Journal articleWind Energy · February 1, 2020
This study investigates the potential of using tilt-based wake steering to alleviate wake shielding problems experienced by downwind turbines. Numerical simulations of turbine wakes have been conducted using a hybrid free-wake analysis combining vortex lat ...
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Journal articleThe Journal of the Acoustical Society of America · April 2019
Analytical solutions are presented for broadband sound fields in three rectangular enclosures with absorption applied on the floor and ceiling, rigid sidewalls, and a vertically oriented dipole source. The solutions are intended to serve as benchmarks that ...
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Journal articleRenewable Energy · February 1, 2019
A new free-wake analysis for wind turbine aerodynamics is developed to accurately predict turbine performance and downstream wake evolution. A key feature is the Constant Circulation Contour Method (CCCM) which is a novel free-wake model for wind turbine w ...
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Journal articleAIAA Journal · September 1, 2013
Piston theory is an inherently quasi-steady theory, in that higher powers of frequency do not appear, as well as a local theory in that the pressure at a point on the airfoil only depends on the downwash at the same point. In the extension to piston theory ...
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Journal article2008 Proceedings of the Noisecon ASME Ncad Ncad 2008 · October 16, 2009
A theory based on cross-sectional averaging is developed to analyze quasi-one-dimensional acoustic propagation in hybrid ducts with two propagation media in the cross-section. Specifically, ducts lined with a thick layer of porous material are considered. ...
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Journal article2008 Proceedings of the Noisecon ASME Ncad Ncad 2008 · October 16, 2009
Sound transmission through multi-element flexible barriers is studied. Configurations analyzed include panels with different thickness and elastic modulus in different regions and layered structures connected by an elastic suspension. The purpose of the re ...
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Journal article2008 Proceedings of the Noisecon ASME Ncad Ncad 2008 · October 16, 2009
In the high frequency limit, a vibrating panel subject to spatially-random temporally-broadband forcing is shown to have broadband power and directivity properties that can be expressed in simple analytical terms by a limited set of parameters. A lightly-l ...
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Journal article2008 Proceedings of the Noisecon ASME Ncad Ncad 2008 · October 16, 2009
Enclosures with difliise reflection boundaries are modeled with an energy-intensity boundary element method using uncorrelated broadband directional sources. Input power is assumed to enter the enclosure through the walls, which are also absorptive. An abs ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication Ncad · December 1, 2008
In the high frequency limit, a vibrating panel subject to spatially-random temporally-broadband forcing is shown to have broadband power and directivity properties that can be expressed in simple analytical terms by a limited set of parameters. A lightly-l ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication Ncad · December 1, 2008
Sound transmission through multi-element flexible barriers is studied. Configurations analyzed include panels with different thickness and elastic modulus in different regions and layered structures connected by an elastic suspension. The purpose of the re ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication Ncad · December 1, 2008
Enclosures with diffuse reflection boundaries are modeled with an energy-intensity boundary element method using uncorrelated broadband directional sources. Input power is assumed to enter the enclosure through the walls, which are also absorptive. An abso ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication Ncad · December 1, 2008
A theory based on cross-sectional averaging is developed to analyze quasi-one-dimensional acoustic propagation in hybrid ducts with two propagation media in the cross-section. Specifically, ducts lined with a thick layer of porous material are considered. ...
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Journal article12th International Congress on Sound and Vibration 2005 Icsv 2005 · December 1, 2005
Sound propagation of one-dimensional waves through a tube with periodic area changes is studied theoretically and experimentally. The resulting wave behavior is similar to that observed for periodic structures, with Bloch waves, pass-bands and stop-bands. ...
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Journal article12th International Congress on Sound and Vibration 2005 Icsv 2005 · December 1, 2005
Local-Global Homogenization (LGH) is a method to predict directly the smooth global response of periodic fluid-loaded structures in a self-contained manner. Many fluid-loaded structures, such as fuselages and hulls, have periodically spaced braces, ribs, o ...
