Skip to main content
Erschienen in: Foundations of Computational Mathematics 4/2020

05.08.2019

Convergence of Finite Volume Schemes for the Euler Equations via Dissipative Measure-Valued Solutions

verfasst von: Eduard Feireisl, Mária Lukáčová-Medvid’ová, Hana Mizerová

Erschienen in: Foundations of Computational Mathematics | Ausgabe 4/2020

Einloggen

Aktivieren Sie unsere intelligente Suche, um passende Fachinhalte oder Patente zu finden.

search-config
loading …

Abstract

The Cauchy problem for the complete Euler system is in general ill-posed in the class of admissible (entropy producing) weak solutions. This suggests that there might be sequences of approximate solutions that develop fine-scale oscillations. Accordingly, the concept of measure-valued solution that captures possible oscillations is more suitable for analysis. We study the convergence of a class of entropy stable finite volume schemes for the barotropic and complete compressible Euler equations in the multidimensional case. We establish suitable stability and consistency estimates and show that the Young measure generated by numerical solutions represents a dissipative measure-valued solution of the Euler system. Here dissipative means that a suitable form of the second law of thermodynamics is incorporated in the definition of the measure-valued solutions. In particular, using the recently established weak-strong uniqueness principle, we show that the numerical solutions converge pointwise to the regular solution of the limit systems at least on the lifespan of the latter.

Sie haben noch keine Lizenz? Dann Informieren Sie sich jetzt über unsere Produkte:

Springer Professional "Wirtschaft+Technik"

Online-Abonnement

Mit Springer Professional "Wirtschaft+Technik" erhalten Sie Zugriff auf:

  • über 102.000 Bücher
  • über 537 Zeitschriften

aus folgenden Fachgebieten:

  • Automobil + Motoren
  • Bauwesen + Immobilien
  • Business IT + Informatik
  • Elektrotechnik + Elektronik
  • Energie + Nachhaltigkeit
  • Finance + Banking
  • Management + Führung
  • Marketing + Vertrieb
  • Maschinenbau + Werkstoffe
  • Versicherung + Risiko

Jetzt Wissensvorsprung sichern!

Springer Professional "Technik"

Online-Abonnement

Mit Springer Professional "Technik" erhalten Sie Zugriff auf:

  • über 67.000 Bücher
  • über 390 Zeitschriften

aus folgenden Fachgebieten:

  • Automobil + Motoren
  • Bauwesen + Immobilien
  • Business IT + Informatik
  • Elektrotechnik + Elektronik
  • Energie + Nachhaltigkeit
  • Maschinenbau + Werkstoffe




 

Jetzt Wissensvorsprung sichern!

Springer Professional "Wirtschaft"

Online-Abonnement

Mit Springer Professional "Wirtschaft" erhalten Sie Zugriff auf:

  • über 67.000 Bücher
  • über 340 Zeitschriften

aus folgenden Fachgebieten:

  • Bauwesen + Immobilien
  • Business IT + Informatik
  • Finance + Banking
  • Management + Führung
  • Marketing + Vertrieb
  • Versicherung + Risiko




Jetzt Wissensvorsprung sichern!

