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arXiv 1701.02097math.AP
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不同尺度下非线性声学的多谐分析

Multiharmonic analysis for nonlinear acoustics with different scales

Anastasia Thoens-Zueva, Kersten Schmidt, Adrien Semin

摘要:

没有平均流动和热通量的声波传播可以通过可压缩非线性斯托克斯方程根据速度和压力来描述,其中边界层由于粘性而出现在壁处,并且出现频率相互作用,由于非线性平流而产生处于激发频率$ω$的高次谐波的$\textit{i.e.}$声音。我们使用的多谐分析,以获得小的声音振幅和小的粘度都为$\varepsilon^2$阶的渐近展开,其中速度和压力场被分离成远场和校正近场靠近墙壁和到$ω$的倍数的贡献。基于渐近展开,我们提出了$0$、$1$和$2$阶的压力或速度的近似模型,其中阻抗边界条件包括粘性边界层的影响,频率$0$和$2\cdotω$的贡献非线性地依赖于频率$ω$的近似。在时域中的Navier-斯托克斯方程,这是必须解决的数值网格自适应细化到壁面边界和显式格式需要使用非常小的时间步长,不同的是,近似模型可以在频域中的宏观网格上求解。通过数值实验,与时域参考解比较,研究了不同阶次近似模型的精度。

英文摘要:

The acoustic wave-propagation without mean flow and heat flux can be described in terms of velocity and pressure by the compressible nonlinear Navier-Stokes equations, where boundary layers appear at walls due to the viscosity and a frequency interaction appears, $\textit{i.e.}$ sound at higher harmonics of the excited frequency $ω$ is generated due to nonlinear advection. We use the multiharmonic analysis to derive asymptotic expansions for small sound amplitudes and small viscosities both of order $\varepsilon^2$ in which velocity and pressure fields are separated into far field and correcting near field close to walls and into contributions to the multiples of $ω$. Based on the asymptotic expansion we present approximate models for either the pressure or the velocity for order $0$, $1$ and $2$, in which impedance boundary conditions include the effect of viscous boundary layers and contributions at frequencies $0$ and $2\cdotω$ depend nonlinearly on the approximation at frequency $ω$. In difference to the Navier-Stokes equations in time domain, which has to be resolved numerically with meshes adaptively refined towards the wall boundaries and explicit schemes require the use of very small time steps, the approximative models can be solved in frequency domain on macroscopic meshes. We studied the accuracy of the approximated models of different orders in numerical experiments comparing with reference solutions in time-domain.

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