 있다. 본 연구에서는 램제트 엔진에서 발생하는 연소 현상과 동일한 메카니즘을 모사할 수 있는 연료분사장치 및 V-gutter 형태의 화염안정화장치를 장착한 소형 연소기를 설계/제작하여, 램제트 연소기에서 발생할 수 있는 연소불안정 현상을 시현하였다. 이 연소기에서 발생한 연소불안정은 연소시스템의 음향학적인 공진 주파수와 유사하게 나타남을 확인하였으며, 이를 통해 thermo-acoustic coupling에 의한 전형적인 연소 불안정이 발생하였음을 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.291-291
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• 2013

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. HMC is interested in the numerical prediction of this aerodynamic noise generated by the car windows with the final objective of improving the products design and reducing this noise. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using the CAA(Computational aeroacoustics) solver CAA++. The second step consists in the computation of the vibro-acoustic transmission through the side window using the finite element vibro-acoustic solver Actran. The internal air cavity including trim component are included in the simulation. In order to validate the numerical process, an experimental set-up has been created based on a generic car shape. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. First, this paper describes the method including the CAA and the vibro-acoustic models, from the boundary conditions to the different components involved, like the windows, the trims and the car cavity is detailed. In a second step, the experimental set-up is described. In the last part, the vibration of the windshield and windows, the total wind noise level results and the relative contributions of the different windows are then presented and compared to measurements. The influence of the flow yaw angle (different wind orientation) is also assessed.

• Advances in nano research
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• 제13권4호
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• pp.341-350
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• 2022

The continuous elements method, also known as the dynamic stiffness method, is effective for solving structural dynamics problems, especially over a large frequency range. Before applying this method to fluid-structure interactions, it is advisable to check its validity for pure acoustics, without considering the different coupling parameters. This paper describes a procedure for taking wave propagation into account in the formulation of a Dynamic Stiffness Matrix. The procedure is presented in the context of the harmonic response of acoustic pressure. This development was validated by comparing the harmonic response calculations performed using the continuous element model with the analytical solution. In addition, this paper illustrates the application of this method to a simple compressible flow problem, since it has been applied solely to structural problems to date.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.797-801
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• 2003

The Statistical Energy Analysis is based on the power flow and the energy conservation between sub-systems, which enable the prediction of acoustic and structural vibration behavior in mid-high frequency ranges. This paper discusses the identification of SEA coupling loss factor parameters from experimental measurements of small reverberation chamber sound pressure levels and structural accelerations. As structural subsystems, steel plates with and without damping treatment are considered. Calculated CLFs were verified by both transmission loss values for air-borne CLF case and running SEA commercial software As a result, CLFs have shown a good agreement with those computed by software. Acoustical behavior of air-borne noise and structure-borne noise has been examined. which shows reasonable results, too.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.81-89
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• 1999

The major source of noise in the process of transporting liquids is related to the cavitation phenomenon. The control valve noise is mostly dominated by bubble dynamics under cavitating conditions. In this investigation, an orifice configuration is set-up to correlate its flow-field and acoustic signatures with those from a control valve device. The performance and noise characteristics form the orifice configuration in anechoic surroundings were measured to reveal the noise sources depending on pressure differences across the orifice configuration. The sound powers from the orifice configuration are effectively normalized using proposed scaling parameters. Flow-excited dynamic systems for which there is no strong coupling between the flow and the system response can be described using a linear source-filter model. On this assumption, the normalized sound powers can be decomposed of noise source function and a response function. To find noise sources, pressure spectra measured over a range of pressure differences are transformed into the product of two non-dimensional frequency function : $P_{ss}(He,f_{ca},x/D) = F(f_{ca})\;G(He,x/D)$. This scheme of finding noise sources is shown to be applicable to the cavitation noise from the control valve effectively Two kinds of cavitating modes based on our experimental data are found and discussed.