Instability
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Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be marginally stable or exhibit limit cycle behavior.
In control theory, a system is unstable if any of the roots of its S-function has real part greater than zero. This is equivalent to any of the eigenvalues of the state matrix having real part greater than zero.
In structural engineering, a structure can become unstable when excessive load is applied. Beyond a certain threshold, structural deflections magnify stresses, which in turn increases deflections. This is can take the form of buckling or crippling. The general field of study is called structural stability.
Fluid instabilities
Fluid instabilities occur in liquids, gases and plasmas, and are often characterised by the shape that form; they are studied in fluid dynamics and magnetohydrodynamics. Fluid instabilities include:
- Ballooning mode instability (some analogy to the Rayleigh-Taylor instability); found in the magnetosphere
- Baroclinic Instability
- Benard Instability
- Drift mirror instability
- Kelvin-Helmholtz instability
- Rayleigh-Taylor instability
Some plamsa instabilities include:
- Bennett Pinch instability (also called the z-pinch instability )
- Diocotron instability (simiar to, but different to the Kelvin-Helmholtz instability).
- Drift wave instability
- Farley-Buneman instability
- Firehose instability
- Helical instability (helix instability)
- Kink instability
- Non-Abelian instability
- Pair instability
- Peratt instabilities
- Sausage instability
- Tearing mode instability
- Two stream instability
- Weibel instability
Web links
eFluids Fluid Flow Image Gallery (http://www.efluids.com/efluids/pages/gallery.htm)