About

John Fahnline is an Assistant Research Professor affiliated with the Applied Research Laboratory and the Acoustics Center for Acoustics and Vibration at Penn State University. His research interests include numerical computations of fluid-structure interaction problems, boundary and finite element analysis, design optimization, and experimental modal analysis. He is involved in advancing the understanding and application of acoustics through computational and experimental methods, contributing to the interdisciplinary graduate program in acoustics at Penn State, which offers degrees such as the Master of Engineering in Acoustics, Master of Science in Acoustics, and Doctor of Philosophy in Acoustics.

Research topics

• Computer Science
• Acoustics
• Mechanics
• Algorithm
• Mathematical analysis
• Physics
• Optics
• Mathematics

Selected publications

• Improved accuracy for radiation damping in coupled finite element/equivalent source computations

  The Journal of the Acoustical Society of America · 2021 · 1 citations

  1st authorCorresponding
  • Computer Science
  • Acoustics
  • Mathematical analysis

  In coupled structural-acoustic computations, radiation damping is due to the resistive component of the surface pressure created by structural vibrations. Equivalent sources using tripole sources as basis functions can be used to compute the surface pressure forces for exterior radiation problems. This technique is similar to the Burton and Miller method for eliminating numerical difficulties due to interior acoustic resonances in boundary element computations and has been proven to yield unique solutions. However, numerical computations presented here will show that for the specific equivalent source formulation under investigation, tripole sources overpredict the resistive component of the surface impedance, especially in the mid-to-high frequency range. It will also be shown that for frequency domain calculations, an accurate representation for the resistive component of the pressure forces can be derived from an analytical representation for the source radiation resistance. Unfortunately, this technique is not applicable to time domain computations. It is also shown that more accurate results can be obtained by allowing both the simple and dipole source amplitudes to be independent variables and enforcing boundary conditions in both the exterior and interior directions simultaneously to reduce the magnitude of the interior acoustic field.

  PublisherDOI

• Efficient, wide-band rigid-body and elastic scattering computations using transient equivalent sources

  The Journal of the Acoustical Society of America · 2019-09-01 · 2 citations

  articleOpen access1st authorCorresponding

  A previous paper by the author has shown that transient structural-acoustic problems can be solved using time stepping procedures with the structure and fluid modeled using finite elements and equivalent sources, respectively. Here, the analysis is extended to included scattering problems. Although scattering problems have been discussed extensively in the literature, the current formulation is unique because the acoustic coupling matrix is treated as sparse. Also, most of the previous analyses have assumed the problem is time harmonic, and there is an advantage to performing the computations in the time domain because only a limited number of time steps are required to obtain wideband frequency resolution. This is especially true if the main emphasis is on the mid- to high-frequencies since the ringing response is typically dominated by the lowest frequency modes. Several examples are solved to validate the computations and to document the computation times and solution accuracy.

  PublisherOA PDFDOI

• Efficient, wide-band coupled structural-acoustic computations combining time and frequency domain finite elements/equivalent sources

  The Journal of the Acoustical Society of America · 2019-10-01

  article1st authorCorresponding

  Time and frequency domain computations are complementary, and here, the overall goal is to combine them to generate wide-band solutions of coupled structural-acoustic problems. Modal frequency response computations are efficient for low frequencies but become inefficient as the number of basis functions required to represent the response grows large. Modal formulations are required for large problems because the coupled equation system becomes densely populated when acoustic pressure forces are included. In contrast, the equation system remains sparsely populated in time domain formulations when the time step size is chosen appropriately, allowing large problems to be solved efficiently in terms of nodal degrees-of-freedom. However, the analysis times depend linearly on the number of time steps and a large number are generally required to represent the ringing response of low frequency modes. Here, the number of time steps is limited by applying an exponential taper to the time domain solution and truncating the computations. This reduces leakage effects, but does not affect components of response that have damped out before it is applied. Examples are given to illustrate the computations and the tradeoff between number of basis functions in the modal frequency response computations and number of time steps in the transient analyses.

  PublisherDOI

• Efficient, wide-band rigid-body and elastic scattering computations using transient equivalent sources

  The Journal of the Acoustical Society of America · 2018-03-01

  article1st authorCorresponding

  Previous analyses by the author have shown that transient structural-acoustic problems can be solved using time stepping procedures with the structure and fluid modeled using finite elements and equivalent sources, respectively. Here, the analysis is extended to include scattering problems. Although scattering problems have been discussed extensively in the literature, the current formulation is unique because it approximates the acoustic coupling matrix as sparse. Also, most of the previous analyses have assumed the problem is time harmonic, and there is an advantage to performing the computations in the time domain because only a limited number of time steps are required to obtain wideband frequency resolution. This is especially true if the main emphasis is on the mid- to high-frequencies since the ringing response is typically dominated by the lowest frequency modes. Several examples are solved to validate the computations and to document the computation times and solution accuracy.

