We are seeking a full time PhD researcher with interests in granular physics, continuum mechanics and computer modelling to join University of Twente (Netherlands), and work on a novel, unified constitutive model for saturated granular fluids and solids.
This project is part of the EU funded Marie Curie Doctoral Network POSEIDON – Improve offshore infrastructure resilience against geohazards towards a changing climate (www.poseidon-dn.eu). The overarching objective of POSEIDON
is to develop, solutions to improve the resilience of offshore infrastructures. POSEIDON will train 13 researchers within a collaborative multidisciplinary and inter-sectorial network involving 9 universities, 3 research institutes and 4 industrial partners across Europe. Background and aim:
Submarine landslides, from the mobilization to the transport of fluid-saturated sediments, involve the understanding and modelling of geomechanical processes at multiple length and time scales. One of the main challenges in submarine granular flows is the complex yielding transition from static to motion, which is governed by the spatially and/or temporally varying length scales, i.e., landslide threshold, and back to static conditions. This gap creates considerable difficulty in predicting the initiation and post-failure behaviour of submarine landslides. Questions such as the runout distance cannot be answered without understanding and quantifying the dissipation during this fluid-solid transition and back. The current frameworks (e.g., plasticity and effective stress theories) for modelling soil-fluid interactions going from fluid saturated solids to a fluid-dominated mixture have to be revised and improved.
Based on the simulation data of particle-fluid interaction (developed in a parallel DC project) and machine learning tools (GrainLearning) that aid constitutive modelling established in the group, we will enrich existing constitutive frameworks for describing the behaviour of saturated granular masses in the solid and fluid regimes, and their transition. Particle-scale simulations provide the essential data for this task, as they uniquely can inform the continuum framework. The end goal is to come up with a sensible model structure for a unified granular micromechanically based solid-fluid model by learning model structures from fully-resolved simulations particle-fluid systems, with the help of Bayesian learning. Objectives:
i) Understand the capabilities of fluid-solid models for granular media and their limitations to model the collapse of saturated granular flows;
ii) Study the complex transitions from static to motion and back using coarse grained fluid-DEM simulations;
iii) Implement the unified model in a continuum solver to accurately predict the runout distance of submarine landslide and compare the results with experimental data. Expected Results:
i) Assessment of the suitability of theoretical frameworks to describe solid-to-fluid (collapse) and fluid-to-solid (runout) transition in saturated granular masses;
ii) Micromechanical-based unified constitutive models that correctly capture these transitions;
iii) Comparison and validation via laboratory experiments. Planned Secondment(s):
Dr Xue Zhang (University of Liverpool, 3 months): collaborate with the DC on the implementation of the new constitutive model/framework into a particle finite element code available at University of Liverpool.
Dr. Alex X. Jerves and Dr. Hans Petter Jostad (NGI, 3 months): discuss continuum frameworks for saturated granular fluid-solid transition; collaborate with the DC on the effect of particle shape on fluid-particle coupled systems; collaborate on the implementation and validation of the new constitutive model/framework with existing data.
Mr. Willem Hendrik Pater (State of the Art Engineering BV, 3 month): transfer the numerical results of submarine landslide simulations (e.g., runout distance, impact loads) onto the finite element model of offshore wind turbine foundations.