PERIODIC OSCILLATIONS IN THE RESTRICTED HIP-HOP 2N1-BODY PROBLEM ANDR ES RIVERA1 OSCAR PERDOMO2 NELSON CASTA NEDA2.

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PERIODIC OSCILLATIONS IN THE RESTRICTED HIP-HOP 2N+1-BODY
PROBLEM
ANDR´
ES RIVERA 1, OSCAR PERDOMO 2, NELSON CASTA ˜
NEDA 2.
Abstract. We prove the existence of periodic solutions of the restricted (2N+1)-body
problem when the 2N-primaries move on a periodic Hip-Hop solution and the massless body
moves on the line that contains the center of mass and is perpendicular to the base of the
antiprism formed by the 2N-primaries.
1. Introduction.
In a classical restricted (n+1)-body problem the motion of one body (that we call the plus
one body) with mass m00 is affected only by the gravitational force of the other n-bodies
and does not perturb the motion of the n-bodies, which interact only with gravitational
forces. When the n-bodies have the same mass m>0 they are usually called primaries. This
mathematical model can be used to describe motions of comets, spacecraft and asteroids (see
[17] and the references therein). In the literature, there is a remarkable example of a restricted
3-body problem called the Sitnikov problem (proposed in 1960 by K.A. Sitnikov [18]). Here
the two primaries move in elliptic orbits lying in the xy-plane around the center of mass
(barycenter) as solutions of the 2-body problem. Finally, the plus one body moves along the
z-axis passing through the barycenter of the primaries. The Sitnikov problem deals with the
orbits of the plus one body. Since its formulation, this particular 3-body problem has been
treated in several papers [1,4,6,7,9,10,12,16,18] from both, numerical and analytical point
of view. Concerning the existence of periodic motions for the plus one body in the Sitnikov
problem, we refer to [10,12] where the authors prove the existence of families of symmetric
periodic orbits which depend continuously on the eccentricity of the primaries, by means of
the Leray-Schauder continuation method. Using the same technique, in [15] the author proves
that these families also exist in a particular generalization of the Sitnikov problem where the
number of primaries is n2. More precisely, in [15] the authors find the existence of periodic
motions in a restricted (n+1)-body problem where each primary body is at the vertex of a
regular n-gon and moves on elliptic orbits lying in the xy-plane around their barycenter and
the plus one body moves on the z-axis. The link https://youtu.be/RjlZpqDFsDM leads to
a video showing some of these periodic motions when the plus one body remains still at the
2010 Mathematics Subject Classification. 70F10, 37C27, 34A12.
Key words and phrases. N-body problem, periodic orbits, hip-hop solutions, implicit function theorem,
bifurcations.
1
arXiv:2210.01740v1 [math.DS] 4 Oct 2022
2 ANDR´
ES RIVERA, OSCAR PERDOMO, NELSON CASTA ˜
NEDA
origin (the center of mass). Moreover, when the eccentricity of orbits is zero, all the primaries
have the same circular orbit, i.e., the primaries perform a choreography.
In this paper we are considering also n-primaries but this time they do not move on a plane,
they are periodic Hip-hop solutions of the n-body problem. The existence of these solutions
were studied in [2,3] and more recently, in [13] we found the existence of families of periodic
Hip-hop solutions for a 2N-body problem. A hip-hop solution satisfies i)All the bodies have
the same mass. ii)at every instante of time t,Nof the bodies are at the vertices of a regular
N-gon contained in a plane Π1(t)and the other N-bodies are at the vertices of a second regular
N-gon contained in a plane Π2(t)which is obtained from the first N-gon by the reflection in
a fixed plane Π0followed by a rotation of πNradians around a fixed-line l0perpendicular
to the three planes and passing through the center of the two N-gons. When Π1(t)Π2(t),
the 2N-bodies are at the vertices of an antiprism that degenerates to a regular 2N-gon when
Π1(t)=Π2(t). At any time t, the oriented distance from the plane Π0to Π1(t)is given by a
function d(t)and the distance of any primary body to the line l0is given by a function r(t).
Without loss of generality, it is possible to assume that the line l0is the z-axis and the plane
Π0is the xy-plane. Let us explain in more detail the new type of restricted (2N+1)-body
problem which can be thought of as a sort of Sitnikov problem.
The restricted hip-hop body problem. Consider 2N-bodies with equal mass (called
primaries) located at any time at the vertices of a regular antiprism, moving as a periodic
Hip-hop solution of a 2N-body problem and a massless body moving on the straight line
orthogonal to the two regular N-gons that form the antiprism and passes through their center
of mass. The restricted hip-hop body problem will consist in describing the motion of the
massless body.
Figure 1. Restricted hip-hop body problem with four primaries. At any time,
the primaries are placed at the vertices of a regular 4-gonal antiprism and the
plus one body moves on the line orthogonal to the two 2-gons that are the base
face of the antiprism.
HIP-HOP SOLUTIONS 3
The main objective of this paper is to analytically prove the existence of symmetric periodic
orbits for the restricted antiprism body problem. To this end, the paper is divided as follows.
In Section 2we deduce the equation of motion for the 2N-primaries and the plus one body. In
Section 3, we apply the same techniques found in [13] by reducing the problem of the existence
of periodic solutions to the problem of solving a system of three equations in four variables.
The main results of the paper are contained in Section 4and some numerical periodic solutions
of the restricted hip-hop problem for 6 primaries are given in Section 5.
2. The differential equations
We will follow the same set up as in the references [13] and [2]. To describe the motion of the
primaries we consider Q1, Q2,...,Q2Nbodies with equal mass m>0, located on the vertices
of a regular anti-prism. If rj(t)is the position of the body Qj, j =1,...,2Nat each instant t
then
rj(t)=Rj1r1(t), j =1,...,2N,
where r1(t)=(r(t)cos(θ(t)), r(t)sin(θ(t)), d(t))and Ris a rotation/reflection matrix given
by
R=
cos(π
N)sin(π
N)0
sin(π
N)cos(π
N)0
0 0 1
.
We have that the functions r(t),θ(t)and d(t)that define r1(t)satisfy the equations
¨r=f(r, d),
¨
d=g(r, d),
˙
θ=ar2,
(1)
where ais the angular momentum of the system and
f(r, d)=a2
r32rm
2N1
k=1
sin2(kπ2N)
4r2sin2(kπ2N)+((1)k1)2d23/2,
g(r, d)=m d
2
2N1
k=1((1)k1)2
4r2sin2(kπ2N)+((1)k1)2d23/2.
Now that we have a description of the 2Nprimaries, we describe the motion of the plus
one body. Since this body moves on the z-axis, then its motion is describedby the map
r2N+1(t)=(0,0, z(t)). Notice that the equation of the primaries do not change because of our
assumption, also we notice in this model the mass of the plus one body is irrelevant because
it cancels out from the equations.
A direct computation shows that z(t)satisfies the following differential equation.
¨z=h(r, d, z)=mN zd
((zd)2+r2)3/2+z+d
((z+d)2+r2)3/2(2)
摘要:

PERIODICOSCILLATIONSINTHERESTRICTEDHIP-HOP2N1-BODYPROBLEMANDRESRIVERA1,OSCARPERDOMO2,NELSONCASTA~NEDA2.Abstract.Weprovetheexistenceofperiodicsolutionsoftherestrictedˆ2N1-bodyproblemwhenthe2N-primariesmoveonaperiodicHip-Hopsolutionandthemasslessbodymovesonthelinethatcontainsthecenterofmassandispe...

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