The erosion of riverbeds and riverbanks depends, among other causes, both on the velocity fields ... more The erosion of riverbeds and riverbanks depends, among other causes, both on the velocity fields and on their gradient near their boundaries, with the generation of shear stresses. The presence of sediments modifies the viscosity and, accordingly, modifies the profiles, particularly near the edges right where they are generated. Therefore, in this work, the distortion of the velocity profiles due to an imposed spatial variability of viscosity, was studied applying the Computational Fluid Dynamics (CFD). In particular, as test cases, laminar and turbulent Plane Poiseuille flows, were selected. For simplicity, it was assumed that the sediment distribution and therefore the viscosity distribution was not influenced by the mixing due to velocity field. That is, the equilibrium configuration was determined as a consequence of a spatially variable distribution of viscosity. The 2D Navier-Stokes equations, in steady state conditions, were numerically solved exploiting a research software developed and discussed by the author [1]. The turbulence was considered through the RANS (Reynolds Averaged Navier Stokes) approach. The two equations k ƒ{ ƒÕ models were employed. The turbulence phenomena near solid boundaries was simulated by the means of Wall-Functions. Spatial discretization was carried out using the Finite Element Method (FEM). A structured meshing with h like adaptability was developed. Then, in order to avoid velocities and pressure instabilities, the Characteristic-based split algorithm (CBS) was applied, while, in order to correctly consider incompressibility, by a numerical point of view, the Method of Artificial Compressibility (AC) was selected. Accordingly, the related CBS-AC three steps algorithm was implemented [1]. Then, some parametric numerical experiments were performed, considering a semi-implicit, approach. As was to be expected, the velocity profiles, for both laminar and turbulent were influenced by the viscosity distribution. The discussion of the overall results points out the sensitivity of the algorithms not only to the meshes size, to their distribution and to the number of iterations, but also to some intrinsic ¡§experimental numerical dials¡¨ (safe coefficients, explicit vs implicit ratio), specific of the selected approach. Moreover, suggestions have emerged for more complex and more complete simulations which, necessarily, would use methods based on iterations internal to each time-step
In order to study the behavior of soil materials affected by geotechnical parameters heterogeneit... more In order to study the behavior of soil materials affected by geotechnical parameters heterogeneities, the implementation of a specific mathematical algorithm into a commonly used commercial computer code, FLAC2D, is discussed. The selected code is based on Finite Difference Method (FDM) applied to continuum mechanics. The framework of its most common use is the study of slopes stability, but, notwithstanding it is very popular in geotechnical and geology engineering fields, it was not conceived, in particular, to handle statistical variability of the most important mechanical parameters. Thus, after a brief discussion of the selected mathematical model, the description of the algorithm implementation, based on the interactive code FISH used in order to make the FLAC2D suitable for Monte Carlo multiple realizations of possible real structural configurations, follows. Then, a simple test showing the statistical realization of the density distribution along a virtual column, obtained just by successive runs of the code, is discussed. Finally, preliminary results related to the spatial assignment of mechanical parameters values, belonging to a Gaussian numerical ensemble, based on real data and representative of an actual slope is reported.
The present work regards the study of soil-structure interaction, in particular during pull-out t... more The present work regards the study of soil-structure interaction, in particular during pull-out tests on anchorages. Due to the complexity of the system, numerical analyses carried out by a commercial code, based on the Finite Difference Method (FDM), were performed. In order to calibrate the overall selected approach, first of all, a simple two-dimensional model of the system was firstly study. The preliminary results and suggestions for incoming 3D modeling improvements are discussed. Furthermore attention has been focused on the nature of the impulsive impacting force due to a virtual debris flow or avalanches striking on the structure, including the anchorages, in order to correctly simulate the test of pull out. Accordingly, a simplified, preliminary model of the anchorages-net system, including the effect of the mass deposition, is proposed and discussed.
Abstract The Reynolds decomposition is used to derive a new set of mean-flow equations for linear... more Abstract The Reynolds decomposition is used to derive a new set of mean-flow equations for linear viscous fluids, with low compressibility (fluids in the liquid state). Additional shear and normal stresses are related to the velocity turbulent fluctuations in order to interpret the considerable energy dissipation in processes which are accompanied by rapid changes in liquid density, at least within the frame of the local thermodynamic equilibrium (LTE) approximation. A constitutive equation for the normal turbulent stresses, which involves the turbulent bulk viscosity, is given. A closure equation for the turbulent bulk viscosity is suggested. In the field of hydraulic engineering, the model is applied to investigate the classical problem of 1D finite amplitude pressure waves propagation in liquid-filled pipes (water hammer phenomenon). Available experimental pressure data are used to calibrate the model parameters and to demonstrate the capability of the proposed theoretical model in reproducing the experimental trials. The model results are discussed with attention paid to the role played by the turbulent bulk viscosity on the energy dissipation processes.