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Journal article12th International Congress on Sound and Vibration 2005 Icsv 2005 · December 1, 2005
A novel analysis for steady-state or time-dependent broadband diffuse sound fields in enclosures is developed. Beginning with a formulation utilizing broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers ...
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Journal articleJournal of the Acoustical Society of America · November 1, 2004
The method of analytical-numerical matching (ANM) is applied to several example problems involving the radiation and vibration of a fluid-loaded cylindrical shell with structural discontinuities. These problems are used to verify the accuracy of the method ...
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Journal articleJournal of the Acoustical Society of America · August 1, 2004
A novel homogenization method for periodic structures that utilizes a local/global separation of the high and low wavenumber spectrum is presented. The low-wavenumber global problem has an infinite-order operator. The global problem is self-contained; loca ...
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Journal articleProceedings of the Tenth International Congress on Sound and Vibration · December 1, 2003
Many periodic structures are subjected to forcing by a propagating pressure field. Examples include incident sound fields reflected off submerged ribbed hulls, and interior noise radiated from aircraft fuselages forced by an external turbulent boundary lay ...
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Journal articleProceedings of the Tenth International Congress on Sound and Vibration · December 1, 2003
Solving structural acoustic problems in the mid-frequency range is a challenging task. Computation is expensive due to the large well-coupled nature of the fluid-structure system. Discrete structural elements cause localized discontinuities that require mu ...
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Journal articleProceedings of the Tenth International Congress on Sound and Vibration · December 1, 2003
Very often structures are designed to perform a primary function and vibration is an unwanted consequence. It is desirable to develop structural configurations that naturally resist vibration while still satisfying their basic function. This paper describe ...
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Journal articleJournal of Aircraft · January 1, 2003
It is well known that the effectiveness of a trailing-edge control surface can be substantially diminished due to the elastic twist of an airfoil or wing. This aeroelastic phenomenon is known as control surface reversal when the lift or roll rate vanishes ...
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Journal articleJournal of the Acoustical Society of America · December 29, 2001
A boundary element method is formulated in terms of time-averaged energy and intensity variables. The approach is applicable to high modal density fields but is not restricted to the usual low-absorption, diffuse, and quasiuniform assumptions. A broadband ...
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Journal article6th Aeroacoustics Conference and Exhibit · December 1, 2000
Airframe noise due to structural vibration is estimated. This estimate shows that panel vibration driven by turbulent boundary layer fluctuations can produce airframe noise levels comparable to those measured on aerodynamically "clean" airframe configurati ...
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Journal article6th Aeroacoustics Conference and Exhibit · December 1, 2000
An acoustic boundary element method is formulated using the time-averaged intensity and mean-square pressure. A continuous distribution of uncorrelated broadband high frequency sources is used to represent the boundaries of the enclosure. Local correlation ...
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Journal articleJournal of the Acoustical Society of America · September 1, 1999
Acoustic scattering from an infinitely long, thin elastic cylindrical shell with axially periodic circumferential constraints leads to the excitation of flexural, longitudinal, and shear waves on the shell. Of interest is the interaction of these structura ...
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Journal articleJournal of the American Helicopter Society · January 1, 1999
A method for calculating parallel blade vortex interaction (BVI) has been developed. The technique is based on the application of a three-dimensional aeroacoustic boundary element formulation using Analytical/Numerical Matching in conjunction with a recent ...
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Journal articleJournal of the Acoustical Society of America · April 1, 1998
Structural discontinuities in highly coupled fluid-structure systems are modeled by an approach called analytical/numerical matching (ANM). This method separates the low-resolution global influence of a discontinuity from the relatively high-resolution loc ...
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Journal articleJournal of the Acoustical Society of America · April 1, 1998
Modal analysis is often used to solve problems in acoustics, leading to a system of coupled equations for the modal amplitudes. A common practice in analytical work utilizing modal analysis has been to assume that weak modal coupling is negligible, thereby ...
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Journal articleAIAA Journal · January 1, 1998
An analytical method has been developed to predict the structure of a fully developed trailing vortex with a viscous core. Vortex structure is calculated from the load distribution on the generating wing and fundamental conservation laws are satisfied. The ...
