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arXiv 2111.04863math.NAcs.NAphysics.comp-phphysics.flu-dyn
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初值问题的动态Galerkin格式自适应解

Adaptive solution of initial value problems by a dynamical Galerkin scheme

Rodrigo M. Pereira, Natacha Nguyen van yen, Kai Schneider, Marie Farge

摘要:

研究了演化偏微分方程的动态Galerkin格式,其中投影算子随时间变化。当选择基函数的子集时,投影算子在时间上是不可微的,并且必须使用积分公式。我们分析了投影方程的解的存在性和唯一性,并证明了非光滑投影算子引入耗散,这一结果对偏微分方程的自适应离散化至关重要,例如,自适应小波方法对于Burgers方程,我们数值说明阈值的小波系数,从而改变投影空间,确实会引入能量耗散。我们讨论的后果,所谓的“伪自适应”的模拟,在傅立叶空间的时间演化和去混叠,而阈值进行小波空间。给出了一维无粘Burgers方程和二维及三维不可压Euler方程的数值算例。

英文摘要:

We study dynamical Galerkin schemes for evolutionary partial differential equations (PDEs), where the projection operator changes over time. When selecting a subset of basis functions, the projection operator is non-differentiable in time and an integral formulation has to be used. We analyze the projected equations with respect to existence and uniqueness of the solution and prove that non-smooth projection operators introduce dissipation, a result which is crucial for adaptive discretizations of PDEs, e.g., adaptive wavelet methods. For the Burgers equation we illustrate numerically that thresholding the wavelet coefficients, and thus changing the projection space, will indeed introduce dissipation of energy. We discuss consequences for the so-called `pseudo-adaptive' simulations, where time evolution and dealiasing are done in Fourier space, whilst thresholding is carried out in wavelet space. Numerical examples are given for the inviscid Burgers equation in 1D and the incompressible Euler equations in 2D and 3D.

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