Analysis of steady combustion processes in a recombination reaction

In the present paper, the combustion processes, represented by steady deflagration or detonation waves, are studied for a set of balance laws in the framework of Navier–Stokes reactive equations related to a diatomic recombination reaction. Moreover, a systematic analysis of the combustion solutions is carried out, investigating the influence of all the physical parameters present in the hydrodynamical equations: the Mach number of the gas mixture in the unburned state, the chemical link energy of the diatomic molecule and the activation energy of the reaction. Results are discussed according to several numerical experiments.     

Propagation of seismic waves in a continuum modeled as a granular material

The interaction between near-surface geology and seismic radiation determines the features of wave propagation in terms of path, amplification or damping of the seismic signal, which in certain cases might cause the so called site effect. Here, we consider the propagation of seismic waves in a geological site modeled as a granular material. The model equations have been integrated with null initial conditions by means of a finite element method for the spatial components and a finite difference scheme with respect to time evolution. The numerical results so obtained refer to the case of a homogeneous not layered domain with different physical conditions.

     

Shock structure and multiple sub-shocks in Grad 10-moment binary mixtures of monoatomic gases

The problem of sub-shock occurrence within a shock structure solution is investigated for an inert binary mixture of monoatomic gases, modelled by a Grad 10-moment approximation of the Boltzmann equations. The main purpose of this paper is to show by numerical simulations the existence of discontinuous shock structure solutions for values of the shock speed below the maximum unperturbed characteristic velocity. Moreover, for suitable concentrations of the two species, and for shock velocities beyond the maximum unperturbed characteristic velocity, each constituent of the mixture generates a jump discontinuity, and the shock structure solution exhibits two sub-shocks.

     

Body Wave Propagation and Site Effects

The interaction between seismic radiation and near-surface geology plays a role of primary importance in the risk hazard mitigation especially due to the so called site effects. Such kind of phenomena depends on the geological conditions that may cause spatial variability of ground motion, such as producing an amplification of the seismic signal at defined frequencies. For this reason the analysis of site effects plays a key role in the seismic risk mitigation and the numerical simulation represents a powerful tool in this field. This work contemplates the simulation of seismic signals and analysis of their power spectra, varying the intensity of the impulse and its location in the domain, as well as the number of layers and/or their physical properties in order to guess a possible relation between the maximum of peak amplification and the geometrical and physical characteristics of the medium where seismic waves propagate. The seismic wave propagation is described by means of an Initial Boundary Value Problem on a three-dimensional domain with an arbitrary topography, whose numerical integration, obtained by implementing the Finite Element Method, provides the analyzed seismic signals. We present several cases and analyze the corresponding power spectra in order to recognize the maximum frequency involved in the soil shaking amplification.     

Discontinuous Shock Structure in a Reacting Mixture Modelled by Grad 13 Moment Approximation

A preliminary analysis on the possible occurrence of sub-shocks into a gas mixture is carried out. The mixture, undergoing a reversible bimolecular reaction, is described by macroscopic equations obtained by Grad 13 moment approximation of the reactive Boltzmann equation.