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Journal articleJournal of the Acoustical Society of America · February 1, 1997
Analytical/numerical matching (ANM) is introduced to more efficiently model structural discontinuities in structural/acoustic problems. The general method is explained in detail for the simple example problem of normal incidence acoustic scattering from a ...
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Journal articleJournal of the Acoustical Society of America · January 1, 1997
Analytical/numerical matching (ANM) is a hybrid scheme combining a low- resolution global numerical solution with a high-resolution local solution to form a composite solution. ANM is applied to a harmonically oscillating body to calculate the radiated aco ...
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Journal articleAIAA Journal · January 1, 1997
A unified aeroacoustic boundary element theory has been formulated using analytical/numerical matching (ANM). ANM is a hybrid scheme combining a low-resolution global numerical solution with high-resolution local solutions to form a composite solution. ANM ...
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Journal articleAIAA Journal · January 1, 1996
Analytical/numerical matching (ANM) is a hybrid scheme combining a low-resolution global numerical solution with a high-resolution local solution to form a composite solution. ANM is applied to lifting surfaces in steady potential flow to calculate the aer ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · December 1, 1995
Accurate knowledge of rotorcraft tip vortex structure is essential to the prediction of rotorcraft free-wake aerodynamics and sound radiation due to blade-vortex interaction. A novel analytical method has been developed to accurately predict the turbulent ...
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Journal articleAIAA Journal · January 1, 1995
The motion of a free vortex system is predicted using a novel method called analytical/numerical matching (ANM). Analytical/numerical matching is a hybrid mathematical and numerical technique that results in a new problem formulation with high accuracy and ...
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Journal articleJournal of the American Helicopter Society · January 1, 1994
This paper describes the development and implementation of a unified model of rotorcraft interactional aerodynamics using advanced methods in vortex dynamics. The model incorporates several recently-developed tools for the analysis of vortex wake dynamics ...
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Journal articleAnnual Forum Proceedings - American Helicopter Society · 1994
The study of helicopter aerodynamic loading for acoustics applications requires the application of efficient yet accurate simulations of the velocity field induced by the rotor's vortex wake. This paper summarizes work to date on the development of such an ...
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Journal articleJournal of the American Helicopter Society · January 1, 1993
Periodic Inversion is a new approach for the calculation of rotor free wakes which solves directly for periodically steady-state solutions, at all advance ratios including low speed and hover. This is a unique capability as traditional time marching soluti ...
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Journal articleJournal of the American Helicopter Society · January 1, 1993
A hybrid analytical and numerical method called analytical/numerical matching is used to calculate the velocity field of rotor wake vortex filaments. A simple discretization of the Biot-Savart law is used to obtain an efficient but low order numerical calc ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · December 1, 1992
This paper describes the development and implementation of a unified model of rotorcraft interactional aerodynamics using advanced methods in vortex dynamics. The model incorporates several recently-developed tools for the analysis of vortex wake dynamics ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication NCA · December 1, 1991
The analysis of sound transmission across panel/frame structures is important in the design of noise reduction strategies for vehicular interior-noise control. A recently developed two-scale perturbation expansion theory for such problems formulates a comp ...
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Journal articleAIAA Journal · January 1, 1991
The prediction of noise due to the impingement of the main-rotor wake of a helicopter on the tail rotor and other main-rotor blades requires the efficient computation of the wake-induced velocity field. This paper describes the development of a new treatme ...
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Journal articleJournal of Computational Physics · January 1, 1991
A Lanczos procedure is applied to a Navier-Stokes solver for computing eigenvalues and eigenvectors. These eigenvalues and eigenvectors are associated with small perturbation analysis of a finite difference representation of the Navier-Stokes equations for ...
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Journal articleAIAA Journal · January 1, 1991
A method is proposed to determine directly the amount of artificial viscosity needed for stability using an eigenvalue analysis for a finite difference representation of the Navier-Stokes equations. The stability and growth of small perturbations about a s ...
