The project consists on the development on a computer program in C++ or MATLAB for simulation of repeated minority games. The program will include a system of agents: In each time each agent has to decide whether to sell or buy. The agents taking the minority action win. Each agent has a number of strategies to play, and they are provided by a limited rationality. The main objective of this project is to find how much this simple model can reproduce the real features of the stock markets. The applicant needs to be skilled in programming and have strong interest in developing economics model using Object-Oriented Programming.
D. Challet, M. Marsili, and R. Zecchina, Phys. Rev. Lett. 84, 1824 2000.
J.D. Farmer, D. Foley (2009), 'The economy needs agent-based modelling. Nature, Vol. 460, No. 7256. (05 August 2009), pp. 685-686.
One of the key findings in traffic flow is the so-called Braessâ€™ paradox that states that "an extension of the road network by an additional road can cause redistribution of the flow in such a way that increased travel time is the result" [1]. In pedestrian dynamics, this occurs within a crowd which is multiple pedestrians wide. Experimental with ants and numerical simulations have shown that by placing an obstacle near the exit of a room, decreasing the number of routes available, will decrease the evacuation time in an emergency [3]. This project will consist of including the social forces proposed by Helbing [2] in a particle-based model [3] to investigate the origin of the Braess paradox and the effect of cooperation on the flowrate. Candidates need to have programming skills and interest in particle-based simulations.
Braess, D. (1968). Über ein Paradoxon aus der Verkehrsplanung [On a Paradox of Traffic Planning]. Über ein Paradoxon aus der Verkehrsplanung, 12, 10.
Helbing, D., Farkas, I. & Vicsek, T. 2000. Simulating dynamical features of escape panic. Nature, 407.
Alonso-Marroquin, F., Azeezullah, S. I., Galindo-Torres, S. A. & Olsen-Kettle, L. M. 2011. Bottlenecks in granular flow: When does an obstacle increase the flow rate in a hourglass?
This project deals with the long-term stability analysis of a constrained landslide. The landslide is constrained by a rock where zero displacements are observed. Measurements of the slide displacements show a total downhill displacement of few centimetres per year. The project will use experimental data to obtain the unknown parameters of the soil using inverse analysis. The main goal is to further develop an analytical model to obtain realistic evolution of the earth pressure along the landslide. This model will be used to investigate whether the landslide will remain stable in the future. The applicant needs to have strong skills in analytical mathematical modelling and interest in geotechnical engineering.
Puzrin A. M. and Sterba I., 2004. Inverse long-term stability analysis of a constrained landslide. Geotechnique 56, 7 483–489.
Puzrin A. and Schmid A., 2011. Progressive failure of a constrained creeping landslide. Proceedings of the Royal Society A March 30, 2011, doi: 10.1098/rspa.2011.0063.
Granular materials are ubiquitous in nature and are, behind water, the most manipulated materials in the construction and industry. Within this project we will perform element-test simulations of quasistatic and dynamics flow of granular materials. Using our in-house discrete element model Morphological Dynamics, we investigate at first instance how particle aspect ratio and rolling resistance affect dynamics at the mesoscale: The buckling of force chains (filamentary structure of the stress propagation in granular soils) and its effect on stress fluctuations (tectonic-like behavior of granular materials under shear). This project will involve both discrete/finite element modeling and its ultimate goal is to construct a hybrid discrete/continuum model for geological materials. This project will be developed in the Centre of Geotechnical Research, in collaboration with Prof. Antoinette Tordesillas from the University of Melbourne, and Dr. Hongyuan Liu from Golder Geomechanics Centre, The University of Queensland.
Empirical placement of inserts (obstacles) in silos before outlet openings to improve the flow regime and remove stagnant zones in silos has been utilized since the sixties. We have examined granular flow across a bottleneck and find that contrary to expectations, the flow rate of particulate materials across a bottleneck actually increases if an optimized obstacle is placed before it. We also confirm that the obstacle allows transition from funnel flow to uniform (mass) flow. The aim of this project is to further investigate this effect, and show who it depends on the particle shape and the shape of the obstacle, and to give a physical explanation by using conservation equations of granular flow and empirical relation from traffic flow and funnel flow. This project will be developed in the Centre of Geotechnical Research, and it will be supported by experimental results provided by key European Researchers: Alvaro Ramirez, from Polytechnic University of Madrid, and Iker Zuriguel from the University of Navarra, Spain.
The main outcome of this project will be a Virtual Simulator, where the user can fully visualize the system in 3D and interact with the objects during the simulations. We will focus on particle-based simulations or many rigid-bodies. Such systems span a wide range of applications, such as computer-aid design of new drugs, nanotechnologies oriented to hydrogen fuel production and carbon sequestration, design of prototypes for mining-related processes, and architectural/urban design for pedestrian and traffic flow. We are seeking a PhD student with strong background in physics, mathematics and computer science, will be involved in the development of the following milestones:
Developments of methods to reconstruct realistic morphologies of geological materials (morphological erosion and Minkowski - Voronoi diagrams).
Implementation of simulator's classes using template meta-programming techniques.
Development of a user & developer -friendly platform in C++ , using the philosophy of Object Oriented Programming and the concepts of encapsulated containers.
