Yunfan Hwang - Academia.edu (original) (raw)

Papers by Yunfan Hwang

Research paper thumbnail of Deflection of a plane wave by an oscillating wall and the one-dimensional sound field in a duct with one rigid and one oscillating termination

The Journal of the Acoustical Society of America, 1974

As a part of the Pennsylvania State University research program on the effect of a moving boundar... more As a part of the Pennsylvania State University research program on the effect of a moving boundary on the sound field in reverberation chambers, a theoretical model consisting of a parallelopiped with one wall oscillating at large amplitude has been developed. In this paper, the first part of the study is presented. Equations for the reflection of the plane monochromatic wave (ω0) perpendicularly incidenting on an oscillating wall (Ω) using transformation of the coordinate system in the moving wall were derived. The reflected wave has a line spectrum represented by ∑ n=−∞∝ An exp{− i [(ω0 ± nΩ) − ky]}. The method of calculating An is presented. A further step consists of a study of the sound field in a finite-length duct, with one termination oscillating at large amplitudes and the other reflective.

Research paper thumbnail of Vibrations of infinite plates and the mean value vibrations of finite plates excited by turbulent boundary layer flows

The Journal of the Acoustical Society of America, 2002

The vibration response of a turbulent boundary layer (TBL) excited flat plate is analyzed using a... more The vibration response of a turbulent boundary layer (TBL) excited flat plate is analyzed using a finite-element model and infinite plate theory. For the finite-element models, discretization sufficient to resolve the convective fluctuations in the flow excitation field is used for the study. Clamped boundary conditions are assumed for the finite-element models and analyses are conducted at a variety of flow speeds and structural loss factors. Two equivalent TBL wall pressure excitation models are applied to the plates: (1) a modified Corcos cross-spectrum model for the finite-element models, and (2) a wave-vector-frequency spectrum model (the Fourier transform of the modified Corcos cross spectra) for the infinite plate theory. The TBL wall pressure autospectrum is approximated using the model derived by Smolyakov and Tkachenko. The infinite plate predicts the mean value response of the finite plate very well for all speeds and loss factors considered, showing consistency with Skud...

Research paper thumbnail of The Solberg Award for 1991

Naval Engineers Journal, 1992

Research paper thumbnail of Sound-structure interactions in a Japanese drum

The Journal of the Acoustical Society of America, 2011

Previous studies of the sound-structure interaction of a Japanese drum conducted by the authors w... more Previous studies of the sound-structure interaction of a Japanese drum conducted by the authors were focused on the vibration of and the coupling between the two membranes attached at both ends of an air-filled hollow wood body which was treated as a rigid cylindrical shell. This is satisfactory for the lower modes where sound is produced primarily by the vibration of membranes. At higher frequencies, the vibration of the wood barrel cannot be ignored. In the current study, the wood barrel is modeled by using conical shell elements. Orthotropic conical shell finite-elements, which include the rotary inertia and transverse shear deformation, have been developed and coded in MATLAB. Experimental verification of the computed results and the effect of wood barrel vibrations on the acoustical characteristics of a drum are discussed. [This paper is dedicated to honor Dr. Gideon Maidanik for his monumental contributions in structural acoustics. The authors would like to thank Miyamoto Unosuke Shouten Co., Ltd., for providing the Japanese drum in this study.]

Research paper thumbnail of Air loading effect on the resonance frequencies of a piano soundboard modeled by a rectangular orthotropic plate