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Journal articleVertica · December 1, 1990
A new free-wake analysis has been developed to predict the performance of rotors in hover and axial flight. The analysis finds the rotor wake geometry using a novel influence coefficient/relaxation scheme. In this paper, the features of the analysis are re ...
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Journal articleAmerican Society of Mechanical Engineers Noise Control and Acoustics Division Publication NCA · December 1, 1990
Low frequency sound transmission through flexible walls is an important vehicle noise control problem, particularly for aircraft interior noise. The coupled structural/acoustic problem for spatially periodic wall structures is solved using a two-scale pert ...
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Journal articleVertica · December 1, 1990
The principal objective of this work was to explore the applicability of recent innovations in the analysis of vortex dynamics to problems of interest in rotorcraft interactional aerodynamics. Using a novel, full-span rotor wake representation constructed ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · May 1, 1990
The model incorporates a variety of recently-developed tools for the analysis of vortex dynamics and vortex/surface interaction, including a full-span free wake model of the rotor coupled to a panelled body, as well as new methods for the prediction of sur ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · May 1, 1990
Periodic Inversion is a new approach for the calculation of rotor free wakes which guarantees periodically steady-state solutions, and provides the means to solve for wake dynamics at all advance ratios including low speed and hover. The method is based on ...
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Journal articleJournal of Aircraft · January 1, 1989
Free-wake analyses of helicopter rotor wakes in hover using time stepping have been shown to encounter instabilities which preclude convergence to valid free-vortex solutions for rotor-wake geometries. Previous work has demonstrated that these convergence ...
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Journal article · December 1, 1987
A method using curved vortex elements has been developed for helicopter rotor free wake calculations. The Basic Curved Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · December 1, 1987
The effect of various wake models on the prediction of rotor vibratory airloading has been studied in an ongoing research program on wake aerodynamics in high speed flight. At high advance ratios, the rotor wake structure is particularly complicated and th ...
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Journal articleAnnual Forum Proceedings American Helicopter Society · December 1, 1985
A new approach to the free wake problem for a hovering rotor has been developed. An influence coefficient solution method is used to find the rotor wake solution which is steady in a reference frame rotating with the blades. This solution scheme solves dir ...
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Journal articleAnnual Forum Proceedings - American Helicopter Society · 1985
A new approach to the free wake problem for a hovering rotor has been developed. An influence coefficient solution method is used to find the rotor wake solution which is steady in a reference frame rotating with the blades. This solution scheme solves dir ...
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Journal articleundefined · January 1, 1984
Studies the behaviour of isolated holes and slots in wind tunnel walls. Uses a potential flow approach to determine the pressure differential/flowrate relationship for various hole planforms in high speed subsonic flow. For low aspect ratio planforms, resu ...
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Journal article · January 1, 1984
Studies the behaviour of isolated holes and slots in wind tunnel walls. Uses a potential flow approach to determine the pressure differential/flowrate relationship for various hole planforms in high speed subsonic flow. For low aspect ratio planforms, resu ...
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Journal articleJournal of the Acoustical Society of America · March 1, 1982
A local boundary condition to account for the effect of bulk reaction on the performance of sound absorbing layers was proposed by D. Bliss [J. Acoust. Soc. Am. 71, 533–545 (1982)]. The new boundary condition differs from the usual impedance boundary condi ...
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Journal articleundefined · January 1, 1982
A study was undertaken to predict steady flow conditions in two-phase steam/water flows in safety/relief discharge piping systems. The approach can also accommodate single phase flows of superheated system of subcooled liquid. Subroutines were developed to ...
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Journal articleAIAA Journal · January 1, 1982
A theoretical model for the flow through a single slot of finite length in a wall separating a uniform freestream and a quiescent fluid at different static pressures is constructed. This problem is relevant to understanding the aerodynamic behavior of slot ...
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Journal articleJournal of Aircraft · January 1, 1982
An analytical model of the vortex wake instability subject to forcing by unsteady lift fluctuations has been developed. These lift fluctuations can be caused either by variations in angle of attack or by flying through atmospheric turbulence. The effect of ...