  PublisherDOI

• Low Wavenumber Models for Turbulent Boundary Layer Excitation of Structures

  2018-05-25 · 3 citations

  book-chapterSenior author
  PublisherDOI

• Computing head related impulse responses and transfer functions using time domain equivalent sources

  The Journal of the Acoustical Society of America · 2017-05-01

  article1st authorCorresponding

  In the past, head-related impulse responses (HRIR) and head-related transfer functions (HRTF) have primarily been computed using frequency domain boundary element methods or finite-difference time domain methods. The possibility of computing HRIRs and HRTFs using transient equivalent sources is examined using a lumped parameter technique for enforcing the specified boundary condition. It is demonstrated that performing the computations in the time domain is advantageous because only a few thousand time steps are need to fully define the HRIRs and nonuniform meshes can be used to reduce the number of acoustic variables drastically without significantly degrading the solution accuracy. It is also shown that the computations adapt well to parallel processing environments and the times associated with the equivalent source calculations are proportional to the number of processors.

  PublisherDOI

• Applying time domain equivalent sources to the computation of head related impulse responses and transfer functions

  Proceedings of meetings on acoustics · 2017-01-01 · 1 citations

  articleOpen access1st authorCorresponding

  Head-related impulse responses (HRIRs) and transfer functions (HRTFs) have primarily been computed using frequency-domain boundary element methods or finite-difference time domain methods. The possibility of computing HRIRs and HRTFs using transient equivalent sources is examined here using a lumped parameter technique for enforcing the specified boundary condition. The computation is performed as a scattering problem with rigid boundary conditions specified for the surface of the head and torso. It is shown that performing the computations in the time domain is advantageous because only a few thousand time steps are needed to fully define the HRIRs. In addition to uniform meshes sized for different upper frequencies, the possibility of performing the computations using a nonuniform mesh is also explored. Comparisons between direct and reciprocal computations are given to demonstrate solution consistency. Various tests are performed to illustrate the variation in the solution with time step size and inner ear receiver position. The numerical results show that the various meshes produce consistent solutions except with some discrepancies in predicting HRTF minimums. It is also shown that the computations adapt well to parallel processing environments and the times associated with computing the matrices and convolution summations are proportional to the number of processors.

  PublisherOA PDFDOI

• Modal forcing functions for structural vibration from turbulent boundary layer flow

  Journal of Sound and Vibration · 2017-02-13 · 19 citations

  articleOpen access
  PublisherOA PDFDOI

• Transient finite element/equivalent sources using direct coupling and treating the acoustic coupling matrix as sparse

  The Journal of the Acoustical Society of America · 2017-08-01 · 3 citations

  article1st authorCorresponding

  Transient structural-acoustic problems can be solved using time stepping procedures with the structure and fluid modeled using finite elements and equivalent sources, respectively. Limitations on the time step size for stable solutions have led to the current popularity of iterative coupling to enforce the boundary conditions at the fluid-structure interface, which also helps to alleviate difficulties caused by the fully populated acoustic coupling matrix. The research presented here examines a monolithic approach using a stabilized equivalent source formulation where the acoustic coupling matrix is either fully diagonal or treated as sparse. In theory, the matrix should be sparse because it relates nodal velocities to nodal acoustic pressure forces during a single time step, and the pressure waves can only travel a distance equal to the sound speed multiplied by the time step. The numerical results demonstrate that for the chosen example problems accurate results are obtained for either diagonal coupling matrices or with a large percentage of the terms set to zero. It is also demonstrated that the formulation adapts well to parallel processing environments and that the times associated with the equivalent source computations are proportional to the number of processors.

  PublisherDOI

• Solving transient acoustic boundary value problems with equivalent sources using a lumped parameter approach

  The Journal of the Acoustical Society of America · 2016-12-01 · 4 citations

  article1st authorCorresponding

  An equivalent source method is developed for solving transient acoustic boundary value problems. The method assumes the boundary surface is discretized in terms of triangular or quadrilateral elements and that the solution is represented using the acoustic fields of discrete sources placed at the element centers. Also, the boundary condition is assumed to be specified for the normal component of the surface velocity as a function of time, and the source amplitudes are determined to match the known elemental volume velocity vector at a series of discrete time steps. Equations are given for marching-on-in-time schemes to solve for the source amplitudes at each time step for simple, dipole, and tripole source formulations. Several example problems are solved to illustrate the results and to validate the formulations, including problems with closed boundary surfaces where long-time numerical instabilities typically occur. A simple relationship between the simple and dipole source amplitudes in the tripole source formulation is derived so that the source radiates primarily in the direction of the outward surface normal. The tripole source formulation is shown to eliminate interior acoustic resonances and long-time numerical instabilities.

  PublisherDOI

Frequent coauthors

• Gary H. Koopmann

  Pennsylvania State University

  38 shared

• Stephen A. Hambric

  HEAD Acoustics (Germany)

  27 shared

• Stephen C. Conlon

  Applied Research Laboratory at Penn State

  21 shared

• Micah R. Shepherd

  Brigham Young University

  10 shared

• Steven Hambric

  Applied Research (United States)

  9 shared

• Robert L. Campbell

  University of Strathclyde

  8 shared

• Dean E. Capone

  Pennsylvania State University

  7 shared

• Benjamin J. Doty

  University of Kentucky

  7 shared