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arXiv 2102.01654math.DSmath-phmath.MP
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内波台球桌和类似的桌子

Internal-wave billiards in trapezoids and similar tables

Marco Lenci, Claudio Bonanno, Giampaolo Cristadoro

摘要:

我们称内波台球为一个点粒子的动力系统,该点粒子在平面区域(桌子)内自由运动,并根据以下规则被其边界反射:反射是标准的菲涅耳反射,但假设任何碰撞点的边界要么是水平的,要么是垂直的(相对于代表重力的预定方向)。这些系统是封闭容器中内部重力波运动的点粒子近似,因此得名。对于一类类似于长方形拟阵的表,但其斜腿被一条向下的曲线所代替,我们证明了动力学只有三个渐近区域:(1)存在一个全局吸引子和一个全局排斥子,它们是周期的且可能重合;(2)存在一束周期轨迹,其边界(如果有的话)包括所有其他轨迹的吸引子和排斥子;(3)所有的轨迹都是稠密的(即系统是最小的)。此外,在突出的情况下,该表是一个实际的梯形,我们研究了在参数空间相对于三个政权的集合。我们特别证明了(1)的集合有正测度(给出了内波台球Arnol'd舌存在的严格证明),而(2)和(3)的集合是非空的,但测度为零。

英文摘要:

We call internal-wave billiard the dynamical system of a point particle that moves freely inside a planar domain (the table) and is reflected by its boundary according to this rule: reflections are standard Fresnel reflections but with the pretense that the boundary at any collision point is either horizontal or vertical (relative to a predetermined direction representing gravity). These systems are point particle approximations for the motion of internal gravity waves in closed containers, hence the name. For a class of tables similar to rectangular trapezoids, but with the slanted leg replaced by a general curve with downward concavity, we prove that the dynamics has only three asymptotic regimes: (1) there exist a global attractor and a global repellor, which are periodic and might coincide; (2) there exists a beam of periodic trajectories, whose boundary (if any) comprises an attractor and a repellor for all the other trajectories; (3) all trajectories are dense (that is, the system is minimal). Furthermore, in the prominent case where the table is an actual trapezoid, we study the sets in parameter space relative to the three regimes. We prove in particular that the set for (1) has positive measure (giving a rigorous proof of the existence of Arnol'd tongues for internal-wave billiards), whereas the sets for (2) and (3) are non-empty but have measure zero.

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