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  • 1. Hedberg, Claes
    et al.
    Haller, Kristian
    Arnoldsson, Sven
    Non-contact nonlinear acoustic damage localization in plates. Part 1: Resonance of air between plates2007In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 93, no 1, p. 13-21Article in journal (Refereed)
    Abstract [en]

    This is the first of three articles that deals with the goal of using non-contact nonlinear acoustic methods for the damage localization in plates. In this first part, the resonant air gap wave field between one active and one passive reflecting plate was investigated experimentally. Of particular interest is the wave field amplitude strength, and its distribution on the passive surface. The wave amplitude may be increased by choosing one plate to be concave, overcoming the nonlinear damping taking place for two flat plates. Applications are connected with an increased wave field having advantages for processes taking place under open conditions and for a non-contact transducers' efficiency of transferring energy into an object. A double resonance gives highest air pressure, while a triple provides most energy in the passive object. By choosing the gap distance, frequency and transducer width, the appearing resonant wave will have a considerably larger amplitude at the object surface. The work through the interface from air to object is investigated and the wave field in a resonant air-plate system is shown.

  • 2. Sjösten, Per
    et al.
    Johansson, Sven
    Claesson, Ingvar
    Nordebo, Sven
    Considerations on Large Applications of Active Noise Control, Part I: Theory2003In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 89, no 5, p. 822-833Article in journal (Refereed)
    Abstract [en]

    The application of active noise or vibration control to a real situation is usually a great challenge. The step from computer simulations, or even lab studies, to the actual implementation is often much larger than first expected. This is especially true for multiple-error, multiple-output control, in which careful planning and a very great deal of preparatory work is crucial to the success of the project. The present paper is the first in a series of two, that treat the process of preparing and evaluating an active noise control system. Part I gives a general discussion on proposed methods from a theoretical standpoint. Part II describes the application of these methods in practical measurements in an aircraft application. The emphasis is on multiple-error, multiple-output control but the general guidelines haves proven to be useful even in small applications. The discussion covers some acoustical aspects as well as the signal processing view. A method, based on simulated annealing using the metropolis sampler is suggested for searching the suboptimal positions for the control sources and sensors, including a thorough discussion on the preparation of input data for the optimisation process. Finally, a version of the complex lms algorithm, normalised individually for each actuator, is discussed.

  • 3. Sjösten, Per
    et al.
    Johansson, Sven
    Persson, Per
    Claesson, Ingvar
    Considerations on Large Applications of Active Noise Control, Part II: Experimental Results2003In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 89, no 5, p. 834-843Article in journal (Refereed)
    Abstract [en]

    This paper treats the practical aspects of the prediction, implementation and verification of an active noise control system. The system was implemented in a mock-up of a Saab 340 propeller aircraft. A search algorithm, based on simulated annealing using the metropolis sampler was used to determine the positions for the control sources and sensors. The sound field was generated by a specially designed noise simulation system, using 12 individually controlled loudspeakers and a DSP--based signal generator. A version of the individually normalized complex lms algorithm was implemented for the control of the sound field. The prediction and verification of the active control system, was made in 20 evaluation positions, distributed at ear level above the seats. This is the second paper in a series of two, concerning the preparation, selection and verification of an active noise control system. Part I contains a theoretical treatment with some general guidelines for the implementation. Paper II is focused on the practical aspects of the implementation and verification.

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