arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.14855math.AP
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如何定义时间分数阶相场方程的耗散保持能量

How to Define Dissipation-Preserving Energy for Time-Fractional Phase-Field Equations

Chaoyu Quan, Tao Tang, Jiang Yang

摘要:

对于满足耗散律的经典相场方程,存在一个定义明确的能量,即,能量相对于时间不增加。然而,如何将能量定义推广到时间分数阶相场方程,使得相应的耗散律仍然满足,目前还不清楚。在这项工作中,我们将试图解决这个问题的相场方程与Caputo时间分数阶导数,通过定义一个非局部能量的平均的经典能量与时间相关的权函数。由于控制方程具有非局部和非线性的特性,耗散分析具有挑战性。为了解决这个问题,我们提出了一个新的定理,判断一个对称函数的正定性,这是来自一个特殊的Cholesky分解。然后,证明了非局部能量在权函数的简单约束下是耗散的。在同样的框架下,时间分数阶相场模型的经典能量的时间分数阶导数总是非正的。

英文摘要:

There exists a well defined energy for classical phase-field equations under which the dissipation law is satisfied, i.e., the energy is non-increasing with respect to time. However, it is not clear how to extend the energy definition to time-fractional phase-field equations so that the corresponding dissipation law is still satisfied. In this work, we will try to settle this problem for phase-field equations with Caputo time-fractional derivative, by defining a nonlocal energy as an averaging of the classical energy with a time-dependent weight function. As the governing equation exhibits both nonlocal and nonlinear behavior, the dissipation analysis is challenging. To deal with this, we propose a new theorem on judging the positive definiteness of a symmetric function, that is derived from a special Cholesky decomposition. Then, the nonlocal energy is proved to be dissipative under a simple restriction of the weight function. Within the same framework, the time fractional derivative of classical energy for time-fractional phase-field models can be proved to be always nonpositive.

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