Literatur
1.
Zurück zum Zitat E. Audussse, F. Bouchut, M.-O. Bristeau, and J. Sainte-Marie. Kinetic entropy inequality and hydrostatic reconstruction scheme for the Saint-Venant system. Math. Comp.85 (2016), 2815–2837.MathSciNetMATH E. Audussse, F. Bouchut, M.-O. Bristeau, and J. Sainte-Marie. Kinetic entropy inequality and hydrostatic reconstruction scheme for the Saint-Venant system. Math. Comp.85 (2016), 2815–2837.MathSciNetMATH
2.
Zurück zum Zitat J. J. Alibert, and G. Bouchitté. Non-uniform integrability and generalized Young measures. J. Convex Anal.4(1) (1997), 129–147.MathSciNetMATH J. J. Alibert, and G. Bouchitté. Non-uniform integrability and generalized Young measures. J. Convex Anal.4(1) (1997), 129–147.MathSciNetMATH
3.
Zurück zum Zitat J.M. Ball. A version of the fundamental theorem for Young measures. In Lect. Notes in Physics 344, Springer-Verlag, 1989, pp. 207–215. J.M. Ball. A version of the fundamental theorem for Young measures. In Lect. Notes in Physics 344, Springer-Verlag, 1989, pp. 207–215.
4.
Zurück zum Zitat Y. Brenier, C. De Lellis, and L. Székelihidi, Jr.. Weak-strong uniqueness for measure-valued solutions Comm. Math. Phys.305(2) (2011), 351–361.MathSciNetMATH Y. Brenier, C. De Lellis, and L. Székelihidi, Jr.. Weak-strong uniqueness for measure-valued solutions Comm. Math. Phys.305(2) (2011), 351–361.MathSciNetMATH
5.
Zurück zum Zitat A. Bressan, G. Crasta, and B. Piccoli. Well-posedness of the Cauchy problem for $n \times n$ systems of conservation laws. Memoirs of the AMS146(694) (2000). A. Bressan, G. Crasta, and B. Piccoli. Well-posedness of the Cauchy problem for $n \times n$ systems of conservation laws. Memoirs of the AMS146(694) (2000).
6.
Zurück zum Zitat A. Bressan. Uniqueness and stability for one dimensional hyperbolic systems of conservation laws. In XIIIth International Congress on Mathematical Physics (London, 2000), Int. Press, Boston, MA, 2001, pp. 311-317. A. Bressan. Uniqueness and stability for one dimensional hyperbolic systems of conservation laws. In XIIIth International Congress on Mathematical Physics (London, 2000), Int. Press, Boston, MA, 2001, pp. 311-317.
7.
Zurück zum Zitat F. Berthelin, and F. Bouchut. Relaxation to isentropic gas dynamics for a BGK system with single kinetic entropy. Meth. Appl. Anal.9 (2002), 313–327.MathSciNetMATH F. Berthelin, and F. Bouchut. Relaxation to isentropic gas dynamics for a BGK system with single kinetic entropy. Meth. Appl. Anal.9 (2002), 313–327.MathSciNetMATH
8.
Zurück zum Zitat F. Bouchut. Entropy satisfying flux vector splittings and kinetic BGK models. Numer. Math.94 (2003), 623–672.MathSciNetMATH F. Bouchut. Entropy satisfying flux vector splittings and kinetic BGK models. Numer. Math.94 (2003), 623–672.MathSciNetMATH
10.
Zurück zum Zitat F. Berthelin. Convergence of flux vector splitting schemes with single entropy inequality for hyperbolic systems of conservation laws. Numer. Math.99 (2005), 585–604.MathSciNetMATH F. Berthelin. Convergence of flux vector splitting schemes with single entropy inequality for hyperbolic systems of conservation laws. Numer. Math.99 (2005), 585–604.MathSciNetMATH
11.
Zurück zum Zitat Y. Brenier, C. De Lellis, and L. Székelyhidi, Jr.. Weak-strong uniqueness for measure-valued solutions. Commun. Math. Phys.305(2) (2011), 351–361.MathSciNetMATH Y. Brenier, C. De Lellis, and L. Székelyhidi, Jr.. Weak-strong uniqueness for measure-valued solutions. Commun. Math. Phys.305(2) (2011), 351–361.MathSciNetMATH
12.
Zurück zum Zitat J. Březina, and E. Feireisl. Measure-valued solutions to the complete Euler system. J. Math. Soc. Jpn.70(4) (2018), 1227–1245.MathSciNetMATH J. Březina, and E. Feireisl. Measure-valued solutions to the complete Euler system. J. Math. Soc. Jpn.70(4) (2018), 1227–1245.MathSciNetMATH
