Introduction Of Debris Research Articles

Detection of sub-surface damage in wind turbine bearings using acoustic emissions and probabilistic modelling

Bearings are the culprit of a large quantity of Wind Turbine (WT) gearbox failures and account for a high percentage of the total of global WT downtime. Damage within rolling element bearings have been shown to initiate beneath the surface which defies detection by conventional vibration monitoring as the geometry of the rolling surface is unaltered. However, once bearing damage reaches the surface, it generates spalling and quickly drives the deterioration of the entire gearbox through the introduction of debris into the oil system. There is a pressing need for performing damage detection before damage reaches the bearing surface. This paper presents a methodology for detecting sub-surface damage using Acoustic Emission (AE) measurements. AE measurements are well known for their sensitivity to incipient damage. However, the background noise and operational variations within a bearing necessitate the use of a principled statistical procedure for damage detection. This is addressed here through the use of probabilistic modelling, more specifically Gaussian mixture models. The methodology is validated using a full-scale rig of a WT bearing. The bearings are seeded with sub-surface and early-stage surface defects in order to provide a comparison of the detectability at each level of a fault progression.

Coastal progradation and very early diagenesis of ultramafic sands as a result of rubble discharge from asbestos excavations (northern Corsica, western Mediterranean)

The western coast of Cape Corse in northern Corsica is a remarkable area by virtue of its geological, biological and landscape diversity. Asbestos extraction between 1948 and 1965 however at Canari Mine, has modified the natural rocky escarpments, cutting the mountain into steps and has altered the coastal and marine zones from Punta di Canella to Farinole. Albo harbour was filled with rubble discharging directly to the sea, and the coast prograded 400 m after 4 years between 1954 and 1958. Artificial shores of up to 300 m in width appeared at the bottom of existing steep cliffs over a distance of more than 5 km between 1948 and 1973. The Posidonia seagrass was buried by the introduction of debris. Since June 1965, the mine is closed and coastal modification results from material movement from north to south. As an exception, Campana beach appeared in the northern part of the discharge area in 1973. The sediment on Nonza beach already displays cemented slabs that attest to very early diagenesis. This particular environment of ultramafic sands and pebbles appear to have produced alkaline conditions and probably enhances carbonate precipitation.