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http://hdl.handle.net/2122/288
2015-03-29T12:26:36ZA second order finite-difference ghost-point method for elasticity problems on unbounded domains with applications to volcanology
http://hdl.handle.net/2122/9375
Title: A second order finite-difference ghost-point method for elasticity problems on unbounded domains with applications to volcanology
Authors: Coco, A.; Bristol University; Currenti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Del Negro, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Russo, G.; Università di Catania
Abstract: We propose a novel nite-di erence approach for the numerical solution of linear elasticity problems in
arbitrary unbounded domains. The method is an extension of a recently proposed ghost-point method
for the Poisson equation on bounded domains with arbitrary boundary conditions (Coco, Russo, JCP,
2013) to the case of the Cauchy-Navier equations on unbounded domains. The technique is based on
a smooth coordinate transformation, which maps an unbounded domain into a unit square. Arbitrary
geometries are de ned by suitable level-set functions. The equations are discretized by classical ninepoint
stencil on interior points, while boundary conditions and high order reconstructions are used to
de ne the eld variable at ghost-point, which are grid nodes external to the domain with a neighbor
inside the domain. The approach is then adopted to solve elasticity problems applied to volcanology
for computing the displacement caused by an underground pressure source. The method is suitable
to treat problems in which the geometry of the source often changes (explore the e ects of di erent
scenarios, or solve inverse problems in which the geometry itself is part of the unknown), since it
does not require complex re-meshing when the geometry is modi ed. Several numerical tests are
performed, which asses the e ectiveness of the present approach.
Keywords: Linear Elasticity, Cauchy-Navier equations, ground deformation, unbounded domain,
coordinate transformation method, Cartesian grid, Ghost points, Level-set methods2013-12-31T23:00:00ZCorrection’s method of the electron density model in ionosphere by ray tracing techniques
http://hdl.handle.net/2122/9340
Title: Correction’s method of the electron density model in ionosphere by ray tracing techniques
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Università Sapienza, Dipartimento di Fisica, p.le Aldo Moro 2, I-00185 Rome, Italy; Baskaradas, J. A.; School of Electrical & Electronics Engineering, Shanmugha Arts, Science, Technology & Research Academy (SASTRA) University, Tirumalaisamudram, Thanjavur, 613 401 Tamilnadu, India
Abstract: When applying the ray tracing in ionospheric propagation, the electron density modelling is the main input of the algorithm, since phase refractive index strongly depends on it. Also the magnetic field and frequency collision modelling have their importance, the former as responsible for the azimuth angle deviation of the vertical plane containing the radio wave, the latter for the evaluation of the absorption of the wave. Anyway, the electron density distribution is strongly dominant when one wants to evaluate the group delay time characterizing the ionospheric propagation. From the group delay time, azimuth and elevation angles it is possible to determine the point of arrival of the radio wave when it reaches the Earth surface. Moreover, the procedure to establish the target (T) position is one of the essential steps in the Over The Horizon Radar (OTHR) techniques which require the correct knowledge of the electron density distribution. The group delay time generally gives rough information of the ground range, which depends on the exact path of the radio wave in the ionosphere. This paper focuses on the lead role that is played by the variation of the electron density grid into the ray tracing algorithm, which is correlated to the change of the electron content along the ionospheric ray path, for obtaining a ray tracing as much reliable as possible. In many cases of practical interest, the group delay time depends on the geometric length and the electron content of the ray path. The issue is faced theoretically, and a simple analytical relation, between the variation of the electron content along the path and the difference in time between the group delays, calculated and measured, both in the ionosphere and in the vacuum, is obtained and discussed. An example of how an oblique radio link can be improved by varying the electron density grid is also shown and discussed.2015-03-14T23:00:00ZRay theory formulation and ray tracing method. Application in ionospheric propagation
http://hdl.handle.net/2122/9139
