PH316 Non-Linear Phenomena and Chaos.
Write illustrated notes describing the three broad categories of
dynamical systems: flows, maps and cellula automata. Explain why different
mathematical techniques must be adopted for the study of each of these.
In the case of cellula automata list the possible behaviour patterns which are associated with the following dynamical features: a fixed point, a limit cycle, an attractor (or repellor), a basin of attraction, stability (or instability) and chaos.
Explain the basics of linear stability analysis for one-dimensional
flows by cone solutions of the equation:
of the form
in the vicinity of the solution at the fixed point
.
Show that e(t) grows exponentially if the Lyapunov exponent
and decays exponentially if
.
Show how a graphical method may be used to determine stability in the
case when .
Indicate how such an analysis can lead to the provision of characteristic time scales.
Analyse the stability of the following system: f(x)=x(1-x)(3-x).
Defining a potential function V(x) by f(x)=-dV/dx determine and sketch V(x) for the one-dimensional system and characterize all of the equilibrium points.
Provide suitably labelled sketches of the control space diagram and the phase-plane behaviour as the control parameter passes therough the critical point.
Describe briefly subcritical pitchfork bifurcations.
OR
By transforming to Cartesian coordinates and evaluating the Jacobian
at the origin show that the non-linear system:
gives rise to a Hopf bifurcation as , the control parameter, changes sign.
Describe briefly the role played by such bifurcations in the various routes to chaos.
Provide an outline strategy of how to obtain global solutions of
two-dimensional non-linear flows.
Locate and classify the fixed points of the following nonlinear system:
Plot the local phase portrait near each equilibrium point and indicate the global behaviour.
as the control parameter L is increased from the value minus one, through zero to positive values.
Explain with the aid of suitable diagrams how period-2 and period-3
points arise as L increases beyond the vaule three.
What did Feigenbaum discover about this map?
What role did this system play in exploring the various routes to chaos?
(a) Specify the circumstances for which invertible maps, non-invertible
maps and systems of first order ordinary differential equations can exhibit
chaotic behaviour.
Provide examples for each one of these.
(b) Express the non-linear equation:
as a system of first order equations.
Describe in geometric terms how its dynamics changes as a changes
sign whilst b remains positive.
State briefly the effect on the dynamics when a time dependent driving
term is added to the original equation.
(c) EITHER
Describe how von Koch curves can be used to illustrate the concept of fractal dimension. Show why they have infinite length.
OR
Define what is meant by the fractal dimension of a phase space attractor.
Describe how Lyapunov exponents can be used to determine the fractal
dimension of a strange attractor in a dissipative system.