Acoustical Science and Technology, 2012

Research paper thumbnail of Coupling between two membranes of a Japanese drum

Acoustical Science and Technology, 2008

Some of drums have two membranes on both sides of a hollow trunk or a barrel. In this type of the... more Some of drums have two membranes on both sides of a hollow trunk or a barrel. In this type of the drum structure, the two membranes interact with each other through the air inside the body. Even if the two membranes have an identical resonance frequency, there exist two resulting resonance frequencies. At the lower resonance, the two membranes vibrate in phase. Since the membranes must move the internal air, the lower resonance is lower than the original resonance frequency (without air loading). At the higher resonance, they vibrate out-of-phase squeezing or expanding the air simultaneously. This resonance is higher than the original resonance since the air works as a spring. In this paper, resonance frequencies and mode shapes of two membranes coupled with each other through the air inside the body are investigated using an analytical model. The membranes are assumed to be ideal (i.e., no stiffness) and the body is assumed to be ideally rigid. Since it is a common practice that the two membranes are slightly (intentionally) miss-tuned, the main interest of this paper is to simulate the effect of this miss-tuning on the resulting resonance frequencies and mode shapes.

Research paper thumbnail of Acoustic Modulation by Time-Harmonic Boundary Motion

Research paper thumbnail of An exploratory study of using external fluid loading on a vibrating tube for measuring suspended sediment concentration in water

Journal of Physics D: Applied Physics, 2008

ABSTRACT This paper presents an exploratory study of using external fluid loading on a vibrating ... more ABSTRACT This paper presents an exploratory study of using external fluid loading on a vibrating tube for measuring the suspended sediment concentration (SSC) in bodies of water such as rivers and reservoirs. This new measuring concept provides an opportunity for an automated on-site monitoring of the conditions in a body of water by taking the fluid sample instantaneously in the area surrounding the vibrating tube. The physical properties of the fluid sample are those of the fluid that naturally flows around the tube, and are more representative of those of the water with SSC to be measured. The theoretical analysis presented in this paper shows that the resonance frequencies of an immersed vibrating tube change significantly with mass density variations that normally occur in bodies of water with suspended sediment. These changes are sensitive enough to have a possible 1% resolution of the measured fluid density. The signal processing issues are discussed, and a schematic of a conceptual measuring setup is proposed. Based on the theoretical analyses and other measurement issues presented in the paper, using the loading by external fluid on a vibrating tube is feasible for measuring the SSC in water bodies.

Research paper thumbnail of Deflection of a plane wave by an oscillating wall and the one-dimensional sound field in a duct with one rigid and one oscillating termination

The Journal of the Acoustical Society of America, 1974

As a part of the Pennsylvania State University research program on the effect of a moving boundar... more As a part of the Pennsylvania State University research program on the effect of a moving boundary on the sound field in reverberation chambers, a theoretical model consisting of a parallelopiped with one wall oscillating at large amplitude has been developed. In this paper, the first part of the study is presented. Equations for the reflection of the plane monochromatic wave (ω0) perpendicularly incidenting on an oscillating wall (Ω) using transformation of the coordinate system in the moving wall were derived. The reflected wave has a line spectrum represented by ∑ n=−∞∝ An exp{− i [(ω0 ± nΩ) − ky]}. The method of calculating An is presented. A further step consists of a study of the sound field in a finite-length duct, with one termination oscillating at large amplitudes and the other reflective.

Research paper thumbnail of Vibrations of infinite plates and the mean value vibrations of finite plates excited by turbulent boundary layer flows

The Journal of the Acoustical Society of America, 2002

The vibration response of a turbulent boundary layer (TBL) excited flat plate is analyzed using a... more The vibration response of a turbulent boundary layer (TBL) excited flat plate is analyzed using a finite-element model and infinite plate theory. For the finite-element models, discretization sufficient to resolve the convective fluctuations in the flow excitation field is used for the study. Clamped boundary conditions are assumed for the finite-element models and analyses are conducted at a variety of flow speeds and structural loss factors. Two equivalent TBL wall pressure excitation models are applied to the plates: (1) a modified Corcos cross-spectrum model for the finite-element models, and (2) a wave-vector-frequency spectrum model (the Fourier transform of the modified Corcos cross spectra) for the infinite plate theory. The TBL wall pressure autospectrum is approximated using the model derived by Smolyakov and Tkachenko. The infinite plate predicts the mean value response of the finite plate very well for all speeds and loss factors considered, showing consistency with Skud...