Title: Ray theory formulation and ray tracing method. Application in ionospheric propagation
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, S.; Dipartimento di Fisica, Università “Sapienza”, p.le Aldo Moro 2, 00185 Roma, Italia
Abstract: This work will lead to ray theory and ray tracing formulation. To deal with this problem the theory of classical geometrical optics is presented, and applications to ionospheric propagation will be described. This provides useful theoretical basis for scientists involved in research on radio propagation in inhomogeneous anisotropic media, especially in a magneto-plasma. Application in high frequencies (HF) radio propagation, radio communication, over-the-horizon-radar (OTHR) coordinate registration and related homing techniques for direction finding of HF wave, all rely on ray tracing computational algorithm. In this theory the formulation of the canonical, or Hamiltonian, equations related to the ray, which allow calculating the wave direction of propagation in a continuous, inhomogeneous and anisotropic medium with minor gradient, will be dealt. At least six Hamilton’s equations will be written both in Cartesian and spherical coordinates in the simplest way. These will be achieved by introducing the refractive surface index equations and the ray surface equations in an appropriate free-dimensional space. By the combination of these equations even the Fermat’s principle will be derived to give more generality to the formulation of ray theory. It will be shown that the canonical equations are dependent on a constant quantity H and the Cartesian coordinates and components of wave vector along the ray path. These quantities respectively indicated as ri(τ), pi(τ) are dependent on the parameter τ, that must increase monotonically along the path. Effectively, the procedure described above is the ray tracing formulation. In ray tracing computational techniques, the most convenient Hamiltonian describing the medium can be adopted, and the simplest way to choose properly H will be discussed. Finally, a system of equations, which can be numerically solved, is generated.2014-10-22T22:00:00ZThe calculation of ionospheric absorption with modern computers
http://hdl.handle.net/2122/9104
Title: The calculation of ionospheric absorption with modern computers
Authors: Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: New outcomes are proposed for ionospheric absorption starting from the Appleton-Hartree formula, in its complete form. The range of applicability is discussed for the approximate formulae, which are usually employed in the calculation of non-deviative absorption coefficient. These results were achieved by performing a more refined approximation that is valid under quasi-longitudinal (QL) propagation conditions. The more refined QL approximation and the usually employed non-deviative absorption are compared with that derived from a complete formulation. Their expressions, nothing complicated, can usefully be implemented in a software program running on modern computers. Moreover, the importance of considering Booker’s rule is highlighted. A radio link of ground range D = 1000 km was also simulated using ray tracing for a sample daytime ionosphere. Finally, some estimations of the integrated absorption for the radio link considered are provided for different frequencies.2014-10-14T22:00:00ZScientific review on the ionospheric absorption and research prospects of a Complex Eikonal model for one-layer ionosphere
http://hdl.handle.net/2122/9071
Title: Scientific review on the ionospheric absorption and research prospects of a Complex Eikonal model for one-layer ionosphere
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ippolito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cesaroni, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: Thepresent paper conducts a scientific review on ionospheric absorption, extrapolating the research prospects of a complex eikonal
model for one-layer ionosphere. As regards the scientific review, here a quasi-longitudinal (QL) approximation for nondeviative
absorption is deduced which is more refined than the corresponding equation reported by Davies (1990). As regards the research
prospects, a complex eikonal model for one-layer ionosphere is analyzed in depth here, already discussed by Settimi et al. (2013). A
simple formula is deduced for a simplified problem. A flat, layered ionospheric medium is considered, without any horizontal
gradient. The authors prove that the QL nondeviative amplitude absorption according to the complex eikonal model is more
accurate than Rawer’s theory (1976) in the range of middle critical frequencies.2014-08-05T22:00:00ZThe COMPLEIK subroutine of the IONORT-ISP system for calculating the non-deviative absorption: A comparison with the ICEPAC formula