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Journal article · January 1, 1982
A study was undertaken to predict steady flow conditions in two-phase steam/water flows in safety/relief discharge piping systems. The approach can also accommodate single phase flows of superheated system of subcooled liquid. Subroutines were developed to ...
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Journal articleJournal of Pressure Vessel Technology Transactions of the ASME · January 1, 1982
A study was undertaken to predict steady flow conditions in two-phase steam/water flows in safety/relief discharge piping systems. The homogeneous-equilibrium model was used for the two-phase flow along with the ASME Steam Tables in subroutine form as a st ...
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Journal articleJ. Acoust. Soc. Am. (USA) · 1981
The case of a structural (elastic) wall on which is mounted an absorptive material does not appear to have a self-consistent derivation of a physically correct boundary condition. Such a derivation is the authors' goal ...
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Journal articleSemiconductor International · January 1, 1981
E. H. Dowell's linear theory of acoustoelasticity, which is capable of predicting the interior sound field for any structural model surrounding an arbitrarily shaped acoustic cavity subject to a prescribed internal sound source and/or external noise fields ...
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Journal articleAmmonia Plant Safety and Related Facilities · January 1, 1980
The paper discusses the interaction between the (acoustic) sound pressure field and the (elastic) flexible wall of an enclosure. Such problems frequently arise when the vibrating walls of a transportation vehicle induce a significant internal sound field. ...
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Journal articleS V Sound and Vibration · October 1, 1974
This article summarizes the salient aspects of the wind forces, including their spatial and temporal distributions, outlines a response calculation approach, suggests a method for selecting a design value for the maximum expected modal displacement, and pr ...
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Journal articleJournal of Fluid Mechanics · January 1, 1974
A simple model for the experimentally observed instability of the vortex ring to azimuthal bending waves of wavelength comparable with the core size is presented. Short-wave instabilities are discussed for both the vortex ring and the vortex pair. Instabil ...
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Journal articleundefined · January 1, 1974
THE SELF-INDUCED MOTION AND STABILITY OF VORTEX FILAMENTS WAS INVESTIGATED BOTH THEORETICALLY AND EXPERIMENTALLY.THOUGH AN APPLICATION OF THE METHOD OF MATCHED ASYMPTOTIC EXPANSIONS, A GENERAL SOLUTION IS OBTAINED FOR THE SELF-INDUCED MOTION OF A VORTEX FI ...
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Journal articleArch Mech Arch Mech Stosow · January 1, 1974
The self-induced motion and stability of vortex filaments is investigated both theoretically and experimentally. Through an application of the method of matched asymptotic expansions, a general solution is obtained for the self-induced motion of a vortex f ...
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Journal articleJournal of Fluid Mechanics · 1974
A simple model for the experimentally observed instability of the vortex ring to azimuthal bending waves of wavelength comparable with the core size is presented. Short-wave instabilities are discussed for both the vortex ring and the vortex pair. Instabil ...
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Journal article · January 1, 1974
THE SELF-INDUCED MOTION AND STABILITY OF VORTEX FILAMENTS WAS INVESTIGATED BOTH THEORETICALLY AND EXPERIMENTALLY.THOUGH AN APPLICATION OF THE METHOD OF MATCHED ASYMPTOTIC EXPANSIONS, A GENERAL SOLUTION IS OBTAINED FOR THE SELF-INDUCED MOTION OF A VORTEX FI ...
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Journal articleJ. Fluid Mech. (UK) · 1971
Results concerning the effects of axial velocity on the motion of vortex filaments are reviewed. These results suggest that a slender body force balance between the Kutta-Joukowski lift on the vortex cross-section and the momentum flux within the curved fi ...
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Journal articleTool Manuf. Eng. (USA) · 1969
Discusses the development of a low-cost remote-access terminal for a time-shared computer which extends engineering and decision making capabilities of the small job shop. Tape preparation for numerically controlled machine tools is among the topics discus ...
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