13.
Zurück zum Zitat J. Březina, and E. Feireisl. Maximal dissipation principle for the complete Euler system. Preprint arXiv:1712.04761, 2018. J. Březina, and E. Feireisl. Maximal dissipation principle for the complete Euler system. Preprint arXiv:1712.04761, 2018.
14.
Zurück zum Zitat E. Chiodaroli, C. De Lellis, and O. Kreml. Global ill-posedness of the isentropic system of gas dynamics. Comm. Pure Appl. Math.68(7) (2015), 1157–1190.MathSciNetMATH E. Chiodaroli, C. De Lellis, and O. Kreml. Global ill-posedness of the isentropic system of gas dynamics. Comm. Pure Appl. Math.68(7) (2015), 1157–1190.MathSciNetMATH
15.
Zurück zum Zitat C. Christoforou, M. Galanopoulou, and A.E. Tzavaras. A symmetrizable extension of polyconvex thermoelasticity and applications to zero-viscosity limits and weak-strong uniqueness. Commun. Part. Diff. Eq.43(7) (2018), 1019–1050.MathSciNetMATH C. Christoforou, M. Galanopoulou, and A.E. Tzavaras. A symmetrizable extension of polyconvex thermoelasticity and applications to zero-viscosity limits and weak-strong uniqueness. Commun. Part. Diff. Eq.43(7) (2018), 1019–1050.MathSciNetMATH
16.
Zurück zum Zitat F. Coquel, and P. LeFloch. An entropy satisfying MUSCL scheme for systems of conservation laws. Numer. Math.74 (1996), 1–33.MathSciNetMATH F. Coquel, and P. LeFloch. An entropy satisfying MUSCL scheme for systems of conservation laws. Numer. Math.74 (1996), 1–33.MathSciNetMATH
17.
Zurück zum Zitat C. M. Dafermos. The second law of thermodynamics and stability. Arch. Rational Mech. Anal.94 (1979), 373–389.MathSciNetMATH C. M. Dafermos. The second law of thermodynamics and stability. Arch. Rational Mech. Anal.94 (1979), 373–389.MathSciNetMATH
18.
Zurück zum Zitat C. M. Dafermos. Hyperbolic Conservation Laws in Continuum Physics. Springer-Verlag, New York, 2000.MATH C. M. Dafermos. Hyperbolic Conservation Laws in Continuum Physics. Springer-Verlag, New York, 2000.MATH
19.
Zurück zum Zitat C. De Lellis, and L. Székelyhidi, Jr.. The Euler equations as a differential inclusion. Ann. of Math.170(2) (2009), 1417–1436.MathSciNetMATH C. De Lellis, and L. Székelyhidi, Jr.. The Euler equations as a differential inclusion. Ann. of Math.170(2) (2009), 1417–1436.MathSciNetMATH
20.
Zurück zum Zitat C. De Lellis, and L. Székelyhidi, Jr.. On admissibility criteria for weak solutions of the Euler equations. Arch. Ration. Mech. Anal.195(1) (2010), 225–260.MathSciNetMATH C. De Lellis, and L. Székelyhidi, Jr.. On admissibility criteria for weak solutions of the Euler equations. Arch. Ration. Mech. Anal.195(1) (2010), 225–260.MathSciNetMATH
21.
Zurück zum Zitat S. Demoulini, D. M. A. Stuart, and A. E. Tzavaras. Weak-strong uniqueness of dissipative measure-valued solutions for polyconvex elastodynamics. Arch. Ration. Mech. Anal.205(3) (2012), 927–961.MathSciNetMATH S. Demoulini, D. M. A. Stuart, and A. E. Tzavaras. Weak-strong uniqueness of dissipative measure-valued solutions for polyconvex elastodynamics. Arch. Ration. Mech. Anal.205(3) (2012), 927–961.MathSciNetMATH
22.
Zurück zum Zitat R. DiPerna. Uniqueness of solutions to hyperbolic conservation laws. Indiana Univ. Math. J.28 (1979), 137–188.MathSciNetMATH R. DiPerna. Uniqueness of solutions to hyperbolic conservation laws. Indiana Univ. Math. J.28 (1979), 137–188.MathSciNetMATH
23.
Zurück zum Zitat R. DiPerna. Convergence of approximate solutions to conservation laws. Arch. Ration. Mech. Anal.82 (1983), 27–70.MathSciNetMATH R. DiPerna. Convergence of approximate solutions to conservation laws. Arch. Ration. Mech. Anal.82 (1983), 27–70.MathSciNetMATH
24.