The erosion of riverbeds and riverbanks depends, among other causes, both on the velocity fields ... more The erosion of riverbeds and riverbanks depends, among other causes, both on the velocity fields and on their gradient near their boundaries, with the generation of shear stresses. The presence of sediments modifies the viscosity and, accordingly, modifies the profiles, particularly near the edges right where they are generated. Therefore, in this work, the distortion of the velocity profiles due to an imposed spatial variability of viscosity, was studied applying the Computational Fluid Dynamics (CFD). In particular, as test cases, laminar and turbulent Plane Poiseuille flows, were selected. For simplicity, it was assumed that the sediment distribution and therefore the viscosity distribution was not influenced by the mixing due to velocity field. That is, the equilibrium configuration was determined as a consequence of a spatially variable distribution of viscosity. The 2D Navier-Stokes equations, in steady state conditions, were numerically solved exploiting a research software developed and discussed by the author [1]. The turbulence was considered through the RANS (Reynolds Averaged Navier Stokes) approach. The two equations k ƒ{ ƒÕ models were employed. The turbulence phenomena near solid boundaries was simulated by the means of Wall-Functions. Spatial discretization was carried out using the Finite Element Method (FEM). A structured meshing with h like adaptability was developed. Then, in order to avoid velocities and pressure instabilities, the Characteristic-based split algorithm (CBS) was applied, while, in order to correctly consider incompressibility, by a numerical point of view, the Method of Artificial Compressibility (AC) was selected. Accordingly, the related CBS-AC three steps algorithm was implemented [1]. Then, some parametric numerical experiments were performed, considering a semi-implicit, approach. As was to be expected, the velocity profiles, for both laminar and turbulent were influenced by the viscosity distribution. The discussion of the overall results points out the sensitivity of the algorithms not only to the meshes size, to their distribution and to the number of iterations, but also to some intrinsic ¡§experimental numerical dials¡¨ (safe coefficients, explicit vs implicit ratio), specific of the selected approach. Moreover, suggestions have emerged for more complex and more complete simulations which, necessarily, would use methods based on iterations internal to each time-step
In order to study the behavior of soil materials affected by geotechnical parameters heterogeneit... more In order to study the behavior of soil materials affected by geotechnical parameters heterogeneities, the implementation of a specific mathematical algorithm into a commonly used commercial computer code, FLAC2D, is discussed. The selected code is based on Finite Difference Method (FDM) applied to continuum mechanics. The framework of its most common use is the study of slopes stability, but, notwithstanding it is very popular in geotechnical and geology engineering fields, it was not conceived, in particular, to handle statistical variability of the most important mechanical parameters. Thus, after a brief discussion of the selected mathematical model, the description of the algorithm implementation, based on the interactive code FISH used in order to make the FLAC2D suitable for Monte Carlo multiple realizations of possible real structural configurations, follows. Then, a simple test showing the statistical realization of the density distribution along a virtual column, obtained just by successive runs of the code, is discussed. Finally, preliminary results related to the spatial assignment of mechanical parameters values, belonging to a Gaussian numerical ensemble, based on real data and representative of an actual slope is reported.
The present work regards the study of soil-structure interaction, in particular during pull-out t... more The present work regards the study of soil-structure interaction, in particular during pull-out tests on anchorages. Due to the complexity of the system, numerical analyses carried out by a commercial code, based on the Finite Difference Method (FDM), were performed. In order to calibrate the overall selected approach, first of all, a simple two-dimensional model of the system was firstly study. The preliminary results and suggestions for incoming 3D modeling improvements are discussed. Furthermore attention has been focused on the nature of the impulsive impacting force due to a virtual debris flow or avalanches striking on the structure, including the anchorages, in order to correctly simulate the test of pull out. Accordingly, a simplified, preliminary model of the anchorages-net system, including the effect of the mass deposition, is proposed and discussed.
Abstract The Reynolds decomposition is used to derive a new set of mean-flow equations for linear... more Abstract The Reynolds decomposition is used to derive a new set of mean-flow equations for linear viscous fluids, with low compressibility (fluids in the liquid state). Additional shear and normal stresses are related to the velocity turbulent fluctuations in order to interpret the considerable energy dissipation in processes which are accompanied by rapid changes in liquid density, at least within the frame of the local thermodynamic equilibrium (LTE) approximation. A constitutive equation for the normal turbulent stresses, which involves the turbulent bulk viscosity, is given. A closure equation for the turbulent bulk viscosity is suggested. In the field of hydraulic engineering, the model is applied to investigate the classical problem of 1D finite amplitude pressure waves propagation in liquid-filled pipes (water hammer phenomenon). Available experimental pressure data are used to calibrate the model parameters and to demonstrate the capability of the proposed theoretical model in reproducing the experimental trials. The model results are discussed with attention paid to the role played by the turbulent bulk viscosity on the energy dissipation processes.
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