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arXiv 2401.00844physics.flu-dyncs.NAmath.NA
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有限深度驻波的半解析理论与计算

The semi-analytic theory and computation of finite-depth standing water waves

Ahmad Abassi, Jon Wilkening

AI总结:

本文提出有限深度驻波的Stokes展开与递归算法,证明几乎处处小除数有界,并发现小除数激活次级驻波,Padé逼近与打靶法结果在大振幅下吻合。

摘要:

我们针对二维有限深度驻波提出了一种Stokes展开假设,并设计了一种递归算法来计算展开系数。我们在超级计算机上使用任意精度算术实现了该算法。Stokes展开引入了需要幂级数求指数的双曲项,我们利用Bell多项式高效地处理了这些项。尽管在可数的稠密流体深度集合上会发生精确共振,但我们证明了对于几乎所有的深度,递归中出现的除数被一个随波数缓慢衰减的函数从零界定。我们观察到小除数与不完全分岔之间存在直接联系。这些小除数被发现会激活次级驻波,这些驻波在主波之上以非均匀的空间和时间方式振荡,并且在每个分岔分支上具有不同的振幅和相位。我们使用打靶法计算了新的驻波族,并发现随着新的小除数进入递归,Stokes展开的Padé逼近在较大振幅下仍能收敛到打靶法的解。我们观察到Padé逼近的极点和零点紧密间隔,这表明分岔分支被分支切割所分隔。

英文摘要:

We propose a Stokes expansion ansatz for finite-depth standing water waves in two dimensions and devise a recursive algorithm to compute the expansion coefficients. We implement the algorithm on a supercomputer using arbitrary-precision arithmetic. The Stokes expansion introduces hyperbolic terms that require exponentiation of power series, which we handle efficiently using Bell polynomials. Although exact resonances occur at a countable dense set of fluid depths, we prove that for almost every depth, the divisors that arise in the recurrence are bounded away from zero by a slowly decaying function of the wave number. A direct connection between small divisors and imperfect bifurcations is observed. They are found to activate secondary standing waves that oscillate non-uniformly in space and time on top of the primary wave, with different amplitudes and phases on each bifurcation branch. We compute new families of standing waves using a shooting method and find that Padé approximants of the Stokes expansion continue to converge to the shooting method solutions at large amplitudes as new small divisors enter the recurrence. Closely spaced poles and zeros of the Padé approximants are observed, which suggests that the bifurcation branches are separated by branch cuts.

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