01398nas a2200121   4500008004100000245014300041210006900184260001000253520092300263100002301186700001901209856004801228       2018                        en  d00aCharacteristic boundary layers for mixed hyperbolic systems in one space dimension and applications to the Navier-Stokes and MHD equations0 aCharacteristic boundary layers for mixed hyperbolic systems in o  bSISSA3 aWe provide a detailed analysis of the boundary layers for mixed hyperbolic-parabolic systems in one space dimension and small amplitude regimes. As an application of our results, we describe the solution of the so-called boundary Riemann problem recovered as the zero viscosity limit of the physical viscous approximation. In particular, we tackle the so called doubly characteristic case, which is considerably more demanding from the technical viewpoint and occurs when the boundary is characteristic for both the
mixed hyperbolic-parabolic system and for the hyperbolic system obtained by neglecting the second order terms. Our analysis applies in particular to the compressible Navier-Stokes and MHD equations in Eulerian coordinates, with both positive and null conductivity. In these cases, the doubly characteristic case occurs when the velocity is close to 0. The analysis extends to non-conservative systems.1 aBianchini, Stefano1 aSpinolo, Laura  uhttp://preprints.sissa.it/handle/1963/3532500383nas a2200109   4500008004300000245007000043210006900113260001300182100002300195700001900218856003600237       2011                        en_Ud  00aInvariant manifolds for a singular ordinary differential equation0 aInvariant manifolds for a singular ordinary differential equatio  bElsevier1 aBianchini, Stefano1 aSpinolo, Laura  uhttp://hdl.handle.net/1963/255402193nas a2200109   4500008004300000245008700043210006900130520180600199100002302005700001902028856003602047       2009                        en_Ud  00aThe boundary Riemann solver coming from the real vanishing viscosity approximation0 aboundary Riemann solver coming from the real vanishing viscosity3 aWe study the limit of the hyperbolic-parabolic approximation $$ \\\\begin{array}{lll} v_t + \\\\tilde{A} ( v, \\\\, \\\\varepsilon v_x ) v_x = \\\\varepsilon \\\\tilde{B}(v ) v_{xx} \\\\qquad v \\\\in R^N\\\\\\\\ \\\\tilde \\\\beta (v (t, \\\\, 0)) =  \\\\bar g \\\\\\\\ v (0, \\\\, x) =  \\\\bar v_0. \\\\\\\\ \\\\end{array} \\\\right. $$\\nThe function $\\\\tilde \\\\beta$ is defined in such a way to guarantee that the initial boundary value problem is well posed even if $\\\\tilde \\\\beta$ is not invertible.\\nThe data $\\\\bar g$ and $\\\\bar v_0$ are constant. When $\\\\tilde B$ is invertible, the previous problem takes the simpler form $$ \\\\left\\\\{ \\\\begin{array}{lll} v_t + \\\\tilde{A} \\\\big( v, \\\\, \\\\varepsilon v_x \\\\big) v_x = \\\\varepsilon \\\\tilde{B}(v ) v_{xx} \\\\qquad v \\\\in \\\\mathbb{R}^N\\\\\\\\  v (t, \\\\, 0) \\\\equiv \\\\bar v_b \\\\\\\\ v (0, \\\\, x) \\\\equiv \\\\bar{v}_0. \\\\\\\\ \\\\end{array} \\\\right. $$\\nAgain, the data $\\\\bar v_b$ and $\\\\bar v_0$ are constant. The conservative case is included in the previous formulations. It is assumed convergence of the v, smallness of the total variation and other technical hypotheses and it is provided a complete characterization of the limit. The most interesting points are the following two. First, the boundary characteristic case is considered, i.e. one eigenvalue of $\\\\tilde A$ can be 0.\\n Second, as pointed out before we take into account the possibility that $\\\\tilde B$ is not invertible. To deal with this case, we take as hypotheses conditions that were introduced by Kawashima and Shizuta relying on physically meaningful examples. We also introduce a new condition of block linear degeneracy. We prove that, if it is not satisfied, then pathological behaviours may occur.1 aBianchini, Stefano1 aSpinolo, Laura  uhttp://hdl.handle.net/1963/183100337nas a2200097   4500008004300000245006000043210005800103100002300161700001900184856003600203       2009                        en_Ud  00aA connection between viscous profiles and singular ODEs0 aconnection between viscous profiles and singular ODEs1 aBianchini, Stefano1 aSpinolo, Laura  uhttp://hdl.handle.net/1963/255500382nas a2200097   4500008004300000245009400043210006900137100002300206700001900229856003600248       2008                        en_Ud  00aInvariant Manifolds for Viscous Profiles of a Class of Mixed Hyperbolic-Parabolic Systems0 aInvariant Manifolds for Viscous Profiles of a Class of Mixed Hyp1 aBianchini, Stefano1 aSpinolo, Laura  uhttp://hdl.handle.net/1963/3400