Research paper thumbnail of The Solberg Award for 1991

Naval Engineers Journal, 1992

Research paper thumbnail of Sound-structure interactions in a Japanese drum

The Journal of the Acoustical Society of America, 2011

Previous studies of the sound-structure interaction of a Japanese drum conducted by the authors w... more Previous studies of the sound-structure interaction of a Japanese drum conducted by the authors were focused on the vibration of and the coupling between the two membranes attached at both ends of an air-filled hollow wood body which was treated as a rigid cylindrical shell. This is satisfactory for the lower modes where sound is produced primarily by the vibration of membranes. At higher frequencies, the vibration of the wood barrel cannot be ignored. In the current study, the wood barrel is modeled by using conical shell elements. Orthotropic conical shell finite-elements, which include the rotary inertia and transverse shear deformation, have been developed and coded in MATLAB. Experimental verification of the computed results and the effect of wood barrel vibrations on the acoustical characteristics of a drum are discussed. [This paper is dedicated to honor Dr. Gideon Maidanik for his monumental contributions in structural acoustics. The authors would like to thank Miyamoto Unosuke Shouten Co., Ltd., for providing the Japanese drum in this study.]

Research paper thumbnail of Air loading effect on the resonance frequencies of a piano soundboard modeled by a rectangular orthotropic plate

Acoustical Science and Technology, 2012

Research paper thumbnail of Coupling between two membranes of a Japanese drum

Acoustical Science and Technology, 2008

Some of drums have two membranes on both sides of a hollow trunk or a barrel. In this type of the... more Some of drums have two membranes on both sides of a hollow trunk or a barrel. In this type of the drum structure, the two membranes interact with each other through the air inside the body. Even if the two membranes have an identical resonance frequency, there exist two resulting resonance frequencies. At the lower resonance, the two membranes vibrate in phase. Since the membranes must move the internal air, the lower resonance is lower than the original resonance frequency (without air loading). At the higher resonance, they vibrate out-of-phase squeezing or expanding the air simultaneously. This resonance is higher than the original resonance since the air works as a spring. In this paper, resonance frequencies and mode shapes of two membranes coupled with each other through the air inside the body are investigated using an analytical model. The membranes are assumed to be ideal (i.e., no stiffness) and the body is assumed to be ideally rigid. Since it is a common practice that the two membranes are slightly (intentionally) miss-tuned, the main interest of this paper is to simulate the effect of this miss-tuning on the resulting resonance frequencies and mode shapes.

Research paper thumbnail of Acoustic Modulation by Time-Harmonic Boundary Motion

Research paper thumbnail of An exploratory study of using external fluid loading on a vibrating tube for measuring suspended sediment concentration in water

Journal of Physics D: Applied Physics, 2008

ABSTRACT This paper presents an exploratory study of using external fluid loading on a vibrating ... more ABSTRACT This paper presents an exploratory study of using external fluid loading on a vibrating tube for measuring the suspended sediment concentration (SSC) in bodies of water such as rivers and reservoirs. This new measuring concept provides an opportunity for an automated on-site monitoring of the conditions in a body of water by taking the fluid sample instantaneously in the area surrounding the vibrating tube. The physical properties of the fluid sample are those of the fluid that naturally flows around the tube, and are more representative of those of the water with SSC to be measured. The theoretical analysis presented in this paper shows that the resonance frequencies of an immersed vibrating tube change significantly with mass density variations that normally occur in bodies of water with suspended sediment. These changes are sensitive enough to have a possible 1% resolution of the measured fluid density. The signal processing issues are discussed, and a schematic of a conceptual measuring setup is proposed. Based on the theoretical analyses and other measurement issues presented in the paper, using the loading by external fluid on a vibrating tube is feasible for measuring the SSC in water bodies.