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Published Articles

The Volume 8, No 3, September 2003

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A Fluid Dynamics Approach to Cosmology Incorporating a Unified Theory of Acoustics and Electromagnetic Radiation

Geoffrey M. Lilley


The present paper is a revised and shortened version of that presented to the Seventh International Congress on Sound and Vibration held in Garmisch-Partenkirchen, Germany. It presents speculative and controversial ideas on a possible fluid mechanics model for 'dark matter' in the Universe and the impact it would have on the established theory of light propagation and its relation to sound propagation. Since 'dark matter' has escaped all observations on Earth it must be assumed that should it be a particulate its particle mass and size will be almost infinitesimal compared with all existing atomic and subatomic matter. Thus, its thermodynamic properties of mean particle speed and wave propagation speed will approach that of light, and therefore provide the medium for the propagation of electromagnetic radiation. The model satisfies the 'Principle of Relativity' and the classical theories of fluid mechanics, gas dynamics, and thermodynamics, and reopens discussion on the hypotheses introduced by Einstein concerning laws of nature, the propagation of wave motion in a void, and the absolute speed of light. The presence of this form of 'dark matter' is shown to unify the theories of sound and light propagation even though their speeds of wave propagation differ by an order of a million times. Hence both disciplines obey the laws of space-time for they are solutions of the same homogeneous 'unique' wave equation, and the corresponding convected wave equation for the case of moving sources. These equations satisfy covariant and coordinate invariance and are therefore laws of nature for all speed ratios. When this model of 'dark matter' is applied to cosmology, it provides a model for the expanding Universe. The results of electromagnetic and acoustic wave motion generated by bodies and electric charges in motion, for the same speed ratio with respect to wave propagation speed, are found, as expected, to be similar to the propagation of capillary waves in a ripple tank.

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Propagation of High Frequency Waves in Slender Engineering Structures

Alexander K. Belyaev, Thurid Gloetzl, Franz Ziegler


A one-dimensional wave-guide based on a Cosserat-type primary structure with secondary substructures of oscillator-type attached is developed. Propagating longitudinal waves are studied under simplifying assumptions: e.g., straight axis, frictionally damped principal rod-structure with variable cross-section, unloaded mantle, i.e., excitation is solely concentrated at the foundation of the building model, etc. Using harmonic linearisation, the resulting integral equation is solved by taking the logarithmic derivative and filtering out negligible contribu- tions. The main results, crucial in tall building acoustics, are critical frequencies and the separation for spatially increasing or decreasing amplitude frequency response functions, and the input-independent upper limit for the strain amplitude. Two main counteracting effects on the propagating wave are identified: energy absorption (due to friction in the primary structure and due to energy absorption in local resonance of the secondary systems) and amplification by decreasing cross-sectional area.

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GSM TDMA Frame Rate Internal Active Noise Cancellation

Ingvar Claesson, Andreas Nilsson


A common problem in the world's most widely-used cellular telephone system, the GSM system, is the interfer- ing signal generated by the switching nature of TDMA cellular telephony in handheld and other terminals. Sig- nals are sent as chunks of data, speech frames, equivalent to 160 samples of data corresponding to 20 ms at sam- pling rate of 8 kHz. This paper describes a study of two different software solutions designed to suppress such interference internally in the mobile handset. The methods are 1) notch filtering, which is multiplicative in fre- quency, and 2) subtractive noise cancellation, which is an alternative method employing correlators. The latter solution is a straigtforward, although somewhat unorthodox, application of ?in-wire? active noise control. Since subtraction is performed directly in the time domain, and we have access to the state of the mobile, it is also pos- sible to consider a recurring pause in the interference caused by the idle frame in the transmission, when the mo- bile listens to other base stations communicating. More complex control algorithms, based on the state of the communication between the handset and the base station, can be utilised.

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Sound Source Characterisation and Transfer Path Analysis with Time Histories

Nicklas Frenne and Orjan Johansson


The article describes a method to separate time histories of partial sound sources. The goal is to develop a noise control engineering tool for use in sound quality improvement applications. Contributions from partial sound sources are identified. The partial sound sources may be ranked for the purpose of creating a better mixture of sound in selected listening positions. The strategy is to reproduce time histories of sources of importance. The method described includes experimental and calculation parts. The experimental part consists of the recording of sound pressure time signals, reciprocal measurement of frequency response functions, and source strength esti- mation of partial sound sources. The calculation part comprises calculation of the cross-spectral matrix of source strength, calculation of filters, and filtered sound pressure recording to obtain time signals of the individual sources. Usually the contribution from partial sources is impossible to record directly. In this laboratory experi- ment, such control was possible. The laboratory experiment shows that the method described makes it possible to produce informative separation of time histories of partial sound sources. The effects of the errors in the cal- culated time histories are audible but not pronounced.

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Acausality Alleviation via Nonlinear Future Prediction in Feedforward Control of Vibrations

Venkata R. Sonti and Anindya Chatterjee


An augmented version of the LMS feedforward algorithm is used, in discrete time simulation, to control a twobeam and one-spring system in an acausal configuration. For perfect control, the required control force is unbounded due to acausality. Imperfect but good control is possible if about-to-act disturbances are known slightly in advance. In the simulations, a broadband yet deterministic chaotic time series is used as the disturbance (a brief characterisation of measured fan noise is presented for comparison). Signal determinism is exploited using a neural network trained to predict some future values of the signal, and the prediction is included in the feedforward loop of an augmented version of the filtered-X LMS algorithm. This controller significantly outperforms the standard algorithm without future prediction. The present controller can be viewed as a neural network based and disturbance-dependent approximation to an acausal controller; but also as a causal nonlinear controller for a linear system in an acausal configuration.

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