The Experts below are selected from a list of 36 Experts worldwide ranked by ideXlab platform

N. Engheta - One of the best experts on this subject based on the ideXlab platform.

  • On fractional calculus and fractional multipoles in electromagnetism
    IEEE Transactions on Antennas and Propagation, 1996
    Co-Authors: N. Engheta
    Abstract:

    Using the concept and tools of fractional calculus, we introduce a definition for "fractional-order" multipoles of electric-charge densities, and we show that as far as their scalar potential distributions are concerned, such fractional-order multipoles effectively behave as "intermediate" sources bridging the gap between the cases of integer-order Point multipoles such as Point Monopoles, Point dipoles, Point quadrupoles, etc. This technique, which involves fractional differentiation or integration of the Dirac delta function, provides a tool for formulating an electric source distribution whose potential functions can be obtained by using fractional differentiation or integration of potentials of integer-order Point-multipoles of lower or higher orders. As illustrative examples, the cases of three-dimensional (Point source) and two-dimensional (line source) problems in electrostatics are treated in detail, and an extension to the time-harmonic case is also addressed. In the three-dimensional electrostatic example, we suggest an electric-charge distribution which can be regarded as an "intermediate" case between cases of the electric-Point monopole (Point charge) and the electric-Point dipole (Point dipole), and we present its electrostatic potential which behaves as r/sup -(1+/spl alpha/)/P/sub /spl alpha//(-cos/spl theta/) where 0

Florence V. Hutcheson - One of the best experts on this subject based on the ideXlab platform.

  • Advanced modeling of active control of fan noise for ultra high bypass turbofan engines
    1999
    Co-Authors: Florence V. Hutcheson
    Abstract:

    An advanced model of active control of fan noise for ultra high bypass turbofan engines has been developed. This model is based on a boundary integral equation method and simulates the propagation, radiation and control of the noise generated by an engine fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow. Control sources, modeled by Point Monopoles placed along the wall of the engine inlet or outlet duct, inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The duct inner wall can be lined or rigid. Unlike current methods, reflection from the duct openings is taken into account, as well as the presence of the evanescent modes. Forward, as well as backward (i.e., from the rear of the engine), external radiation is computed. The development of analytical expressions for the sound field resulting from both the fan loading noise and the control sources is presented. Two fan models are described. The first model uses spinning line sources with radially distributed strength to model the loading force that the fan blades exert on the medium. The second model uses radial arrays of spinning Point dipoles to simulate the generation of fan modes of specific modal amplitudes. It is shown that these fan models can provide a reasonable approximation of actual engine fan noise in the instance when the modal amplitude of the propagating modes or the loading force distribution on the fan blades, is known.

  • Advanced modeling of active control of fan noise for turbofan engines
    Journal of the Acoustical Society of America, 1998
    Co-Authors: Florence V. Hutcheson, Chris R. Fuller, Ricardo A. Burdisso, Mark H. Dunn
    Abstract:

    An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR‐97‐206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by Point Monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First‐ and fourth‐order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far‐field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and o...

Mark H. Dunn - One of the best experts on this subject based on the ideXlab platform.

  • Advanced modeling of active control of fan noise for turbofan engines
    Journal of the Acoustical Society of America, 1998
    Co-Authors: Florence V. Hutcheson, Chris R. Fuller, Ricardo A. Burdisso, Mark H. Dunn
    Abstract:

    An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR‐97‐206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by Point Monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First‐ and fourth‐order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far‐field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and o...

Chris R. Fuller - One of the best experts on this subject based on the ideXlab platform.

  • Advanced modeling of active control of fan noise for turbofan engines
    Journal of the Acoustical Society of America, 1998
    Co-Authors: Florence V. Hutcheson, Chris R. Fuller, Ricardo A. Burdisso, Mark H. Dunn
    Abstract:

    An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR‐97‐206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by Point Monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First‐ and fourth‐order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far‐field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and o...

Ricardo A. Burdisso - One of the best experts on this subject based on the ideXlab platform.

  • Advanced modeling of active control of fan noise for turbofan engines
    Journal of the Acoustical Society of America, 1998
    Co-Authors: Florence V. Hutcheson, Chris R. Fuller, Ricardo A. Burdisso, Mark H. Dunn
    Abstract:

    An advanced model of active control of fan noise for turbofan engines is being developed using the ducted fan noise prediction code TBIEM3D [M. H. Dunn, NASA/CR‐97‐206232, Sept. 1997]. An engine fan surrounded by a duct of finite length and cylindrical profile, translating in its axial direction with a uniform speed, is considered. A collection of spinning line sources located inside the duct are used to simulate the fan noise. Control sources modeled by Point Monopoles are placed along the duct inner wall to generate the secondary field that destructively interferes with the fan noise. A feedforward active noise control algorithm is simulated. Test cases were performed to demonstrate the feasibility of the model to perform active noise control studies. First‐ and fourth‐order circumferential modes generated at a blade passage frequency of 1000 Hz were generated and targeted for control using far‐field and inlet error sensors combined with a rigid or lined duct inner wall. Interference between inlet and o...