Zurück zum Zitat R. DiPerna. Measure valued solutions to conservation laws. Arch. Ration. Mech. Anal.88(3) (1985), 223–270.MathSciNetMATH R. DiPerna. Measure valued solutions to conservation laws. Arch. Ration. Mech. Anal.88(3) (1985), 223–270.MathSciNetMATH
25.
Zurück zum Zitat R. DiPerna, and A. Majda. Oscillations and concentrations in weak solutions of the incompressible fluid equations. Commun. Math. Phys.108(4) (1987), 667–689.MathSciNetMATH R. DiPerna, and A. Majda. Oscillations and concentrations in weak solutions of the incompressible fluid equations. Commun. Math. Phys.108(4) (1987), 667–689.MathSciNetMATH
26.
Zurück zum Zitat E. Feireisl, P. Gwiazda, A. Świerczewska-Gwiazda, and E. Wiedemann. Dissipative measure-valued solutions to the compressible Navier–Stokes system. Calc. Var. Partial Differential Equations 55(6) (2016), 55–141.MathSciNetMATH E. Feireisl, P. Gwiazda, A. Świerczewska-Gwiazda, and E. Wiedemann. Dissipative measure-valued solutions to the compressible Navier–Stokes system. Calc. Var. Partial Differential Equations 55(6) (2016), 55–141.MathSciNetMATH
27.
Zurück zum Zitat E. Feireisl, and M. Lukáčová-Medvid’ová. Convergence of a mixed finite element finite volume scheme for the isentropic Navier-Stokes system via dissipative measure-valued solutions, Found. Comput. Math.18(3) (2018), 703–730.MathSciNetMATH E. Feireisl, and M. Lukáčová-Medvid’ová. Convergence of a mixed finite element finite volume scheme for the isentropic Navier-Stokes system via dissipative measure-valued solutions, Found. Comput. Math.18(3) (2018), 703–730.MathSciNetMATH
28.
Zurück zum Zitat E. Feireisl, C. Klingenberg, O. Kreml, and S. Markfelder. On oscillatory solutions to the complete Euler system. Preprint arXiv:1710.10918, 2017. E. Feireisl, C. Klingenberg, O. Kreml, and S. Markfelder. On oscillatory solutions to the complete Euler system. Preprint arXiv:1710.10918, 2017.
29.
Zurück zum Zitat M. Feistauer. Mathematical Methods in Fluid Dynamics. Pitman Monographs and Surveys in Pure and Applied Mathematics Series 67, Longman Scientific & Technical, Harlow, 1993. M. Feistauer. Mathematical Methods in Fluid Dynamics. Pitman Monographs and Surveys in Pure and Applied Mathematics Series 67, Longman Scientific & Technical, Harlow, 1993.
30.
Zurück zum Zitat M. Feistauer, J. Felcman, and I. Straškraba. Mathematical and Computational Methods for Compressible Flow. Clarendon Press, Oxford, 2003.MATH M. Feistauer, J. Felcman, and I. Straškraba. Mathematical and Computational Methods for Compressible Flow. Clarendon Press, Oxford, 2003.MATH
31.
Zurück zum Zitat U. Fjordholm. High-order accurate entropy stable numerical schemes for hyperbolic conservation laws. ETH Zürich dissertation Nr. 21025, 2013. U. Fjordholm. High-order accurate entropy stable numerical schemes for hyperbolic conservation laws. ETH Zürich dissertation Nr. 21025, 2013.
32.
Zurück zum Zitat U. Fjordholm, S. Mishra, and E. Tadmor. On the computation of measure-valued solutions. Acta Numer.25 (2016), 567–679.MathSciNetMATH U. Fjordholm, S. Mishra, and E. Tadmor. On the computation of measure-valued solutions. Acta Numer.25 (2016), 567–679.MathSciNetMATH
33.
Zurück zum Zitat U. Fjordholm, S. Mishra, and E. Tadmor. Arbitrary order accurate essentially non-oscillatory entropy stable schemes for systems of conservation laws. SIAM J. Num. Anal.50(2) (2012), 544–573.MATH U. Fjordholm, S. Mishra, and E. Tadmor. Arbitrary order accurate essentially non-oscillatory entropy stable schemes for systems of conservation laws. SIAM J. Num. Anal.50(2) (2012), 544–573.MATH
34.
