Use Of Numerical Codes Research Articles

El código HYDROTHERM como herramienta de integración de la geofísica en prospección geotérmica

The use of numerical codes in simulating geothermal reservoirs is one of the most powerful tools for integrating geology, geochemistry, and geophysics in high enthalpy geothermal research processes. This paper summarizes some examples of USGS HYDROTHERM code application results on the islands of Gran Canaria, Lanzarote, and Tenerife, which are considered very different geothermal models. The first island has normal geothermal gradient, the second has magmatic bodies near the surface and Tenerife has a comparison between geophysical techniques to determine the recharge-discharge flows of the Cañadas-Teide system. In the first two islands there are boreholes that allow adjusting and validating the models, whereas Tenerife or La Palma have been studied using the same methodology but lack verification boreholes. Nevertheless, their model results are consistent with other geophysical techniques. This highlights the great potential of this code as an integrating tool for the different prospecting techniques to understand geothermal system operations and determine the most suitable location for deep exploration drilling. The significant benefit of this code is the capability to reproduce different evolutionary and casuistry models reliably using the same geological and thermal parameters for all islands.

Keynote lecture. Constitutive modelling of phase transitions in granular soils

The use of numerical codes for simulating the propagation phase of fast landslides requires the definition of constitutive relationships suitable for the description of the mechanical behaviour of granular soils, under both solid and fluid conditions. In this paper, the authors briefly illustrate a constitutive modelling approach interpreting the material as a bi-phasic continuum, according to which the solid phase may behave like a solid, under quasi-static conditions, and a fluid, under collisional/dynamic conditions. The model presented seems to satisfactorily reproduce a series of results obtained by using a discrete element numerical code on mono and polydisperse granular specimens. The constitutive model has been implemented in a Material Point Method code to solve boundary value problems, in which strain rate large values are expected to influence the material response.

Multilayer modelling of waves generated by explosive subaqueous volcanism

Abstract. Theoretical source models of underwater explosions are often applied in studying tsunami hazards associated with subaqueous volcanism; however, their use in numerical codes based on the shallow water equations can neglect the significant dispersion of the generated wavefield. A non-hydrostatic multilayer method is validated against a laboratory-scale experiment of wave generation from instantaneous disturbances and at field-scale subaqueous explosions at Mono Lake, California, utilising the relevant theoretical models. The numerical method accurately reproduces the range of observed wave characteristics for positive disturbances and suggests a relationship of extended initial troughs for negative disturbances at low-dispersivity and high-non-linearity parameters. Satisfactory amplitudes and phase velocities within the initial wave group are found using underwater explosion models at Mono Lake. The scheme is then applied to modelling tsunamis generated by volcanic explosions at Lake Taupō, New Zealand, for a magnitude representing an ejecta volume of 0.1 km3. Waves reach all shores within 15 min with maximum incident crest amplitudes around 0.2 m at shores near the source. This work shows that the multilayer scheme used is computationally efficient and able to capture a wide range of wave characteristics, including dispersive effects, which is necessary when investigating subaqueous explosions. This research therefore provides the foundation for future studies involving a rigorous probabilistic hazard assessment to quantify the risks and relative significance of this tsunami source mechanism.

Two Improvements to Gardner's Method of Measuring the Hydraulic Conductivity of Non‐saturated Media: Accounting for Impedance Effects and Non‐constant Imposed Suction Increment

AbstractGardner's (1956, https://doi.org/10.2136/sssaj1956.03615995002000030006x) transient method of measuring the hydraulic conductivity function of unsaturated media has been largely used, together with the improved graphical method proposed by Kunze and Kirkham (1962, https://doi.org/10.2136/sssaj1962.03615995002600050006x) to account for the impedance effect resulting from using a low hydraulic conductivity ceramic disk in porous plate testing. These methods are nowadays seldom used, since they have been replaced by numerical back analysis and methods for parameter optimization. Based on tests carried out on a specific device allowing to determine the water retention and transport properties of water in a coarse granular media at low suctions (up to 50 kPa), it was found necessary to account (i) for impedance effects and (ii) for the effects of nonconstant suction increments, as is often the case when using the hanging column technique. A new method is proposed to account for impedance effects, based on an analytical solution of the equations governing water transfer. The validity of this method is tested by considering experimental data from three distinct materials: a coarse green roof volcanic substrate, poorly graded sand, and undisturbed silty clay. Compared to the graphical method Kunze and Kirkham's method, it is less operator‐dependent and hence more objective. It is also simpler than numerical back analysis methods, since it does not require any use of numerical code or parameter optimization algorithm, providing a more direct and reliable access to the hydraulic conductivity. An analytical solution is also proposed to solve the problem resulting from the application of a nonconstant suction increment.

A Library of Fokker‐Planck Coefficients for Coulomb Scattering

ABSTRACTThe time evolution of electron distribution functions in hot, ionized gases can be described in terms of a Fokker‐Planck equation. We have previously developed and described a coupled Monte Carlo/Fokker‐Planck code for astrophysical problems of time‐dependent photon and electron transport, which made use of extensive libraries of energy exchange and dispersion coefficients for electron‐electron (Møller) and electron‐proton Coulomb scattering. We have made those libraries publicly available to the scientific community for use in numerical codes dealing with similar physical problems. Here we briefly describe the libraries and present the Web address where they can be accessed.

Line fluorescence in astrophysics

view Abstract Citations (38) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Line fluorescence in astrophysics Elitzur, M. ; Netzer, H. Abstract A formalism to calculate emission-line strengths in the case of partial or complete overlapping of two spectral lines (so-called 'line fluorescence') is developed. The procedure is based on the escape probability method and is particularly suitable for use in numerical codes where line and continuum transfer is treated in this way. The method is applied to two cases of astrophysical interest: Fe II fluorescence with Ly-alpha and Ly-beta fluorescence with O I 1025 A in quasar clouds. The first of these is found to be mostly unimportant, while the second case results in an improvement over previously used methods. Publication: The Astrophysical Journal Pub Date: April 1985 DOI: 10.1086/163085 Bibcode: 1985ApJ...291..464E Keywords: Astronomical Spectroscopy; Fluorescence; Line Spectra; Nebulae; Quasars; Radiative Transfer; Computational Astrophysics; H Alpha Line; Lyman Alpha Radiation; Lyman Beta Radiation; Oxygen Spectra; Astrophysics full text sources ADS |

Computation of Tokamak transport

The complexity of the equations describing the transport phenomena in Tokamaks requires the use of numerical codes for simulation. These codes assume that the plasma is a multifluid medium. They involve equations for the evolution of electrons, light ions and current density, equations for heavy ions (impurities) and elaborate models for the evolution of the neutrals of light atoms. These codes allow testing of the existing theories and deduction of empirical rules and coefficients. After we have presented in more detail the Fontenay-aux-Roses code, we give examples of a few applications of this code.