Dynamisches Mehrphasenmodell mit hypoplastischer Materialformulierung der Feststoffphase
The numerical simulation of heterogeneous materials with solid and pore filling fluid phases becomes more and more important in different areas of engineering practice due to the availability of high performance computers. The classical application area of multiphase models is the investigation of complex geotechnical problems considering the influence of the pore fluid on the bearing behaviour of soils. In addition to simple consolidation the model is applicable for the simulation of the phenomenon of soil liquefaction initiated by earthquake induced failures in saturated or partially saturated soils. Further applications in geotechnical engineering like water drainage using compressed air and sump drainage contain active generated flows, where the water within the soil is pushed away by compressed air or pumped down by a negative pressure. Fluid flows and transport processes can also be found in other areas like oil-production, material science and biomechanics.The present work aims at developing a stable and reliable multiphase model with nonlinear material formulation for the solid phase, that can applied to most of the geotechnical problems. Up to now, such a general applicable model is not available in the literature.The derivation of the multiphase model is based on the theory of porous media in which the material mixture is divided into its components solid phase, water and air. By using the principle of effective stresses and enhanced Darcy equations for two fluids the mass balance equations of the constitutive phases are evaluated. The resulting differential equations are approximated by the finite element method. The variable implementation of the numerical integration according to Gauß allows the automatic adjustment of the integration degree in case of a discontinuous saturation fronts.The formulation of the deformable granular structure is represented by the hypoplasticity and its extension by the intergranular strain approach. This material law allows the realistic characterisation of stress- and strain states in cohesionless media under static and dynamic loading. The multiphase model is implemented into the FE-program ANSYS®.The model verification and validation is carried out by comparison with analytic results, experimental data taken from literature and simulation results of other authors.The performance of the model is demonstrated by means of practical examples from literature. The presented examples differ regarding the observation period, the number of constitutive phases and the material formulation of the solid phase. The model affords the simulation of consolidations, saturation- and dewatering processes with arbitrary capillary pressure-saturation-relationships and enables a realistic prediction of irreversible deformations in static, quasi-static and dynamic simulations. The modular design of the program in combination with the interface to ANSYS® allows the usage of arbitrary material-laws for the solid phase and the coupling to existing structural elements.The present work provides an efficient tool for the simulation of geotechnical problems. The implementation of a dynamic nonlinear material model for the solid phase into a multiphase model enables the assessment of structural integrity of foundations, slopes, shoreline stabilisations and dams.
info:eu-repo/classification/ddc/620, Ingenieurwissenschaften, Mehrphasenströmung, Plastizität, Dynamik, Biomechanik, Mehrphasensystem, Porosität, Finite-Elemente-Methode, hypoplasticity, intergranular strain
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