Control and exploitation of nonlinearity in smart structures
In this Chapter the control and exploitation of nonlinearity are considered when applied to so called ‘smart structures’. Here we consider how active control can be applied to structures particularly in the presence of nonlinearity. We also consider how s
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ntroduction
The phrase “smart structure” is increasingly used to describe structural systems which have characteristics which go beyond the traditional definition of a structure (sometimes also called adaptive or intelligent structures). These new “smart” characteristics include things such as: (i) monitoring the structure for signs of damage, (ii) reducing unwanted vibrations, or (iii) changing the shape of the structure. The general trend in structural design is towards lighter structures, which typically leads to increased flexibility. In order for structures to carry out the smart functions it is now possible for structural elements to have actuator and sensor networks. Nonlinear behaviour in structural dynamics arises naturally from a range of common nonlinearities. In some cases nonlinearities either cannot be avoided, or add some potential benefit, which leads to designing in the presence of nonlinearity. The most common form of nonlinearity for structural dynamics is geometric nonlinearity. For example, in the design and construction of bridges there has always been the desire to build longer spans, and therefore more flexible bridges. Figure 1 shows the Sutong Bridge which is a cable-stayed bridge that spans the Yangtze River in China. It is currently the cable stay bridge with the longest main span in the world, with ∗
The author would also like to acknowledge the work of Simon Neild, Peter Gawthrop, Jack Potter, Andres Arrieta Diaz, Nihal Malik and Lin Yang, who contributed to the results shown in this chapter. JP and NM were supported for PhD studies by EPSRC studentships; AAD and LY were supported by ORS scholarships.
D. J. Wagg et al. (eds.), Exploiting Nonlinear Behavior in Structural Dynamics © CISM, Udine 2012
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Figure 1. The Sutong Bridge is currently (in 2011) the world’s longest span cable-stay bridge. It spans the Yangtze River between Nantong and Changshu in the People’s Republic of China. It has a main span of 1,088 metres, and two side spans are 300 metres each, and there are also four small cable spans. Photo credit: Wikipedia.
a span of 1,088 metres (3,570 ft). In fact suspension bridges can be even longer, and the Akashi Kaikyo bridge in Japan has a main span of 1.9 kilometres, which is more than a mile long. Some of the structural elements for these bridges, especially the cables, have very low damping, and as a result large deflections become unavoidable. There are also structures where flexibility occurs primarily as a result of the requirement of low weight. For example, Figure 2 shows the NASA Helios which was designed as an unmanned long-term, high-altitude aircraft powered by solar and fuel cells. It suffered a structural failure and crashed during a flight across the pacific on June 26, 2003. The cause of the failure was due to higher than expected wind loads which led to an unexpected, persistent, high deformation of the wing. This in turn led to
Control and Exploitation of Nonlinearity in Smart Structures
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Figure 2. The Helios was designed as a long duration sola
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