Zurück zum Zitat U. Fjordholm, R. Käppeli, S. Mishra, and E. Tadmor. Construction of approximate entropy measure-valued solutions for hyperbolic systems of conservation laws. Found. Comput. Math.17 (2017), 763–827.MathSciNetMATH U. Fjordholm, R. Käppeli, S. Mishra, and E. Tadmor. Construction of approximate entropy measure-valued solutions for hyperbolic systems of conservation laws. Found. Comput. Math.17 (2017), 763–827.MathSciNetMATH
35.
Zurück zum Zitat J. Glimm. Solutions in the large for nonlinear hyperbolic systems of equations. Comm. Pure Appl. Math.18 (1965), 697–715.MathSciNetMATH J. Glimm. Solutions in the large for nonlinear hyperbolic systems of equations. Comm. Pure Appl. Math.18 (1965), 697–715.MathSciNetMATH
36.
Zurück zum Zitat E. Godlewski, and P.-A. Raviart. Numerical Approximation of Hyperbolic Systems of Conservation Laws. Springer, New York, 1996.MATH E. Godlewski, and P.-A. Raviart. Numerical Approximation of Hyperbolic Systems of Conservation Laws. Springer, New York, 1996.MATH
37.
Zurück zum Zitat P. Gwiazda, A. Świerczewska-Gwiazda, and E. Wiedemann. Weak-strong uniqueness for measure-valued solutions of some compressible fluid models. Nonlinearity28(11) (2015), 3873–3890.MathSciNetMATH P. Gwiazda, A. Świerczewska-Gwiazda, and E. Wiedemann. Weak-strong uniqueness for measure-valued solutions of some compressible fluid models. Nonlinearity28(11) (2015), 3873–3890.MathSciNetMATH
38.
Zurück zum Zitat A. Harten. On the symmetric form of systems of conservation laws with entropy. J. Comput. Phys.49 (1983), 151–164.MathSciNetMATH A. Harten. On the symmetric form of systems of conservation laws with entropy. J. Comput. Phys.49 (1983), 151–164.MathSciNetMATH
39.
Zurück zum Zitat V. Jovanović, and Ch. Rohde. Error estimates for finite volume approximations of classical solutions for nonlinear systems of hyperbolic balance laws. SIAM J. Numer. Anal.43(6) (2006), 2423–2449.MathSciNetMATH V. Jovanović, and Ch. Rohde. Error estimates for finite volume approximations of classical solutions for nonlinear systems of hyperbolic balance laws. SIAM J. Numer. Anal.43(6) (2006), 2423–2449.MathSciNetMATH
40.
Zurück zum Zitat S. N. Kruzkhov. First order quasilinear equations in several independent variables. USSR Math. Sbornik10(2) (1970), 217–243. S. N. Kruzkhov. First order quasilinear equations in several independent variables. USSR Math. Sbornik10(2) (1970), 217–243.
41.
Zurück zum Zitat D. Kröner. Numerical Schemes for Conservation Laws. John Wiley, Chichester, 1997.MATH D. Kröner. Numerical Schemes for Conservation Laws. John Wiley, Chichester, 1997.MATH
42.
Zurück zum Zitat D. Kröner,and W. M. Zajaczkowski. Measure-valued solutions of the Euler equations for ideal compressible polytropic fluids. Math. Methods Appl. Sci.19(3) (1996), 235–252.MathSciNetMATH D. Kröner,and W. M. Zajaczkowski. Measure-valued solutions of the Euler equations for ideal compressible polytropic fluids. Math. Methods Appl. Sci.19(3) (1996), 235–252.MathSciNetMATH
43.
Zurück zum Zitat P. LeFloch, J.M. Mercier, and C. Rohde. Fully discrete, entropy conservative schemes of arbitrary order. SIAM J. Numer. Anal.40 (2002), 1968–1992.MathSciNetMATH P. LeFloch, J.M. Mercier, and C. Rohde. Fully discrete, entropy conservative schemes of arbitrary order. SIAM J. Numer. Anal.40 (2002), 1968–1992.MathSciNetMATH
44.
Zurück zum Zitat R. LeVeque. Finite Volume Methods for Hyperbolic Problems. Cambridge University Press, Texts in Applied Mathematics, 2002. R. LeVeque. Finite Volume Methods for Hyperbolic Problems. Cambridge University Press, Texts in Applied Mathematics, 2002.
45.
Zurück zum Zitat P.-L. Lions. Mathematical Topics in Fluid Mechanics, Vol. 1. Incompressible models. Oxford Lecture Series in Mathematics and its Applications, Oxford University Press, 1996. P.-L. Lions. Mathematical Topics in Fluid Mechanics, Vol. 1. Incompressible models. Oxford Lecture Series in Mathematics and its Applications, Oxford University Press, 1996.