Incorporation of new techniques for Molecular Dynamics to achieve real time simulations, including high order integrators and extension of collision detection algorithms for 3D simulations.
Incorporation of interaction of particles in fluids, and coupling with continuum equations for multi-physics simulations.
Lateral loads produced by the wind and waves are transferred by the wind turbines to their foundation, and hence they affect their stability and service life. Discrete element simulations of cyclic loading will be compared to experiments of piles under cyclic lateral load on saturated beds of granular material. The key objectives of this collaboration are:
Use the in-house Discrete Element Model (DEM) of Morphological Dynamics to simulate the cyclic loading response of a foundation of the structure, according to the small scale physical model of a monopile wind turbine developed in BAM.
Investigate the underlying mechanics of the convective movement in the sand in the foundation around the supporting structure of wind farms.
Validate the DEM model by reproducing the pressure - displacement relation of the foundation of the physical model.
Establish the basis for large scale simulation of soil-structure interaction taking into account pore pressure effects.
Several models have been presented to evaluate flow rates in pedestrian dynamics, yet very few focus on the calculation of the stress experienced by pedestrians under high density. With this aim, a pedestrian dynamics model is implemented to calculate the stress developed under crowd conditions.
The model is based on an extension of a granular dynamics model to account contact forces, ground reaction forces and torques in the pedestrians. Contact stiffness is obtained from biomedical journal articles, and coefficient of restitution is obtained by direct observations of energy loss in collisions.
Existing rotational equations of motion are modified to incorporate a rotational viscous component, which allows pedestrians to come to a comfortable stop after a collision rather than rotating indefinitely. The shape of the pedestrian is obtained from a bird's eye, cross sectional view of the human chest cavity and arms, which was edited to produce an enclosed shape. This shape is then approximated by a spheropolygon, which is a mathematical object that allow real-time simulation of complex-shape particles. The proposed method provides real benefits to the accuracy on particle shape representation, and rotational dynamics of pedestrians at micro-simulation level, and it provides a new tool to calculate the risk of injuries and asphyxiation when people are trapped in dense crowds that lead to development of high pressure.
The aim of this project is to determine the bulk mechanical properties of granular materials in terms of the topographical structures of contacting inter-granular surfaces. The project will be based on experimental, numerical, and theoretical analyses of surface force - deformation behaviour to interpret the dependence of inter-granular micromechanics on fractal particle surface structures.This will facilitate the derivation of parameters for discrete element modelling (DEM). The in-house software, SPOLY, along with extensive experimental validation will be employed to test the derived force-deformation relations. The project will facilitate the effective use of DEM for large-scale problems of granular flow, where the rheology of grains with complex surface structures is of great significance. This is of particular importance in the food and minerals industries and is of relevance across a broad range of disciplines.
This project entails the development of a Discrete Element Model (DEM) to explore microscopic soil erosion due to water flow in flooding events. In the mode, both sand and silt particles will be represented by Voronoi polygons. Contact interaction will include repulsive, viscoelastic, and friction forces. The cohesion of the soil due to its clay content will be represented by link elements between the polygons in contact. Following our approach, the strength of the links will depend on the suction and will be calculated in terms of the saturation of the soil. The breakage of links due to drag forces and dispersion of clay will be executed using a microscopic criterion of fracture. Simulations will be used to calculate the erosion velocity for different fluid velocities.
An experimental prototype will be used to validate the model. The experiment includes two interconnected containers. The first one will be filled with gravel; and the second one with the test soil. A small orifice will be drilled in the soil sample to initiate the erosion, then water with a controlled flow rate will be injected in the gravel container and pass through the soil container. The proposal includes five preliminary tests on soil samples, to investigate the effect of flow rate on erosion.
The discrete element development and the experimental tests entail the basis for a proof-of-principle for future research in multiscale modelling of erosion. After the model validation, we will be able to take a further step – toward building a multiscale model of erosion (not included in this quotation). This would be three-years PhD project. In the first year, a hybrid continuum – discrete model would be developed to incorporate pressure head into the discrete element model. The model includes the solution of the Richards equations to determine the time evolution of the pressure head in the soil. The pressure will be coupled with soil in two ways: the discrete model passes to the Richards equation the boundary conditions where the soil is fully saturated; and vice versa, the equations calculate the pressure heat used to update the link elements. In the second and third years, we would develop a macroscopic model to simulate erosion at the scale of kilometres. The velocity – erosion curve obtained from the microscopic model will be incorporated in a macroscopic model of erosion based on the macroscopic balance equation for conservation of mass and momentum.
This project is to use simulations to analyse the effective interaction of key-lock mechanism due to random motion of the molecules. The aim will be to observe an attractive force between key and lock and to check whether the attractive force at zero distance is consistent to the kinetic theory.
Self-assembly is one effective method for uncovering supramolecular architectures. It is commonly found in nature: lipid molecules form oil drops in water; four hemoglobin polypeptides form a functional tetrameric hemoglobin protein; ribosomal proteins and RNA coalesce in functional ribosomes. Nature has transformed the self-assembly of simple basic subunits into complex, functional structures with outstanding precision.