1. Answer the questions on the text.
A. In what context has the energy-momentum method also been used ?
B. What generalizes Hamiltonian structures found by Zakharov?
C. When is the system unstable?
D. Are there many formally unstable systems?
E. What situation is delicate to prove analytically?
2. What are the key words in the text?
3. Give a short summary of the text using the key words. Часть II Text 1. The Poincaré-Melnikov Method
The Forced Pendulum. To begin with a simple example, consider the equation of a forced pendulum:
Here
is a constant angular forcing frequency and
is
a small parameter. Systems of this or a similar nature arise in many
interesting situations. For example, a double planar pendulum and
other "executive toys" exhibit chaotic motion that is
analogous to the behavior of this equation; see Burov [1986] and
Shinbrot, Grebogi, Wisdom, and Yorke [1992].
For
= 0 (1.9.1) has the phase portrait of a simple pendulum (the same as
shown later in Figure 2.8.2a). For
small but nonzero, (1.9.1) possesses no analytic integrals of the
motion. In fact, it possesses transversal intersecting stable
and unstable manifolds (separatrices); that is, the Poincaré map Pto
: R2
→ R2
defined as the map that advance solutions by one period T
=
starting at time to possess transversal homoclinic points. This type
of dynamic behavior has several consequences, besides precluding the
existence of analytic integrals, that lead one to use the term
"chaotic." For example, (1.9.1) has infinitely many
periodic solutions of arbitrarily high period. Also, using the
shadowing lemma, one sees that given any bi-infinite sequence of
zeros and ones, there exists a corresponding solution of (1.9.1)
that successively crosses the plane
= 0 (the pendulum's vertically downward configuration) with
> 0
corresponding to a zero and
< 0
corresponding to a one. The origin of this chaos on an intuitive
level lies in the motion of the pendulum near its unperturbed
homoclinic orbit, the orbit that does one revolution in infinite
time. Near the top of its motion (where
)
small
nudges from the forcing term can cause the pendulum to fall to the
left or right in a temporally complex way.
The dynamical systems theory needed to justify the preceding statements is available in Smale [1967], Moser [1973], Guckenheimer and Holmes [1983], and Wiggins [1988, 1990]. Some key people responsible for the development of the basic theory are Poincaré, Birkhoff, Kolmogorov, Melnikov, Arnold, Smale, and Moser.
1. Are these statements true or false according to the text?
A. Here
is constant angular forcing frequency and
is a big parameter.
B. A double planar pendulum exhibits chaotic motion.
C.
small but nonzero possesses some analytic integrals of the motion.
D. The origin of the chaos on an intuitive level lies in the destruction of the pendulum near its unperturbed homoclinic orbit.
E. Some key people responsible for the development of the basic theory are Newton and Mozart.