46.
Zurück zum Zitat A. Mielke. Flow properties for Young-measure solutions of semilinear hyperbolic problems. Proc. R. Soc. Edin. A-MA 129(1) (1999), 85–123.MathSciNetMATH A. Mielke. Flow properties for Young-measure solutions of semilinear hyperbolic problems. Proc. R. Soc. Edin. A-MA 129(1) (1999), 85–123.MathSciNetMATH
47.
Zurück zum Zitat P. Pedregal. Parametrized Measures and Variational Principles. Birkhäuser, Basel, 1997.MATH P. Pedregal. Parametrized Measures and Variational Principles. Birkhäuser, Basel, 1997.MATH
48.
Zurück zum Zitat B. Perthame, and C.-W. Shu. On positivity preserving finite volume schemes for Euler equations. Numer. Math.73 (1996), 119–130.MathSciNetMATH B. Perthame, and C.-W. Shu. On positivity preserving finite volume schemes for Euler equations. Numer. Math.73 (1996), 119–130.MathSciNetMATH
49.
Zurück zum Zitat S. Schochet. Examples of measure-valued solutions. Commun. Part. Diff. Eq.14(5) (1989), 545–575.MathSciNetMATH S. Schochet. Examples of measure-valued solutions. Commun. Part. Diff. Eq.14(5) (1989), 545–575.MathSciNetMATH
50.
Zurück zum Zitat D. Serre. Systems of Conservation Laws, 1: Hyperbolicity, Entropies, Shock Waves (English translation). Cambridge University Press, Cambridge, 1999. D. Serre. Systems of Conservation Laws, 1: Hyperbolicity, Entropies, Shock Waves (English translation). Cambridge University Press, Cambridge, 1999.
51.
Zurück zum Zitat L. Székelyhidi, Jr., and E. Wiedemann. Young measures generated by ideal incompressible fluid flows. Arch. Rational Mech. Anal.206 (2012), 333–366.MathSciNetMATH L. Székelyhidi, Jr., and E. Wiedemann. Young measures generated by ideal incompressible fluid flows. Arch. Rational Mech. Anal.206 (2012), 333–366.MathSciNetMATH
52.
Zurück zum Zitat E. Tadmor. The numerical viscosity of entropy stable schemes for systems of conservation laws. Math. Comp.49(179) (1987), 91–103.MathSciNetMATH E. Tadmor. The numerical viscosity of entropy stable schemes for systems of conservation laws. Math. Comp.49(179) (1987), 91–103.MathSciNetMATH
53.
Zurück zum Zitat E. Tadmor. Entropy stability theory for difference approximations of nonlinear conservation laws and related time dependent problems. Acta Numer.12 (2003), 451–512.MathSciNetMATH E. Tadmor. Entropy stability theory for difference approximations of nonlinear conservation laws and related time dependent problems. Acta Numer.12 (2003), 451–512.MathSciNetMATH
54.
Zurück zum Zitat E. Tadmor. Minimum entropy principle in the gas dynamic equations Appl. Num. Math.2 (1986), 211–219.MathSciNetMATH E. Tadmor. Minimum entropy principle in the gas dynamic equations Appl. Num. Math.2 (1986), 211–219.MathSciNetMATH
55.
Zurück zum Zitat E. Wiedemann. Weak-strong uniqueness in fluid dynamics. Partial differential equations in fluid mechanics, 289–326, London Math. Soc. Lecture Note Ser. 452, Cambridge Univ. Press, 2018. E. Wiedemann. Weak-strong uniqueness in fluid dynamics. Partial differential equations in fluid mechanics, 289–326, London Math. Soc. Lecture Note Ser. 452, Cambridge Univ. Press, 2018.
Metadaten
Titel
Convergence of Finite Volume Schemes for the Euler Equations via Dissipative Measure-Valued Solutions
verfasst von
Eduard Feireisl
Mária Lukáčová-Medvid’ová
Hana Mizerová
Publikationsdatum
05.08.2019
Verlag
Springer US
Erschienen in
Foundations of Computational Mathematics / Ausgabe 4/2020
Print ISSN: 1615-3375
Elektronische ISSN: 1615-3383
DOI
https://doi.org/10.1007/s10208-019-09433-z

Weitere Artikel der Ausgabe 4/2020

Foundations of Computational Mathematics 4/2020 Zur Ausgabe