http://hdl.handle.net/2122/8864
Title: The COMPLEIK subroutine of the IONORT-ISP system for calculating the non-deviative absorption: A comparison with the ICEPAC formula
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The present paper proposes to discuss the ionospheric absorption, assuming a quasi-flat layered ionospheric medium, with small horizontal gradients. A recent complex eikonal model [Settimi et al., 2013b] is applied, useful to calculate the absorption due to the ionospheric D-layer, which can be approximately characterized by a linearized analytical profile of complex refractive index, covering a short range of heights between h1= 50 km and h2= 90 km. Moreover, Settimi et al. [2013c] have already compared the complex eikonal model for the D-layer with the analytical Chapman’s profile of ionospheric electron density; the corresponding absorption coefficient is more accurate than Rawer’s theory [1976] in the range of middle critical frequencies. Finally, in this paper, the simple complex eikonal equations, in quasi-longitudinal (QL) approximation, for calculating the non-deviative absorption coefficient due to the propagation across the D-layer are encoded into a so called COMPLEIK (COMPLex EIKonal) subroutine of the IONORT (IONOspheric Ray-Tracing) program [Azzarone et al., 2012]. The IONORT program, which simulates the three-dimensional (3-D) ray-tracing for high frequencies (HF) waves in the ionosphere, runs on the assimilative ISP (IRI-SIRMUP-P) discrete model over the Mediterranean area [Pezzopane et al., 2011]. As main outcome of the paper, the simple COMPLEIK algorithm is compared to the more elaborate semi-empirical ICEPAC formula [Stewart, undated], which refers to various phenomenological parameters such as the critical frequency of E-layer. COMPLEIK is reliable just like the ICEPAC, with the advantage of being implemented more directly. Indeed, the complex eikonal model depends just on some parameters of the electron density profile, which are numerically calculable, such as the maximum height.2014-01-14T23:00:00ZMonitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismico
http://hdl.handle.net/2122/8813
Title: Monitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismico
Authors: Sergio, Guardato; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia
Abstract: Il sistema CUMAS (Cabled Underwater Module
for Acquisition of Seismological data) è un
prodotto tecnologico-scientifico complesso nato
con il Progetto V4 [Iannaccone et al., 2008] allo
scopo di monitorare l’area vulcanica dei Campi
Flegrei (fenomeno del bradisismo).
Si tratta di un modulo sottomarino cablato e
connesso a una boa galleggiante (meda elastica). Il
sistema è in grado di acquisire e trasmettere alla
sala di monitoraggio dell’OV, in continuo e in
tempo reale, sia i segnali sismologici sia quelli di
interesse geofisico ed oceanografico (maree,
correnti marine, segnali acustici subacquei,
parametri funzionali di varia natura).
Il sistema è in grado di ricevere comandi da remoto
per variare diversi parametri di acquisizione e di
monitorare un cospicuo numero di variabili di
funzionamento.
Il sistema si avvale del supporto di una boa
galleggiante attrezzata. La boa è installata a largo
del golfo di Pozzuoli (Napoli) a circa 3 km dalla
costa. Il modulo sottomarino, collegato via cavo
alla parte fuori acqua della boa, è installato sul
fondale marino a una profondità di circa 100 metri.2010-12-31T23:00:00ZScientific review on the Complex Eikonal, and research perspectives for the Ionospheric Ray-tracing and Absorption
http://hdl.handle.net/2122/8712
Title: Scientific review on the Complex Eikonal, and research perspectives for the Ionospheric Ray-tracing and Absorption
Authors: Settimi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The present paper conducts a scientific review on the complex eikonal, extrapolating the research perspectives on the
ionospheric ray-tracing and absorption. As regards the scientific review, the eikonal equation is expressed, and some
complex-valued solutions are defined corresponding to complex rays and caustics. Moreover, the geometrical optics
is compared to the beam tracing method, introducing the limit of the quasi-isotropic and paraxial complex optics
approximations. Finally, the quasi-optical beam tracing is defined as the complex eikonal method applied to ray-tracing,
discussing the beam propagation in a cold magnetized plasma. As regards the research perspectives, this paper proposes to
address the following scientific problem: in absence of electromagnetic (e.m.) sources, consider a material medium which is
