## About lifespan of regular solutions of equations related to viscoelastic fluids.(English)Zbl 1007.76003

The authors consider the system of equations $$v_t +v\cdot\nabla v-\nu\Delta v=\mu _1 \nabla\cdot\tau,$$ $$\tau_t +v\cdot\nabla\tau +a\tau +Q(\tau,\nabla v)=\mu _2 D(v),$$ $$\text{div }v=0$$ describing flows of viscoelastic fluids. Here $$\tau$$ is the elastic part of stress tensor, and $$Q(\tau,\nabla v)=\tau W(v)-W(v)\tau -b[D(v)\tau +\tau D(v)],$$ $$2D(v)_{ij}=\partial _j v_i +\partial _i v_j ,$$ $$2W(v)_{ij}=\partial _j v_i -\partial _i v_j .$$ The constants $$\nu$$, $$\mu _i$$, $$a$$ and $$b$$ are assumed to be non-negative. The authors discuss Cauchy problem and $$x$$-periodic problem. A unique solvability theorem is proved for some maximal time interval $$(0,T)$$ under the necessary blow-up condition $$T<\infty \Longrightarrow\int\limits_0 ^T \frac{\mu_1 }{\nu\mu_2 }\|\tau\|_{\infty}^2 +\|\nabla v\|_{\infty}dt=\infty.$$ In two space dimensions, the necessary blow-up condition writes $$T<\infty \Longrightarrow\int\limits_0 ^T \|\tau\|_{\infty} +|b|\|\tau\|_{2}^2 dt=\infty.$$ Finally, with the use of Besov spaces, the authors prove a unique global solvability for small initial data.

### MSC:

 76A10 Viscoelastic fluids 35Q35 PDEs in connection with fluid mechanics
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