Real-time enhancement of reference signals for feedforward controlof random noise due to multiple uncorrelated sources

The problem envisaged in this paper is the optimization of the reference set for broadband feedforward control of sound and vibration in the presence of multiple, uncorrelated primary sources. A real-time algorithm is presented that generates a set of orthogonal virtual references out of a given set of reference signals. The algorithm is based on recursive singular value decomposition (SVD) techniques. The technique simplifies controller design in the sense that primarily, comparable control performance can be achieved using a reduced set of virtual references instead of the extensive original reference set. Hence, controller dimensions (and, thus, the memory requirements for implementation) and the computational burden reduce accordingly. Second, it is shown that convergence speed of the adaptive filtered-X LMS feedforward control algorithm is enhanced. The technique is applied to active control of structure-borne road noise inside a car cabin. Time domain simulation of a control configuration, utilizing either an extensive set of original references as well as a reduced virtual reference set, shows that in the frequency ranges of interest, a set of four virtual references yields the same noise reductions as the original set of 12 references     

Characterisation of induced discontinuities in the Boom Clay around the underground excavations (URF, Mol, Belgium)

Excavation works were carried out in Boom Clay to extend the underground research facility in Mol (Belgium) located at a depth of 223 m below the surface. The attempt to characterise the extent of the Excavation Damaged Zone, or EDZ, around the second shaft, using seismic measurements and cored borings, was successful, as proven by observations during further excavation works in the investigated area. No evidence for the occurrence of natural discontinuities was found. Using an industrial technique, an 84-m-long gallery was excavated in the Boom Clay. These excavation works induced a symmetrical pattern of discontinuities and clearly limited the EDZ extent.     

A subspace algorithm for the identification of discrete time frequency domain power spectra

In this paper we present a new subspace algorithm for the identification of multi-input multi-output linear discrete time systems from measured power spectrum data. We show how the state space system matrices can be determined by taking the inverse discrete Fourier transform of the given data and applying the result to a new realization algorithm. Special attention is paid to ensure the positive realness of the identified power spectrum. The computational speed is improved by applying a Lanczos algorithm. The algorithm is illustrated with two practical examples.     

Microfabric of fractured Boom Clay at depth: a case study of brittle–ductile transitional clay behaviour

Recent Underground Research Facility (URF) gallery excavation works in the Boom Clay at 224 m below the surface revealed intense fracturing of this weak claystone. Large fault planes (meter-scale) and joints were observed during tunnelling and found to belong to the excavation-disturbed zone (EDZ). Samples taken from the new gallery have been investigated using scanning electron microscope (SEM) imagery and microstructural analysis. This revealed a brittle–ductile transitional behaviour of the mudstone sediment regarding deformation, implying dilatant shear and hybrid fractures in high strain zones and ductile, compacted plastic shear bands in the lower strain zones, following an elasto-plastic constitutive model. Microfabric analysis contributed in this way to a better understanding of clay behaviour and effective fracturing. This information is primordial for understanding the rheology of the clay and assessing the influence of fracturing on permeability, critical issues in radioactive waste management.