time invariant, linear, optically isotropic, generally dispersive in frequency and inhomogeneous in space, with the additional
condition that the refractive index is assumed varying even strongly in space. The paper continues the topics discussed by
Bianchi et al. [2009], proposing a novelty with respect to the other referenced bibliography: indeed, the Joule’s effect is assumed
non negligible, so the medium is dissipative, and its electrical conductivity is not identically zero. In mathematical terms, the
refractive index belongs to the field of complex numbers. The dissipation plays a significant role, and even the eikonal function
belongs to the complex numbers field. Under these conditions, for the first time to the best of our knowledge, suitable
generalized complex eikonal and transport equations are derived, never discussed in literature. Moreover, in order to solve the
ionospheric ray-tracing and absorption problems, we hint a perspective viewpoint. The complex eikonal equations are derived
assuming the medium as optically isotropic. However, in agreement with the quasi isotropic approximation of geometrical optics,
these equations can be referred to the Appleton-Hartree’s refractive index for an ionospheric magneto-plasma, which becomes
only weakly anisotropic in the presence of Earth’s magnetic induction field. Finally, a simple formula is deduced for a simplified
problem. Consider a flat layering ionospheric medium, so without any horizontal gradient. The paper proposes a new formula,
useful to calculate the amplitude absorption due to the ionospheric D-layer, which can be approximately modelled by a linearized
complex refractive index, because covering a short range of heights, between h1= 50 km and h2= 80 km about.2013-03-19T23:00:00ZRepeat-station surveys: implications from chaos and ergodicity of the recent geomagnetic field
http://hdl.handle.net/2122/8683
Title: Repeat-station surveys: implications from chaos and ergodicity of the recent geomagnetic field
Authors: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Qamili, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The present geomagnetic field is chaotic and ergodic: chaotic because it can no longer be predicted beyond around 6 years; and ergodic in the sense that time averages correspond to phase-space averages. These properties have already been deduced from complex analyses of observatory time series in
a reconstructed phase space [Barraclough and De Santis 1997] and from global predicted and definitive models of differences in the time domain [De Santis et al. 2011]. These results imply that there is a strong necessity to make repeat-station magnetic surveys more frequently than every 5 years. This, in turn, will also improve the geomagnetic field secular variation models. This report provides practical examples and case studies.2013-04-17T22:00:00ZHigh resolution finite volume central schemes for a compressibile two-phase model
http://hdl.handle.net/2122/8273
Title: High resolution finite volume central schemes for a compressibile two-phase model
Authors: La Spina, G.; Dipartimento di Matematica L.Tonelli, University of Pisa, Italy; De' Michieli Vitturi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia
Abstract: A modi_cation of the Kurganov, Noelle, Petrova central-upwind scheme [A. Kurganov et al., SIAM J. Sci. Comput., 23 (2001), pp. 707{740] for hyperbolic systems of conservation laws is presented. In this work, the numerical scheme is applied to a single-temperature model for compressible two-phase ow with pressure and velocity relaxations [E. Romenski et al., J. Sci. Comput., 42 (2010), pp. 68{95]. The system of governing equations of this model are expressed in conservative form, which is the necessary condition to use a central scheme. The numerical scheme presented is not based on the complete characteristic decomposition, but only on the information about the local speeds of propagation given by the maximum and minimum eigenvalue of the Jacobian of the uxes. We propose to use the numerical ux formulation of the central-upwind scheme in conjunction with a second-order reconstruction of the primitive variables and the MUSCL-Hancock method, where the boundary extrapolated values are evolved by half time step before the computation of the numerical uxes. To investigate the accuracy and robustness of the proposed scheme, two 1D Riemann-problems of an air/water mixture and a 2D shock-bubble-interaction problem are presented. Furthermore, a detailed comparison with the second order GFORCE scheme and the _rst order Lax-Friedrichs scheme is shown. To integrate the source terms an operator splitting approach is used and, under suitable conditions, it is shown that this integration can be computed analytically.2011-12-31T23:00:00Z