English

Incompressible Navier-Stokes Equations: Example of no solution at $R^3$ and $t=0$

Fluid Dynamics 2016-08-18 v1

Abstract

We provide an example of a smooth, divergence-free u(x)=0\nabla \cdot \vec{u}(\vec{x})=0 velocity vector field u(x)\vec{u}(\vec{x}) for incompressible fluid occupying all of R3R^{3} space, and smooth vector field f(x,t)\vec{f}(\vec{x}, t) for which the Navier-Stokes equation for incompressible fluid does not have a solution for any position in space xR3\vec{x}\in R^{3} at t=0t=0. The velocity vector field ui(x)=2xh(i1)xh(i+1)(1+j=13xj2)2u_{i} (\vec{x})=2\frac{x_{h(i-1)} -x_{h(i+1)} }{\left(1+\sum _{j=1}^{3}x_{j}^{2} \right)^{2} } ; i={1,2,3}i=\{ 1,2,3\} where h(l)={l;1l31;l=43;l=0h(l)=\left\{\begin{array}{ccc} {l} & {;1\le l\le 3} & {} \\ {1} & {;l=4} & {} \\ {3} & {;l=0} & {} \end{array}\right. is smooth, divergence-free, continuously differentiable u(x)Cu(\vec{x})\in C^{\infty }, has bounded energy R3u2dx=π2\int _{R^{3} }\left|\vec{u}\right|^{2} dx=\pi ^{2}, zero velocity at coordinate origin, and velocity converges to zero for x\left|\vec{x}\right|\to \infty. The vector field f(x,t)=(0,0,11+t2(j=13xj)2)\vec{f}(\vec{x},t)=(0,0,\frac{1}{1+t^{2} (\sum _{j=1}^{3}x_{j} )^{2} )} is smooth, continuously differentiable f(x,t)Cf(\vec{x},t)\in C^{\infty }, converging to zero for x\left|\vec{x}\right|\to \infty. Applying u(x)\vec{u}(\vec{x}) and f(x,t)\vec{f}(\vec{x}, t) in the Navier-Stokes equation for incompressible fluid results with three mutually different solutions for pressure p(x,t)p(\vec{x}, t), one of which includes zero division with zero 00\frac{0}{0} term at t=0t=0, which is indeterminate for all positions xR3\vec{x} \in R^{3}.

Keywords

Cite

@article{arxiv.1608.04975,
  title  = {Incompressible Navier-Stokes Equations: Example of no solution at $R^3$ and $t=0$},
  author = {Dejan Kovacevic},
  journal= {arXiv preprint arXiv:1608.04975},
  year   = {2016}
}