Conference Papers

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Two mounts were added to a helicopter making it possible to carry different payloads. To validate the structural effects of these modifications, modal tests were performed on-ground on the helicopter in its standard configuration as well as in its modified configuration with the added payloads. In addition, an in-flight test was performed to verify the impact on the existing flight envelope. For all tests, Operational Modal Analysis was used. The obtained results allowed for updating the flight procedures and operating profiles for the helicopter and provided added flexibility with respect to the best possible helicopter configuration to obtain the mission objectives, while maintaining optimum safety for the flight crew.

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In this work, the noise sources on three types of construction equipment are imaged with a beamforming array, while simultaneously the radiated sound powers are determined by a sixmicrophone hemisphere per ISO 6393 or ISO 6395. Of particular interest are: noise induced by turbulent flow at the exit of an exhaust stack, the effect of a noise reduction package in the engine compartment, and crawler track noise during motion. The absolute levels of the mapped source regions are compared with the total radiated sound power.

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Over the last 10 years, the use of Sound Quality (SQ) has become an accepted automotive industry standard.

This “newer” field of acoustics has proven to be quite useful in many areas, such as; new product design, quantifying subjective opinions on products with objective metrics, troubleshooting current models, and acoustic modeling of products. This paper will cover the basics in sound quality and apply some of these fundamental concepts in a few examples of the use of sound quality in a practical engineering environment.

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A new ASTM standard has been adopted for characterizing acoustical materials in a tube. This new standard is ASTM E2611-09, Measurement of Normal Incidence Sound Transmission of Materials Based on the Transfer Matrix Method. This test method describes the use of a tube, four microphones, and a digital frequency analysis system for the measurement of normal incidence transmission loss and other important acoustical properties of materials by determination of the sample’s acoustic transfer matrix.

In this paper the two and four microphone methods for calculating the reflection coefficient and the related normal incidence sound absorption coefficient will be compared with each other and with the results predicted using finite element software.

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The authors previously presented an extension of operational modal analysis to linear time periodic systems. This paper builds on that work, revealing how more advanced operational modal analysis methods can be extended to linear time-periodic systems.
These extensions are found to provide more accurate estimates of the damping of the modes of the time-periodic systems, and to provide good estimates of the mode shapes of the systems so long as the measurements stand out clearly above the noise. Application of the complex mode indicator function an the EMIF algorithm makes it possible to separate the forward and backward whirling modes of a wind turbine, which is difficult since each of these modes is manifest at several harmonics due to the anisotropy in the tower supporting the turbine.

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Work presented in the current paper in an extension of the pervious work and describes the details of the measurement campaign aimed at identifying modal parameters of ALSTOM’s ECO 100 wind turbine. Since measuring on an operational wind turbine is a challenging job in itself, the paper also describes measurement planning and execution phases. The paper illustrates various key aspects related to practical measurements on an actual wind turbine and underlines the importance of proper planning and experiment design. The importance of a priori nowledge provided by finite element model based simulations is also underlined.

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The influence of different sound fields on the measurement error is discussed in some detail with practical examples and it is shown how a worst-case error exceeding 10 dB @ 20 kHz is a real risk. After a brief discussion of a condenser microphone which drastically reduces the error caused by influence of an unknown sound field or varying angle of incidence. Finally, test results from production samples of the new microphone are shown.

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Aerodynamic noise is particularly important for passenger car driving comfort and high speed train community comfort. This paper describes the application of acoustic array systems in wind tunnels to minimise this noise exposure.

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The study demonstrates the method using simulated vibrational responses of operational 3MW wind turbine. The responses of the tower and blades were obtained from the simulation of operational wind turbine dynamics under realistic wind load using commercial aeroelastic code.

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The study suggests a novel approach which is intended to solve a known TMM weakness due to noncausality of transmissibility functions. The study compares the results obtained using the new approach with two other implementations found in the literature.

The paper is organized as follows: the first section explains the application of the transmissibility matrix method to TPA; next section compares different interpretations of the indicator signals. Section 3 introduces a simple mechanical system and discusses results obtained by different implementations of TMM.