Measured insertion losses due to the ground effects associated with low configurations of loosely stacked household bricks on a car park are reported. A particularly successful design has the form of a two brick high square lattice which is found to offer a similar insertion loss to regularly-spaced parallel wall arrays of the same height but twice the total width. Part of the insertion loss due to the roughness configurations is the result of transfer of incident sound energy to surface waves which can be reduced by introducing wall absorption or material absorption in the form, for example, of shallow gravel layer. Predicted finite length effects have been explored using a Pseudo-Spectral Time Domain Method, which models the complete 3D roughness profile. It is concluded from measurements and predictions that the lattice design has less dependence on azimuthal source-receiver angle than parallel wall configurations. These predictions are supported by measurements of level difference spectra as a function of azimuthal angle. A 2D Boundary Element Method gives predictions that agree well with data for parallel wall arrays up to 16m long and it is used to investigate the potential insertion loss of longer configurations up to 0.3m high. It has been found possible also to make predictions of the insertion loss due to infinitely long 3D lattices using the 2D BEM with the lattice represented by the surface impedance derived from fitting short range data with a slit-pore impedance model. The insertion losses of recessed configurations are predicted to be approximately 3dB less than those of embossed configurations of the same size. Outdoor experiments also show that pathways can be made through such roughness configurations without significantly affecting their insertion loss. It is concluded that artificial roughness configurations could achieve substantial noise reduction along surface transport corridors without breaking line of sight between source and receiver, thereby proving useful alternatives to noise barriers.

With growing maturity in the Wind power industry has come the need to maximise the efficiency and reliability of turbine equipment. One key aspect of this is weight reduction, both to reduce manufacturing cost and to reduce loading on gearboxes, bearings and associated equipment. However to reduce the weight of the blades we must ensure that they perform as designed. non–destructive testing is a key element of this. Most Turbine blade structures contain a large amount of glass-fibre, which is a notoriously difficult material to inspect with ultrasonic techniques. Sonatest have developed a variant of their Array wheel probe, optimised for inspection of Difficult composite materials and employing ‘lower than normal’ inspection frequencies. This paper discusses the design optimisations, and details the results obtained. Opracowanie optymalnej glowicy oponowej Phased array do badan kompozytow z wloknem szklanym Streszczenie Wraz z rosnącym zaawansowaniem energetyki wia- trowej pojawila sie potrzeba maksymalizacji sprawności i pewności elementow turbiny wiatrowej. Jednym z waz- niejszych zadan byla redukcja masy, kosztow wytwarza- nia i ciezaru przekladni, lozysk oraz innego wyposazenia. Redukcja masy lopat wirnika musi byc związana z pewnością bezaawaryjnego dzialania zgodnie z zalozeniami projektowymi. Badania nieniszczące (nDT) są jednym z narzedzi kontrolnych. Wiekszośc konstrukcji lopat wirnikow zawiera duze ilości wlokna szklanego, ktore jest znane jako bardzo trudny material do badan technikami ultradźwiekowymi. Sonatest udoskonalil wariant oponowej glowicy Phased Array, optymalizując ją do badan tych trudnych kompozytow przez zastosowanie czestotliwości nizszej niz normalnie. Ten artykul pokazuje dokonaną optymalizacje oraz osiągniete rezultaty.

Recent developments in the use of transient eddy current methods have demonstrated the advanced ability to detect and characterise corrosion and cracks within complex structures, using a single acquisition scan. In addition, the use of Hall sensors to measure the magnetic field directly enables measurements at greater depths in metals than is achieved using a conventional coil sensor. However, the rapid increase in effective field size with depth in the structure means that there is always a trade-off between defect sensitivity and susceptibility to the presence of nearby edges, fasteners and other sub-structure. The ability to characterise the defect in terms of metal loss, size and depth can also suffer when defect sensitivity is increased. This paper reports an investigation to determine how the sensitivity could be increased for metal-loss defects deeper than 15 mm (0.625) in the case when the proximity of structural changes is not an issue. The essential requirement is to increase the contrast between good and defective structure by either reducing noise levels or increasing the strength of the field reflected from the defect. An increase in the reflected field can be achieved by either increasing the incident field strength, or changing its spatial characteristics. Results have shown that defect sensitivity can be increased using these methods to enable a considerable improvement in detectability of metal loss deep in thick aluminium structure.

Heat transfer between a solidifying aluminium alloy casting and a mould is dominated by the thermal resistance created by the interface. Interfacial heat transfer occurs by conduction through the atmosphere between the two surfaces and by conduction through the points of actual contact. (Heat transfer by radiation is probably significant only for ferrous castings.) The extent of real physical contact between two surfaces is difficult to quantify. This paper explains a method, using ultrasonic flaw detection techniques, whereby an estimate of the propagation of an ultrasonic signal through a casting-chill interface is used to infer the degree of actual contact occurring between them. In experiments involving casting and solidification of an aluminium alloy onto a copper chill the technique was found to give information for the first two seconds of the casting process only. In this time a peak in ultrasound transmission was observed, correlating to a maximum in the area of casting-chill contact, followed by a decrease in the ultrasound transmission that corresponded to actual contact areas between the casting and the chill in the region of 5 to 10%.

COMPARED with rivets, bolts or other mechanical fasteners, the adhesive bonding of metallic and composite materials in airframe structural components produces higher strength, better fatigue resistance, and significant weight and cost reductions. Such structures are, however, only as good as the adhesive bonding. Dry coupling ultrasonic non‐destructive inspection, although a comparatively recent innovation, is already a proven and effective method of detecting disbonds. The technique is far less laborious and more reliable than any other so far devised for this purpose.