Let e0e\geq0 be locally integrable on a space-time cylinder in dimension n2n\geq2. An Euler subsolution with energy bound ee is a triple (v,S,q)(v,S,q), with vLloc2v\in L^2_{\rm loc}, SLloc1S\in L^1_{\rm loc} and , and qq a distribution, such that

tv+divS+q=0,divv=0,vvS2enI.\partial_t v+\operatorname{div}S+\nabla q=0,\qquad \operatorname{div}v=0,\qquad v\otimes v-S\leq\frac{2e}{n}I.

The equations use ; the inequality says that (2e/n)Ivv+S(2e/n)I-v\otimes v+S is almost everywhere. A smooth strict subsolution has smooth v,S,qv,S,q, continuous ee, and a positive definite gap everywhere.

The products are , the coefficients have the indicated , and the pressure is a . This formulation relaxes while keeping its constraints.

Recovering Euler

Taking the trace gives v2/2e|v|^2/2\leq e. If equality holds almost everywhere, the positive semidefinite gap has zero trace and is zero. Then S=vv(2e/n)IS=v\otimes v-(2e/n)I, and vv satisfies with pressure p=q2e/np=q-2e/n.

References