In the field of mechanics, rapid progress in the past two centuries has occurred, due in large measure to the ability of investigators to represent physical laws in terms of rather simple equations. In many cases the governing equations were not so simple; therefore, certain assumptions, more or less consistent with the physical situation, were employed to reduce the equations to types more easily soluble. Thus, the process of linearization has become an intrinsic part of the rational analysis of physical problems. An analysis based on linearized equations, then, may be thought of as an analysis of a corresponding but idealized problem.

Bladed disk systems

Bladed disks are used in several engineering systems such as fans, impeller pumps, turbine generators and jet engines (Fig. 1).

Ideally, these systems are tuned and all blades are identical but, in practice there always exist small, random differences among the blades. Mistuning, imperfections in cyclical symmetry of bladed disks is an inevitable and perilous occurrence due to many factors including manufacturing tolerances, variations in material properties and wear in service. Each blade on a disk is almost always slightly different to the others. It can cause some unpredictable phenomena such as dramatic difference in forced vibration response. This survey explains the fundamental techniques of mistuning in some details.

Birds with different orientations when impacting an aeroengine (Courtesy of Luis Pontes)

Bird strikes have been one of the most dangerous threats to both civil and military flight safety. The consequences of bird strike can be fatal, therefore, it is critical to ensure that different structural parts such as compressor blades, windshield, wing and tail leading edges are able to resist such high energy impacts and guarantee safe landing of the aircraft when impacted by birds.

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