On the stochastic quasi-linear symmetric hyperbolic system

We establish the existence and uniqueness of a local smooth solution to the Cauchy problem for a quasi-linear symmetric hyperbolic system with random noise in Rd. When the noise is multiplicative satisfying some nondegenerate conditions and the initial data are sufficiently small, we show that the solution exists globally in time in probability, i.e., the probability of global existence can be made arbitrarily close to one if the initial date are small accordingly.     

Almost global existence of solutions of quasi-linear hyperbolic equations

We consider the quasi-linear hyperbolic initial value problem (1) of the Introduction, and prove that for any T>0 there is a bound such that if the norm of the initial data is smaller than that bound then the solution of (1) exists on all of [0, T].     

Approximation of pseudodifferential operators in absorbing boundary conditions for hyperbolic equations

Summary Engquist and Majda [3] proposed a pseudodifferential operator as asymptotically valid absorbing boundary condition for hyperbolic equations. (In the case of the wave equation this boundary condition is valid at all frequencies.) Here, least-squares approximation of the symbol of the pseudodifferential operator is proposed to obtain differential operators as boundary conditions. It is shown that for the wave equation this approach leads to Kreiss well-posed initial boundary value problems and that the expectation of the reflected energy is lower than in the case of Taylor- and Padé-approximations [3, 4]. Numerical examples indicate that this method works even more effectively for hyperbolic systems. The least-squares approach may be used to generate the boundary conditions automatically.     

Boundary control of a hyperbolic system of heat equations

We consider a boundary value problem modeling heat propagation in a rod in the framework of a hyperbolic thermal conduction law. We compute the temperature mode (control) at one end of the rod, the temperature at the other end being given, so as to ensure the desired rod temperature at a given time.     

The behaviour of induced discontinuities behind a first order discontinuity wave for a quasi-linear hyperbolic system

Summary In the present paper we study the propagation into a constant state of the induced discontinuities associated with a first order discontinuity wave for a quasi-linear hyperbolic system. Making use of the theory of singular surfaces and the ray-theory, we derive and solve completely the equations which the induced discontinuity vector must obey along the rays associated with the wave front. So we determine the evolution law of and find that it depends non-linearly on the first order discontinuities and on the geometrical features of the wave front; thus the behaviour of the induced discontinuities is known once the evolution law of the first order discontinuity wave is obtained explicitly.

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Riassunto In questa nota studiamo la propagazione, in uno stato costante, delle discontinuità indotte associate a un'onda di discontinuità del primo ordine per un sistema iperbolico quasi-lineare. Adottando un'opportuna combinazione della teoria delle superfici singolari e delle teoria dei raggi, determiniamo in maniera completa il comportamento del vettore delle discontinuità indotte lungo i raggi associati al fronte d'onda. Troviamo che la legge di evoluzione di dipende non linearmente dalle discontinuità del primo ordine e dalle caratteristiche geometriche del fronte d'onda. L'andamento di è perciò noto una volta nota esplicitamente la legge di evoluzione delle discontinuità del primo ordine.

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Work performed under the auspices of C.N.R. (G.N.F.M.) and supported by M.P.I. of Italy.     

Approximation of a linear system of second-order differential equations

In a Hilbert space H we consider the approximation by systems $$\frac{{d^2 u_1 }}{{dt^2 }} = A_{11} u_1 + A_{12} u_2 + f_1 ,\varepsilon \frac{{d^2 u_2 }}{{dt^2 }} = A_{21} u_1 + A_{22} u_2 + f_2 ,\varepsilon > 0,$$ of the semievolutionary system obtained from (1) when ∈=0. Under certain conditions on the solutions of the Cauchy problem for system (1) and the existence of a bounded linear operator A ₂₂ ^?1 we establish the convergence of the solutions u^∈(∈ → 0) to a solution of the corresponding problem for system (1) with ∈=0. We also establish the uniform correctness of the Cauchy problem for the above system.     

Wellposedness in the Lipschitz class for a quasi-linear hyperbolic system arising from a model of the atmosphere including water phase transitions

In this paper wellposedness is proved for a diagonal quasilinear hyperbolic system containing integral quadratic and Lipschitz continuous terms which prevent from looking for classical solutions in Sobolev spaces. It is the hyperbolic part of the system introduced in [Selvaduray and Fujita Yashima on Atti dell’Accademia delle Scienze di Torino 2011] as a model for air motion in ${\mathbf{R}^3}$ including water phase transitions. Unknown functions are: the densities ρ of dry air, π of water vapor, σ and ν of water in the liquid and solid state, dependent also on the mass m of the droplets or ice particles. Air velocity v and temperature T are assumed to be known. Solutions (ρ, π, σ, ν) lie in ${L^\infty(]0,\tau^*[; W^{1,\infty}(\Omega))^2 \times L^\infty(]0,\tau^*[; W^{1,\infty}(\Omega^+))^2}$ , where ${\Omega^+ = \Omega \times]0, +\infty[,\Omega \subset \mathbf{R}^3}$ is open and bounded, and τ* is sufficiently small; they depend continuously on initial data, temperature and velocities, which are tangent to ${\partial\Omega}$ ; they lie also in ${W^{1,q}(]0,\tau^*[;L^\infty(\Omega))^2 \times\,W^{1,q}(]0,\tau^*[;L^\infty(\Omega^+))^2}$ , where ${q \in [1, \infty]}$ .     

Galerkin alternating-direction method for a kind of second-order quasi-linear hyperbolic problems

A kind of second-order quasi-linear hyperbolic equation is firstly transformed into a first-order system of equations, then the Galerkin alternating-direction procedure for the system is derived. The optimal order estimates in H¹ norm and L² norm of the procedure are obtained respectively by using the theory and techniques of priori estimate of differential equations. The numerical experiment is also given to support the theoretical analysis. Comparing the results of numerical example with the theoretical analysis, they are uniform.